Time Travel

Transcript

Time Travel A brief history PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information. PDF generated at: Fri, 01 Jun 2012 17:22:04 UTC Contents Articles Overview Time travel 1 1 24 24 30 47 54 61 75 77 77 86 90 101 122 122 125 141 156 164 171 175 178 185 Physics Multiverse Many-worlds interpretation Novikov self-consistency principle Wormhole Faster-than-light Chronology protection conjecture Philosophy Philosophy of space and time Eternalism Determinism Free will Fiction Time travel in fiction Parallel universe Alternate history Time loop Temporal paradox Grandfather paradox Ontological paradox Predestination paradox List of time travel science fiction References Article Sources and Contributors Image Sources, Licenses and Contributors 204 210 Article Licenses License 211 1 Overview Time travel Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space. Time travel could hypothetically involve moving backward in time to a moment earlier than the starting point, or forward to the future of that point without the need for the traveler to experience the intervening period (at least not at the normal rate). Any technological device – whether fictional or hypothetical – that would be used to achieve time travel is commonly known as a time machine.[1] Although time travel has been a common plot device in science fiction since the late 19th century, and the theories of special and general relativity allow methods for forms of one-way travel into the future via time dilation, it is currently unknown whether the laws of physics would allow time travel into the past. Such backward time travel would have the potential to introduce paradoxes related to causality, and a variety of hypotheses have been proposed to resolve them, as discussed in the sections Paradoxes and Rules of time travel below. Origins of the concept Literature timeline • • • • • • • • • • • • • • • • • • • • • 700s BCE to 300s CE – Story of Raivata in the Mahabharata 200s to 400s CE – Story of Honi HaM'agel in the Talmud 720 CE – "Urashima Tarō" in the Nihon Shoki 1733 – Samuel Madden's Memoirs of the Twentieth Century 1771 – Louis-Sébastien Mercier's L'An 2440, rêve s'il en fût jamais 1781 – Johan Herman Wessel's Anno 7603 1819 – Washington Irving's "Rip Van Winkle" 1824 – Faddey Bulgarin's "Pravdopodobnie Nebylitsi" 1827 – Goethe Faust fragment 1828 – Hans Christian Andersen's Journey on Foot from Holmen's Canal to the East Point of Amager 1832 – Goethe's Faust: The Second Part of the Tragedy 1836 – Alexander Veltman's Predki Kalimerosa 1838 – Hans Christian Andersen's The Goloshes of Fortune 1838 – Missing One's Coach: An Anachronism 1843 – Charles Dickens' A Christmas Carol 1861 – Pierre Boitard's Paris avant les hommes 1881 – Edward Page Mitchell's The Clock That Went Backward 1887 – Enrique Gaspar y Rimbau's El anacronópete 1888 – H. G. Wells' The Chronic Argonauts 1889 – Mark Twain's A Connecticut Yankee in King Arthur's Court 1895 – H. G. Wells' The Time Machine Time travel 2 Forward time travel There is no widespread agreement as to which written work should be recognized as the earliest example of a time travel story, since a number of early works feature elements ambiguously suggestive of time travel. Ancient folk tales and myths sometimes involved something akin to travelling forward in time; for example, in Hindu mythology, the Mahabharata mentions the story of the King Revaita, who travels to heaven to meet the creator Brahma and is shocked to learn that many ages have passed when he returns to Earth.[2][3] Another one of the earliest known stories to involve traveling forward in time to a distant future was the Japanese tale of "Urashima Tarō",[4] first described in the Nihongi (720).[5] It was about a young fisherman named Urashima Taro who visits an undersea palace and stays there for three days. After returning home to his village, he finds himself 300 years in the future, when he is long forgotten, his house in ruins, and his family long dead. Another very old example of this type of story can be found in the Talmud with the story of Honi HaM'agel who went to sleep for 70 years and woke up to a world where his grandchildren were grandparents and where all his friends and family were dead.[6] More recently, Washington Irving's famous 1819 story "Rip Van Winkle" tells of a man named Rip Van Winkle who takes a nap on a mountain and wakes up 20 years in the future, when he has been forgotten, his wife dead, and his daughter grown up.[4] Sleep was also used for time travel in Faddey Bulgarin's story "Pravdopodobnie Nebylitsi" in which the protagonist wakes up in the 29th century. Another more recent story involving travel to the future is Louis-Sébastien Mercier's L'An 2440, rêve s'il en fût jamais ("The Year Statue of Rip van Winkle in Irvington, New York 2440: A Dream If Ever There Were One"), a utopian novel in which the main character is transported to the year 2440. An extremely popular work (it went through 25 editions after its first appearance in 1771), it describes the adventures of an unnamed man who, after engaging in a heated discussion with a philosopher friend about the injustices of Paris, falls asleep and finds himself in a Paris of the future. Robert Darnton writes that "despite its self-proclaimed character of fantasy...L'An 2440 demanded to be read as a serious guidebook to the future."[7] Backward time travel Backwards time travel seems to be a more modern idea, but its origin is also somewhat ambiguous. One early story with hints of backwards time travel is Memoirs of the Twentieth Century (1733) by Samuel Madden, which is mainly a series of letters from English ambassadors in various countries to the British Lord High Treasurer, along with a few replies from the British Foreign Office, all purportedly written in 1997 and 1998 and describing the conditions of that era.[8] However, the framing story is that these letters were actual documents given to the narrator by his guardian angel one night in 1728; for this reason, Paul Alkon suggests in his book Origins of Futuristic Fiction that "the first time-traveler in English literature is a guardian angel who returns with state documents from 1998 to the year 1728",[9] although the book does not explicitly show how the angel obtained these documents. Alkon later qualifies this by writing, "It would be stretching our generosity to praise Madden for being the first to show a traveler arriving from the future", but also says that Madden "deserves recognition as the first to toy with the rich idea of time-travel in the form of an artifact sent backwards from the future to be discovered in the present."[8] Time travel 3 In 1836 Alexander Veltman published Predki Kalimerosa: Aleksandr Filippovich Makedonskii (The forebears of Kalimeros: Alexander, son of Philip of Macedon), which has been called the first original Russian science fiction novel and the first novel to use time travel.[10] In it the narrator rides to ancient Greece on a hippogriff, meets Aristotle, and goes on a voyage with Alexander the Great before returning to the 19th century. In the science fiction anthology Far Boundaries (1951), the editor August Derleth identifies the short story "Missing One's Coach: An Anachronism", written for the Dublin Literary Magazine[11] by an anonymous author in 1838, as a very early time travel story.[12] In this story, the narrator is waiting under a tree to be picked up by a coach which will take him out of Newcastle, when he suddenly finds himself transported back over a thousand years. He encounters the Venerable Bede in a monastery, and gives him somewhat ironic explanations of the developments of the coming centuries. It is never Mr. and Mrs. Fezziwig dance in a vision the Ghost of Christmas Past shows Scrooge. entirely clear whether these events actually occurred or were merely a dream—the narrator says that when he initially found a comfortable-looking spot in the roots of the tree, he sat down, "and as my sceptical reader will tell me, nodded and slept", but then says that he is "resolved not to admit" this explanation. A number of dreamlike elements of the story may suggest otherwise to the reader, such as the fact that none of the members of the monastery seem to be able to see him at first, and the abrupt ending in which Bede has been delayed talking to the narrator and so the other monks burst in thinking that some harm has come to him, and suddenly the narrator finds himself back under the tree in the present (August 1837), with his coach having just passed his spot on the road, leaving him stranded in Newcastle for another night.[13] Charles Dickens' 1843 book A Christmas Carol is considered by some[14] to be one of the first depictions of time travel in both directions, as the main character, Ebenezer Scrooge, is transported to Christmases past, present and yet to come. These might be considered mere visions rather than actual time travel, though, since Scrooge only viewed each time period passively, unable to interact with them. A more clear example of backwards time travel is found in the popular 1861 book Paris avant les hommes (Paris before Men) by the French botanist and geologist Pierre Boitard, published posthumously. In this story the main character is transported into the prehistoric past by the magic of a "lame demon" (a French pun on Boitard's name), where he encounters such extinct animals as a Plesiosaur, as well as Boitard's imagined version of an apelike human ancestor, and is able to actively interact with some of them.[15] Another early example of backwards time travel in fiction is the short story The Clock That Went Backward by Edward Page Mitchell,[16] which appeared in the New York Sun in 1881. Mark Twain's A Connecticut Yankee in King Arthur's Court (1889), in which the protagonist finds himself in the time of King Arthur after a fight in which he is hit with a sledge hammer, was another early time travel story which helped bring the concept to a wide audience, and was also one of the first stories to show history being changed by the time traveler's actions. The first time travel story to feature time travel by means of a time machine was Enrique Gaspar y Rimbau's 1887 book El Anacronópete.[17] This idea gained popularity with the H. G. Wells story The Time Machine, published in 1895 (preceded by a less influential story of time travel Wells wrote in 1888, titled The Chronic Argonauts), which also featured a time machine and which is often seen as an inspiration for all later science fiction stories featuring time travel using a vehicle that allows an operator to travel purposefully and selectively. The term "time machine", Time travel coined by Wells, is now universally used to refer to such a vehicle. Since that time, both science and fiction (see Time travel in fiction) have expanded on the concept of time travel. 4 Theory Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime, or specific types of motion in space, might allow time travel into the past and future if these geometries or motions are possible.[18] In technical papers, physicists generally avoid the commonplace language of "moving" or "traveling" through time ("movement" normally refers only to a change in spatial position as the time coordinate is varied), and instead discuss the possibility of closed timelike curves, which are worldlines that form closed loops in spacetime, allowing objects to return to their own past. There are known to be solutions to the equations of general relativity that describe spacetimes which contain closed timelike curves (such as Gödel spacetime), but the physical plausibility of these solutions is uncertain. Relativity predicts that if one were to move away from the Earth at relativistic velocities and return, more time would have passed on Earth than for the traveler, so in this sense it is accepted that relativity allows "travel into the future" (according to relativity there is no single objective answer to how much time has really passed between the departure and the return, but there is an objective answer to how much proper time has been experienced by both the Earth and the traveler, i.e., how much each has aged; see twin paradox). On the other hand, many in the scientific community believe that backwards time travel is highly unlikely. Any theory that would allow time travel would require that problems of causality be resolved. The classic example of a problem involving causality is the "grandfather paradox": what if one were to go back in time and kill one's own grandfather before one's father was conceived? But some scientists believe that paradoxes can be avoided, by appealing either to the Novikov self-consistency principle or to the notion of branching parallel universes (see the 'Paradoxes' section below). Tourism in time Stephen Hawking has suggested that the absence of tourists from the future is an argument against the existence of time travel—a variant of the Fermi paradox. Of course this would not prove that time travel is physically impossible, since it might be that time travel is physically possible but that it is never developed (or is cautiously never used); and even if it is developed, Hawking notes elsewhere that time travel might only be possible in a region of spacetime that is warped in the correct way, and that if we cannot create such a region until the future, then time travelers would not be able to travel back before that date, so "This picture would explain why we haven't been over run by tourists from the future."[19] Carl Sagan also once suggested the possibility that time travelers could be here, but are disguising their existence or are not recognized as time travelers.[20] General relativity However, the theory of general relativity does suggest a scientific basis for the possibility of backwards time travel in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed.[21] These semiclassical arguments led Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel,[22] but physicists cannot come to a definite judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory.[23] Time travel 5 In physics Time travel to the past is theoretically allowed using the following methods:[24] • Travelling faster than the speed of light • The use of cosmic strings and black holes • Wormholes and Alcubierre drive Via faster-than-light (FTL) travel If one were able to move information or matter from one point to another faster than light, then according to special relativity, there would be some inertial frame of reference in which the signal or object was moving backward in time. This is a consequence of the relativity of simultaneity in special relativity, which says that in some cases different reference frames will disagree on whether two events at different locations happened "at the same time" or not, and they can also disagree on the order of the two events (technically, these disagreements occur when the spacetime interval between the events is 'space-like', meaning that neither event lies in the future light cone of the other).[25] If one of the two events represents the sending of a signal from one location and the second event represents the reception of the same signal at another location, then as long as the signal is moving at the speed of light or slower, the mathematics of simultaneity ensures that all reference frames agree that the transmission-event happened before the reception-event.[25] However, in the case of a hypothetical signal moving faster than light, there would always be some frames in which the signal was received before it was sent, so that the signal could be said to have moved backwards in time. And since one of the two fundamental postulates of special relativity says that the laws of physics should work the same way in every inertial frame, then if it is possible for signals to move backwards in time in any one frame, it must be possible in all frames. This means that if observer A sends a signal to observer B which moves FTL (faster than light) in A's frame but backwards in time in B's frame, and then B sends a reply which moves FTL in B's frame but backwards in time in A's frame, it could work out that A receives the reply before sending the original signal, a clear violation of causality in every frame. An illustration of such a scenario using spacetime diagrams can be found here.[26] The scenario is sometimes referred to as a tachyonic antitelephone. According to special relativity, it would take an infinite amount of energy to accelerate a slower-than-light object to the speed of light. Although relativity does not forbid the theoretical possibility of tachyons which move faster than light at all times, when analyzed using quantum field theory, it seems that it would not actually be possible to use them to transmit information faster than light.[27] There is also no widely agreed-upon evidence for the existence of tachyons; the faster-than-light neutrino anomaly had suggested that neutrinos were possibly tachyons, but the results of the experiment were found to be invalid upon further analysis. Another group of experimenters state that a lack of radiation posited by a theory indicates the neutrinos cannot have really been traveling faster than light.[28] The OPERA team leader, Dario Autiero, and CERN's research director, Sergio Bertolucci, note other explanations are possible for the lack of neutrino energy loss via radiation.[29][30] Special spacetime geometries The general theory of relativity extends the special theory to cover gravity, illustrating it in terms of curvature in spacetime caused by mass-energy and the flow of momentum. General relativity describes the universe under a system of field equations, and there exist solutions to these equations that permit what are called "closed time-like curves," and hence time travel into the past.[18] The first of these was proposed by Kurt Gödel, a solution known as the Gödel metric, but his (and many others') example requires the universe to have physical characteristics that it does not appear to have.[18] Whether general relativity forbids closed time-like curves for all realistic conditions is unknown. Time travel 6 Using wormholes Wormholes are a hypothetical warped spacetime which are also permitted by the Einstein field equations of general relativity,[31] although it would be impossible to travel through a wormhole unless it were what is known as a traversable wormhole. A proposed time-travel machine using a traversable wormhole would (hypothetically) work in the following way: One end of the wormhole is accelerated to some significant fraction of the speed of light, perhaps with some advanced propulsion system, and then brought back to the point of origin. Alternatively, another way is to take one entrance of the wormhole and move it to within the gravitational field of an object that has higher gravity than the other entrance, and then return it to a position near the other entrance. For both of these methods, time dilation causes the end of the wormhole that has been moved to have aged less than the stationary end, as seen by an external observer; however, time connects differently through the wormhole than outside it, so that synchronized clocks at either end of the wormhole will always remain synchronized as seen by an observer passing through the wormhole, no matter how the two ends move around.[32] This means that an observer entering the accelerated end would exit the stationary end when the stationary end was the same age that the accelerated end had been at the moment before entry; for example, if prior to entering the wormhole the observer noted that a clock at the accelerated end read a date of 2007 while a clock at the stationary end read 2012, then the observer would exit the stationary end when its clock also read 2007, a trip backwards in time as seen by other observers outside. One significant limitation of such a time machine is that it is only possible to go as far back in time as the initial creation of the machine;[33] in essence, it is more of a path through time than it is a device that itself moves through time, and it would not allow the technology itself to be moved backwards in time. This could provide an alternative explanation for Hawking's observation: a time machine will be built someday, but has not yet been built, so the tourists from the future cannot reach this far back in time. According to current theories on the nature of wormholes, construction of a traversable wormhole would require the existence of a substance with negative energy (often referred to as "exotic matter"). More technically, the wormhole spacetime requires a distribution of energy that violates various energy conditions, such as the null energy condition along with the weak, strong, and dominant energy conditions.[34] However, it is known that quantum effects can lead to small measurable violations of the null energy condition,[34] and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics.[35] Although early calculations suggested a very large amount of negative energy would be required, later calculations showed that the amount of negative energy can be made arbitrarily small.[36] In 1993, Matt Visser argued that the two mouths of a wormhole with such an induced clock difference could not be brought together without inducing quantum field and gravitational effects that would either make the wormhole collapse or the two mouths repel each other.[37] Because of this, the two mouths could not be brought close enough for causality violation to take place. However, in a 1997 paper, Visser hypothesized that a complex "Roman ring" (named after Tom Roman) configuration of an N number of wormholes arranged in a symmetric polygon could still act as a time machine, although he concludes that this is more likely a flaw in classical quantum gravity theory rather than proof that causality violation is possible.[38] Other approaches based on general relativity Another approach involves a dense spinning cylinder usually referred to as a Tipler cylinder, a GR solution discovered by Willem Jacob van Stockum[39] in 1936 and Kornel Lanczos[40] in 1924, but not recognized as allowing closed timelike curves[41] until an analysis by Frank Tipler[42] in 1974. If a cylinder is infinitely long and spins fast enough about its long axis, then a spaceship flying around the cylinder on a spiral path could travel back in time (or forward, depending on the direction of its spiral). However, the density and speed required is so great that ordinary matter is not strong enough to construct it. A similar device might be built from a cosmic string, but none are known to exist, and it does not seem to be possible to create a new cosmic string. Time travel Physicist Robert Forward noted that a naïve application of general relativity to quantum mechanics suggests another way to build a time machine. A heavy atomic nucleus in a strong magnetic field would elongate into a cylinder, whose density and "spin" are enough to build a time machine. Gamma rays projected at it might allow information (not matter) to be sent back in time; however, he pointed out that until we have a single theory combining relativity and quantum mechanics, we will have no idea whether such speculations are nonsense. A more fundamental objection to time travel schemes based on rotating cylinders or cosmic strings has been put forward by Stephen Hawking, who proved a theorem showing that according to general relativity it is impossible to build a time machine of a special type (a "time machine with the compactly generated Cauchy horizon") in a region where the weak energy condition is satisfied, meaning that the region contains no matter with negative energy density (exotic matter). Solutions such as Tipler's assume cylinders of infinite length, which are easier to analyze mathematically, and although Tipler suggested that a finite cylinder might produce closed timelike curves if the rotation rate were fast enough,[43] he did not prove this. But Hawking points out that because of his theorem, "it can't be done with positive energy density everywhere! I can prove that to build a finite time machine, you need negative energy."[44] This result comes from Hawking's 1992 paper on the chronology protection conjecture, where he examines "the case that the causality violations appear in a finite region of spacetime without curvature singularities" and proves that "[t]here will be a Cauchy horizon that is compactly generated and that in general contains one or more closed null geodesics which will be incomplete. One can define geometrical quantities that measure the Lorentz boost and area increase on going round these closed null geodesics. If the causality violation developed from a noncompact initial surface, the averaged weak energy condition must be violated on the Cauchy horizon."[45] However, this theorem does not rule out the possibility of time travel 1) by means of time machines with the non-compactly generated Cauchy horizons (such as the Deutsch-Politzer time machine) and 2) in regions which contain exotic matter (which would be necessary for traversable wormholes or the Alcubierre drive). Because the theorem is based on general relativity, it is also conceivable a future theory of quantum gravity which replaced general relativity would allow time travel even without exotic matter (though it is also possible such a theory would place even more restrictions on time travel, or rule it out completely as postulated by Hawking's chronology protection conjecture). 7 Experiments carried out Certain experiments carried out give the impression of reversed causality but are interpreted in a different way by the scientific community. For example, in the delayed choice quantum eraser experiment performed by Marlan Scully, pairs of entangled photons are divided into "signal photons" and "idler photons", with the signal photons emerging from one of two locations and their position later measured as in the double slit experiment, and depending on how the idler photon is measured, the experimenter can either learn which of the two locations the signal photon emerged from or "erase" that information. Even though the signal photons can be measured before the choice has been made about the idler photons, the choice seems to retroactively determine whether or not an interference pattern is observed when one correlates measurements of idler photons to the corresponding signal photons. However, since interference can only be observed after the idler photons are measured and they are correlated with the signal photons, there is no way for experimenters to tell what choice will be made in advance just by looking at the signal photons, and under most interpretations of quantum mechanics the results can be explained in a way that does not violate causality. The experiment of Lijun Wang might also show causality violation since it made it possible to send packages of waves through a bulb of caesium gas in such a way that the package appeared to exit the bulb 62 nanoseconds before its entry. But a wave package is not a single well-defined object but rather a sum of multiple waves of different frequencies (see Fourier analysis), and the package can appear to move faster than light or even backwards in time even if none of the pure waves in the sum do so. This effect cannot be used to send any matter, energy, or information faster than light,[46] so this experiment is understood not to violate causality either. Time travel The physicists Günter Nimtz and Alfons Stahlhofen, of the University of Koblenz, claim to have violated Einstein's theory of relativity by transmitting photons faster than the speed of light. They say they have conducted an experiment in which microwave photons – energetic packets of light – traveled "instantaneously" between a pair of prisms that had been moved up to 3 ft (unknown operator: u'strong' m) apart, using a phenomenon known as quantum tunneling. Nimtz told New Scientist magazine: "For the time being, this is the only violation of special relativity that I know of." However, other physicists say that this phenomenon does not allow information to be transmitted faster than light. Aephraim Steinberg, a quantum optics expert at the University of Toronto, Canada, uses the analogy of a train traveling from Chicago to New York, but dropping off train cars at each station along the way, so that the center of the train moves forward at each stop; in this way, the center of the train exceeds the speed of any of the individual cars.[47] Some physicists have performed experiments which attempted to show causality violations, but so far without success. The "Space-time Twisting by Light" (STL) experiment run by physicist Ronald Mallett attempts to observe a violation of causality when a neutron is passed through a circle made up of a laser whose path has been twisted by passing it through a photonic crystal. Mallett has some physical arguments that suggest that closed timelike curves would become possible through the center of a laser which has been twisted into a loop. However, other physicists dispute his arguments (see objections). Shengwang Du claims in a peer reviewed journal to have observed single photons' precursors, saying that they travel no faster than c in a vacuum. His experiment involved slow light as well as passing light through a vacuum. He generated two single photons, passing one through rubidium atoms that had been cooled with a laser (thus slowing the light) and passing one through a vacuum. Both times, apparently, the precursors preceded the photons' main bodies, and the precursor traveled at c in a vacuum. According to Du, this implies that there is no possibility of light traveling faster than c (and, thus, violating causality).[48] Some members of the media took this as an indication of proof that time travel was impossible.[49][50] Non-physics-based experiments Several experiments have been carried out to try to entice future humans, who might invent time travel technology, to come back and demonstrate it to people of the present time. Events such as Perth's Destination Day (2005) or MIT's Time Traveler Convention heavily publicized permanent "advertisements" of a meeting time and place for future time travelers to meet. Back in 1982, a group in Baltimore, MD., identifying itself as the Krononauts, hosted an event of this type welcoming visitors from the future.[51][52] These experiments only stood the possibility of generating a positive result demonstrating the existence of time travel, but have failed so far—no time travelers are known to have attended either event. It is hypothetically possible that future humans have traveled back in time, but have traveled back to the meeting time and place in a parallel universe.[53] Another factor is that for all the time travel devices considered under current physics (such as those that operate using wormholes), it is impossible to travel back to before the time machine was actually made.[54][55] 8 Time travel 9 Time travel to the future in physics There are various ways in which a person could "travel into the future" in a limited sense: the person could set things up so that in a small amount of his own subjective time, a large amount of subjective time has passed for other people on Earth. For example, an observer might take a trip away from the Earth and back at relativistic velocities, with the trip only lasting a few years according to the observer's own clocks, and return to find that thousands of years had passed on Earth. It should be noted, though, that according to relativity there is no objective answer to the question of how much time "really" passed during the trip; it would be equally valid to say that the trip had lasted only a few years or that the trip had lasted thousands of years, depending on your choice of reference frame. Twin paradox diagram This form of "travel into the future" is theoretically allowed (and has been demonstrated at very small time scales) using the following methods:[24] • Using velocity-based time dilation under the theory of special relativity, for instance: • Traveling at almost the speed of light to a distant star, then slowing down, turning around, and traveling at almost the speed of light back to Earth[56] (see the Twin paradox) • Using gravitational time dilation under the theory of general relativity, for instance: • Residing inside of a hollow, high-mass object; • Residing just outside of the event horizon of a black hole, or sufficiently near an object whose mass or density causes the gravitational time dilation near it to be larger than the time dilation factor on Earth. Additionally, it might be possible to see the distant future of the Earth using methods which do not involve relativity at all, although it is even more debatable whether these should be deemed a form of "time travel": • Hibernation • Suspended animation Time dilation Time dilation is permitted by Albert Einstein's special and general theories of relativity. These theories state that, relative to a given observer, time passes more slowly for bodies moving quickly relative to that observer, or bodies that are deeper within a gravity well.[57] For example, a clock which is moving relative to the observer will be measured to run slow in that observer's rest frame; as a clock approaches the speed of light it will almost slow to a stop, although it can never quite reach light speed so it will never completely stop. For two clocks moving inertially (not accelerating) relative to one another, this effect is reciprocal, with each clock measuring the other to be ticking slower. However, the symmetry is broken if one clock accelerates, as in the twin paradox where one twin stays on Earth while the other travels into space, turns around (which involves acceleration), and returns—in this case both agree the traveling twin has aged less. General relativity states that time dilation effects also occur if one Transversal time dilation Time travel clock is deeper in a gravity well than the other, with the clock deeper in the well ticking more slowly; this effect must be taken into account when calibrating the clocks on the satellites of the Global Positioning System, and it could lead to significant differences in rates of aging for observers at different distances from a black hole. It has been calculated that, under general relativity, a person could travel forward in time at a rate four times that of distant observers by residing inside a spherical shell with a diameter of 5 meters and the mass of Jupiter.[24] For such a person, every one second of their "personal" time would correspond to four seconds for distant observers. Of course, squeezing the mass of a large planet into such a structure is not expected to be within our technological capabilities in the near future. There is a great deal of experimental evidence supporting the validity of equations for velocity-based time dilation in special relativity[58] and gravitational time dilation in general relativity.[59][60][61] However, with current technologies it is only possible to cause a human traveller to age less than companions on Earth by a very small fraction of a second, the current record being about 20 milliseconds for the cosmonaut Sergei Avdeyev. 10 Time perception Time perception can be apparently sped up for living organisms through hibernation, where the body temperature and metabolic rate of the creature is reduced. A more extreme version of this is suspended animation, where the rates of chemical processes in the subject would be severely reduced. Time dilation and suspended animation only allow "travel" to the future, never the past, so they do not violate causality, and it's debatable whether they should be called time travel. However time dilation can be viewed as a better fit for our understanding of the term "time travel" than suspended animation, since with time dilation less time actually does pass for the traveler than for those who remain behind, so the traveler can be said to have reached the future faster than others, whereas with suspended animation this is not the case. Other ideas from mainstream physics Paradoxes The Novikov self-consistency principle and calculations by Kip S. Thorne indicate that simple masses passing through time travel wormholes could never engender paradoxes—there are no initial conditions that lead to paradox once time travel is introduced. If his results can be generalized, they would suggest, curiously, that none of the supposed paradoxes formulated in time travel stories can actually be formulated at a precise physical level: that is, that any situation you can set up in a time travel story turns out to permit many consistent solutions. The circumstances might, however, turn out to be almost unbelievably strange. Parallel universes might provide a way out of paradoxes. Everett's many-worlds interpretation (MWI) of quantum mechanics suggests that all possible quantum events can occur in mutually exclusive histories.[62] These alternate, or parallel, histories would form a branching tree symbolizing all possible outcomes of any interaction. If all possibilities exist, any paradoxes could be explained by having the paradoxical events happening in a different universe. This concept is most often used in science-fiction, but some physicists such as David Deutsch have suggested that if time travel is possible and the MWI is correct, then a time traveler should indeed end up in a different history than the one he started from.[63][64] On the other hand, Stephen Hawking has argued that even if the MWI is correct, we should expect each time traveler to experience a single self-consistent history, so that time travelers remain within their own world rather than traveling to a different one.[19] And the physicist Allen Everett argued that Deutsch's approach "involves modifying fundamental principles of quantum mechanics; it certainly goes beyond simply adopting the MWI." Everett also argues that even if Deutsch's approach is correct, it would imply that any macroscopic object composed of multiple particles would be split apart when traveling back in time through a wormhole, with different particles emerging in different worlds.[65] Time travel Daniel Greenberger and Karl Svozil proposed that quantum theory gives a model for time travel without paradoxes.[66][67] In quantum theory observation causes possible states to 'collapse' into one measured state; hence, the past observed from the present is deterministic (it has only one possible state), but the present observed from the past has many possible states until our actions cause it to collapse into one state. Our actions will then be seen to have been inevitable. 11 Using quantum entanglement Quantum-mechanical phenomena such as quantum teleportation, the EPR paradox, or quantum entanglement might appear to create a mechanism that allows for faster-than-light (FTL) communication or time travel, and in fact some interpretations of quantum mechanics such as the Bohm interpretation presume that some information is being exchanged between particles instantaneously in order to maintain correlations between particles.[68] This effect was referred to as "spooky action at a distance" by Einstein. Nevertheless, the fact that causality is preserved in quantum mechanics is a rigorous result in modern quantum field theories, and therefore modern theories do not allow for time travel or FTL communication. In any specific instance where FTL has been claimed, more detailed analysis has proven that to get a signal, some form of classical communication must also be used.[69] The no-communication theorem also gives a general proof that quantum entanglement cannot be used to transmit information faster than classical signals. The fact that these quantum phenomena apparently do not allow FTL time travel is often overlooked in popular press coverage of quantum teleportation experiments. How the rules of quantum mechanics work to preserve causality is an active area of research. Philosophical understandings of time travel Theories of time travel are riddled with questions about causality and paradoxes. Compared to other fundamental concepts in modern physics, time is still not understood very well. Philosophers have been theorizing about the nature of time since the era of the ancient Greek philosophers and earlier. Some philosophers and physicists who study the nature of time also study the possibility of time travel and its logical implications. The probability of paradoxes and their possible solutions are often considered. For more information on the philosophical considerations of time travel, consult the work of David Lewis or Ted Sider [70]. For more information on physics-related theories of time travel, consider the work of Kurt Gödel (especially his theorized universe) and Lawrence Sklar. Presentism vs. eternalism The relativity of simultaneity in modern physics favors the philosophical view known as eternalism or four-dimensionalism (Sider, 2001), in which physical objects are either temporally extended spacetime worms, or spacetime worm stages, and this view would be favored further by the possibility of time travel (Sider, 2001). Eternalism, also sometimes known as "block universe theory", builds on a standard method of modeling time as a dimension in physics, to give time a similar ontology to that of space (Sider, 2001). This would mean that time is just another dimension, that future events are "already there", and that there is no objective flow of time. This view is disputed by Tim Maudlin in his The Metaphysics Within Physics. Presentism is a school of philosophy that holds that neither the future nor the past exist, and there are no non-present objects. In this view, time travel is impossible because there is no future or past to travel to. However, some 21st century presentists have argued that although past and future objects do not exist, there can still be definite truths about past and future events, and thus it is possible that a future truth about a time traveler deciding to travel back to the present date could explain the time traveler's actual appearance in the present.[71][72] Time travel 12 The grandfather paradox One subject often brought up in philosophical discussion of time is the idea that, if one were to go back in time, paradoxes could ensue if the time traveler were to change things. The best examples of this are the grandfather paradox and the idea of autoinfanticide. The grandfather paradox is a hypothetical situation in which a time traveler goes back in time and attempts to kill his grandfather at a time before his grandfather met his grandmother. If he did so, then his mother or father never would have been born, and neither would the time traveler himself, in which case the time traveler never would have gone back in time to kill his grandfather. Autoinfanticide works the same way, where a traveler goes back and attempts to kill himself as an infant. If he were to do so, he never would have grown up to go back in time to kill himself as an infant. This discussion is important to the philosophy of time travel because philosophers question whether these paradoxes make time travel impossible. Some philosophers answer the paradoxes by arguing that it might be the case that backwards time travel could be possible but that it would be impossible to actually change the past in any way,[73] an idea similar to the proposed Novikov self-consistency principle in physics. Theory of compossibility David Lewis's analysis of compossibility and the implications of changing the past is meant to account for the possibilities of time travel in a one-dimensional conception of time without creating logical paradoxes. Consider Lewis’ example of Tim. Tim hates his grandfather and would like nothing more than to kill him. The only problem for Tim is that his grandfather died years ago. Tim wants so badly to kill his grandfather himself that he constructs a time machine to travel back to 1955 when his grandfather was young and kill him then. Assuming that Tim can travel to a time when his grandfather is still alive, the question must then be raised: can Tim kill his grandfather? For Lewis, the answer lies within the context of the usage of the word "can". Lewis explains that the word "can" must be viewed against the context of pertinent facts relating to the situation. Suppose that Tim has a rifle, years of rifle training, a straight shot on a clear day and no outside force to restrain Tim’s trigger finger. Can Tim shoot his grandfather? Considering these facts, it would appear that Tim can in fact kill his grandfather. In other words, all of the contextual facts are compossible with Tim killing his grandfather. However, when reflecting on the compossibility of a given situation, we must gather the most inclusive set of facts that we are able to. Consider now the fact that Tim’s grandfather died in 1993 and not in 1955. This new fact about Tim’s situation reveals that him killing his grandfather is not compossible with the current set of facts. Tim cannot kill his grandfather because his grandfather died in 1993 and not when he was young. Thus, Lewis concludes, the statements "Tim doesn’t but can, because he has what it takes," and, "Tim doesn’t, and can’t, because it is logically impossible to change the past," are not contradictions; they are both true given the relevant set of facts. The usage of the word "can" is equivocal: he "can" and "can not" under different relevant facts. So what must happen to Tim as he takes aim? Lewis believes that his gun will jam, a bird will fly in the way, or Tim simply slips on a banana peel. Either way, there will be some logical force of the universe that will prevent Tim every time from killing his grandfather.[74] Ideas from fiction Further information: Time travel in fiction Rules of time travel Time travel themes in science fiction and the media can generally be grouped into two general categories (based on effect—methods are extremely varied and numerous), each of which can be further subdivided.[75][76][77][78] However, there are no formal names for these two categories, so concepts rather than formal names will be used with notes regarding what categories they are placed under (Note: These classifications do not address the method of time Time travel travel itself, i.e. how to travel through time, but instead call to attention differing rules of what happens to history.). As used in this section, timeline refers to all physical events in history, so that in time travel stories where events can be changed, the time traveler can create a new or altered timeline. This usage of "timeline" is fairly common in time travel fiction,[1] and is distinct from the usage of "timeline" to refer to a type of chart created by humans to illustrate a particular series of events (see timeline). This concept is also distinct from the concept of a world line, a term from Einstein's theory of relativity which refers to the entire history of a single object (usually idealized as a point particle) that forms a distinct path through 4-dimensional spacetime. 1. There is a single fixed history, which is self-consistent and unchangeable. In this version, everything happens on a single timeline which does not contradict itself and cannot interact with anything potentially existing outside of it. 1.1 This can be simply achieved by applying the Novikov self-consistency principle, named after Dr. Igor Dmitrievich Novikov, Professor of Astrophysics at Copenhagen University. The principle states that the timeline is totally fixed, and any actions taken by a time traveler were part of history all along, so it is impossible for the time traveler to "change" history in any way. The A man travelling a few seconds into the past in a time traveler's actions may be the cause of events in their single self-consistent timeline. This scenario own past though, which leads to the potential for circular raises questions about free will, since once the causation and the predestination paradox; for examples of traveller has decided to enter the time machine, then as soon as his own double appears, there is circular causation, see Robert A. Heinlein's story "By His absolutely no way for him to change his mind. Bootstraps". The Novikov self-consistency principle proposes that the local laws of physics in a region of spacetime containing time travelers cannot be any different from the local laws of physics in any other region of spacetime.[79] An example of such kind of time travel occurs in the japanese light novel and anime The Melancholy of Haruhi Suzumiya. In this story, every time a time traveler has to go back in the past, he or she gets the feeling he should make sure everything happens exactly as it is remembered. No indication is given about what would happen otherwise, though. Also, in the first episode of the second season, an apparent causal loop is noticed, which is then explained by a reformulation of Gödel's theorem. 1.2 Alternatively, new physical laws take effect regarding time travel that thwarts attempts to change the past (contradicting the assumption mentioned in 1.1 above that the laws that apply to time travelers are the same ones that apply to everyone else). These new physical laws can be as unsubtle as to reject time travelers who travel to the past to change it by pulling them back to the point from when they came as Michael Moorcock's The Dancers at the End of Time or where the traveler is rendered a noncorporeal phantom unable to physically interact with the past such as in some Pre-Crisis Superman stories and Michael Garrett's "Brief Encounter" in Twilight Zone Magazine May 1981. 2. History is flexible and is subject to change (Plastic Time) 2.1 Changes to history are easy and can impact the traveler, the world, or both Examples include Doctor Who and the Back to the Future trilogy. In some cases, any resulting paradoxes can be devastating, threatening the very existence of the universe. In other cases the traveler simply cannot return home. The extreme version of this (Chaotic Time) is that history is very sensitive to changes with even small changes having large impacts such as in Ray Bradbury's "A Sound of Thunder". 13 Time travel 2.2 History is change resistant in direct relationship to the importance of the event i.e., small trivial events can be readily changed but large ones take great effort. In the Twilight Zone episode "Back There" a traveler tries to prevent the assassination of President Lincoln and fails, but his actions have made subtle changes to the status quo in his own time (e.g. a man who had been the butler of his gentleman's club is now a rich tycoon). In the 2002 remake of The Time Machine, it is explained via a vision why Hartdegen could not save his sweetheart Emma—doing so would have resulted in his never developing the time machine he used to try and save her. In The Saga of Darren Shan, major events in the past cannot be changed, but their details can alter while providing the same outcome. Under this model, if a time traveler were to go back in time and kill Hitler, another Nazi would simply take his place and commit his same actions, leaving the broader course of history unchanged. In the Doctor Who episode The Waters of Mars, Captain Adelaide Brooke's death on Mars is the most singular catalyst of human travel outside the solar system. At first, the Doctor realizes her death is a "fixed point in time" and does not intervene, but later defies this rule and transports her and her crew to Earth. Rather than allow human history to change, Captain Brooke commits suicide on Earth, leaving history mostly unchanged. 3. Alternate timelines. In this version of time travel, there are multiple coexisting alternate histories, so that when the traveler goes back in time, he/she ends up in a new timeline where historical events can differ from the timeline he/she came from, but her original timeline does not cease to exist (this means the grandfather paradox can be avoided since even if the time traveler's grandfather is killed at a young age in the new timeline, he still survived to have children in the original timeline, so there is still a causal explanation for the traveler's existence). Time travel may actually create a new timeline that diverges from the original timeline at the moment the time traveler appears in the past, or the traveler may arrive in an already existing parallel universe (though unless the parallel universe's history was identical to the time traveler's history up until the point where the time traveler appeared, it is questionable whether the latter version qualifies as 'time travel'). 14 Time travel under the parallel universe hypothesis. This scenario has the potential to preserve free will, but breaks symmetry between universes. James P. Hogan's The Proteus Operation fully explains parallel universe time travel in chapter 20 where it has Einstein explaining that all the outcomes already exist and all time travel does is change which already existing branch you will experience. Though Star Trek has a long tradition of using the 2.1 mechanic, as seen in "The City on the Edge of Forever", "Tomorrow is Yesterday", "Time and Again", "Future's End", "Before and After", "Endgame" and as late as Enterprise's Temporal Cold War, "Parallels" had an example of what Data called "quantum realities." His exact words on the matter were "But there is a theory in quantum physics that all possibilities that can happen do happen in alternate quantum realities," suggesting the writers were thinking of the many-worlds interpretation of quantum mechanics. Michael Crichton's novel Timeline takes the approach that all time travel really is travel to an already existing parallel universe where time passes at a slower rate than our own but actions in any of these parallel universes may have already occurred in our past. It is unclear from the novel if any sizable Time travel change in events of these parallel universe can be made. In the Homeline setting of GURPS Infinite Worlds there are echos—parallel universes at an early part of Homeline's history but changes to their history do not affect Homeline's history. However tampering with their history can cause them to shift quanta making access harder if not impossible. A type of story which could be placed in this category is one where the alternative version of the past lies not in some other dimension, but simply at a distant location in space or a future period of time that replicates conditions in the traveler's past. For example, in a Futurama episode called The Late Philip J. Fry, the professor designed a forward-only time travel device. Trapped in the future, he and two colleagues travel forward all the way to the end of the universe, at which point they witness a new Big Bang which gives rise to a new universe whose history mirrors their own history. Then they continue to go forward until they reach the exact time of their initial departure. Although this journey is not exactly a backward time travel, the final result is the same. In the Japanese manga, Dragon Ball Z, the character Trunks travels back in time to warn the characters of their deaths soon to come. This does not change his time line, only creates a new one in which they do not die. Soon two of the characters destroy the lab where the monster Cell is being created, stopping him from absorbing the androids, creating a third time line. Later it is revealed that Trunks is killed by Cell in the future, then travels to three years before any of the events occurs, which creates a fourth time line. No matter what any character does in the past, their own original time line is unchanged. Immutable timelines Time travel in a type 1 universe does not allow paradoxes such as the grandfather paradox to occur, where one deduces both a conclusion and its opposite (in the case of the grandfather paradox, one can start with the premise of the time traveler killing his grandfather, and reach the conclusion that the time traveler will not be able to kill his grandfather since he was never born) though it can allow other paradoxes to occur. In 1.1, the Novikov self-consistency principle asserts that the existence of a method of time travel constrains events to remain self-consistent. This will cause any attempt to violate such consistency to fail, even if seemingly extremely improbable events are required. Example: You have a device that can send a single bit of information back to itself at a precise moment in time. You receive a bit at 10:00:00 p.m., then no bits for thirty seconds after that. If you send a bit back to 10:00:00 p.m., everything works fine. However, if you try to send a bit to 10:00:15 p.m. (a time at which no bit was received), your transmitter will mysteriously fail. Or your dog will distract you for fifteen seconds. Or your transmitter will appear to work, but as it turns out your receiver failed at exactly 10:00:15 p.m., etc. Examples of this kind of universe are found in Robert Forward's novel Timemaster, the Twilight Zone episode "No Time Like the Past", and the 1980 Jeannot Szwarc film Somewhere In Time (based on Richard Matheson's novel Bid Time Return). In 1.2, time travel is constrained to prevent paradox. How this occurs is dependent on whether interaction with the past is possible. If interaction with the past is possible and one attempts to make a paradox, one undergoes involuntary or uncontrolled time travel. In the time-travel stories of Connie Willis, time travelers encounter "slippage" which prevents them from either reaching the intended time or translates them a sufficient distance from their destination at the intended time, as to prevent any paradox from occurring. Example: A man who travels into the past with intentions to kill Hitler finds himself on a Montana farm in late April 1945. In the The Dancers at the End of Time series, Michael Moorcock invented a plot device called the Morphail Effect. This causes a time traveler to be ejected from the time in which he or she is about to cause a paradox. 15 Time travel Example 1: A man from the End of Time period travels to the past and is executed. Instead of dying (which would cause a paradox), he experiences a return to the End of Time Example 2: Time travelers sometimes visit the End of Time from their own epochs in the past. Those that attempt to return to their own period are likely to reappear inadvertently at the End of Time. The general consequences are that time travel to the traveler's past is difficult, and many time travelers find themselves adventuring deeper and deeper into their future. If interaction with the past is not possible then the traveler simply becomes an invisible insubstantial phantom unable to interact with the past as in the case of James Harrigan in Michael Garrett's "Brief Encounter". While a Type 1 universe will prevent a grandfather paradox it doesn't prevent paradoxes in other aspects of physics such as the predestination paradox and the ontological paradox (GURPS Infinite Worlds calls this "Free Lunch Paradox"). The predestination paradox is where the traveler's actions create some type of causal loop, in which some event A in the future helps cause event B in the past via time travel, and the event B in turn is one of the causes of A. For instance, a time traveler might go back to investigate a specific historical event like the Great Fire of London, and their actions in the past could then inadvertently end up being the original cause of that very event. Examples of this kind of causal loop are found in Robert Forward's novel Timemaster, the Twilight Zone episode "No Time Like the Past", EC Comics stories like "Man who was Killed in Time" (Weird Science #5), "Why Papa Left Home" (Weird Science #11), "Only Time will Tell" (Weird Fantasy #1), "The Connection" (Weird Fantasy #9), "Skeleton Key" (Weird Fantasy #16), and "Counter Clockwise" (Weird Fantasy #18), the 1980 Jeannot Szwarc film Somewhere In Time (based on Richard Matheson's novel Bid Time Return) the Michael Moorcock novel Behold the Man. In a scene in Harry Potter and the Prisoner of Azkaban by J. K. Rowling, Harry Potter and his friend Hermione Granger are being attacked by Dementors when Harry sees somebody whom he thinks is his father come up and cast a charm to save them. Later, Harry and Hermione go back in time to save 'an innocent man from a terrible fate'. During the period they are back in time, Harry ends up casting the charm to save his own life, and realises that it was himself whom he saw, not his father. Casual loops are also featured in 1972's Doctor Who, in the three part The Day of the Daleks, where three freedom fighters from the future attempt to kill a British diplomat they believe responsible for World War Three, and the subsequent easy conquest of Earth by the Daleks. In the future they were taught an explosion at the diplomat's (Sir Reginald Styles) mansion with foreign delegates inside caused the nations of the world to attack each other. The Doctor (Jon Pertwee), figures out that they caused the explosion all along by way of a temporal paradox. In the 2006 crime thriller Déjà Vu there appears to be causal loops, as Agent Doug Carlin decides to send a message back in time to save his partner's life, but this will eventually cause his death. Later in the movie, though, Carlin is able to change events and create an alternate reality. This apparent paradox can be explained by multiple previous unseen time travels in a type 3 universe. In the videogame Escape from Monkey Island there's a section in which the player, controlling Guybrush Threepwood, gets some items from his future self in the Swamp of Time. Soon after that, he will become the future Guybrush and will have to give the items to his past self in the same order. This is an example of causal loop because those items were created purely from the time travel. Anyway if the player doesn't repeat every action properly, will cause a paradox that sends Guybrush back to the entrance of the swamp, implying a type 1.2 universe. 16 Time travel 17 The Novikov self-consistency principle can also result in an ontological paradox (also known as the knowledge or information paradox)[80] where the very existence of some object or information is a time loop. GURPS Infinite Worlds gives the example (from The Eyre Affair) of a time traveler going to Shakespeare's time with a book of all his works. Shakespeare pressed for time simply copies the information in the book from the future. The paradox is that nobody actually writes the plays. The philosopher Kelley L. Ross argues in "Time Travel Paradoxes"[81] that in an ontological paradox scenario involving a physical object, there can be a violation of the second law of thermodynamics. Ross uses Somewhere in Time as an example where Jane Seymour's character gives Christopher Reeve's character a watch she has owned for many years, and when he travels back in time he gives the same watch to Jane Seymour's character 60 years in the past. As Ross states "The watch is an impossible object. It violates the Second Law of Thermodynamics, the Law of Entropy. If time travel makes that watch possible, then time travel itself is impossible. The watch, indeed, must be absolutely identical to itself in the 19th and 20th centuries, since Reeve carries it with him from the future instantaneously into the past and bestows it on Seymour. The watch, however, cannot be identical to itself, since all the years in which it is in the possession of Seymour and then Reeve it will wear in the normal manner. It's [sic] entropy will increase. The watch carried back by Reeve will be more worn that [sic] the watch that would have been acquired by Seymour." On the other hand, the second law of thermodynamics is understood by modern physicists to be a statistical law rather than an absolute one, so spontaneous reversals of entropy or failure to increase in entropy are not impossible, just improbable (see for example the fluctuation theorem). In addition, the second law of thermodynamics only states that entropy should increase in systems which are isolated from interactions with the external world, so Igor Novikov (creator of the Novikov self-consistency principle) has argued that in the case of macroscopic objects like the watch whose worldlines form closed loops, the outside world can expend energy to repair wear/entropy that the object acquires over the course of its history, so that it will be back in its original condition when it closes the loop.[82] Mutable timelines Time travel in a Type 2 universe is much more complex. The biggest problem is how to explain changes in the past. One method of explanation is that once the past changes, so do the memories of all observers. This would mean that no observer would ever observe the changing of the past (because they will not remember changing the past). This would make it hard to tell whether you are in a Type 1 universe or a Type 2 universe. You could, however, infer such information by knowing if a) communication with the past were possible or b) it appeared that the time line had never been changed as a result of an action someone remembers taking, although evidence exists that other people are changing their time lines fairly often. An example of this kind of universe is presented in Thrice Upon a Time, a novel by James P. Hogan. The Back to the Future trilogy films also seem to feature a single mutable timeline (see the "Back to the Future FAQ [83]" for details on how the writers imagined time travel worked in the movies' world). By contrast, the short story "Brooklyn Project" by William Tenn provides a sketch of life in a Type 2 world where no one even notices as the timeline changes repeatedly. In type 2.1, attempts are being made at changing the timeline, however, all that is accomplished in the first tries is that the method in which decisive events occur is changed; final conclusions in the bigger scheme cannot be brought to a different outcome. A version of the ontological paradox. The appearance of the traveler is the result of his disappearance a few seconds later. In this scenario, the traveler is traveling along a closed timelike curve. Time travel As an example, the movie Déjà Vu depicts a paper note sent to the past with vital information to prevent a terrorist attack. However, the vital information results in the killing of an ATF agent, but does not prevent the terrorist attack; the very same agent died in the previous version of the timeline as well, albeit under different circumstances. Finally, the timeline is changed by sending a human into the past, arguably a "stronger" measure than simply sending back a paper note, which results in preventing both a murder and the terrorist attack. As in the Back to the Future movie trilogy, there seems to be a ripple effect too as changes from the past "propagate" into the present, and people in the present have altered memory of events that occurred after the changes made to the timeline. The science fiction writer Larry Niven suggests in his essay "The Theory and Practice of Time Travel" that in a type 2.1 universe, the most efficient way for the universe to "correct" a change is for time travel to never be discovered, and that in a type 2.2 universe, the very large (or infinite) number of time travelers from the endless future will cause the timeline to change wildly until it reaches a history in which time travel is never discovered. However, many other "stable" situations might also exist in which time travel occurs but no paradoxes are created; if the changeable-timeline universe finds itself in such a state no further changes will occur, and to the inhabitants of the universe it will appear identical to the type 1.1 scenario. This is sometimes referred to as the "Time Dilution Effect". Few if any physicists or philosophers have taken seriously the possibility of "changing" the past except in the case of multiple universes, and in fact many have argued that this idea is logically incoherent,[73] so the mutable timeline idea is rarely considered outside of science fiction. Also, deciding whether a given universe is of Type 2.1 or 2.2 can not be done objectively, as the categorization of timeline-invasive measures as "strong" or "weak" is arbitrary, and up to interpretation: An observer can disagree about a measure being "weak", and might, in the lack of context, argue instead that simply a mishap occurred which then led to no effective change. An example would be the paper note sent back to the past in the film Déjà Vu, as described above. Was it a "too weak" change, or was it just a local-time alteration which had no extended effect on the larger timeline? As the universe in Déjà Vu seems not entirely immune to paradoxes (some arguably minute paradoxes do occur), both versions seem to be equally possible. Alternate histories In Type 3, any event that appears to have caused a paradox has instead created a new time line. The old time line remains unchanged, with the time traveler or information sent simply having vanished, never to return. A difficulty with this explanation, however, is that conservation of mass-energy would be violated for the origin timeline and the destination timeline. A possible solution to this is to have the mechanics of time travel require that mass-energy be exchanged in precise balance between past and future at the moment of travel, or to simply expand the scope of the conservation law to encompass all timelines. Some examples of this kind of time travel can be found in David Gerrold's book The Man Who Folded Himself and The Time Ships by Stephen Baxter, plus several episodes of the TV show Star Trek: The Next Generation and the android saga in the anime Dragon Ball Z. 18 Time travel 19 Gradual and instantaneous In literature, there are two methods of time travel: 1. The most commonly used method of time travel in science fiction is the instantaneous movement from one point in time to another, like using the controls on a CD player to skip to a previous or next song, though in most cases, there is a machine of some sort, and some energy expended in order to make this happen (like the time-traveling De Lorean in Back to the Future or the TARDIS (Time and Relative Dimension in Space) that traveled through time in Doctor Who). In some cases, there is not even the beginning of a scientific explanation for this kind of time travel; it's popular probably because it is more spectacular and makes time travel easier. The "Universal Remote" used by Adam Sandler in the movie Click works in the same manner, although only in one direction, the future. While his character Michael Newman can travel back to a previous point it is merely a playback with which he cannot interact. A gradual time travel, as in the movie Primer. When the time machine is red, everything inside is going through time at normal rate, but backwards. During entry/exit it seems there would have to be fusion/separation between the forward and reversed versions of the traveler. 2. In The Time Machine, H.G. Wells explains that we are moving through time with a constant speed. Time travel then is, in Wells' words, "stopping or accelerating one's drift along the time-dimension, or even turning about and traveling the other way." George Pal, director of the 1960 adaptation based on Wells's classic, accordingly chose to depict time travel by employing time-lapse photography. To expand on the audio playback analogy used above, this would be like rewinding or fast forwarding an analogue audio cassette and playing the tape at a chosen point. Perhaps the oldest example of this method of time travel is in Lewis Carroll's Through the Looking-Glass (1871): the White Queen is living backwards, hence her memory is working both ways. Her kind of time travel is uncontrolled: she moves through time with a constant speed of −1 and she cannot change it. T.H. White, in the first part of his Arthurian novel The Once and Future King, The Sword in the Stone (1938) used the same idea: the wizard Merlyn lives backward in time, because he was born "at the wrong end of time" and has to live backwards from the front. "Some people call it having second sight", he says. This method of gradual time travel is not as popular in modern science fiction, though a form of it does occur in the film Primer. Time travel or spacetime travel An objection that is sometimes raised against the concept of time machines in science fiction is that they ignore the motion of the Earth between the date the time machine departs and the date it returns. The idea that a traveler can go into a machine that sends him or her to 1865 and step out into the exact same spot on Earth might be said to ignore the issue that Earth is moving through space around the Sun, which is moving in the galaxy, and so on, so that advocates of this argument imagine that "realistically" the time machine should actually reappear in space far away from the Earth's position at that date. However, the theory of relativity rejects the idea of absolute time and space; in relativity there can be no universal truth about the spatial distance between events which occur at different times[84] (such as an event on Earth today and an event on Earth in 1865), and thus no objective truth about which point in space at one time is at the "same position" that the Earth was at another time. In the theory of special relativity, which deals with situations where gravity is negligible, the laws of physics work the same way in every inertial frame of reference and therefore no frame's perspective is physically better than any other frame's, and different frames disagree about whether two events at different times happened at the "same position" or "different positions". In the theory of general relativity, which incorporates the effects of gravity, all coordinate systems are on equal footing because of a feature known as "diffeomorphism invariance".[85] Nevertheless, the idea that the Earth moves away from the time traveler when he takes a trip through time has been used in a few science fiction stories, such as the 2000 AD comic Strontium Dog, in which Johnny Alpha uses "Time Time travel Bombs" to propel an enemy several seconds into the future, during which time the movement of the Earth causes the unfortunate victim to re-appear in space. Much earlier, Clark Ashton Smith used this form of time travel in several stories such as "The Letter from Mohaun Los" (1932) where the protagonist ends up on a planet millions of years in the future which "happened to occupy the same space through which Earth had passed". Other science fiction stories try to anticipate this objection and offer a rationale for the fact that the traveler remains on Earth, such as the 1957 Robert Heinlein novel The Door into Summer where Heinlein essentially handwaved the issue with a single sentence: "You stay on the world line you were on." In his 1980 novel The Number of the Beast a "continua device" allows the protagonists to dial in the coordinates of space and time and it instantly moves them there—without explaining how such a device might work. The television series Seven Days also dealt with this problem; when the chrononaut would be 'rewinding', he would also be propelling himself backwards around the Earth's orbit, with the intention of landing at some chosen spatial location, though seldom hitting the mark precisely. In Piers Anthony's Bearing an Hourglass, the potent Hourglass of the Incarnation of Time naturally moves the Incarnation in space according to the numerous movements of the globe through the solar system, the solar system through the galaxy, etc.; but by carefully negating some of the movements he can also travel in space within the limits of the planet. The television series Doctor Who avoided this issue by establishing early on in the series that the Doctor's TARDIS is able to move about in space in addition to traveling in time. 20 Notes [1] Brave New Words: The Oxford Dictionary of Science Fiction by Jeff Prucher (2007), p. 230 (http:/ / books. google. com/ books?id=iYzi8m8FbEsC& lpg=PP1& pg=PA230#v=onepage& q& f=false). [2] Revati (http:/ / www. mythfolklore. net/ india/ encyclopedia/ revati. htm), Encyclopedia for Epics of Ancient India [3] Lord Balarama (http:/ / mayapur. com/ node/ 1160/ ), Sri Mayapur [4] Yorke, Christopher (February 2006). "Malchronia: Cryonics and Bionics as Primitive Weapons in the War on Time" (http:/ / jetpress. org/ volume15/ yorke-rowe. html). Journal of Evolution and Technology 15 (1): 73–85. . Retrieved 2009-08-29. [5] Rosenberg, Donna (1997). Folklore, myths, and legends: a world perspective. McGraw-Hill. p. 421. ISBN 0-8442-5780-X. [6] "Choni HaMe'agel" (http:/ / www. jewishsearch. com/ article_395. html). Jewish search. . Retrieved November 6, 2009. [7] Robert Darnton, The Forbidden Best-Sellers of Pre-Revolutionary France (New York: W.W. Norton, 1996), 120. [8] Alkon, Paul K. (1987). Origins of Futuristic Fiction. The University of Georgia Press. pp. 95–96. ISBN 0-8203-0932-X. [9] Alkon, Paul K. (1987). Origins of Futuristic Fiction. The University of Georgia Press. p. 85. ISBN 0-8203-0932-X. [10] Yury Akutin, Александр Вельтман и его роман "Странник" (http:/ / az. lib. ru/ w/ welxtman_a_f/ text_0090. shtml) (A.V. and his novel Strannik), 1978 (in Russian). [11] "Missing One's Coach: An Anachronism" (http:/ / books. google. com/ books?id=jfPAwAnj9JUC& pg=RA1-PA701#v=onepage& q& f=false). Dublin University magazine: a literary and political journal, Volume 11. books.google.com. . Retrieved 4 December 2011. [12] Derleth, August (1951). Far Boundaries. Pellegrini & Cudahy. p. 3. [13] Derleth, August (1951). Far Boundaries. Pellegrini & Cudahy. pp. 11–38. [14] Flynn, John L.. "Time Travel Literature" (http:/ / web. archive. org/ web/ 20060929071327/ http:/ / www. towson. edu/ ~flynn/ timetv. html). Archived from the original (http:/ / www. towson. edu/ ~flynn/ timetv. html) on 2006-09-29. . Retrieved 2006-10-28. [15] Rudwick, Martin J. S. (1992). Scenes From Deep Time. The University of Chicago Press. pp. 166–169. ISBN 0-226-73105-7. [16] Page Mitchell, Edward. "The Clock That Went Backward" (http:/ / www. horrormasters. com/ Text/ a2221. pdf) (PDF). . Retrieved 4 December 2011. [17] Uribe, Augusto (June 1999). "The First Time Machine: Enrique Gaspar's Anacronópete". The New York Review of Science Fiction 11, no. 10 (130): 12. [18] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. p. 499. ISBN 0-393-31276-3. [19] Hawking, Stephen. "Space and Time Warps" (http:/ / www. hawking. org. uk/ space-and-time-warps. html). . Retrieved 2012-02-26. [20] "NOVA Online – Sagan on Time Travel" (http:/ / www. pbs. org/ wgbh/ nova/ time/ sagan. html). Pbs.org. . Retrieved 2010-05-25. [21] Matt Visser (2002). "The quantum physics of chronology protection". arXiv:gr-qc/0204022 [gr-qc]. [22] Hawking, Stephen (1992). "Chronology protection conjecture". Physical Review D 46 (2): 603. Bibcode 1992PhRvD..46..603H. doi:10.1103/PhysRevD.46.603. [23] Hawking, Stephen; Kip Thorne, Igor Novikov, Timothy Ferris, Alan Lightman (2002). The Future of Spacetime. W. W. Norton. p. 150. ISBN 0-393-02022-3. [24] Gott, J. Richard (2002). Time Travel in Einstein's Universe. p.33-130 [25] Jarrell, Mark. "The Special Theory of Relativity" (http:/ / web. archive. org/ web/ 20060913173236/ http:/ / www. physics. uc. edu/ ~jarrell/ COURSES/ ELECTRODYNAMICS/ Chap11/ chap11. pdf) (PDF). pp. 7–11. Archived from the original (http:/ / www. physics. uc. edu/ Time travel ~jarrell/ COURSES/ ELECTRODYNAMICS/ Chap11/ chap11. pdf) on 2006-09-13. . Retrieved 2006-10-27. [26] "Sharp Blue: Relativity, FTL and causality – Richard Baker" (http:/ / www. theculture. org/ rich/ sharpblue/ archives/ 000089. html). Theculture.org. . Retrieved 2010-05-25. [27] Chase, Scott I.. "Tachyons entry from Usenet Physics FAQ" (http:/ / math. ucr. edu/ home/ baez/ physics/ ParticleAndNuclear/ tachyons. html). . Retrieved 2006-10-27. [28] "New Analysis Deals Critical Blow to Faster-than-Light Results" by Natalie Wolchover (http:/ / www. livescience. com/ 17154-analysis-deals-critical-blow-faster-light-results. html) [29] Paul Rincon (October 28, 2011). "Faster-than-light neutrino experiment to be run again" (http:/ / www. bbc. co. uk/ news/ science-environment-15471118). BBC. . Retrieved October 28, 2011. [30] Eugenie Samuel Reich (November 18, 2011). "Neutrino experiment replicates faster-than-light finding" (http:/ / www. nature. com/ news/ neutrino-experiment-replicates-faster-than-light-finding-1. 9393). Nature News. . Retrieved November 18, 2011. [31] Visser, Matt (1996). Lorentzian Wormholes. Springer-Verlag. p. 100. ISBN 1-56396-653-0. [32] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. p. 502. ISBN 0-393-31276-3. [33] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. p. 504. ISBN 0-393-31276-3. [34] Visser, Matt (1996). Lorentzian Wormholes. Springer-Verlag. p. 101. ISBN 1-56396-653-0. [35] Cramer, John G.. "NASA Goes FTL Part 1: Wormhole Physics" (http:/ / web. archive. org/ web/ 20060627211046/ http:/ / www. npl. washington. edu/ av/ altvw69. html). Archived from the original (http:/ / www. npl. washington. edu/ av/ altvw69. html) on 2006-06-27. . Retrieved 2006-12-02. [36] Visser, Matt; Sayan Kar, Naresh Dadhich (2003). "Traversable wormholes with arbitrarily small energy condition violations". Physical Review Letters 90 (20): 201102.1–201102.4. arXiv:gr-qc/0301003. Bibcode 2003PhRvL..90t1102V. doi:10.1103/PhysRevLett.90.201102. [37] Visser, Matt (1993). "From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture". Physical Review D 47 (2): 554–565. arXiv:hep-th/9202090. Bibcode 1993PhRvD..47..554V. doi:10.1103/PhysRevD.47.554. [38] Visser, Matt (1997). "Traversable wormholes: the Roman ring". Physical Review D 55 (8): 5212–5214. arXiv:gr-qc/9702043. Bibcode 1997PhRvD..55.5212V. doi:10.1103/PhysRevD.55.5212. [39] van Stockum, Willem Jacob (1936). "The Gravitational Field of a Distribution of Particles Rotating about an Axis of Symmetry" (http:/ / www-lorentz. leidenuniv. nl/ history/ stockum/ Proc_R_Soc_Edinb_57_135_1937. jpg). Proceedings of the Royal Society of Edinburgh. . [40] Lanczos, Kornel (1924, republished in 1997). "On a Stationary Cosmology in the Sense of Einsteins Theory of Gravitation". General Relativity and Gravitation (Springland Netherlands) 29 (3): 363–399. doi:10.1023/A:1010277120072. [41] Earman, John (1995). Bangs, Crunches, Whimpers, and Shrieks: Singularities and Acausalities in Relativistic Spacetimes. Oxford University Press. p. 21. ISBN 0-19-509591-X. [42] Tipler, Frank J (1974). "Rotating Cylinders and the Possibility of Global Causality Violation". Physical Review D 9 (8): 2203. Bibcode 1974PhRvD...9.2203T. doi:10.1103/PhysRevD.9.2203. [43] Earman, John (1995). Bangs, Crunches, Whimpers, and Shrieks: Singularities and Acausalities in Relativistic Spacetimes. Oxford University Press. p. 169. ISBN 0-19-509591-X. [44] Hawking, Stephen; Kip Thorne, Igor Novikov, Timothy Ferris, Alan Lightman (2002). The Future of Spacetime. W. W. Norton. p. 96. ISBN 0-393-02022-3. [45] Hawking, Stephen (1992). "Chronology protection conjecture". Physical Review D 46 (2): 603–611. Bibcode 1992PhRvD..46..603H. doi:10.1103/PhysRevD.46.603. [46] Wright, Laura (November 6, 2003). "Score Another Win for Albert Einstein" (http:/ / discovermagazine. com/ 2003/ nov/ score-another-win-for-einstein1106). Discover. . [47] Anderson, Mark (August 18–24, 2007). "Light seems to defy its own speed limit" (http:/ / www. eurekalert. org/ pub_releases/ 2007-08/ ns-lst081607. php). New Scientist 195 (2617): p. 10. . [48] The Hong Kong University of Science & Technology (http:/ / www. ust. hk/ eng/ news/ press_20110719-893. html). Ust.hk. Retrieved on 2011-09-05. [49] It's official: Time machines won't work – latimes.com (http:/ / latimesblogs. latimes. com/ technology/ 2011/ 07/ time-travel-impossible. html). Latimesblogs.latimes.com (2011-07-25). Retrieved on 2011-09-05. [50] Time travel is sci-fi fantasy: Scientists prove nothing can travel faster than the speed of light | Mail Online (http:/ / www. dailymail. co. uk/ sciencetech/ article-2018498/ Time-travel-sci-fi-fantasy-Scientists-prove-travel-faster-speed-light. html). Dailymail.co.uk. Retrieved on 2011-09-05. [51] Franklin, Ben A. (March 11, 1982), "The night the planets were aligned with Baltimore lunacy" (http:/ / select. nytimes. com/ gst/ abstract. html?res=F70E13FD395F0C728DDDAA0894DA484D81), New York Times. [52] "Museum of the Future" (http:/ / www. lehman. cuny. edu/ vpadvance/ artgallery/ gallery/ talkback/ issue3/ gallery/ muse9. html). Lehman.cuny.edu. . Retrieved 2010-05-25. [53] Jaume Garriga; Alexander Vilenkin (2001). "[gr-qc/0102010] Many worlds in one". Phys.Rev. D (Arxiv.org) 64 (4): 043511. arXiv:gr-qc/0102010. Bibcode 2001PhRvD..64d3511G. doi:10.1103/PhysRevD.64.043511. [54] "Taking the Cosmic Shortcut – ABC Science Online" (http:/ / www. abc. net. au/ science/ slab/ wormholes/ default. htm). Abc.net.au. 2002-02-21. . Retrieved 2010-05-25. [55] "Transcript of interview with Dr. Marc Rayman at "Space Place"" (http:/ / web. archive. org/ web/ 20100603155626/ http:/ / spaceplace. nasa. gov/ en/ educators/ podcast/ transcripts/ 071129_time_travel. shtml). Spaceplace.nasa.gov. 2005-09-08. Archived from the original 21 Time travel (http:/ / spaceplace. nasa. gov/ en/ educators/ podcast/ transcripts/ 071129_time_travel. shtml) on June 3, 2010. . Retrieved 2010-05-25. [56] http:/ / www. pbs. org/ wgbh/ nova/ time/ thinktime. html. [57] Physics for Scientists and Engineers with Modern Physics, Fifth Edition, p.1258. [58] Roberts, Tom (October). "What is the experimental basis of Special Relativity?" (http:/ / math. ucr. edu/ home/ baez/ physics/ Relativity/ SR/ experiments. html#Tests_of_time_dilation). . Retrieved 4 December 2009. [59] "Scout Rocket Experiment" (http:/ / hyperphysics. phy-astr. gsu. edu/ hbase/ relativ/ gratim. html#c3). . Retrieved 4 December 2009. [60] "Hafele-Keating Experiment" (http:/ / hyperphysics. phy-astr. gsu. edu/ hbase/ relativ/ airtim. html#c3). . Retrieved 4 December 2009. [61] Pogge, Richard W. (27 April 2009). "GPS and Relativity" (http:/ / www. astronomy. ohio-state. edu/ ~pogge/ Ast162/ Unit5/ gps. html). . Retrieved 4 December 2009. [62] Vaidman, Lev. "Many-Worlds Interpretation of Quantum Mechanics" (http:/ / plato. stanford. edu/ entries/ qm-manyworlds/ ). . Retrieved 2006-10-28. [63] Deutsch, David (1991). "Quantum mechanics near closed timelike curves". Physical Review D 44 (10): 3197–3217. Bibcode 1991PhRvD..44.3197D. doi:10.1103/PhysRevD.44.3197. [64] See also the discussion in "Quantum Mechanics to the Rescue?" (http:/ / plato. stanford. edu/ entries/ time-travel-phys/ #9) from the Stanford Encyclopedia of Philosophy article "Time travel and Modern Physics" (http:/ / plato. stanford. edu/ entries/ time-travel-phys/ ). [65] Everett, Allen (2004). "Time travel paradoxes, path integrals, and the many worlds interpretation of quantum mechanics". Physical Review D 69 (124023). arXiv:gr-qc/0410035. Bibcode 2004PhRvD..69l4023E. doi:10.1103/PhysRevD.69.124023. [66] Greenberger, Daniel M; Karl Svozil (2005). Quantum Theory Looks at Time Travel. arXiv:quant-ph/0506027. Bibcode 2005quant.ph..6027G. [67] Kettlewell, Julianna (2005-06-17). "New model 'permits time travel'" (http:/ / news. bbc. co. uk/ 2/ hi/ 4097258. stm). BBC News. . Retrieved 2010-05-25. [68] Goldstein, Sheldon. "Bohmian Mechanics" (http:/ / plato. stanford. edu/ entries/ qm-bohm/ ). . Retrieved 2006-10-30. [69] Nielsen, Michael; Chuang, Isaac (2000). Quantum Computation and Quantum Information. Cambridge. p. 28. ISBN 0-521-63235-8. [70] http:/ / tedsider. org/ [71] Keller, Simon; Michael Nelson (September 2001). "Presentists should believe in time-travel" (http:/ / people. bu. edu/ stk/ Papers/ Timetravel. pdf) (PDF). Australian Journal of Philosophy 79.3 (3): 333–345. doi:10.1080/713931204. . [72] This view is contested by another contemporary advocate of presentism, Craig Bourne, in his recent book A Future for Presentism, although for substantially different (and more complex) reasons. [73] see this discussion (http:/ / www. sfu. ca/ ~swartz/ time_travel1. htm) between two philosophers, for example [74] Lewis, David (1976). "The paradoxes of time travel" (http:/ / www. csus. edu/ indiv/ m/ merlinos/ Paradoxes of Time Travel. pdf). American Philosophical Quarterly 13: 145–52. arXiv:gr-qc/9603042. Bibcode 1996gr.qc.....3042K. . [75] Grey, William (1999). "Troubles with Time Travel". Philosophy (Cambridge University Press) 74 (1): 55–70. doi:10.1017/S0031819199001047. [76] Rickman, Gregg (2004). The Science Fiction Film Reader. Limelight Editions. ISBN 0-87910-994-7. [77] Nahin, Paul J. (2001). Time machines: time travel in physics, metaphysics, and science fiction. Springer. ISBN 0-387-98571-9. [78] Schneider, Susan (2009). Science Fiction and Philosophy: From Time Travel to Superintelligence. Wiley-Blackwell. ISBN 1-4051-4907-8. [79] Friedman, John; Michael Morris, Igor Novikov, Fernando Echeverria, Gunnar Klinkhammer, Kip Thorne, Ulvi Yurtsever (1990). "Cauchy problem in spacetimes with closed timelike curves" (http:/ / authors. library. caltech. edu/ 3737/ ). Physical Review D 42 (6): 1915. Bibcode 1990PhRvD..42.1915F. doi:10.1103/PhysRevD.42.1915. . [80] Sukys, Paul (1999). Lifting the scientific veil: science appreciation for the nonscientist. Ardsley House Publishers. pp. 236–237. ISBN 0-8476-9600-6. [81] Kelley L. Ross, " Time Travel Paradoxes (http:/ / www. friesian. com/ paradox. htm)" [82] Gott, J. Richard (2001). Time Travel in Einstein's Universe. Houghton Mifflin. p. 23. ISBN 0-395-95563-7. [83] http:/ / web. archive. org/ web/ 20040405144429/ http:/ / www. bttf. com/ film_faq. htm [84] Geroch, Robert (1978). General Relativity From A to B. The University of Chicago Press. p. 124. ISBN 0-226-28863-3. [85] Max Planck Institut für Gravitationsphysik (2005-09-12). "Einstein Online: Actors on a changing stage" (http:/ / www. einstein-online. info/ en/ spotlights/ background_independence/ index. html). Einstein-online.info. . Retrieved 2010-05-25. 22 Time travel 23 Bibliography • • • • • • • • • • Curley, Mallory (2005). Beatle Pete, Time Traveller. Randy Press. Davies, Paul (1996). About Time. Pocket Books. ISBN 0-684-81822-1. Davies, Paul (2002). How to Build a Time Machine. Penguin Books Ltd. ISBN 0-14-100534-3. Gale, Richard M (1968). The Philosophy of Time. Palgrave Macmillan. ISBN 0-333-00042-0. Gott, J. Richard (2002). Time Travel in Einstein's Universe: The Physical Possibilities of Travel Through Time. Boston: Mariner Books. ISBN 0-618-25735-7. Gribbin, John (1985). In Search of Schrödinger's Cat. Corgi Adult. ISBN 0-552-12555-5. Miller, Kristie (2005). "Time travel and the open future". Disputatio 1 (19): 223–232. Nahin, Paul J. (2001). Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction. Springer-Verlag New York Inc.. ISBN 0-387-98571-9. Nahin, Paul J. (1997). Time Travel: A writer's guide to the real science of plausible time travel. Writer's Digest Books. Cincinnati, Ohio. ISBN 0-89879-748-9 Nikolic, H (2006). "Causal paradoxes: a conflict between relativity and the arrow of time". Foundations of Physics Letters 19 (3): 259. arXiv:gr-qc/0403121. Bibcode 2006FoPhL..19..259N. doi:10.1007/s10702-006-0516-5. • Pagels, Heinz (1985). Perfect Symmetry, the Search for the Beginning of Time. Simon & Schuster. ISBN 0-671-46548-1. • Pickover, Clifford (1999). Time: A Traveler's Guide. Oxford University Press Inc, USA. ISBN 0-19-513096-0. • Randles, Jenny (2005). Breaking the Time Barrier. Simon & Schuster Ltd. ISBN 0-7434-9259-5. • Shore, Graham M (2003). "Constructing Time Machines". Int. J. Mod. Phys. A, Theoretical 18 (23): 4169. arXiv:gr-qc/0210048. Bibcode 2003IJMPA..18.4169S. doi:10.1142/S0217751X03015118. • Toomey, David (2007). The New Time Travelers: A Journey to the Frontiers of Physics. W.W. Norton & Company. ISBN 978-0-393-06013-3. External links • Black holes, Wormholes and Time Travel (http://www.vega.org.uk/video/programme/61), a Royal Society Lecture • SF Chronophysics (http://www.xibalba.demon.co.uk/jbr/chrono.html), a discussion of Time Travel as it relates to science fiction • On the Net: Time Travel (http://www.asimovs.com/_issue_0407/onthenet2.shtml) by James Patrick Kelly • How Time Travel Will Work (http://www.howstuffworks.com/time-travel.htm.htm) at HowStuffWorks • Time Travel in Flatland? (http://www.theory.caltech.edu/people/patricia/lctoc.html) • NOVA Online: Time Travel (http://www.pbs.org/wgbh/nova/time) • Professor Predicts Human Time Travel This Century (http://www.physorg.com/news63371210.html) • Time Traveler Convention (http://web.mit.edu/adorai/timetraveler) at MIT • Time Machines in Physics (http://www.math.siu.edu/Kocik/tm/tm-all-ch.htm) – almost 200 citations from 1937 through 2001 • Time Travel and Modern Physics (http://plato.stanford.edu/entries/time-travel-phys/) at the Stanford Encyclopedia of Philosophy • Time Travel (http://www.iep.utm.edu/t/timetrav.htm) at the Internet Encyclopedia of Philosophy • Aparta Krystian: Conventional Models of Time and Their Extensions in Science Fiction (http://timetravel.net46. net/Aparta_Models_of_Time.pdf) • Time travellers from the future 'could be here in weeks' (http://www.telegraph.co.uk/science/ large-hadron-collider/3324491/Time-travellers-from-the-future-could-be-here-in-weeks.html) • Time machine on arxiv.org (http://xstructure.inr.ac.ru/x-bin/theme3.py?level=1&index1=-166308) 24 Physics Multiverse The multiverse (or meta-universe, metaverse) is the hypothetical set of multiple possible universes (including the historical universe we consistently experience) that together comprise everything that exists and can exist: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them. The term was coined in 1895 by the American philosopher and psychologist William James.[1] The various universes within the multiverse are sometimes called parallel universes. The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes, depend on the specific multiverse hypothesis considered. Multiverses have been hypothesized in cosmology, physics, astronomy, religion, philosophy, transpersonal psychology and fiction, particularly in science fiction and fantasy. In these contexts, parallel universes are also called "alternative universes", "quantum universes", "interpenetrating dimensions", "parallel dimensions", "parallel worlds", "alternative realities", "alternative timelines", and "dimensional planes," among others. Multiverse hypotheses in physics Tegmark's classification Cosmologist Max Tegmark has provided a taxonomy of universes beyond the familiar observable universe. The levels according to Tegmark's classification are arranged such that subsequent levels can be understood to encompass and expand upon previous levels, and they are briefly described below.[2][3] Artistic impression of a level 2 multiverse Level I: Beyond our cosmological horizon A generic prediction of chaotic inflation is an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions. Accordingly, an infinite universe will contain an infinite number of Hubble volumes, all having the same physical laws and physical constants. In regard to configurations such as the distribution of matter, almost all will differ from our Hubble volume. However, because there are infinitely many, far beyond the cosmological horizon, there will eventually be Hubble volumes with similar, and even identical, configurations. Tegmark estimates that an identical volume to ours should be about 1010115 meters away from us.[4][5] This estimate implies use of the cosmological principle, wherein one assumes our Hubble volume is not special or unique. By extension of the same reasoning, there would, in fact, be an infinite number of Hubble volumes identical to ours in the universe. Multiverse Level II: Universes with different physical constants In the chaotic inflation theory, a variant of the cosmic inflation theory, the multiverse as a whole is stretching and will continue doing so forever, but some regions of space stop stretching and form distinct bubbles, like gas pockets in a loaf of rising bread. Such bubbles are embryonic level I multiverses. Linde and Vanchurin calculated the number of these universes to be on the scale of 101010,000,000.[6] Different bubbles may experience different spontaneous symmetry breaking resulting in different properties such as different physical constants.[4] This level also includes John Archibald Wheeler's oscillatory universe theory and Lee Smolin's fecund universes theory. Level III: Many-worlds interpretation of quantum mechanics Hugh Everett's many-worlds interpretation (MWI) is one of several mainstream interpretations of quantum mechanics. In brief, one aspect of quantum mechanics is that certain observations cannot be predicted absolutely. Instead, there is a range of possible observations, each with a different probability. According to the MWI, each of these possible observations corresponds to a different universe. Suppose a die is thrown that contains six sides and that the numeric result of the throw corresponds to a quantum mechanics observable. All six possible ways the die can fall correspond to six different universes. (More correctly, in MWI there is only a single universe but after the "split" into "many worlds" these cannot in general interact.)[7] Tegmark argues that a level III multiverse does not contain more possibilities in the Hubble volume than a level I-II multiverse. In effect, all the different "worlds" created by "splits" in a level III multiverse with the same physical constants can be found in some Hubble volume in a level I multiverse. Tegmark writes that "The only difference between Level I and Level III is where your doppelgängers reside. In Level I they live elsewhere in good old three-dimensional space. In Level III they live on another quantum branch in infinite-dimensional Hilbert space." Similarly, all level II bubble universes with different physical constants can in effect be found as "worlds" created by "splits" at the moment of spontaneous symmetry breaking in a level III multiverse.[4] Related to the many-worlds idea are Richard Feynman's multiple histories interpretation and H. Dieter Zeh's many-minds interpretation. Level IV: Ultimate Ensemble The Ultimate Ensemble is the hypothesis of Tegmark himself. This level considers equally real all universes that can be described by different mathematical structures. Tegmark writes that "abstract mathematics is so general that any Theory Of Everything (TOE) that is definable in purely formal terms (independent of vague human terminology) is also a mathematical structure. For instance, a TOE involving a set of different types of entities (denoted by words, say) and relations between them (denoted by additional words) is nothing but what mathematicians call a set-theoretical model, and one can generally find a formal system that it is a model of." He argues this "implies that any conceivable parallel universe theory can be described at Level IV" and "subsumes all other ensembles, therefore brings closure to the hierarchy of multiverses, and there cannot be say a Level V."[8] Jürgen Schmidhuber, however, says the "set of mathematical structures" is not even well-defined, and admits only universe representations describable by constructive mathematics, that is, computer programs. He explicitly includes universe representations describable by non-halting programs whose output bits converge after finite time, although the convergence time itself may not be predictable by a halting program, due to Kurt Gödel's limitations.[9][10][11] He also explicitly discusses the more restricted ensemble of quickly computable universes.[12] "Bubble universes": every disk is a bubble universe (Universe 1 to Universe 6 are different bubbles; they have physical constants that are different from our universe); our universe is just one of the bubbles. 25 Multiverse 26 Cyclic theories In several theories there is a series of infinite, self-sustaining cycles (for example: an eternity of Big Bang-Big crunches). M-theory A multiverse of a somewhat different kind has been envisaged within the multi-dimensional extension of string theory known as M-theory, also known as Membrane Theory.[13] In M-theory our universe and others are created by collisions between p-branes in a space with 11 and 26 dimensions (the number of dimensions depends on the chirality of the observer);[14][15] each universe takes the form of a D-brane.[14][15] Objects in each universe are essentially confined to the D-brane of their universe, but may be able to interact with other universes via gravity, a force which is not restricted to D-branes.[16] This is unlike the universes in the "quantum multiverse", but both concepts can operate at the same time. Anthropic principle The concept of other universes has been proposed to explain how our Universe appears to be fine-tuned for conscious life as we experience it. If there were a large (possibly infinite) number of universes, each with possibly different physical laws (or different fundamental physical constants), some of these universes, even if very few, would have the combination of laws and fundamental parameters that are suitable for the development of matter, astronomical structures, elemental diversity, stars, and planets that can exist long enough for life to emerge and evolve. The weak anthropic principle could then be applied to conclude that we (as conscious beings) would only exist in one those few universes that happened to be finely tuned, permitting the existence of life with developed consciousness. Thus, while the probability might be extremely small that any particular universe would have the requisite conditions for life (as we understand life) to emerge and evolve, this does not require intelligent design per the teleological argument as the only explanation for the conditions in the Universe that promote our existence in it. Criticism Non-scientific claims In his book, A Brief History of the Multiverse, author and cosmologist, Paul Davies, offers a variety of arguments that multiverse theories are non-scientific :[17] For a start, how is the existence of the other universes to be tested? To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there are an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions. Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith. — Paul Davies, A Brief History of the Multiverse Taking cosmic inflation as a popular case in point, George Ellis provides a balanced criticism of not only the science, but as he suggests, the scientific philosophy, by which multiverse theories are generally substantiated. He, like most cosmologists, accepts Tegmark's level I “domains”, even though they lie far beyond the cosmological horizon. Likewise, the multiverse of cosmic inflation is said to exist very far away. It would be so far away, however, that it's very unlikely any evidence of an early interaction will be found. He argues that for many theorists, the lack of empirical testability or falsifiability is not a major concern. “Many physicists who talk about the multiverse, especially advocates of the string landscape, do not care much about parallel universes per se. For them, objections Multiverse to the multiverse as a concept are unimportant. Their theories live or die based on internal consistency and, one hopes, eventual laboratory testing.” Although he believes there's little hope that will ever be possible, he grants that the theories on which the speculation is based, are not without scientific merit. He concludes that multiverse theory is a “productive research program”:[18] As skeptical as I am, I think the contemplation of the multiverse is an excellent opportunity to reflect on the nature of science and on the ultimate nature of existence: why we are here… In looking at this concept, we need an open mind, though not too open. It is a delicate path to tread. Parallel universes may or may not exist; the case is unproved. We are going to have to live with that uncertainty. Nothing is wrong with scientifically based philosophical speculation, which is what multiverse proposals are. But we should name it for what it is. — George Ellis, Scientific American, Does the Multiverse Really Exist? Occam's razor Critics argue that to postulate a practically infinite number of unobservable universes just to explain our own seems contrary to Occam's razor.[19] Max Tegmark answers: "A skeptic worries about all the information necessary to specify all those unseen worlds. But an entire ensemble is often much simpler than one of its members. This principle can be stated more formally using the notion of algorithmic information content. The algorithmic information content in a number is, roughly speaking, the length of the shortest computer program that will produce that number as output. For example, consider the set of all integers. Which is simpler, the whole set or just one number? Naively, you might think that a single number is simpler, but the entire set can be generated by quite a trivial computer program, whereas a single number can be hugely long. Therefore, the whole set is actually simpler. Similarly, the set of all solutions to Einstein's field equations is simpler than a specific solution. The former is described by a few equations, whereas the latter requires the specification of vast amounts of initial data on some hypersurface. The lesson is that complexity increases when we restrict our attention to one particular element in an ensemble, thereby losing the symmetry and simplicity that were inherent in the totality of all the elements taken together. In this sense, the higher-level multiverses are simpler. Going from our universe to the Level I multiverse eliminates the need to specify initial conditions, upgrading to Level II eliminates the need to specify physical constants, and the Level IV multiverse eliminates the need to specify anything at all." He continues: "A common feature of all four multiverse levels is that the simplest and arguably most elegant theory involves parallel universes by default. To deny the existence of those universes, one needs to complicate the theory by adding experimentally unsupported processes and ad hoc postulates: finite space, wave function collapse and ontological asymmetry. Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words. Perhaps we will gradually get used to the weird ways of our cosmos and find its strangeness to be part of its charm."[4] 27 Multiverse 28 Multiverse hypotheses in philosophy and logic Modal realism Possible worlds are a way of explaining probability, hypothetical statements and the like, and some philosophers such as David Lewis believe that all possible worlds exist, and are just as real as the actual world (a position known as modal realism).[20] Trans-world identity A metaphysical issue that crops up in multiverse schema that posit infinite identical copies of any given universe is that of the notion that there can be identical objects in different possible worlds. According to the counterpart theory of David Lewis, the objects should be regarded as similar rather than identical.[21][22] Fictional realism The view that because fictions exist, fictional characters exist as well. There are fictional entities, in the same sense in which, setting aside philosophical disputes, there are people, Mondays, numbers and planets.[23][24] References Notes [1] James, William, The Will to Believe, 1895; and earlier in 1895, as cited in OED's new 2003 entry for "multiverse": "1895 W. JAMES in Internat. Jrnl. Ethics 6 10. Visible nature is all plasticity and indifference, a multiverse, as one might call it, and not a universe." [2] Tegmark, Max (May 2003). "Parallel Universes". Scientific American. [3] Tegmark, Max (January 23 2003) (PDF). Parallel Universes (http:/ / space. mit. edu/ home/ tegmark/ multiverse. pdf). . Retrieved 2006-02-07. [4] "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations.", Tegmark M., Sci Am. 2003 May;288(5):40-51. [5] Max Tegmark (2003). "Parallel Universes". In "Science and Ultimate Reality: from Quantum to Cosmos", honoring John Wheeler's 90th birthday. J. D. Barrow, P.C.W. Davies, & C.L. Harper eds. Cambridge University Press (2003). arXiv:astro-ph/0302131. Bibcode 2003astro.ph..2131T. [6] Zyga, Lisa "Physicists Calculate Number of Parallel Universes" (http:/ / www. physorg. com/ news174921612. html), PhysOrg, 16 October 2009. [7] Tegmark, Max, The Interpretation of Quantum Mechanics: Many Worlds or Many Words? (http:/ / www. arxiv. org/ abs/ quant-ph/ 9709032/ ), 1998. Deutsch, David, David Deutsch's Many Worlds (http:/ / www. qubit. org/ people/ david/ Articles/ Frontiers. html), Frontiers, 1998. [8] Tegmark, Max (January 23 2003) (PDF). Parallel Universes (http:/ / www. wintersteel. com/ files/ ShanaArticles/ multiverse. pdf). . Retrieved 2006-02-07. (PDF). [9] J. Schmidhuber (1997): A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science, pp. 201-208, Springer: IDSIA - Dalle Molle Institute for Artificial Intelligence (http:/ / www. idsia. ch/ ~juergen/ everything/ ) [10] J. Schmidhuber (2000): Algorithmic Theories of Everything arXiv.org e-Print archive (http:/ / arxiv. org/ abs/ quant-ph/ 0011122) [11] J. Schmidhuber (2002): Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit. International Journal of Foundations of Computer Science 13(4):587-612 IDSIA - Dalle Molle Institute for Artificial Intelligence (http:/ / www. idsia. ch/ ~juergen/ kolmogorov. html) [12] J. Schmidhuber (2002): The Speed Prior: A New Simplicity Measure Yielding Near-Optimal Computable Predictions. Proc. 15th Annual Conference on Computational Learning Theory (COLT 2002), Sydney, Australia, Lecture Notes in Artificial Intelligence, pp. 216-228. Springer: IDSIA - Dalle Molle Institute for Artificial Intelligence (http:/ / www. idsia. ch/ ~juergen/ speedprior. html) [13] Steven Weinberg(2005)" Living in the Multiverse (http:/ / arxiv. org/ abs/ hep-th/ 0511037v1)" [14] Richard J Szabo, An introduction to string theory and D-brane dynamics (2004) [15] Maurizio Gasperini, Elements of String Cosmology (2007) [16] Paul Halpern, The Great Beyond, 2005 [17] Davies, Paul (12 April 2003). "A Brief History of the Multiverse" (http:/ / www. nytimes. com/ 2003/ 04/ 12/ opinion/ a-brief-history-of-the-multiverse. html?pagewanted=all). New York Times. . Retrieved 16 August 2011. [18] George Ellis (2011). "Does the Multiverse Really Exist?" (http:/ / www. scientificamerican. com/ article. cfm?id=does-the-multiverse-really-exist). Scientific American 305 (2): 38–43. . Retrieved 16 August 2011. Multiverse [19] Trinh, Xuan Thuan (2006). Staune, Jean. ed. Science & the Search for Meaning: Perspectives from International Scientists. West Conshohocken, PA: Templeton Foundation. p. 186. ISBN 1-59947-102-7. [20] Lewis, David (1986). On the Plurality of Worlds. Basil Blackwell. ISBN 0-631-22426-2. [21] Deutsch, Harry, "Relative Identity", The Stanford Encyclopedia of Philosophy (Summer '02), Edward N. Zalta (ed.) (http:/ / plato. stanford. edu/ archives/ sum2002/ entries/ identity-relative/ ) [22] Paul B. Kantor "The Interpretation of Cultures and Possible Worlds", 1 October 2002 (http:/ / www. scils. rutgers. edu/ ~kantor/ 601/ Ex_1Overview. html) [23] IngentaConnect Home (http:/ / www. ingentaconnect. com/ content/ bpl/ phiq/ 2009/ 00000059/ 00000234/ art00009) [24] The Australian National University (http:/ / consciousness. anu. edu. au/ thomasson/ Fictional Entities. doc) 29 Bibliography • Bernard Carr, ed. (2007) Universe or Multiverse? Cambridge Univ. Press. • Deutsch, David (45841 1985). Splash. ed. Quantum theory, the Church-Turing principle and the universal quantum computer (Proceedings of the Royal Society of London A 400 ed.). pp. 97–117. • Ellis, George F.R.; U. Kirchner, William R. Stoeger (2004). "Multiverses and physical cosmology". Monthly Notices of the Royal Astronomical Society 347 (3): 921–936. arXiv:astro-ph/0305292. Bibcode 2004MNRAS.347..921E. doi:10.1111/j.1365-2966.2004.07261.x. • Surya-Siddhanta: A Text Book of Hindu Astronomy by Ebenezer Burgess, ed. Phanindralal Gangooly (1989/1997) with a 45-page commentary by P. C. Sengupta (1935). External links • Aurélien Barrau, " Physics in the Multiverse. (http://lpsc.in2p3.fr/ams/aurelien/aurelien/CCDecMULTIV. pdf)" • --------, " Multiple Universes? (http://www.laviedesidees.fr/Des-univers-multiples.html)" (in French). Review of Carr (2007). • Davies, Paul (2004). "Multiverse Cosmological Models". Mod.Phys.Lett. A 19: 727–744. arXiv:astro-ph/0403047. Bibcode 2003MPLA...18.2895M. doi:10.1142/S0217732303012325. • Max Tegmark (2003) " Parallel Universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations. (http://space.mit.edu/home/tegmark/PDF/multiverse_sciam.pdf)" • David Deutsch (2001) " The Structure of the Multiverse. (http://xxx.lanl.gov/abs/quant-ph/0104033)" • BBC Horizon -Parallel Universes. (http://www.bbc.co.uk/science/horizon/2001/parallelunitrans.shtml) • Michael Price's Everett FAQ. (http://www.hedweb.com/manworld.htm) • Jürgen Schmidhuber, " The ensemble of universes describable by constructive mathematics. (http://www.idsia. ch/~juergen/computeruniverse.html)" • Interview with Tufts cosmologist Alex Vilenkin (http://thoughtcast.org/casts/ the-end-of-our-universe-among-other-timely-topics) on his new book, "Many Worlds in One: The Search for Other Universes" on the podcast and public radio interview program ThoughtCast. (http://www.thoughtcast. org) • Joseph Pine II about Multiverse (http://www.upstream.nl/comments.php?id=751_0_1_0_C), Presentation at Mobile Monday Amsterdam, 2008 • Multiverse - Radio-discussion on [[BBC Four (http://www.bbc.co.uk/programmes/b008z744)] with Melvyn Bragg] • Multiverse theory suggested by microwave background (http://www.bbc.co.uk/news/ science-environment-14372387), BBC news website, 2011/08/03 Many-worlds interpretation 30 Many-worlds interpretation The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an actual "world" (or "universe"). It is also referred to as MWI, the relative state formulation, the Everett interpretation, the theory of the universal wavefunction, many-universes interpretation, or just many-worlds. The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation every event is a branch point; the cat is both alive and dead, even before the box is opened, but the "alive" and "dead" cats are in different branches of the universe, both of which are equally real, but which cannot interact with [1] each other. The original relative state formulation is due to Hugh Everett in 1957.[2][3] Later, this formulation was popularized and renamed many-worlds by Bryce Seligman DeWitt in the 1960s and 1970s.[1][4][5][6] The decoherence approaches to interpreting quantum theory have been further explored and developed,[7][8][9] becoming quite popular. MWI is one of many multiverse hypotheses in physics and philosophy. It is currently considered a mainstream interpretation along with the other decoherence interpretations and the Copenhagen interpretation. Prior to many-worlds, reality had always been viewed as a single unfolding history. Many-worlds, however, views reality as a many-branched tree, wherein every possible quantum outcome is realised.[10] Many-worlds claims to reconcile the observation of non-deterministic events, such as the random radioactive decay, with the fully deterministic equations of quantum physics. In many-worlds, the subjective appearance of wavefunction collapse is explained by the mechanism of quantum decoherence, which resolves all of the correlation paradoxes of quantum theory, such as the EPR paradox[11][12] and Schrödinger's cat,[1] since every possible outcome of every event defines or exists in its own "history" or "world". In lay terms, there is a very large—perhaps infinite[13]—number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes. Outline Although several versions of many-worlds have been proposed since Hugh Everett's original work,[3] they all contain one key idea: the equations of physics that model the time evolution of systems without embedded observers are sufficient for modelling systems which do contain observers; in particular there is no observation-triggered wave function collapse which the Copenhagen interpretation proposes. Provided the theory is linear with respect to the wavefunction, the exact form of the quantum dynamics modelled, be it the non-relativistic Schrödinger equation, relativistic quantum field theory or some form of quantum gravity or string theory, does not alter the validity of MWI since MWI is a metatheory applicable to all linear quantum theories, and there is no experimental evidence for any non-linearity of the wavefunction in physics.[14][15] MWI's main conclusion is that the universe (or multiverse in this context) is composed of a quantum superposition of very many, possibly even non-denumerably infinitely[13] many, increasingly divergent, non-communicating parallel universes or quantum worlds.[6] The idea of MWI originated in Everett's Princeton Ph.D. thesis "The Theory of the Universal Wavefunction",[6] developed under his thesis advisor John Archibald Wheeler, a shorter summary of which was published in 1957 Many-worlds interpretation entitled "Relative State Formulation of Quantum Mechanics" (Wheeler contributed the title "relative state";[16] Everett originally called his approach the "Correlation Interpretation", where "correlation" refers to quantum entanglement). The phrase "many-worlds" is due to Bryce DeWitt,[6] who was responsible for the wider popularisation of Everett's theory, which had been largely ignored for the first decade after publication. DeWitt's phrase "many-worlds" has become so much more popular than Everett's "Universal Wavefunction" or Everett-Wheeler's "Relative State Formulation" that many forget that this is only a difference of terminology; the content of both of Everett's papers and DeWitt's popular article is the same. The many-worlds interpretation shares many similarities with later, other "post-Everett" interpretations of quantum mechanics which also use decoherence to explain the process of measurement or wavefunction collapse. MWI treats the other histories or worlds as real since it regards the universal wavefunction as the "basic physical entity"[17] or "the fundamental entity, obeying at all times a deterministic wave equation".[18] The other decoherent interpretations, such as consistent histories, the Existential Interpretation etc., either regard the extra quantum worlds as metaphorical in some sense, or are agnostic about their reality; it is sometimes hard to distinguish between the different varieties. MWI is distinguished by two qualities: it assumes realism,[17][18] which it assigns to the wavefunction, and it has the minimal formal structure possible, rejecting any hidden variables, quantum potential, any form of a collapse postulate (i.e., Copenhagenism) or mental postulates (such as the many-minds interpretation makes). Decoherent interpretations of many-worlds using einselection to explain how a small number of classical pointer states can emerge from the enormous Hilbert space of superpositions have been proposed by Wojciech H. Zurek. "Under scrutiny of the environment, only pointer states remain unchanged. Other states decohere into mixtures of stable pointer states that can persist, and, in this sense, exist: They are einselected."[19] These ideas complement MWI and bring the interpretation in line with our perception of reality. Many-worlds is often referred to as a theory, rather than just an interpretation, by those who propose that many-worlds can make testable predictions (such as David Deutsch) or is falsifiable (such as Everett) or by those who propose that all the other, non-MW interpretations, are inconsistent, illogical or unscientific in their handling of measurements; Hugh Everett argued that his formulation was a metatheory, since it made statements about other interpretations of quantum theory; that it was the "only completely coherent approach to explaining both the contents of quantum mechanics and the appearance of the world."[20] Deutsch is dismissive that many-worlds is an "interpretation", saying that calling it an interpretation "is like talking about dinosaurs as an interpretation of the fossil record."[21] 31 Interpreting wavefunction collapse As with the other interpretations of quantum mechanics, the many-worlds interpretation is motivated by behavior that can be illustrated by the double-slit experiment. When particles of light (or anything else) are passed through the double slit, a calculation assuming wave-like behavior of light can be used to identify where the particles are likely to be observed. Yet when the particles are observed in this experiment, they appear as particles (i.e., at definite places) and not as non-localized waves. Some versions of the Copenhagen interpretation of quantum mechanics proposed a process of "collapse" in which an indeterminate quantum system would probabilistically collapse down onto, or select, just one determinate outcome to "explain" this phenomenon of observation. Wavefunction collapse was widely regarded as artificial and ad-hoc, so an alternative interpretation in which the behavior of measurement could be understood from more fundamental physical principles was considered desirable. Everett's Ph.D. work provided such an alternative interpretation. Everett noted that for a composite system – for example a subject (the "observer" or measuring apparatus) observing an object (the "observed" system, such as a particle) – the statement that either the observer or the observed has a well-defined state is meaningless; in modern parlance the observer and the observed have become entangled; we can only specify the state of one relative to the Many-worlds interpretation other, i.e., the state of the observer and the observed are correlated after the observation is made. This led Everett to derive from the unitary, deterministic dynamics alone (i.e., without assuming wavefunction collapse) the notion of a relativity of states. Everett noticed that the unitary, deterministic dynamics alone decreed that after an observation is made each element of the quantum superposition of the combined subject-object wavefunction contains two "relative states": a "collapsed" object state and an associated observer who has observed the same collapsed outcome; what the observer sees and the state of the object have become correlated by the act of measurement or observation. The subsequent evolution of each pair of relative subject-object states proceeds with complete indifference as to the presence or absence of the other elements, as if wavefunction collapse has occurred, which has the consequence that later observations are always consistent with the earlier observations. Thus the appearance of the object's wavefunction's collapse has emerged from the unitary, deterministic theory itself. (This answered Einstein's early criticism of quantum theory, that the theory should define what is observed, not for the observables to define the theory).[22] Since the wavefunction appears to have collapsed then, Everett reasoned, there was no need to actually assume that it had collapsed. And so, invoking Occam's razor, he removed the postulate of wavefunction collapse from the theory. 32 Probability A consequence of removing wavefunction collapse from the quantum formalism is that the Born rule requires derivation, since many-worlds claims to derive its interpretation from the formalism. Attempts have been made, by many-world advocates and others, over the years to derive the Born rule, rather than just conventionally assume it, so as to reproduce all the required statistical behaviour associated with quantum mechanics. There is no consensus on whether this has been successful.[23][24][25] Everett, Gleason and Hartle Everett (1957) briefly derived the Born rule by showing that the Born rule was the only possible rule, and that its derivation was as justified as the procedure for defining probability in classical mechanics. Everett stopped doing research in theoretical physics shortly after obtaining his Ph.D., but his work on probability has been extended by a number of people. Andrew Gleason (1957) and James Hartle (1965) independently reproduced Everett's work, known as Gleason's theorem[26][27] which was later extended.[28][29] De Witt and Graham Bryce De Witt and his doctoral student R. Neill Graham later provided alternative (and longer) derivations to Everett's derivation of the Born rule. They demonstrated that the norm of the worlds where the usual statistical rules of quantum theory broke down vanished, in the limit where the number of measurements went to infinity. Deutsch et al. An information-theoretic derivation of the Born rule from Everettarian assumptions, was produced by David Deutsch (1999)[30] and refined by Wallace (2002–2009)[31][32][33][34] and Saunders (2004).[35][36] Deutsch's derivation is a two-stage proof: first he shows that the number of orthonormal Everett-worlds after a branching is proportional to the conventional probability density. Then he uses game theory to show that these are all equally likely to be observed. The last step in particular has been criticised for circularity.[37][38] Other reviews have been positive, although the status of these arguments remains highly controversial; some theoretical physicists have taken them as supporting the case for parallel universes.[39][40] In the New Scientist article, reviewing their presentation at a September 2007 conference,[41][42] Andy Albrecht, a physicist at the University of California at Davis, is quoted as saying "This work will go down as one of the most important developments in the history of science."[39] Wojciech H. Zurek (2005)[43] has produced a derivation of the Born rule, where decoherence has replaced Deutsch's informatic assumptions.[44] Lutz Polley (2000) has produced Born rule derivations where the informatic assumptions Many-worlds interpretation are replaced by symmetry arguments.[45][46] The Born rule and the collapse of the wave function have been obtained in the framework of the relative-state formulation of quantum mechanics by Armando V.D.B. Assis. He has proved that the Born rule and the collapse of the wave function follow from a game-theoretical strategy, namely the Nash equilibrium within a von Neumann zero-sum game between nature and observer.[47] 33 Properties of the theory • MWI removes the observer-dependent role in the quantum measurement process by replacing wavefunction collapse with quantum decoherence. Since the role of the observer lies at the heart of most if not all "quantum paradoxes," this automatically resolves a number of problems; see for example Schrödinger's cat thought-experiment, the EPR paradox, von Neumann's "boundary problem" and even wave-particle duality. Quantum cosmology also becomes intelligible, since there is no need anymore for an observer outside of the universe. • MWI is a realist, deterministic, local theory, akin to classical physics (including the theory of relativity), at the expense of losing counterfactual definiteness. MWI achieves this by removing wavefunction collapse, which is indeterministic and non-local, from the deterministic and local equations of quantum theory.[48][49] • MWI (or other, broader multiverse considerations) provides a context for the anthropic principle which may provide an explanation for the fine-tuned universe.[50][51] • MWI, being a decoherent formulation, is axiomatically more streamlined than the Copenhagen and other collapse interpretations; and thus favoured under certain interpretations of Occam's razor.[52] Of course there are other decoherent interpretations that also possess this advantage with respect to the collapse interpretations. Common objections and misconceptions • The many-worlds interpretation is very vague about the ways to determine when splitting happens, and nowadays usually the criterion is that the two branches have decohered. However, present day understanding of decoherence does not allow a completely precise, self contained way to say when the two branches have decohered/"do not interact", and hence many-worlds interpretation remains arbitrary. This is the main objection opponents of this interpretation raise, saying that it is not clear what is precisely meant by branching, and point to the lack of self contained criteria specifying branching. MWI response: the decoherence or "splitting" or "branching" is complete when the measurement is complete. In Dirac notation a measurement is complete when: where represents the observer having detected the object system in the i-th state. Before the measurement has started the observer states are identical; after the measurement is complete the observer states are orthonormal.[3][6] Thus a measurement defines the branching process: the branching is as well- or ill- defined as the measurement is; the branching is as complete as the measurement is complete - which is to say that the delta function above represents an idealised measurement. Although true "for all practical purposes" in reality the measurement, and hence the branching, is never fully complete, since delta functions are unphysical,[53] Since the role of the observer and measurement per se plays no special role in MWI (measurements are handled as all other interactions are) there is no need for a precise definition of what an observer or a measurement is — just as in Newtonian physics no precise definition of either an observer or a measurement was required or expected. In all circumstances the universal wavefunction is still available to give a complete description of reality. Many-worlds interpretation Also, it is a common misconception to think that branches are completely separate. In Everett's formulation, they may in principle quantum interfere (i.e., "merge" instead of "splitting") with each other in the future,[54] although this requires all "memory" of the earlier branching event to be lost, so no observer ever sees two branches of reality.[55][56] • MWI states that there is no special role nor need for precise definition of measurement in MWI, yet Everett uses the word "measurement" repeatedly throughout its exposition. MWI response: "measurements" are treated as a subclass of interactions, which induce subject-object correlations in the combined wavefunction. There is nothing special about measurements (such as the ability to trigger a wave function collapse), that cannot be dealt with by the usual unitary time development process.[2] This is why there is no precise definition of measurement in Everett's formulation, although some other formulations emphasise that measurements must be effectively irreversible or create classical information. • The splitting of worlds forward in time, but not backwards in time (i.e., merging worlds), is time asymmetric and incompatible with the time symmetric nature of Schrödinger's equation, or CPT invariance in general.[57] MWI response: The splitting is time asymmetric; this observed temporal asymmetry is due to the boundary conditions imposed by the Big Bang[58] • There is circularity in Everett's measurement theory. Under the assumptions made by Everett, there are no 'good observations' as defined by him, and since his analysis of the observational process depends on the latter, it is void of any meaning. The concept of a 'good observation' is the projection postulate in disguise and Everett's analysis simply derives this postulate by having assumed it, without any discussion.[59] MWI response: Everett's treatment of observations / measurements covers both idealised good measurements and the more general bad or approximate cases.[60] Thus it is legitimate to analyse probability in terms of measurement; no circularity is present. • Talk of probability in Everett presumes the existence of a preferred basis to identify measurement outcomes for the probabilities to range over. But the existence of a preferred basis can only be established by the process of decoherence, which is itself probabilistic[37] or arbitrary.[61] MWI response: Everett analysed branching using what we now call the "measurement basis". It is fundamental theorem of quantum theory that nothing measurable or empirical is changed by adopting a different basis. Everett was therefore free to choose whatever basis he liked. The measurement basis was simply the simplest basis in which to analyse the measurement process.[62][63] • We cannot be sure that the universe is a quantum multiverse until we have a theory of everything and, in particular, a successful theory of quantum gravity.[64] If the final theory of everything is non-linear with respect to wavefunctions then many-worlds would be invalid.[1][3][4][5][6] MWI response: All accepted quantum theories of fundamental physics are linear with respect to the wavefunction. While quantum gravity or string theory may be non-linear in this respect there is no evidence to indicate this at the moment.[14][15] • Conservation of energy is grossly violated if at every instant near-infinite amounts of new matter are generated to create the new universes. MWI response: There are two responses to this objection. First, the law of conservation of energy says that energy is conserved within each universe. Hence, even if "new matter" were being generated to create new universes, this would not violate conservation of energy. Second, conservation of energy is not violated since the energy of each branch has to be weighted by its probability, according to the standard formula for the conservation of energy in quantum theory. This results in the total energy of the multiverse being conserved.[65] 34 Many-worlds interpretation • Occam's Razor rules against a plethora of unobservable universes — Occam would prefer just one universe; i.e., any non-MWI. MWI response: Occam's razor actually is a constraint on the complexity of physical theory, not on the number of universes. MWI is a simpler theory since it has fewer postulates.[52] Occams's razor is often cited by MWI adherents as an advantage of MWI. • Unphysical universes: If a state is a superposition of two states weighted by coefficients a and b, then if and , i.e., , i.e., 35 , what principle allows a universe with vanishingly small probability b to be instantiated on an equal footing with the much more probable one with probability a? This seems to throw away the information in the probability amplitudes. Such a theory makes little sense. MWI response: The magnitude of the coefficients provides the weighting that makes the branches or universes "unequal", as Everett and others have shown, leading the emergence of the conventional probabilistic rules.[1][3][4][5][6][66] • Violation of the principle of locality, which contradicts special relativity: MWI splitting is instant and total: this may conflict with relativity, since an alien in the Andromeda galaxy can't know I collapse an electron over here before she collapses hers there: the relativity of simultaneity says we can't say which electron collapsed first — so which one splits off another universe first? This leads to a hopeless muddle with everyone splitting differently. Note: EPR is not a get-out here, as the alien's and my electrons need never have been part of the same quantum, i.e., entangled. MWI response: the splitting can be regarded as causal, local and relativistic, spreading at, or below, the speed of light (e.g., we are not split by Schrödinger's cat until we look in the box).[67] For spacelike separated splitting you can't say which occurred first — but this is true of all spacelike separated events, simultaneity is not defined for them. Splitting is no exception; many-worlds is a local theory.[49] Brief overview In Everett's formulation, a measuring apparatus M and an object system S form a composite system, each of which prior to measurement exists in well-defined (but time-dependent) states. Measurement is regarded as causing M and S to interact. After S interacts with M, it is no longer possible to describe either system by an independent state. According to Everett, the only meaningful Schematic representation of pair of "smallest possible" quantum mechanical systems prior descriptions of each system are relative to interaction: Measured system S and measurement apparatus M. Systems such as S are states: for example the relative state of referred to as 1-qubit systems. S given the state of M or the relative state of M given the state of S. In DeWitt's formulation, the state of S after a sequence of measurements is given by a quantum superposition of states, each one corresponding to an alternative measurement history of S. Many-worlds interpretation 36 For example, consider the smallest possible truly quantum system S, as shown in the illustration. This describes for instance, the spin-state of an electron. Considering a specific axis (say the z-axis) the north pole represents spin "up" and the south pole, spin "down". The superposition states of the system are described by (the surface of) a sphere called the Bloch sphere. To perform a measurement on S, it is made to interact with another similar system M. After the interaction, the combined Schematic illustration of splitting as a result of a repeated measurement. system is described by a state that ranges over a six-dimensional space (the reason for the number six is explained in the article on the Bloch sphere). This six-dimensional object can also be regarded as a quantum superposition of two "alternative histories" of the original system S, one in which "up" was observed and the other in which "down" was observed. Each subsequent binary measurement (that is interaction with a system M) causes a similar split in the history tree. Thus after three measurements, the system can be regarded as a quantum superposition of 8= 2 × 2 × 2 copies of the original system S. The accepted terminology is somewhat misleading because it is incorrect to regard the universe as splitting at certain times; at any given instant there is one state in one universe. Relative state The goal of the relative-state formalism, as originally proposed by Everett in his 1957 doctoral dissertation, was to interpret the effect of external observation entirely within the mathematical framework developed by Paul Dirac, von Neumann and others, discarding altogether the ad-hoc mechanism of wave function collapse. Since Everett's original work, there have appeared a number of similar formalisms in the literature. One such idea is discussed in the next section. The relative-state interpretation makes two assumptions. The first is that the wavefunction is not simply a description of the object's state, but that it actually is entirely equivalent to the object, a claim it has in common with some other interpretations. The second is that observation or measurement has no special role, unlike in the Copenhagen interpretation which considers the wavefunction collapse as a special kind of event which occurs as a result of observation. The many-worlds interpretation is DeWitt's popularisation of Everett's work, who had referred to the combined observer-object system as being split by an observation, each split corresponding to the different or multiple possible outcomes of an observation. These splits generate a possible tree as shown in the graphic below. Subsequently DeWitt introduced the term "world" to describe a complete measurement history of an observer, which corresponds roughly to a single branch of that tree. Note that "splitting" in this sense, is hardly new or even quantum mechanical. The idea of a space of complete alternative histories had already been used in the theory of probability since the mid 1930s for instance to model Brownian motion. Many-worlds interpretation 37 Under the many-worlds interpretation, the Schrödinger equation, or relativistic analog, holds all the time everywhere. An observation or measurement of an object by an observer is modeled by applying the wave equation to the entire system comprising the observer and the object. One consequence is that every observation can be thought of as causing the combined observer-object's wavefunction to change into a quantum superposition of two or more non-interacting branches, or split into many "worlds". Since many observation-like events have happened, and are constantly happening, there are an enormous and growing number of simultaneously existing states. If a system is composed of two or more subsystems, the system's state will be a superposition of products of the subsystems' states. Once the subsystems interact, their states are no longer independent. Each product of subsystem states in the overall superposition evolves over time independently of other products. The subsystems states have become correlated or entangled and it is no longer possible to consider them independent of one another. In Everett's terminology each subsystem state was now correlated with its relative state, since each subsystem must now be considered relative to the other subsystems with which it has interacted. Partial trace as relative state. Light blue rectangle on upper left denotes system in pure state. Trellis shaded rectangle in upper right denotes a (possibly) mixed state. Mixed state from observation is partial trace of a linear superposition of states as shown in lower right-hand corner. Successive measurements with successive splittings Comparative properties and possible experimental tests One of the salient properties of the many-worlds interpretation is that it does not require an exceptional method of wave function collapse to explain it. “It seems that there is no experiment distinguishing the MWI from other no-collapse theories such as Bohmian mechanics or other variants of MWI... In most no-collapse interpretations, the evolution of the quantum state of the Universe is the same. Still, one might imagine that there is an experiment distinguishing the MWI from another no-collapse interepretation based on the difference in the correspondence between the formalism and the experience (the results of experiments).” [68] However, in 1985 David Deutsch published three related thought experiments which could test the theory vs the Copenhagen interpretation.[69] The experiments require macroscopic quantum state preparation and quantum erasure by a hypothetical quantum computer which is currently outside experimental possibility. Since then Lockwood (1989), Vaidman and others have made similar proposals.[68] These proposals also require an advanced technology Many-worlds interpretation which is able to place a macroscopic object in a coherent superposition, another task for which it is uncertain whether it will ever be possible. Many other controversial ideas have been put forward though, such as a recent claim that cosmological observations could test the theory,[70] and another claim by Rainer Plaga (1997), published in Foundations of Physics, that communication might be possible between worlds.[71] As of 2010, there are no feasible experiments to test the differences between MWI and other theories. 38 Copenhagen interpretation In the Copenhagen interpretation, the mathematics of quantum mechanics allows one to predict probabilities for the occurrence of various events. In the many-worlds interpretation, all these events occur simultaneously. What meaning should be given to these probability calculations? And why do we observe, in our history, that the events with a higher computed probability seem to have occurred more often? One answer to these questions is to say that there is a probability measure on the space of all possible universes, where a possible universe is a complete path in the tree of branching universes. This is indeed what the calculations seem to give. Then we should expect to find ourselves in a universe with a relatively high probability rather than a relatively low probability: even though all outcomes of an experiment occur, they do not occur in an equal way. As an interpretation which is consistent with the equations , it is hard to find tests of MWI that distinguish it from other mainstream interpretations. The universe decaying to a new vacuum state Any event that changes the number of observers in the universe may have experimental consequences.[72] Quantum tunneling to new vacuum state would reduce the number of observers to zero (i.e., kill all life). Some Cosmologists argue that the universe is in a false vacuum state and that consequently the universe should have already experienced quantum tunneling to a true vacuum state. This has not happened and is cited as evidence in favor of many-worlds. In some worlds quantum tunneling to a true vacuum state has happened but most other worlds escape this tunneling and remain viable. This can be thought of as a variation on Quantum Suicide. Many-minds The many-worlds interpretation should not be confused with the similar many-minds interpretation which defines the split on the level of the observers' minds. The many-worlds interpretation leads to a deterministic view of nature in which there is no special role for the human mind.[71] Reception There is a wide range of claims that are considered "many-worlds" interpretations. It was often claimed by those who do not believe in MWI[73] that Everett himself was not entirely clear[74] as to what he believed; however MWI adherents (such as DeWitt, Tegmark, Deutsch and others) believe they fully understand Everett's meaning as implying the literal existence of the other worlds. Additionally, recent biographical sources make it clear that Everett believed in the literal reality of the other quantum worlds.[21] Everett's son reported that Hugh Everett "never wavered in his belief over his many-worlds theory".[75] Also Everett was reported to believe "his many-worlds theory guaranteed him immortality".[76] Advocates of MWI often cite a poll of 72 "leading cosmologists and other quantum field theorists"[77] conducted by the American political scientist David Raub in 1995 showing 58% agreement with "Yes, I think MWI is true".[78] The poll is controversial: for example, Victor J. Stenger remarks that Murray Gell-Mann's published work explicitly rejects the existence of simultaneous parallel universes. Collaborating with James Hartle, Gell-Mann is working toward the development a more “palatable” post-Everett quantum mechanics. Stenger thinks it's fair to say that most physicists dismiss the many-world interpretation as too extreme, while noting it “has merit in finding a place for the observer inside the system being analyzed and doing away with the troublesome notion of wave function Many-worlds interpretation collapse”.[79] Max Tegmark also reports the result of a (in his words) 'highly unscientific' poll taken at a 1997 quantum mechanics workshop.[80] According to Tegmark, "The many worlds interpretation (MWI) scored second, comfortably ahead of the consistent histories and Bohm interpretations." Such polls have been taken at other conferences, for example, in response to Sean Carroll's observation, “As crazy as it sounds, most working physicists buy into the many-worlds theory”[81] Michael Nielsen counters: “at a quantum computing conference at Cambridge in 1998, a many-worlder surveyed the audience of approximately 200 people… Many-worlds did just fine, garnering support on a level comparable to, but somewhat below, Copenhagen and decoherence.” However, Nielsen notes that it seemed most attendees found it to be a waste of time: Asher Peres “got a huge and sustained round of applause… when he got up at the end of the polling and asked ‘And who here believes the laws of physics are decided by a democratic vote?’”[82] A 2005 poll of fewer than 40 students and researchers taken after a course on the Interpretation of Quantum Mechanics at the Institute for Quantum Computing University of Waterloo found “Many Worlds (and decoherence) ” to be the least favored.[83] One of MWI's strongest advocates is David Deutsch.[84] According to Deutsch, the single photon interference pattern observed in the double slit experiment can be explained by interference of photons in multiple universes. Viewed in this way, the single photon interference experiment is indistinguishable from the multiple photon interference experiment. In a more practical vein, in one of the earliest papers on quantum computing,[85] he suggested that parallelism that results from the validity of MWI could lead to "a method by which certain probabilistic tasks can be performed faster by a universal quantum computer than by any classical restriction of it". Deutsch has also proposed that when reversible computers become conscious that MWI will be testable (at least against "naive" Copenhagenism) via the reversible observation of spin.[55] According to David Deutsch probably less than ten percent of the physicists are talking parallel universes language.[86] Asher Peres was an outspoken critic of MWI, for example a section in his 1993 textbook had the title Everett's interpretation and other bizarre theories. In fact, Peres not only questioned whether MWI is really an "interpretation", but rather, if any interpretations of quantum mechanics are needed at all. Indeed, an interpretation can be regarded as a purely formal transformation, which adds nothing to the rules of the quantum mechanics. Peres seems to suggest that positing the existence of an infinite number of non-communicating parallel universes is highly suspect per those who interpret it as a violation of Occam's Razor, i.e., that it does not minimize the number of hypothesized entities. However, precisely the opposite conclusion is drawn, simply by applying Occam's Razor to the set of assumptions. It's understood the number of elementary particles are not a gross violation of Occam's Razor, one counts the types, not the tokens. Max Tegmark remarks that the alternative to many-worlds is "many words", an allusion to the complexity of von Neumann's collapse postulate. MWI is considered by some to be unfalsifiable and hence unscientific because the multiple parallel universes are non-communicating, in the sense that no information can be passed between them. Others[55] claim MWI is directly testable. Everett regarded MWI as falsifiable since any test that falsifies conventional quantum theory would also falsify MWI.[20] According to Martin Gardner, the "other" worlds of MWI have two different interpretations: real or unreal, and claims that Stephen Hawking and Steve Weinberg both favour the unreal interpretation.[87] Gardner also claims that the nonreal interpretation is favoured by the majority of physicists, whereas the "realist" view is only supported by MWI experts such as David Deutsch and Bryce DeWitt. Hawking has said that "according to Feynman's idea", all the other histories are as "equally real" as our own,[88] and Martin Gardner reports Hawking saying that MWI is "trivially true", which is an academic way of saying "obviously true".[89] In a 1983 interview Hawking also said he regarded the MWI as "self-evidently correct" but was dismissive towards questions about the interpretation of quantum mechanics, saying "when I hear of Schrödinger's cat, I reach for my gun". In the same interview he also said, "But, look: All that one does, really, is to calculate conditional probabilities—in other words, the probability of A happening, given B. I think that that's all the many worlds interpretation is. Some people overlay it with a lot of 39 Many-worlds interpretation mysticism about the wave function splitting into different parts. But all that you're calculating is conditional probabilities."[90] Elsewhere Hawking contrasted his attitude towards the "reality" of physical theories with that of his colleague Roger Penrose, saying "He's a Platonist and I'm a positivist. He's worried that Schrödinger's cat is in a quantum state, where it is half alive and half dead. He feels that can't correspond to reality. But that doesn't bother me. I don't demand that a theory correspond to reality because I don't know what it is. Reality is not a quality you can test with litmus paper. All I'm concerned with is that the theory should predict the results of measurements. Quantum theory does this very successfully."[91] For his own part, Penrose agrees with Hawking that QM applied to the universe implies MW, although he considers the current lack of a successful theory of quantum gravity negates the claimed universality of conventional QM.[64] 40 Speculative implications Speculative physics deals with questions which are also discussed in science fiction. Quantum suicide thought experiment It has been claimed that there is a thought experiment that would clearly differentiate between the many-worlds interpretation and other interpretations of quantum mechanics. It involves a quantum suicide machine and an experimenter willing to risk death. However, at best, this would only decide the issue for the experimenter; bystanders would learn nothing. Weak coupling Another speculation is that the separate worlds remain weakly coupled (e.g., by gravity) permitting "communication between parallel universes". A possible test of this using quantum-optical equipment is described in a 1997 Foundations of Physics article by Rainer Plaga.[71] It involves an isolated ion in an ion trap, a quantum measurement that would yield two parallel worlds (their difference just being in the detection of a single photon), and the excitation of the ion from only one of these worlds. If the excited ion can be detected from the other parallel universe, then this would constitute direct evidence in support of the many-worlds interpretation and would automatically exclude the orthodox, "logical", and "many-histories" interpretations. The reason the ion is isolated is to make it not participate immediately in the decoherence which insulates the parallel world branches, therefore allowing it to act as a gateway between the two worlds, and if the measure apparatus could perform the measurements quickly enough before the gateway ion is decoupled then the test would succeed (with electronic computers the necessary time window between the two worlds would be in a time scale of milliseconds or nanoseconds, and if the measurements are taken by humans then a few seconds would still be enough). R. Plaga shows that macroscopic decoherence timescales are a possibility. The proposed test is based on technical equipment described in a 1993 Physical Review article by Itano et al.[92] and R. Plaga says that this level of technology is enough to realize the proposed inter-world communication experiment. The necessary technology for precision measurements of single ions already exists since the 1970s, and the ion recommended for excitation is 199Hg+. The excitation methodology is described by Itano et al. and the time needed for it is given by the Rabbi flopping formula[93] Such a test as described by R. Plaga would mean that energy transfer is possible between parallel worlds. This does not violate the fundamental principles of physics because these require energy conservation only for the whole universe and not for the single parallel branches.[71] Neither the excitation of the single ion (which is a degree of freedom of the proposed system) leads to decoherence, something which is proven by Welcher Weg detectors which can excite atoms without momentum transfer (which causes the loss of coherence).[94] The proposed test would allow for low-bandwidth inter-world communication, the limiting factors of bandwidth and time being dependent on the technology of the equipment. Because of the time needed to determine the state of the partially decohered isolated excited ion based on Itano et al.'s methodology, the ion would decohere by the time its Many-worlds interpretation state is determined during the experiment, so Plaga's proposal would pass just enough information between the two worlds to confirm their parallel existence and nothing more. The author contemplates that with increased bandwidth, one could even transfer television imagery across the parallel worlds.[71] For example, Itano et al.'s methodology could be improved (by lowering the time needed for state determination of the excited ion) if a more efficient process were found for the detection of fluorescence radiation using 194 nm photons.[71] A 1991 article by J.Polchinski also supports the view that inter-world communication is a theoretical possibility.[95] Other authors in a 1994 preprint article also contemplated similar ideas.[96] The reason inter-world communication seems like a possibility is because decoherence which separates the parallel worlds is never fully complete,[97][98] therefore weak influences from one parallel world to another can still pass between them,[97][99] and these should be measurable with advanced technology. Deutsch proposed such an experiment in a 1985 International Journal of Theoretical Physics article,[100] but the technology it requires involves human-level artificial intelligence,[71] still not implemented as of 2012. 41 Similarity to modal realism The many-worlds interpretation has some similarity to modal realism in philosophy, which is the view that the possible worlds used to interpret modal claims exist and are of a kind with the actual world. Unlike the possible worlds of philosophy, however, in quantum mechanics counterfactual alternatives can influence the results of experiments, as in the Elitzur–Vaidman bomb-testing problem or the Quantum Zeno effect. Also, while the worlds of the many-worlds interpretation all share the same physical laws, modal realism postulates a world for every way things could conceivably have been. Time travel The many-worlds interpretation could be one possible way to resolve the paradoxes [84] that one would expect to arise if time travel turns out to be permitted by physics (permitting closed timelike curves and thus violating causality). Entering the past would itself be a quantum event causing branching, and therefore the timeline accessed by the time traveller simply would be another timeline of many. In that sense, it would make the Novikov self-consistency principle unnecessary. Many-worlds interpretation 42 Many-worlds in literature and science fiction The many-worlds interpretation (and the somewhat related concept of possible worlds) has been associated to numerous themes in literature, art and science fiction. Some of these stories or films violate fundamental principles of causality and relativity, and are extremely misleading since the information-theoretic structure of the path space of multiple universes (that is information flow between different paths) is very likely extraordinarily complex. Also see Michael Clive Price's FAQ referenced in the external links section below where these issues (and other similar ones) are dealt with more decisively. Another kind of popular illustration of many-worlds splittings, which does not involve information flow between paths, or information flow backwards in time considers alternate outcomes of historical events. According to the many-worlds interpretation, all of the historical speculations entertained within the alternate history genre are realized in parallel universes.[1] A map from Robert Sobel's novel For Want of a Nail, an artistic illustration of how small events – in this example the branching or point of divergence from our timeline's history is in October 1777 – can profoundly alter the course of history. According to the many-worlds interpretation every event, even microscopic, is a [1] branch point; all possible alternative histories actually exist. Notes [1] Bryce Seligman DeWitt, Quantum Mechanics and Reality: Could the solution to the dilemma of indeterminism be a universe in which all possible outcomes of an experiment actually occur?, Physics Today, 23(9) pp 30-40 (September 1970) "every quantum transition taking place on every star, in every galaxy, in every remote corner of the universe is splitting our local world on earth into myriads of copies of itself." See also Physics Today, letters followup, 24(4), (April 1971), pp 38-44 [2] Hugh Everett Theory of the Universal Wavefunction (http:/ / www. pbs. org/ wgbh/ nova/ manyworlds/ pdf/ dissertation. pdf), Thesis, Princeton University, (1956, 1973), pp 1-140 [3] Everett, Hugh (1957). "Relative State Formulation of Quantum Mechanics" (http:/ / www. univer. omsk. su/ omsk/ Sci/ Everett/ paper1957. html). Reviews of Modern Physics 29: 454–462. Bibcode 1957RvMP...29..454E. doi:10.1103/RevModPhys.29.454. . [4] Cecile M. DeWitt, John A. Wheeler eds, The Everett-Wheeler Interpretation of Quantum Mechanics, Battelle Rencontres: 1967 Lectures in Mathematics and Physics (1968) [5] Bryce Seligman DeWitt, The Many-Universes Interpretation of Quantum Mechanics, Proceedings of the International School of Physics "Enrico Fermi" Course IL: Foundations of Quantum Mechanics, Academic Press (1972) [6] Bryce Seligman DeWitt, R. Neill Graham, eds, The Many-Worlds Interpretation of Quantum Mechanics, Princeton Series in Physics, Princeton University Press (1973), ISBN 0-691-08131-X Contains Everett's thesis: The Theory of the Universal Wavefunction, pp 3-140. [7] H. Dieter Zeh, On the Interpretation of Measurement in Quantum Theory, Foundation of Physics, vol. 1, pp. 69-76, (1970). [8] Wojciech Hubert Zurek, Decoherence and the transition from quantum to classical, Physics Today, vol. 44, issue 10, pp. 36-44, (1991). [9] Wojciech Hubert Zurek, Decoherence, einselection, and the quantum origins of the classical, Reviews of Modern Physics, 75, pp 715-775, (2003) [10] David Deutsch argues that a great deal of fiction is close to a fact somewhere in the so called multiverse, Beginning of Infinity, p. 294 [11] Bryce Seligman DeWitt, R. Neill Graham, eds, The Many-Worlds Interpretation of Quantum Mechanics, Princeton Series in Physics, Princeton University Press (1973), ISBN 0-691-08131-X Contains Everett's thesis: The Theory of the Universal Wavefunction, where the claim to resolves all paradoxes is made on pg 118, 149. [12] Hugh Everett, Relative State Formulation of Quantum Mechanics (http:/ / www. univer. omsk. su/ omsk/ Sci/ Everett/ paper1957. html), Reviews of Modern Physics vol 29, (July 1957) pp 454-462. The claim to resolve EPR is made on page 462 [13] Osnaghi, Stefano; Freitas, Fabio; Olival Freire, Jr (2009). "The Origin of the Everettian Heresy" (http:/ / stefano. osnaghi. free. fr/ Everett. pdf) (PDF). Studies in History and Philosophy of Modern Physics 40: 97–123. doi:10.1016/j.shpsb.2008.10.002. . [14] Steven Weinberg, Dreams of a Final Theory: The Search for the Fundamental Laws of Nature (1993), ISBN 0-09-922391-0, pg 68-69 Many-worlds interpretation [15] Steven Weinberg Testing Quantum Mechanics, Annals of Physics Vol 194 #2 (1989), pg 336-386 [16] John Archibald Wheeler, Geons, Black Holes & Quantum Foam, ISBN 0-393-31991-1. pp 268-270 [17] Everett 1957, section 3, 2nd paragraph, 1st sentence [18] Everett [1956]1973, "Theory of the Universal Wavefunction", chapter 6 (e) [19] Zurek, Wojciech (March 2009). Quantum Darwinism. 5. Nature Physics. arXiv:0903.5082. Bibcode 2009NatPh...5..181Z. doi:10.1038/nphys1202. [20] Everett (http:/ / space. mit. edu/ home/ tegmark/ everett/ ) [21] Peter Byrne, The Many Worlds of Hugh Everett III: Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family (http:/ / www. amazon. co. uk/ dp/ 0199552274), ISBN 978-0-19-955227-6 [22] "Whether you can observe a thing or not depends on the theory which you use. It is the theory which decides what can be observed." Albert Einstein to Werner Heisenberg, objecting to placing observables at the heart of the new quantum mechanics, during Heisenberg's 1926 lecture at Berlin; related by Heisenberg in 1968, quoted by Abdus Salam, Unification of Fundamental Forces, Cambridge University Press (1990) ISBN 0-521-37140-6, pp 98-101 [23] N.P. Landsman, "The conclusion seems to be that no generally accepted derivation of the Born rule has been given to date, but this does not imply that such a derivation is impossible in principle." (http:/ / www. math. ru. nl/ ~landsman/ Born. pdf), in Compendium of Quantum Physics (eds.) F.Weinert, K. Hentschel, D.Greenberger and B. Falkenburg (Springer, 2008), ISBN 3-540-70622-4 [24] Adrian Kent (May 5, 2009), One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation (http:/ / arxiv. org/ pdf/ 0905. 0624v1) [25] Kent, Adrian (1990). "Against Many-Worlds Interpretations". Int.J.Mod.Phys A5: 1745. arXiv:gr-qc/9703089. Bibcode 1990IJMPA...5.1745K. doi:10.1142/S0217751X90000805. [26] Gleason, A. M. (1957). "Measures on the closed subspaces of a Hilbert space". Journal of Mathematics and Mechanics 6: 885–893. doi:10.1512/iumj.1957.6.56050. MR0096113. [27] James Hartle, Quantum Mechanics of Individual Systems, American Journal of Physics, 1968, vol 36 (#8), pp. 704-712 [28] E. Farhi, J. Goldstone & S. Gutmann. How probability arises in quantum mechanics., Ann. Phys. (N.Y.) 192, 368-382 (1989). [29] Pitowsky, I. (2005). "Quantum mechanics as a theory of probability". Eprint arXiv:quant-ph/0510095: 10095. arXiv:quant-ph/0510095. Bibcode 2005quant.ph.10095P. [30] Deutsch, D. (1999). Quantum Theory of Probability and Decisions. Proceedings of the Royal Society of London A455, 3129–3137. (http:/ / www. arxiv. org/ abs/ quant-ph/ 9906015). [31] David Wallace: Quantum Probability and Decision Theory, Revisited (http:/ / arxiv. org/ abs/ quant-ph/ 0211104) [32] David Wallace. Everettian Rationality: defending Deutsch’s approach to probability in the Everett interpretation. Stud. Hist. Phil. Mod. Phys. 34 (2003), 415-438. [33] David Wallace (2003), Quantum Probability from Subjective Likelihood: improving on Deutsch's proof of the probability rule (http:/ / arxiv. org/ abs/ quant-ph/ 0312157) [34] David Wallace, 2009, A formal proof of the Born rule from decision-theoretic assumptions (http:/ / arxiv. org/ abs/ 0906. 2718) [35] Simon Saunders: Derivation of the Born rule from operational assumptions. Proc. Roy. Soc. Lond. A460, 1771-1788 (2004). [36] Simon Saunders, 2004: What is Probability? (http:/ / arxiv. org/ abs/ quant-ph/ 0412194) [37] David J Baker, Measurement Outcomes and Probability in Everettian Quantum Mechanics (http:/ / philsci-archive. pitt. edu/ archive/ 00002717/ 01/ OutcomeProbEverett. pdf), Studies In History and Philosophy of Science Part B: Studies In History and Philosophy of Modern Physics, Volume 38, Issue 1, March 2007, Pages 153-169 [38] H. Barnum, C. M. Caves, J. Finkelstein, C. A. Fuchs, R. Schack: Quantum Probability from Decision Theory? (http:/ / lanl. arxiv. org/ abs/ quant-ph/ 9907024) Proc. Roy. Soc. Lond. A456, 1175-1182 (2000). [39] Merali, Zeeya (2007-09-21). "Parallel universes make quantum sense" (http:/ / space. newscientist. com/ article/ mg19526223. 700-parallel-universes-make-quantum-sense. html). New Scientist (2622). . Retrieved 2007-10-20 (Summary only). [40] Breitbart.com, Parallel universes exist - study, Sept 23 2007 (http:/ / www. breitbart. com/ article. php?id=paUniverse_sun14_parallel_universes& show_article=1& cat=0) [41] Perimeter Institute, Seminar overview, Probability in the Everett interpretation: state of play, David Wallace - Oxford University, 21 Sept 2007 (http:/ / www. perimeterinstitute. ca/ index. php?option=com_content& task=view& id=50& Itemid=83& lecture_id=6167) [42] Perimeter Institute, Many worlds at 50 conference, September 21-24, 2007 (http:/ / www. perimeterinstitute. ca/ manyworlds/ ) [43] Wojciech H. Zurek: Probabilities from entanglement, Born’s rule from envariance (http:/ / arxiv. org/ abs/ quant-ph/ 0405161v2), Phys. Rev. A71, 052105 (2005). [44] M. Schlosshauer & A. Fine: On Zurek's derivation of the Born rule. (http:/ / arxiv. org/ abs/ quant-ph/ 0312058v3) Found. Phys. 35, 197-213 (2005). [45] Lutz Polley, Position eigenstates and the statistical axiom of quantum mechanics (http:/ / arxiv. org/ abs/ quant-ph/ 0102113v2), contribution to conference Foundations of Probability and Physics, Vaxjo, Nov 27 - Dec 1, 2000 [46] Lutz Polley, Quantum-mechanical probability from the symmetries of two-state systems (http:/ / arxiv. org/ abs/ quant-ph/ 9906124v3) [47] Armando V.D.B. Assis (2011). "Assis, Armando V.D.B. On the nature of and the emergence of the Born rule. Annalen der Physik, 2011." (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1002/ andp. 201100062/ abstract). Annalen der Physik (Berlin) 523: 883–897. Bibcode 2011AnP...523..883A. doi:10.1002/andp.201100062. . [48] Everett FAQ "Is many-worlds a local theory?" (http:/ / www. hedweb. com/ manworld. htm#local) 43 Many-worlds interpretation [49] Mark A. Rubin, Locality in the Everett Interpretation of Heisenberg-Picture Quantum Mechanics, Foundations of Physics Letters, 14, (2001) , pp. 301–322, arXiv:quant-ph/0103079 [50] Paul C.W. Davies, Other Worlds, chapters 8 & 9 The Anthropic Principle & Is the Universe an accident?, (1980) ISBN 0-460-04400-1 [51] Paul C.W. Davies, The Accidental Universe, (1982) ISBN 0-521-28692-1 [52] Everett FAQ "Does many-worlds violate Ockham's Razor?" (http:/ / www. hedweb. com/ manworld. htm#ockham's) [53] Penrose, R. The Road to Reality, §21.11 [54] Tegmark, Max The Interpretation of Quantum Mechanics: Many Worlds or Many Words? (http:/ / www. arxiv. org/ abs/ quant-ph/ 9709032/ ), 1998. To quote: "What Everett does NOT postulate: “At certain magic instances, the world undergoes some sort of metaphysical 'split' into two branches that subsequently never interact.” This is not only a misrepresentation of the MWI, but also inconsistent with the Everett postulate, since the subsequent time evolution could in principle make the two terms...interfere. According to the MWI, there is, was and always will be only one wavefunction, and only decoherence calculations, not postulates, can tell us when it is a good approximation to treat two terms as non-interacting." [55] Paul C.W. Davies, J.R. Brown, The Ghost in the Atom (1986) ISBN 0-521-31316-3, pp. 34-38: "The Many-Universes Interpretation", pp83-105 for David Deutsch's test of MWI and reversible quantum memories [56] Christoph Simon, 2009, Conscious observers clarify many worlds (http:/ / arxiv. org/ abs/ 0908. 0322v1) [57] Joseph Gerver, The past as backward movies of the future, Physics Today, letters followup, 24(4), (April 1971), pp 46-7 [58] Bryce Seligman DeWitt, Physics Today,letters followup, 24(4), (April 1971), pp 43 [59] Arnold Neumaier's comments on the Everett FAQ, 1999 & 2003 (http:/ / www. mat. univie. ac. at/ ~neum/ manyworlds. txt) [60] Everett [1956] 1973, "Theory of the Universal Wavefunction", chapter V, section 4 "Approximate Measurements", pp. 100–103 (e) [61] Henry Stapp, The basis problem in many-world theories, Canadian J. Phys. 80,1043–1052 (2002) (http:/ / www-physics. lbl. gov/ ~stapp/ bp. PDF) [62] Harvey R Brown and David Wallace, Solving the measurement problem: de Broglie-Bohm loses out to Everett, Foundations of Physics 35 (2005), pp. 517-540. (http:/ / philsci-archive. pitt. edu/ archive/ 00001659/ 01/ Cushing. pdf) [63] Mark A Rubin (2005), There Is No Basis Ambiguity in Everett Quantum Mechanics (http:/ / arxiv. org/ abs/ quant-ph/ 0310186v2), Foundations of Physics Letters, Volume 17, Number 4 / August, 2004, pp 323-341 [64] Penrose, Roger (August 1991). "Roger Penrose Looks Beyond the Classic-Quantum Dichotomy" (http:/ / www. sciencewatch. com/ interviews/ roger_penrose2. htm). Sciencewatch. . Retrieved 2007-10-21. [65] Everett FAQ "Does many-worlds violate conservation of energy?" (http:/ / www. hedweb. com/ manworld. htm#conservation) [66] Everett FAQ "How do probabilities emerge within many-worlds?" (http:/ / www. hedweb. com/ manworld. htm#probabilities) [67] Everett FAQ "When does Schrodinger's cat split?" (http:/ / www. hedweb. com/ manworld. htm#splitsh) [68] Vaidman, Lev. "Many-Worlds Interpretation of Quantum Mechanics" (http:/ / plato. stanford. edu/ entries/ qm-manyworlds/ ). The Stanford Encyclopedia of Philosophy. . [69] Deutsch, D., (1986) ‘Three experimental implications of the Everett interpretation’, in R. Penrose and C.J. Isham (eds.), Quantum Concepts of Space and Time, Oxford: The Clarendon Press, pp. 204-214. [70] Page, D., (2000) ‘ Can Quantum Cosmology Give Observational Consequences of Many-Worlds Quantum Theory? (http:/ / xxx. lanl. gov/ abs/ gr-qc/ 0001001)’ [71] Plaga, R. (1997). "' Proposal for an experimental test of the many-worlds interpretation of quantum mechanics (http:/ / xxx. lanl. gov/ abs/ quant-ph/ 9510007)'". Foundations of Physics 27: 559–577. arXiv:quant-ph/9510007. Bibcode 1997FoPh...27..559P. doi:10.1007/BF02550677. [72] Page (2000). "Can Quantum Cosmology Give Observational Consequences of Many-Worlds Quantum Theory?". arXiv:gr-qc/0001001 [gr-qc]. doi:10.1063/1.1301589. [73] Jeffrey A. Barrett, The Quantum Mechanics of Minds and Worlds, Oxford University Press, 1999. According to Barrett (loc. cit. Chapter 6) "There are many many-worlds interpretations." [74] Barrett, Jeffrey A. (2010). "Everett's Relative-State Formulation of Quantum Mechanics" (http:/ / plato. stanford. edu/ archives/ fall2010/ entries/ qm-everett/ ). In Zalta, Edward N.. The Stanford Encyclopedia of Philosophy. . Again, according to Barrett "It is... unclear precisely how this was supposed to work." [75] Aldhous, Peter (2007-11-24). "Parallel lives can never touch" (http:/ / www. newscientist. com/ article/ mg19626311. 800-interview-parallel-lives-can-never-touch. html). New Scientist (2631). . Retrieved 2007-11-21. [76] Eugene Shikhovtsev's Biography of Everett, in particular see "Keith Lynch remembers 1979-1980" (http:/ / space. mit. edu/ home/ tegmark/ everett/ everett. html#e23) [77] Elvridge., Jim (2008-01-02). The Universe - Solved!. pp. 35–36. ISBN 978-1-4243-3626-5. OCLC 247614399. "58% believed that the Many Worlds Interpretation (MWI) was true, including Stephen Hawking and Nobel Laureates Murray Gell-Mann and Richard Feynman" [78] Bruce., Alexandra. "How does reality work?". Beyond the bleep : the definitive unauthorized guide to What the bleep do we know!?. p. 33. ISBN 978-1-932857-22-1. "[the poll was] published in the French periodical Sciences et Avenir in January 1998" [79] Stenger, V.J. (1995). The Unconscious Quantum: Metaphysics in Modern Physics and Cosmology (http:/ / books. google. com/ books?id=1ZbvAAAAMAAJ). Prometheus Books. p. 176. ISBN 978-1-57392-022-3. LCCN lc95032599. . "Gell-Man and collaborator James Hartle, along with a score of others, have been working to develop a more palatable interpretation of quantum mechanics that is free of the problems that plague all the interpretations we have considered so far. This new interpretation is called, in its various incarnations, post-Everett quantum mechanics, alternate histories, consistent histories, or decoherent histories. I will not be overly concerned with the 44 Many-worlds interpretation detailed differences between these characterizations and will use the terms more or less interchangeably." [80] Max Tegmark on many-worlds (contains MWI poll) (http:/ / space. mit. edu/ home/ tegmark/ quantum. html) [81] Caroll, Sean (1 April 2004). "Preposterous Universe" (http:/ / preposterousuniverse. blogspot. com/ 2004_04_01_preposterousuniverse_archive. html#108087902367974365). Archived from the original (http:/ / web. archive. org/ web/ 20040908014703/ http:/ / preposterousuniverse. blogspot. com/ 2004_04_01_preposterousuniverse_archive. html#108087902367974365) on 8 September 2004. . [82] Nielsen, Michael (3 April 2004). "Michael Nielsen: The Interpretation of Quantum Mechanics" (http:/ / www. qinfo. org/ people/ nielsen/ blog/ archive/ 000060. html). Archived from the original (http:/ / web. archive. org/ web/ 20040520222807/ http:/ / www. qinfo. org/ people/ nielsen/ blog/ archive/ 000060. html) on 20 May 2004. . [83] Interpretation of Quantum Mechanics class survey (http:/ / www. iqc. ca/ ~qipcourse/ interpret/ survey. html) [84] David Deutsch, The Fabric of Reality: The Science of Parallel Universes And Its Implications, Penguin Books (1998), ISBN 0-14-027541-X [85] David Deutsch, Quantum theory, the Church-Turing principle and the universal quantum computer, Proceedings of the Royal Society of London A 400, (1985), pp. 97–117 [86] http:/ / 193. 189. 74. 53/ ~qubitor/ people/ david/ structure/ Documents/ By%20Other%20People/ PhilosophyNow. html [87] A response to Bryce DeWitt (http:/ / findarticles. com/ p/ articles/ mi_m2843/ is_3_26/ ai_85932634), Martin Gardner, May 2002 [88] Award winning 1995 Channel 4 documentary "Reality on the rocks: Beyond our Ken" (http:/ / www. windfallfilms. com/ html/ awards. htm) where, in response to Ken Campbell's question "all these trillions of Universes of the Multiverse, are they as real as this one seems to be to me?" Hawking states "Yes.... According to Feynman's idea, every possible history (of Ken) is equally real" (http:/ / www. youtube. com/ watch?v=S3aadgf0GH8& feature=related) [89] Gardner, Martin (2003). Are universes thicker than blackberries? (http:/ / books. google. com/ books?id=z9jH9mYiO5IC& pg=PA10& lpg=PA10). W.W. Norton. p. 10. ISBN 978-0-393-05742-3. . [90] Ferris, Timothy (1997). The Whole Shebang. Simon & Schuster. pp.  345 (http:/ / books. google. com/ books?id=qjYbQ7EBAKwC& lpg=PP1& pg=PA345#v=onepage& q& f=false). ISBN 978-0-684-81020-1. [91] Hawking, Stephen; Roger Penrose (1996). The Nature of Space and Time. Princeton University Press. pp.  121 (http:/ / books. google. com/ books?id=LstaQTXP65cC& lpg=PP1& pg=PA121#v=onepage& q& f=false). ISBN 978-0-691-03791-2. [92] W.M.Itano et al., Phys.Rev. A47,3354 (1993). [93] M.SargentIII,M.O.Scully and W.E.Lamb, Laser physics (Addison-Wesley, Reading, 1974), p.27. [94] M.O.Scully and H.Walther, Phys.Rev. A39,5229 (1989). [95] J.Polchinski, Phys.Rev.Lett. 66,397 (1991). [96] M.Gell-Mann and J.B.Hartle, Equivalent Sets of Histories and Multiple Quasiclassical Domains, preprint University of California at Santa Barbara UCSBTH-94-09 (1994). [97] H.D.Zeh, Found.Phys. 3,109 (1973). [98] H.D.Zeh, Phys.Lett.A 172,189 (1993). [99] A.Albrecht, Phys.Rev. D48,3768 (1993). [100] D.Deutsch, Int.J.theor.Phys. 24,1 (1985). 45 Further reading • Jeffrey A. Barrett, The Quantum Mechanics of Minds and Worlds, Oxford University Press, Oxford, 1999. • Peter Byrne, The Many Worlds of Hugh Everett III: Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family, Oxford University Press, 2010. • Jeffrey A. Barrett and Peter Byrne, eds., "The Everett Interpretation of Quantum Mechanics: Collected Works 1955-1980 with Commentary", Princeton University Press, 2012. • Julian Brown, Minds, Machines, and the Multiverse, Simon & Schuster, 2000, ISBN 0-684-81481-1 • Paul C.W. Davies, Other Worlds, (1980) ISBN 0-460-04400-1 • James P. Hogan, The Proteus Operation (science fiction involving the many-worlds interpretation, time travel and World War 2 history), Baen, Reissue edition (August 1, 1996) ISBN 0-671-87757-7 • Adrian Kent, One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation (http://arxiv.org/abs/0905.0624) * Asher Peres, Quantum Theory: Concepts and Methods, Kluwer, Dordrecht, 1993. • Andrei Linde and Vitaly Vanchurin, How Many Universes are in the Multiverse? (http://arxiv.org/abs/0910. 1589v1) • Stefano Osnaghi, Fabio Freitas, Olival Freire Jr, The Origin of the Everettian Heresy (http://stefano.osnaghi. free.fr/Everett.pdf), Studies in History and Philosophy of Modern Physics 40(2009)97–123. A study of the painful three-way relationship between Hugh Everett, John A Wheeler and Niels Bohr and how this affected the Many-worlds interpretation early development of the many-worlds theory. Mark A. Rubin, Locality in the Everett Interpretation of Heisenberg-Picture Quantum Mechanics, Foundations of Physics Letters, 14, (2001), pp. 301–322, arXiv:quant-ph/0103079 David Wallace, Harvey R. Brown, Solving the measurement problem: de Broglie-Bohm loses out to Everett, Foundations of Physics, arXiv:quant-ph/0403094 David Wallace, Worlds in the Everett Interpretation, Studies in the History and Philosophy of Modern Physics, 33, (2002), pp. 637–661, arXiv:quant-ph/0103092 John A. Wheeler and Wojciech Hubert Zurek (eds), Quantum Theory and Measurement, Princeton University Press, (1983), ISBN 0-691-08316-9 46 • • • • External links • Everett's Relative-State Formulation of Quantum Mechanics (http://plato.stanford.edu/entries/qm-everett/) Jeffrey A. Barrett's article on Everett's formulation of quantum mechanics in the Stanford Encyclopedia of Philosophy. • Many-Worlds Interpretation of Quantum Mechanics (http://plato.stanford.edu/entries/qm-manyworlds/) - Lev Vaidman's article on the many-worlds interpretation of quantum mechanics in the Stanford Encyclopedia of Philosophy. • Hugh Everett III Manuscript Archive (UC Irvine) (http://ucispace.lib.uci.edu/handle/10575/1060) - Jeffrey A. Barrett, Peter Byrne, and James O. Weatherall (eds.). • Michael C Price's Everett FAQ (http://www.hedweb.com/manworld.htm) -- a clear FAQ-style presentation of the theory. • The Many-Worlds Interpretation of Quantum Mechanics (http://frombob.to/many.html) - a description for the lay reader with links. • Against Many-Worlds Interpretations by Adrian Kent (http://arxiv.org/abs/gr-qc/9703089) • Many-Worlds is a "lost cause" (http://www.mth.kcl.ac.uk/~streater/lostcauses.html#XII) according to R. F. Streater • The many worlds of quantum mechanics (http://www.johnsankey.ca/qm.html) John Sankey • Max Tegmark's web page (http://space.mit.edu/home/tegmark/quantum.html) • Henry Stapp's critique of MWI, focusing on the basis problem (http://www-physics.lbl.gov/~stapp/bp.PDF) Canadian J. Phys. 80,1043–1052 (2002). • Everett hit count on arxiv.org (http://xstructure.inr.ac.ru/x-bin/theme2.py?arxiv=quant-ph&level=1& index1=5693) • Many Worlds 50th anniversary conference at Oxford (http://users.ox.ac.uk/~everett/abstracts.htm) • "Many Worlds at 50" conference (http://www.perimeterinstitute.ca/en/Events/Many_Worlds_at_50/ Many_Worlds_at_50/) at Perimeter Institute • Scientific American report on the Many Worlds 50th anniversary conference at Oxford (http://www. scientificamerican.com/blog/post.cfm?id=many-worlds-in-oxford) • Highfield, Roger (September 21, 2007). Parallel universe proof boosts time travel hopes (http://web.archive. org/web/20071020024203/http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/09/21/ sciuni121.xml). The Daily Telegraph. Archived from the original (http://www.telegraph.co.uk/earth/main. jhtml?xml=/earth/2007/09/21/sciuni121.xml) on 2007-10-20. Retrieved 2007-10-26. • HowStuffWorks article (http://science.howstuffworks.com/quantum-suicide2.htm) • Physicists Calculate Number of Parallel Universes (http://www.physorg.com/news174921612.html) Physorg.com October 16, 2009. • TED-Education video (http://www.youtube.com/user/TEDEducation?feature=watch) - How many universes are there? (http://www.youtube.com/watch?v=a1bWKZFP2Tc&feature=relmfu). Novikov self-consistency principle 47 Novikov self-consistency principle The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s to solve the problem of paradoxes in time travel, which is theoretically permitted in certain solutions of general relativity (solutions containing what are known as closed timelike curves). Stated simply, the Novikov consistency principle asserts that if an event exists that would give rise to a paradox, or to any "change" to the past whatsoever, then the probability of that event is zero. In short, it says that it's impossible to create time paradoxes. History of the principle Physicists have long been aware that there are solutions to the theory of general relativity which contain closed timelike curves, or CTCs—see for example the Gödel metric. Novikov discussed the possibility of CTCs in books written in 1975 and 1983, offering the opinion that only self-consistent trips back in time would be permitted. In a 1990 paper by Novikov and several others, Cauchy problem in spacetimes with closed timelike curves,[1] the authors state: The only type of causality violation that the authors would find unacceptable is that embodied in the science-fiction concept of going backward in time and killing one's younger self ("changing the past"). Some years ago one of us (Novikov10) briefly considered the possibility that CTCs might exist and argued that they cannot entail this type of causality violation: Events on a CTC are already guaranteed to be self-consistent, Novikov argued; they influence each other around a closed curve in a self-adjusted, cyclical, self-consistent way. The other authors recently have arrived at the same viewpoint. We shall embody this viewpoint in a principle of self-consistency, which states that the only solutions to the laws of physics that can occur locally in the real Universe are those which are globally self-consistent. This principle allows one to build a local solution to the equations of physics only if that local solution can be extended to a part of a (not necessarily unique) global solution, which is well defined throughout the nonsingular regions of the spacetime. Among the coauthors of this 1990 paper were Kip Thorne, Mike Morris, and Ulvi Yurtsever, who in 1988 had stirred up renewed interest in the subject of time travel in general relativity with their paper Wormholes, Time Machines, and the Weak Energy Condition,[2] which showed that a new general relativity solution known as a traversable wormhole could lead to closed timelike curves, and unlike previous CTC-containing solutions it did not require unrealistic conditions for the universe as a whole. After discussions with another coauthor of the 1990 paper, John Friedman, they convinced themselves that time travel need not lead to unresolvable paradoxes, regardless of what type of object was sent through the wormhole.[3] In response, another physicist named Joseph Polchinski sent them a letter in which he argued that one could avoid questions of free will by considering a potentially paradoxical situation involving a billiard ball sent through a wormhole which sends it back in time. In this scenario, the ball is fired into a wormhole at an angle such that, if it continues along that path, it will exit the wormhole in the past at just the right angle to collide with its earlier self, thereby knocking it off course and preventing it from entering the wormhole in the first place. Thorne deemed this problem "Polchinski's paradox".[4] After considering the problem, two students at Caltech (where Thorne taught), Fernando Echeverria and Gunnar Klinkhammer, were able to find a solution beginning with the original billiard ball trajectory proposed by Polchinski which managed to avoid any inconsistencies. In this situation, the billiard ball emerges from the future at a different angle than the one used to generate the paradox, and delivers its younger self a glancing blow instead of knocking it completely away from the wormhole, a blow which changes its trajectory in just the right way so that it will travel back in time with the angle required to deliver its younger self this glancing blow. Echeverria and Klinkhammer Novikov self-consistency principle actually found that there was more than one self-consistent solution, with slightly different angles for the glancing blow in each case. Later analysis by Thorne and Robert Forward showed that for certain initial trajectories of the billiard ball, there could actually be an infinite number of self-consistent solutions.[5] Echeverria, Klinkhammer and Thorne published a paper discussing these results in 1991;[6] in addition, they reported that they had tried to see if they could find any initial conditions for the billiard ball for which there were no self-consistent extensions, but were unable to do so. Thus it is plausible that there exist self-consistent extensions for every possible initial trajectory, although this has not been proven.[7] This only applies to initial conditions which are outside of the chronology-violating region of spacetime,[8] which is bounded by a Cauchy horizon.[9] This could mean that the Novikov self-consistency principle does not actually place any constraints on systems outside of the region of spacetime where time travel is possible, only inside it. Even if self-consistent extensions can be found for arbitrary initial conditions outside the Cauchy Horizon, the finding that there can be multiple distinct self-consistent extensions for the same initial condition—indeed, Echeverria et al. found an infinite number of consistent extensions for every initial trajectory they analyzed[7]—can be seen as problematic, since classically there seems to be no way to decide which extension the laws of physics will choose. To get around this difficulty, Thorne and Klinkhammer analyzed the billiard ball scenario using quantum mechanics,[10] performing a quantum-mechanical sum over histories (path integral) using only the consistent extensions, and found that this resulted in a well-defined probability for each consistent extension. The authors of Cauchy problem in spacetimes with closed timelike curves write: The simplest way to impose the principle of self-consistency in quantum mechanics (in a classical space-time) is by a sum-over-histories formulation in which one includes all those, and only those, histories that are self-consistent. It turns out that,14 at least formally (modulo such issues as the convergence of the sum), for every choice of the billiard ball's initial, nonrelativistic wave function before the Cauchy horizon, such a sum over histories produces unique, self-consistent probabilities for the outcomes of all sets of subsequent measurements. ... We suspect, more generally, that for any quantum system in a classical wormhole spacetime with a stable Cauchy horizon, the sum over all self-consistent histories will give unique, self-consistent probabilities for the outcomes of all sets of measurements that one might choose to make. 48 Potential implications for paradoxes The Novikov Principle is able to circumvent most commonly-cited paradoxes which are often alleged to exist should time travel be possible (and are often claimed to make it impossible). A common example of the principle in action is the idea of preventing disasters from happening in the past and the potential paradoxes this may cause (notably the idea that preventing the disaster would remove the motive for the traveller to go back and prevent it and so on). The Novikov self-consistency principle states that a time traveller would not be able to do so. An example is the Titanic sinking; even if there were time travellers on the Titanic, they obviously failed to stop the ship from sinking. The Novikov Principle does not allow a time traveller to change the past in any way at all, but it does allow them to affect past events in a way that produces no inconsistencies—for example, a time traveller could rescue people from a disaster, and replace them with realistic corpses if history recorded that bodies of victims had been found. Provided that the rescuees were not known to have survived prior to the date that the time traveler stepped into the time machine (perhaps because they were taken forward in time to a later date, or because their identities were hidden), the time traveler's motivation to travel back in time and save them will be preserved. In this example, it must always have been true that the people were rescued by a time traveller and replaced with realistic corpses, and there would be no "original" history where they were actually killed, since the notion of "changing" the past is deemed impossible by the self-consistency principle. Novikov self-consistency principle 49 Assumptions of the Novikov self-consistency principle The Novikov consistency principle assumes certain conditions about what sort of time travel is possible. Specifically, it assumes either that there is only one timeline, or that any alternative timelines (such as those postulated by the many-worlds interpretation of quantum mechanics) are not accessible. Given these assumptions, the constraint that time travel must not lead to inconsistent outcomes could be seen merely as a tautology, a self-evident truth that cannot possibly be false, because if you make the assumption that it is false this would lead to a logical paradox. However, the Novikov self-consistency principle is intended to go beyond just the statement that history must be consistent, making the additional nontrivial assumption that the universe obeys the same local laws of physics in situations involving time travel that it does in regions of spacetime that lack closed timelike curves. This is made clear in the above-mentioned Cauchy problem in spacetimes with closed timelike curves,[1] where the authors write: That the principle of self-consistency is not totally tautological becomes clear when one considers the following alternative: The laws of physics might permit CTC's; and when CTC's occur, they might trigger new kinds of local physics which we have not previously met. ... The principle of self-consistency is intended to rule out such behavior. It insists that local physics is governed by the same types of physical laws as we deal with in the absence of CTC's: the laws that entail self-consistent single valuedness for the fields. In essence, the principle of self-consistency is a principle of no new physics. If one is inclined from the outset to ignore or discount the possibility of new physics, then one will regard self-consistency as a trivial principle. Time loop logic Time loop logic, coined by the roboticist and futurist Hans Moravec,[11] is the name of a hypothetical system of computation that exploits the Novikov self-consistency principle to compute answers much faster than possible with the standard model of computational complexity using Turing machines. In this system, a computer sends a result of a computation backwards through time and relies upon the self-consistency principle to force the sent result to be correct. A program exploiting time loop logic can be quite simple in outline. For example, to compute one prime factor of the natural number N in polynomial time (no polynomial time factorization algorithm is known in traditional complexity theory; see integer factorization): 1. 2. 3. 4. If N is 0 or 1, abort. Allocate a communication channel c. Receive one prime factor, F, of N from the future on channel c. Test that F ≠ N, that F divides N (time complexity O(log N)), and that F is prime (polynomial time; see AKS primality test). 1. If so, send F backwards in time on channel c. 2. If not, send F + 1 backwards in time on channel c. Note that this results in a paradox, as the number received in step 3 above is not the same as that sent in this step. The self-consistency principle guarantees that the sequence of events generating the paradox in the nested conditional has zero probability. Note that if N is itself prime, i.e., there is no such prime F ≠ N, then some event will prevent the execution of step 3 that receives the value F from the future. Assuming the machine executing the program itself continues to function, it can detect this failure and abort. Physicist David Deutsch showed in 1991 that this model of computation could solve NP problems in polynomial time,[12] and Scott Aaronson later extended this result to show that the model could also be used to solve PSPACE problems in polynomial time.[13][14] Novikov self-consistency principle 50 Pre-Novikov examples Claims, arguments, or philosophical principles logically equivalent to the Novikov self-consistency principle have been published before Novikov's own publication. This makes the principle an example of Stigler's law of eponymy. • Something resembling the idea can be found in Greek mythology, in the story of Cassandra. Cassandra was given the gift of prophecy by Apollo but also cursed such that no one would believe her predictions. This left her unable to avert any of the disastrous events she foresaw. The metaphor has been adopted in modern times into the notion of a "Cassandra Complex". • H. P. Lovecraft discussed this idea of time travel in a 1930 letter to Clark Ashton Smith, where he wrote:[15] Your idea for a time-voyaging machine is ideal—for in spite of Wells, no really satisfactory thing of this sort has ever been written. The weakness of most tales with this theme is they do not provide for the recording, in history, of those inexplicable events in the past which were caused by the backward time-voyagings of persons of the present and future. It must be remembered that if a man of 1930 travels back to B.C. 400, the strange phenomenon of his appearance actually occurred in B.C. 400, and must have excited notice wherever it took place. Of course, the way to get around this is to have the voyager conceal himself when he reaches the past, conscious of what an abnormality he must seem. Or rather, he ought simply to conceal his identity—hiding the evidences of his "futurity" and mingling with the ancients as best he can on their own plane. It would be excellent to have him know to some extent of his past appearance before making the voyage. Let him, for example, encounter some private document of the past in which a record of the advent of a mysterious stranger—unmistakably himself—is made. This might be the provocation for his voyage—that is, the conscious provocation. • In "Via the Time Accelerator" by F. J. Bridge (a pseudonym of Francis J. Brueckel[16]), from the January 1931 issue of Amazing Stories, a time traveler in 1930 wonders if he should travel to the future, and then he sees himself returning from the future, which reassures him about the success of his voyage. Later, in a situation where he finds himself in danger, he tells himself "I would escape ... It was so decreed. Had I not, with my own eyes, seen myself appear out of the fourth dimension back there in the Twentieth Century, and glide down to my landing-field? Surely, then, I was destined to return to my own age safe and sound." The time traveler eventually arrives in a ruined city in A.D. 1,001,930, where he is met by an old man who claims to be the Last Man still alive, and who says he knew the time traveler was coming because he read in an ancient history book that he himself (the Last Man) had arrived from the future in A.D. 502,101 in the same time machine the time traveler was using. When the time traveler goes to sleep, the Last Man does indeed take the time machine back to A.D. 502,101, leaving the time traveler stranded. The time traveler then wanders around the ruined city until he finds a museum, where preserved in a glass case is his time machine, which had been put there after it had appeared in A.D. 502,101. The time traveler adds some oil to its engine, and uses it to travel back to 1930, arriving there just as he had seen himself do.[17] • Robert A. Heinlein's By His Bootstraps (1941) features a plot in which a man interacts with different older versions of himself that travel by way of a "Time Gate", with all the interactions revisited later in the story from the perspective of the now-older man, everything being tied together in a completely self-consistent way. Heinlein later revisited a similar theme in his 1958 story —All You Zombies—, in which the main character's interactions with sex-changed versions of himself/herself at various points in his/her life result in a bizarre version of the ontological paradox in which the character becomes his/her own mother and father. • In Chris Marker's film La jetée (1962) the protagonist remembers, when he was a child, seeing a man killed at an airport jetty. He later travels back in time and is killed at the same airport jetty, and realizes that, as a child, he had seen his future self being killed. • In Harry Harrison's The Technicolor Time Machine (1967), main characters go back in time to shoot a movie about founding a Viking colony in North America, only to discover to their surprise that the colony they founded turned out to be written into the history as the original Viking colony in North America—and some of them are Novikov self-consistency principle even featured in Norse sagas. • In Michael Moorcock's Behold the Man (1969), a time traveler goes back to 28 A.D. in hopes of meeting Jesus, only to end up playing the role of Jesus himself, just as described in the Bible. • Science fiction author Larry Niven called this idea the "law of conservation of history" in an essay titled "The Theory and Practice of Time Travel," which was published in his book "All the Myriad Ways" in 1971. 51 Fictional usage • The movie 12 Monkeys appears to obey Novikov's principle. All attempts by the main character James Cole (played by Bruce Willis) to change the past prove unsuccessful, and in the end his death is witnessed by his own childhood self in exactly the way he had remembered earlier in the movie. Additionally, the scientists in charge of the time travel mission have no interest in attempting to avert the release of the deadly virus which killed most of the human population, and are instead only trying to obtain a pure strain of the original virus, in hopes that it will help them to cure the disease in their own time. • Something close to this principle is used in season 5 of the TV series Lost. The show's version is often referred to by characters and fans as "Whatever Happened, Happened" (also the title of an episode). It is supported by various implications in-show, chief of which is the fact that, in travelling to the past to prevent the 'future' crashing of their plane, the survivors actually set in motion the chain of events that ultimately caused it. However, the episode "Flashes Before Your Eyes" suggests that minor changes are possible, unlike the totally fixed timeline postulated by Novikov's principle: in this episode Desmond's consciousness time travels back to a point in his past, where he ends up in a bar, where he remembers (from his previous experience of this time) a man named Jimmy Lennon entering and attacking the bartender; in his attempt to warn the bartender, he himself gets attacked instead. Additionally, when Desmond meets a mysterious woman with apparent knowledge of the future (later revealed as Eloise Hawking), she points out a man with red shoes, who moments later is killed by falling scaffolding; when Desmond asks why she didn't try to save the man, she says that "it wouldn't matter. Had I warned him about the scaffolding, tomorrow he'd be hit by a taxi. If I warned him about the taxi, he'd fall in the shower and break his neck. The universe, unfortunately, has a way of course correcting. That man was supposed to die." Again, this suggests that although major events (like the man's death) are unchangeable, minor ones (like the precise cause of his death) can be changed, in violation of Novikov's principle. • The first-season 2002 TV series Twilight Zone episode "Cradle of Darkness" featured a woman who traveled from the modern day back in time to kill the infant Adolf Hitler to prevent his future atrocities. The woman, posing as the family nurse, disposes of the Hitlers' baby and replaces him with a beggar woman's child so as not to arouse suspicion. This replacement infant is the child who then grows up to become the infamous Adolf Hitler. • Each episode of the Irwin Allen series The Time Tunnel (less the few set in the future) depicted the time-traveling duo arriving at the scene of an historic tragedy, days or hours before the event, and invariably failing in their attempts to prevent it. This was also true in the 1976 revival pilot, and the similar 1982–83 series, Voyagers!. • In the Star Trek: The Next Generation episode "Time's Arrow", a 500-year old copy of the android Data's head is unearthed in an excavation near San Francisco on Earth. In the sequence of events that ensues upon investigation, Data is sent back in time to 19th century San Francisco. Later in this time frame, the shock of another temporal event causes his head to be split from his body and remain in the 19th century, while the rest of his body travels forward to the original point in time, when it is re-attached to the 500 year old head. Thus Data remains, as does the causality of time. However, the series does not consistently obey the Novikov principle in episodes featuring time travel, as episodes like Time Squared and Yesterday's Enterprise show history being changed as a result of time travel. • The video game series Legacy of Kain uses the same principle, although one can possibly break away from the timeline during a temporal distortion, that is, whenever two identical bodies meet in time and space. Novikov self-consistency principle • While predating Novikov's thesis, the film Timerider: The Adventure of Lyle Swann presents a similar predestination paradox, wherein the title character becomes his own great-great-grandfather thus causing his own existence and time-travel. The same film, however, contains an ontological paradox in that Swann's heirloom necklace which his great-great-grandmother took from his great-great-grandfather (i.e., himself) is never created and is perpetually in the time-loop. • The events of the first Terminator film appear to respect the self-consistency principle. In the film, a sentient computer called Skynet attempts to exterminate the human race, but faces difficulty in dealing with a human resistance effort led by a man called John Connor. In a last-ditch attempt to win the war, Skynet sends a cybernetic assassin called a Terminator back through time to murder Connor's mother Sarah before he is born, thereby preventing Connor's existence and the success of his future rebellion. Connor sends a soldier named Kyle Reese back to the same time to protect Sarah. Rather than altering history, these time travellers end up creating the timeline as it was meant to be. While on the run from the Terminator, Kyle and Sarah have sex and conceive the child who will become John Connor. Likewise, the Terminator is destroyed in a factory and its remains are claimed by Cyberdyne Systems, the factory's owner. This company uses the Terminator's remains as the basis for a research project that will ultimately result in the creation of the malevolent computer Skynet. (It should be noted, however, that only the first film respects this principle. In the sequels, the main characters are able to significantly alter the timeline. Also, even in the first film Skynet's plan would not really make sense unless it believed that history could be changed, and when Sarah Connor asks Kyle Reese if he's saying the Terminator is from the future, he responds 'One possible future. From your point of view. I don't know tech stuff.') • In Roswell That Ends Well, episode 19 of season 3 of the series Futurama, the protagonist Fry returns to the past and accidentally kills his young grandfather in an attempt to protect him from harm. Fry visits his young grandmother whom he'd been introduced to earlier as his grandfather's fiancee, and convincing himself that she can't actually be his grandmother as he is still alive, allows himself to be seduced by her. The explanation at the end of the show is that Fry has become his own grandfather. By the laws of genetic relatedness, one might find a paradox here, in that Fry being his own grandfather means his father is both 50% related to him (since he is Fry's father) and 62.5% related to him (since Fry's father is also his son and the son of Fry's grandmother, who's by virtue of being Fry's grandmother, is 25% related to Fry). However, these laws are probabilistic and Fry being his own grandfather is not necessarily a violation of Novikov's principle. This is illustrated on this episode's page on InfoSphere [18]. The reason is that while Fry may have obtained 50% of his SNPs from his father, his grandmother might have been similar enough to him (his grandfather) that his father is 62.5% related to him. Regardless, it's clear that Fry's just very inbred. • In The Final Countdown, the aircraft carrier USS Nimitz, based at Pearl Harbor, is sent back in time from 1980 to December 6, 1941. Aboard is a civilian consultant from one of the companies which contributed to the design of the ship. One of the ship's officers, a historian, is lost and presumed dead while transporting a rescued senator and his secretary to a small island for safety in advance of the coming battle; according to history, the pair and his chief of staff were believed to have been killed by the Japanese. The senator dies trying to escape the island. Just as the ship's complement prepare to go into battle the next morning to stop the Japanese attack, the ship returns to 1980 – their minor involvement having had no net effect on history. Back in port, the consultant meets his reclusive boss who helped design the ship – he and his wife are the pilot and the senator's secretary who assumed false names during the war. • Throughout the plot of Harry Potter and the Prisoner of Azkaban, two unexplained events that greatly affect the plot are later seen to be caused by the protagonists using a time-turner, a small hourglass allowing its user to travel back in time. Hermione Granger uses the time-turner to go back in time and do a different lesson than the current Hermione is doing and thus appears to be in multiple places at once. In the same book, Harry Potter saved himself from a Dementor attack, realizing at the last moment that his savior was not his father as he had initially thought, but was in fact, himself. 52 Novikov self-consistency principle • Novikov is alluded to by name in the comic Nth Man: The Ultimate Ninja. One of the characters is Colonel Vavara Novikova (Russian surnames having masculine and feminine forms), who accompanies the protagonist and antagonist back in time to their birth so that they can be delivered to the orphanage where their story begins. • In the book (and later the film) The Time Traveler's Wife, the main character's mother is killed in a car crash while he is young. He escapes injury by time travelling out of the car. Although he frequently revisits the scene and time of the accident throughout his life, he can never alter the outcome as to do so would remove his desire to be there. • In Season 4 episode 2 of the TV series Eureka The Novikov Self Consistency Principle is explicitly mentioned to justify the many similarities between the "alternative timeline" experienced by the protagonists and their "original timeline". In the brief discussion the character Dr. Henry Deacon (Joe Morton), using the analogy of ripples in a pond, explains that the further one travels from the point where the timeline is changed the less noticeable are the effects of that change. This is not however an accurate depiction of the principle, since the principle actually forbids any changes to the timeline. • In The Time Machine (2002), the protagonist invented a time machine in order to go back and save his sweetheart, only to find that he couldn't do it, as that would remove his reason to invent the time machine. Again, this is not exactly the principle, as he changes the method of her death. 53 References [1] Friedman, John; Michael Morris, Igor Novikov, Fernando Echeverria, Gunnar Klinkhammer, Kip Thorne, Ulvi Yurtsever (1990). "Cauchy problem in spacetimes with closed timelike curves" (http:/ / authors. library. caltech. edu/ 3737/ ). Physical Review D 42 (6): 1915. Bibcode 1990PhRvD..42.1915F. doi:10.1103/PhysRevD.42.1915. . [2] Thorne, Kip; Michael Morris, Ulvi Yurtsever (1988). "Wormholes, Time Machines, and the Weak Energy Condition". Physical Review Letters 61 (13): 1446. Bibcode 1988PhRvL..61.1446M. doi:10.1103/PhysRevLett.61.1446. PMID 10038800. [3] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. pp. 509. ISBN 0-393-31276-3. [4] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. pp. 510–511. ISBN 0-393-31276-3. [5] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. pp. 511–513. ISBN 0-393-31276-3. [6] Echeverria, Fernando; Gunnar Klinkhammer, Kip Thorne (1991). "Billiard balls in wormhole spacetimes with closed timelike curves: Classical theory" (http:/ / authors. library. caltech. edu/ 6469/ ). Physical Review D 44 (4): 1077. Bibcode 1991PhRvD..44.1077E. doi:10.1103/PhysRevD.44.1077. . [7] Earman, John (1995). Bangs, Crunches, Whimpers, and Shrieks: Singularities and Acausalities in Relativistic Spacetimes. Oxford University Press. pp. 184. ISBN 0-19-509591-X. [8] Earman, John (1995). Bangs, Crunches, Whimpers, and Shrieks: Singularities and Acausalities in Relativistic Spacetimes. Oxford University Press. pp. 187. ISBN 0-19-509591-X. [9] Nahin, Paul J. (1999). Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction. American Institute of Physics. pp. 508. ISBN 0-387-98571-9. [10] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. pp. 514–515. ISBN 0-393-31276-3. [11] Hans Moravec (1991). "Time Travel and Computing" (http:/ / www. frc. ri. cmu. edu/ users/ hpm/ project. archive/ general. articles/ 1991/ TempComp. html). . Retrieved 2008-07-28. [12] Deutsch, David (1991). "Quantum mechanics near closed timelike lines" (http:/ / www. hpc. unm. edu/ ~alsing/ Courses/ RQI/ articles/ deutsch_prd44_p3197_Y91_qm_closed_timelike_curves. pdf). Physical Review D 44 (10): 3197–3217. Bibcode 1991PhRvD..44.3197D. doi:10.1103/PhysRevD.44.3197. . [13] "The Limits of Quantum Computers" (http:/ / www. scottaaronson. com/ writings/ limitsqc-draft. pdf). Scientific American: 68–69. March 2008. . [14] Aaronson, Scott; John Watrous (2009). "Closed Timelike Curves Make Quantum and Classical Computing Equivalent" (http:/ / www. scottaaronson. com/ papers/ ctc. pdf). Proceedings of the Royal Society A 465 (2102): 631–647. Bibcode 2009RSPSA.465..631A. doi:10.1098/rspa.2008.0350. . [15] Lord of a Visible World: An Autobiography in Letters, edited by S. T. Joshi (2000), p. 328. [16] Science-Fiction: The Gernsback Years by Everett F. Bleiler and Richard Bleiler (1998), p. 36 (http:/ / books. google. com/ books?id=PbMdeizaCNcC& lpg=PP1& pg=PA36#v=onepage& q& f=false) [17] The plot of this story is outlined on p. 206 of Paul J. Nahin's Time Machines: Time Travel in Physics, Metaphysics, and Science Fiction (1993), which also discusses many other early time travel stories, along with discussions of time travel paradoxes. [18] http:/ / theinfosphere. org/ Roswell_that_Ends_Well Novikov self-consistency principle 54 External links • Notion of the Past & Can We Change It? (http://www.iap.fr/eas/EAS18/time18/ontime.html) – speech by Novikov • From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture (http://arxiv.org/ abs/hep-th/9202090), which also addresses the Novikov self-consistency principle • Einstein Physics prevent paradoxical time travel (http://news.bbc.co.uk/2/hi/science/nature/4097258.stm) • Time Travel and Modern Physics (http://plato.stanford.edu/entries/time-travel-phys/) Wormhole In physics, a wormhole is a hypothetical topological feature of spacetime that would be, fundamentally, a "shortcut" through spacetime. For a simple visual explanation of a wormhole, consider spacetime visualized as a two-dimensional (2D) surface. If this surface is folded along a third dimension, it allows one to picture a wormhole "bridge". (Please note, though, that this is merely a visualization displayed to convey an essentially unvisualisable structure existing in 4 or more dimensions. The parts of the wormhole could be higher-dimensional analogues for the parts of the curved 2D surface; for example, instead of mouths which are circular holes in a 2D plane, a real wormhole's mouths could be spheres in 3D space.) A wormhole is, in theory, much like a tunnel with two ends each in separate points in spacetime. Embedded diagram of a Schwarzschild wormhole (see also below) There is no observational evidence for wormholes, but on a theoretical level there are valid solutions to the equations of the theory of general relativity which contain wormholes. Because of its robust theoretical strength, a wormhole is also known as one of the great physics metaphors for teaching general relativity. The first type of wormhole solution discovered was the Schwarzschild wormhole which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that this type of wormhole would collapse too quickly for anything to cross from one end to the other. Wormholes which could actually be crossed, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them. (Many physicists such as Stephen Hawking,[1] Kip Thorne,[2] and others[3][4][5] believe that the Casimir effect is evidence that negative energy densities are possible in nature.) Physicists have not found any natural process which would be predicted to form a wormhole naturally in the context of general relativity, although the quantum foam hypothesis is sometimes used to suggest that tiny wormholes might appear and disappear spontaneously at the Planck scale,[6][7] and stable versions of such wormholes have been suggested as dark matter candidates.[8][9] It has also been proposed that if a tiny wormhole held open by a negative-mass cosmic string had appeared around the time of the Big Bang, it could have been inflated to macroscopic size by cosmic inflation.[10] The American theoretical physicist John Archibald Wheeler coined the term wormhole in 1957; however, in 1921, the German mathematician Hermann Weyl already had proposed the wormhole theory, in connection with mass analysis of electromagnetic field energy.[11] This analysis forces one to consider situations...where there is a net flux of lines of force, through what topologists would call "a handle" of the multiply-connected space, and what physicists might perhaps be excused for more vividly terming a "wormhole". —John Wheeler in Annals of Physics Wormhole 55 Definition The basic notion of an intra-universe wormhole is that it is a compact region of spacetime whose boundary is topologically trivial but whose interior is not simply connected. Formalizing this idea leads to definitions such as the following, taken from Matt Visser's Lorentzian Wormholes. If a Minkowski spacetime contains a compact region Ω, and if the topology of Ω is of the form Ω ~ R x Σ, where Σ is a three-manifold of the nontrivial topology, whose boundary has topology of the form ∂Σ ~ S2, and if, furthermore, the hypersurfaces Σ are all spacelike, then the region Ω contains a quasipermanent intra-universe wormhole. Characterizing inter-universe wormholes is more difficult. For example, one can imagine a 'baby' universe connected to its 'parent' by a narrow 'umbilicus'. One might like to regard the umbilicus as the throat of a wormhole, but the spacetime is simply connected. For this reason wormholes have been defined geometrically, as opposed to topologically, as regions of spacetime that constrain the incremental deformation of closed surfaces. For example, in Enrico Rodrigo’s The Physics of Stargates a wormhole is defined informally as a region of spacetime containing a "world tube" (the time evolution of a closed surface) that cannot be continuously deformed (shrunk) to a world line [(the time evolution of a point)]. Schwarzschild wormholes Lorentzian wormholes known as Schwarzschild wormholes or Einstein-Rosen bridges are connections between areas of space that can be modeled as vacuum solutions to the Einstein field equations, and which are now understood to be intrinsic parts of the maximally extended version of the Schwarzschild metric describing an eternal black hole with no charge and no rotation. Here, "maximally extended" refers to the idea that the spacetime should not have any "edges": for any possible trajectory of a free-falling particle (following a geodesic) in the spacetime, it should be possible to continue this path arbitrarily far into the particle's future or past, unless the trajectory hits a An artist's impression of a wormhole from an observer's perspective, crossing the event horizon gravitational singularity like the one at the center of the black hole's of a Schwarzschild wormhole which bridges two interior. In order to satisfy this requirement, it turns out that in addition different universes. The observer originates from to the black hole interior region which particles enter when they fall the right, and another universe becomes visible in through the event horizon from the outside, there must be a separate the center of the wormhole’s shadow once the horizon is crossed, the observer seeing light that white hole interior region which allows us to extrapolate the has fallen into the black hole interior region from trajectories of particles which an outside observer sees rising up away the other universe; however, this other universe is from the event horizon. And just as there are two separate interior unreachable in the case of a Schwarzschild regions of the maximally extended spacetime, there are also two wormhole, as the bridge always collapses before the observer has time to cross it, and everything separate exterior regions, sometimes called two different "universes", that has fallen through the event horizon of either with the second universe allowing us to extrapolate some possible universe is inevitably crushed in the singularity. particle trajectories in the two interior regions. This means that the interior black hole region can contain a mix of particles that fell in from either universe (and thus an observer who fell in from one universe might be able to see light that fell in from the other one), and likewise particles from the interior white hole region can escape into either universe. All four regions can be seen in a spacetime diagram which uses Kruskal–Szekeres coordinates. In this spacetime, it is possible to come up with coordinate systems such that if you pick a hypersurface of constant time (a set of points that all have the same time coordinate, such that every point on the surface has a space-like separation, giving what is called a 'space-like surface') and draw an "embedding diagram" depicting the curvature of Wormhole space at that time, the embedding diagram will look like a tube connecting the two exterior regions, known as an "Einstein–Rosen bridge". Note that the Schwarzschild metric describes an idealized black hole that exists eternally from the perspective of external observers; a more realistic black hole that forms at some particular time from a collapsing star would require a different metric. When the infalling stellar matter is added to a diagram of a black hole's history, it removes the part of the diagram corresponding to the white hole interior region, along with the part of the diagram corresponding to the other universe.[12] The Einstein–Rosen bridge was discovered by Albert Einstein and his colleague Nathan Rosen, who first published the result in 1935. However, in 1962 John A. Wheeler and Robert W. Fuller published a paper showing that this type of wormhole is unstable, and that it will pinch off too quickly for light (or any particle moving slower than light) that falls in from one exterior region to make it to the other exterior region. Before the stability problems of Schwarzschild wormholes were apparent, it was proposed that quasars were white holes forming the ends of wormholes of this type. While Schwarzschild wormholes are not traversable, their existence inspired Kip Thorne to imagine traversable wormholes created by holding the 'throat' of a Schwarzschild wormhole open with exotic matter (material that has negative mass/energy). 56 Traversable wormholes Lorentzian traversable wormholes would allow travel from one part of the universe to another part of that same universe very quickly or would allow travel from one universe to another. The possibility of traversable wormholes in general relativity was first demonstrated by Kip Thorne and his graduate student Mike Morris in a 1988 paper. For this reason, the type of traversable wormhole they proposed, held open by a spherical shell of exotic matter, is referred to as a Morris-Thorne wormhole. Later, other types of traversable wormholes were discovered as allowable solutions to the equations of general relativity, Image of a traversable wormhole which connects including a variety analyzed in a 1989 paper by Matt Visser, in which a the place in front of the physical institutes of path through the wormhole can be made where the traversing path does Tübingen University with the sand dunes near not pass through a region of exotic matter. However, in the pure Boulogne sur Mer in the north of France. The image is calculated with 4D raytracing in a Gauss–Bonnet gravity (a modification to general relativity involving Morris-Thorne wormhole metric, but the extra spatial dimensions which is sometimes studied in the context of gravitational effects on the wavelength of light [13] brane cosmology) exotic matter is not needed in order for wormholes have not been simulated. to exist—they can exist even with no matter.[14] A type held open by negative mass cosmic strings was put forth by Visser in collaboration with Cramer et al.,[10] in which it was proposed that such wormholes could have been naturally created in the early universe. Wormholes connect two points in spacetime, which means that they would in principle allow travel in time, as well as in space. In 1988, Morris, Thorne and Yurtsever worked out explicitly how to convert a wormhole traversing space into one traversing time.[2] However, according to general relativity it would not be possible to use a wormhole to travel back to a time earlier than when the wormhole was first converted into a time machine by accelerating one of its two mouths.[15] Wormhole 57 Raychaudhuri's theorem and exotic matter To see why exotic matter is required, consider an incoming light front traveling along geodesics, which then crosses the wormhole and re-expands on the other side. The expansion goes from negative to positive. As the wormhole neck is of finite size, we would not expect caustics to develop, at least within the vicinity of the neck. According to the optical Raychaudhuri's theorem, this requires a violation of the averaged null energy condition. Quantum effects such as the Casimir effect cannot violate the averaged null energy condition in any neighborhood of space with zero curvature,[16] but calculations in semiclassical gravity suggest that quantum effects may be able to violate this condition in curved spacetime.[17] Although it was hoped recently that quantum effects could not violate an achronal version of the averaged null energy condition,[18] violations have nevertheless been found,[19] thus eliminating a basis on which traversable wormholes could be rendered unphysical. Faster-than-light travel The impossibility of faster-than-light relative speed only applies locally. Wormholes allow superluminal (faster-than-light) travel by ensuring that the speed of light is not exceeded locally at any time. While traveling through a wormhole, subluminal (slower-than-light) speeds are used. If two points are connected by a wormhole, the time taken to traverse it would be less than the time it would take a light beam to make the journey if it took a path through the space outside the wormhole. However, a light beam traveling through the wormhole would always beat the traveler. As an analogy, running around to the opposite side of a mountain at maximum speed may take longer than walking through a tunnel crossing it. Time travel The theory of general relativity predicts that if traversable wormholes exist, they could allow time travel.[2] This would be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around.[20] This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry. For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2005 while the stationary mouth's clock read 2010. A traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2005, in the same region but now five years in the past. Such a configuration of wormholes would allow for a particle's world line to form a closed loop in spacetime, known as a closed timelike curve. It is thought that it may not be possible to convert a wormhole into a time machine in this manner; the predictions are made in the context of general relativity, but general relativity does not include quantum effects. Some analyses using the semiclassical approach to incorporating quantum effects into general relativity indicate that a feedback loop of virtual particles would circulate through the wormhole with ever-increasing intensity, destroying it before any information could be passed through it, in keeping with the chronology protection conjecture. This has been called into question by the suggestion that radiation would disperse after traveling through the wormhole, therefore preventing infinite accumulation. The debate on this matter is described by Kip S. Thorne in the book Black Holes and Time Warps, and a more technical discussion can be found in The quantum physics of chronology protection by Matt Visser.[21] There is also the Roman ring, which is a configuration of more than one wormhole. This ring seems to allow a closed time loop with stable wormholes when analyzed using semiclassical gravity, although without a full theory of quantum gravity it is uncertain whether the semiclassical approach is reliable in this case. Wormhole 58 Inter-Universe travel A possible resolution to the paradoxes resulting from wormhole-enabled time travel rests on the Many Worlds Interpretation of quantum mechanics. In 1991 David Deutsch showed that quantum theory is fully consistent (in the sense that the so-called density matrix can be made free of discontinuities) in spacetimes with closed timelike curves.[22] However, later it was shown that such model of closed time like curve can have internal inconsistencies as it will lead to strange phenomena like distinguishing non orthogonal quantum states and distinguishing proper and improper mixture.[23][24] Accordingly, the destructive positive feedback loop of virtual particles circulating through a wormhole time machine, a result indicated by semi-classical calculations, is averted. A particle returning from the future does not return to its universe of origination but to a parallel universe. This suggests that a wormhole time machine with an exceedingly short time jump is a theoretical bridge between contemporaneous parallel universes.[25] Because a wormhole time-machine introduces a type of nonlinearity into quantum theory, this sort of communication between parallel universes is consistent with Joseph Polchinski’s discovery of an “Everett phone” in Steven Weinberg’s formulation of nonlinear quantum mechanics.[26] Metrics Theories of wormhole metrics describe the spacetime geometry of a wormhole and serve as theoretical models for time travel. An example of a (traversable) wormhole metric is the following: One type of non-traversable wormhole metric is the Schwarzschild solution (see the first diagram): In fiction Wormholes are a common element in science fiction as they allow interstellar (and sometimes interuniversal) travel within human timescales. Notes [1] "Space and Time Warps" (http:/ / www. hawking. org. uk/ index. php/ lectures/ 63). Hawking.org.uk. . Retrieved 2010-11-11. [2] Morris, Michael; Thorne, Kip; Yurtsever, Ulvi (1988). "Wormholes, Time Machines, and the Weak Energy Condition". Physical Review Letters 61 (13): 1446–1449. Bibcode 1988PhRvL..61.1446M. doi:10.1103/PhysRevLett.61.1446. PMID 10038800. [3] Sopova; Ford (2002). "The Energy Density in the Casimir Effect". Physical Review D 66 (4): 045026. arXiv:quant-ph/0204125. Bibcode 2002PhRvD..66d5026S. doi:10.1103/PhysRevD.66.045026. [4] Ford; Roman (1995). "Averaged Energy Conditions and Quantum Inequalities". Physical Review D 51 (8): 4277–4286. arXiv:gr-qc/9410043. Bibcode 1995PhRvD..51.4277F. doi:10.1103/PhysRevD.51.4277. [5] Olum (1998). "Superluminal travel requires negative energies". Physical Review Letters 81 (17): 3567–3570. arXiv:gr-qc/9805003. Bibcode 1998PhRvL..81.3567O. doi:10.1103/PhysRevLett.81.3567. [6] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. pp. 494–496. ISBN 0-393-31276-3. [7] Ian H., Redmount; Wai-Mo Suen (1994). "Quantum Dynamics of Lorentzian Spacetime Foam". Physical Review D 49 (10): 5199. arXiv:gr-qc/9309017. Bibcode 1994PhRvD..49.5199R. doi:10.1103/PhysRevD.49.5199. [8] Kirillov, A.A.; E.P. Savelova (21 February 2008). "Dark Matter from a gas of wormholes". Physics Letters B 660 (3): 93. arXiv:0707.1081. Bibcode 2008PhLB..660...93K. doi:10.1016/j.physletb.2007.12.034. [9] Rodrigo, Enrico (30 November 2009). "Denouement of a Wormhole-Brane Encounter". International Journal of Modern Physics D 18 (12): 1809. arXiv:0908.2651. Bibcode 2009IJMPD..18.1809R. doi:10.1142/S0218271809015333. [10] John G. Cramer, Robert L. Forward, Michael S. Morris, Matt Visser, Gregory Benford, and Geoffrey A. Landis (1995). "Natural Wormholes as Gravitational Lenses". Physical Review D 51 (6): 3117–3120. arXiv:astro-ph/9409051. Bibcode 1995PhRvD..51.3117C. doi:10.1103/PhysRevD.51.3117. [11] Coleman, Korte, Hermann Weyl's Raum - Zeit - Materie and a General Introduction to His Scientific Work, p. 199 [12] "Collapse to a Black Hole" (http:/ / casa. colorado. edu/ ~ajsh/ collapse. html#kruskal). Casa.colorado.edu. 2010-10-03. . Retrieved 2010-11-11. This is a tertiary source that clearly includes information from other sources but does not name them. Wormhole [13] Other computer-rendered images and animations of traversable wormholes can be seen on this page (http:/ / www. spacetimetravel. org/ wurmlochflug/ wurmlochflug. html) by the creator of the image in the article, and this page (http:/ / www. vis. uni-stuttgart. de/ ~muelleta/ MTvis/ ) has additional renderings. [14] Elias Gravanis; Steven Willison (2007). "`Mass without mass' from thin shells in Gauss-Bonnet gravity". Phys.Rev.D75:084025,2007 75 (8). arXiv:gr-qc/0701152. Bibcode 2007PhRvD..75h4025G. doi:10.1103/PhysRevD.75.084025. [15] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. p. 504. ISBN 0-393-31276-3. [16] Fewster, Christopher J.; Ken D. Olum, Michael J. Pfenning (10 January 2007). "Averaged null energy condition in spacetimes with boundaries". Physical Review D 75 (2): 025007. arXiv:gr-qc/0609007. Bibcode 2007PhRvD..75b5007F. doi:10.1103/PhysRevD.75.025007. [17] Visser, Matt (15 October 1996). "Gravitational vacuum polarization. II. Energy conditions in the Boulware vacuum". Physical Review D 54 (8): 5116. arXiv:gr-qc/9604008. Bibcode 1996PhRvD..54.5116V. doi:10.1103/PhysRevD.54.5116. [18] Graham, Noah; Ken D. Olum (4 September 2007). "Achronal averaged null energy condition". Physical Review D 76 (6): 064001. arXiv:0705.3193. Bibcode 2007PhRvD..76f4001G. doi:10.1103/PhysRevD.76.064001. [19] Urban, Douglas; Ken D. Olum (1 June 2010). "Spacetime averaged null energy condition". Physical Review D 81 (6): 124004. arXiv:1002.4689. Bibcode 2010PhRvD..81l4004U. doi:10.1103/PhysRevD.81.124004. [20] Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton. p. 502. ISBN 0-393-31276-3. [21] The quantum physics of chronology protection (http:/ / arxiv. org/ abs/ gr-qc/ 0204022) [22] Deutsch, David (1991). "Quantum Mechanics Near Closed Timelike Lines". Physical Review D 44 (10): 3197. Bibcode 1991PhRvD..44.3197D. doi:10.1103/PhysRevD.44.3197. [23] Brun et.al (2009). "Localized Closed Timelike Curves Can Perfectly Distinguish Quantum States". Physics Review Letters 102 (21): 210402. Bibcode 2009PhRvL..102.210402. doi:10.1103/PhysRevLett.102.210402. [24] Pati, Chakrabarty, Agrawal (2011). "Purification of mixed states with closed timelike curve is not possible". Physical Review A 84 (6): 062325. Bibcode 2011PhRvA..84f2325P. doi:10.1103/PhysRevA.84.062325. [25] Rodrigo, Enrico (2010). The Physics of Stargates. Eridanus Press. p. 281. ISBN 0-9841500-0-5. [26] Polchinski, Joseph (1991). "Weinberg’s Nonlinear quantum Mechanics and the Einstein-Podolsky-Rosen Paradox". Physical Review Letters 66 (4): 397. Bibcode 1991PhRvL..66..397P. doi:10.1103/PhysRevLett.66.397. 59 References • DeBenedictis, Andrew and Das, A. (2001). "On a General Class of Wormhole Geometries". Classical and Quantum Gravity 18 (7): 1187–1204. arXiv:gr-qc/0009072. Bibcode 2001CQGra..18.1187D. doi:10.1088/0264-9381/18/7/304. • Dzhunushaliev, Vladimir (2002). "Strings in the Einstein's paradigm of matter". Classical and Quantum Gravity 19 (19): 4817–4824. arXiv:gr-qc/0205055. Bibcode 2002CQGra..19.4817D. doi:10.1088/0264-9381/19/19/302. • Einstein, Albert and Rosen, Nathan (1935). "The Particle Problem in the General Theory of Relativity". Physical Review 48: 73. Bibcode 1935PhRv...48...73E. doi:10.1103/PhysRev.48.73. • Fuller, Robert W. and Wheeler, John A. (1962). "Causality and Multiply-Connected Space-Time". Physical Review 128: 919. Bibcode 1962PhRv..128..919F. doi:10.1103/PhysRev.128.919. • Garattini, Remo (2004). "How Spacetime Foam modifies the brick wall". Modern Physics Letters A 19 (36): 2673–2682. arXiv:gr-qc/0409015. Bibcode 2004gr.qc.....9015G. doi:10.1142/S0217732304015658. • González-Díaz, Pedro F. (1998). "Quantum time machine". Physical Review D 58 (12): 124011. arXiv:gr-qc/9712033. Bibcode 1998PhRvD..58l4011G. doi:10.1103/PhysRevD.58.124011. • González-Díaz, Pedro F. (1996). "Ringholes and closed timelike curves". Physical Review D 54 (10): 6122–6131. arXiv:gr-qc/9608059. Bibcode 1996PhRvD..54.6122G. doi:10.1103/PhysRevD.54.6122. • Khatsymosky, Vladimir M. (1997). "Towards possibility of self-maintained vacuum traversable wormhole". Physics Letters B 399 (3–4): 215–222. arXiv:gr-qc/9612013. Bibcode 1997PhLB..399..215K. doi:10.1016/S0370-2693(97)00290-6. • Krasnikov, Serguei (2006). "Counter example to a quantum inequality". Gravity and Cosmology 46: 195. arXiv:gr-qc/0409007. Bibcode 2006GrCo...12..195K. • Krasnikov, Serguei (2003). "The quantum inequalities do not forbid spacetime shortcuts". Physical Review D 67 (10): 104013. arXiv:gr-qc/0207057. Bibcode 2003PhRvD..67j4013K. doi:10.1103/PhysRevD.67.104013. • Li, Li-Xin (2001). "Two Open Universes Connected by a Wormhole: Exact Solutions". Journal of Geometrical Physics 40 (2): 154–160. arXiv:hep-th/0102143. Bibcode 2001JGP....40..154L. doi:10.1016/S0393-0440(01)00028-6. Wormhole • Morris, Michael S., Thorne, Kip S., and Yurtsever, Ulvi (1988). "Wormholes, Time Machines, and the Weak Energy Condition". Physical Review Letters 61 (13): 1446. Bibcode 1988PhRvL..61.1446M. doi:10.1103/PhysRevLett.61.1446. PMID 10038800. • Morris, Michael S. and Thorne, Kip S. (1988). "Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity". American Journal of Physics 56 (5): 395–412. Bibcode 1988AmJPh..56..395M. doi:10.1119/1.15620. • Nandi, Kamal K. and Zhang, Yuan-Zhong (2006). "A Quantum Constraint for the Physical Viability of Classical Traversable Lorentzian Wormholes". Journal of Nonlinear Phenomena in Complex Systems 9: 61–67. arXiv:gr-qc/0409053. Bibcode 2004gr.qc.....9053N. • Ori, Amos (2005). "A new time-machine model with compact vacuum core". Physical Review Letters 95 (2). arXiv:gr-qc/0503077. Bibcode 2005PhRvL..95b1101O. doi:10.1103/PhysRevLett.95.021101. • Poplawski, Nikodem J. (2010). "Radial motion into an Einstein-Rosen bridge". Physics Letters B 687: 110. Bibcode 2010PhLB..687..110P. doi:10.1016/j.physletb.2010.03.029. • Roman, Thomas, A. (2004). "Some Thoughts on Energy Conditions and Wormholes". arXiv:gr-qc/0409090 [gr-qc]. • Teo, Edward (1998). "Rotating traversable wormholes". Physical Review D 58 (2). arXiv:gr-qc/9803098. Bibcode 1998PhRvD..58b4014T. doi:10.1103/PhysRevD.58.024014. • Visser, Matt (2002). "The quantum physics of chronology protection by Matt Visser". arXiv:gr-qc/0204022 [gr-qc]. An excellent and more concise review. • Visser, Matt (1989). "Traversable wormholes: Some simple examples". Physical Review D 39 (10): 3182–3184. Bibcode 1989PhRvD..39.3182V. doi:10.1103/PhysRevD.39.3182. 60 External links • White Holes and Wormholes (http://casa.colorado.edu/~ajsh/schww.html) External links • What exactly is a 'wormhole'? (http://www.scientificamerican.com/article.cfm?id=follow-up-what-exactly-is) answered by Richard F. Holman, William A. Hiscock and Matt Visser. • Why wormholes? (http://www.mcs.vuw.ac.nz/~visser/general.shtml#why-wormholes) by Matt Visser. • Wormholes in General Relativity (http://www.bun.kyoto-u.ac.jp/~suchii/wormholes.html) by Soshichi Uchii. • White holes and Wormholes (http://casa.colorado.edu/~ajsh/schww.html) provides a very good description of Schwarzschild wormholes with graphics and animations, by Andrew J. S. Hamilton. • Questions and Answers about Wormholes (http://www.webfilesuci.org/WormholeFAQ.html) a comprehensive wormhole FAQ by Enrico Rodrigo. • Large Hadron Collider (http://www.independent.co.uk/news/science/ the-big-question-is-time-travel-possible-and-is-there-any-chance-that-it-will-ever-take-place-779761.html) – Theory on how the collider could create a small wormhole, possibly allowing time travel into the past. • animation that simulates traversing a wormhole (http://www.spacetimetravel.org/wurmlochflug/ wurmlochflug.html) • renderings and animations of a Morris-Thorne wormhole (http://www.vis.uni-stuttgart.de/~muelleta/MTvis/) • N.A.S.A's current theory on wormhole creation (http://www.nasa.gov/centers/glenn/technology/warp/ ideachev.html) Faster-than-light 61 Faster-than-light Faster-than-light (also superluminal or FTL) communications and travel refer to the propagation of information or matter faster than the speed of light. Under the special theory of relativity, a particle (that has rest mass) with subluminal velocity needs infinite energy to accelerate to the speed of light, although special relativity does not forbid the existence of particles that travel faster than light at all times (tachyons). On the other hand, what some physicists refer to as "apparent" or "effective" FTL[1][2][3][4] depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal or undistorted spacetime. Although according to current theories matter is still required to travel subluminally with respect to the locally distorted spacetime region, apparent FTL is not excluded by general relativity. Examples of FTL proposals are changing the "frequency" of mass to a higher state by applying high-frequency waves of energy, the Alcubierre drive, and the traversable wormhole, although the physical plausibility of some of these solutions is uncertain. FTL travel of non-information In the context of this article, FTL is the transmission of information or matter faster than c, a constant equal to the speed of light in a vacuum, which is 299,792,458 meters per second (by definition) or about 186,282.4 miles per second. This is not quite the same as traveling faster than light, since: • Some processes propagate faster than c, but cannot carry information (see examples in the sections immediately following). • Light travels at speed c/n when not in a vacuum but travelling through a medium with refractive index = n (causing refraction), and in some materials other particles can travel faster than c/n (but still slower than c), leading to Cherenkov radiation (see phase velocity below). Neither of these phenomena violates special relativity or creates problems with causality, and thus neither qualifies as FTL as described here. In the following examples, certain influences may appear to travel faster than light, but they do not convey energy or information faster than light, so they do not violate special relativity. Daily sky motion For an earthbound observer, objects in the sky complete one revolution around the Earth in 1 day. Proxima Centauri, which is the nearest star outside the solar system, is about 4 light-years away.[5] On a geostationary view Alpha Centauri has a speed many times greater than c as the rim speed of an object moving in a circle is a product of the radius and angular speed.[5] It is also possible on a geostatic view for objects such as comets to vary their speed from subluminal to superluminal and vice versa simply because the distance from the Earth varies. Comets may have orbits which take them out to more than 1000 AU.[6] The circumference of a circle with a radius of 1000 AU is greater than one light day. In other words, a comet at such a distance is superluminal in a geostatic frame. This is not a problem simply because a geostatic frame is clearly not an inertial rest frame. Faster-than-light 62 Light spots and shadows If a laser is swept across a distant object, the spot of laser light can easily be made to move across the object at a speed greater than c.[7] Similarly, a shadow projected onto a distant object can be made to move across the object faster than c.[8] In neither case does the light travel from the source to the object faster than c, nor does any information travel faster than light.[7][8][9][10] Apparent FTL propagation of static field effects Since there is no "retardation" (or aberration) of the apparent position of the source of a gravitational or electric static field when the source moves with constant velocity, the static field "effect" may seem at first glance to be "transmitted" faster than the speed of light. However, uniform motion of the static source may be removed with a change in reference frame, causing the direction of the static field to change immediately, at all distances. This is not a change of position which "propagates", and thus this change cannot be used to transmit information from the source. No information or matter can be FTL-transmitted or propagated from source to receiver/observer by an electromagnetic field. Closing speeds The rate at which two objects in motion in a single frame of reference get closer together is called the mutual or closing speed. This may approach twice the speed of light, as in the case of two particles travelling at close to the speed of light in opposite directions with respect to the reference frame. Imagine two fast-moving particles approaching each other from opposite sides of a particle accelerator of the collider type. The closing speed would be the rate at which the distance between the two particles is decreasing. From the point of view of an observer standing at rest relative to the accelerator, this rate will be slightly less than twice the speed of light. Special relativity does not prohibit this. It tells us that it is wrong to use Galilean relativity to compute the velocity of one of the particles, as would be measured by an observer traveling alongside the other particle. That is, special relativity gives the right formula for computing such relative velocity. It is instructive to compute the relative velocity of particles moving at v and -v in accelerator frame, which corresponds to the closing speed of 2v > c. Expressing the speeds in units of c, β = v/c: Proper speeds If a spaceship travels to a planet one light-year (as measured in the Earth's rest frame) away from Earth at high speed, the time taken to reach that planet could be less than one year as measured by the traveller's clock (although it will always be more than one year as measured by a clock on Earth). The value obtained by dividing the distance traveled, as determined in the Earth's frame, by the time taken, measured by the traveller's clock, is known as a proper speed or a proper velocity. There is no limit on the value of a proper speed as a proper speed does not represent a speed measured in a single inertial frame. A light signal that left the Earth at the same time as the traveller would always get to the destination before the traveller. Faster-than-light 63 How far can one travel from the Earth? Since one might not travel faster than light, one might conclude that a human can never travel further from the earth than 40 light-years if the traveler is active between the age of 20 and 60. A traveler would then never be able to reach more than the very few star systems which exist within the limit of 20-40 light-years from the Earth. This is a mistaken conclusion; due to time dilation, the traveler can travel thousands of light-years during his 40 active years. If the spaceship accelerates at a constant 1 g (in its own changing frame of reference), it will, after 354 days, reach speeds a little under the speed of light (for an observer on Earth), and time dilation will increase his lifespan to thousands of Earth years, seen from the reference system of the Solar System, but the traveler's subjective lifespan will not thereby change. If the traveler returns to the Earth, he will land thousands of years into the future. His speed will not be seen as higher than the speed of light by observers on Earth, and the traveler will not measure their speed as being higher than the speed of light, but will see a length contraction of the universe in his direction of travel. And as the traveler turns around to return, the Earth will seem to experience much more time than the traveler does. So, although his (ordinary) speed cannot exceed c, the four-velocity (distance as seen by Earth divided by his proper (i.e. subjective) time) can be much greater than c. This is seen in statistical studies of muons traveling much further than c times their half-life (at rest), if traveling close to c.[11] Phase velocities above c The phase velocity of an electromagnetic wave, when traveling through a medium, can routinely exceed c, the vacuum velocity of light. For example, this occurs in most glasses at X-ray frequencies.[12] However, the phase velocity of a wave corresponds to the propagation speed of a theoretical single-frequency (purely monochromatic) component of the wave at that frequency. Such a wave component must be infinite in extent and of constant amplitude (otherwise it is not truly monochromatic), and so cannot convey any information.[13] Thus a phase velocity above c does not imply the propagation of signals with a velocity above c.[14] Group velocities above c The group velocity of a wave (e.g. a light beam) may also exceed c in some circumstances. In such cases, which typically at the same time involve rapid attenuation of the intensity, the maximum of the envelope of a pulse may travel with a velocity above c. However, even this situation does not imply the propagation of signals with a velocity above c,[15] even though one may be tempted to associate pulse maxima with signals. The latter association has been shown to be misleading, basically because the information on the arrival of a pulse can be obtained before the pulse maximum arrives. For example, if some mechanism allows the full transmission of the leading part of a pulse while strongly attenuating the pulse maximum and everything behind (distortion), the pulse maximum is effectively shifted forward in time, while the information on the pulse does not come faster than c without this effect.[16] Universal expansion The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies. However, in general relativity, velocity is a local notion, so velocity calculated using comoving coordinates does not have any simple relation to velocity calculated locally[17] (see comoving distance for a discussion of different notions of 'velocity' in cosmology). Rules that apply to relative velocities in special relativity, such as the rule that relative velocities cannot increase past the speed of light, do not apply to relative velocities in comoving coordinates, which are often described in terms of the "expansion of space" between galaxies. This expansion rate is thought to have been at its peak during the inflationary epoch thought to have occurred in a tiny fraction of the second after the Big Bang (models suggest the period would have been from around 10−36 seconds after the Big Bang to around 10−33 seconds), when the universe may have rapidly expanded by a factor of around 1020 to 1030.[18] Faster-than-light There are many galaxies visible in telescopes with red shift numbers of 1.4 or higher. All of these are currently traveling away from us at speeds greater than the speed of light. Because the Hubble parameter is decreasing with time, there can actually be cases where a galaxy that is receding from us faster than light does manage to emit a signal which reaches us eventually.[19][20] However, because the expansion of the universe is accelerating, it is projected that most galaxies will eventually cross a type of cosmological event horizon where any light they emit past that point will never be able to reach us at any time in the infinite future,[21] because the light never reaches a point where its "peculiar velocity" towards us exceeds the expansion velocity away from us (these two notions of velocity are also discussed in Comoving distance#Uses of the proper distance). The current distance to this cosmological event horizon is about 16 billion light-years, meaning that a signal from an event happening at present would eventually be able to reach us in the future if the event was less than 16 billion light-years away, but the signal would never reach us if the event was more than 16 billion light-years away.[20] 64 Astronomical observations Apparent superluminal motion is observed in many radio galaxies, blazars, quasars and recently also in microquasars. The effect was predicted before it was observed by Martin Rees and can be explained as an optical illusion caused by the object partly moving in the direction of the observer,[22] when the speed calculations assume it does not. The phenomenon does not contradict the theory of special relativity. Interestingly, corrected calculations show these objects have velocities close to the speed of light (relative to our reference frame). They are the first examples of large amounts of mass moving at close to the speed of light.[23] Earth-bound laboratories have only been able to accelerate small numbers of elementary particles to such speeds. Quantum mechanics Certain phenomena in quantum mechanics, such as quantum entanglement, appear to transmit information faster than light. According to the no-communication theorem these phenomena do not allow true communication; they only let two observers in different locations see the same event simultaneously, without any way of controlling what either sees. Wavefunction collapse can be viewed as an epiphenomenon of quantum decoherence, which in turn is nothing more than an effect of the underlying local time evolution of the wavefunction of a system and all of its environment. Since the underlying behaviour doesn't violate local causality or allow FTL it follows that neither does the additional effect of wavefunction collapse, whether real or apparent. The uncertainty principle implies that individual photons may travel for short distances at speeds somewhat faster (or slower) than c, even in a vacuum; this possibility must be taken into account when enumerating Feynman diagrams for a particle interaction.[24] It has since been proven that not even a single photon may travel faster than "c".[25] In quantum mechanics, virtual particles may travel faster than light, and this phenomenon is related to the fact that static field effects (which are mediated by virtual particles in quantum terms) may travel faster than light (see section on static fields above). However, macroscopically these fluctuations average out, so that photons do travel in straight lines over long (i.e., non-quantum) distances, and they do travel at the speed of light on average. Therefore, this does not imply the possibility of superluminal information transmission. There have been various reports in the popular press of experiments on faster-than-light transmission in optics—most often in the context of a kind of quantum tunnelling phenomenon. Usually, such reports deal with a phase velocity or group velocity faster than the vacuum velocity of light. However, as stated above, a superluminal phase velocity cannot be used for faster-than-light transmission of information. There has sometimes been confusion concerning the latter point. Additionally a channel that permits such propagation cannot be laid out faster than the speed of light. Quantum teleportation transmits quantum information at whatever speed is used to transmit the same amount of classical information, likely the speed of light. This quantum information may theoretically be used in ways that classical information can not, such as in quantum computations involving quantum information only available to the Faster-than-light recipient. Hartman effect The Hartman effect is the tunnelling effect through a barrier where the tunnelling time tends to a constant for large barriers.[26] This was first described by Thomas Hartman in 1962.[27] This could, for instance, be the gap between two prisms. When the prisms are in contact, the light passes straight through, but when there is a gap, the light is refracted. There is a nonzero probability that the photon will tunnel across the gap rather than follow the refracted path. For large gaps between the prisms the tunnelling time approaches a constant and thus the photons appear to have crossed with a superluminal speed.[28] However, an analysis by Herbert G. Winful from the University of Michigan suggests that the Hartman effect cannot actually be used to violate relativity by transmitting signals faster than c, because the tunnelling time "should not be linked to a velocity since evanescent waves do not propagate".[29] The evanescent waves in the Hartman effect are due to virtual particles and a non-propagating static field, as mentioned in the sections above for gravity and electromagnetism. Casimir effect In physics, the Casimir effect or Casimir-Polder force is a physical force exerted between separate objects due to resonance of vacuum energy in the intervening space between the objects. This is sometimes described in terms of virtual particles interacting with the objects, due to the mathematical form of one possible way of calculating the strength of the effect. Because the strength of the force falls off rapidly with distance, it is only measurable when the distance between the objects is extremely small. Because the effect is due to virtual particles mediating a static field effect, it is subject to the comments about static fields discussed above. EPR Paradox The EPR paradox refers to a famous thought experiment of Einstein, Podolski and Rosen that was realized experimentally for the first time by Alain Aspect in 1981 and 1982 in the Aspect experiment. In this experiment, the measurement of the state of one of the quantum systems of an entangled pair apparently instantaneously forces the other system (which may be distant) to be measured in the complementary state. However, no information can be transmitted this way; the answer to whether or not the measurement actually affects the other quantum system comes down to which interpretation of quantum mechanics one subscribes to. An experiment performed in 1997 by Nicolas Gisin at the University of Geneva has demonstrated non-local quantum correlations between particles separated by over 10 kilometers.[30] But as noted earlier, the non-local correlations seen in entanglement cannot actually be used to transmit classical information faster than light, so that relativistic causality is preserved; see no-communication theorem for further information. A 2008 quantum physics experiment also performed by Nicolas Gisin and his colleagues in Geneva, Switzerland has determined that in any hypothetical non-local hidden-variables theory the speed of the quantum non-local connection (what Einstein called spooky action at a distance) is at least 10,000 times the speed of light.[31] Delayed choice quantum eraser Delayed choice quantum eraser (an experiment of Marlan Scully) is a version of the EPR paradox in which the observation or not of interference after the passage of a photon through a double slit experiment depends on the conditions of observation of a second photon entangled with the first. The characteristic of this experiment is that the observation of the second photon can take place at a later time than the observation of the first photon,[32] which may give the impression that the measurement of the later photons "retroactively" determines whether the earlier photons show interference or not, although the interference pattern can only be seen by correlating the measurements of both members of every pair and so it can't be observed until both photons have been measured, ensuring that an experimenter watching only the photons going through the slit does not obtain information about the other photons in 65 Faster-than-light an FTL or backwards-in-time manner. 66 FTL communication possibility Faster-than-light communication is, by Einstein's theory of relativity, equivalent to time travel. According to Einstein's theory of special relativity, what we measure as the speed of light in a vacuum is actually the fundamental physical constant c. This means that all inertial observers, regardless of their relative velocity, will always measure zero-mass particles such as photons traveling at c in a vacuum. This result means that measurements of time and velocity in different frames are no longer related simply by constant shifts, but are instead related by Poincaré transformations. These transformations have important implications: • The relativistic momentum of a massive particle would increase with speed in such a way that at the speed of light an object would have infinite momentum. • To accelerate an object of non-zero rest mass to c would require infinite time with any finite acceleration, or infinite acceleration for a finite amount of time. • Either way, such acceleration requires infinite energy. • Some observers with sub-light relative motion will disagree about which occurs first of any two events that are separated by a space-like interval.[33] In other words, any travel that is faster-than-light will be seen as traveling backwards in time in some other, equally valid, frames of reference, or need to assume the speculative hypothesis of possible Lorentz violations at a presently unobserved scale (for instance the Planck scale). Therefore any theory which permits "true" FTL also has to cope with time travel and all its associated paradoxes,[34] or else to assume the Lorentz invariance to be a symmetry of thermodynamical statistical nature (hence a symmetry broken at some presently unobserved scale). • In special relativity the coordinate speed of light is only guaranteed to be c in an inertial frame, in a non-inertial frame the coordinate speed may be different than c;[35] in general relativity no coordinate system on a large region of curved spacetime is "inertial", so it's permissible to use a global coordinate system where objects travel faster than c, but in the local neighborhood of any point in curved spacetime we can define a "local inertial frame" and the local speed of light will be c in this frame,[36] with massive objects moving through this local neighborhood always having a speed less than c in the local inertial frame. Justifications Faster light (Casimir vacuum and quantum tunnelling) Raymond Y. Chiao was first to measure the quantum tunnelling time, which was found to be between 1.5 to 1.7 times the speed of light. Einstein's equations of special relativity postulate that the speed of light in a vacuum is invariant in inertial frames. That is, it will be the same from any frame of reference moving at a constant speed. The equations do not specify any particular value for the speed of the light, which is an experimentally determined quantity for a fixed unit of length. Since 1983, the SI unit of length (the meter) has been defined using the speed of light. The experimental determination has been made in vacuum. However, the vacuum we know is not the only possible vacuum which can exist. The vacuum has energy associated with it, unsurprisingly called the vacuum energy. This vacuum energy can perhaps be changed in certain cases.[37] When vacuum energy is lowered, light itself has been predicted to go faster than the standard value c. This is known as the Scharnhorst effect. Such a vacuum can be produced by bringing two perfectly smooth metal plates together at near atomic diameter spacing. It is called a Casimir vacuum. Calculations imply that light will go faster in such a vacuum by a minuscule amount: a photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 1036.[38] Accordingly there has as yet been no experimental verification of the prediction. A recent analysis[39] argued that the Scharnhorst effect cannot be used to send information backwards in time with a single set of plates Faster-than-light since the plates' rest frame would define a "preferred frame" for FTL signalling. However, with multiple pairs of plates in motion relative to one another the authors noted that they had no arguments that could "guarantee the total absence of causality violations", and invoked Hawking's speculative chronology protection conjecture which suggests that feedback loops of virtual particles would create "uncontrollable singularities in the renormalized quantum stress-energy" on the boundary of any potential time machine, and thus would require a theory of quantum gravity to fully analyze. Other authors argue that Scharnhorst's original analysis which seemed to show the possibility of faster-than-c signals involved approximations which may be incorrect, so that it is not clear whether this effect could actually increase signal speed at all.[40] The physicists Günter Nimtz and Alfons Stahlhofen, of the University of Cologne, claim to have violated relativity experimentally by transmitting photons faster than the speed of light.[28] They say they have conducted an experiment in which microwave photons—relatively low energy packets of light—travelled "instantaneously" between a pair of prisms that had been moved up to 3 ft (unknown operator: u'strong' m) apart. Their experiment involved an optical phenomenon known as "evanescent modes", and they claim that since evanescent modes have an imaginary wave number, they represent a "mathematical analogy" to quantum tunnelling.[28] Nimtz has also claimed that "evanescent modes are not fully describable by the Maxwell equations and quantum mechanics have to be taken into consideration."[41] Other scientists such as Herbert G. Winful and Robert Helling have argued that in fact there is nothing quantum-mechanical about Nimtz's experiments, and that the results can be fully predicted by the equations of classical electromagnetism (Maxwell's equations).[42][43] Nimtz told New Scientist magazine: "For the time being, this is the only violation of special relativity that I know of." However, other physicists say that this phenomenon does not allow information to be transmitted faster than light. Aephraim Steinberg, a quantum optics expert at the University of Toronto, Canada, uses the analogy of a train traveling from Chicago to New York, but dropping off train cars at each station along the way, so that the center of the ever shrinking main train moves forward at each stop; in this way, the speed of the center of the train exceeds the speed of any of the individual cars.[44] Herbert G. Winful argues that the train analogy is a variant of the "reshaping argument" for superluminal tunneling velocities, but he goes on to say that this argument is not actually supported by experiment or simulations, which actually show that the transmitted pulse has the same length and shape as the incident pulse.[42] Instead, Winful argues that the group delay in tunneling is not actually the transit time for the pulse (whose spatial length must be greater than the barrier length in order for its spectrum to be narrow enough to allow tunneling), but is instead the lifetime of the energy stored in a standing wave which forms inside the barrier. Since the stored energy in the barrier is less than the energy stored in a barrier-free region of the same length due to destructive interference, the group delay for the energy to escape the barrier region is shorter than it would be in free space, which according to Winful is the explanation for apparently superluminal tunneling.[45][46] A number of authors have published papers disputing Nimtz's claim that Einstein causality is violated by his experiments, and there are many other papers in the literature discussing why quantum tunneling is not thought to violate causality.[47] It was later claimed by the Keller group in Switzerland that particle tunneling does indeed occur in zero real time. Their tests involved tunneling electrons, where the group argued a relativistic prediction for tunneling time should be 500-600 attoseconds (an attosecond is one quintillionth (10−18) of a second). All that could be measured was 24 attoseconds, which is the limit of the test accuracy.[48] Again, though, other physicists believe that tunneling experiments in which particles appear to spend anomalously short times inside the barrier are in fact fully compatible with relativity, although there is disagreement about whether the explanation involves reshaping of the wave packet or other effects.[45][46][49] 67 Faster-than-light 68 Give up causality Another approach is to accept special relativity, but to posit that mechanisms allowed by general relativity (e.g., wormholes) will allow traveling between two points without going through the intervening space. While this gets around the infinite acceleration problem, it still would lead to closed timelike curves (i.e., time travel) and causality violations. Causality is not required by special or general relativity, but is nonetheless generally considered a basic property of the universe that cannot be sensibly dispensed with. Because of this, most physicists expect that quantum gravity effects will preclude this option. An alternative is to conjecture that, while time travel is possible, it never leads to paradoxes; this is the Novikov self-consistency principle. Give up (absolute) relativity Because of the strong empirical support for special relativity, any modifications to it must necessarily be quite subtle and difficult to measure. The best-known attempt is doubly special relativity, which posits that the Planck length is also the same in all reference frames, and is associated with the work of Giovanni Amelino-Camelia and João Magueijo. One consequence of this theory is a variable speed of light, where photon speed would vary with energy, and some zero-mass particles might possibly travel faster than c. However, even if this theory is accurate, it is still very unclear whether it would allow information to be communicated, and appears not in any case to allow massive particles to exceed c. There are speculative theories that claim inertia is produced by the combined mass of the universe (e.g., Mach's principle), which implies that the rest frame of the universe might be preferred by conventional measurements of natural law. If confirmed, this would imply special relativity is an approximation to a more general theory, but since the relevant comparison would (by definition) be outside the observable universe, it is difficult to imagine (much less construct) experiments to test this hypothesis. Space-time distortion Although the theory of special relativity forbids objects to have a relative velocity greater than light speed, and general relativity reduces to special relativity in a local sense (in small regions of spacetime where curvature is negligible), general relativity does allow the space between distant objects to expand in such a way that they have a "recession velocity" which exceeds the speed of light, and it is thought that galaxies which are at a distance of more than about 14 billion light-years from us today have a recession velocity which is faster than light.[50] Miguel Alcubierre theorized [51] that it would be possible to create an Alcubierre drive, in which a ship would be enclosed in a "warp bubble" where the space at the front of the bubble is rapidly contracting and the space at the back is rapidly expanding, with the result that the bubble can reach a distant destination much faster than a light beam moving outside the bubble, but without objects inside the bubble locally traveling faster than light. However, several objections raised against the Alcubierre drive appear to rule out the possibility of actually using it in any practical fashion. Another possibility predicted by general relativity is the traversable wormhole, which could create a shortcut between arbitrarily distant points in space. As with the Alcubierre drive, travelers moving through the wormhole would not locally move faster than light which travels through the wormhole alongside them, but they would be able to reach their destination (and return to their starting location) faster than light traveling outside the wormhole. Dr. Gerald Cleaver, associate professor of physics at Baylor University, and Richard Obousy, a Baylor graduate student, theorize that by manipulating the extra spatial dimensions of string theory around a spaceship with an extremely large amount of energy, it would create a "bubble" that could cause the ship to travel faster than the speed of light. To create this bubble, the physicists believe manipulating the 10th spatial dimension would alter the dark energy in three large spatial dimensions: height, width and length. Cleaver said positive dark energy is currently responsible for speeding up the expansion rate of our universe as time moves on.[52] Faster-than-light 69 Heim theory In 1977, a paper on Heim theory theorized that it may be possible to travel faster than light by using magnetic fields to enter a higher-dimensional space.[53] MiHsC/Quantised inertia A new theory has been proposed that Modifies inertia by assuming it is due to Unruh radiation subject to a Hubble scale Casimir effect (MiHsC, or quantised inertia). MiHsC predicts a minimum possible acceleration[54] even at light speed, implying that this speed can be exceeded. Lorentz symmetry violation The possibility that Lorentz symmetry may be violated has been seriously considered in the last two decades, particularly after the development of a realistic effective field theory that describes this possible violation, the so-called Standard-Model Extension.[55][56][57] This general framework has allowed experimental searches by ultra-high energy cosmic-ray experiments[58] and a wide variety of experiments in gravity, electrons, protons, neutrons, neutrinos, mesons, and photons.[59] The breaking of rotation and boost invariance causes direction dependence in the theory as well as unconventional energy dependence that introduces novel effects, including Lorentz-violating neutrino oscillations and modifications to the dispersion relations of different particle species, which naturally could make particles move faster than light. In some models of broken Lorentz symmetry, it is postulated that the symmetry is still built into the most fundamental laws of physics, but that spontaneous symmetry breaking of Lorentz invariance[60] shortly after the Big Bang could have left a "relic field" throughout the universe which causes particles to behave differently depending on their velocity relative to the field;[61] however, there are also some models where Lorentz symmetry is broken in a more fundamental way. If Lorentz symmetry can cease to be a fundamental symmetry at Planck scale or at some other fundamental scale, it is conceivable that particles with a critical speed different from the speed of light be the ultimate constituents of matter. In current models of Lorentz symmetry violation, the phenomenological parameters are expected to be energy-dependent. Therefore, as widely recognized,[62][63] existing low-energy bounds cannot be applied to high-energy phenomena; however, many searches for Lorentz violation at high energies have been carried out using the Standard-Model Extension.[59] Lorentz symmetry violation is expected to become stronger as one gets closer to the fundamental scale. Another recent theory (see EPR paradox above) resulting from the analysis of an EPR communication set up, has the simple device based on removing the effective retarded time terms in the Lorentz transform to yield a preferred absolute reference frame. This frame cannot be used to do physics (i.e. compute the influence of light-speed limited signals) but it provides an objective, absolute frame all could agree upon, if superluminal communication is possible. If this sounds indulgent, it allows simultaneity, absolute space and time and a deterministic universe (along with decoherence theory) whilst the status-quo permits time travel/causality paradoxes, subjectivity in the measurement process and multiple universes. Superfluid theories of physical vacuum In this approach the physical vacuum is viewed as the quantum superfluid which is essentially non-relativistic whereas the Lorentz symmetry is not an exact symmetry of nature but rather the approximate description valid only for the small fluctuations of the superfluid background.[64] Within the framework of the approach a theory was proposed in which the physical vacuum is conjectured to be the quantum Bose liquid whose ground-state wavefunction is described by the logarithmic Schrödinger equation. It was shown that the relativistic gravitational interaction arises as the small-amplitude collective excitation mode[65] whereas relativistic elementary particles can be described by the particle-like modes in the limit of low momenta.[66] The important fact is that at very high Faster-than-light velocities the behavior of the particle-like modes becomes distinct from the relativistic one - they can reach the speed of light limit at finite energy; also the faster-than-light propagation is possible without requiring moving objects to have imaginary mass.[67][68] 70 Time of flight of neutrinos MINOS experiment In 2007 MINOS collaboration reported results measuring the flight-time of 3 GeV neutrinos yielding a speed exceeding that of light by 1.8-sigma significance.[69] However, those measurements were considered to be statistically consistent with neutrinos traveling at the speed of light.[70] Currently the detectors for the project are being upgraded, and new results are not expected until at least 2012. OPERA neutrino anomaly On September 22, 2011, a paper[71] from the OPERA Collaboration indicated detection of 17 and 28 GeV muon neutrinos, sent 730 kilometers (454 miles) from CERN near Geneva, Switzerland to the Gran Sasso National Laboratory in Italy, traveling faster than light by a factor of 2.48×10−5 (approximately 1 in 40,000), a statistic with 6.0-sigma significance.[72] On 18 November 2011, a second followup experiment by OPERA scientists confirmed their initial results.[73][74] However, scientists are sceptical about the results of these experiments,[75] which are currently disputed.[76] In March 2012, the ICARUS collaboration failed to reproduce the OPERA results with their equipment, detecting neutrino travel time from CERN to the Gran Sasso National Laboratory indistinguishable from the speed of light.[77] Tachyons In special relativity, it is impossible to accelerate an object to the speed of light, or for a massive object to move at the speed of light. However, it might be possible for an object to exist which always moves faster than light. The hypothetical elementary particles with this property are called tachyonic particles. Attempts to quantize them failed to produce faster-than-light particles, and instead illustrated that their presence leads to an instability.[78][79] Various theorists have suggested that the neutrino might have a tachyonic nature,[80][81][82][83][84] while others have disputed the possibility.[85] General relativity General relativity was developed after special relativity to include concepts like gravity. It maintains the principle that no object can accelerate to the speed of light in the reference frame of any coincident observer. However, it permits distortions in spacetime that allow an object to move faster than light from the point of view of a distant observer. One such distortion is the Alcubierre drive, which can be thought of as producing a ripple in spacetime that carries an object along with it. Another possible system is the wormhole, which connects two distant locations as though by a shortcut. Both distortions would need to create a very strong curvature in a highly localized region of space-time and their gravity fields would be immense. To counteract the unstable nature, and prevent the distortions from collapsing under their own 'weight', one would need to introduce hypothetical exotic matter or negative energy. General relativity also agrees that any technique for faster-than-light travel could also be used for time travel. This raises problems with causality. Many physicists believe that the above phenomena are in fact impossible, and that future theories of gravity will prohibit them. One theory states that stable wormholes are possible, but that any attempt to use a network of wormholes to violate causality would result in their decay. In string theory, Eric G. Gimon and Petr Hořava have argued[86] that in a supersymmetric five-dimensional Gödel universe, quantum corrections to general relativity effectively cut off regions of spacetime with causality-violating closed timelike Faster-than-light curves. In particular, in the quantum theory a smeared supertube is present that cuts the spacetime in such a way that, although in the full spacetime a closed timelike curve passed through every point, no complete curves exist on the interior region bounded by the tube. 71 Variable speed of light In conventional physics, the speed of light in a vacuum is assumed to be a constant. However, theories exist which postulate that the speed of light is not a constant. The interpretation of this statement is as follows. The speed of light is a dimensional quantity and so, as has been emphasized in this context by João Magueijo, it cannot be measured.[87] Measurable quantities in physics are, without exception, dimensionless, although they are often constructed as ratios of dimensional quantities. For example, when you measure the height of a mountain you really measure the ratio of its height to the length of a meter stick. The conventional SI system of units is based on seven basic dimensional quantities, namely distance, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.[88] These units are defined to be independent and so cannot be described in terms of each other. As an alternative to using a particular system of units, one can reduce all measurements to dimensionless quantities expressed in terms of ratios between the quantities being measured and various fundamental constants such as Newton's constant, the speed of light and Planck's constant; physicists can define at least 26 dimensionless constants which can be expressed in terms of these sorts of ratios and which are currently thought to be independent of one another.[89] By manipulating the basic dimensional constants one can also construct the Planck time, Planck length and Planck energy which make a good system of units for expressing dimensional measurements, known as Planck units. Magueijo's proposal used a different set of units, a choice which he justifies with the claim that some equations will be simpler in these new units. In the new units he fixes the fine structure constant, a quantity which some people, using units in which the speed of light is fixed, have claimed is time-dependent. Thus in the system of units in which the fine structure constant is fixed, the observational claim is that the speed of light is time-dependent. While it may be mathematically possible to construct such a system, it is not clear what additional explanatory power or physical insight such a system would provide, assuming that it does indeed accord with existing empirical data. Notes [1] Gonzalez-Diaz, P. F. (2000). "Warp drive space-time" (http:/ / omnis. if. ufrj. br/ ~mbr/ warp/ etc/ PRD62_44005. pdf). Physical Review D 62 (4): 044005. arXiv:gr-qc/9907026. Bibcode 2000PhRvD..62d4005G. doi:10.1103/PhysRevD.62.044005. . [2] Loup, F.; Waite, D.; Halerewicz, E. Jr. (2001). "Reduced total energy requirements for a modified Alcubierre warp drive spacetime". arXiv:gr-qc/0107097 [gr-qc]. [3] Visser, M.; Bassett, B.; Liberati, S. (2000). "Superluminal censorship". Nuclear Physics B: Proceedings Supplement 88: 267–270. arXiv:gr-qc/9810026. Bibcode 2000NuPhS..88..267V. doi:10.1016/S0920-5632(00)00782-9. [4] Visser, M.; Bassett, B.; Liberati, S. (1999). "Perturbative superluminal censorship and the null energy condition". AIP Conference Proceedings 493: 301–305. arXiv:gr-qc/9908023. doi:10.1063/1.1301601. ISBN 1-56396-905-X. [5] See Salters Horners Advanced Physics A2 Student Book, Oxford etc. (Heinemann) 2001, pp. 302 and 303 [6] see http:/ / www. oarval. org/ furthest. htm [7] Gibbs, Philip (1997). Is Faster-Than-Light Travel or Communication Possible? (http:/ / math. ucr. edu/ home/ baez/ physics/ Relativity/ SpeedOfLight/ FTL. html). University of California, Riverside. . Retrieved 20 August 2008 [8] Wertheim, M. (20 June 2007). "The Shadow Goes" (http:/ / www. nytimes. com/ 2007/ 06/ 20/ opinion/ 20wertheim. html?_r=1& scp=1& sq='the shadow goes'& st=cse& oref=slogin). New York Times. [9] Salmon, Wesley C. (2006). Four Decades of Scientific Explanation (http:/ / books. google. com/ books?id=FHqOXCd06e8C). University of Pittsburgh Pre. p. 107. ISBN 0-8229-5926-7. ., Extract of page 107 (http:/ / books. google. com/ books?id=FHqOXCd06e8C& pg=PA107) [10] Steane, Andrew (2012). The Wonderful World of Relativity: A Precise Guide for the General Reader (http:/ / books. google. com/ books?id=4m14K1PpJwMC). Oxford University Press. p. 180. ISBN 0-19-969461-3. ., Extract of page 180 (http:/ / books. google. com/ books?id=4m14K1PpJwMC& pg=PA180) [11] Special Theory of Relativity (http:/ / library. thinkquest. org/ C0116043/ specialtheorytext. htm) [12] Hecht, Eugene (1987). Optics (2nd ed.). Addison Wesley. p. 62. ISBN 0-201-11609-X. [13] Sommerfeld, Arnold (1907). "An Objection Against the Theory of Relativity and its Removal". Physikalische Zeitschrift 8 (23): 841–842. Faster-than-light [14] "MathPages - Phase, Group, and Signal Velocity" (http:/ / www. mathpages. com/ home/ kmath210/ kmath210. htm). . Retrieved 2007-04-30. [15] Brillouin, Léon; Wave Propagation and Group Velocity, Academic Press, 1960 [16] Withayachumnankul, W.; et al.; "A systemized view of superluminal wave propagation," (http:/ / www. eleceng. adelaide. edu. au/ personal/ dabbott/ publications/ PIE_withayachumnankul2010. pdf) Proceedings of the IEEE, Vol. 98, No. 10, pp. 1775-1786, 2010 [17] "Cosmology Tutorial - Part 2" (http:/ / www. astro. ucla. edu/ ~wright/ cosmo_02. htm#MD). Astro.ucla.edu. 2009-06-12. . Retrieved 2011-09-26. [18] "Inflationary Period from HyperPhysics" (http:/ / hyperphysics. phy-astr. gsu. edu/ hbase/ astro/ planck. html#c5). Hyperphysics.phy-astr.gsu.edu. . Retrieved 2011-09-26. [19] Is the universe expanding faster than the speed of light? (http:/ / curious. astro. cornell. edu/ question. php?number=575) (see the last two paragraphs) [20] Lineweaver, Charles; Davis, Tamara M. (2005). "Misconceptions about the Big Bang" (http:/ / space. mit. edu/ ~kcooksey/ teaching/ AY5/ MisconceptionsabouttheBigBang_ScientificAmerican. pdf). Scientific American. . Retrieved 2008-11-06. [21] Loeb, Abraham (2002). "The Long-Term Future of Extragalactic Astronomy". Physical Review D 65 (4). arXiv:astro-ph /0107568. Bibcode 2002PhRvD..65d7301L. doi:10.1103/PhysRevD.65.047301. [22] Rees, Martin J. (1966). "Appearance of relativistically expanding radio sources". Nature 211 (5048): 468. Bibcode 1966Natur.211..468R. doi:10.1038/211468a0. [23] Blandford, Roger D.; McKee, C. F.; Rees, Martin J. (1977). "Super-luminal expansion in extragalactic radio sources". Nature 267 (5608): 211. Bibcode 1977Natur.267..211B. doi:10.1038/267211a0. [24] Feynman. "Chapter 3". QED. p. 89. ISBN 981-256-914-6. [25] Zhang, Shanchao. "Single photons obey the speed limits" (http:/ / physics. aps. org/ synopsis-for/ 10. 1103/ PhysRevLett. 106. 243602). Physics. American Physical Society. . Retrieved 25 July 2011. [26] Martinez, J. C.; and Polatdemir, E.; "Origin of the Hartman effect", Physics Letters A, Vol. 351, Iss. 1-2, 20 February 2006, pp. 31-36 [27] Hartman, Thomas E.; "Tunneling of a wave packet", Journal of Applied Physics 33, 3427 (1962) [28] Nimtz, Günter; Stahlhofen, Alfons (2007). "Macroscopic violation of special relativity". arXiv:0708.0681 [quant-ph]. [29] Winful, Herbert G.; "Tunneling time, the Hartman effect, and superluminality: A proposed resolution of an old paradox" (http:/ / sitemaker. umich. edu/ herbert. winful/ files/ physics_reports_review_article__2006_. pdf), Physics Reports, Vol. 436, Iss. 1-2, December 2006, pp. 1-69 [30] "History" (http:/ / www. quantumphil. org/ history. htm). Quantumphil.org. . Retrieved 2011-09-26. [31] Salart; Baas; Branciard; Gisin; Zbinden (2008). "Testing spooky action at a distance". Nature 454 (7206): 861–864. arXiv:0808.3316. Bibcode 2008Natur.454..861S. doi:10.1038/nature07121. PMID 18704081. [32] "Delayed Choice Quantum Eraser" (http:/ / www. bottomlayer. com/ bottom/ kim-scully/ kim-scully-web. htm). Bottomlayer.com. 2002-09-04. . Retrieved 2011-09-26. [33] Einstein, Albert, Relativity:the special and the general theory, Methuen & Co, 1927, pp. 25-27 [34] Gott, J. Richard (2002). Time Travel in Einstein's Universe. pp. pp. 82–83. [35] Petkov, Vesselin; Relativity and the Nature of Spacetime, p. 219 (http:/ / books. google. com/ books?id=AzfFo6A94WEC& lpg=PR1& pg=PA219#v=onepage& q& f=false) [36] Raine, Derek J.; Thomas, Edwin George; and Thomas, E. G.; An Introduction to the Science of Cosmology, p. 94 (http:/ / books. google. com/ books?id=RK8qDGKSTPwC& lpg=PR1& pg=PA94#v=onepage& q& f=false) [37] "What is the 'zero-point energy' (or 'vacuum energy') in quantum physics? Is it really possible that we could harness this energy?" (http:/ / www. scientificamerican. com/ article. cfm?id=follow-up-what-is-the-zer). Scientific American. 1997-08-18. . Retrieved 2009-05-27. [38] Scharnhorst, Klaus (1990-05-12). "Secret of the vacuum: Speedier light" (http:/ / www. nat. vu. nl/ ~scharnh/ m16scine. htm). . Retrieved 2009-05-27. [39] Visser, Matt; Liberati, Stefano; and Sonego, Sebastiano (2001-07-27). "Faster-than-c signals, special relativity, and causality". Annals of Physics 298 (2002) 167-185 298: 167–185. arXiv:gr-qc/0107091. Bibcode 2002AnPhy.298..167L. doi:10.1006/aphy.2002.6233. [40] Fearn, Heidi (2007). "Can Light Signals Travel Faster than c in Nontrivial Vacuua in Flat space-time? Relativistic Causality II". LaserPhys.17:695-699,2007 17 (5): 695–699. arXiv:0706.0553. Bibcode 2007LaPhy..17..695F. doi:10.1134/S1054660X07050155. [41] Nimtz, Günter; Superluminal Tunneling Devices (http:/ / cdsweb. cern. ch/ record/ 547324/ files/ 0204043. pdf?version=1), 2001 [42] Winful, Herbert G. (2007-09-18). "Comment on "Macroscopic violation of special relativity" by Nimtz and Stahlhofen". arXiv:0709.2736 [quant-ph]. [43] Helling, Robert C. (http:/ / www. atdotde. de/ ); "Faster than light or not" (http:/ / atdotde. blogspot. com/ 2005/ 09/ faster-than-light-or-not. html) (blog) [44] Anderson, Mark (18–24 August 2007). "Light seems to defy its own speed limit" (http:/ / www. eurekalert. org/ pub_releases/ 2007-08/ ns-lst081607. php). New Scientist 195 (2617): p. 10. [45] Winful, Herbert G. (December 2006). "Tunneling time, the Hartman effect, and superluminality: A proposed resolution of an old paradox" (http:/ / sitemaker. umich. edu/ herbert. winful/ files/ physics_reports_review_article__2006_. pdf). Physics Reports 436 (1–2): 1–69. Bibcode 2006PhR...436....1W. doi:10.1016/j.physrep.2006.09.002. . [46] For a summary of Herbert G. Winful's explanation for apparently superluminal tunneling time which does not involve reshaping, see http:/ / spie. org/ x18001. xml?ArticleID=x18001 72 Faster-than-light [47] A number of papers are listed at Literature on Faster-than-light tunneling experiments (http:/ / www. aei. mpg. de/ ~mpoessel/ Physik/ FTL/ tunnelingftl. html) [48] Eckle, P.; et al., "Attosecond Ionization and Tunneling Delay Time Measurements in Helium", Science, 322 (2008) 1525 [49] Sokolovski, D. (8 February 2004). "Why does relativity allow quantum tunneling to 'take no time'?" (http:/ / rspa. royalsocietypublishing. org/ content/ 460/ 2042/ 499. full. pdf). Proceedings of the Royal Society A 460 (2042): 499–506. Bibcode 2004RSPSA.460..499S. doi:10.1098/rspa.2003.1222. . [50] Lineweaver, Charles H.; and Davis, Tamara M. (March 2005). "Misconceptions about the Big Bang" (http:/ / www. sciam. com/ article. cfm?id=misconceptions-about-the-2005-03). Scientific American. . [51] http:/ / www. iop. org/ EJ/ abstract/ 0264-9381/ 11/ 5/ 001 [52] Traveling Faster Than the Speed of Light: A New Idea That Could Make It Happen (http:/ / newswise. com/ articles/ view/ 543391/ ) Newswise, retrieved on 24 August 2008. [53] Heim, Burkhard (1977). "Vorschlag eines Weges einer einheitlichen Beschreibung der Elementarteilchen [Recommendation of a Way to a Unified Description of Elementary Particles]". Zeitschrift für Naturforschung 32a: 233–243. Bibcode 1977ZNatA..32..233H. [54] McCulloch, M. E. (2010). "Minimum accelerations from quantised inertia". EPL 90 (2): 29001. arXiv:1004.3303. Bibcode 2010EL.....9029001M. doi:10.1209/0295-5075/90/29001. [55] Colladay, Don; Kostelecký, V. Alan (1997). "CPT violation and the standard model". Physical Review D 55 (11): 6760. arXiv:hep-ph/9703464. Bibcode 1997PhRvD..55.6760C. doi:10.1103/PhysRevD.55.6760. [56] Colladay, Don; Kostelecký, V. Alan (1998). "Lorentz-violating extension of the standard model". Physical Review D 58 (11). arXiv:hep-ph/9809521. Bibcode 1998PhRvD..58k6002C. doi:10.1103/PhysRevD.58.116002. [57] Kostelecký, V. Alan (2004). "Gravity, Lorentz violation, and the standard model". Physical Review D 69 (10). arXiv:hep-th/0312310. Bibcode 2004PhRvD..69j5009K. doi:10.1103/PhysRevD.69.105009. [58] Gonzalez-Mestres, Luis (2009). "AUGER-HiRes results and models of Lorentz symmetry violation". Nuclear Physics B: Proceedings Supplements 190: 191–197. arXiv:0902.0994. Bibcode 2009NuPhS.190..191G. doi:10.1016/j.nuclphysbps.2009.03.088. [59] Kostelecký, V. Alan; Russell, Neil (2011). "Data tables for Lorentz and CPT violation". Review of Modern Physics 83: 11. arXiv:0801.0287. Bibcode 2011RvMP...83...11K. doi:10.1103/RevModPhys.83.11. [60] Kostelecký, V. Alan; and Samuel, S.; Spontaneous Breaking of Lorentz Symmetry in String Theory, Physical Review D 39, 683 (1989) [61] "PhysicsWeb - Breaking Lorentz symmetry" (http:/ / web. archive. org/ web/ 20040405031103/ http:/ / physicsweb. org/ article/ world/ 17/ 3/ 7). Web.archive.org. 2004-04-05. . Retrieved 2011-09-26. [62] Mavromatos, Nick E.; Testing models for quantum gravity, CERN Courier, http:/ / cerncourier. com/ cws/ article/ cern/ 28696 (August 2002) [63] Overbye, Dennis; Interpreting the Cosmic Rays (http:/ / www. nytimes. com/ 2002/ 12/ 31/ science/ interpreting-the-cosmic-rays. html?n=Top/ News/ Science/ Topics/ Space), The New York Times, 31 December 2002 [64] Volovik, G. E. (2003). "The Universe in a helium droplet". International Series of Monographs on Physics 117: 1–507. [65] Zloshchastiev, Konstantin G. (2009). "Spontaneous symmetry breaking and mass generation as built-in phenomena in logarithmic nonlinear quantum theory". Acta Physica Polonica B 42 (2): 261–292. arXiv:0912.4139. doi:10.5506/APhysPolB.42.261. [66] Avdeenkov, Alexander V.; Zloshchastiev, Konstantin G. (2011). "Quantum Bose liquids with logarithmic nonlinearity: Self-sustainability and emergence of spatial extent". Journal of Physics B: Atomic, Molecular and Optical Physics 44 (19): 195303. arXiv:1108.0847. Bibcode 2011JPhB...44s5303A. doi:10.1088/0953-4075/44/19/195303. [67] Zloshchastiev, Konstantin G.; Chakrabarti, Sandip K.; Zhuk, Alexander I.; Bisnovatyi-Kogan, Gennady S. (2010). Logarithmic nonlinearity in theories of quantum gravity: Origin of time and observational consequences. AIP Conference Proceedings. pp. 112. arXiv:0906.4282. Bibcode 2010AIPC.1206..112Z. doi:10.1063/1.3292518. [68] Zloshchastiev, Konstantin G. (2011). "Vacuum Cherenkov effect in logarithmic nonlinear quantum theory". Physics Letters A 375 (24): 2305. arXiv:1003.0657. Bibcode 2011PhLA..375.2305Z. doi:10.1016/j.physleta.2011.05.012. [69] Adamson, P.; Andreopoulos, C.; Arms, K.; Armstrong, R.; Auty, D.; Avvakumov, S.; Ayres, D.; Baller, B. et al. (2007). "Measurement of neutrino velocity with the MINOS detectors and NuMI neutrino beam". Physical Review D 76 (7). arXiv:0706.0437. Bibcode 2007PhRvD..76g2005A. doi:10.1103/PhysRevD.76.072005. [70] Overbye, Dennis (22 September 2011). "Tiny neutrinos may have broken cosmic speed limit" (http:/ / www. nytimes. com/ 2011/ 09/ 23/ science/ 23speed. html). New York Times. . "That group found, although with less precision, that the neutrino speeds were consistent with the speed of light." [71] Adam; Agafonova; Aleksandrov; Altinok; Alvarez Sanchez; Aoki; Ariga; Ariga et al. (2011). "Measurement of the neutrino velocity with the OPERA detector in the CNGS beam". arXiv:1109.4897 [hep-ex]. [72] Cho, Adrian; Neutrinos Travel Faster Than Light, According to One Experiment (http:/ / news. sciencemag. org/ sciencenow/ 2011/ 09/ neutrinos-travel-faster-than-lig. html), Science NOW, 22 September 2011 [73] Overbye, Dennis (18 November 2011). "Scientists Report Second Sighting of Faster-Than-Light Neutrinos" (http:/ / www. nytimes. com/ 2011/ 11/ 19/ science/ space/ neutrino-finding-is-confirmed-in-second-experiment-opera-scientists-say. html). New York Times. . Retrieved 2011-11-18. [74] Adam, T.; et al.; (OPERA Collaboration) (17 November 2011). " Measurement of the neutrino velocity with the OPERA detector in the CNGS beam (http:/ / arxiv. org/ ftp/ arxiv/ papers/ 1109/ 1109. 4897. pdf)". arXiv:1109.4897v2 [hep-ex]. [75] Faster than light (http:/ / www. science-niblets. org/ physics/ faster-than-light. html) Science Niblets, 27 September 2011 73 Faster-than-light [76] http:/ / www. reuters. com/ article/ 2011/ 11/ 20/ us-science-neutrinos-idUSTRE7AJ0ZX20111120 Reuters: Study rejects "faster than light" particle finding [77] ICARUS collaboration (March 15, 2012), Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam, arXiv:1203.3433 [78] Randall, Lisa; Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions, p. 286: "People initially thought of tachyons as particles travelling faster than the speed of light...But we now know that a tachyon indicates an instability in a theory that contains it. Regrettably for science fiction fans, tachyons are not real physical particles that appear in nature." [79] Gates, S. James. Superstring Theory: The DNA of Reality. [80] Chodos, A.; Hauser, A. I.; and Kostelecký, V. Alan; The Neutrino As A Tachyon, Physics Letters B 150, 431 (1985) [81] Chodos, Alan; Kostelecký, V. Alan; IUHET 280 (1994). "Nuclear Null Tests for Spacelike Neutrinos". Physics Letters B 336 (3–4): 295–302. arXiv:hep-ph/9409404. Bibcode 1994PhLB..336..295C. doi:10.1016/0370-2693(94)90535-5. [82] Chodos, Alan; Kostelecký, V. Alan; Potting, R.; and Gates, E.; Null experiments for neutrino masses, Modern Physics Letters A7, 467 (1992) [83] List of articles on the tachyonic neutrino idea (may be incomplete) (http:/ / inspirebeta. net/ search?ln=en& p=refersto:recid:15887). InSPIRE database. http:/ / arxiv. org/ abs/ hep-ph/ 0208239] [84] Chang, Taso; Parity Violation and Neutrino Mass, Nuclear Science and Techniques, Vol. 13, No. 3 (2002) 129 [85] Hughes, R. J.; and Stephenson, G. J., Jr.; Against tachyonic neutrinos, Physics Letters B 244, 95-100 (1990) [86] Gimon, Eric G.; Hořava, Petr (2004). "Over-rotating black holes, Gödel holography and the hypertube". arXiv:hep-th/0405019 [hep-th]. [87] Magueijo, João; Albrecht, Andreas (1999). "A time varying speed of light as a solution to cosmological puzzles". Physical Review D 59 (4). arXiv:astro-ph/9811018. Bibcode 1999PhRvD..59d3516A. doi:10.1103/PhysRevD.59.043516. [88] "SI base units" (http:/ / physics. nist. gov/ cuu/ Units/ units. html). . [89] "constants" (http:/ / math. ucr. edu/ home/ baez/ constants. html). . 74 References • Falla, D. F.; Floyd, M. J. (2002). "Superluminal motion in astronomy". European Journal of Physics 23: 69–81. Bibcode 2002EJPh...23...69F. doi:10.1088/0143-0807/23/1/310. • Kaku, Michio (2008). "Faster than Light". Physics of the Impossible. Allen Lane. pp. 197–215. ISBN 978-0-7139-9992-1. • Nimtz, Günter (2008). Zero Time Space. Wiley-VCH. ISBN 978-3-527-40735-4. • Cramer, J. G. (2009). "Faster-than-Light Implications of Quantum Entanglement and Nonlocality". In Millis, M. G.; et al.. Frontiers of Propulsion Science. American Institute of Aeronautics and Astronautics. pp. 509–529. ISBN 1-56347-956-7. External links Scientific links • Measurement of the neutrino velocity with the OPERA detector in the CNGS beam (http://iysn.org/2011/10/ 19/measurement-of-the-neutrino-velocity-with-the-opera-detector-in-the-cngs-beam/) • Encyclopedia of laser physics and technology on "superluminal transmission" (http://www.rp-photonics.com/ superluminal_transmission.html), with more details on phase and group velocity, and on causality • July 22, 1997, The New York Times Company: Signal Travels Farther and Faster Than Light (http://dustbunny. physics.indiana.edu/~dzierba/HonorsF97/Week1/NYTJuly22.html) • Markus Pössel: Faster-than-light (FTL) speeds in tunneling experiments: an annotated bibliography (http://www. aei-potsdam.mpg.de/~mpoessel/Physik/FTL/tunnelingftl.html) • Alcubierre, Miguel; The Warp Drive: Hyper-Fast Travel Within General Relativity, Classical and Quantum Gravity 11 (1994), L73–L77 (http://www.yellowknife.com/warp/) • A systemized view of superluminal wave propagation (http://www.eleceng.adelaide.edu.au/personal/dabbott/ publications/PIE_withayachumnankul2010.pdf) • Relativity and FTL Travel FAQ (http://www.physicsguy.com/ftl/index.html) • Usenet Physics FAQ: is FTL travel or communication Possible? (http://math.ucr.edu/home/baez/physics/ Relativity/SpeedOfLight/FTL.html) Faster-than-light • Superluminal (http://scienceworld.wolfram.com/physics/Superluminal.html) • Relativity, FTL and causality (http://www.theculture.org/rich/sharpblue/archives/000089.html) • Superluminal velocity (http://adsabs.harvard.edu/abs/2006PrGeo..21...38Y) fusing with Einstein special relativity • Stimulated Generation of Superluminal Light Pulses via Four-Wave Mixing (http://prl.aps.org/abstract/PRL/ v108/i17/e173902) 75 Proposed FTL Methods links • Conical and paraboloidal superluminal particle accelerators (http://www.petar-bosnic-petrus.com/ science-articles/conical-and-paraboloidal-superluminal-particle-accelerators/) • Relativity and FTL (=Superluminal motion) Travel Homepage (http://www.physicsguy.com/ftl/) • Advanced Interstellar Propulsion (http://www.ovalecotech.ca) How to Travel Extreme Distances in Space. Past, Present and Proposed ideas of interstellar travel. Chronology protection conjecture The chronology protection conjecture is a conjecture by the physicist Professor Stephen Hawking that the laws of physics are such as to prevent time travel on all but sub-microscopic scales. Mathematically, the permissibility of time travel is represented by the existence of closed timelike curves. The chronology protection conjecture should be distinguished from chronological censorship under which every closed timelike curve passes through an event horizon, which might prevent an observer from detecting the causal violation.[1] Origin In a 1992 paper, Hawking uses the metaphorical device of a "Chronology Protection Agency" as a personification of the aspects of physics which make time travel impossible at macroscopic scales, thus apparently preventing time paradoxes. He says: It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians. The idea of the Chronology Protection Agency appears to be drawn playfully from the Time Patrol or Time Police concept present in works of science fiction such as Isaac Asimov's novel The End of Eternity. Quantum corrections Many attempts to generate scenarios for closed timelike curves have been suggested, and the theory of general relativity does allow them in certain circumstances (for example, it would allow for a time machine constructed from a wormhole – see Wormholes and time travel). But attempts to incorporate quantum effects into general relativity using semiclassical gravity seem to make it plausible that vacuum fluctuations would drive the energy density on the boundary of the time machine (the Cauchy horizon of the region where closed timelike curves become possible) to infinity, destroying the time machine at the instant it was created or at least preventing anyone outside it from entering it. The question then arises: is this apparent censorship of closed timelike curves a global constraint of physics, in the same way as a conservation law, or is it a series of accidental coincidences? A definite theoretical decision on the status of the chronology protection conjecture would require a full theory of quantum gravity as opposed to the semiclassical arguments that have been mainly used to support it (there are also some arguments from string theory which seem to support chronology protection, but string theory is not yet a complete theory of quantum gravity). Experimental observation of closed timelike curves would of course Chronology protection conjecture demonstrate this conjecture to be false, but short of that, if physicists had a theory of quantum gravity whose predictions had been well-confirmed in other areas, this would give them a significant degree of confidence in the theory's predictions about the possibility or impossibility of time travel. Other proposals which allow for backwards time travel but prevent time paradoxes, such as the Novikov self-consistency principle which would ensure the timeline stays consistent, or the idea that a time traveler is taken to a parallel universe while his original timeline remains intact, do not qualify as "chronology protection". 76 References • Hawking, S.W., (1992) The chronology protection conjecture. Phys. Rev. D46, 603-611. • Matt Visser, "The quantum physics of chronology protection" [2] in The Future of Theoretical Physics and Cosmology: Celebrating Stephen Hawking's 60th Birthday by G. W. Gibbons (Editor), E. P. S. Shellard (Editor), S. J. Rankin (Editor) • Li-Xin Li, "Must Time Machine Be Unstable against Vacuum Fluctuations?" [3], Class.Quant.Grav. 13 (1996) 2563-2568. External links • http://www.hawking.org.uk/index.php/lectures/63 • http://plus.maths.org/content/time-travel-allowed — Kip Thorne discusses time travel in general relativity, and the basis in quantum physics for the chronology protection conjecture References [1] http:/ / dx. doi. org/ 10. 1007/ s10701-008-9254-9 [2] http:/ / arxiv. org/ abs/ gr-qc/ 0204022 [3] http:/ / arxiv. org/ abs/ gr-qc/ 9703024 77 Philosophy Philosophy of space and time Philosophy of space and time is the branch of philosophy concerned with the issues surrounding the ontology, epistemology, and character of space and time. While such ideas have been central to philosophy from its inception, the philosophy of space and time was both an inspiration for and a central aspect of early analytic philosophy. The subject focuses on a number of basic issues, including—but not limited to—whether or not time and space exist independently of the mind, whether they exist independently of one another, what accounts for time's apparently unidirectional flow, whether times other than the present moment exist, and questions about the nature of identity (particularly the nature of identity over time). Ancient and medieval views The earliest recorded Western philosophy of time was expounded by the ancient Egyptian thinker Ptahhotep (c. 2650–2600 BCE), who said: "Do not lessen the time of following desire, for the wasting of time is an abomination to the spirit." The Vedas, the earliest texts on Indian philosophy and Hindu philosophy dating back to the late 2nd millennium BCE, describe ancient Hindu cosmology, in which the universe goes through repeated cycles of creation, destruction and rebirth, with each cycle lasting 4,320,000 years. Ancient Greek philosophers, including Parmenides and Heraclitus, wrote essays on the nature of time.[1] Incas regarded space and time as a single concept, named pacha (Quechua: pacha, Aymara: pacha).[2][3][4] Plato, in the Timaeus, identified time with the period of motion of the heavenly bodies, and space as that in which things come to be. Aristotle, in Book IV of his Physica defined time as the number of change with respect to before and after, and the space of an object as the innermost motionless boundary of that which surrounds it. In Book 11 of St. Augustine's Confessions, he ruminates on the nature of time, asking, "What then is time? If no one asks me, I know: if I wish to explain it to one that asketh, I know not." He settles on time being defined more by what it is not than what it is.[5] In contrast to ancient Greek philosophers who believed that the universe had an infinite past with no beginning, medieval philosophers and theologians developed the concept of the universe having a finite past with a beginning. This view was inspired by the creation belief shared by the three Abrahamic religions: Judaism, Christianity and Islam. The Christian philosopher, John Philoponus, presented the first such argument against the ancient Greek notion of an infinite past. His were adopted by many including, most notably, early Muslim philosopher, Al-Kindi (Alkindus); the Jewish philosopher, Saadia Gaon (Saadia ben Joseph); and the Muslim theologian, Al-Ghazali (Algazel). They used his two logical arguments against an infinite past, the first being the "argument from the impossibility of the existence of an actual infinite", which states:[6] "An actual infinite cannot exist." "An infinite temporal regress of events is an actual infinite." "∴ An infinite temporal regress of events cannot exist." The second argument, the "argument from the impossibility of completing an actual infinite by successive addition", states:[6] "An actual infinite cannot be completed by successive addition." "The temporal series of past events has been completed by successive addition." Philosophy of space and time "∴ The temporal series of past events cannot be an actual infinite." Both arguments were adopted by later Christian philosophers and theologians, and the second argument in particular became more famous after it was adopted by Immanuel Kant in his thesis of the first antinomy concerning time.[6] In the early 11th century, the Muslim physicist, Ibn al-Haytham (Alhacen or Alhazen), discussed space perception and its epistemological implications in his Book of Optics (1021). His experimental proof of the intromission model of vision led to changes in the way the visual perception of space was understood, contrary to the previous emission theory of vision supported by Euclid and Ptolemy. In "tying the visual perception of space to prior bodily experience, Alhacen unequivocally rejected the intuitiveness of spatial perception and, therefore, the autonomy of vision. Without tangible notions of distance and size for correlation, sight can tell us next to nothing about such things."[7] 78 Realism and anti-realism A traditional realist position in ontology is that time and space have existence apart from the human mind. Idealists deny or doubt the existence of objects independent of the mind. Some anti-realists whose ontological position is that objects outside the mind do exist, nevertheless doubt the independent existence of time and space. Kant, in the Critique of Pure Reason, described time as an a priori notion that, together with other a priori notions such as space, allows us to comprehend sense experience. Kant denies that either space or time are substance, entities in themselves, or learned by experience; he holds rather that both are elements of a systematic framework we use to structure our experience. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantitatively compare the interval between (or duration of) events. Although space and time are held to be transcendentally ideal in this sense, they are also empirically real, i.e. not mere illusions. Idealist writers such as J. M. E. McTaggart in The Unreality of Time have argued that time is an illusion (see also The flow of time below). The writers discussed here are for the most part realists in this regard; for instance, Gottfried Leibniz held that his monads existed, at least independently of the mind of the observer. Absolutism and relationalism Leibniz and Newton The great debate between defining notions of space and time as real objects themselves (absolute), or whether they are merely orderings upon actual objects (relational), began between physicists Isaac Newton (via his spokesman, Samuel Clarke) and Gottfried Leibniz in the papers of the Leibniz-Clarke correspondence. Arguing against the absolutist position, Leibniz offers a number of thought experiments with the purpose of showing that there is contradiction in assuming the existence of facts such as absolute location and velocity. These arguments trade heavily on two principles central to his philosophy: the principle of sufficient reason and the identity of indiscernibles. The principle of sufficient reason holds that for every fact there is a reason that is sufficient to explain what and why it is the way it is and not otherwise. The identity of indiscernibles states that if there is no way of telling two entities apart then they are one and the same thing. The example Leibniz uses involves two proposed universes situated in absolute space. The only discernible difference between them is that the latter is positioned five feet to the left of the first. The possibility of the example is only available if such a thing as absolute space exists. Such a situation, however, is not possible according to Leibniz, for if it were, where a universe was positioned in absolute space would have no sufficient reason, as it might very well have been anywhere else. Therefore, it is contradicting the principle of sufficient reason, and there could exist two distinct universes that were in all ways indiscernible, thus contradicting the identity of indiscernibles. Standing out in Clarke’s (and Newton’s) response to Leibniz arguments is the bucket argument: Water in a bucket, hung from a rope and set to spin, will start with a flat surface. As the water begins to spin in the bucket, the surface Philosophy of space and time of the water will become concave. If the bucket is stopped, the water will continue to spin, and while the spin continues the surface will remain concave. The concave surface is apparently not the result of the interaction of the bucket and the water, since the water is flat when the bucket first starts to spin, becomes concave as the water starts to spin, and remains concave as the bucket stops. In this response, Clarke argues for the necessity of the existence of absolute space to account for phenomena like rotation and acceleration that cannot be accounted for on a purely relationalist account. Clarke argues that since the curvature of the water occurs in the rotating bucket as well as in the stationary bucket containing spinning water, it can only be explained by stating that the water is rotating in relation to the presence of some third thing—absolute space. Leibniz describes a space that exists only as a relation between objects, and which has no existence apart from the existence of those objects. Motion exists only as a relation between those objects. Newtonian space provided the absolute frame of reference within which objects can have motion. In Newton’s system the frame of reference exists independently of the objects which are contained in it. These objects can be described as moving in relation to space itself. For many centuries, the evidence of a concave water surface held authority. 79 Mach Another important figure in this debate is 19th century physicist, Ernst Mach. While he did not deny the existence of phenomena like that seen in the bucket argument, he still denied the absolutist conclusion by offering a different answer as to what the bucket was rotating in relation to: the fixed stars. Mach suggested that thought experiments like the bucket argument are problematic. If we were to imagine a universe that only contains a bucket, on Newton’s account, this bucket could be set to spin relative to absolute space, and the water it contained would form the characteristic concave surface. But, in the absence of anything else in the universe it would be difficult to confirm that the bucket was indeed spinning. It seems equally possible that the surface of the water in the bucket would remain flat. Mach argued that, in effect, the water experiment in an otherwise empty universe would remain flat. But if another object was introduced into this universe, perhaps a distant star, there is now something relative to which the bucket could be seen as rotating. The water inside the bucket could possibly have a slight curve. To account for the curve that we observe, an increase in the number of objects in the universe also increases the curvature in the water. Mach argued that the momentum of an object, whether angular or linear, exists as a result of the sum of the effects of other objects in the universe (Mach's Principle). Einstein Albert Einstein proposed that relativistics are based on the principle of relativity. This theory holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used, and that light propagates at the same speed in all reference frames. This theory was motivated by Maxwell’s equations. These equations show that electromagnetic waves propagate in a vacuum at the speed of light. However, Maxwell's equations give no indication of what this speed is relative to. Prior to Einstein, it was thought that this speed was relative to a fixed medium, called the luminiferous ether. In contrast, the theory of special relativity postulates that light propagates at the speed of light in all inertial frames, and examines the implications of this postulate. All attempts to measure any speed relative to this ether failed, which can be seen as a confirmation of Einstein's postulate that light propagates at the same speed in all reference frames. Special relativity is a formalization of the principle of relativity which does not contain a privileged inertial frame of reference such as the luminiferous ether or absolute space, from which Einstein inferred that no such frame exists. Einstein generalized relativity to frames of reference that were non-inertial. He achieved this by positing the Equivalence Principle, which states that the force felt by an observer in a given gravitational field and that felt by an observer in an accelerating frame of reference are indistinguishable. This led to the conclusion that the mass of an Philosophy of space and time object warps the geometry of the space-time surrounding it, as described in Einstein’s field equations. In classical physics, an inertial reference frame is one in which an object that experiences no forces does not accelerate. In general relativity, an inertial frame of reference is one that is following a geodesic of space-time. An object that moves against a geodesic experiences a force. An object in free fall does not experience a force, because it is following a geodesic. An object standing on the earth, however, will experience a force, as it is being held against the geodesic by the surface of the planet. In light of this, the bucket of water rotating in empty space will experience a force because it rotates with respect to the geodesic. The water will become concave, not because it is rotating with respect to the distant stars, but because it is rotating with respect to the geodesic. Einstein partially advocates Mach’s principle in that distant stars explain inertia because they provide the gravitational field against which acceleration and inertia occur. But contrary to Leibniz’ account, this warped space-time is as integral a part of an object as are its other defining characteristics such as volume and mass. If one holds, contrary to idealist beliefs, that objects exist independently of the mind, it seems that Relativistics commits them to also hold that space and temporality have exactly the same type of independent existence. 80 Conventionalism The position of conventionalism states that there is no fact of the matter as to the geometry of space and time, but that it is decided by convention. The first proponent of such a view, Henri Poincaré, reacting to the creation of the new non-euclidean geometry, argued that which geometry applied to a space was decided by convention, since different geometries will describe a set of objects equally well, based on considerations from his sphere-world. This view was developed and updated to include considerations from relativistic physics by Hans Reichenbach. Reichenbach's conventionalism, applying to space and time, focuses around the idea of coordinative definition. Coordinative definition has two major features. The first has to do with coordinating units of length with certain physical objects. This is motivated by the fact that we can never directly apprehend length. Instead we must choose some physical object, say the Standard Metre at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures), or the wavelength of cadmium to stand in as our unit of length. The second feature deals with separated objects. Although we can, presumably, directly test the equality of length of two measuring rods when they are next to one another, we can not find out as much for two rods distant from one another. Even supposing that two rods, whenever brought near to one another are seen to be equal in length, we are not justified in stating that they are always equal in length. This impossibility undermines our ability to decide the equality of length of two distant objects. Sameness of length, to the contrary, must be set by definition. Such a use of coordinative definition is in effect, on Reichenbach's conventionalism, in the General Theory of Relativity where light is assumed, i.e. not discovered, to mark out equal distances in equal times. After this setting of coordinative definition, however, the geometry of spacetime is set. As in the absolutism/relationalism debate, contemporary philosophy is still in disagreement as to the correctness of the conventionalist doctrine. While conventionalism still holds many proponents, cutting criticisms concerning the coherence of Reichenbach's doctrine of coordinative definition have led many to see the conventionalist view as untenable. Philosophy of space and time 81 The structure of spacetime Building from a mix of insights from the historical debates of absolutism and conventionalism as well as reflecting on the import of the technical apparatus of the General Theory of Relativity, details as to the structure of spacetime have made up a large proportion of discussion within the philosophy of space and time, as well as the philosophy of physics. The following is a short list of topics. The relativity of simultaneity According to special relativity each point in the universe can have a different set of events that compose its present instant. This has been used in the Rietdijk-Putnam argument to demonstrate that relativity predicts a block universe in which events are fixed in four dimensions. Invariance vs. covariance Bringing to bear the lessons of the absolutism/relationalism debate with the powerful mathematical tools invented in the 19th and 20th century, Michael Friedman draws a distinction between invariance upon mathematical transformation and covariance upon transformation. Invariance, or symmetry, applies to objects, i.e. the symmetry group of a space-time theory designates what features of objects are invariant, or absolute, and which are dynamical, or variable. Covariance applies to formulations of theories, i.e. the covariance group designates in which range of coordinate systems the laws of physics hold. This distinction can be illustrated by revisiting Leibniz's thought experiment, in which the universe is shifted over five feet. In this example the position of an object is seen not to be a property of that object, i.e. location is not invariant. Similarly, the covariance group for classical mechanics will be any coordinate systems that are obtained from one another by shifts in position as well as other translations allowed by a Galilean transformation. In the classical case, the invariance, or symmetry, group and the covariance group coincide, but, interestingly enough, they part ways in relativistic physics. The symmetry group of the general theory of relativity includes all differentiable transformations, i.e., all properties of an object are dynamical, in other words there are no absolute objects. The formulations of the general theory of relativity, unlike those of classical mechanics, do not share a standard, i.e., there is no single formulation paired with transformations. As such the covariance group of the general theory of relativity is just the covariance group of every theory. Historical frameworks A further application of the modern mathematical methods, in league with the idea of invariance and covariance groups, is to try to interpret historical views of space and time in modern, mathematical language. In these translations, a theory of space and time is seen as a manifold paired with vector spaces, the more vector spaces the more facts there are about objects in that theory. The historical development of spacetime theories is generally seen to start from a position where many facts about objects are incorporated in that theory, and as history progresses, more and more structure is removed. For example, Aristotle's theory of space and time holds that not only is there such a thing as absolute position, but that there are special places in space, such as a center to the universe, a sphere of fire, etc. Newtonian spacetime has absolute position, but not special positions. Galilean spacetime has absolute acceleration, but not absolute position or velocity. And so on. Philosophy of space and time 82 Holes With the general theory of relativity, the traditional debate between absolutism and relationalism has been shifted to whether or not spacetime is a substance, since the general theory of relativity largely rules out the existence of, e.g., absolute positions. One powerful argument against spacetime substantivalism, offered by John Earman is known as the "hole argument". This is a technical mathematical argument but can be paraphrased as follows: Define a function d as the identity function over all elements over the manifold M, excepting a small neighbourhood H belonging to M. Over H d comes to differ from identity by a smooth function. With use of this function d we can construct two mathematical models, where the second is generated by applying d to proper elements of the first, such that the two models are identical prior to the time t=0, where t is a time function created by a foliation of spacetime, but differ after t=0. These considerations show that, since substantivalism allows the construction of holes, that the universe must, on that view, be indeterministic. Which, Earman argues, is a case against substantivalism, as the case between determinism or indeterminism should be a question of physics, not of our commitment to substantivalism. The direction of time The problem of the direction of time arises directly from two contradictory facts. Firstly, the fundamental physical laws are time-reversal invariant; if a cinematographic film were taken of any process describable by means of the aforementioned laws and then played backwards, it would still portray a physically possible process. Secondly, our experience of time, at the macroscopic level, is not time-reversal invariant.[8] Glasses can fall and break, however shards of glass cannot reassemble and fly up onto tables. We have memories of the past, and none of the future. We feel we can't change the past but can influence the future. The causation solution One solution to this problem takes a metaphysical view, in which the direction of time follows from an asymmetry of causation. We know more about the past because the elements of the past are causes for the effect that is our perception. We feel we can't affect the past and can affect the future because we can't affect the past and can affect the future. There are two main objections to this view. First is the problem of distinguishing the cause from the effect in a non-arbitrary way. The use of causation in constructing a temporal ordering could easily become circular. The second problem with this view is its explanatory power. While the causation account, if successful, may account for some time-asymmetric phenomena like perception and action, it does not account for many others. However, asymmetry of causation can be observed in a non-arbitrary way which is not metaphysical in the case of a human hand dropping a cup of water which smashes into fragments on a hard floor, spilling the liquid. In this order, the causes of the resultant pattern of cup fragments and water spill is easily attributable in terms of the trajectory of the cup, irregularities in its structure, angle of its impact on the floor, etc. However, applying the same event in reverse, it is difficult to explain why the various pieces of the cup should fly up into the human hand and reassemble precisely into the shape of a cup, or why the water should position itself entirely within the cup. The causes of the resultant structure and shape of the cup and the encapsulation of the water by the hand within the cup are not easily attributable, as neither hand nor floor can achieve such formations of the cup or water. This asymmetry is perceivable on account of two features:- i) the relationship between the agent capacities of the human hand (i.e., what it is and is not capable of & what it is for) and non-animal agency (i.e., what floors are and are not capable of and what they are for) and ii) that the pieces of cup came to possess exactly the nature and number of those of a cup before assembling. In short, such asymmetry is attributable to the relationship between temporal direction on the one hand and the implications of form and functional capacity on the other. Philosophy of space and time The application of these ideas of form and functional capacity only dictates temporal direction in relation to complex scenarios involving specific, non-metaphysical agency which is not merely dependent on human perception of time. However, this last observation in itself is not sufficient to invalidate the implications of the example for the progressive nature of time in general. 83 The thermodynamics solution The second major family of solutions to this problem, and by far the one that has generated the most literature, finds the existence of the direction of time as relating to the nature of thermodynamics. The answer from classical thermodynamics states that while our basic physical theory is, in fact, time-reversal symmetric, thermodynamics is not. In particular, the second law of thermodynamics states that the net entropy of a closed system never decreases, and this explains why we often see glass breaking, but not coming back together. But in statistical mechanics things get more complicated. On one hand, statistical mechanics is far superior to classical thermodynamics, in that thermodynamic behavior, such as glass breaking, can be explained by the fundamental laws of physics paired with a statistical postulate. But statistical mechanics, unlike classical thermodynamics, is time-reversal symmetric. The second law of thermodynamics, as it arises in statistical mechanics, merely states that it is overwhelmingly likely that net entropy will increase, but it is not an absolute law. Current thermodynamic solutions to the problem of the direction of time aim to find some further fact, or feature of the laws of nature to account for this discrepancy. The laws solution A third type of solution to the problem of the direction of time, although much less represented, argues that the laws are not time-reversal symmetric. For example, certain processes in quantum mechanics, relating to the weak nuclear force, are not time-reversible, keeping in mind that when dealing with quantum mechanics time-reversibility comprises a more complex definition. But this type of solution is insufficient because 1) the time-asymmetric phenomena in quantum mechanics are too few to account for the uniformity of macroscopic time-asymmetry and 2) it relies on the assumption that quantum mechanics is the final or correct description of physical processes. One recent proponent of the laws solution is Tim Maudlin who argues that the fundamental laws of physics are laws of temporal evolution (see Maudlin [2007]). However, elsewhere Maudlin argues: "[the] passage of time is an intrinsic asymmetry in the temporal structure of the world... It is the asymmetry that grounds the distinction between sequences that runs from past to future and sequences which run from future to past" [ibid, 2010 edition, p. 108]. Thus it is arguably difficult to assess whether Maudlin is suggesting that the direction of time is a consequence of the laws or is itself primitive. The flow of time The problem of the flow of time, as it has been treated in analytic philosophy, owes its beginning to a paper written by J. M. E. McTaggart. In this paper McTaggart proposes two "temporal series". The first series, which means to account for our intuitions about temporal becoming, or the moving Now, is called the A-series. The A-series orders events according to their being in the past, present or future, simpliciter and in comparison to each other. The B-series eliminates all reference to the present, and the associated temporal modalities of past and future, and orders all events by the temporal relations earlier than and later than. McTaggart, in his paper The Unreality of Time, argues that time is unreal since a) the A-series is inconsistent and b) the B-series alone cannot account for the nature of time as the A-series describes an essential feature of it. Building from this framework, two camps of solution have been offered. The first, the A-theorist solution, takes becoming as the central feature of time, and tries to construct the B-series from the A-series by offering an account of how B-facts come to be out of A-facts. The second camp, the B-theorist solution, takes as decisive McTaggart's Philosophy of space and time arguments against the A-series and tries to construct the A-series out of the B-series, for example, by temporal indexicals. 84 Dualities Quantum field theory models have shown that it is possible for theories in two different spacetime backgrounds, like AdS/CFT or T-duality, to be equivalent. Presentism and Eternalism According to Presentism, time is an ordering of various realities. At a certain time some things exist and others do not. This is the only reality we can deal with and we cannot for example say that Homer exists because at the present time he does not. An Eternalist, on the other hand, holds that time is a dimension of reality on a par with the three spatial dimensions, and hence that all things—past present and future—can be said to be just as real as things in the present are. According to this theory, then, Homer really does exist, though we must still use special language when talking about somebody who exists at a distant time—just as we would use special language when talking about something a long way away (the very words near, far, above, below, over there, and such are directly comparable to phrases such as in the past, a minute ago, and so on). Endurantism and perdurantism The positions on the persistence of objects are somewhat similar. An endurantist holds that for an object to persist through time is for it to exist completely at different times (each instance of existence we can regard as somehow separate from previous and future instances, though still numerically identical with them). A perdurantist on the other hand holds that for a thing to exist through time is for it to exist as a continuous reality, and that when we consider the thing as a whole we must consider an aggregate of all its "temporal parts" or instances of existing. Endurantism is seen as the conventional view and flows out of our pre-philosophical ideas (when I talk to somebody I think I am talking to that person as a complete object, and not just a part of a cross-temporal being), but perduranists have attacked this position. (An example of a perdurantist is David Lewis.) One argument perdurantists use to state the superiority of their view is that perdurantism is able to take account of change in objects. The relations between these two questions mean that on the whole Presentists are also endurantists and Eternalists are also perdurantists (and vice versa), but this is not a necessary connection and it is possible to claim, for instance, that time's passage indicates a series of ordered realities, but that objects within these realities somehow exist outside of the reality as a whole, even though the realities as wholes are not related. However, such positions are rarely adopted. Notes [1] Dagobert Runes, Dictionary of Philosophy, p. 318 [2] Atuq Eusebio Manga Qespi, Instituto de lingüística y Cultura Amerindia de la Universidad de Valencia. Pacha: un concepto andino de espacio y tiempo (http:/ / revistas. ucm. es/ ghi/ 05566533/ articulos/ REAA9494110155A. PDF). Revísta española de Antropología Americana, 24, p. 155-189. Edit. Complutense, Madrid. 1994 [3] Stephen Hart, Peruvian Cultural Studies:Work in Progress (http:/ / www. ucl. ac. uk/ spanish-latinamerican/ Resources/ Peru_cult) [4] Paul Richard Steele, Catherine J. Allen, Handbook of Inca mythology, p. 86, (ISBN 1-57607-354-8) [5] St. Augustine, Confessions, Book 11. http:/ / ccat. sas. upenn. edu/ jod/ augustine/ Pusey/ book11 (Accessed 5/26/07). [6] Craig, William Lane (June 1979), "Whitrow and Popper on the Impossibility of an Infinite Past", The British Journal for the Philosophy of Science 30 (2): 165–170 [165–6], doi:10.1093/bjps/30.2.165 [7] Smith, A. Mark (2005), "The Alhacenian Account Of Spatial Perception And Its Epistemological Implications", Arabic Sciences and Philosophy (Cambridge University Press) 15 (02): 219–40, doi:10.1017/S0957423905000184 [8] Borchert, D.M. (2006) Encyclopedia of Philosophy, 2nd Ed. Vol. 9. MI: Cengage Learning. P. 468. • Zade, Allan (2011) Z-Theory and Its Applications. AuthorHouse. ISBN 978-1-4520-1893-5 Philosophy of space and time • Albert, David (2000) Time and Chance. Harvard Univ. Press. • Dainton, Barry (2010) Time and Space, Second Edition. McGill-Queens University Press. ISBN 978-0-7735-3747-7 • Earman, John (1989) World Enough and Space-Time. MIT Press. • Friedman, Michael (1983) Foundations of Space-Time Theories. Princeton Univ. Press. • Grunbaum, Adolf (1974) Philosophical Problems of Space and Time, 2nd ed. Boston Studies in the Philosophy of Science. Vol XII. D. Reidel Publishing • Horwich, Paul (1987) Asymmetries in Time. MIT Press. • Lucas, John Randolph, 1973. A Treatise on Time and Space. London: Methuen. • Mellor, D.H. (1998) Real Time II. Routledge. • Hans Reichenbach (1958) The Philosophy of Space and Time. Dover • Hans Reichenbach (1991) The Direction of Time. University of California Press. • Rochelle, Gerald (1998) Behind Time. Ashgate. • Lawrence Sklar (1976) Space, Time, and Spacetime. University of California Press. • Turetzky, Philip (1998) Time. Routledge. • Bas Van Fraassen, 1970. An Introduction to the Philosophy of Space and Time. Random House. • Gal-Or, Benjamin "Cosmology, Physics and Philosophy". Springer-Verlag, New York, 1981, 1983, 1987 ISBN 0-387-90581-2 85 External links • Stanford Encyclopedia of Philosophy: • " Time (http://plato.stanford.edu/entries/time/)" by Ned Markosian; • " Being and Becoming in Modern Physics (http://plato.stanford.edu/entries/spacetime-bebecome/)" by Steven Savitt; • " Absolute and Relational Theories of Space and Motion (http://plato.stanford.edu/entries/ spacetime-theories/)" by Nick Huggett and Carl Hoefer. Internet Encyclopedia of Philosophy: " Time (http://www.iep.utm.edu/t/time.htm)" by Bradley Dowden. Brown, C.L., 2006, " What is Space?" (http://www.unrestrictedphilosophy.com) A largely Wittgensteinian, approach towards a dissolution of the question: "What is space?" Rea, M. C., " Four Dimensionalism (http://www.nd.edu/~mrea/papers/Four Dimensionalism.pdf)" in The Oxford Handbook for Metaphysics. Oxford Univ. Press. Describes presentism and four-dimensionalism. CEITT - Time and Temporality Research Center. " Time and Temporality (http://ceitt.com/index-en.html)". http://www.exactspent.com/philosophy_of_space_and_time.htm and related subjects " Gods and the Universe in Buddhist Perspective (http://www.bps.lk/olib/wh/wh180-p.html), Essays on Buddhist Cosmology" by Francis Story. • • • • • • Eternalism 86 Eternalism Eternalism is a philosophical approach to the ontological nature of time, which takes the view that all points in time are equally "real", as opposed to the presentist idea that only the present is real.[1] Modern advocates often take inspiration from the way time is modeled as a dimension in the theory of relativity, giving time a similar ontology to that of space (although the basic idea dates back at least to McTaggart's B-Theory of time, first published in The Unreality of Time in 1908, only three years after the first paper on relativity). This would mean that time is just another dimension, that future events are "already there", and that there is no objective flow of time. It is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block",[2] as opposed to the view of the world as a three-dimensional space modulated by the passage of time. Problems with the flow of time Conventionally, time is divided into three distinct regions; the "past", the "present", and the "future". Using that representational model, the past is generally seen as being immutably fixed, and the future as undefined and nebulous. As time passes, the moment that was once the present becomes part of the past; and part of the future, in turn, becomes the new present. In this way time is said to pass, with a distinct present moment "moving" forward into the future and leaving the past behind. This view of time is given the name presentism by philosophers. This conventional model presents a number of difficult philosophical problems, and seems difficult to reconcile with currently accepted scientific theories such as the theory of relativity. Simultaneity Special relativity has shown that the concept of simultaneity is not universal: observers in different frames of reference can have different perceptions of whether a given pair of events happened at the same time or at different times, with there being no physical basis for preferring one frame's judgments over another's (though in a case where one event A happens in the past light cone of another event B, all frames will agree that A happened in the past of B). So, in special relativity there can be no physical basis for picking out a unique set of events that are all happening simultaneously in "the present". Uniqueness of a present moment There is no fundamental reason why a particular "present" should be more valid than any other; observers at any point in time will always consider themselves to be in the present. However, every moment of time has a "turn" at being a present moment in flow-of-time theories, so the situation ends up symmetrical even though there is still an ontological distinction between past, future, and present that is not itself symmetrical. Rate of flow The concept of "time passing" can be considered to be internally inconsistent, by asking "how much time goes by in an hour?" However, the question could be no different from "how much space is contained in a meter?" — all measurements being equally arbitrary. Eternalism 87 McTaggart's argument In The Unreality of Time, J. M. E. McTaggart divided time into an A-series and a B-series, with the A-series describing events in absolute tensed terms (past, present, and future) and the B-series describing events in terms of untensed temporal relations (before and after). He went on to argue that the A-series was logically incoherent and should be discarded, and that the B-series was insufficient for a proper understanding of time. He endorsed the C-series instead, which is a fixed, changeless (and therefore timeless), non-directional ordering of events. While McTaggart concluded that time is unreal, various philosophers and physicists have held that the remaining B-series is all that is needed for a complete theory of time, sometimes referred to as the B-Theory of time. The Eternalist alternative Eternalism addresses these various difficulties by considering all points in time to be equally valid frames of reference—or equally "real", if one prefers. It does not do away with the concept of past and future, but instead considers them directions rather than states of being; whether some point in time is in the future or past is entirely dependent on which frame of reference you are using as a basis for observing it. Since an observer at any given point in time can only remember events that are in the past relative to him, and not events that are in the future relative to him, the subjective illusion of the passage of time is maintained. The asymmetry of remembering past events but not future ones, as well as other irreversible events that progress in only one temporal direction (such as the increase in entropy) gives rise to the arrow of time. In the view suggested by Eternalism, there is no passage of time; the ticking of a clock measures durations between events much as the marks on a measuring tape measures distances between places. Eternalism has implications for the concept of free will, in that it proposes that future events are as immutably fixed and impossible to change as past events (see determinism). However as the human subject, and any free will they have, is also 'present' throughout time, during their life, they may be exercising free will in the 'future' as it were. Eternalism makes two assumptions, which are separable. One is that time is a full-fledged real dimension. The other is immutability. The latter is not a necessary consequence of the first. A universe in which random changes are possible may be indistinguishable from the many-worlds interpretation of quantum mechanics in which there are multiple "block times." Augustine of Hippo wrote that God is outside of time—that time exists only within the created universe. Many theologians agree. On this view, God would perceive something like a block universe, while time might appear differently to the finite beings contained within it. Philosophical objections Philosophers such as John Lucas argue that "The Block universe gives a deeply inadequate view of time. It fails to account for the passage of time, the pre-eminence of the present, the directedness of time and the difference between the future and the past"[3] The comment summarizes the main objections. In more detail, they are: Subjective sense of flow Whilst the idea that there is some objective sense in which time is flowing can be denied, the fact that conscious beings feel as though it is in some sense flowing cannot. However, if the flow of time didn't have an objective existence, then it is argued conscious beings would simultaneously experience all moments in their lives. A response is that since the brain presumably perceives time through information processing of external stimuli, not by extrasensory perception, and obeys the laws of causality, it is hard to see how the flow of time, whether it exists or not, could make any subjective difference: all conscious beings are built to perceive time as a chain of events, whether or not it occurs as such. Eternalism 88 Apparent differences between past, present and future Many of our common-sense attitudes treat the past, present and future differently. 1. We apparently fear death because we believe that we will no longer exist after we die. But if Eternalism is correct, death is just one of our temporal borders, and should be no more worrisome than birth. 2. You are about to go to the dentist, or you have already been. Commonsense says you should prefer to have been. But if Eternalism is correct, it shouldn't matter which situation you're in. 3. When some unpleasant experience is behind us, we feel glad that it is over. But if the Eternalism is correct, there is no such property as being over or no longer happening now—it continues to exist timelessly. Status of conscious observers Eternalists often appeal to the idea that the flow of time is a subjective illusion. However, Eternalism takes its inspiration from physics and needs to give a physical account of observers. One could, for instance, portray conscious observers as moving through the block universe, in some physically inexplicable way, in order to account for the subjective sense of a flow of time. But there is no need to do so to explain the subjective flow of time. Their opponents claim that the time-flow itself, as an objective phenomenon, is physically inexplicable, and that physics is simply misrepresenting time in treating it as a dimension. Determinism and indeterminism Previously, it was noted that people tend to have very different attitudes towards the past and the future. This might be explained by an underlying attitude that the future is not fixed, but can be changed, and is therefore worth worrying about.* If that is correct, the flow of time is perhaps less important to our intuitions than an open, undetermined, future. In other words, a flow-of-time theory with a strictly determined future (which nonetheless does not exist at the present) would not satisfy common-sense intuitions about time. If indeterminism can be removed from flow-of-time theories, can it be added to Eternalist theories? Surprisingly, the answer is a qualified "yes" in the form of multiverse theories, where multiple alternate futures exist in a fixed framework, but individual observers have no way of knowing which alternative, or "branch" they will end up in. [* Another, perhaps more compelling, explanation for this difference of attitudes would be that it really is worse to be having a bad experience than to have had one. A bad experience in the future is seen as one that has not been had, but will be. Unfortunately for Eternalism, though, it appears to lack the conceptual apparatus needed to explain 'having an experience', as distinct from having had, or being about to have, that experience. This is why most people find Eternalism strongly counter-intuitive.] Relation to physics Eternalism takes its inspiration from physics, especially the Rietdijk-Putnam argument, in which the relativity of simultaneity is used to show that each point in the universe can have a different set of events that are in its present moment. According to Presentism this is impossible because there is only one present moment that is instantaneous and encompasses the entire universe. Some philosophers also appeal to a specific theory which is "timeless" in a more radical sense than the rest of physics, the theory of quantum gravity. This theory is used, for instance, in Julian Barbour's theory of timelessness.[4] On the other hand, George Ellis argues that time is absent in cosmological theories because of the details they leave out.[5] Eternalism 89 Relation to Eastern body of thought In Buddhism, a special term Dharmadhatu is translated as 'total field of events and meanings' or 'field of all events and meanings.' Here the 'Block Universe' seems to be encompassing not only every possible event in the physical universe but also having a psychological component. See: Śūnyatā, section "Eternalism" In fiction Eternalism is a major theme in Kurt Vonnegut’s novel, Slaughterhouse-Five. The Tralfamadorians, an alien species in the novel, have a four-dimensional sight and can therefore see all points in time simultaneously. They explain that since all moments exist simultaneously, everyone is always alive. The hero, Billy Pilgrim, lives his life out of sequence, which, among other things, means that his point of death occurs at a random point in his life rather than at the end of it. Eternalism also appears in the comic book series Watchmen by Alan Moore. In one chapter, Dr. Manhattan explains how he perceives time. Since past, present, and future events all occur at the "same time" for him, he speaks about them all in the present tense. For example, he says "Forty years ago, cogs rain on Brooklyn" referring to an event in his youth when his father throws old watch parts out a window. His last line of the series is "Nothing ends, Adrian. Nothing ever ends." Footnotes and references [1] Kuipers, Theo A.F. (2007). General Philosophy of Science: Focal Issues (http:/ / books. google. com/ books?id=qUMuFaXjNjEC& lpg=PP1& pg=PA326#v=onepage& q& f=false). North Holland. p. 326. ISBN 978-0-444-51548-3. . [2] "Block" here refers to the idea of spacetime as something fixed and unchanging, like a solid block, and not to the actual geometric shape of space or spacetime. [3] John LucasThe Future p8 [4] "Platonia", Julian Barbour's time-skeptical website (http:/ / www. platonia. com) [5] Ellis (2006). "Physics in the Real Universe: Time and Spacetime". Gen.Rel.Grav. 38 (2006)-1824 38 (12): 1797–1824. arXiv:gr-qc/0605049. doi:10.1007/s10714-006-0332-z. External links • Biswas; Shaw; Modak (1999). "Time in Quantum Gravity". Int.J.Mod.Phys. D10 (2001) 595-606 10 (4): 595. arXiv:gr-qc/9906010. doi:10.1142/S0218271801001384. • Davies, Paul (September 2002). "That Mysterious Flow". Scientific American 287 (3): 40–45. doi:10.1038/scientificamerican0902-40. • Dorato,Mauro - Kant, Godel and Relativity (http://philsci-archive.pitt.edu/638/) • Markosian, Ned (2002). "Time: 8. The 3D/4D Controversy" (http://plato.stanford.edu/entries/time/#3D4Con). Stanford Encyclopedia of Philosophy. Retrieved 2006-12-20. • Nikolic, Hrvoje. "Block time: Why many physicists still don't accept it?" (http://fqxi.org/data/ essay-contest-files/Nikolic_FQXi_time.pdf). • Petkov, Vesselin (2005). "Is There an Alternative to the Block Universe View?" (http://Philsci-Archive.Pitt. EDU/archive/00002408/) (PDF). PhilSci Archive. Retrieved 2006-12-20. • Duda, J (2009). "Four-dimensional understanding of quantum mechanics". arXiv:0910.2724/. Determinism 90 Determinism Determinism is a philosophy stating that for everything that happens there are conditions such that, given them, nothing else could happen. Different versions of this theory depend upon various alleged connections, and interdependencies of things and events, asserting that these hold without exception. Deterministic theories throughout the history of philosophy have sprung from diverse motives and considerations, some of which overlap. They can be understood in relation to their historical significance and alternative theories. Some forms of determinism can be tested empirically with ideas stemming from physics and the philosophy of physics. The opposite of determinism is some kind of indeterminism (otherwise called nondeterminism). Determinism is often contrasted with free will. Determinism is often taken to mean simply causal determinism: an idea known in physics as cause-and-effect. It is the concept that events within a given paradigm are bound by causality in such a way that any state (of an object or event) is completely determined by prior states. This can be distinguished from other varieties of determinism mentioned below. Other debates often concern the scope of determined systems, with some maintaining that the entire universe (or multiverse) is a single determinate system and others identifying other more limited determinate systems. Within numerous historical debates, many varieties and philosophical positions on the subject of determinism exist. This includes debates concerning human action and free will, where opinions might be sorted as compatibilistic and incompatibilistic. Determinism should not be confused with self-determination of human actions by reasons, motives, and desires. Determinism rarely requires that perfect prediction be practically possible - only prediction in theory. Varieties Below are some of the more common viewpoints meant by, or confused with "Determinism". Causal (or Nomological) determinism[1] and related Predeterminism propose that there is an unbroken chain of prior occurrences stretching back to the origin of the universe. The relation between events may not be specified, nor the origin of that universe. Causal determinists believe that there is nothing uncaused or self-caused. Quantum mechanics poses a serious challenge to this view (see 'Arguments' section below). Causal determinism is sometimes illustrated by the thought experiment of Laplace's demon. Historical determinism (a sort of path dependence) can also be synonymous with causal determinism. Necessitarianism is very related to the causal determinism described above. It is a metaphysical principle that denies all mere possibility; there is exactly one way for the world to be. Leucippus claimed there were no uncaused events, and that everything occurs for a reason and by necessity.[2] Many philosophical theories of determinism frame themselves with the idea that reality follows a sort of predetermined path Fatalism is normally distinguished from "determinism".[3] Fatalism is the idea that everything is fated to happen, so that humans have no control over their future. Notice that fate has arbitrary power. Fate also need not follow any causal or otherwise deterministic laws.[1] Types of Fatalism include Theological determinism and the idea of predestination, where there is a God who determines all that humans will do. This may be accomplished either by knowing their actions in advance, via some form of omniscience[4] or by decreeing their actions in advance.[5] Logical determinism or Determinateness is the notion that all propositions, whether about the past, present, or future, are either true or false. Note that one can support Causal Determinism without necessarily supporting Logical Determinism and vice versa (depending on one's views on the nature of time, but also randomness). The problem of free will is especially salient now with Logical Determinism: how can choices be free, given that propositions about the future already have a truth value in the present (i.e. it is already determined as either true or false)? This is Determinism referred to as the problem of future contingents. Often synonymous with Logical Determinism are the ideas behind Spatio-temporal Determinism or Eternalism: the view of special relativity. J. J. C. Smart, a proponent of this view, uses the term "tenselessness" to describe the simultaneous existence of past, present, and future. In physics, the "block universe" of Hermann Minkowski and Albert Einstein assumes that time is a fourth dimension (like the three spatial dimensions). In other words, all the other parts of time are real, like the city blocks up and down a street, although the order in which they appear depends on the driver (see Rietdijk–Putnam argument). Adequate determinism is the idea that quantum indeterminacy can be ignored fact that, even without a full for most macroscopic events. This is because of quantum decoherence. Random understanding of microscopic physics, we can predict the distribution of 1000 quantum events "average out" in the limit of large numbers of particles (where coin tosses the laws of quantum mechanics asymptotically approach the laws of classical mechanics).[6] Stephen Hawking explains a similar idea: he says that the microscopic world of quantum mechanics is one of determined probabilities. That is, quantum effects rarely alter the predictions of classical mechanics, which are quite accurate (albeit still not perfectly certain) at larger scales.[7] Something as large as an animal cell, then, would be "adequately determined" (even in light of quantum indeterminacy). Adequate determinism focuses on the 91 Determined by nature or nurture Although some of the above forms of determinism concern human behaviors and cognition, others frame themselves as an answer to the Nature or Nurture debate. They will suggest that one factor will entirely determine behavior. As scientific understanding has grown, however, the strongest versions of these theories have been widely rejected as a single cause fallacy.[8] In other words, the modern deterministic theories attempt to explain how the interaction of both nature and nurture is entirely predictable. The concept of heritability has been helpful to make this distinction. Biological determinism, sometimes called Genetic determinism, is the idea that each of our behaviors, beliefs, and desires are fixed by our genetic nature. Nature and nurture interact in humans. A scientist looking at a sculpture after some time does not ask whether we are seeing the effects of the starting materials OR environmental influences. Behaviorism is the idea that all behavior can be traced to specific causes—either environmental or reflexive. This Nurture-focused determinism was developed by John B. Watson and B. F. Skinner. Cultural determinism or social determinism is the nurture-focused theory that it is the culture in which we are raised that determines who we are. Environmental determinism is also known as climatic or geographical determinism. It holds the view that the physical environment, rather than social conditions, determines culture. Supporters often also support Behavioral determinism. Key proponents of this notion have included Ellen Churchill Semple, Ellsworth Huntington, Thomas Griffith Taylor and possibly Jared Diamond, although his status as an environmental determinist is debated.[9] Determinism 92 Factor priority Other 'deterministic' theories actually seek only to highlight the importance of a particular factor in predicting the future. These theories often use the factor as a sort of guide or constraint on the future. They need not suppose that complete knowledge of that one factor would allow us to make perfect predictions. Psychological determinism can mean that humans must act according to reason, but it can also be synonymous with some sort of Psychological egoism. The latter is the view that humans will always act according to their perceived best interest. Linguistic determinism claims that our language determines (at least limits) the things we can think and say and thus know. The Sapir–Whorf hypothesis argues that individuals experience the world based on the grammatical structures they habitually use. Economic determinism is the theory which attributes primacy to the economic structure over politics in the development of human history. It is associated with the dialectical materialism of Karl Marx. A technological determinist might suggest that technology, like the mobile phone, is the greatest factor shaping human civilization. Technological determinism is a reductionist theory that presumes that a society's technology drives the development of its social structure and cultural values. Media determinism, a subset of technological determinism, is a philosophical and sociological position which posits the power of the media to impact society. Two leading media determinists are the Canadian scholars Harold Innis and Marshall McLuhan. Free will and determinism Philosophers have argued that either Determinism is true or Indeterminism is true, but also that Free Will either exists or it does not. This creates four possible positions. Compatibilism refers to the view that free will is, in some sense, compatible with Determinism. The three Incompatibilist positions, on the other hand, deny this possibility. They instead suggest there is a dichotomy between determinism and free will (only one can be true). To the Incompatibilists, one must choose either free will or Determinism, and maybe even reject both. The result is one of three positions: A table showing the different positions related to free will and determinism • Metaphysical Libertarianism (free will, and no determinism) a position not to be confused with the more commonly cited Political Libertarianism. • Hard Determinism (Determinism, and no free will). • Hard Indeterminism (No Determinism, and no free will either). Thus, although many Determinists are Compatibilists, calling someone a 'Determinist' is often done to denote the 'Hard Determinist' position. The Standard argument against free will, according to philosopher J. J. C. Smart focuses on the implications of Determinism for 'free will'.[10] He suggests that, if determinism is true, all our actions are predicted and we are not free; if determinism is false, our actions are random and still we do not seem free. Determinism In his book, The Moral Landscape, author and neuroscientist Sam Harris mentions some ways that determinism and modern scientific understanding might challenge the idea of a contra-causal free will. He offers one thought experiment where a mad scientist represents determinism. In Harris' example, the mad scientist uses a machine to control all the desires, and thus all the behaviour, of a particular human. Harris believes that it is no longer as tempting, in this case, to say the victim has "free will". Harris says nothing changes if the machine controls desires at random - the victim still seems to lack free will. Harris then argues that we are also the victims of such unpredictable desires (but due to the unconscious machinations of our brain, rather than those of a mad scientist). This implicitly assumes a philosophy of materialism, which could be disputed along with Harris's hard determinism. Based on this introspection, he writes "This discloses the real mystery of free will: if our experience is compatible with its utter absence, how can we say that we see any evidence for it in the first place?"[11] adding that "Whether they are predictable or not, we do not cause our causes."[12] That is, he believes there is compelling evidence of absence of free will. Research has found that reducing a person's belief in free will can make them less helpful and more aggressive.[13] This could occur because the individual's sense of Self-efficacy suffers. 93 Determinism and mind Some determinists argue that materialism does not present a complete understanding of the universe, because while it can describe determinate interactions among material things, it ignores the minds or souls of conscious beings. A number of positions can be delineated: 1. Immaterial souls are all that exist (Idealism). 2. Immaterial souls exist and exert a non-deterministic causal influence on bodies. (Traditional free-will, interactionist dualism).[14][15] 3. Immaterial souls exist, but are part of deterministic framework. 4. Immaterial souls exist, but exert no causal influence, free or determined (epiphenomenalism, occasionalism) 5. Immaterial souls do not exist — there is no mind-body dichotomy, and there is a Materialistic explanation for intuitions to the contrary. Another topic of debate is the implication that Determinism has on morality. Hard determinism (a belief in determinism, and not free will) is particularly criticized for seeming to make traditional moral judgments impossible. Some philosophers, however, find this an acceptable conclusion. Philosopher and incompatibilist Peter van Inwagen introduces this thesis as such: Argument that Free Will is Required for Moral Judgments 1. 2. 3. 4. 5. The moral judgment that you shouldn’t have done X implies that you should have done something else instead That you should have done something else instead implies that there was something else for you to do That there was something else for you to do implies that you could have done something else That you could have done something else implies that you have free will If you don’t have free will to have done other than X we cannot make the moral judgment that you shouldn’t have done X.[16] Determinism 94 History Some of the main philosophers who have dealt with this issue are Marcus Aurelius, Omar Khayyám, Thomas Hobbes, Baruch Spinoza, Gottfried Leibniz, David Hume, Baron d'Holbach (Paul Heinrich Dietrich), Pierre-Simon Laplace, Arthur Schopenhauer, William James, Friedrich Nietzsche, Albert Einstein, Niels Bohr, and, more recently, John Searle, Ted Honderich, and Daniel Dennett. Mecca Chiesa notes that the probabilistic or selectionistic determinism of B.F. Skinner comprised a wholly separate conception of determinism that was not mechanistic at all. Mechanistic determinism assumes that every event has an unbroken chain of prior occurrences, but a selectionistic or probabilistic model does not.[17][18] Eastern tradition The idea that the entire universe is a deterministic system has been articulated in both Eastern and non-Eastern religion, philosophy, and literature. In I Ching and Philosophical Taoism, the ebb and flow of favorable and unfavorable conditions suggests the path of least resistance is effortless (see wu wei). In the philosophical schools of India, the concept of precise and continual effect of laws of Karma on the existence of all sentient beings is analogous to western deterministic concept. Karma is the concept of "action" or "deed" in Indian religions. It is understood as that which causes the entire cycle of cause and effect (i.e., the cycle called saṃsāra) originating in ancient India and treated in Hindu, Jain, Sikh and Buddhist philosophies. Karma is considered predetermined and deterministic in the universe, with the exception of a human, who through free will can influence the future. See Karma in Hinduism. Western tradition The notion of determinism was introduced into the West through the adoption of the Abrahamic religions. The Christian concept of predestination led to the first Western debates over determinism, an issue that is known in theology as the paradox of free will. The Jewish philosopher Moses Maimonides said of the determinstic implications of an omniscient god:[19] "Does God know or does He not know that a certain individual will be good or bad? If thou sayest 'He knows', then it necessarily follows that [that] man is compelled to act as God knew beforehand he would act, otherwise God's knowledge would be imperfect.…"[20] Determinism in the West is often associated with Newtonian physics, which depicts the physical matter of the universe as operating according to a set of fixed, knowable laws. The "billiard ball" hypothesis, a product of Newtonian physics, argues that once the initial conditions of the universe have been established, the rest of the history of the universe follows inevitably. If it were actually possible to have complete knowledge of physical matter and all of the laws governing that matter at any one time, then it would be theoretically possible to compute the time and place of every event that will ever occur (Laplace's demon). In this sense, the basic particles of the universe operate in the same fashion as the rolling balls on a billiard table, moving and striking each other in predictable ways to produce predictable results. Whether or not it is all-encompassing in so doing, Newtonian mechanics deals only with caused events, e.g.: If an object begins in a known position and is hit dead on by an object with some known velocity, then it will be pushed straight toward another predictable point. If it goes somewhere else, the Newtonians argue, one must question one's measurements of the original position of the object, the exact direction of the striking object, gravitational or other fields that were inadvertently ignored, etc. Then, they maintain, repeated experiments and improvements in accuracy will always bring one's observations closer to the theoretically predicted results. When dealing with situations on an ordinary human scale, Newtonian physics has been so enormously successful that it has no competition. But it fails spectacularly as velocities become some substantial fraction of the speed of light and when interactions at the atomic scale are studied. Before the discovery of quantum effects and other challenges to Newtonian physics, "uncertainty" Determinism was always a term that applied to the accuracy of human knowledge about causes and effects, and not to the causes and effects themselves. Newtonian mechanics as well as any following physical theories are results of observations and experiments, and so they describe "how it all works" within a tolerance. However, old western scientists believed if there are any logical connections found between an observed cause and effect, there must be also some absolute natural laws behind. Belief in perfect natural laws driving everything, instead of just describing what we should expect, led to searching for a set of universal simple laws that rule the world. This movement significantly encouraged deterministic views in western philosophy.[21] 95 Modern perspectives Cause and effect Since the early twentieth century when astronomer Edwin Hubble first hypothesized that redshift shows the universe is expanding, prevailing scientific opinion has been that the current state of the universe is the result of a process described by the Big Bang. Many theists and deists claim that it therefore has a finite age, pointing out that something cannot come from nothing (the definition of nothing, however, is problematic at the most arcane level of physics). The big bang does not describe from where the compressed universe came; instead it leaves the question open. Different astrophysicists hold different views about precisely how the universe originated (Cosmogony). The philosophical argument here would be that the big bang triggered every single action, and possibly mental thought, through the system of cause and effect. Generative processes Although it was once thought by scientists that any indeterminism in quantum mechanics occurred at too small a scale to influence biological or neurological systems, there is evidence that nervous systems are indeterministic. It is unclear what implications this has for free will given various possible reactions to the standard problem in the first place.[22] Certainly not all biologists grant determinism: Christof Koch argues against it, and in favour of libertarian free will, by making arguments based on Generative processes (emergence).[23] Other proponents of emergentist or generative philosophy, cognitive sciences and evolutionary psychology, argue that determinism is true.[24][25][26][27] They suggest instead that an illusion of free will is experienced due to the generation of infinite behaviour from the interaction of finite-deterministic set of rules and parameters. Thus the unpredictability of the emerging behaviour from deterministic processes leads to a perception of free will, even though free will as an ontological entity does not exist.[24][25][26][27] Certain experiments looking at the Neuroscience of free will can be said to support this possibility. As an illustration, the strategy board-games chess and Go have rigorous rules in which no information (such as cards' face-values) is hidden from either player and no random events (such as dice-rolling) happen within the game. Yet, chess and especially Go with its extremely simple deterministic rules, can still have an extremely large number of unpredictable moves. By this analogy, it is suggested, the experience of free will emerges from the interaction of finite rules and deterministic In Conway's Game of Life, the parameters that generate nearly infinite and practically unpredictable behaviour. In interaction of just 4 simple rules theory, if all these events were accounted for, and there were a known way to creates patterns that seem evaluate these events, the seemingly unpredictable behaviour would become somehow "alive". [24][25][26][27] predictable. Another hands-on example of generative processes is John Horton Conway's playable Game of Life.[28] Nassim Taleb is wary of such models, and coined the term "Ludic fallacy". Determinism 96 Mathematical models Many mathematical models of physical systems are deterministic. This is true of most models involving differential equations (notably, those measuring rate of change over time). Mathematical models that are not deterministic because they involve randomness are called stochastic. Because of sensitive dependence on initial conditions, some deterministic models may appear to behave non-deterministically; in such cases, a deterministic interpretation of the model may not be useful due to numerical instability and a finite amount of precision in measurement. Such considerations can motivate the consideration of a stochastic model even though the underlying system is governed by deterministic equations.[29][30][31] Quantum mechanics and classical physics Day-to-day physics Since the beginning of the 20th century, quantum mechanics - the physics of the extremely small - has revealed previously concealed aspects of events. Before that, Newtonian physics - the physics of everyday life - dominated. Taken in isolation (rather than as an approximation to quantum mechanics), Newtonian physics depicts a universe in which objects move in perfectly determined ways. At the scale where humans exist and interact with the universe, Newtonian mechanics remain useful, and make relatively accurate predictions (e.g. calculating the trajectory of a bullet). In theory, absolute knowledge of the forces accelerating a bullet could produce an absolutely accurate prediction of its path. Modern quantum mechanics, however, casts reasonable doubt on this main thesis of determinism. Relevant is the fact that certainty is never absolute in practice (and not just because of David Hume's problem of induction). The equations of Newtonian mechanics can exhibit sensitive dependence on initial conditions. This is an example of the Butterfly effect, which is one of the subjects of chaos theory. The idea is that something even as small as a butterfly could cause a chain reaction leading to a hurricane years later. Consequently, even a very small error in knowledge of initial conditions can result in arbitrarily large deviations from predicted behavior. Chaos theory thus explains why it may be practically impossible to predict real life, whether determinism is true or false. On the other hand, the issue may not be so much about human abilities to predict or attain certainty as much as it is the nature of reality itself. For that, a closer, scientific look at nature is necessary. Quantum world The quantum physics used at atomic scales works differently in many ways from Newtonian physics. Indeed, some findings are unintuitive and difficult to believe. Physicist Aaron D. O'Connell explains that understanding our universe, at such small scales as atoms, requires a different logic than day to day life. O'Connell does not deny that it is all interconnected: the scale of human existence ultimately does emerge from the quantum scale. O'Connell argues that we must simply use different models and constructs when dealing with the quantum world.[32] As a result, these branches of physics are sometimes misrepresented or misunderstood, making some claims seem more scientific than they are (e.g. The Secret (book)[33] or What The Bleep Do We Know!?[34]). Quantum mechanics remain, however, the product of careful application of the scientific method, logic and empiricism. For instance, Werner Heisenberg's carefully formulated Uncertainty principle explains why the paths of objects can only be predicted in a probabilistic way (the reasoning is nuanced, involving, among other things, the observer effect). Determinism 97 This is where statistical mechanics come into play, and where physicists begin to require rather unintuitive mental models: A particle's path simply cannot be exactly specified in its full quantum description. "Path" is a classical, practical attribute in our every day life, but one which quantum particles do not meaningfully possess. The probabilities discovered in quantum mechanics do nevertheless arise from measurement (of the perceived path of the particle). As Stephen Hawking explains, the result is not traditional determinism, but rather determined probabilities.[35] In some cases, a quantum particle may indeed trace an exact path, and the probability of finding the particles in that path is one. In fact, as far as prediction goes, the quantum development is at least as predictable as the classical motion, but the key is that it describes wave functions that cannot be easily expressed in ordinary language. As far as the thesis of determinism is concerned, these probabilities, at least, are quite determined. These findings from quantum mechanics have found many applications, and allow us to build transistors and lasers. Put another way: personal computers, Blu-ray players and the internet all work because humankind discovered the determined probabilities of the quantum world.[] None of that should be taken to imply that other aspects of quantum mechanics are not still up for debate. On the topic of predictable probabilities, the double-slit experiments are a popular example. Photons are fired one-by-one through a double-slit apparatus at a distant screen. Curiously, they do not arrive at any single point, nor even the two points lined up with the slits (the way you might expect of bullets fired by a fixed gun at a Although it is not possible to distant target). Instead, the light arrives in varying concentrations at widely predict the trajectory of any one separated points, and the distribution of its collisions with the target can be particle, they all obey determined calculated reliably. In that sense the behavior of light in this apparatus is probabilities which do permit deterministic, but there is no way to predict where in the resulting interference some prediction. pattern any individual photon will make its contribution (although, there may be ways to use weak measurement to acquire more information without violating the Uncertainty principle). Some (including Albert Einstein) argue that our inability to predict any more than probabilities is simply due to ignorance.[36] The idea is that, beyond the conditions and laws we can observe or deduce, there are also hidden factors or "hidden variables" that determine absolutely in which order photons reach the detector screen. They argue that the course of the universe is absolutely determined, but that humans are screened from knowledge of the determinative factors. So, they say, it only appears that things proceed in a merely probabilistically determinative way. In actuality, they proceed in an absolutely deterministic way. These matters continue to be subject to some dispute. A critical finding was that quantum mechanics can make statistical predictions which would be violated if local hidden variables really existed. There have been a number of experiments to verify such predictions, and so far they do not appear to be violated. This would suggest there are no hidden variables, although many physicists believe better experiments are needed to conclusively settle the issue (see also Bell test experiments). Furthermore, it is possible to augment quantum mechanics with non-local hidden variables to achieve a deterministic theory that is in agreement with experiment. An example is the Bohm interpretation of quantum mechanics. This debate is relevant because it is easy to imagine specific situations in which the arrival of an electron at a screen at a certain point and time would trigger one event, whereas its arrival at another point would trigger an entirely different event (e.g. see Schrödinger's cat - a thought experiment used as part of a deeper debate). Thus, the world of quantum physics casts reasonable doubt on the traditional determinism that is so intuitive in classical, Newtonian physics. At the small scales, our reality does not seem to be absolutely determined. Yet this was precisely the subject of the famous Bohr–Einstein debates between Einstein and Niels Bohr. There is still no Determinism consensus. In the meantime, humans continue to benefit from the fact that reality obeys determined probabilities at the quantum scale. Such adequate determinism (see Varieties, above) is the reason that Stephen Hawking calls Libertarian free will "just an illusion".[35] Compatibilistic free will (which is deterministic) may be the only kind of "free will" that can exist. However, Daniel Dennett, in his book Elbow Room, says that this means we have the only kind of free will "worth wanting". For even more discussion, see Free will. Other matters of quantum determinism All uranium found on earth is thought to have been synthesized during a supernova explosion that occurred roughly 5 billion years ago. Even before the laws of quantum mechanics were developed to their present level, the radioactivity of such elements has posed a challenge to determinism due to its unpredictability. One gram of uranium-238, a commonly occurring radioactive substance, contains some 2.5 x 1021 atoms. Each of these atoms are identical and indistinguishable according to all tests known to modern science. Yet about 12600 times a second, one of the atoms in that gram will Chaotic radioactivity is the next decay, giving off an alpha particle. The challenge for determinism is to explanatory challenge for physicists explain why and when decay occurs, since it does not seem to depend on supporting determinism external stimulus. Indeed, no extant theory of physics makes testable predictions of exactly when any given atom will decay. At best scientists can discover determined probabilities in the form of the element's half life. The time dependent Schrödinger equation gives the first time derivative of the quantum state. That is, it explicitly and uniquely predicts the development of the wave function with time. 98 So if the wave function itself is reality (rather than probability of classical coordinates), quantum mechanics can be said to be deterministic. Since we have no practical way of knowing the exact magnitudes, and especially the phases, in a full quantum mechanical description of the causes of an observable event, this turns out to be philosophically similar to the "hidden variable" doctrine. According to some, quantum mechanics is more strongly ordered than Classical Mechanics, because while Classical Mechanics is chaotic (appears random, specifically due to minor details - perhaps at a smaller scale), quantum mechanics is not. For example, the classical problem of three bodies under a force such as gravity is not integrable, while the quantum mechanical three body problem is tractable and integrable, using the Faddeev Equations. This does not mean that quantum mechanics describes the world as more deterministic, unless one already considers the wave function to be the true reality. Even so, this does not get rid of the probabilities, because we can't do anything without using classical descriptions, but it assigns the probabilities to the classical approximation, rather than to the quantum reality. Asserting that quantum mechanics is deterministic by treating the wave function itself as reality implies a single wave function for the entire universe, starting at the origin of the universe. Such a "wave function of everything" would carry the probabilities of not just the world we know, but every other possible world that could have evolved. For example, large voids in the distributions of galaxies are believed by many cosmologists to have originated in quantum fluctuations during the big bang. (See cosmic inflation and primordial fluctuations.) If so, the "wave function of everything" would carry the possibility that the region where our Milky Way galaxy is located could have been a void and the Earth never existed at all. (See large-scale structure of the cosmos.) Determinism 99 Notes [1] [2] [3] [4] [5] [6] http:/ / plato. stanford. edu/ entries/ incompatibilism-arguments/ Leucippus, Fragment 569 - from Fr. 2 Actius I, 25, 4 SEP, Causal Determinism (http:/ / plato. stanford. edu/ entries/ determinism-causal/ ) Fischer, John Martin (1989) God, Foreknowledge and Freedom. Stanford, CA: Stanford University Press. ISBN 1-55786-857-3 Watt, Montgomery (1948) Free-Will and Predestination in Early Islam. London:Luzac & Co. The Information Philosopher website (http:/ / www. informationphilosopher. com/ freedom/ adequate_determinism. html), "Adequate Determinism", from the site: "We are happy to agree with scientists and philosophers who feel that quantum effects are for the most part negligible in the macroscopic world. We particularly agree that they are negligible when considering the causally determined will and the causally determined actions set in motion by decisions of that will." [7] Grand Design (2010), page 32: "the molecular basis of biology shows that biological processes are governed by the laws of physics and chemistry and therefore are as determined as the orbits of the planets.", and page 72: "Quantum physics might seem to undermine the idea that nature is governed by laws, but that is not the case. Instead it leads us to accept a new form of determinism: Given the state of a system at some time, the laws of nature determine the probabilities of various futures and pasts rather than determining the future and past with certainty." (emphasis in original, discussing a Many worlds interpretation) [8] de Melo-Martín I (2005). "Firing up the nature/nurture controversy: bioethics and genetic determinism". J Med Ethics 31 (9): 526–30. doi:10.1136/jme.2004.008417. PMC 1734214. PMID 16131554. [9] Andrew, Sluyter. "Neo-Environmental Determinism, Intellectual Damage Control, and Nature/Society Science". Antipode 4 (35). [10] J. J. C. Smart, "Free-Will, Praise and Blame,"Mind, July 1961, p.293-4. [11] Sam Harris, The Moral Landscape (2010), pg.216, note102 [12] Sam Harris, The Moral Landscape (2010), pg.217, note109 [13] Baumeister RF, Masicampo EJ, Dewall CN. (2009). Prosocial benefits of feeling free: disbelief in free will increases aggression and reduces helpfulness. Pers Soc Psychol Bull. 35(2):260-8. PMID 19141628 doi:10.1177/0146167208327217 [14] By 'soul' in the context of (1) is meant an autonomous immaterial agent that has the power to control the body but not to be controlled by the body (this theory of determinism thus conceives of conscious agents in dualistic terms). Therefore the soul stands to the activities of the individual agent's body as does the creator of the universe to the universe. The creator of the universe put in motion a deterministic system of material entities that would, if left to themselves, carry out the chain of events determined by ordinary causation. But the creator also provided for souls that could exert a causal force analogous to the primordial causal force and alter outcomes in the physical universe via the acts of their bodies. Thus, it emerges that no events in the physical universe are uncaused. Some are caused entirely by the original creative act and the way it plays itself out through time, and some are caused by the acts of created souls. But those created souls were not created by means of physical processes involving ordinary causation. They are another order of being entirely, gifted with the power to modify the original creation. However, determinism is not necessarily limited to matter; it can encompass energy as well. The question of how these immaterial entities can act upon material entities is deeply involved in what is generally known as the mind-body problem. It is a significant problem which philosophers have not reached agreement about [15] Free Will (Stanford Encyclopedia of Philosophy) (http:/ / plato. stanford. edu/ entries/ freewill/ ) [16] van Inwagen, Peter (2009). The Powers of Rational Beings: Freedom of the Will. Oxford. [17] Chiesa, Mecca (2004) Radical Behaviorism: The Philosophy & The Science. [18] Ringen, J. D. (1993). Adaptation, teleology, and selection by consequences. Journal of Applied Behavior Analysis. 60,3–15. (http:/ / www. pubmedcentral. nih. gov/ articlerender. fcgi?artid=1322142) [19] Though Moses Maimonides was not arguing against the existence of God, but rather for the incompatibility between the full exercise by God of his omniscience and genuine human free will, his argument is considered by some as affected by Modal Fallacy. See, in particular, the article by Prof. Norman Swartz for Internet Encyclopedia of Philosophy, Foreknowledge and Free Will (http:/ / www. iep. utm. edu/ f/ foreknow. htm) and specifically Section 6: The Modal Fallacy (http:/ / www. iep. utm. edu/ f/ foreknow. htm#section6) [20] The Eight Chapters of Maimonides on Ethics (Semonah Perakhim), edited, annotated, and translated with an Introduction by Joseph I. Gorfinkle, pp. 99–100. (New York: AMS Press), 1966. [21] Swartz, Norman (2003) The Concept of Physical Law / Chapter 10: Free Will and Determinism ( http:/ / www. sfu. ca/ philosophy/ physical-law/ ) [22] Lewis, E.R.; MacGregor, R.J. (2006). "On Indeterminism, Chaos, and Small Number Particle Systems in the Brain" (http:/ / www. eecs. berkeley. edu/ ~lewis/ LewisMacGregor. pdf). Journal of Integrative Neuroscience 5 (2): 223–247. doi:10.1142/S0219635206001112. . [23] Koch, Christof (September 2009). "Free Will, Physics, Biology and the Brain". In Murphy, Nancy; Ellis, George; O'Connor, Timothy. Downward Causation and the Neurobiology of Free Will. New York, USA: Springer. ISBN 978-3-642-03204-2. [24] Kenrick, D. T., Li, N. P., & Butner, J. (2003) "Dynamical evolutionary psychology: Individual decision rules and emergent social norms," Psychological Review 110: 3–28. [25] Nowak A., Vallacher R.R., Tesser A., Borkowski W., (2000) "Society of Self: The emergence of collective properties in self-structure," Psychological Review 107. [26] Epstein J.M. and Axtell R. (1996) Growing Artificial Societies - Social Science from the Bottom. Cambridge MA, MIT Press. [27] Epstein J.M. (1999) Agent Based Models and Generative Social Science. Complexity, IV (5) [28] John Conway's Game of Life (http:/ / www. bitstorm. org/ gameoflife/ ) Determinism [29] Werndl, Charlotte (2009). Are Deterministic Descriptions and Indeterministic Descriptions Observationally Equivalent? (http:/ / dx. doi. org/ 10. 1016/ j. shpsb. 2009. 06. 004). Studies in History and Philosophy of Modern Physics 40, 232-242. [30] Werndl, Charlotte (2009). Deterministic Versus Indeterministic Descriptions: Not That Different After All? (http:/ / philsci-archive. pitt. edu/ archive/ 00004775/ ). In: A. Hieke and H. Leitgeb (eds), Reduction, Abstraction, Analysis, Proceedings of the 31st International Ludwig Wittgenstein-Symposium. Ontos, 63-78. [31] J. Glimm, D. Sharp, Stochastic Differential Equations: Selected Applications in Continuum Physics, in: R.A. Carmona, B. Rozovskii (ed.) Stochastic Partial Differential Equations: Six Perspectives, American Mathematical Society (October 1998) (ISBN 0-8218-0806-0). [32] "Struggling with quantum logic: Q&A with Aaron O'Connell (http:/ / blog. ted. com/ 2011/ 06/ 02/ struggling-with-quantum-logic-qa-with-aaron-oconnell/ ?utm_content=awesm-bookmarklet& utm_medium=on. ted. com-static& utm_source=facebook. com) [33] Scientific American, "What is Quantum Mechanics Good For?" (http:/ / www. scientificamerican. com/ article. cfm?id=everyday-quantum-physics) [34] Mone, Gregory (October 2004). "Cult Science Dressing Up Mysticism as Quantum Physics" (http:/ / www. popsci. com/ scitech/ article/ 2004-10/ cult-science). Popular Science. . Retrieved 2008-02-17. [35] Grand Design (2010), page 32: "the molecular basis of biology shows that biological processes are governed by the laws of physics and chemistry and therefore are as determined as the orbits of the planets...so it seems that we are no more than biological machines and that free will is just an illusion", and page 72: "Quantum physics might seem to undermine the idea that nature is governed by laws, but that is not the case. Instead it leads us to accept a new form of determinism: Given the state of a system at some time, the laws of nature determine the probabilities of various futures and pasts rather than determining the future and past with certainty." (discussing a Many worlds interpretation) [36] Albert Einstein insisted that, "I am convinced God does not play dice" in a private letter to Max Born, 4 December 1926, Albert Einstein Archives (http:/ / www. alberteinstein. info/ db/ ViewDetails. do?DocumentID=38009) reel 8, item 180 100 References and bibliography • Daniel Dennett (2003) Freedom Evolves. Viking Penguin. • John Earman (2007) "Aspects of Determinism in Modern Physics" in Butterfield, J., and Earman, J., eds., Philosophy of Physics, Part B. North Holland: 1369-1434. • George Ellis (2005) "Physics and the Real World," Physics Today. • Epstein J.M. (1999) "Agent Based Models and Generative Social Science," Complexity IV (5). • -------- and Axtell R. (1996) Growing Artificial Societies — Social Science from the Bottom. MIT Press. • Kenrick, D. T., Li, N. P., & Butner, J. (2003) "Dynamical evolutionary psychology: Individual decision rules and emergent social norms," Psychological Review 110: 3–28. • Albert Messiah, Quantum Mechanics, English translation by G. M. Temmer of Mécanique Quantique, 1966, John Wiley and Sons, vol. I, chapter IV, section III. • Nowak A., Vallacher R.R., Tesser A., Borkowski W., (2000) "Society of Self: The emergence of collective properties in self-structure," Psychological Review 107. • Schimbera, Jürgen / Schimbera, Peter: Determination des Indeterminierten. Kritische Anmerkungen zur Determinismus- und Freiheitskontroverse. Verlag Dr. Kovac, Hamburg 2010, ISBN 978-3-8300-5099-5. External links • Stanford Encyclopedia of Philosophy entry on Causal Determinism (http://plato.stanford.edu/entries/ determinism-causal/) • Determinism in History (http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv2-02) from the Dictionary of the History of Ideas • Philosopher Ted Honderich's Determinism web resource (http://www.ucl.ac.uk/~uctytho/dfwIntroIndex.htm) • Determinism on Information Philosopher (http://www.informationphilosopher.com/freedom/determinism. html) • An Introduction to Free Will and Determinism (http://www.galilean-library.org/int13.html) by Paul Newall, aimed at beginners. • The Society of Natural Science (http://www.determinism.com) • Determinism and Free Will in Judaism (http://www.chabad.org/article.asp?AID=3017) Determinism • Snooker, Pool, and Determinism (http://www.jottings.ca/john/cogitations.html) 101 Free will Free will is the ability of agents to make choices free from certain kinds of constraints. The existence of free will and its exact nature and definition have long been debated in philosophy. Historically, the constraint of dominant concern has been the metaphysical constraint of determinism. The two main positions within that debate are metaphysical libertarianism, the claim that determinism is false and thus that free will exists (or is at least possible); and hard determinism, the claim that determinism is true and thus that free will does not exist. Both of these positions, which agree that causal determination is the relevant factor in the question of free will, are classed as incompatibilist. Positions that deny that determinism is relevant are classified as compatibilist, and offer various alternative explanations of what constraints are relevant, such as physical constraints (e.g. chains or imprisonment), social constraints (e.g. threat of punishment or censure), or psychological constraints (e.g. compulsions or phobias). In fact, compatibilists will often assert that determinism is not just compatible with free will, but actually necessary for it. A domino's movement is determined completely by laws of physics. Incompatibilists say that this is a threat to free will, but compatibilists argue that, even if we are similar to dominoes, we can have a form of free will. The principle of free will has religious, ethical, and scientific implications. For example, in the religious realm, free will implies that individual will and choices can coexist with an omnipotent divinity. In ethics, it may hold implications for whether individuals can be held morally accountable for their actions. In science, neuroscientific findings regarding free will may suggest different ways of predicting human behavior. A simplified taxonomy of the most important philosophical positions regarding free will. In Western philosophy Free will 102 Incompatibilism Incompatibilism is the position that free will and determinism are logically incompatible, and that the major question regarding whether or not people have free will is thus whether or not their actions are determined. "Hard determinists", such as Martin Luther and d'Holbach, are those incompatibilists who accept determinism and reject free will. "Metaphysical libertarians", such as Thomas Reid, Peter van Inwagen, and Robert Kane, are those incompatibilists who accept free will and deny determinism, holding the view that some form of indeterminism is true.[1] Another view is that of hard incompatibilists, which state that free will is incompatible with both determinism and indeterminism. This view is defended by Derk Pereboom.[2] Traditional arguments for incompatibilism are based on an "intuition pump": if a person is like other mechanical things that are determined in their behavior such as a wind-up toy, a billiard ball, a puppet, or a robot, then people must not have free will.[1][3] This argument has been rejected by compatibilists such as Daniel Dennett on the grounds that, even if humans have something in common with these things, it remains possible and plausible that we are different from such objects in important ways.[4] Another argument for incompatibilism is that of the "causal chain." Incompatibilism is key to the idealist theory of free will. Most incompatibilists reject the idea that freedom of action consists simply in "voluntary" behavior. They insist, rather, that free will means that man must be the "ultimate" or "originating" cause of his actions. He must be causa sui, in the traditional phrase. To be responsible for one's choices is to be the first cause of those choices, where first cause means that there is no antecedent cause of that cause. The argument, then, is that if man has free will, then man is the ultimate cause of his actions. If determinism is true, then all of man's choices are caused by events and facts outside his control. So, if everything man does is caused by events and facts outside his control, then he cannot be the ultimate cause of his actions. Therefore, he cannot have free will.[5][6][7] This argument has also been challenged by various compatibilist philosophers.[8][9] A third argument for incompatibilism was formulated by Carl Ginet in the 1960s and has received much attention in the modern literature. The simplified argument runs along these lines: if determinism is true, then we have no control over the events of the past that determined our present state and no control over the laws of nature. Since we can have no control over these matters, we also can have no control over the consequences of them. Since our present choices and acts, under determinism, are the necessary consequences of the past and the laws of nature, then we have no control over them and, hence, no free will. This is called the consequence argument.[10][11] Peter van Inwagen remarks that C.D. Broad had a version of the consequence argument as early as the 1930s.[12] The difficulty of this argument for compatibilists lies in the fact that it entails the impossibility that one could have chosen other than one has. For example, if Jane is a compatibilist and she has just sat down on the sofa, then she is committed to the claim that she could have remained standing, if she had so desired. But it follows from the consequence argument that, if Jane had remained standing, she would have either generated a contradiction, violated the laws of nature or changed the past. Hence, compatibilists are committed to the existence of "incredible abilities", according to Ginet and van Inwagen. One response to this argument is that it equivocates on the notions of abilities and necessities, or that the free will evoked to make any given choice is really an illusion and the choice had been made all along, oblivious to its "decider".[11] David Lewis suggests that compatibilists are only committed to the ability to do something otherwise if different circumstances had actually obtained in the past.[13] Martin Luther was a hard determinist. Free will Hard determinism Determinism is a broad term with a variety of meanings. Corresponding to each of these different meanings, there arises a different problem of free will.[14] Hard determinism is a view on free will which holds that some form of determinism is true, and that it is incompatible with free will, and therefore that free will does not exist. Forms of determinism can include:• Causal determinism states that future events are necessitated by past and present events combined with the laws of nature. Such determinism is sometimes illustrated by the thought experiment of Laplace's demon. Imagine an entity that knows all facts about the past and the present, and knows all natural laws that govern the universe. If the laws of nature were determinate, then such an entity would be able to use this knowledge to foresee the future, down to the smallest detail.[15] • Logical determinism is the notion that all propositions, whether about the past, present or future, are either true or false. The problem of free will, in this context, is the problem of how choices can be free, given that what one does in the future is already determined as true or false in the present.[14] • Theological determinism is the idea that God determines all that humans will do, either by knowing their actions in advance, via some form of omniscience[16] or by decreeing their actions in advance.[17] The problem of free will, in this context, is the problem of how our actions can be free if there is a being who has determined them for us in advance. • Biological determinism is the idea that all behaviors, beliefs, and desires are fixed by our genetic endowment and our biochemical makeup, the latter of which is affected by both genes and environment. • Other forms of determinism include: cultural determinism and psychological determinism.[14] Combinations and syntheses of determinist theses, e.g. bio-environmental determinism, are even more common. 103 Free will Metaphysical libertarianism Metaphysical libertarianism is one philosophical position of incompatibilism. Libertarianism holds onto a concept of free will that implies the individual may be able to take more than one possible course of action under a set of circumstances. Accounts of libertarianism subdivide into non-physical theories and physical or naturalistic theories. Non-physical theories hold that the events in the brain that lead to the performance of actions do not have an entirely physical explanation, which requires that the world is not closed under physics. Such interactionist dualists believe that some non-physical mind, will, or soul overrides physical causality. Explanations of libertarianism that do not involve dispensing with [18] physicalism require physical Various definitions of free will that have been proposed, for both Compatibilism, and [19] [2] Incompatibilism (Hard Determinism, Hard Incompatibilism, Libertarianism indeterminism, such as probabilistic [20] [21] Traditional, and Libertarianism Volition ). Red circles represent mental states; subatomic particle behavior – theory blue circles represent physical states; arrows describe causal interaction. unknown to many of the early writers on free will. Physical determinism, under the assumption of physicalism, implies there is only one possible future and is therefore not compatible with libertarian free will. Some libertarian explanations involve invoking panpsychism, the theory that a quality of mind is associated with all particles, and pervades the entire universe, in both animate and inanimate entities. Other approaches do not require free will to be a fundamental constituent of the universe; ordinary randomness is appealed to as supplying the "elbow room" believed to be necessary by libertarians. Free volition is regarded as a particular kind of complex, high-level process with an element of indeterminism. An example of this kind of approach has been developed by Robert Kane,[21] where he hypothesises that, In each case, the indeterminism is functioning as a hindrance or obstacle to her realizing one of her purposes—a hindrance or obstacle in the form of resistance within her will which has to be overcome by effort. Although at the time C. S. Lewis wrote Miracles,[22] Quantum Mechanics (and physical indeterminism) was only in the initial stages of acceptance, he stated the logical possibility that if the physical world was proved to be indeterministic this would provide an entry (interaction) point into the traditionally viewed closed system, where a scientifically described physically probable/improbable event could be philosophically described as an action of a non-physical entity on physical reality. 104 Free will Two-stage models In 1884 William James described a two-stage model of free will: in the first stage the mind develops random alternative possibilities for action, and in the second an adequately determined will selects one option. A number of other thinkers have since refined this idea, including Henri Poincaré, Arthur Holly Compton, Karl Popper, Henry Margenau, Robert Kane, Alfred Mele, and Martin Heisenberg. Each of these models tries to reconcile libertarian free will with the existence of irreducible chance (today in the form of quantum indeterminacy), which threatens to make an agent's decision random, thus denying the control needed for responsibility. If a single event is caused by chance, then logically indeterminism would be "true." For centuries, philosophers have said this would undermine the very possibility of certain knowledge. Some go to the extreme of saying that real chance would make the whole state of the world totally independent of any earlier states. The Stoic Chrysippus said that a single uncaused cause could destroy the universe (cosmos), "Everything that happens is followed by something else which depends on it by causal necessity. Likewise, everything that happens is preceded by something with which it is causally connected. For nothing exists or has come into being in the cosmos without a cause. The universe will be disrupted and disintegrate into pieces and cease to be a unity functioning as a single system, if any uncaused movement is introduced into it." James said most philosophers have an "antipathy to chance."[23] His contemporary John Fiske described the absurd decisions that would be made if chance were real, "If volitions arise without cause, it necessarily follows that we cannot infer from them the character of the antecedent states of feeling. .. . The mother may strangle her first-born child, the miser may cast his long-treasured gold into the sea, the sculptor may break in pieces his lately-finished statue, in the presence of no other feelings than those which before led them to cherish, to hoard, and to create."[24] In modern times, J. J. C. Smart has described the problem of admitting indeterminism, "Indeterminism does not confer freedom on us: I would feel that my freedom was impaired if I thought that a quantum mechanical trigger in my brain might cause me to leap into the garden and eat a slug."[25] The challenge for two-stage models is to admit some indeterminism but not permit it to produce random actions, as determinists fear. And of course a model must limit determinism but not eliminate it as some libertarians think necessary. Two-stage models limit the contribution of random chance to the generation of alternative possibilities for action. But note that, in recent years, compatibilist analytic philosophers following Harry Frankfurt have denied the existence of alternative possibilities. They develop "Frankfurt-type examples" (thought experiments) in which they argue an agent is free even though no alternative possibilities exist, or the agent is prevented at the last moment by neuroscientific demons from "doing otherwise."[26] Hard incompatibilism John Locke denied that the phrase "free will" made any sense (compare with theological noncognitivism, a similar stance on the existence of God). He also took the view that the truth of determinism was irrelevant. He believed that the defining feature of voluntary behavior was that individuals have the ability to postpone a decision long enough to reflect or deliberate upon the consequences of a choice: "...the will in truth, signifies nothing but a power, or ability, to prefer or choose".[27] 105 Free will The contemporary philosopher Galen Strawson agrees with Locke that the truth or falsity of determinism is irrelevant to the problem.[28] He argues that the notion of free will leads to an infinite regress and is therefore senseless. According to Strawson, if one is responsible for what one does in a given situation, then one must be responsible for the way one is in certain mental respects. But it is impossible for one to be responsible for the way one is in any respect. This is because to be responsible in some situation "S", one must have been responsible for the way one was at "S−1". To be responsible for the way one was at "S−1", one must have been responsible for the way one was at "S−2", and so on. At some point in the chain, there must have been an act of origination of a new causal chain. But this is impossible. Man cannot create himself or his mental states ex nihilo. This argument entails that free will itself is absurd, but not that it is incompatible with determinism. Strawson calls his own view "pessimism" but it can be classified as hard incompatibilism.[28] 106 Compatibilism Compatibilists maintain that determinism is compatible with free will. It may, however, be more accurate to say that compatibilists define "free will" in a way that allows it to co-exist with determinism (in the same way that incompatibilists define "free will" such that it cannot). Compatibilists believe freedom can be present or absent in a situation for reasons that have nothing to do with metaphysics. For instance, courts of law make judgments about whether individuals are acting under their own free will under certain circumstances without bringing in metaphysics. Similarly, political liberty is a non-metaphysical concept. Likewise, compatibilists define free will as freedom to act according to one's determined motives without hindrance from other individuals. In contrast, the incompatibilist positions are concerned Thomas Hobbes was a classical compatibilist. with a sort of "metaphysically free will," which compatibilists claim has never been coherently defined. Compatibilists argue that determinism does not matter; what matters is that individuals' wills are the result of their own desires and are not overridden by some external force.[18][29] To be a compatibilist, one need not endorse any particular conception of free will, but only deny that determinism is at odds with free will.[30] Free will as lack of physical restraint Most "classical compatibilists", such as Thomas Hobbes, claim that a person is acting on the person's own will only when it is the desire of that person to do the act, and also for the person to be able to choose otherwise, if the person had decided to. Hobbes sometimes attributes such compatibilist freedom to each individual and not to some abstract notion of will, asserting, for example, that "no liberty can be inferred to the will, desire, or inclination, but the liberty of the man; which consisteth in this, that he finds no stop, in doing what he has the will, desire, or inclination to do."[29] In articulating this crucial proviso, David Hume writes, "this hypothetical liberty is universally allowed to belong to every one who is not a prisoner and in chains".[18] Free will as a psychological state "Modern compatibilists", such as Harry Frankfurt and Daniel Dennett, argue that there are cases where a coerced agent's choices are still free because such coercion coincides with the agent's personal intentions and desires.[4][31] Frankfurt, in particular, argues for a version of compatibilism called the "hierarchical mesh". The idea is that an individual can have conflicting desires at a first-order level and also have a desire about the various first-order desires (a second-order desire) to the effect that one of the desires prevails over the others. A person's will is to be identified with their effective first-order desire, i.e., the one that they act on. So, for example, there are "wanton Free will addicts", "unwilling addicts" and "willing addicts." All three groups may have the conflicting first-order desires to want to take the drug to which they are addicted and to not want to take it. The first group, "wanton addicts", have no second-order desire not to take the drug. The second group, "unwilling addicts", have a second-order desire not to take the drug, while the third group, "willing addicts", have a second-order desire to take it. According to Frankfurt, the members of the first group are to be considered devoid of will and therefore no longer persons. The members of the second group freely desire not to take the drug, but their will is overcome by the addiction. Finally, the members of the third group willingly take the drug to which they are addicted. Frankfurt's theory can ramify to any number of levels. Critics of the theory point out that there is no certainty that conflicts will not arise even at the higher-order levels of desire and preference.[32] Others argue that Frankfurt offers no adequate explanation of how the various levels in the hierarchy mesh together.[33] Free will as unpredictability In Elbow Room, Dennett presents an argument for a compatibilist theory of free will, which he further elaborated in the book Freedom Evolves.[34] The basic reasoning is that, if one excludes God, an infinitely powerful demon, and other such possibilities, then because of chaos and epistemic limits on the precision of our knowledge of the current state of the world, the future is ill-defined for all finite beings. The only well-defined things are "expectations". The ability to do "otherwise" only makes sense when dealing with these expectations, and not with some unknown and unknowable future. According to Dennett, because individuals have the ability to act differently from what anyone expects, free will can exist.[34] Incompatibilists claim the problem with this idea is that we may be mere "automata responding in predictable ways to stimuli in our environment". Therefore, all of our actions are controlled by forces outside ourselves, or by random chance.[35] More sophisticated analyses of compatibilist free will have been offered, as have other critiques.[30] In the philosophy of decision theory, a fundamental question is: From the standpoint of statistical outcomes, to what extent do the choices of a conscious being have the ability to influence the future? Newcomb's paradox and other philosophical problems pose questions about free will and predictable outcomes of choices. 107 Other views Some philosophers' views are difficult to categorize as either compatibilist or incompatibilist, hard determinist or libertarian. For example, Ted Honderich holds the view that "determinism is true, compatibilism and incompatibilism are both false" and the real problem lies elsewhere. Honderich maintains that determinism is true because quantum phenomena are not events or things that can be located in space and time, but are abstract entities. Further, even if they were micro-level events, they do not seem to have any relevance to how the world is at the macroscopic level. He maintains that incompatibilism is false because, even if determinism is true, incompatibilists have not provided, and cannot provide, an adequate account of origination. He rejects compatibilism because it, like incompatibilism, assumes a single, fundamental notion of freedom. There are really two notions of freedom: voluntary action and origination. Both notions are required to explain freedom of will and responsibility. Both determinism and indeterminism are threats to such freedom. To abandon these notions of freedom would be to abandon moral responsibility. On the one side, we have our intuitions; on the other, the scientific facts. The "new" problem is how to resolve this conflict.[36] Free will Free will as an illusion David Hume discussed the possibility that the entire debate about free will is nothing more than a merely "verbal" issue. He suggested that it might be accounted for by "a false sensation or seeming experience" (a velleity), which is associated with many of our actions when we perform them. On reflection, we realize that they were necessary and determined all along.[37] Arthur Schopenhauer put the puzzle of free will and moral responsibility in these terms: Everyone believes himself a priori to be perfectly free, even in his individual actions, and thinks that at every moment he can commence another manner of life. ... But a posteriori, through experience, he finds to his astonishment that he is not free, but subjected to necessity, that in spite of all his resolutions and reflections he does not change his conduct, and that from the beginning of his life to the end of it, he must carry out the very character which he himself condemns...[38] In his On the Freedom of the Will, Schopenhauer stated, "You can do what you will, but in any given moment of your life you can will only one definite thing and absolutely nothing other than that one thing."[39] 108 Rudolf Steiner, who collaborated in a complete edition of Arthur Schopenhauer's work,[40] wrote The Philosophy of Freedom, which focuses on the problem of free will. Steiner (1861–1925) initially divides this into the two aspects of freedom: freedom of thought and freedom of action. He argues that inner freedom is achieved when we bridge the gap between our sensory impressions, which reflect the outer appearance of the world, and our thoughts, which give us access to the inner nature of the world. Acknowledging the many influences on our choice, he points to the impact of our becoming aware of just these determinants. Outer freedom is attained by permeating our deeds with moral imagination. Steiner aims to show that these two aspects of inner and outer freedom are integral to one another, and that true freedom is only achieved when they are united.[41] Free will as a pragmatically useful concept William James' views were ambivalent. While he believed in free will on "ethical grounds," he did not believe that there was evidence for it on scientific grounds, nor did his own introspections support it.[42] Moreover, he did not accept incompatibilism as formulated below; he did not believe that the indeterminism of human actions was a prerequisite of moral responsibility. In his work Pragmatism, he wrote that "instinct and utility between them can safely be trusted to carry on the social business of punishment and praise" regardless of metaphysical theories.[43] He did believe that indeterminism is important as a "doctrine of relief"—it allows for the view that, although the world may be in many respects a bad place, it may, through individuals' actions, become a better one. Determinism, he argued, undermines meliorism—the idea that progress is a real concept leading to improvement in the world.[43] Much of Arthur Schopenhauer's writing is focused on the notion of will and its relation to freedom. Free will 109 In science Physics Early scientific thought often portrayed the universe as deterministic – for example in the thought of Democritus or the Cārvākans – and some thinkers claimed that the simple process of gathering sufficient information would allow them to predict future events with perfect accuracy. Modern science, on the other hand, is a mixture of deterministic and stochastic theories.[44] Quantum mechanics predicts events only in terms of probabilities, casting doubt on whether the universe is deterministic at all. Current physical theories cannot resolve the question of whether determinism is true of the world, being very far from a potential Theory of Everything, and open to many different interpretations.[45][46] Assuming that an indeterministic interpretation of quantum mechanics is correct, one may still object that such indeterminism is for all practical purposes confined to microscopic phenomena.[48] This is not always the case: many macroscopic phenomena are based on quantum effects. For instance, some hardware random number generators work by amplifying quantum effects into practically usable signals. A more significant question is whether the indeterminism of quantum mechanics allows for the traditional idea of free will (based on a perception of free will). If a person's action is the result of complete quantum randomness, however, this in itself would mean that such traditional free will does not exist (because the action was not controllable by the physical being who claims to possess the free will).[49] Quantum mechanics defines probabilities to predict the behavior of particles, "rather than determining the future and past with certainty". Because the human brain is composed of particles, and their behavior is governed by the laws of nature, Stephen Hawking says that free will is "just an [47] illusion". Under the assumption of physicalism it has been argued that the laws of quantum mechanics provide a complete probabilistic account of the motion of particles, regardless of whether or not free will exists.[50] Physicist Stephen Hawking describes such ideas in his 2010 book The Grand Design. According to Hawking, these findings from quantum mechanics suggest that humans are sorts of complicated biological machines; although our behavior is impossible to predict perfectly in practice, "free will is just an illusion."[47] In other words, Hawking thinks that only compatibilistic (deterministic) free will is possible based on the data. Erwin Schrödinger, a nobel laureate in physics and one of the founders of quantum mechanics, came to a different conclusion than Hawking. Near the end of his 1944 essay titled What Is Life? he says that there is "incontrovertible direct experience" that humans have free will. He also states that the human body is wholly or at least partially determined, leading him to conclude that "...'I' -am the person, if any, who controls the 'motion of the atoms' according to the Laws of Nature." He explains this position on free will by appealing to a notion of self that is emergent from the entire collection of atoms in his body, and other convictions about conscious experience. However, he also qualifies the conclusion as "necessarily subjective" in its "philosophical implications." Contrasting the views of Hawking and Schrödinger, it is clear that even among eminent physicists there is not unanimity regarding free will. Free will 110 Genetics Like physicists, biologists have frequently addressed questions related to free will. One of the most heated debates in biology is that of "nature versus nurture", concerning the relative importance of genetics and biology as compared to culture and environment in human behavior.[51] The view of many researchers is that many human behaviors can be explained in terms of humans' brains, genes, and evolutionary histories.[52][53][54] This point of view raises the fear that such attribution makes it impossible to hold others responsible for their actions. Steven Pinker's view is that fear of determinism in the context of "genetics" and "evolution" is a mistake, that it is "a confusion of explanation with exculpation". Responsibility doesn't require behavior to be uncaused, as long as behavior responds to praise and blame.[55] Moreover, it is not certain that environmental determination is any less threatening to free will than genetic determination.[56] Neuroscience It has become possible to study the living brain, and researchers can now watch the brain's decision-making process at work. A seminal experiment in this field was conducted by Benjamin Libet in the 1980s, in which he asked each subject to choose a random moment to flick her wrist while he measured the associated activity in her brain; in particular, the build-up of electrical signal called the readiness potential (after German Bereitschaftspotential). Although it was well known that the readiness potential caused and preceded the physical action, Libet asked whether it could be recorded before the conscious intention to move. To determine when subjects felt the intention to move, he asked them to watch the second hand of a clock. After making a movement, the volunteer reported the time on the clock when they first felt the conscious intention to move; this became known as Libet's W time.[57] Libet found that the unconscious brain activity of the readiness potential leading up to subjects' movements began approximately half a second before the subject was aware of a conscious intention to move.[57][58] More studies have since been conducted, including some that try to: • • • • support Libet's original findings suggest that the cancelling or "veto" of an action may first arise subconsciously as well explain the underlying brain structures involved suggest models that explain the relationship between conscious intention and action Neurology and psychiatry There are several brain-related conditions in which an individual's actions are not felt to be entirely under his or her control. Although the existence of such conditions does not directly refute the existence of free will, the study of such conditions, like the neuroscientific studies above, is valuable in developing models of how the brain may construct our experience of free will. For example, people with Tourette syndrome and related tic disorders make involuntary movements and utterances, called tics, despite the fact that they would prefer not to do so when it is socially inappropriate. Tics are described as semi-voluntary or "unvoluntary",[59] because they are not strictly involuntary: they may be experienced as a voluntary response to an unwanted, premonitory urge. Tics are experienced as irresistible and must eventually be expressed.[59] People with Tourette syndrome are sometimes able to suppress their tics for limited periods, but doing so often results in an explosion of tics afterward. The control exerted (from seconds to hours at a time) may merely postpone and exacerbate the ultimate expression of the tic.[60] In alien hand syndrome, the afflicted individual's limb will produce meaningful behaviors without the intention of the subject. The affected limb effectively demonstrates 'a will of its own.' The sense of agency does not emerge in conjunction with the overt appearance of the purposeful act even though the sense of ownership in relationship to the body part is maintained. This phenomenon corresponds with an impairment in the premotor mechanism manifested temporally by the appearance of the readiness potential (see section on the Neuroscience of Free Will above) Free will recordable on the scalp several hundred milliseconds before the overt appearance of a spontaneous willed movement. Using functional magnetic resonance imaging with specialized multivariate analyses to study the temporal dimension in the activation of the cortical network associated with voluntary movement in human subjects, an anterior-to-posterior sequential activation process beginning in the supplementary motor area on the medial surface of the frontal lobe and progressing to the primary motor cortex and then to parietal cortex has been observed.[61] The sense of agency thus appears to normally emerge in conjunction with this orderly sequential network activation incorporating premotor association cortices together with primary motor cortex. In particular, the supplementary motor complex on the medial surface of the frontal lobe appears to activate prior to primary motor cortex presumably in associated with a preparatory pre-movement process. In a recent study using functional magnetic resonance imaging, alien movements were characterized by a relatively isolated activation of the primary motor cortex contralateral to the alien hand, while voluntary movements of the same body part included the concomitant activation of motor association cortex associated with the premotor process.[62] The clinical definition requires "feeling that one limb is foreign or has a will of its own, together with observable involuntary motor activity" (emphasis in original).[63] This syndrome is often a result of damage to the corpus callosum, either when it is severed to treat intractable epilepsy or due to a stroke. The standard neurological explanation is that the felt will reported by the speaking left hemisphere does not correspond with the actions performed by the non-speaking right hemisphere, thus suggesting that the two hemispheres may have independent senses of will.[64][65] Similarly, one of the most important ("first rank") diagnostic symptoms of schizophrenia is the delusion of being controlled by an external force.[66] People with schizophrenia will sometimes report that, although they are acting in the world, they did not initiate, or will, the particular actions they performed. This is sometimes likened to being a robot controlled by someone else. Although the neural mechanisms of schizophrenia are not yet clear, one influential hypothesis is that there is a breakdown in brain systems that compare motor commands with the feedback received from the body (known as proprioception), leading to attendant hallucinations and delusions of control.[67] 111 Determinism and emergent behavior In some generative philosophies of cognitive sciences and evolutionary psychology, free will is assumed not to exist.[68][69] However, an illusion of free will is created, within this theoretical context, due to the generation of infinite or computationally complex behavior from the interaction of a finite set of rules and parameters. Thus, the unpredictability of the emerging behavior from deterministic processes leads to a perception of free will, even though free will as an ontological entity is assumed not to exist.[68][69] In this picture, even if the behavior could be computed ahead of time, no way of doing so will be simpler than just observing the outcome of the brain's own computations.[70] As an illustration, some strategy board games have rigorous rules in which no information (such as cards' face values) is hidden from either player and no random events (such as dice rolling) occur in the game. Nevertheless, strategy games like chess and especially Go, with its simple deterministic rules, can have an extremely large number of unpredictable moves. By analogy, "emergentists" suggest that the experience of free will emerges from the interaction of finite rules and deterministic parameters that generate infinite and unpredictable behavior. Yet, if all these events were accounted for, and there were a known way to evaluate these events, the seemingly unpredictable behavior would become predictable.[68][69][71] Cellular automata and the generative sciences can model emergent processes of social behavior on this philosophy.[68] In their book "The Grand Design" [72] Hawking and Mlodinow suggest a thought experiment in which one encounters an alien that may be a robot: "... how can one tell if it is just a robot or it has a mind of its own? The behavior of a robot would be completely determined, unlike that of a being with free will. Thus one could in principle detect a robot as a being whose actions can be predicted. . . . [however] . . . even if the alien were a robot, it would be impossible to solve the equations and predict what it would do [because of the complexity of such a creature]. We would Free will therefore have to say that any complex being has free will -- not as a fundamental feature, but as an effective theory, an admission of our inability do the calculations that would enable us to predict its actions. (p. 178)" 112 Experimental psychology Experimental psychology's contributions to the free will debate have come primarily through social psychologist Daniel Wegner's work on conscious will. In his book, The Illusion of Conscious Will[73] Wegner summarizes what he believes is empirical evidence supporting the view that human perception of conscious control is an illusion. Wegner summarizes some empirical evidence that may suggest that the perception of conscious control is open to modification (or even manipulation). Wegner observes that one event is inferred to have caused a second event when two requirements are met: 1. The first event immediately precedes the second event, and 2. The first event is consistent with having caused the second event. For example, if a person hears an explosion and sees a tree fall down that person is likely to infer that the explosion caused the tree to fall over. However, if the explosion occurs after the tree falls down (i.e., the first requirement is not met), or rather than an explosion, the person hears the ring of a telephone (i.e., the second requirement is not met), then that person is not likely to infer that either noise caused the tree to fall down. Wegner has applied this principle to the inferences people make about their own conscious will. People typically experience a thought that is consistent with a behavior, and then they observe themselves performing this behavior. As a result, people infer that their thoughts must have caused the observed behavior. However, Wegner has been able to manipulate people's thoughts and behaviors so as to conform to or violate the two requirements for causal inference.[73][74] Through such work, Wegner has been able to show that people will often experience conscious will over behaviors that they have in fact not caused, and conversely, that people can be led to experience a lack of will over behaviors that they did cause. For instance, priming subjects with information about an effect increases the probability that a person falsely believes to be the cause of it.[75] The implication for such work is that the perception of conscious will (which he says might be more accurately labelled as 'the emotion of authorship') is not tethered to the execution of actual behaviors, but is inferred from various cues through an intricate mental process, authorship processing. Although many interpret this work as a blow against the argument for free will, both psychologists[76][77] and philosophers[78][79] have criticized Wegner's theories. Emily Pronin has argued that the subjective experience of free will is supported by the introspection illusion. This is the tendency for people to trust the reliability of their own introspections while distrusting the introspections of other people. The theory implies that people will more readily attribute free will to themselves rather than others. This prediction has been confirmed by three of Pronin and Kugler's experiments. When college students were asked about personal decisions in their own and their roommate's lives, they regarded their own choices as less predictable. Staff at a restaurant described their co-workers' lives as more determined (having fewer future possibilities) than their own lives. When weighing up the influence of different factors on behavior, students gave desires and intentions the strongest weight for their own behavior, but rated personality traits as most predictive of other people.[80] Psychologists have shown that reducing a person's belief in free will makes them less helpful and more aggressive.[81] This may occur because the subject loses a sense of Self-efficacy. Free will 113 In Eastern philosophy In Hindu philosophy The six orthodox (astika) schools of thought in Hindu philosophy do not agree with each other entirely on the question of free will. For the Samkhya, for instance, matter is without any freedom, and soul lacks any ability to control the unfolding of matter. The only real freedom (kaivalya) consists in realizing the ultimate separateness of matter and self.[82] For the Yoga school, only Ishvara is truly free, and its freedom is also distinct from all feelings, thoughts, actions, or wills, and is thus not at all a freedom of will. The metaphysics of the Nyaya and Vaisheshika schools strongly suggest a belief in determinism, but do not seem to make explicit claims about determinism or free will.[83] A quotation from Swami Vivekananda, a Vedantist, offers a good example of the worry about free will in the Hindu tradition. Therefore we see at once that there cannot be any such thing as free-will; the very words are a contradiction, because will is what we know, and everything that we know is within our universe, and everything within our universe is moulded by conditions of time, space and causality. ... To acquire freedom we have to get beyond the limitations of this universe; it cannot be found here.[84] However, the preceding quote has often been misinterpreted as Vivekananda implying that everything is predetermined. What Vivekananda actually meant by lack of free will was that the will was not "free" because it was heavily influenced by the law of cause and effect—"The will is not free, it is a phenomenon bound by cause and effect, but there is something behind the will which is free."[84] Vivekananda never said things were absolutely determined and placed emphasis on the power of conscious choice to alter one's past karma: "It is the coward and the fool who says this is his fate. But it is the strong man who stands up and says I will make my own fate."[84] In Buddhist philosophy Buddhism accepts both freedom and determinism (or something similar to it), but rejects the idea of an agent, and thus the idea that freedom is a free will belonging to an agent.[85] According to the Buddha, "There is free action, there is retribution, but I see no agent that passes out from one set of momentary elements into another one, except the [connection] of those elements."[85] Buddhists believe in neither absolute free will, nor determinism. It preaches a middle doctrine, named pratitya-samutpada in Sanskrit, which is often translated as "inter-dependent arising". It is part of the theory of karma in Buddhism. The concept of karma in Buddhism is different from the notion of karma in Hinduism. In Buddhism, the idea of karma is much less deterministic. The Buddhist notion of karma is primarily focused on the cause and effect of moral actions in this life, while in Hinduism the concept of karma is more often connected with determining one's destiny in future lives. In Buddhism it is taught that the idea of absolute freedom of choice (i.e. that any human being could be completely free to make any choice) is unwise, because it denies the reality of one's physical needs and circumstances. Equally incorrect is the idea that humans have no choice in life or that their lives are pre-determined. To deny freedom would be to deny the efforts of Buddhists to make moral progress (through our capacity to freely choose compassionate action). Pubbekatahetuvada, the belief that all happiness and suffering arise from previous actions, is considered a wrong view according to Buddhist doctrines. Because Buddhists also reject agenthood, the traditional compatibilist strategies are closed to them as well. Instead, the Buddhist philosophical strategy is to examine the metaphysics of causality. Ancient India had many heated arguments about the nature of causality with Jains, Nyayists, Samkhyists, Cārvākans, and Buddhists all taking slightly different lines. In many ways, the Buddhist position is closer to a theory of "conditionality" than a theory of "causality", especially as it is expounded by Nagarjuna in the Mūlamadhyamakakārikā.[85] Free will 114 In other theology Further information: Free will in theology The theological doctrine of divine foreknowledge is often alleged to be in conflict with free will, particularly in Reformed circles. For if God knows exactly what will happen, right down to every choice one makes, the status of choices as free is called into question. If God had timelessly true knowledge about one's choices, this would seem to constrain one's freedom.[86] This problem is related to the Aristotelian problem of the sea battle: tomorrow there will or will not be a sea battle. If there will be one, then it seems that it was true yesterday that there would be one. Then it would be necessary that the sea battle will occur. If there won't be one, then by similar reasoning, it is necessary that it won't occur.[87] This means that the future, whatever it is, is completely fixed by past truths—true propositions about the future. However, some philosophers follow William of Ockham in holding that necessity and possibility are defined with respect to a given point in time and a given matrix of empirical circumstances, and so something that is merely possible from the perspective of one observer may be necessary from the perspective of an omniscient.[88] Some philosophers follow Philo of Alexandria, a philosopher known for his homocentrism, in holding that free will is a feature of a human's soul, and thus that non-human animals lack free will.[89] Some views in Jewish philosophy stress that free will is a product of the intrinsic human soul, using the word neshama (from the Hebrew root n.sh.m. or .‫ נ.ש.מ‬meaning "breath"), but the ability to make a free choice is through Yechida (from Hebrew word "yachid", ‫ ,יחיד‬singular), the part of the soul that is united with God, the only being that is not hindered by or dependent on cause and effect (thus, freedom of will does not belong to the realm of the physical reality, and inability of natural philosophy to account for it is expected). While there are other views of free will in Judaism, most share the same basic Kabbalah principles. In Islam the theological issue is not usually how to reconcile free will with God's foreknowledge, but with God's jabr, or divine commanding power. al-Ash'ari developed an "acquisition" or "dual-agency" form of compatibilism, in which human free will and divine jabr were both asserted, and which became a cornerstone of the dominant Ash'ari position.[90] In Shia Islam, Ash'aris understanding of a higher balance toward predestination is challenged by most theologians.[91] Free will, according to Islamic doctrine is the main factor for man's accountability in his/her actions throughout life. All actions taken by man's free will are said to be counted on the Day of Judgement because they are his/her own and not God's. The philosopher Søren Kierkegaard claimed that divine omnipotence cannot be separated from divine goodness.[92] As a truly omnipotent and good being, God could create beings with true freedom over God. Furthermore, God would voluntarily do so because "the greatest good ... which can be done for a being, greater than anything else that one can do for it, is to be truly free."[93] Alvin Plantinga's "free will defense" is a contemporary expansion of this theme, adding how God, free will, and evil are consistent.[94] Believing in free will In recent years, free will belief in individuals has been analysed with respect to traits in social behaviour. In general the concept of free will researched to date in this context has been that of the incompatabilist, or more specifically, the libertarian, i.e. freedom from determinism. What people believe Whether people naturally adhere to an incompatibilist model of free will has been questioned in the research. Eddy Nahmias has found that incompatibilism is not intuitive – it was not adhered to, in that determinism does not negate belief in moral responsibility (based on an empirical study of people's responses to moral dilemmas under a deterministic model of reality).[95] Edward Cokely has found that incompatibilism is intuitive – it was naturally adhered to, in that determinism does indeed negate belief in moral responsibility in general.[96] Joshua Knobe and Free will Shaun Nichols have proposed that incompatibilism may or may not be intuitive, and that it is dependent to some large degree upon the circumstances; whether or not the crime incites an emotional response – for example if it involves harming another human being.[97] They found that belief in free will is a cultural universal, and that the majority of participants said that (a) our universe is indeterministic and (b) moral responsibility is not compatible with determinism.[98] Studies have been conducted indicating that peoples' belief in free will appears to be inconsistent. Emily Pronin and Matthew Kugler have found that people believe they have more free will than others.[99] Studies have also been conducting indicating there exists a correlation between one's likelihood of accepting a deterministic model of mind, and their personality type. For example, Adam Feltz and Edward Cokely have found that people of an extrovert personality type are more likely to dissociate belief in determinism from belief in moral responsibility.[100] Roy Baumeister and colleagues reviewed literature on the psychological effects of a belief (or disbelief) in free will. The first part of their analysis (which is all that we are concerned with here) was not meant to discover which types of free will actually exist. The researchers instead sought to identify what other people believe, how many people believed it, and the effects of those beliefs. Baumeister found that most people tend to believe in a sort of "naive compatibilistic free will".[101][102] The researchers also found that people consider acts more "free" when they involve a person opposing external forces, planning, or making random actions.[103] Notably, the last behaviour, "random" actions, may not be possible; when participants attempt to perform tasks in a random manner (such as generating random numbers), their behaviour betrays many patterns.[104][105] 115 Effects of the belief itself “An alternative explanation builds on the idea that subjects tend to confuse determinism with fatalism... What happens then when agents’ self-efficacy is undermined? It is not that their basic desires and drives are defeated. It is rather, I suggest, that they become skeptical that they will be able to control those desires; and in the face of that skepticism, they fail to apply the effort that is needed even to try. If they were tempted to behave badly, then coming to believe in fatalism makes them less likely to resist that temptation.” —Richard Holton [106] Baumeister and colleagues found that provoking disbelief in free will seems to cause various negative effects. The authors concluded, in their paper, that it is belief in determinism that causes those negative effects.[101] This may not be a very justified conclusion, however.[106] First of all, free will can at least refer to either libertarian (indeterministic) free will or compatibilistic (deterministic) free will. Having participants read articles that simply "disprove free will" is unlikely to increase their understanding of determinism, or the compatibilistic free will that it still permits.[106] In other words, "provoking disbelief in free will" probably causes a belief in fatalism. As discussed earlier in this article, compatibilistic free will is illustrated by statements like "my choices have causes, and an effect – so I affect my future", whereas fatalism is more like "my choices have causes, but no effect – I am powerless". Fatalism, then, may be what threatens people's sense of self-efficacy. Lay people should not confuse fatalism with determinism, and yet even professional philosophers occasionally confuse the two. It is thus likely that the negative consequences below can be accounted for by participants developing a belief in fatalism when experiments attack belief in "free will".[106] To test the effects of belief in determinism, future studies would need to provide articles that do not simply "attack free will", but instead focus on explaining determinism and compatibilism. Some studies have been conducted indicating that people react strongly to the way in which mental determinism is described, when reconciling it with moral responsibility. Eddy Nahmias has noted that when peoples actions are framed with respect to their beliefs and desires (rather than their neurological underpinnings) they are more likely to dissociate determinism from moral responsibility.[107] Free will Various social behavioural traits have been correlated with the belief in deterministic models of mind, some of which involved the experimental subjection of individuals to libertarian and deterministic perspectives. After researchers provoked volunteers to disbelieve in free will, participants lied, cheated, and stole more. Kathleen Vohs has found that those whose belief in free will had been eroded were more likely to cheat.[108] In a study conducted by Roy Baumeister, after participants read an article disproving free will, they were more likely to lie about their performance on a test where they would be rewarded with cash.[109] Provoking a rejection of free will has also been associated with increased aggression and less helpful behaviour[110][111] as well as mindless conformity.[112] Disbelief in free will can even cause people to feel less guilt about transgressions against others.[113] Baumeister and colleagues also note that volunteers disbelieving in free will are less capable of counterfactual thinking.[101][114] This is worrying because counterfactual thinking ("If I had done something different...") is an important part of learning from one's choices, including those that harmed others.[115] Again, this cannot be taken to mean that belief in determinism is to blame; these are the results we would expect from increasing people's belief in fatalism.[106] Along similar lines, Tyler Stillman has found that belief in free will predicts better job performance.[116] 116 References [1] [2] [3] [4] [5] [6] [7] van Invagen, P. (1983) An Essay on Free Will. Oxford: Clarendon Press. ISBN 0-19-824924-1 Pereboom, D. (2003) Living without Free Will. Cambridge University Press. Fischer, J.M. (1983). "Incompatibilism". Philosophical Studies 43: 121–37. Dennett, D., (1984) Elbow Room: The Varieties of Free Will Worth Wanting. Bradford Books. ISBN 0-262-54042-8 Kane, R. (1996) The Significance of Free Will, Oxford: Oxford University Press. ISBN 0-19-512656-4 Campbell, C.A. (1957) On Selfhood and Godhood, London: George Allen and Unwin. ISBN 0-415-29624-2 Sartre, J.P. (1943) Being and Nothingness, reprint 1993. New York: Washington Square Press. Sartre also provides a psychological version of the argument by claiming that if man's actions are not his own, he would be in bad faith. [8] Fischer, R.M. (1994) The Metaphysics of Free Will, Oxford:Blackwell [9] Bok, H. (1998) Freedom and Responsibility, Princeton:Princeton University Press. ISBN 0-691-01566-X [10] Ginet, C. (1966) "Might We Have No Choice?" In Lehrer, 1966: 87–104. [11] Van Inwagen, P. and Zimmerman, D. (1998) Metaphysics: The Big Questions. Oxford:Blackwell [12] Inwagen, P. (n.d.) "How to think about free will" (http:/ / philosophy. nd. edu/ people/ all/ profiles/ van-inwagen-peter/ documents/ HowThinkFW. doc), p. 15. [13] Lewis, D. (2008). "Are We Free to Break the Laws?". Theoria 47 (3): 113–21. doi:10.1111/j.1755-2567.1981.tb00473.x. [14] Vihvelin, Kadri, "Arguments for Incompatibilism", The Stanford Encyclopedia of Philosophy (Winter 2003 Edition), Edward N. Zalta (ed.), ((online)) (http:/ / plato. stanford. edu/ archives/ win2003/ entries/ incompatibilism-arguments/ ) [15] Suppes, P. (1993). "The Transcendental Character of Determinism". Midwest Studies in Philosophy 18: 242–257. doi:10.1111/j.1475-4975.1993.tb00266.x. [16] Fischer, John Martin (1989) God, Foreknowledge and Freedom. Stanford, CA: Stanford University Press. ISBN 1-55786-857-3 [17] Watt, Montgomery (1948) Free-Will and Predestination in Early Islam. London: Luzac & Co. [18] Hume, D. (1740). A Treatise of Human Nature SECTION VIII.: " Of liberty and necessity (http:/ / oll. libertyfund. org/ index. php?option=com_staticxt& staticfile=show. php& title=341& search="prisoner+ chains"& chapter=61966& layout=html#a_606067)" (1967 edition). Oxford University Press, Oxford. ISBN 0-87220-230-5 [19] Paul Henri Thiry, Baron d'Holbach, System of Nature; or, the Laws of the Moral and Physical World (London, 1797), Vol. 1, p. 92 [20] Descartes, René (1649). Passions of the Soul. ISBN 0-87220-035-3. [21] Kane, Robert; John Martin Fischer, Derk Pereboom, Manuel Vargas (2007). Four Views on Free Will (Libertarianism). Oxford UK: Blackwell Publishing. p. 39. ISBN 1-4051-3486-0. [22] Lewis, C.S. (1947). Miracles. p. 24. ISBN 0-688-17369-1. [23] "The Dilemma of Determinism, in The Will to Believe, Dover (1956), p.153; first delivered as an address to Harvard Divinity Students in Lowell Lecture Hall, and published in the Unitarian Review for September 1884 [24] John Fiske, Outline of Cosmic Philosophy, part. H. chap. xvii, cited by William James, Principles of Psychology, Vol. 2. Dover (1950) p. 577 [25] Atheism and Theism, Wiley-Blackwell (2003) p.63 [26] Frankfurt, Harry (1969). "Alternate possibilities and moral responsibility". Journal of Philosophy 66 (23): 829–39. doi:10.2307/2023833. JSTOR 2023833. [27] Locke, J. (1689). An Essay Concerning Human Understanding (1998, ed). Book II, Chap. XXI, Sec. 17. Penguin Classics, Toronto. Free will [28] Strawson, G. (1998, 2004). "Free will". In E. Craig (Ed.), Routledge Encyclopedia of Philosophy. London: Routledge. Retrieved August 17, 2006, ((online)) (http:/ / www. rep. routledge. com/ article/ V014) [29] Hobbes, T. (1651) Leviathan CHAPTER XXI.: "Of the liberty of subjects" (http:/ / oll. libertyfund. org/ index. php?option=com_staticxt& staticfile=show. php& title=585& search="finds+ no+ stop"& chapter=89860& layout=html#a_2025807) (1968 edition). London: Penguin Books. [30] McKenna, Michael, "Compatibilism", The Stanford Encyclopedia of Philosophy (Summer 2004 Edition), Edward N. Zalta (ed.), ((online)) (http:/ / plato. stanford. edu/ archives/ sum2004/ entries/ compatibilism/ ) [31] Frankfurt, H. (1971). "Freedom of the Will and the Concept of the Person". Journal of Philosophy 68 (1): 5–20. doi:10.2307/2024717. JSTOR 2024717. [32] Watson, D. 1982. Free Will. New York: Oxford University Press. [33] Fischer, John Martin, and Mark Ravizza. 1998. Responsibility and Control: An Essay on Moral Responsibility. Cambridge: Cambridge University Press. [34] Dennett, D. (2003) Freedom Evolves. Viking Books. ISBN 0-670-03186-0 [35] Kane, R. The Oxford Handbook to Free Will. Oxford University Press. ISBN 0-19-513336-6. [36] Honderich, T. "Determinism as True, Compatibilism and Incompatibilism as Both False and the Real Problem" in The Free Will Handbook , edited by Robert Kane of the University of Texas, published by Oxford University Press in 2001. [37] Hume, D. (1765)An Enquiry Concerning Human Understanding, Indianapolis: Hacket Publishing Co. Second edition. 1993. ISBN 0-87220-230-5 [38] Schopenhauer, Arthur, The Wisdom of Life, p 147 [39] Schopenhauer, Arthur, On the Freedom of the Will, Oxford: Basil Blackwell ISBN 0-631-14552-4 [40] Rudolf Steiner. "Arthur Schopenhauers sämtliche Werke in zwölf Bänden. Mit Einleitung von Dr. Rudolf Steiner, Stuttgart: Verlag der J.G. Cotta'schen Buchhandlung Nachfolger, o.J. (1894–96)" (http:/ / www. pitt. edu/ ~kafka/ k_s_bibII. html). . [41] Steiner, R. (1964). Rudolf Steiner Press, London, 1964, 1970, 1972, 1979, 230 pp., translated from the 12th German edition of 1962 by Michael Wilson. ((online)) (http:/ / www. rsarchive. org/ Books/ GA004/ ) [42] See Bricklin, Jonathan, "A Variety of Religious Experience: William James and the Non-Reality of Free Will", in Libet (1999), The Volitional Brain: Toward a Neuroscience of Free Will (Thorverton UK: Imprint Academic). [43] James, W. (1907) Pragmatism (1979 edition). Cambridge, MA: Harvard University Press [44] Boniolo, G. and Vidali, P. (1999) Filosofia della Scienza, Milan: Mondadori. ISBN 88-424-9359-7 [45] Hoefer, Carl (2008-04-01). "Causal Determinism" (http:/ / plato. stanford. edu/ entries/ determinism-causal/ ). Stanford Encyclopedia of Philosophy. . Retrieved 2008-11-01. [46] Vedral, Vlatko (2006-11-18). "Is the Universe Deterministic?". New Scientist 192 (2578). "Physics is simply unable to resolve the question of free will, although, if anything, it probably leans towards determinism." [47] Grand Design (2010), page 32: "the molecular basis of biology shows that biological processes are governed by the laws of physics and chemistry and therefore are as determined as the orbits of the planets...so it seems that we are no more than biological machines and that free will is just an illusion", and page 72: "Quantum physics might seem to undermine the idea that nature is governed by laws, but that is not the case. Instead it leads us to accept a new form of determinism: Given the state of a system at some time, the laws of nature determine the probabilities of various futures and pasts rather than determining the future and past with certainty." (emphasis in original, discussing a Many worlds interpretation) [48] "Honderich, E. ''Determinism as True, Compatibilism and Incompatibilism as Both False, and the Real Problem''" (http:/ / www. ucl. ac. uk/ ~uctytho/ dfwVariousHonderichKanebook. htm). Ucl.ac.uk. . Retrieved 2010-11-21. [49] "Infidels. "Metaphysical Freedom"" (http:/ / www. infidels. org/ library/ modern/ features/ 2000/ lujan1. html). Infidels.org. . Retrieved 2010-11-21. [50] Loewer, Barry (1996). "Freedom from Physics: Quantum Mechanics and Free Will". Philosophical Topics 24: 91–112. [51] Pinel, P.J. (1990) Biopsychology. Prentice Hall Inc. ISBN 88-15-07174-1 [52] DeFries, J. C., McGuffin, P., McClearn, G. E., Plomin, R. (2000) Behavioral Genetics 4th ED. W H Freeman & Co. [53] Morris, D. (1967) The Naked Ape. New York:McGraw-Hill. ISBN 0-385-33430-3 [54] Dawkins, R. (1976) The Selfish Gene. Oxford: Oxford University Press. ISBN 88-04-39318-1 [55] Pinker, S.(2002) The Blank Slate: The Modern Denial of Human Nature. London:Penguin. p.179 ISBN 0-14-200334-4 [56] Lewontin, R. (2000)It Ain't Necessarily So: The Dream of the Human Genome and other Illusions. New York: NYREV Inc. ISBN 88-420-6418-1 [57] Libet, B.; Gleason, C.A.; Wright, E.W.; Pearl, D.K. (1983). "Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act". Brain 106 (3): 623–642. doi:10.1093/brain/106.3.623. PMID 6640273. [58] Libet, B. (1985). "Unconscious cerebral initiative and the role of conscious will in voluntary action". Behavioral and Brain Sciences 8 (4): 529–566. doi:10.1017/S0140525X00044903. [59] Tourette Syndrome Association. Definitions and Classification of Tic Disorders. (http:/ / web. archive. org/ web/ 20050322170245/ http:/ / www. tsa-usa. org/ research/ definitions. html). Retrieved 19 August 2006. [60] Zinner, S.H. (2000). "Tourette disorder". Pediatric Review 21 (11): 372–83. PMID 11077021. 117 Free will [61] Kayser, A.S.; Sun, F.T.; D'Esposito, M. (2009). "A comparison of Granger causality and coherency in fMRI-based analysis of the motor system". Human Brain Mapping 30 (11): 3475–3494. doi:10.1002/hbm.20771. PMC 2767459. PMID 19387980. [62] Assal, F.; Schwartz, S.; Vuilleumier, P. (2007). "Moving with or without will: Functional neural correlates of alien hand syndrome". Annals of Neurology 62 (3): 301–306. doi:10.1002/ana.21173. PMID 17638304. [63] Doody, RS; Jankovic, J. (1992). "The alien hand and related signs". Journal of Neurology, Neurosurgery and Psychiatry 55 (9): 806–810. doi:10.1136/jnnp.55.9.806. PMC 1015106. PMID 1402972. [64] Scepkowski, L.A.; Cronin-Golomb, A. (2003). "The alien hand: cases, categorizations, and anatomical correlates". Behavioral and Cognitive Neuroscience Reviews 2 (4): 261–277. doi:10.1177/1534582303260119. PMID 15006289. [65] Bundick, T.; Spinella, M. (2000). "Subjective experience, involuntary movement, and posterior alien hand syndrome". Journal of Neurology, Neurosurgery and Psychiatry 68 (1): 83–85. doi:10.1136/jnnp.68.1.83. PMC 1760620. PMID 10601408. [66] Schneider, K. (1959). Clinical Psychopathology. New York: Grune and Stratton. [67] Frith, CD; Blakemore, S; Wolpert, DM (2000). "Explaining the symptoms of schizophrenia: abnormalities in the awareness of action". Brain research. Brain research reviews 31 (2–3): 357–63. doi:10.1016/S0165-0173(99)00052-1. PMID 10719163. [68] Kenrick, DT; Li, NP; Butner, J (2003). "Dynamical evolutionary psychology: individual decision rules and emergent social norms". Psychological review 110 (1): 3–28. doi:10.1037/0033-295X.110.1.3. PMID 12529056. [69] Epstein, Joshua M.; Axtell, Robert L. (1996). Growing Artificial Societies: Social Science From the Bottom Up. Cambridge MA: MIT/Brookings Institution. p. 224. ISBN 978-0-262-55025-3. [70] Wolfram, Stephen, A New Kind of Science. Wolfram Media, Inc., May 14, 2002. ISBN 1-57955-008-8 [71] Epstein, J.M. (1999). "Agent Based Models and Generative Social Science". Complexity IV (5). [72] Hawking, Stephen, and Mlodinow, Leonard, The Grand Design, New York, Bantam Books, 2010, p. 178 ISBN 978-0-553-80537-6 [73] Wegner, D.M. (2002). The illusion of conscious will. Cambridge, MA: MIT Press. [74] Wegner, D.M.; Wheatley, T. (1999). "Apparent mental causation: sources of the experience of will". American Psychologist 54 (7): 480–491. doi:10.1037/0003-066X.54.7.480. PMID 10424155. [75] Aarts, H.; Custers, R.; Wegner, D. (2005). "On the inference of personal authorship: enhancing experienced agency by priming effect information.". Consciousness and cognition 14 (3): 439–458. doi:10.1016/j.concog.2004.11.001. PMID 16091264. [76] Kihlstrom, John (2004). "An unwarrantable impertinence" (http:/ / journals. cambridge. org/ action/ displayAbstract;jsessionid=296A64B183C6566E52D74D437D1169D2. tomcat1?fromPage=online& aid=287753#). Behavioral and Brain Sciences 27 (5): 666–667. doi:10.1017/S0140525X04300154. . [77] John Baer, James C. Kaufman and Roy F. Baumeister (2008). Are We Free? Psychology and Free Will (http:/ / socrates. berkeley. edu/ ~kihlstrm/ AutomaticityJuggernaut. htm). New York: Oxford University Press.. pp. 155–180. ISBN 0-19-518963-9. . [78] Nahmias, Eddy (2002). "When consciousness matters: a critical review of Daniel Wegner's The illusion of conscious will" (http:/ / www2. gsu. edu/ ~phlean/ papers/ When_Consciousness_Matters. pdf). Philosophical Psychology 15 (4): 527. doi:10.1080/0951508021000042049. . [79] Mele, Alfred R. (2009). Effective Intentions: The Power of Conscious Will (http:/ / ukcatalogue. oup. com/ product/ academic/ pn/ 9780199764686. do?sortby=bookTitleAscend). USA: Oxford University Press,. ISBN 978-0-19-538426-0. . [80] Pronin, Emily (2009). "The Introspection Illusion". In Mark P. Zanna. Advances in Experimental Social Psychology, Vol. 41. 41. Academic Press. pp. 42–43. doi:10.1016/S0065-2601(08)00401-2. ISBN 978-0-12-374472-2 [81] Baumeister RF, Masicampo EJ, Dewall CN. (2009). Prosocial benefits of feeling free: disbelief in free will increases aggression and reduces helpfulness. Pers Soc Psychol Bull. 35(2):260-8. PMID 19141628 doi:10.1177/0146167208327217 [82] Flood, Gavin (2004). The ascetic self: subjectivity, memory and tradition (http:/ / books. google. com/ books?id=fapXqp-JSL0C& printsec=frontcover& dq=The+ ascetic+ self:+ subjectivity,+ memory+ and+ tradition& hl=en& sa=X& ei=BU0wT_GFJeXi0QG55Jn4Cg& ved=0CDIQ6AEwAA#v=onepage& q=kaivalya& f=false). Cambridge University Press. p. 73. ISBN 978-0-521-60401-7. . [83] Koller, J. (2007) Asian Philosophies. 5th ed. Prentice Hall. ISBN 0-13-092385-0 [84] Swami Vivekananda (1907) "Sayings and utterances" (http:/ / www. ramakrishnavivekananda. info/ vivekananda/ volume_5/ sayings_and_utterances. htm). ramakrishnavivekananda.info. . [85] Gier, Nicholas and Kjellberg, Paul. "Buddhism and the Freedom of the Will: Pali and Mahayanist Responses" in Freedom and Determinism. Campbell, Joseph Keim; O'Rourke, Michael; and Shier, David. 2004. MIT Press [86] Alston, William P. (1985). "Divine Foreknowledge and Alternative Conceptions of Human Freedom". International Journal for Philosophy of Religion 18 (1): 19–32. doi:10.1007/BF00142277. [87] Aristotle. "De Interpretatione" in The Complete Works of Aristotle, vol. I, ed. Jonathan Barnes. Princeton University Press, Princeton, New Jersey, 1984. [88] Ockham, William. Predestination, God's Knowledge, and Future Contingents, early 14th century, trans. Marilyn McCord Adams and Norman Kretzmann 1982, Hackett, esp p. 46–7 [89] H. A. Wolfson, Philo, 1947 Harvard University Press; Religious Philosophy, 1961 Harvard University Press; and "St. Augustine and the Pelagian Controversy" in Religious Philosophy [90] Watt, Montgomery. Free-Will and Predestination in Early Islam. Luzac & Co.: London 1948; Wolfson, Harry. The Philosophy of Kalam, Harvard University Press 1976 [91] "Man and His Destiny" (http:/ / www. al-islam. org/ mananddestiny/ 3. htm). Al-islam.org. . Retrieved 2010-11-21. [92] Jackson, Timothy P. (1998) "Arminian edification: Kierkegaard on grace and free will" in Cambridge Companion to Kierkegaard, Cambridge University Press, Cambridge, 1998. 118 Free will [93] Kierkegaard, Søren. (1848) Journals and Papers, vol. III. Reprinted in Indiana University Press, Bloomington, 1967–78. [94] Mackie, J.L. (1955) "Evil and Omnipotence," Mind, new series, vol. 64, pp. 200–212. [95] NAHMIAS, Eddy; STEPHEN G MORRIS, Thomas NADELHOFFER, Jason TURNER (2006-07-01). "Is Incompatibilism Intuitive?" (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1111/ j. 1933-1592. 2006. tb00603. x/ abstract). Philosophy and Phenomenological Research 73 (1): 28–53. doi:10.1111/j.1933-1592.2006.tb00603.x. ISSN 1933-1592. . Retrieved 2011-04-29. [96] FELTZ, ADAM; EDWARD T COKELY, THOMAS NADELHOFFER (2009-02-01). "Natural Compatibilism versus Natural Incompatibilism: Back to the Drawing Board" (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1111/ j. 1468-0017. 2008. 01351. x/ abstract). Mind & Language 24 (1): 1–23. doi:10.1111/j.1468-0017.2008.01351.x. ISSN 1468-0017. . Retrieved 2011-04-29. [97] Nichols, Shaun; Joshua Knobe (2007-12-01). "Moral Responsibility and Determinism: The Cognitive Science of Folk Intuitions" (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1111/ j. 1468-0068. 2007. 00666. x/ abstract). NoÃ"s 41 (4): 663–685. doi:10.1111/j.1468-0068.2007.00666.x. ISSN 1468-0068. . Retrieved 2011-04-29. [98] Sarkissian, HAGOP; AMITA CHATTERJEE, FELIPE DE BRIGARD, JOSHUA KNOBE, SHAUN NICHOLS, SMITA SIRKER (2010-06-01). "Is Belief in Free Will a Cultural Universal?" (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1111/ j. 1468-0017. 2010. 01393. x/ abstract). Mind & Language 25 (3): 346–358. doi:10.1111/j.1468-0017.2010.01393.x. ISSN 1468-0017. . Retrieved 2011-04-29. [99] Pronin, Emily; Matthew B. Kugler (2010-12-28). "People believe they have more free will than others" (http:/ / www. pnas. org/ content/ 107/ 52/ 22469. abstract). Proceedings of the National Academy of Sciences 107 (52): 22469–22474. doi:10.1073/pnas.1012046108. . Retrieved 2011-04-29. [100] Feltz, Adam; Edward T. Cokely (2009-03). "Do judgments about freedom and responsibility depend on who you are? Personality differences in intuitions about compatibilism and incompatibilism" (http:/ / www. sciencedirect. com/ science/ article/ B6WD0-4TGGCRP-1/ 2/ 49d6f7959d2e37c9d864d0151cac8575). Consciousness and Cognition 18 (1): 342–350. doi:10.1016/j.concog.2008.08.001. ISSN 1053-8100. PMID 18805023. . Retrieved 2011-04-29. [101] Baumeister, R., A. W. Crescioni, and J. Alquist. 2009. Free will as advanced action control for human social life and culture. Neuroethics. doi:10.1007/s12152-009-9047-7. [102] Paulhus, D.L., and A. Margesson. 1994. Free Will and Determinism (FAD) scale. Unpublished manuscript, University of British Columbia,Vancouver, British Columbia, Canada. [103] Stillman, T.F., R.F. Baumeister, F.D. Fincham, T.E. Joiner, N.M. Lambert, A.R. Mele, and D.M. Tice. 2008. Guilty, free, and wise. Belief in free will promotes learning from negative emotions. Manuscript in preparation. [104] Bar-Hillel, M. 2007. Randomness is too important to be trusted to chance. Presented at the 2007 Summer Institute in Informed Patient Choice, Dartmouth Medical School, NH [105] Wagenaar, W.A. (1972). "Generation of random sequences by human subjects: A critical survey of literature". Psychological Bulletin 77: 65–72. doi:10.1037/h0032060. [106] Holton, Richard. (2011). Response to ‘Free Will as Advanced Action Control for Human Social Life and Culture’ by Roy F. Baumeister, A. William Crescioni and Jessica L. Alquist. Neuroethics 4:13–16. DOI 10.1007/s12152-009-9046-8 [107] NAHMIAS, EDDY; D. JUSTIN COATES, TREVOR KVARAN (2007-09-01). "Free Will, Moral Responsibility, and Mechanism: Experiments on Folk Intuitions" (http:/ / onlinelibrary. wiley. com/ doi/ 10. 1111/ j. 1475-4975. 2007. 00158. x/ abstract). Midwest Studies in Philosophy 31 (1): 214–242. doi:10.1111/j.1475-4975.2007.00158.x. ISSN 1475-4975. . Retrieved 2011-04-29. [108] Vohs, Kathleen D.; Jonathan W. Schooler (2008-01-01). "The Value of Believing in Free Will" (http:/ / pss. sagepub. com/ content/ 19/ 1/ 49. abstract). Psychological Science 19 (1): 49–54. doi:10.1111/j.1467-9280.2008.02045.x. PMID 18181791. . Retrieved 2011-04-29. [109] Vohs, K.D.; Schooler, J.W. (2008). "The value of believing in free will: Encouraging a belief in determinism increases cheating". Psychological Science 19 (1): 49–54. doi:10.1111/j.1467-9280.2008.02045.x. PMID 18181791. [110] Baumeister, R.F.; Masicampo, E.J.; DeWall, C.N. (2009). "Prosocial benefits of feeling free: Disbelief in free will increases aggression and reduces helpfulness". Personality and Social Psychology Bulletin 35 (2): 260–268. doi:10.1177/0146167208327217. PMID 19141628. [111] Baumeister, Roy F.; E.J. Masicampo, C. Nathan DeWall (2009-02-01). "Prosocial Benefits of Feeling Free: Disbelief in Free Will Increases Aggression and Reduces Helpfulness" (http:/ / psp. sagepub. com/ content/ 35/ 2/ 260. abstract). Personality and Social Psychology Bulletin 35 (2): 260–268. doi:10.1177/0146167208327217. PMID 19141628. . Retrieved 2011-04-29. [112] Alquist, J.L., and R.F. Baumeister. 2008. [Free will and conformity]. Unpublished raw data / manuscript in preparation, Florida State University. [113] Stillman, T.F. and Baumeister, R.F. 2008. Belief in free will supports guilt over personal misdeeds. Unpublished findings. Florida State University, Tallahassee, FL. [114] Alquist, J.L., M. Daly, T. Stillman, and R.F. Baumeister. 2009. [Belief in determinism decreases counterfactual thinking]. Unpublished raw data. [115] Epstude, K., and N.J. Roese. 2008. The functional theory of counterfactual thinking. Personality and Social Psychology 12: 168–192. [116] Stillman, Tyler F.; Roy F. Baumeister, Kathleen D. Vohs, Nathaniel M. Lambert, Frank D. Fincham, Lauren E. Brewer (2010-01-01). "Personal Philosophy and Personnel Achievement: Belief in Free Will Predicts Better Job Performance" (http:/ / spp. sagepub. com/ content/ 1/ 1/ 43. abstract). Social Psychological and Personality Science 1 (1): 43–50. doi:10.1177/1948550609351600. . Retrieved 2011-04-29. 119 Hawking, Stephen, and Mlodinow, Leonard, The Grand Design, New York, Bantam Books, 2010. Free will 120 Further reading • Bischof, Michael H. (2004). Kann ein Konzept der Willensfreiheit auf das Prinzip der alternativen Möglichkeiten verzichten? Harry G. Frankfurts Kritik am Prinzip der alternativen Möglichkeiten (PAP). In: Zeitschrift für philosophische Forschung (ZphF), Heft 4. • Dennett, Daniel C. (2003). Freedom Evolves. New York: Viking Press ISBN 0-670-03186-0 • Epstein J.M. (1999). Agent Based Models and Generative Social Science. Complexity, IV (5). • Gazzaniga, M. & Steven, M.S. (2004) Free Will in the 21st Century: A Discussion of Neuroscience and Law, in Garland, B. (ed.) Neuroscience and the Law: Brain, Mind and the Scales of Justice, New York: Dana Press, ISBN 1-932594-04-3, pp51–70. • Goodenough, O.R. (2004). "Responsibility and punishment". Philosophical Transactions of the Royal Society: Biological Sciences 359 (1451): 1805–1809. doi:10.1098/rstb.2004.1548. • Harnad, Stevan (2009) The Explanatory Gap (http://www.google.com/search?q=harnad+"explanatory+gap"+ site:http://philpapers.org/&hl=en&num=10&lr=&ft=i&cr=&safe=images) PhilPapers (http://philpapers. org/) • Harnad, Stevan (2001). "No Easy Way Out" (http://cogprints.org/1624/). The Sciences 41 (2): 36–42. • Harnad, Stevan (1982). "Consciousness: An Afterthought" (http://cogprints.org/1570/). Cognition and Brain Theory 5: 29–47. • Hofstadter, Douglas. (2007) I Am A Strange Loop. Basic Books. ISBN 978-0-465-03078-1 • Kane, Robert (1998). The Significance of Free Will. New York: Oxford University Press ISBN 0-19-512656-4 • Lawhead, William F. (2005). The Philosophical Journey: An Interactive Approach. McGraw-Hill Humanities/Social Sciences/Languages ISBN 0-07-296355-7. • Libet, Benjamin; Anthony Freeman; and Keith Sutherland, eds. (1999). The Volitional Brain: Towards a Neuroscience of Free Will. Exeter, UK: Imprint Academic. Collected essays by scientists and philosophers. • Morris, Tom Philosophy for Dummies. IDG Books ISBN 0-7645-5153-1. • Muhm, Myriam (2004). Abolito il libero arbitrio — Colloquio con Wolf Singer. L'Espresso 19.08.2004 larchivio.org (http://www.larchivio.org/xoom/myriam-singer.htm) • Nowak A., Vallacher R.R., Tesser A., Borkowski W. (2000). Society of Self: The emergence of collective properties in self-structure. Psychological Review. 107 • Schopenhauer, Arthur (1839). On the Freedom of the Will., Oxford: Basil Blackwell ISBN 0-631-14552-4. • Van Inwagen, Peter (1986). An Essay on Free Will. New York: Oxford University Press ISBN 0-19-824924-1. • Velmans, Max (2003) How Could Conscious Experiences Affect Brains? Exeter: Imprint Academic ISBN 0-907845-39-8. • Wegner, D. (2002). The Illusion of Conscious Will. Cambridge: Bradford Books • Williams, Clifford (1980). Free Will and Determinism: A Dialogue. Indianapolis: Hackett Publishing Co. • John Baer, James C. Kaufman, Roy F. Baumeister (2008). Are We Free? Psychology and Free Will. Oxford University Press, New York ISBN 0-19-518963-9 • Horst, Steven (2011), Laws, Mind, and Free Will. (http://www.themontrealreview.com/2009/ Freedom-and-the-laws-of-nature.php) (MIT Press) ISBN 0-262-01525-0 Free will 121 External links • Free Will and Determinism (http://www.dmoz.org/Society/Philosophy/Metaphysics/ Free_Will_and_Determinism/) at the Open Directory Project • Stanford Encyclopedia of Philosophy entries: • "Free Will" (http://plato.stanford.edu/entries/freewill/) • "Incompatibilism" (http://plato.stanford.edu/entries/incompatibilism-theories/) • "Divine Foreknowledge and Free Will" (http://plato.stanford.edu/entries/free-will-foreknowledge/) Internet Encyclopedia of Philosophy "Foreknowledge and Free Will" (http://www.iep.utm.edu/foreknow/) by Norman Swartz. "Free Will" (http://www.rep.routledge.com/article/V014) by Galen Strawson in Routledge Encyclopedia of Philosophy "Free Will" (http://www.newadvent.org/cathen/06259a.htm) in Catholic Encyclopedia The Determinism and Freedom Philosophy Website (http://www.ucl.ac.uk/~uctytho/dfwIntroIndex.htm) edited by Ted Honderich "Freedom and the Laws of Nature" (http://www.themontrealreview.com/2009/ Freedom-and-the-laws-of-nature.php) by Steven Horst (The Montréal Review) The Skeptics Dictionary on 'free will' (http://www.skepdic.com/freewill.html) • • • • • • • Jonathan Edwards's Freedom of the Will, slightly modified for easier reading (http://www.earlymoderntexts. com/f_edwards.html) 122 Fiction Time travel in fiction Time travel is a common theme in science fiction and is depicted in a variety of media. It simply means either going forward in time or backward, to experience the future, or the past. Literature Time travel can form the central theme of a book, or it can be simply a plot device. Time travel in fiction can ignore the possible effects of the time traveler's actions, as in A Connecticut Yankee in King Arthur's Court, or it can use one resolution or another of the Grandfather paradox. Early stories featuring time travel Although The Time Machine by H. G. Wells was instrumental in causing the idea of time travel to enter the public imagination, non-technological forms of time travel had appeared in a number of earlier stories, and some even earlier stories featured elements suggestive of time travel, but remain somewhat ambiguous. • In ancient Hindu mythology, the Mahabharatha mentions the story of the King Revaita, who travels to a different world to meet the creator Brahma and is shocked to learn that many ages have passed when he returns to Earth.[1][2] • Another very old example of this type of story can be found in the Talmud with the story of Honi HaM'agel who went to sleep for 70 years and woke up to a world where his grandchildren were grandparents and where all his friends and family were dead.[3] • Urashima Tarō, an early Japanese tale, involves traveling forwards in time to a distant future,[4] and was first described in the Nihongi (720).[5] It was about a young fisherman named Urashima Taro who visits an undersea palace and stays there for three days. After returning home to his village, he finds himself three hundred years in the future, where he is long forgotten, his house in ruins, and his family long dead.[4] • In Walter Map's 12th century De nugis curialium (Courtiers' Trifles), Map tells of the Briton King Herla, who is transported with his hunting party over two centuries into the future by the enchantment of a mysterious harlequin. • Memoirs of the Twentieth Century (1733) by Samuel Madden is mainly a series of letters from English ambassadors in various countries to the British "Lord High Treasurer", along with a few replies from the British foreign office, all purportedly written in 1997 and 1998 and describing the conditions of that era. However, the framing story is that these letters were actual documents given to the narrator by his guardian angel one night in 1728; for this reason, Paul Alkon suggests in his book Origins of Futuristic Fiction that "the first time-traveler in English literature is a guardian angel who returns with state documents from 1998 to the year 1728", although the book does not explicitly show how the angel obtained these documents. Alkon later qualifies this by writing "It would be stretching our generosity to praise Madden for being the first to show a traveler arriving from the future", but also says that Madden "deserves recognition as the first to toy with the rich idea of time-travel in the form of an artifact sent backwards from the future to be discovered in the present." • In the play Anno 7603, written by the Dano-Norwegian poet Johan Herman Wessel in 1781, the two main characters are moved to the future (AD 7603) by a good fairy. • Rip Van Winkle, Washington Irving's 1819 story, is about a man named Rip Van Winkle who takes a nap at a mountain and wakes up twenty years in the future, where he has been forgotten, his wife deceased, and his Time travel in fiction daughter grown up.[4] In the science fiction anthology Far Boundaries (1951), the editor August Derleth identifies the short story Missing One's Coach: An Anachronism, written for the Dublin University Magazine by an anonymous author in 1838, as a very early time travel story. In this story, the narrator is waiting under a tree to be picked up by a coach which will take him out of Newcastle, when he suddenly finds himself transported back over a thousand years, where he encounters the Venerable Bede in a monastery, and gives him somewhat ironic explanations of the developments of the coming centuries. It is never entirely clear whether these events actually occurred or were merely a dream. In 1843, the Charles Dickens novella A Christmas Carol depicts Ebeneezer Scrooge being transported back and forth in time to points in his own lifetime by a series of ghosts to visit Christmases Past, Present and Future. The book Paris avant les hommes (Paris before Men) by the French botanist and geologist Pierre Boiterd, published posthumously in 1861, in which the main character is transported to various prehistoric settings by the magic of a "lame demon", and is able to actively interact with prehistoric life. The short story The Clock That Went Backward [6], written by editor Edward Page Mitchell appeared in the New York Sun in 1881, another early example of time travel in fiction. Looking Backward (1888) by Edward Bellamy and News from Nowhere (1890) by William Morris, which feature a protagonist who wakes up in a socialist utopian future. 123 • • • • • • A Connecticut Yankee in King Arthur's Court (1889) by Mark Twain. • Tourmalin's Time Cheques (1891) by Thomas Anstey Guthrie (written under the pseudonym F. Anstey) was the first story to play with the paradoxes that time travel could cause. • Golf in the Year 2000 (1892) by J. McCullough tells the story of an Englishman who fell asleep in 1892 and awakens in the year 2000. The focus of the book is how the game of golf would have changed by then, but many social and technological themes are also discussed along the way, including a device similar to television and women's equality. Time travel themes and ideological function A number of themes tend to recur in time travel stories, often with enough variations to make them interesting. • Changing the past: in this genre, a visitor to the past changes history using knowledge and/or technology from their own time, either for good or evil, or sometimes accidentally, creating an alternate history as a result. Examples of this genre include Lest Darkness Fall by L. Sprague de Camp. • The Guardians of Time: in this genre, a group of people are charged with ensuring that time turns out 'properly' (or protecting it from changes by other travelers). This includes The Big Time and the other Change War stories by Fritz Leiber, Terry Pratchett's Thief of Time, Simon Hawke's TimeWars series, John Schettler's Meridian Series [7] , Simon Lee's Timekeepers [8], and The End of Eternity by Isaac Asimov. Another example of this concept is the Doctor Who sci-fi series, whose main character is a "Time Lord" called "the Doctor" who personally intervenes to fight the evil he encounters if he is called on to do so and whose people are essentially scholars and historians who usually only observe histories. • Preventing a bad future: in this genre, the main characters learn, either by going to the future and returning or by the arrival of a time traveler from the future, that the future has not turned out well, having either turned into a dystopia or resulting in the end of the world. The characters then try to change something in the present which prevents said future from coming to pass. The Terminator franchise includes several stories of time travelers from the future, waging war to create or prevent a post-apocalyptic future. • Unintentional change or fulfillment: in this genre, a time traveler intends to observe past events, or is taken to the past against his will and tries to return to his proper time. However, the time traveler discovers that his actions have unintentionally altered the future because of the Butterfly effect. A Sound of Thunder is an example of this genre. Time travel in fiction The time travel motif also has an ideological function because it literally provides the necessary distancing effect that science fiction needs to be able to metaphorically address the most pressing issues and themes that concern people in the present. If the modern world is one where the individuals feel alienated and powerless in the face of bureaucratic structures and corporate monopolies, then time travel suggests that Everyman and Everybody is important to shaping history, to making a real and quantifiable difference to the way the world turns out. —Sean Redmond, Liquid Metal: the science fiction film reader (2004)[9] 124 References [1] [2] [3] [4] [5] [6] [7] [8] [9] Encyclopedia for Epics of Ancient India - Revati (http:/ / www. mythfolklore. net/ india/ encyclopedia/ revati. htm) Lord Balarama | Sri Mayapur (http:/ / mayapur. com/ node/ 1160/ ) "Choni HaMe'agel" (http:/ / www. jewishsearch. com/ article_395. html). Jewish search. . Retrieved November 6, 2009. Yorke, Christopher (February 2006), "Malchronia: Cryonics and Bionics as Primitive Weapons in the War on Time" (http:/ / jetpress. org/ volume15/ yorke-rowe. html), Journal of Evolution and Technology 15 (1): 73–85, , retrieved 2009-08-29 Rosenberg, Donna (1997), Folklore, myths, and legends: a world perspective, McGraw-Hill, p. 421, ISBN 0-8442-5780-X http:/ / www. horrormasters. com/ Text/ a2221. pdf http:/ / dharma6. com http:/ / www. timekeepersbook. com Redmond, Sean (editor). Liquid Metal: the Science Fiction Film Reader. London: Wallflower Press, 2004. External links • timelinks - the big list of time travel video, time travel movies, & time travel TV (http://www.aetherco.com/ timelinks/timevideo-thebiglist.html) - over 700 movies and television programs featuring time travel • SciFan: Time Travel - Time Control - Time Warp (http://www.scifan.com/themes/themes. asp?TH_themeid=4&Items=) - list of over 2400 books featuring time travel • Aparta Krystian. Conventional Models of Time and Their Extensions in Science Fiction (http://www.timetravel. 110mb.com) A master's thesis exploring conceptual blending in time travel. • Andy's Anachronisms (http://www.timetravelreviews.com) - Exploring the themes of Time Travel and Alternate Universes in Literature and Entertainment • Ultimate Time Travel (http://www.UltimateTimeTravel.com) - Reviewing books, movies and computer games that deal with concept of Time Travel • Time Travel Movies (http://www.toptenz.net/top-ten-time-travel-movies.php) - Reviews and clips of the some more influential movies involving time travel. Parallel universe 125 Parallel universe A parallel universe or alternative reality is a hypothetical self-contained separate reality coexisting with one's own. A specific group of parallel universes is called a "multiverse", although this term can also be used to describe the possible parallel universes that constitute reality. While the terms "parallel universe" and "alternative reality" are generally synonymous and can be used interchangeably in most cases, there is sometimes an additional connotation implied with the term "alternative reality" that implies that the reality is a variant of our own. The term "parallel universe" is more general, without any connotations implying a relationship, or lack of relationship, with our own universe. A universe where the very laws of nature are different – for example, one in which there are no relativistic limitations and the speed of light can be exceeded – would in general count as a parallel universe but not an alternative reality. The correct quantum mechanical definition of parallel universes is "universes that are separated from each other by a single quantum event." Introduction Fantasy has long borrowed the idea of "another world" from myth, legend and religion. Heaven, Hell, Olympus, and Valhalla are all “alternative universes” different from the familiar material realm. Modern fantasy often presents the concept as a series of planes of existence where the laws of nature differ, allowing magical phenomena of some sort on some planes. This concept was also found in ancient Hindu mythology, in texts such as the Puranas, which expressed an infinite number of universes, each with its own gods.[1] Similarly in Persian literature, "The Adventures of Bulukiya", a tale in the One Thousand and One Nights, describes the protagonist Bulukiya learning of alternative worlds/universes that are similar to but still distinct from his own.[2] In other cases, in both fantasy and science fiction, a parallel universe is a single other material reality, and its co-existence with ours is a rationale to bring a protagonist from the author's reality into the fantasy's reality, such as in The Chronicles of Narnia by C. S. Lewis or even the beyond-the-reflection travel in the two main works of Lewis Carroll. Or this single other reality can invade our own, as when Margaret Cavendish's English heroine sends submarines and "birdmen" armed with "fire stones" back through the portal from The Blazing World to Earth and wreaks havoc on England's enemies. In dark fantasy or horror the parallel world is often a hiding place for unpleasant things, and often the protagonist is forced to confront effects of this other world leaking into his own, as in most of the work of H. P. Lovecraft and the Doom computer game series, or Warhammer/40K miniature and computer games. In such stories, the nature of this other reality is often left mysterious, known only by its effect on our own world. The concept also arises outside the framework of quantum mechanics, as is found in Jorge Luis Borges short story El jardín de senderos que se bifurcan ("The Garden of Forking Paths"), published in 1941 before the many-worlds interpretation had been invented. In the story, a Sinologist discovers a manuscript by a Chinese writer where the same tale is recounted in several ways, often contradictory, and then explains to his visitor (the writer's grandson) that his relative conceived time as a "garden of forking paths", where things happen in parallel in infinitely branching ways. One of the first Sci-Fi examples is John Wyndham's Random Quest about a man who, on awaking after a laboratory accident, finds himself in a parallel universe where World War II never happened with consequences for his professional and personal life, giving him information he can use on return to his own universe. While this is a common treatment in Sci-Fi, it is by no means the only presentation of the idea, even in hard science fiction. Sometimes the parallel universe bears no historical relationship to any other world; instead, the laws of nature are simply different than those in our own, as in the novel Raft by Stephen Baxter, which posits a reality where the gravitational constant is much larger than in our universe. (Note, however, that Baxter explains later in Vacuum Diagrams that the protagonists in Raft are descended from people who came from the Xeelee Sequence universe.) One motif is that the way time flows in a parallel universe may be very different, so that a character returning to one might find the time passed very differently for those he left behind. This is found in folklore: King Herla visited Parallel universe Fairy and returned three centuries later; although only some of his men crumbled to dust on dismounting, Herla and his men who did not dismount were trapped on horseback, this being one folkloric account of the origin of the Wild Hunt.[3] C. S. Lewis made use of this in the Chronicles of Narnia; indeed, a character points out to two skeptics that there is no need for the time between the worlds to match up, but it would be very odd for the girl who claims to have visited a parallel universe to have dreamed up such a different time flow.[4] The division between science fiction and fantasy becomes fuzzier than usual when dealing with stories that explicitly leave the universe we are familiar with, especially when our familiar universe is portrayed as a subset of a multiverse. Picking a genre becomes less a matter of setting, and more a matter of theme and emphasis; the parts of the story the author wishes to explain and how they are explained. Narnia is clearly a fantasy, and the TV series Sliders is clearly science fiction, but works like the World of Tiers series or Glory Road tend to occupy a much broader middle ground. Parallel universes are considered parallel because there is no way of reaching them. All other dimensions are not parallel, but more than likely most of them are. An Einstein Rosen bridge, or Wormhole, can take you to a different dimension. Note that the journey through space-time continuum could backwards age you, or wipe you from existence. More than likely, if you managed to get to the alternate dimension, then you would have no memory of how you got there. The dangers of time-space travel are still being investigated, and possibilities are growing. Typically, parallel universes fall into two classifications. The first may be more accurately called a "diverging universe" whereby two versions of Earth share a common history up to a point of divergence. At this point, the outcome of some even happens differently on the two Earths and the histories continue to become more different as time elapses since that point. (E.g. Parallels (Star Trek: The Next Generation). The second type is where despite certain, often large, difference between the two Earths history and/or culture, they maintain strong similarities. In such cases, it is common that every person in one universe will have a counterpart in the other universe with the same name, ancestry, appearance, and frequently occupation but often a very different personality. (e.g. Mirror, Mirror (Star Trek: The Original Series). 126 Science fiction While technically incorrect, and looked down upon by hard science-fiction fans and authors, the idea of another “dimension” has become synonymous with the term “parallel universe”. The usage is particularly common in movies, television and comic books and much less so in modern prose science fiction. The idea of a parallel world was first introduced in comic books with the publication of Flash #123 - "Flash of Two Worlds". In written science fiction, “new dimensions” more commonly — and more accurately — refer to additional coordinate axes, beyond the three spatial axes with which we are familiar. By proposing travel along these extra axes, which are not normally perceptible, the traveler can reach worlds that are otherwise unreachable and invisible. In 1884, Edwin A. Abbott wrote the seminal novel exploring this concept called Flatland: A Romance of Many Dimensions. It describes a world of two dimensions inhabited by living squares, triangles, and circles, called Flatland, as well as Pointland (0 dimensions), Lineland (1 dimension), and Spaceland (three dimensions) and finally posits the possibilities of even greater dimensions. Isaac Asimov, in his foreword to the Signet Classics 1984 edition, described Flatland as "The best introduction one can find into the manner of perceiving dimensions." In 1895, The Time Machine by H. G. Wells used time as an additional “dimension” in this sense, taking the four-dimensional model of Edwin A. Abbott's Flatland is set in a world of two dimensions. Parallel universe classical physics and interpreting time as a space-like dimension in which humans could travel with the right equipment. Wells also used the concept of parallel universes as a consequence of time as the fourth dimension in stories like The Wonderful Visit and Men Like Gods, an idea proposed by the astronomer Simon Newcomb, who talked about both time and parallel universes; "Add a fourth dimension to space, and there is room for an indefinite number of universes, all alongside of each other, as there is for an indefinite number of sheets of paper when we pile them upon each other".[5] There are many examples where authors have explicitly created additional spatial dimensions for their characters to travel in, to reach parallel universes. In Doctor Who, the Doctor accidentally enters a parallel universe while attempting to repair the TARDIS console in Inferno. The parallel universe was similar to the real universe but with some different aspects. Douglas Adams, in the last book of the Hitchhiker's Guide to the Galaxy series, Mostly Harmless, uses the idea of probability as an extra axis in addition to the classical four dimensions of space and time similar to the many-worlds interpretation of quantum physics. Though, according to the novel, they're not really parallel universes at all but only a model to capture the continuity of space, time and probability. Robert A. Heinlein, in The Number of the Beast, postulated a six-dimensional universe. In addition to the three spatial dimensions, he invoked symmetry to add two new temporal dimensions, so there would be two sets of three. Like the fourth dimension of H. G. Wells’ "Time Traveller", these extra dimensions can be traveled by persons using the right equipment. 127 Hyperspace Perhaps the most common use of the concept of a parallel universe in science fiction is the concept of hyperspace. Used in science fiction, the concept of “hyperspace” often refers to a parallel universe that can be used as a faster-than-light shortcut for interstellar travel. Rationales for this form of hyperspace vary from work to work, but the two common elements are: 1. at least some (if not all) locations in the hyperspace universe map to locations in our universe, providing the "entry" and "exit" points for travellers. 2. the travel time between two points in the hyperspace universe is much shorter than the time to travel to the analogous points in our universe. This can be because of a different speed of light, different speed at which time passes, or the analogous points in the hyperspace universe are just much closer to each other. Sometimes "hyperspace" is used to refer to the concept of additional coordinate axes. In this model, the universe is thought to be "crumpled" in some higher spatial dimension and that traveling in this higher spatial dimension, a ship can move vast distances in the common spatial dimensions. An analogy is to crumple a newspaper into a ball and stick a needle straight through, the needle will make widely spaced holes in the two-dimensional surface of the paper. While this idea invokes a "new dimension", it is not an example of a parallel universe. It is a more scientifically plausible use of hyperspace. (See wormhole.) While use of hyperspace is common, it is mostly used as a plot device and thus of secondary importance. While a parallel universe may be invoked by the concept, the nature of the universe is not often explored. So, while stories involving hyperspace might be the most common use of the parallel universe concept in fiction, it is not the most common source of fiction about parallel universes. Parallel universe 128 Time travel and alternate history The most common use of parallel universes in science fiction, when the concept is central to the story, is as a backdrop and/or consequence of time travel. A seminal example of this idea is in Fritz Leiber’s novel, The Big Time where there’s a war across time between two alternate futures each side manipulating history to create a timeline that results into their own world. Time-travelers in fiction often accidentally or deliberately create alternate histories, such as in The Guns of the South by Harry Turtledove where the Confederate Army is given the technology to produce AK-47 rifles and ends up winning the American Civil War. (However, Ward Moore reversed this staple of alternate history fiction in his Bring the Jubilee (1953), where an alternative world where the Confederate States of America won the Battle of Gettysburg and the American Civil War is destroyed after a historian and time traveller from the defeated United States of that world travels back to the scene of the battle and inadvertently changes the result so that the North wins British author H. G. Wells' 1895 novel The Time Machine is an early example of time travel in that battle.) The alternate history novel 1632 by Eric Flint explicitly modern fiction. states, albeit briefly in a prologue, that the time travelers in the novel (an entire town from West Virginia) have created a new and separate universe when they're transported into the midst of the Thirty Years War in 17th century Germany. (This sort of thing is known as an ISOT among alternate history fans, after S.M. Stirling's Island in the Sea of Time: an ISOT is when territory or a large group of people is transported back in time to another historical period or place. Typically, alternate histories are not technically parallel universes. Though the concepts are similar, there are significant differences. In cases where characters travel to the past, they may cause changes in the timeline (creating a point of divergence) that result in changes to the present. The alternate present will be similar in different degrees to the original present as would be the case with a parallel universe. The main difference is that parallel universes co-exist whereas only one history or alternate history can exist at any one moment. Another difference is that travelling to a parallel universe involves some type of inter-dimensional travel whereas alternative histories involve some type of time travel. (However, since the future is only potential and not actual, it is often conceived that more than one future may exist simultaneously.) The concept of "sidewise" time travel, a term taken from Murray Leinster's "Sidewise in Time", is often used to allow characters to pass through many different alternate histories, all descendant from some common branch point. Often worlds that are similar to each other are considered closer to each other in terms of this sidewise travel. For example, a universe where World War II ended differently would be “closer” to us than one where Imperial China colonized the New World in the 15th century. H. Beam Piper used this concept, naming it "paratime" and writing a series of stories involving the Paratime Police who regulated travel between these alternative realities as well as the technology to do so. Keith Laumer used the same concept of "sideways" time travel in his 1962 novel Worlds of the Imperium. More recently, novels such as Frederik Pohl's The Coming of the Quantum Cats and Neal Stephenson's Anathem explore human-scale readings of the "many worlds" interpretation of quantum mechanics, postulating that historical events or human consciousness spawns or allows "travel" among alternate universes. Frequent 'types' of universe explored in sidewise and alternative history works include worlds in which the Nazis won the Second World War, such as in The Man in the High Castle by Philip K. Dick, SS-GB by Len Deighton and Fatherland by Robert Harris, and worlds in which the Roman Empire never fell, such as in Roma Eterna by Robert Silverberg and Romanitas by Sophia McDougall. In his novel Warlords of Utopia, part of the loosely linked Faction Parallel universe Paradox series, Lance Parkin explored a multiverse in which every universe in which Rome never fell goes to war with every universe in which the Nazis won WWII. The series was created by Lawrence Miles, whose earlier work Dead Romance featured the concept of an artificially created universe existing within another -specifically, within a bottle - and explored the consequences of inhabitants of the 'real' universe entering the Universe-in-a-Bottle. In the His Dark Materials trilogy, the universe the protagonist starts in is a Victorian counterpart to ours, although it takes place at the same time. It also appears that the Protestant Reformation never happened. In his short story, Rumfuddle, Jack Vance invents a doorway to an infinite number of universes at any given time, so that everyone on the planet can have their own private world. Some are inhabited by humans. On some, man doesn't exist. The trouble comes when some of the Rumfuddlers (a term given to an annual gathering to see who can best mess around with what should be) play pranks on parallel world, such as switching the infant Adolf Hitler with a baby from a Jewish couple, or putting together a football team made up of all of the great men in history. 129 Counter-Earth The concept of Counter-Earth is typically similar to that of parallel universes but is actually a distinct idea. A counter-earth is a planet that shares Earth's orbit but is on the opposite side of the Sun and therefore cannot be seen from Earth. There would be no necessity that such a planet would be like Earth in any way though typically in fiction, it is usually nearly identical to Earth. Since counter-earth is always within our own universe (and our own solar system), travel to it can be accomplished with ordinary space travel. See Counter-Earth for literary and film examples. Convergent evolution Convergent evolution is a biological concept whereby unrelated species acquire similar traits because they adapted to a similar environment and/or played similar roles in their ecosystems. In fiction, the concept is extended whereby similar planets will result in races with similar cultures and/or histories. Technically this is not a type of parallel universe since such planets can be reached via ordinary space travel, but the stories are similar in some respects. In "Bread and Circuses (Star Trek: The Original Series)", the enterprise encounters a planet called Magna Roma which has many physical resemblances to Earth such as its atmosphere, land to ocean ratio, and size. The landing party discovers that the planet is at roughly a late 20th-century level of technology but its society is similar to the Roman Empire. It was as if the Roman Empire had not fallen but had continued to that time. There is also a reference to the Roman god Jupiter. At the end of the episode, it is discovered that their own version Jesus, referred simply as "the son". In The Omega Glory (Star Trek), the crew visit a planet on which there is a conflict between two peoples called the Yangs and the Kohms. They discover that the Yangs are like Earth's Yankees (i.e. Americans) and the Kohms are like Earth's communists. The Yangs had a ritual speech that was word for word identical to the American Pledge of Allegiance but at some point in the past the Kohms had taken over. In Miri (Star Trek: The Original Series), the Enterprise crew encounter a planet (later called Onlies) that is physically identical to Earth. History on the two planets were apparently identical until the 20th centuries when scientists on Onlies had accidentally created a deadly virus that killed all the adults but extended the lives of the children. Parallel universe 130 Convergent Evolution due to contamination As similar concept in biology is gene flow. In this case, a planet may start as different from Earth, but due to the influence of Earth culture, the planet come to resemble Earth in some way. Technically this is not a type of parallel universe since such planets can be reached via ordinary space travel, but the stories are similar in some respects. In Patterns of Force (Star Trek: The Original Series), a planet is discovered that has become very similar to Nazi Germany due to the influence of a professor that came to reside there. In A Piece of the Action (Star Trek: The Original Series), the Enterprise crew visits a planet that resembles mob ruled cities of Earth in the 1920s due to a book titled "Chicago Mobs of the Twenties" that had been left behind by previous Earth craft. Fantasy Stranger in a strange land Fantasy authors often want to bring characters from the author's (and the reader's) reality into their created world. Before the mid-20th century, this was most often done by hiding fantastic worlds within hidden parts of the author's own universe. Peasants who seldom if ever traveled far from their villages could not conclusively say that it was impossible that an ogre or other fantastical beings could live an hour away, but increasing geographical knowledge meant that such locations had to be farther and farther off.[6] Characters in the author's world could board a ship and find themselves on a fantastic island, as Oz and its surroundings. Jonathan Swift does in Gulliver's Travels or in the 1949 novel Silverlock by John Myers Myers, or be sucked up into a tornado and land in Oz. These "lost world" stories can be seen as geographic equivalents of a "parallel universe", as the worlds portrayed are separate from our own, and hidden to everyone except those who take the difficult journey there. The geographic "lost world" can blur into a more explicit "parallel universe" when the fantasy realm overlaps a section of the "real" world, but is much larger inside than out, as in Robert Holdstock's novel Mythago Wood. Madeleine L'engle, "Wrinkle in Time" series: characters go from the present time to places in the universe. After the mid-20th century, perhaps influenced by ideas from science fiction, perhaps because exploration had made many places on the map too clear to write "Here there be dragons", many fantasy worlds became completely separate from the author's world.[6] A common trope is a portal or artifact that connects worlds together, prototypical examples being the wardrobe in C. S. Lewis' The Lion, the Witch, and the Wardrobe, or the sigil in James Branch Cabell's The Cream of the Jest. In Hayao Miyazaki's Spirited Away, Chihiro Ogino and her parents climb over a small stream into the spirit world. The main difference between this type of story and the "lost world" above, is that the fantasy realm can only be reached by certain people, or at certain times, or after following certain rituals, or with the proper artifact. In some cases, physical travel is not even possible, and the character in our reality travels in a dream or some other altered state of consciousness. Examples include the Dream Cycle stories by H. P. Lovecraft or the Thomas Covenant stories of Stephen R. Donaldson. Often, stories of this type have as a major theme the nature of reality itself, questioning if the dream-world can have the same "reality" as the waking world. Science fiction often employs this theme (usually without the dream-world being "another" universe) in the ideas of cyberspace and virtual reality. Parallel universe 131 Between the worlds Most stories in this mold simply transport a character from the real world into the fantasy world where the bulk of the action takes place. Whatever gate is used – such as the tollbooth in The Phantom Tollbooth by Norton Juster, or the mirror in Lewis Carroll's Through the Looking-Glass – is left behind for the duration of the story, until the end, and then only if the protagonists will return. However, in a few cases the interaction between the worlds is an Through the Looking-Glass -- and the parallel important element, so that the focus is not on one world or the other, universe Alice found there but on both, and their interaction. After Rick Cook introduced a computer programmer into a high fantasy world, his wizardry series steadily acquired more interactions between this world and ours. In Aaron Allston's Doc Sidhe our "grim world" is paralleled by a "fair world" where the elves live and history echoes ours. A major portion of the plot deals with preventing a change in interactions between the worlds. Margaret Ball, in No Earthly Sunne, depicts the interaction of our world with Faerie, and the efforts of the Queen of Faerie to deal with the slow drifting apart of Earth and Faerie. Poul Anderson depicts Hell as a parallel universe in Operation Chaos, and the need to transfer equivalent amounts of mass between the worlds explains why a changeling is left for a kidnapped child. Interactions between magical and scientific universes, and the protagonists' attempts to restore and maintain the balance between them, are major plot points in Piers Anthony's Apprentice Adept series; he depicts two worlds, the "SF" planet Proton and the fantasy-based Phaze, such that every person born in either world has a physical duplicate on the other world. Only when one duplicate has died can the other cross between the worlds. Several of his Xanth novels also revolve around interactions between the magical realm of Xanth and "Mundania". Multiple worlds, rather than a pair, increase the importance of the relationships. In The Lion, the Witch, and the Wardrobe, there are only our world and Narnia, but in other of C. S. Lewis's works, there are hints of other worlds, and in The Magician's Nephew, the Wood between the Worlds shows many possibilities, and the plot is governed by transportation between worlds, and the effort to right problems stemming from them. In His Dark Materials by Philip Pullman, the two protagonist Lyra and Will find themselves lost amongst many worlds, and travel them looking for the other. In Andre Norton's Witch World, begun with a man from Earth being transported to this world, gates frequently lead to other worlds — or come from them. While an abundance of illusions, disguises, and magic that repels attention make certain parts of Witch World look like parallel worlds, some are clearly parallel in that time runs differently in them, and such gates pose a repeated problem in Witch World. In the radio sitcom Undone, the main character, Edna Turner, prevents people from a parallel version of London called "Undone" from moving to London and making the city too weird. There are other parallel versions of London, and one of the main plots in the series is the attempt by The Prince to unite all versions of London together. Travel between the manyworlds is the central conceit of Planesrunner, where the protagonist travels to a parallel London in a world without fossil fuels. Linking rooms of various types (not all actual rooms) can hook together any number of worlds. The characters may chose only one, but the choice is all important in determining the worlds. Parallel universe 132 Fantasy multiverses The idea of a multiverse is as fertile a subject for fantasy as it is for science fiction, allowing for epic settings and godlike protagonists. Among the most epic and far-ranging fantasy "multiverses" is that of Michael Moorcock. Like many authors after him, Moorcock was inspired by the many worlds interpretation of quantum mechanics, saying: It was an idea in the air, as most of these are, and I would have come across a reference to it in New Scientist (one of my best friends was then editor) ... [or] physicist friends would have been talking about it. ... Sometimes what happens is that you are imagining these things in the context of fiction while the physicists and mathematicians are imagining them in terms of science. I suspect it is the romantic imagination working, as it often does, perfectly efficiently in both the arts and the sciences. Unlike many science-fiction interpretations, Moorcock's Eternal Champion stories go far beyond alternate history to include mythic and sword and sorcery settings as well as some worlds more similar to our own. However, the Eternal Champion himself is incarnate in all of them. Roger Zelazny used a mythic cosmology in his Chronicles of Amber series. His protagonist is a member of the royal family of Amber, whose members represent a godlike pantheon ruling over a prototypical universe that represents Order. All other universes are increasingly distorted "shadows" of it, ending finally at the other extreme, Chaos, which is the complete negation of the prototype. Travel between these "shadow" universes is only possible by beings descended from the blood of this pantheon. Those "of the blood" can walk through Shadow, imagining any possible reality and then walk to it, making their environment more similar to their desire as they go. It is argued between the characters whether these "shadows" even exist before they're imagined by a member of the royal family of Amber, or if the "shadows'" existence can be seen as an act of godlike creation. In the World of Tiers novels by Philip José Farmer, the idea of godlike protagonists is even more explicit. The background of the stories is a multiverse where godlike beings have created a number of pocket universes that represent their own desires. Our own world is part of this series, but interestingly our own universe is revealed to be much smaller than it appears, ending at the edge of the solar system. The term 'polycosmos' was coined as an alternative to 'multiverse' by the author and editor Paul le Page Barnett, best known by the pseudonym John Grant, and is built from Greek rather than Latin morphemes. It is used by Barnett to describe a concept binding together a number of his works, its nature meaning that "all characters, real or fictional [...] have to co-exist in all possible real, created or dreamt worlds; [...] they're playing hugely different roles in their various manifestations, and the relationships between them can vary quite dramatically, but the essence of them remains the same."[7] There are multiverses also in the Warcraft universe, The Chronicles of Narnia, Terry Pratchett's Discworld series, and Diana Wynne Jones's Chrestomanci, Howl's Moving Castle and Deep Secret books and standalone book A Sudden Wild Magic. Fictional universe as alternative universe There are many examples of the meta-fictional idea of having the author's created universe (or any author's universe) rise to the same level of "reality" as the universe we're familiar with. The theme is present in works as diverse as H.G. Wells' Men Like Gods, Myers' Silverlock, and Heinlein’s Number of the Beast. Fletcher Pratt and L. Sprague de Camp took the protagonist of the Harold Shea series through the worlds of Norse myth, Edmund Spenser's Faerie Queene, Ludovico Ariosto's Orlando Furioso, and the Kalevala[8]— without ever quite settling whether writers created these parallel worlds by writing these works, or received impressions from the worlds and wrote them down. In an interlude set in "Xanadu", a character claims that the universe is dangerous because the poem went unfinished, but whether this was his misapprehension or not is not established. Some fictional approaches definitively establish the independence of the parallel world, sometimes by having the world differ from the book's account; other approaches have works of fiction create and affect the parallel world: L. Parallel universe Sprague de Camp's Solomon's Stone, taking place on an astral plane, is populated by the daydreams of mundane people, and in Rebecca Lickiss's Eccentric Circles, an elf is grateful to Tolkien for transforming elves from dainty little creatures. These stories often place the author, or authors in general, in the same position as Zelazny's characters in Amber. Questioning, in a literal fashion, if writing is an act of creating a new world, or an act of discovery of a pre-existing world. Occasionally, this approach becomes self-referential, treating the literary universe of the work itself as explicitly parallel to the universe where the work was created. Stephen King's seven-volume Dark Tower series hinges upon the existence of multiple parallel worlds, many of which are King's own literary creations. Ultimately the characters become aware that they are only "real" in King's literary universe (this can be debated as an example of breaking the fourth wall), and even travel to a world — twice — in which (again, within the novel) they meet Stephen King and alter events in the real Stephen King's world outside of the books. An early instance of this was in works by Gardner Fox for DC Comics in the 1960s, in which characters from the Golden Age (which was supposed to be a series of comic books within the DC Comics universe) would cross over into the main DC Comics universe. One comic book did provide an explanation for a fictional universe existing as a parallel universe. The parallel world does "exist" and it resonates into the "real world." Some people in the "real world" pick up on this resonance, gaining information about the parallel world which they then use to write stories. 133 Elfland Elfland, or Faerie, the otherworldly home not only of elves and fairies but goblins, trolls, and other folkloric creatures, has an ambiguous appearance in folklore. On one hand, the land often appears to be contiguous with 'ordinary' land. Thomas the Rhymer might, on being taken by the Queen of Faerie, be taken on a road like one leading to Heaven or Hell. This is not exclusive to English or French folklore. In Norse mythology, Elfland (Alfheim) was also the name of what today is the Swedish province of Bohuslän. In the sagas, it said that the people of this petty kingdom were more beautiful than other people, as they were related to the elves, showing that not only the territory was associated with elves, but also the race of its people. While sometimes folklore seems to show fairy intrusion into human lands — "Tam Lin" does not show any otherworldly aspects about the land in which the confrontation takes place — at other times the otherworldly aspects are clear. Most frequently, time can flow differently for those trapped by the fairy dance than in the lands they come from; although, in an additional complication, it may only be an appearance, as many returning from Faerie, such as Oisín, have found that time "catches up" with them as soon as they have contact with ordinary lands. Fantasy writers have taken up the ambiguity. Some writers depict the land of the elves as a full-blown parallel universe, with portals the only entry — as in Josepha Sherman's Prince of the Sidhe series or Esther Friesner's Elf Defense — and others have depicted it as the next land over, possibly difficult to reach for magical reasons — Hope Mirrlees's Lud-in-the-Mist, or Lord Dunsany's The King of Elfland's Daughter. In some cases, the boundary between Elfland and more ordinary lands is not fixed. Not only the inhabitants but Faerie itself can pour into more mundane regions. Terry Pratchett's Discworld series proposes that the world of the Elves is a "parasite" universe, that drifts between and latches onto others such as Discworld and our own world (referred to as "Roundworld" in the novels). In the young teenage book Mist by Kathryn James, the Elven world lies through a patch of mist in the woods. It was constructed when the Elven were thrown out of our world. Travel to and fro is possible by those in the know, but can have lethal consequences. Parallel universe 134 Films The most famous treatment of the alternative universe concept in film could be considered The Wizard of Oz, which portrays a parallel world, famously separating the magical realm of the Land of Oz from the mundane world by filming it in Technicolor while filming the scenes set in Kansas in sepia. A later example is the Frank Capra movie, It's a Wonderful Life where the main character George Bailey is shown by a guardian angel the city of Pottersville, which was George Bailey's hometown of Bedford Falls as it would have been if he had never existed. Another notable In Frank Capra's It's A Wonderful Life (1946), depiction of a parallel universe in movies is in Back to the Future Part George Bailey (center, played by James Stewart) is shown by his guardian angel how the world II by Robert Zemeckis, starring Michael J. Fox and Christopher Lloyd, would have been radically different for the worse showing an accidentally created alternative present and future. Like It's if Bailey had never existed. a Wonderful Life, The Big Time, and many other time travel stories using this concept, it is clear that these alternative presents/futures are mutually exclusive with the protagonists' own — so, strictly speaking, the universes are not parallel in that they cannot co-exist, rather they oscillate between one or the other. Another common use of the theme is as a prison for villains or demons. The idea is used in the first two Superman movies starring Christopher Reeve where Kryptonian villains were sentenced to the Phantom Zone from where they eventually escaped. An almost exactly parallel use of the idea is presented in the campy cult film The Adventures of Buckaroo Banzai Across the 8th Dimension, where the "8th dimension" is essentially a "phantom zone" used to imprison the villainous Red Lectroids. Uses in horror films include the 1986 film From Beyond (based on the H. P. Lovecraft story of the same name) where a scientific experiment induces the experimenters to perceive aliens from a parallel universe, with bad results. The 1987 John Carpenter film Prince of Darkness is based on the premise that the essence of a being described as Satan, trapped in a glass canister and found in an abandoned church in Los Angeles, is actually an alien being that is the 'son' of something even more evil and powerful, trapped in another universe. The protagonists accidentally free the creature, who then attempts to release his "father" by reaching in through a reflective glass, or mirror. Some films present parallel realities that are actually different contrasting versions of the narrative itself. Commonly this motif is presented as different points of view revolving around a central (but sometimes unknowable) "truth", the seminal example being Akira Kurosawa's Rashomon. Conversely, often in film noir and crime dramas, the alternative narrative is a fiction created by a central character, intentionally — as in The Usual Suspects — or unintentionally — as in Angel Heart. Less often, the alternative narratives are given equal weight in the story, making them truly alternative universes, such as in the German film Run Lola Run, the short-lived British West End musical Our House and the British film Sliding Doors. More recent films that have explicitly explored parallel universes are: the 2000 film The Family Man, the 2001 cult movie Donnie Darko, which deals with what it terms a "tangent universe" that erupts from our own universe; Super Mario Bros. (1993) has the eponymous heroes cross over into a parallel universe ruled by humanoids who evolved from dinosaurs; The One (2001) starring Jet Li, in which there is a complex system of realities in which Jet Li's character is a police officer in one universe and a serial killer in another, who travels to other universes to destroy versions of himself, so that he can take their energy; and FAQ: Frequently Asked Questions (2004), the main character runs away from a totalitarian nightmare, and he enters into a cyber-afterlife alternative reality. The most recent Star Trek film (2009) had a character create an alternate reality by traveling back in time, thereby rebooting the series' complicated continuity. Parallel universe The film director and screenwriter Quentin Tarantino has been known to create his own brand of reality for each of his movies and for his subjects. In his 2009 film Inglorious Basterds, he created his most effective story in showcasing this kind of creation. At the climax of this film his soldiers trap, surround, and then assassinate both Nazi leader Adolf Hitler and all of his entire High Command (the Oberkommando der Wehrmacht) in a burning Paris, France movie theater in an alternate 1944, theoretically ending the war. 135 Television The idea of parallel universes have received treatment in a number of television series, usually as a single story or episode in a more general science fiction or fantasy storyline. One of the earliest television plots to feature parallel time was a 1970 storyline on soap opera Dark Shadows. Vampire Barnabas Collins found a room in Collinwood which served as a portal to parallel time, and he entered the room in order to escape from his current problems. A year later, the show again traveled to parallel time, the setting this time being 1841. A well known and often imitated example is the original Star Trek episode entitled "Mirror, Mirror". The episode introduced an alternative version of the Star Trek universe where the main characters were barbaric and cruel to the point of being evil. When the parallel universe concept is parodied, the allusion is often to this Star Trek episode. A previous episode for the Trek series first hinted at the potential of differing reality planes (and their occupants) -titled "The Alternative Factor". A mad scientist from "our" universe, named Lazarus B., hunts down the sane Lazarus A.; resident of an antimatter-comprised continuum. His counterpart, in a state of paranoia, claims the double threatens his and the very cosmos' existence. With help from Captain Kirk, A traps B along with him in a "anti"-universe, for eternity, thus bringing balance to both matter oriented realms. A similar plot was used in the Codename: Kids Next Door episode Operation: P.O.O.L.. Multiple episodes of Red Dwarf use the concept. In "Parallel Universe" the crew meet alternative versions of themselves: the analogues of Lister, Rimmer and Holly are female, while the Cat's alternate is a dog. "Dimension Jump" introduces a heroic alternate Rimmer, a version of whom reappears in "Stoke Me a Clipper". The next episode, "Ouroboros", makes contact with a timeline in which Kochanski, rather than Lister, was the sole survivor of the original disaster; this alternate Kochanski then joins the crew for the remaining episodes. Another example is "Spookyfish", an episode of South Park, in which the "evil" universe double of Cartman (who is pleasant and agreeable, unlike the home universe's obnoxious Cartman) sports a goatee, like the "mirror" version of Mr. Spock. Buffy the Vampire Slayer experienced a Parallel universe where she was a mental patient in Normal Again and not really "The Slayer" at all. In the end, she has to choose between a universe where her mother and father are together and alive (mother) or one with her friends and sister in it where she has to fight for her life daily. In another episode, Cordelia Chase inadvertently created a dystopian alternate reality in which Buffy had never moved from LA to Sunnydale. The animated series, Futurama, had an episode where the characters travel between "Universe 1" and "Universe A" via boxes containing each universe; and one of the major jokes is an extended argument between the two sets of characters over which set were the "evil" ones. Doctor Who often features parallel universes as the basis of a plotline. In the episode "Inferno", from Doctor Who the Doctor accidentally travels to a parallel universe where Great Britain is a republic under a fascist leader. In "Rise of the Cybermen", the TARDIS falls out of the Time-Space Continuum, and dies, with the Doctor and his companions inside it. The Doctor believes them to be in the Void, the infinite empty-space between the universes, where no time, space or energy exists. It turns out, however, they fell into another universe; a much more desirable option. In this universe, Britain is a lot more technically advanced, with blimps almost replacing cars. They find a way to revive the TARDIS and travel back to their own universe. According to the Doctor in "Doomsday", a new Parallel universe parallel universe is created by every decision made. The OC had an episode where two main characters fell into a coma, and into an alternate/parallel universe. Friends had an episode in which the characters wonder how different their lives would be with different choices. Parallel universes/alternate futures are also featured in Heroes. The idea of a parallel universe and the concept of deja vu was a major plot line of the first season finale of Fringe, guest-starring Leonard Nimoy of Star Trek. The show has gone on to feature the parallel universe prominently. In the 2010 season of Lost, the result of characters traveling back in time to prevent the crash of Oceanic Flight 815 apparently creates a parallel reality in which the Flight never crashed, rather than resetting time itself in the characters' original timeline. The show continued to show two "sets" of the characters following different destinies, until it was revealed in the series finale that there was really only one reality created by the characters themselves to assist themselves in leaving behind the physical world and passing on to an afterlife after their respective deaths. The anime Turn A Gundam attempted to combine all the parallel Gundam universes (other incarnations of the series, with similar themes but differing stories and characters, that had played out at different times since the debut of the concept in the 1970s) of the metaseries in to one single reality. The anime and manga series Katekyo Hitman Reborn! by Akira Amano features this idea in its third main arc, known as Future arc. The anime Neon Genesis Evangelion features a parallel world in one of the final episodes. This parallel world is a sharp contrast to the harsh, dark "reality" of the show and presents a world where all the characters enjoy a much happier life. This parallel world would become the basis for the new Evangelion manga series Angelic Days. The anime Bakugan series in season 2 & 3 features another unverses where Dan and his team saves the day.They goes to another dimension or universe through a path way . Another universe has also other life forms and other types of technology. In another anime series, Digimon, there is parallel universe called "digital world". The show's child protagonists meet digital monsters, or digimon, from this world and becomes partners and friends. In the anime series Umineko no Naku Koro ni The rounds of the battle between Battler and Beatrice take place in different dimensions, in order to show all kinds of possibilities (much to Battler's dismay) also the character Bernkastel is known for her ability to travel into different worlds by the usage of "fragments". In the animated Disney series Darkwing Duck, the title character's archenemy, Negaduck, comes from a parallel dimension called the Negaverse (not to be confused with the similarly named dimension in the Sailor Moon series). In the Family Guy episode, "Road to the Multiverse", Brian and Stewie get a look at life in other universes that are at the same time and place as Quahog, but under different conditions. In the Star Trek: The Next Generation episode "Parallels", Lt. Worf traveled to several parallel universes when his shuttlecraft went through a time space fissure. The movie for Phineas and Ferb involves Phineas, Ferb, and Perry going to an alternate dimension of the Tri-state area. In the episode "Adventure time" had a gender swapped universe episode. In Season 03, episode 4 of "Community (TV series)" called "Remedial Chaos Theory", different realities are the center of the plot, even with a reference to Spock's goatee. 136 Parallel universe 137 As an ongoing subplot Sometimes a television series will use parallel universes as an ongoing subplot. Star Trek: Deep Space Nine and Star Trek: Enterprise elaborated on the premise of the original series' "Mirror" universe and developed multi-episode story arcs based on the premise. Other examples are the science fiction series Stargate SG-1, the fantasy/horror series Buffy the Vampire Slayer, Supernatural and the romance/fantasy Lois & Clark: The New Adventures of Superman. Following the precedent set by Star Trek, these story arcs show alternative universes that have turned out "worse" than the "original" universe: in Stargate SG-1 the first two encountered parallel realities featured Earth being overwhelmed by an unstoppable Goa'uld onslaught; in Buffy, two episodes concern a timeline in which Buffy came to Sunnydale too late to stop the vampires from taking control; Lois & Clark repeatedly visits an alternative universe where Clark Kent's adoptive parents, Jonathan and Martha Kent, died when he was ten years of age, and Lois Lane is also apparently dead. Clark eventually becomes Superman, with help from the "original" Lois Lane, but he is immediately revealed as Clark Kent and so has no life of his own. In addition to following Star Trek's lead, showing the "evil" variants of the main storyline gives the writers an opportunity to show what is at stake by portraying the worst that could happen and the consequences if the protagonists fail or the importance of a character's presence. The latter could also be seen as the point of the alternative reality portrayed in the movie It's a Wonderful Life. Parallel universe-based series There have been a few series where parallel universes were central to the series itself. Two examples are: • Sliders, where a young man invents a worm-hole generator that allows travel to "alternative" Earths. Several characters travel across a series of "alternative" Earths, trying to get back to their home universe; • Charlie Jade, in which the titular character is accidentally thrown into our universe and is looking for a way back to his own. The series features three universes - alpha, beta and gamma. • Awake In 1986, Disney produced a pilot episode for an animated children's show about interdimensional travel called Fluppy Dogs. In the TV series Fringe, a main element of the series is the loss of balance and the eventual collision of two universes and the moral ramifications of it. Most main characters have a doppelganger who is usually slightly different from their prime selves. Code Lyoko is a French animated show about four youths who attend at Kadic Junior High School. They have the ability to travel to a virtual world called Lyoko, where they fight the creatures of X.A.N.A, the main antagonist of the series whose goal is to take control over the world. Source Code is a 2011 American science fiction-techno-thriller film directed by Duncan Jones, written by Ben Ripley, starring Jake Gyllenhaal, Michelle Monaghan, Vera Farmiga, Russell Peters and Jeffrey Wright which employs the concepts of quantum reality and parallel universes. Comic books Parallel universes in modern comics have become particularly rich and complex, in large part due to the continual problem of continuity faced by the major two publishers, Marvel Comics and DC Comics. The two publishers have used the multiverse concept to fix problems arising from integrating characters from other publishers into their own canon, and from having major serial protagonists having continuous histories lasting, as in the case of Superman, over 70 years. Additionally, both publishers have used new alternative universes to re-imagine their own characters. (See Multiverse (DC Comics) and Multiverse (Marvel Comics)) Because of this, comic books in general are one of the few entertainment mediums where the concept of parallel universes are a major and ongoing theme. DC in particular periodically revisits the idea in major crossover Parallel universe storylines, such as Crisis on Infinite Earths and Infinite Crisis, where Marvel has a series called What If... that's devoted to exploring alternative realities, which sometimes impact the "main" universe's continuity. DC's version of "What If..." is the Elseworlds imprint. Recently DC Comics series 52 heralded the return of the Multiverse. 52 was a mega-crossover event tied to Infinite Crisis which was the sequel to the 1980s Crisis on Infinite Earths. The aim was to yet again address many of the problems and confusions brought on by the Multiverse in the DCU. Now 52 Earths exist and including some Elseworld tales such as Kingdom Come, DC's imprint Wildstorm Comics and an Earth devoted to the Charlton Comics heroes of DC. Countdown and Countdown Presents: The Search for Ray Palmer and the upcoming Tales of the Multiverse stories expand upon this new Multiverse. Marvel has also had many large crossover events which depicted an alternative universe, many springing from events in the X-Men books, such as Days of Future Past, the seminal Age Of Apocalypse, and 2006's House Of M. In addition the Squadron Supreme is a DC inspired Marvel Universe that has been used several times, often crossing over into the mainstream Universe in the Avengers comic. Exiles is an offshoot of the X-Men franchsie that allows characters to hop from one alternative reality to another, leaving the original, main Marvel Universe intact. The Marvel UK line has long had multiverse stories including the Jaspers' Warp storyline of Captain Britain's first series (it was here that the designation Earth-616 was first applied to the mainstream Marvel Universe). Marvel Comics, as of 2000, launched their most popular parallel universe, the Ultimate Universe. It is a smaller subline to the mainstream titles and features Ultimate Spider-Man, Ultimate X-Men, Ultimate Fantastic Four and the Ultimates (their "Avengers"). The line in many ways both inspired and was inspired by aspects of the new movie franchises in addition to creating younger versions of the modern heroes. The graphic novel Watchmen is set in an alternate history in 1985 where superheroes exist, the Vietnam War was won by the United States, and Richard Nixon is in his fifth term as President of the United States. The Soviet Union and the United States are still in a "Cold War" with a threat of a Nuclear War impending. In 1973 Tammy published The Clock and Cluny Jones, where a mysterious grandfather clock hurls bully Cluny Jones into a harsh alternate reality where she becomes the bullied. This story was reprinted in Misty annual 1985 as Grandfather's Clock. In 1978 Misty published The Sentinels. The Sentinels were two crumbling apartment blocks that connected the mainstream world with an alternate reality where Hitler conquered Britain in 1940. In 1981 Jinty published Worlds Apart. Six girls experience alternate worlds ruled by greed, sports-mania, vanity, crime, intellectualism, and fear. These are in fact their dream worlds becoming real after they are knocked out by a mysterious gas from a chemical tanker that crashed into their school. In 1977 Jinty also published Land of No Tears where a lame girl travels to a future world where people with things wrong with them are cruelly treated, and emotions are banned. 138 Video games In the 1999 role-playing game Outcast where a probe is sent to a parallel universe and is attacked by an "entity". Cutter Slade must escort a team of scientists across to the other world to retrieve and repair the damaged probe before the earth is consumed by a black hole. In the popular indie game "Minecraft" The player can access "The Nether", a fiery world of Zombie pigmen, and "The End" A dark place filled with Endermen. In the survival horror video game series Silent Hill, the town of Silent Hill fluctuates between the normal world, a foggy version of the town and a dark and dilapidated version of the town called the "Other World". In the 1993 adventure PC game Myst, the unnamed protagonist travels to multiple alternate worlds through the use of special books, which describe a world within and transport the user to that world when a window on the front page is touched. Parallel universe In the 1996 adventure PC game 9: The Last Resort, after resolving several mind-blowing and unique puzzles, the player gets past "The Tiki Guards" and a door to "The Void" opens up - actually a room to another universe which houses the entirety of space. Both titles of the When They Cry visual novel series (Higurashi and Umineko for short) contain the concept of parallel worlds. These series both involve some kind of murder mystery occurring. As soon as the main character has 'lost', another parallel world, called a Fragment, is chosen to be observed. This continues until the entire mystery is solved. EarthBound features many areas of the game that can be considered alternate dimensions. The first is an illusion created by the Mani Mani Statue that transforms the metropolis of Fourside into a bizarre neon metropolis called Moonside, filled with unusual characters and enemies. The second is Magicant; the world of Ness's subconscious that is accessed after obtaining the Eight Melodies. Finally towards the end of the game the protagonists arrive at the Cave to the Past, where they travel back in time to the haunting past dimension of the cave to face Giygas. The unassuming Tanehineri Island in Mother 3 is transformed after the protagonists consume psychedelic mushrooms. The characters hallucinate, the island appears bright pink and enemies they encounter appear to them as people they know. In Yume Nikki (or "Dream Diary" in English), the protagonist Madotsuki explores the bizarre worlds of her subconscious mind when she goes to sleep. Only two areas of the world are accessible both while awake and asleep: Madotsuki's bedroom and balcony. Super Mario Bros. 2 features a "Magic Potion" item that when used, creates a doorway allowing the player to temporarily access "Subspace"; a mirrored silhouette version of the world where items can be found. After the completion of the Special World in Super Mario World, the overworld transforms from a green-colored springtime to a orange-colored autumnal setting. Many enemies encountered in the game are transformed into bizarre counterparts. Super Mario 64 features a world called "Tiny Huge Island" which has two variants: one scaled up, the other scaled down. The player can only access certain parts of the level to obtain certain stars depending on which variant they are in. The two variants can be switched between via portals in the world. Banjo-Kazooie features a world called "Click Clock Wood", which has spring, summer, autumn and winter variants. The environment develops between the seasons making some areas accessible or inaccessible, and actions taken in one season affect the outcome in others. The video game The Legend of Zelda: A Link to the Past features a dark and twisted parallel version of Hyrule called the "Dark World". The video games The Legend of Zelda: Oracle of Seasons and Oracle of Ages use a similar concept to that which is used in The Legend of Zelda: A Link to the Past. In those games, the player must switch between the parallel past and present worlds (Ages) and between spring, summer, autumn and winter (Seasons) to progress through the game. In the first half of The Legend of Zelda: Twilight Princess, areas of Hyrule are veiled by the Twilight Realm. These areas are dusky and brooding in appearance, Link cannot transform out of wolf form, characters only appear as spirits that cannot be communicated with, and enemies are twilight variations of their regular forms. Otherwise, the Twilight Realm is identical to regular Hyrule. Each Zone in Sonic CD has four variations: Past, Present, Bad Future and Good Future, each displaying some subtle and not-so subtle alterations. The story of Chrono Cross centers around travel between two alternate timelines, the original or "Home" universe and "Another World" which is a branch created by the actions of the heroes of the game's predecessor, Chrono Trigger. 139 Parallel universe Chrono Trigger has time travel as a central aspect of its game-play. Many areas of the game are accessible in more than one time period, and actions taken in one time period change the outcome in others. In Super Paper Mario, the town "Flipside" (which acts as the game's central hub) has an alternate mirrored version called "Flopside". While Flipside appears pristine and the residents there are typically cheerful, Flopside appears somewhat dilapidated and is populated by surly characters. The video game series Legacy of Kain is played through several realms and timelines. The video game Sudeki is set in a realm of light and a parallel realm of darkness. The video game The Elder Scrolls IV: Oblivion features an alternative hellish world called "Oblivion", as well as a painting you can climb into and a quest where you enter a dream world. The video game The Legend of Zelda: Majora's Mask takes place in Termina, a parallel world to Hyrule. Almost all of the characters from The Legend of Zelda: Ocarina of Time reappear in the game. The video game The Darkness pivots around a world of darkness you travel to when you die, which is occupied by World War 1 soldiers. The video game Metroid Prime 2: Echoes involves a world, "Aether", having an alternate self in the, "Dark" realm, universe, or dimension. The protagonist, Samus, finds out that she just dropped in to a hopeless war for the Luminoth, the dominant species of Light Aether against the Ing, the dominant species of Dark Aether. She also finds her counterpart, Dark Samus or Metroid Prime's essence inside Samus's Phazon Suit. The video game Crash Twinsanity features Crash, Cortex, and Nina traveling to the "10th dimension," which could also be a parallel universe (suggested by the theme and how everything seems to be opposite). The video game Minecraft features an alternate dimension called "The Nether", that includes a 'hell' like theme. It also contains a second alternate dimension called "The End," home world of the Endermen, a type of monster that spawns rarely in the main world. The video game Persona 2: Eternal Punishment takes place in an alternate universe called "This Side" where in the events of Innocent Sin did not take place and the characters have never met in the past. The Fallout series take place in a different universe, such as like in 1969, instead of Apollo 11 that landed on the moon, it was a ship called Valiant 11. This universe diverged after World War II, which means, no advanced computers, no Cold War, no VHS, etc. The MMORPG "City of Heroes" features a Player vs Player (PvP) zone called Recluse's Victory. It is an alternate future in a constant state of flux as heroes and villains battle for the future of Earth. 140 References Notes [1] Carl Sagan, Placido P D'Souza (1980s). Hindu cosmology's time-scale for the universe is in consonance with modern science. (http:/ / www. rediff. com/ news/ jan/ 29sagan. htm); Dick Teresi (2002). Lost Discoveries : The Ancient Roots of Modern Science - from the Babylonians to the Maya. [2] Irwin, Robert (2003). The Arabian Nights: A Companion. Tauris Parke Paperbacks. p. 209. ISBN 1-86064-983-1. [3] Briggs (1967) p.50-1 [4] Gareth Matthews, "Plato in Narnia" p 171 Gregory Bassham ed. and Jerry L. Walls, ed. The Chronicles of Narnia and Philosophy ISBN 0-8126-9588-7 [5] Stephen Baxter Speech (http:/ / erkelzaar. tsudao. com/ books/ Baxter2. htm) [6] C. S. Lewis, "On Science Fiction", Of Other Worlds, p68 ISBN 0-15-667897-7 [7] "John Grant" interviewed by Lou Anders (http:/ / www. infinityplus. co. uk/ nonfiction/ intjg. htm), accessed 24 October 2009 [8] Michael Moorcock, Wizardry & Wild Romance: A Study of Epic Fantasy p 88 ISBN 1-932265-07-4 Parallel universe 141 Further reading • Clifford A. Pickover (August 2005). Sex, Drugs, Einstein, and Elves: Sushi, Psychedelics, Parallel Universes, and the Quest for Transcendence (Discusses parallel universes in a variety of settings, from physics to psychedelic visions to Proust parallel worlds to Bonnet syndrome). Smart Publications. ISBN 1-890572-17-9. • Michio Kaku (2004). Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos. Doubleday. ISBN 0-385-50986-3. External links • Max Tegmark's Parallel Universes paper (http://www.hep.upenn.edu/~max/multiverse.pdf), University of Pennsylvania • Comic book universes explained simply (http://princeofoz.blogspot.com/2010/07/ parallel-universes-in-comic-books.html) Alternate history Alternate history or alternative history[1] is a genre of fiction consisting of stories that are set in worlds in which history has diverged from the actual history of the world. It can be variously seen as a sub-genre of literary fiction, science fiction, and historical fiction; different alternate history works may use tropes from any or all of these genres. It is sometimes abbreviated AH.[2] Another occasionally used term for the genre is "allohistory" (literally "other history").[3] Since the 1950s, this type of fiction has to a large extent merged with science fictional tropes involving cross-time travel between alternate histories or psychic awareness of the existence of "our" universe by the people in another; or ordinary voyaging uptime (into the past) or downtime (into the future) that results in history splitting into two or more time-lines. Cross-time, time-splitting and alternate history themes have become so closely interwoven that it is impossible to discuss them fully apart from one another. "Alternate History" looks at "what if" scenarios from some of history's most pivotal turning points and presents a completely different version, sometimes based on science and fact, but often based on conjecture. The exploration of how the world would look today if various changes occurred and what these alternate worlds would be like forms the basis of this vast subject matter. In French, Italian, Spanish and German, alternate history novels are called uchronie. This neologism is based on the prefix u- (as in the word utopia, a place that does not exist) and the Greek for time, chronos. An uchronie, then, is defined as a time that does not exist, a "non-time." This term apparently also inspired the name of the alternate history book list, uchronia.net.[4] Definition In writing an alternate history, the author makes the conscious choice to change something in our past. According to Steven H Silver, alternate history requires three things: 1) the story must have a point of divergence from the history of our world prior to the time at which the author is writing, 2) a change that would alter history as it is known, and 3) an examination of the ramifications of that change.[5] Several genres of fiction have been confused as alternate histories. Science fiction set in what was the future but is now the past, like Arthur C. Clarke's 2001: A Space Odyssey or Nineteen Eighty-Four , are not alternate history because the author has not made the conscious choice to change the past.[5] Secret history, works that document things that are not known to have happened historically but would not have changed history had they happened, is also not to be confused with alternate history.[5][6] Alternate history Alternate history is related to but distinct from counterfactual history—the term used by some professional historians when using thoroughly researched and carefully reasoned speculations on "what might have happened if..." as a tool of academic historical research.[7] 142 History of alternate history literature Antiquity and Medieval The earliest example of an alternate history is Book IX, sections 17–19, of Livy's Ab Urbe condita. Livy contemplated an alternative 4th century BC in which Alexander the Great expanded his empire westward instead of eastward; Livy asked, "What would have been the results for Rome if she had been engaged in war with Alexander?"[8][9][10] Joanot Martorell's 1490 epic romance Tirant lo Blanc, written when the loss of Constantinople to the Turks was still a recent and traumatic memory to Christian Europe, tells the story of the valiant knight Tirant The White from Brittany who gets to the embattled remnant of the Byzantine Empire, becomes a Megaduke and commander of its armies, and manages to fight off the invading Ottoman armies of Mehmet II, save the city from Islamic conquest, and even chase the Turks deeper into lands they had conquered before. 19th century One of the earliest works of alternate history published in large quantities for the reception of a popular audience may be the French Louis Geoffroy's Histoire de la Monarchie universelle: Napoléon et la conquête du monde (1812–1832) (History of the Universal Monarchy: Napoleon And The Conquest Of The World) (1836), which imagines Napoleon's First French Empire victorious in the French invasion of Russia in 1811 and in an invasion of England in 1814, later unifying the world under Bonaparte's rule.[9] In the English language, the first known complete alternate history is Nathaniel Hawthorne's short story "P.'s Correspondence", published in 1845. It recounts the tale of a man who is considered "a madman" due to his perceiving a different 1845, a reality in which long-dead famous people are still alive such as the poets Burns, Byron, Shelley, and Keats, the actor Edmund Kean, the British politician George Canning and even Napoleon Bonaparte. The first novel-length alternate history in English would seem to be Castello Holford's Aristopia (1895). While not as nationalistic as Louis Geoffroy's Napoléon et la conquête du monde, 1812–1823, Aristopia is another attempt to portray a utopian society. In Aristopia, the earliest settlers in Virginia discover a reef made of solid gold and are able to build a Utopian society in North America. Early 20th century and the era of the pulps A number of alternate history stories and novels appeared in the late 19th and early 20th centuries (see, for example, Charles Petrie's If: A Jacobite Fantasy [1926]).[11] In 1931, British historian Sir John Squire collected a series of essays from some of the leading historians of the period in the anthology If It Had Happened Otherwise. In this work, scholars from major universities as well as important non-university-based authors turned their attention to such questions as "If the Moors in Spain Had Won" and "If Louis XVI Had Had an Atom of Firmness". The essays range from serious scholarly efforts to Hendrik Willem van Loon's fanciful and satiric portrayal of an independent 20th century Dutch city state on the island of Manhattan. Among the authors included were Hilaire Belloc, André Maurois, and Winston Churchill. One of the entries in Squire's volume was Churchill's "If Lee Had Not Won the Battle of Gettysburg," written from the viewpoint of a historian in a world where the Confederacy had won the American Civil War, considering what would have happened if the north had been victorious (in other words, a character from an alternate world imagining a world more like the real one we live in, although not identical in every detail). This kind of speculative work, Alternate history which posts from the point of view of an alternate history is variously known as a "recursive alternate history", a "double-blind what-if" or an "alternate-alternate history".[12] American humorist author James Thurber parodied alternate history stories about the American Civil War in his 1930 story, "If Grant had been drinking at Appomattox", which he accompanied with this very brief introduction: “Scribner's magazine is publishing a series of three articles: ‘If Booth Had Missed Lincoln’, ‘If Lee Had Won the Battle of Gettysburg’, and ‘If Napoleon Had Escaped to America’. This is the fourth” Another example of alternate history from this period (and arguably the first to explicitly posit cross-time travel from one universe to another as anything more than a visionary experience) is H.G. Wells' Men Like Gods (1923) in which several Englishmen are transferred via an accidental encounter with a cross-time machine into an alternate universe featuring a seemingly pacifistic and utopian Britain. When the Englishmen, led by a satiric figure based on Winston Churchill, try to seize power, the utopians simply point a ray gun at them and send them on to someone else's universe. Wells describes a multiverse of alternative worlds, complete with the paratime travel machines that would later become popular with U.S. pulp writers, but since his hero experiences only a single alternate world this story is not very different from conventional alternate history.[13] The 1930s would see alternate history move into a new arena. The December 1933 issue of Astounding published Nat Schachner's "Ancestral Voices," quickly followed by Murray Leinster's "Sidewise in Time". While earlier alternate histories examined reasonably straightforward divergences, Leinster attempted something completely different. In his "world gone mad", pieces of Earth traded places with their analogs from different timelines. The story follows Professor Minott and his students from a fictitious Robinson College as they wander through analogues of worlds that followed a different history. A somewhat similar approach was taken by Robert A. Heinlein in his 1941 novelette Elsewhen. A professor trains his mind to move his body across timelines. He then hypnotizes his students so they can explore more of them. Eventually each settles in the reality most suitable for him or her. Some of the worlds they visit are mundane, some very odd, and others follow science fiction or fantasy conventions. World War II produced alternate history for propaganda: both British[14] and [15] American authors wrote works depicting Nazi invasions of their respective countries as cautionary tales. Time travel as a means of creating historical divergences The period around the second World War also saw the publication of the time travel novel Lest Darkness Fall by L. Sprague de Camp where an American academic travels to the Italy of the Ostrogoths at the time of the Byzantine invasion led by Belisarius. De Camp's work is concerned with the historical changes wrought by his time traveler, Martin Padway, thereby making the work an alternate history. Padway is depicted as making permanent changes and implicitly forming a new time branch. Time travel as the cause of a point of divergence (creating two histories where before there was one, or simply replacing the future that existed before the time traveling event) has continued to be a popular theme: in Bring the Jubilee, by Ward Moore, the protagonist, who lives in an alternate history in which the Confederate States of America won the Civil War, travels through time and brings about a Union victory in the Battle of Gettysburg. When a story's assumptions about the nature of time travel lead to the complete replacement of the visited time's future rather than just the creation of an additional time line, the device of a "time patrol" is often used, most notably The world in 1964 in the novel Fatherland where the Germans won World War Two. 143 Alternate history in Poul Anderson's "Time Patrol"—racing uptime and downtime to preserve the "correct" history. In Delenda Est, the interference of time-travelling outlaws causes Carthage to win the Second Punic War and destroy Rome. A more recent example is Making History by Stephen Fry, in which a time machine is used to alter history so that Adolf Hitler was never born. 144 Cross-time stories H.G. Wells' "cross-time"/"many universes" variant (see above) was fully developed by De Camp in his 1940 short story "The Wheels of If" (Unknown Fantasy Fiction, October 1940), in which the hero is repeatedly shifted from one alternate history to another, each more remote from our own than the last. This subgenre was used early on for purposes far removed from quasi-academic examination of alternative outcomes to historical events. Fredric Brown employed it to satirize the science fiction pulps and their adolescent readers—and fears of foreign invasion—in the classic What Mad Universe (1949). In Clifford D. Simak's Ring Around the Sun (1953), the hero ends up in an alternate earth of thick forests in which humanity never developed but where a band of mutants is establishing a colony; the story line appears to frame the author's anxieties regarding McCarthyism and the Cold War. Also in the late 1940s and the 1950s, however, writers such as H. Beam Piper, Sam Merwin, Jr. and Andre Norton wrote thrillers set in a multiverse in which all alternate histories are co-existent and travel between them occurs via a technology involving portals and/or paratime capsules. These authors established the convention of a secret paratime trading empire that exploits and/or protects worlds lacking the paratime technology via a network of James Bond-style secret agents (Piper called them the "paratime police"). This concept provided a convenient framing for packing a smorgasbord of historical alternatives (and even of timeline "branches") into a single novel, either via the hero chasing or being chased by the villain(s) through multiple worlds or (less artfully) via discussions between the paratime cops and their superiors (or between paratime agents and new recruits) regarding the histories of such worlds. The paratime theme is sometimes used without the police; Poul Anderson dreamed up the Old Phoenix tavern as a nexus between alternate histories. A character from a modern American alternate history Operation Chaos can thus appear in the English Civil War setting of A Midsummer's Tempest. In this context, the distinction between an alternate history and a parallel universe with some points in common but no common history may not be feasible, as the writer may not provide enough information to distinguish. Paratime thrillers published in recent decades often cite the many-worlds interpretation of quantum mechanics (first formulated by Hugh Everett III in 1957) to account for the differing worlds. Some science fiction writers interpret the splitting of worlds to depend on human decision-making and free will, while others rely on the butterfly effect from chaos theory to amplify random differences at the atomic or subatomic level into a macroscopic divergence at some specific point in history; either way, science fiction writers usually have all changes flow from a particular historical point of divergence (often abbreviated 'POD' by fans of the genre). Prior to Everett, science-fiction writers drew on higher dimensions and the speculations of P. D. Ouspensky to explain their characters' cross-time journeys. While many justifications for alternate histories involve a multiverse, the "many world" theory would naturally involve many worlds, in fact a continually exploding array of universes. In quantum theory, new worlds would proliferate with every quantum event, and even if the writer uses human decisions, every decision that could be made differently would result in a different timeline. A writer's fictional multiverse may, in fact, preclude some decisions as humanly impossible, as when, in Night Watch, Terry Pratchett depicts a character informing Vimes that while anything that can happen, has happened, nevertheless there is no history whatsoever in which Vimes has ever murdered his wife. When the writer explicitly maintains that all possible decisions are made in all possible ways, one possible conclusion is that the characters were neither brave, nor clever, nor skilled, but simply lucky enough to Alternate history happen on the universe in which they did not choose the cowardly route, take the stupid action, fumble the crucial activity, etc.; few writers focus on this idea, although it has been explored in stories such as Larry Niven's All the Myriad Ways, where the reality of all possible universes leads to an epidemic of suicide and crime because people conclude their choices have no moral import. In any case, even if it is true that every possible outcome occurs in some world, it can still be argued that traits such as bravery and intelligence might still affect the relative frequency of worlds in which better or worse outcomes occurred (even if the total number of worlds with each type of outcome is infinite, it is still possible to assign a different measure to different infinite sets). The physicist David Deutsch, a strong advocate of the many-worlds interpretation of quantum mechanics, has argued along these lines, saying that "By making good choices, doing the right thing, we thicken the stack of universes in which versions of us live reasonable lives. When you succeed, all the copies of you who made the same decision succeed too. What you do for the better increases the portion of the multiverse where good things happen."[16] This view is perhaps somewhat too abstract to be explored directly in science fiction stories, but a few writers have tried, such as Greg Egan in his short story The Infinite Assassin, where an agent is trying to contain reality-scrambling "whirlpools" that form around users of a certain drug, and the agent is constantly trying to maximize the consistency of behavior among his alternate selves, attempting to compensate for events and thoughts he experiences but he guesses are of low measure relative to those experienced by most of his other selves. Many writers—perhaps the majority—avoid the discussion entirely. In one novel of this type, H. Beam Piper's Lord Kalvan of Otherwhen, a Pennsylvania State Police officer, who knows how to make gunpowder, is transported from our world to an alternate universe where the recipe for gunpowder is a tightly held secret and saves a country that is about to be conquered by its neighbors. The paratime patrol members are warned against going into the timelines immediately surrounding it, where the country will be overrun, but the book never depicts the slaughter of the innocent thus entailed, remaining solely in the timeline where the country is saved. The cross-time theme was further developed in the 1960s by Keith Laumer in the first three volumes of his Imperium sequence, which would be completed in Zone Yellow (1990). Piper's politically more sophisticated variant was adopted and adapted by Michael Kurland and Jack Chalker in the 1980s; Chalker's G.O.D. Inc trilogy (1987–89), featuring paratime detectives Sam and Brandy Horowitz, marks the first attempt at merging the paratime thriller with the police procedural. Kurland's Perchance (1988), the first volume of the never-completed "Chronicles of Elsewhen", presents a multiverse of secretive cross-time societies that utilize a variety of means for cross-time travel, ranging from high-tech capsules to mutant powers. Harry Turtledove has launched the Crosstime Traffic series for teenagers featuring a variant of H. Beam Piper's paratime trading empire. The concept of a cross-time version of a world war, involving rival paratime empires, was developed in Fritz Leiber's Change War series, starting with the Hugo Award winning The Big Time (1958); followed by Richard C. Meredith's Timeliner trilogy in the 1970s, Michael McCollum's A Greater Infinity (1982) and John Barnes' Timeline Wars trilogy in the 1990s. Such "paratime" stories may include speculation that the laws of nature can vary from one universe to the next, providing a science fictional explanation—or veneer—for what is normally fantasy. Aaron Allston's Doc Sidhe and Sidhe Devil take place between our world, the "grim world" and an alternate "fair world" where the Sidhe retreated to. Although technology is clearly present in both worlds, and the "fair world" parallels our history, about fifty years out of step, there is functional magic in the fair world. Even with such explanation, the more explicitly the alternate world resembles a normal fantasy world, the more likely the story is to be labeled fantasy, as in Poul Anderson's "House Rule" and "Loser's Night." In both science fiction and fantasy, whether a given parallel universe is an alternate history may not be clear. The writer might allude to a POD only to explain the existence and make no use of the concept, or may present the universe without explanation to its existence. 145 Alternate history 146 Major writers explore alternate histories In 1962, Philip K. Dick published The Man in the High Castle, an alternate history in which Nazi Germany and Imperial Japan won World War II. This book contained an example of "alternate-alternate" history, in that one of its characters is the author of a book in which the Allies won the war. It was followed by Vladimir Nabokov's Ada or Ardor: A Family Chronicle (1969), a story of incest that takes place within an alternate North America settled in part by Czarist Russia, and that borrows from Dick's idea of "alternate-alternate" history (the world of Nabokov's hero is wracked by rumors of a "counter-earth" that apparently is ours). Some critics believe that the references to a counter-earth suggest that the world portrayed in Ada is a delusion in the mind of the hero (another favorite theme of Dick's novels). Strikingly, the characters in Ada seem to acknowledge their own world as the copy or negative version, calling it "Anti-Terra" while its mythical twin is the real "Terra." Not only history but science has followed a divergent path on Anti-Terra: it boasts all the same technology as our world, but all based on water instead of electricity. When a character in Ada makes a long-distance call, all the toilets in the house flush at once to provide hydraulic power. Isaac Asimov's short story What If-- is about a couple who can explore alternate realities by means of a television-like device. This idea can also be found in Asimov's 1955 novel The End of Eternity. In that novel, the "Eternals" can change the realities of the world, without people being aware of it. In his Hugo-winning novel, The Gods Themselves, Asimov imagines parallel universes where the laws of physics, specifically the strong force, are different so that materials transferred between them can be used as energy sources. An isotope of a metal that is stable in one universe is unstable in the other and becomes radioactive, releasing energy, when transferred. The process works both ways, apparently to the benefit of both sets of inhabitants, but in each universe there are those who realize that mixing the laws of physics will eventually destroy our Earth by causing the Sun to explode. Guido Morselli described the defeat of Italy (and subsequently France) in World War I in his 1975 novel Past Conditional (Contro-passato prossimo) where the static Alpine front line which divided Italy from Austria during that war collapses when the Germans and the Austrians forsake trench warfare and adopt blitzkrieg twenty years in advance. Kingsley Amis set his 1976 novel The Alteration in the 20th century, but major events in the Reformation did not take place, and Protestantism is limited to the breakaway Republic of New England. Martin Luther was reconciled to the Roman Catholic Church and later became Pope Germanian I. The Plot Against America (2004) by Philip Roth looks at an America where Franklin D. Roosevelt is defeated in 1940 in his bid for a third term as President of the United States, and Charles Lindbergh is elected, leading to increasing fascism and anti-Semitism in the U.S. Michael Chabon, occasionally an author of speculative fiction, contributed to the genre with his 2007 novel The Yiddish Policemen's Union. This book explores a world in which the State of Israel was destroyed in its infancy and many of the world's Jews instead live in a small strip of Alaska set aside by the US government for Jewish settlement. The story follows a Jewish detective solving a murder case in the Yiddish-speaking city of Sitka. Stylistically, Chabon borrows heavily from the noir and detective fiction genres, while exploring social issues related to Jewish history and culture. Contemporary alternate history in popular literature The late 1980s and the 1990s saw a boom in popular-fiction versions of alternate history, fueled by the emergence of the prolific alternate history author Harry Turtledove, as well as the development of the steampunk genre and two series of anthologies—the What Might Have Been series edited by Gregory Benford and the Alternate ... series edited by Mike Resnick. This period also saw alternate history works by S.M. Stirling, Kim Stanley Robinson, Harry Harrison, Howard Waldrop and others. Alternate history Since the late 1990s, Harry Turtledove has been the most prolific practitioner of alternate history and has been given the title "Master of Alternate History" by some.[17] His books include those of Timeline 191 (a.k.a. Southern Victory), in which Confederate States of America won the American Civil War, and the Worldwar series, in which aliens invaded Earth during World War II. Other stories by Turtledove include A Different Flesh, in which America was not colonized from Asia during the last ice age; In the Presence of Mine Enemies, in which the Nazis won World War II; and Ruled Britannia, in which the Spanish Armada succeeded in conquering Britain in the Elizabethan era, with William Shakespeare being given the task of writing the play that will motivate the Britons to rise up against their Spanish conquerors. He also co-authored a book with actor Richard Dreyfuss The Two Georges, in which the United Kingdom retained the American colonies, with George Washington and King George III making peace. He did a two-volume series in which the Japanese not only bombed Pearl Harbor but also invaded and occupied the Hawaiian Islands. Perhaps the most incessantly explored theme in popular alternate history focuses on worlds in which the Nazis won World War Two. In some versions, the Nazis and/or Axis Powers conquer the entire world; in others, they conquer most of the world but a "Fortress America" exists under siege; while in others, there is a Nazi/Japanese Cold War comparable to the US/Soviet equivalent in 'our' timeline. Fatherland (1992) by Robert Harris, is set in Europe following the Nazi victory. Several writers have posited points of departure for such a world but then have injected time splitters from the future or paratime travel for instance James P. Hogan's The Proteus Operation. Norman Spinrad wrote The Iron Dream in 1972, which is intended to be a science fiction novel written by Adolf Hitler after fleeing from Europe to North America in the 1920s. In Jo Walton's "Small Change" series, the United Kingdom made peace with Hitler before the involvement of the United States in World War II, and fascism slowly strangled the UK. Former House Speaker Newt Gingrich and William R. Forstchen have written a novel, 1945, in which the U.S. defeated Japan but not Germany in World War II, resulting in a Cold War with Germany rather than the Soviet Union. Gingrich and Forstchen neglected to write the promised sequel; instead, they wrote a trilogy about the American Civil War, starting with Gettysburg: A Novel of the Civil War, in which the Confederates win a victory at the Battle of Gettysburg. Also from that general era, Martin Cruz Smith, in his first novel, posited an independent American Indian nation following the defeat of Custer in The Indians Won (1970).[18] Beginning with The Probability Broach in 1981, L. Neil Smith wrote several novels that postulated the disintegration of the U.S. Federal Government during the Whiskey Rebellion and the creation of a libertarian utopia. A recent time traveling splitter variant involves entire communities being shifted elsewhere to become the unwitting creators of new time branches. These communities are transported from the present (or the near-future) to the past or to another time-line via a natural disaster, the action of technologically advanced aliens, or a human experiment gone wrong. S. M. Stirling wrote the Island in the Sea of Time trilogy, in which Nantucket Island and all its modern inhabitants are transported to Bronze Age times to become the world's first superpower. In Eric Flint's 1632 series, a small town in West Virginia is transported to 17th century central Europe and drastically changes the course of the Thirty Years' War, which was then underway. John Birmingham's Axis of Time trilogy deals with the culture shock when a United Nations naval task force from 2021 finds itself back in 1942 helping the Allies against the Empire of Japan and the Germans (and doing almost as much harm as good in spite of its advanced weapons). Similarly, Robert Charles Wilson's Mysterium depicts a failed U.S. government experiment which transports a small American town into an alternative version of the U.S. run by believers in a form of Christianity known as Gnosticism, who are engaged in a bitter war with the "Spanish" in Mexico. (The chief scientist at the laboratory where the experiment occurred is described as a Gnostic, and references to Christian Gnosticism appear repeatedly in the book.) 147 Alternate history 148 Alternate history in the contemporary fantasy genre Many fantasies and science fantasies are set in a world that has a history somewhat similar to our own world, but with magic added. Some posit points of divergence, but some also feature magic altering history all along. One example of a universe that is in part historically recognizable but also obeys different physical laws is Poul Anderson's Three Hearts and Three Lions in which the Matter of France is history, and the fairy folk are real and powerful. A partly familiar European history for which the author provides a point of divergence is Randall Garrett's "Lord Darcy" series: a monk systemizing magic rather than science, so the use of foxglove to treat heart disease is called superstition. The other great point of divergence in this timeline occurs in 1199, when Richard the Lionheart survives the Siege of Chaluz and returns to England, making the Angevin Empire so strong it survives into the 20th century. Jonathan Strange & Mr Norrell takes place in an alternative version of England where a separate Kingdom ruled by the Raven King and founded on magic existed in Northumbria for over 300 years. In Patricia Wrede's Regency fantasies, Great Britain has a Royal Society of Wizards, and in Poul Anderson's A Midsummer Tempest William Shakespeare is remembered as the Great Historian, with the novel itself taking place in the era of Oliver Cromwell and Charles I, with an alternate outcome for the English Civil War and an earlier Industrial Revolution. The Tales of Alvin Maker series by Orson Scott Card (a parallel to the life of Joseph Smith, Jr., founder of the Latter Day Saint movement) takes place in an alternate America, beginning in the early 19th century. Prior to that time, a POD occurred: England, under the control of Oliver Cromwell, had banished "makers", or anyone else demonstrating "knacks" (an ability to perform seemingly supernatural feats) to the North American continent. Thus the early American colonists embraced as perfectly ordinary these gifts, and counted on them as a part of their daily lives. The political divisions of the continent is considerably altered, with two large English colonies bookending a smaller "American" nation, one aligned with England, and the other governed by exiled Cavaliers. Actual historical figures are seen in a much different light: Ben Franklin is revered as the continent's finest "maker", George Washington was executed at the hands of an English army, and "Tom" Jefferson is the first president of "Apallachee", the result of a compromise between the Continentals and the British. On the other hand, when the "Old Ones" still manifest themselves in England in Keith Roberts's Pavane, which takes place in a technologically backward world after a Spanish assassination of Elizabeth I allowed the Spanish Armada to conquer England, the possibility that the fairies were real but retreated from modern advances makes the POD possible: the fairies really were present all along, in a secret history. Again, in the English Renaissance fantasy Armor of Light by Melissa Scott and Lisa A. Barnett, the magic used in the book, by Dr. John Dee and others, actually was practiced in the Renaissance; positing a secret history of effective magic makes this an alternate history with a POD, Sir Philip Sidney's surviving the Battle of Zutphen, and shortly thereafter saving the life of Christopher Marlowe. Many works of fantasy posit a world in which known practitioners of magic were able to make it function, and where the consequences of such reality would not, in fact, disturb history to such an extent as to make it plainly alternate history. Many ambiguous alternate/secret histories are set in Renaissance or pre-Renaissance times, and may explicitly include a "retreat" from the world, which would explain the current absence of such phenomena. When the magical version of our world's history is set in contemporary times, the distinction becomes clear between alternate history on the one hand and contemporary fantasy, using in effect a form of secret history (as when Josepha Sherman's Son of Darkness has an elf living in New York City, in disguise) on the other. In works such as Robert A. Heinlein's Magic, Incorporated where a construction company can use magic to rig up stands at a sporting event and Poul Anderson's Operation Chaos and its sequel Operation Luna, where djinns are serious weapons of war—with atomic bombs—the use of magic throughout the United States and other modern countries makes it clear that this is not secret history—although references in Operation Chaos to degaussing the effects of cold iron make it possible that it is the result of a POD. The sequel clarifies this as the result of a collaboration of Einstein and Planck in 1901, resulting in the theory of "rheatics". Henry Moseley applies this theory to "degauss the effects of cold iron and Alternate history release the goetic forces." This results in the suppression of ferromagnetism and the reemergence of magic and magical creatures. Alternate history shades off into other fantasy subgenres when the use of actual, though altered, history and geography decreases, although a culture may still be clearly the original source; Barry Hughart's Bridge of Birds and its sequels take place in a fantasy world, albeit one clearly based on China, and with allusions to actual Chinese history, such as the Empress Wu. Richard Garfinkle's Celestial Matters incorporates ancient Chinese physics and Greek Aristotelian physics, using them as if factual. A fantasy version of the paratime police was developed by children's writer Diana Wynne Jones in her Chrestomanci quartet (1977–1988), with wizards taking the place of high tech secret agents. Among the novels in this series, Witch Week stands out for its vivid depiction of a history alternate to that of Chrestomanci's own world rather than our own (and yet with a specific POD that turned it away from the "normal" history of most worlds visited by the wizard). Terry Pratchett's works include several references to alternate histories of Discworld. Men At Arms observes that in millions of universes, Edward d'Eath became an obsessive recluse rather than the instigator of the plot that he is in the novel. In Jingo, Vimes accidentally picks up a pocket organizer that should have gone down another leg of the Trousers of Time, and so can hear the organizer reporting on the deaths that would have occurred had his decision gone otherwise. Indeed, Discworld contains an equivalent of the Time Patrol in its History Monks. Night Watch revolves around a repair of history after a time traveler's murder of an important figure in Vimes's past. Thief of Time presents them functioning as a full-scale Time Patrol, ensuring that history occurs at all. 149 Alternate history in other media Radio In 1953, the NBC radio network aired a show called Stroke of Fate that posited different point of divergence creating an alternate time-line for each episode and dramatized the results along with commentary from various historians. Episodes included changes in the American Civil War, Alexander the Great surviving his illness, an alternate fate for James Wolfe at Quebec City, no Julius Caesar assassination, a different outcome of Aaron Burr's duel amongst other stories. All episodes have been preserved. The idea of an alternate history was used for satiric and comedic effect in the BBC Radio comedy Married. The protagonist, a confirmed bachelor, awakes one morning in a world where he has a wife and two children, and people familiar to him are radically changed. One historical divergence in this world, exploited mostly for comedy, was the decision of King Edward VIII not to abdicate in 1936. His heirs were a King Richard and a King John, the latter of whom was openly homosexual. Films Several films have been made that exploit the concepts of alternate history, most notably Kevin Brownlow's It Happened Here (1966), depicting a Nazi-occupied Britain. Other alternate history films include the HBO TV movie Fatherland (1994), set in the 1960s in a world where Germany won World War II, based on Robert Harris's novel of the same name. Although foretelling a world where Germany is poised to be defeated in World War II, Quentin Tarantino's Inglourious Basterds offers a satirical revenge fantasy where a plot to assassinate Adolf Hitler succeeds. Alternate histories in film are sometimes presented as mockumentaries to provide verisimilitude to fictional events, including C.S.A.: The Confederate States of America (2004), a satirical look at the history of an America where the South won the Civil War. Other examples of cinematic alternate history are: 2009 Lost Memories (2002), a Korean film supposing that Hirobumi Ito was not assassinated by An Jung-geun in Harbin, China, in 1909; and Timequest (2002), in which a time traveler prevents the assassination of John F. Kennedy, resulting in an altered subsequent history. Alternate history A few movies about alternative universes focus on individuals rather than historical events, for example, Frank Capra's It's a Wonderful Life, and more recently the Back to the Future series of films, Blind Chance, Sliding Doors, Run Lola Run, Me Myself I, The Butterfly Effect, Groundhog Day, Frequency, Inglourious Basterds and Source Code. 150 Television Several TV series also exploit the concept of alternate history. The science fiction television show Sliders presented alternate histories under the science-inspired guise of quantum-navigating the multiverse. The vast majority of alternate Americas in most episodes are nasty dystopias, although sometimes this is not evident at first. In Lost, the characters time travel to 1977 past and attempt to create an alternate history. However, while the only intended ramifications were for Flight 815 to land in Los Angeles, instead, it is revealed that their actions were the cause of the crash, ultimately. Other non-alternate history television shows have explored the concept. Star Trek has used the theme several times. Examples include: TOS—"The City on the Edge of Forever" (alternate World War II outcome); Animated Series—"Yesteryear"; TNG—"Yesterday's Enterprise", and Enterprise's "Storm Front" Also, the universe of "Mirror, Mirror", while in the original episode was just implied to be a parallel universe, was in later episodes (of DS9 and Enterprise) shown to have an alternate history. The British TV series Doctor Who had a few episodes that involved an alternate Earth where Pete Tyler, father of Rose Tyler, was alive, successful, and rich, unlike the Pete Tyler on the original Earth, who died when Rose was a baby and had been unsuccessful in business. The Tenth Doctor, Rose, and Mickey Smith visited the alternate Earth by accident in "Rise of the Cybermen" and "The Age of Steel". The second season finale "Army of Ghosts" and "Doomsday" also involved travel to the same alternate Earth, and the series four episode "Turn Left" showed an alternate history where the Tenth Doctor has been killed during the Racnoss attack. During the Third Doctor's tenure he visited an alternative Earth with a fascist-style British Government that has executed the Royal Family (and fascist counterparts of his friends/companions Liz Shaw, Brigadier Lethbridge-Stewart and Sergeant Benton) in Inferno, from which he is able to learn of a danger that also threatens his Earth. In the seventies SF children's series The Tomorrow People, "A Rift in Time" (1974) depicted an attempted historical change by time travellers from an alternate-universe Roman Empire that developed steam engines in the 1st century, never fell as a result, had a 1,500-year technological head-start over our own world and by its "20th century," controlled a galactic empire. The fourth season of the television series Fringe takes place in an alternate timeline in which Peter Bishop died shortly after the prime universe's Walter Bishop brought him to the prime universe. This resulted in a butterfly effect in which every main character's life was profoundly changed with the absence of Peter. In the Twilight Zone episode "The Parallel," an astronaut is transported to an alternate Earth where history plays out differently, but no-one believes him when he discovers this. On August 24, 2011, Spike TV aired a special titled Alternate History, a program speculating what would occur if Nazi Germany won World War II and conquered the United States. On October 13, 2011, the Community episode "Remedial Chaos Theory" includes seven alternate timelines in the lives of the show's seven main characters, dependent on which of the seven went to get the pizza delivered to the apartment. Various anime productions have also used the genre: • Zipang (based on a manga of the same name), involves a modern Aegis class destroyer of the Japan Maritime Self-Defense Force being thrown back in time to the Battle of Midway in 1942. The presence of the ship and its crew, their advanced technology and knowledge of the future, change the course of World War II and create an alternate timeline. Alternate history • Konpeki no Kantai (lit. Deep Blue Fleet) depicts a hyper-advanced Japanese navy defeating the United States in World War II. Subsequently, Japan, Britain and the United States join forces to defeat Nazi Germany. 151 Role-playing games The dramatic possibilities of alternate history provide a diverse genre for exploration in role-playing games. Many games use an alternate historical background for their campaigns. In particular, the fourth edition of GURPS uses a setting containing multiple different alternate histories as its default campaign setting, with the supplement GURPS Infinite Worlds detailing a large number of alternate worlds included in the setting, many of them carryovers from the third-edition GURPS supplements GURPS Alternate Earths and GURPS Alternate Earths II. Video games For the same reasons that this genre is explored by role-playing games, alternate history is also an intriguing backdrop for the storylines of many video games. A famous example of an alternate history game is Command & Conquer: Red Alert. Released in 1996, the game presents a point of divergence in 1946 where Albert Einstein goes back in time to prevent World War II from ever taking place by erasing Adolf Hitler from time after he is released from Landsberg Prison in 1924. He is successful in his mission, but in the process allows Joseph Stalin and the Soviet Union to become powerful enough—as a direct result of not having a strong rival dictator like Hitler to keep his power in check—to launch a massive campaign to conquer Europe, sparking an alternate (and ultimately costlier) version of the Second World War and, eventually, World War III not once but twice: one where the USSR invades the continental US in the 1970s, and a second where a small group of Soviet leaders, attempting to preempt their defeat, go back in time and eliminate Einstein but end up in a conflict with both the West and a third Japanese side. In the Civilization Series, the player guides a civilization from prehistory to the present day, creating radically altered versions of history on a long time-scale. Several scenarios recreate a particular period which becomes the "point of divergence" in an alternate history shaped by the player's actions. Popular examples in Sid Meier's Civilization IV include Desert War, set in the Mediterranean theater of World War II and featuring scripted events tied to possible outcomes of battles; Broken Star, set in a hypothetical Russian civil war in 2010; and Rhye's and Fall of Civilization, an 'Earth simulator' designed to mirror a history as closely as possible but incorporating unpredictable elements to provide realistic alternate settings. In some games such as the Metal Gear and Resident Evil series, events that were originally intended to represent the near future at the time the games were originally released later ended up becoming alternative histories in later entries in those franchises. For example, Metal Gear 2: Solid Snake (1990), set in 1997, depicted a near future that ended up becoming an alternative history in Metal Gear Solid (1998). Likewise, Resident Evil (1996) and Resident Evil 2 (1998), both set in 1998, depicted near-future events that had later become an alternative history by the time Resident Evil 4 (2005) was released. Crimson Skies is one example of an alternate history spawning multiple interpretations in multiple genres. The stories and games in Crimson Skies take place in an alternate 1930s United States, where the nation crumbled into many hostile states following the effects of the Great Depression, the Great War, and Prohibition. With the road and railway system destroyed, commerce took to the skies. Great cargo zeppelins escorted by fighter squadrons are the targets of many ruthless air pirates and enemy countries. This world has featured in a board game, a PC game, an Xbox game, a collectible miniature game and various promotional novels, comics and short stories. The game Freedom Fighters portrays a situation similar to that of the movie Red Dawn and Red Alert 2, though less comically than the latter. The point of divergence is during World War II, where the Soviet Union develops an atomic bomb first and uses it on Berlin. With the balance of power and influence tipped in Russia's favor, history diverges; brief summaries at the beginning of the game inform the player of the Communist bloc's complete takeover of Europe by 1953, a different ending to the Cuban Missile Crisis, and the spread of Soviet influence into South America and Mexico. The plot of the game revolves around a Soviet invasion of the United States and the resistance Alternate history fighting in New York City. Similarly, the 2007 video game World in Conflict is set in 1989, with the Soviet Union on the verge of collapse. The point of divergence is several months before the opening of the game, when Warsaw Pact forces staged a desperate invasion of Western Europe. As the game begins, a Soviet invasion force lands in Seattle, taking advantage of the fact that most of the US military is in Europe. The game is divided into three parts: the first focuses on the fighting retreat from Seattle towards Fort Teller in the Cascade Mountains; the second is a flashback to the recent fighting in Europe, which culminated in a Soviet attack on Manhattan; the third chronicles the fight to retake Seattle before a Chinese fleet arrives, which could force the US President to destroy the invaders with a nuclear strike. Turning Point: Fall of Liberty, released in February 2008, is an alternate history first person shooter where Winston Churchill died in 1931 from being hit by a taxi cab. Because of this, Great Britain lacks the charismatic leader needed to keep the country together and Nazi Germany successfully conquers Great Britain via Operation Sealion. Germany later conquers the rest of Europe and North Africa while mass-producing their wunderwaffe. The Axis launch a surprise invasion of an isolationist United States in 1953, which forces the country to surrender and submit to a puppet government. The game's main character is a member of a resistance force against the Germans. Another alternate history game involving Nazis is War Front: Turning Point in which Adolf Hitler died during the early days of World War II and thus, a much more effective leadership rose to power. Under the command of a new Führer (who is referred to as "Chancellor", and his real name is never revealed), Operation Sealion succeeds and the Nazis successfully conquer Britain, sparking a cold war between the Allied Powers and Germany. Another example of alternate history is the Resistance series of first-person shooter games. The point of divergence is in the years following World War I, where an isolationist Russian Empire - and later, Western Europe - is conquered by an alien race called the Chimera. The aliens later invade the United States. The Fallout Series of computer role-playing games is set in a divergent America, where history after World War II diverges from the real world to follow a retro-futuristic timeline. For example, fusion power was invented quite soon after the end of the war, but the transistor was either delayed or never was developed. The result was a future that has a 1950s 'World of Tomorrow' feel to it, with extremely high technology such as artificial intelligence implemented with thermionic valves and other technologies now considered obsolete. Iron Storm is a first person shooter set in 1964, where the Great War still continues and international corporations sell stocks as if "betting" on an outcome. Since profits are so great, they continually press for stalemate to keep the conflict in an ongoing cycle of minor advances and losses. "In the action adventure game inFamous, the main villain of the first game, Kessler, is the main character Cole's future self. He (Kessler) failed to save the world from the Beast (the main villain of the second game) and traveled back in time to insure his past self not to make his grave mistake. 152 Comic books Alternate history has also appeared in comic books. An early example is Captain Confederacy, which is set in a world where the Confederate States of America won its independence and has created a Captain America-type superhero for propaganda purposes. Influential comic writers have also used an alternate history as the background to their story. Alan Moore's 1986 comic series Watchmen is set in an alternate United States that not only has costumed adventurers as commonplace fixtures within American society, but also contains other alternate history elements including an American "victory" in the Vietnam War and Richard Nixon serving five terms as president. Warren Ellis's 2001 comic mini-series Ministry of Space features a British space program that had its foundation in the United Kingdom's recovery of scientists and technology at the German rocket installations in Peenemünde ahead of the US Army and the Soviets. There have also been alternative history webcomics like Roswell, Texas, which diverges when Davy Crockett survived the Alamo, leading to the expansion of Texas. Alternate history Marvel and DC have their own titles where they can tell alternative stories based on their own characters (What If...? and Elseworlds, respectively). Most set the stories in different times or base them on different genres with some based on a divergence in their fictional history, such as the Age of Apocalypse, where Professor X being killed accidentally in the past led to Apocalypse taking over America. The time travelling Marvel Comics villain Kang the Conqueror has created alternate realities and different versions of himself due to his time travelling. However after stumbling into Limbo he succeeds in eliminating all the other versions of himself. Later his Future counterpart Immortus becomes an alternate version of himself. However, some are genuine alternate histories, with Batman: Holy Terror based on the premise that Oliver Cromwell lived for another decade. Some of the newer DC Multiverse alternate Earths could be legitimately described as alternate histories. On Earth-9, the emergence of metahumans led to a limited nuclear exchange ("the Cuban War") in 1962, leading to the destruction of Florida and Cuba, US intervention during the Soviet invasion of Czechoslovakia in 1967 and the survival of the USSR into the nineties (see Tangent Comics.). On Earth-10, Nazi Germany won the Second World War. On Earth-17, the United States and USSR fought a thermonuclear World War III in 1986, with some human survivors. On Earth-30, the Soviet Union won the Cold War due to the technological boost provided by Superman, whose vehicle landed in the Ukraine, instead of Kansas (see Superman: Red Son). In 2009, Bryan Talbot created Grandville, a graphic novel set in a world mostly populated by anthropomorphic animals, in which France won the Napoleonic Wars, invaded Britain and guillotined the British Royal Family. Grandville also features elements of steampunk. In 1978, "The Sentinels", one of the first serials in UK girls' comic Misty, featured an alternate world where Nazi Germany conquered Britain in 1940. The alternate world was connected with the mainstream world via two apartment blocks called "The Sentinels". People kept stumbling in from both sides, causing terror over unexplained disappearances and worse, mix-ups over parallel world doubles. This culminated in the Gestapo mistakenly arresting a man from the mainstream world and people from both worlds uniting for the rescue mission. 153 Online Fans of alternate history have made use of the internet from a very early point to showcase their own works and provide useful tools for those fans searching for anything alternate history, first in mailing lists and usenet groups, later in web databases and forums. The "Usenet Alternate History List" was first posted on April 11, 1991, to the usenet newsgroup rec.arts.sf-lovers. In May 1995, the dedicated newsgroup soc.history.what-if was created for showcasing and discussing alternate histories;[19] it expanded rapidly and at its peak in the early 2000s regularly had over 10,000 posts a month.[20] Its prominence declined with the general migration from unmoderated usenet to moderated web forums, most prominently AlternateHistory.com, today the self-described "largest gathering of alternate history fans on the internet".[21] In addition to these discussion forums, in 1997 after the creation of the world wide web, Uchronia: The Alternate History List was created as an online repository, now containing over 2900 alternate history novels, stories, essays and other printed material, in several different languages. Uchronia was selected as the Sci Fi Channel's "Sci Fi Site of the Week" twice.[22][23] Collaborative attempts by several amateur writers have led to notable accomplishments. The contributors at Ill Bethisad have made two constructed languages: Brithenig[24] and Wenedyk. Alternate history 154 References [1] Brave New Words: The Oxford Dictionary of Science Fiction (Oxford University Press, 2007) notes the preferred usage of "Alternate History" as well as its primacy in coinage, "Alternate History" was coined in 1954 and "Alternative History" was first used in 1977, pp.4–5. [2] "AH" (http:/ / acronyms. thefreedictionary. com/ Alternate+ History+ (fiction+ genre)). The Free Dictionary. . Retrieved 2 January 2009. [3] Allohistory (http:/ / www. worldwidewords. org/ turnsofphrase/ tp-all1. htm) Michael Quinion, World Wide Words. 2002-05-04. [4] See "www.uchronia.net" (http:/ / www. uchronia. net/ intro. html) (Retrieved 2010-09-03). [5] Steven H Silver. "Uchronicle" (http:/ / www. helixsf. com/ uchronicle/ uchronicle0706. htm). Helix. . Retrieved 2009-05-26. [6] Evelyn C. Leeper (August 13, 2001). "Alternate History 101" (http:/ / www. webcitation. org/ 5kmXXAhDa). Archived from the original (http:/ / www. geocities. com/ Athens/ 4824/ ah101. htm) on 2009-10-25. . Retrieved 2009-05-26. Another copy of the foregoing may be found at 'http:/ / www. leepers. us/ evelyn/ ah101. htm' (retrieved 2010-09-03), and a different definition of "secret history" by the same writer may be found at 'http:/ / www. leepers. us/ evelyn/ reviews/ borges. htm' (retrieved 2010-09-03). [7] Martin Bunzl (June 2004). "Counterfactual History: A User's Guide" (http:/ / www. historycooperative. org/ journals/ ahr/ 109. 3/ bunzl. html). American Historical Review. . Retrieved 2009-06-02. [8] Ab Urbe Condita (http:/ / mcadams. posc. mu. edu/ txt/ ah/ Livy/ Livy09. html) Titus Livius, Book 9. [9] Dozois, Gardner; Stanley Schmidt (1998). Roads Not Taken: Tales of Alternate History. New York: Del Rey. pp. 1–5. ISBN 0-345-42194-9. [10] Turtledove, Harry; Martin H. Greenberg (2001). The Best Alternate History Stories of the 20th Century. New York: Del Rey. pp. 1–5. ISBN 978-0-345-43990-1. [11] "If: A Jacobite Fantasy" by Charles Petrie (http:/ / www. jacobite. ca/ essays/ if. htm) [12] Churchill...and War (http:/ / www. winstonchurchill. org/ i4a/ pages/ index. cfm?pageid=674). The Churchill Centre. [13] Men like Gods on Project Gutenberg (http:/ / gutenberg. net. au/ ebooks02/ 0200221. txt) [14] Gavriel D. Rosenfeld, The World Hitler Never Made, p39 ISBN 0-521-84706-0 [15] Gavriel D. Rosenfeld, The World Hitler Never Made, p97-99 ISBN 0-521-84706-0 [16] "Taming the Multiverse" (http:/ / www. kurzweilai. net/ articles/ art0268. html). 2001-06-14. [17] " Master of Alternate History (http:/ / www. publishersweekly. com/ article/ CA6548135. html)" by Melissa Mia Hall, Publishers Weekly, 4/7/2008. [18] Nicholas Wroe, Profile: Martin Cruz Smith (http:/ / www. guardian. co. uk/ books/ 2005/ mar/ 26/ featuresreviews. guardianreview15), The Guardian, 26 March 2005 [19] soc.history.what-if Frequently Asked Questions (http:/ / www. anthonymayer. net/ ah/ faq. html) [20] soc.history.what-if on Google Groups (http:/ / groups. google. com/ group/ soc. history. what-if/ about) [21] AlternateHistory.com (http:/ / www. alternatehistory. com/ ) [22] Berkwits, Jeff. "Sci-Fi Site of the Week: Uchronia: The Alternate History List" (http:/ / www. scifi. com/ sfw/ issue62/ site. html). SciFi.com. . Retrieved 20 November 2008. [23] McGowan, Matthew (2000-09-25). "Sci-Fi Site of the Week: Uchronia: The Alternate History List" (http:/ / www. scifi. com/ sfw/ issue179/ site. html). SciFi.com. . Retrieved 20 November 2008. [24] "Documentation for ISO 639 identifier: bzt" (http:/ / www. sil. org/ iso639-3/ documentation. asp?id=bzt). SIL International. . Retrieved 6 January 2009. Further reading • Chapman, Edgar L., and Carl B. Yoke (eds.). Classic and Iconoclastic Alternate History Science Fiction. Mellen, 2003 • Collins, William Joseph. Paths Not Taken: The Development, Structure, and Aesthetics of the Alternative History. University of California at Davis 1990 • Darius, Julian. 58 Varieties: Watchmen and Revisionism. In Minutes to Midnight: Twelve Essays on Watchmen (http://www.sequart.org/books/6/minutes-to-midnight-twelve-essays-on-watchmen/). Sequart Research & Literacy Organization, 2010. Focuses on Watchmen as alternate history. • Robert Cowley (ed.), What If? Military historians imagine what might have been. Pan Books, 1999. • Gevers, Nicholas. Mirrors of the Past: Versions of History in Science Fiction and Fantasy. University of Cape Town, 1997 • Hellekson, Karen. The Alternate History: Refiguring Historical Time. Kent State University Press, 2001 • Keen, Antony G. "Alternate Histories of the Roman Empire in Stephen Baxter, Robert Silverberg and Sophia McDougall." Foundation: The International Review of Science Fiction 102, Spring 2008. • McKnight, Edgar Vernon, Jr. Alternative History: The Development of a Literary Genre. University of North Carolina at Chapel Hill 1994 Alternate history • Nedelkovh, Aleksandar B. British and American Science Fiction Novel 1950–1980 with the Theme of Alternative History (an Axiological Approach). 1994 (Serbian), 1999 (English) • Rosenfeld, Gavriel David. The World Hitler Never Made. Alternate History and the Memory of Nazism. 2005 • Rosenfeld, Gavriel David. "Why Do We Ask 'What If?' Reflections on the Function of Alternate History." History and Theory 41, Theme Issue 41 (December 2002), 90–103 155 External links Interactive sites • AlternateHistory.com (http://www.alternatehistory.com/) largest alternate history forum on the Internet. • Althistory Wikia (http://althistory.wikia.com/wiki/Main_Page) Alternate History Wikia, maintained by Wikia • Groups-Beta.google.com (http://groups-beta.google.com/group/soc.history.what-if), Soc.history.what-if The usenet newsgroup on alternate history with over a decade of archives. Non-interactive sites • Alternate History Weekly Update (http://alternatehistoryweeklyupdate.blogspot.com/): a blog featuring commentary on alternate history news. • Changing The Times (http://www.changingthetimes.net/), is an Alternate History Electronic Magazine written and maintained by alternate historians. It contains a discussion board. • "For Want of a Genre" (http://www.nebulaawards.com/index.php/guest_blogs/for_want_of_a_genre/), article by Christopher M. Cevasco. • Histalt.com (http://www.histalt.com/) is author Richard J. (Rick) Sutcliffe's collection of Alternate History links. • John Reilly's Alternative History (http://www.johnreilly.info/althis.htm) • Paradox: The Magazine of Historical and Speculative Fiction (http://www.paradoxmag.com), frequently publishes alternate history stories. • Point of Divergence (http://www.dalecozort.com/PODPage.html): Information about the APA Point of Divergence, which has been publishing since 1996. • Shattered World: A Worse World War (http://theshatteredworld.blogspot.com/), a site based on an alternate historical scenario containing an active forum. • The Sidewise Award for Alternate History (http://www.uchronia.net/sidewise) lists all the winners and nominees for the award since its inception and provides information for recommending works for consideration. • This Day in Alternate History (http://thisdayinalternatehistory.blogspot.com/), dedicated to showing significant events in years past on this day that shaped history... just, not our history. • Today in Alternate History (http://www.todayinah.co.uk/), a daily-updated blog, featuring "Important Events In History That Never Occurred Today" in several recurring timelines. • Uchronia (http://www.uchronia.net/) has an introduction to the topic (http://www.uchronia.net/intro.html), and lists over 2000 works of alternate history. Time loop 156 Time loop A time loop or temporal loop is a common plot device in science fiction (especially in universes where time travel is commonplace) in which time runs normally for a set period (usually a day or a few hours) but then skips back like a broken record. When the time loop "resets", the memories of most characters are reset (i.e. they forget all that happened). The plot is advanced by having one or more central characters retain their memory or become aware of the loop through déjà vu. One well-known example of this is in the 1993 film Groundhog Day, in which the main character is the only one aware of the time loop. Stories with time loops commonly center on correcting past mistakes or on getting a character to recognize some key truth; escape from the loop may then follow. Types of Time Loops Physical Time Loop In a physical time loop (rarely seen in the media), the spacetime loops around to form several closed timelike curves. Since the time in that region is looped, you could only escape it by leaving the affected area. Also, there would be an infinite number of copies of any matter in the area, unless an object left the loop. In that case, there would only be as many copies of that object as many times it completed the loop. This type of time loop cannot be ended or destroyed. Conscious Time Loop In a conscious time loop, everyone's consciousness loops through time. In such a time loop, causality could easily be violated. Television The following series featured time loops as a main theme or at least fairly frequently: • Day Break - A police officer relives the same day over and over, and has to figure out how to save himself and those close to him from a host of threats. • Doctor Who makes frequent use of time travel. A number of episodes involve or make mention of a time loop (also referred to as a "chronic hysteresis"): "Image of the Fendahl", "Carnival of Monsters", "The Invasion of Time", "The Armageddon Factor", "The Claws of Axos", "Meglos" and "Father's Day" (a car is stuck in a time loop after history is changed as the universe seemingly tries to 'restore' history). In the episode "Blink" the Doctor knows exactly what clues to leave in the past in order to help a character in the present (Sally Sparrow) deal with an alien threat because she has carefully collected and preserved all the information and gives it to him after the fact. The Master's use of the term "time loop" in "The Claws of Axos" may be the first instance of its use to describe the phenomenon. Beyond the original TV series, the term also appears in the radio play "No More Lies", starring the Eighth Doctor, Paul McGann. In the spinoff series Torchwood, in the first episode of the second series, another time loop is mentioned, where main character Captain Jack Harkness and his partner John Hart were trapped in a two-week time loop for five years. A recent Doctor Who episode to feature a time loop is "The Big Bang", in which River Song is put into a time loop within the TARDIS to keep her alive, the TARDIS 'freezing' itself in the moment of its own destruction. • Higurashi no Naku Koro ni - The story is shown in chapters, each one a variation of the same time period. Each chapter unravels part of an overarching mystery. The chapters typically end with the death of some or all of the main characters. The conclusion of the story comes when the mystery is solved and death is prevented. The reason for these time loops becomes part of the mystery as characters begin to remember scenes from previous time loops. Time loop • The Lexx - Stanley Tweedle, Zev, Kai and 790 travel the span of two universes on a Manhattan-sized living insect ship, in an effort to discover a way to defeat a villain called "His Divine Shadow". Kai is the lone survivor (technically animated dead) of a humanoid species called the Brunen-G, which were eradicated two-thousand years in the past by His Shadow. This event was prophesied by a now deceased Brunen-G Seer to have happened before, and expected to happen again, in a time loop referred to as the "Future-Past". • The Tatami Galaxy - An unnamed student relives the first two years of his college career repeatedly, choosing a different club to join at the beginning each time, unaware consciously of the time loop. One loop ends with two smaller jumps backwards, reliving the iteration's final hours a second and third time, before it fully resets. • Tru Calling - A university graduate working in the city morgue is able to repeat the same day over again to prevent murders or other disasters. • Twin Peaks - The small township of Twin Peaks is shocked by the murder of a High School girl Laura Palmer and disappearance of her classmate Ronette Pulaski. FBI agent Dale Cooper is sent to investigate and quickly finds himself being sucked into the joy and intrigue of a town where nothing is as it appears at the surface. The subplot introduced in Season 1 and elaborated on in Season 2 revolving around the supernatural world of the Black and White Lodge deals with human beings, most obviously Laura Palmer and Dale Cooper, being possessed by entities that are stuck in a temporal loop forced to reenact their roles. But all characters in the series may be viewed in this light as vessels forced to play different roles at different times. Time loops have been featured in individual episodes of many TV series, including: TV Show Andromeda Episode "When Goes Around..." "Time Bomb" Comments It's also hinted that Trance Gemini has experienced the show's time-line several times. 157 Angel The characters do not experience events in a single loop; one character begins randomly jumping through time and experiences events multiple times, sometimes out of order The Angry Beavers Blood Ties "Same Time Last Week" "5:55" The characters discover Pandora's Box, which ends the world whenever it is opened; due to the main character Vicki Nelson having been marked by a powerful demon, history is apparently 'reset' each time the box is opened to give the demon the chance to kill Vicki. One of a trio of geeks puts Buffy into a time loop when she's working at the Magic Box. She has to face the same customer over and over until she's able to satisfy her. Buffy the Vampire Slayer Cardcaptor Sakura "Life Serial" "Sakura's Never-Ending Day" ("Time and Again" in the Nelvana release) "Deja Vu All Over Again" "The Good, the Bad, and the Cursed" "Show Ghouls" A demon tries to repeat the same day over and over again until he can find a strategy to defeat the sisters. Breaking a time loop that others are stuck in is a major plot element, but the sisters and the audience only go through it once. Charmed Code Lyoko "A Great Day" "Temptation" Although the main characters have the ability to relive a day ("Return to the past" or "RTTP") and be the only ones who retain their memories, throughout the entire series these are the only two episodes in which the same day is repeated multiple times. Crime Traveller D.Gray-man "Final Episode" "The Rewinding Town" "Deja Voodoo" The Dead Zone Time loop 158 "Run, Gary, Run" "I Do Over" The main character has to solve what is causing him to relive the same day repeatedly without the help of the geniuses in the town, and he finds that no matter what he changes throughout each repeated day, the end result is still the same. He then realizes that nothing simple he does will change anything, and that if he wants to stop reliving the same day, a drastic measure must be taken. The main character wishes that it was Christmas every day. Early Edition Eureka The Fairly OddParents "Christmas Every Day" "Deja Vu" The main character wishes for a watch that allows him to reset a certain amount of time so that he can undo his mistakes. John Crichton's exposure to the energy of a black hole causes him to experience time jumps where he sees the future. Farscape "Back and Back and Back to the Future" "Gulag" "White Tulip" "The Late Philip J Fry" First Wave Fringe Futurama Fry, Bender and Professor Farnsworth use a forwards time machine and after travelling through multiple times in the future, fast forward to the end of the universe where they witness a second big bang and discover that when the universe ends, another universe exactly the same as the old one is created. Haven "Audrey Parker's Day Off" "The Once and Future Thing: Time Warped" "'Twas the Night Before Mxymas" The villain, Chronos, is trapped in a time loop at the conclusion of the episode and his actions thus undone. Justice League Unlimited Lois & Clark: The New Adventures of Superman Lost "Flashes Before Your Eyes" "Be Kind, Rewind" The "Endless Eight" arc Episodes where the characters relive the same two weeks of summer vacation, as the one behind it attempts to pack as much into these two weeks as possible, but is not satisfied, and thus the loop repeats Medium The Melancholy of Haruhi Suzumiya Monty Python's Flying Circus Déjà vu (skit, a.k.a. "It's the Mind"), episode 16. It's About Time Twilight Sparkle is visited by her future self, from a seemingly apocalyptic world due to her tattered jumpsuit and shocking appearance. Before she can convey an urgent warning, she is forced back to the future, and Twilight attempts to avert the apparent crisis, her paranoia leading to several injuries that match what her future self had possessed. After realizing there will be no disaster, she travels back in time to tell her past self not to bother worrying about an apocalypse, but being forced back into the present day before being able to mention not to worry, setting in motion a time loop. My Little Pony: Friendship is Magic The Outer Limits "Deja Vu" "The Refuge" Painkiller Jane Pepper Ann Pet Alien "Playback" "'T.G.I.F" "The Day That Wouldn't End" "Phineas and Ferb's Quantum Boogaloo" "Toto Day" Phineas and Ferb Phua Chu Kang Time loop 159 "Yesterday Again" "Power Rangers: Lightspeed Rescue" "Power Rangers: Zeo" Red Dwarf "A Brief Mystery of Time" "White Hole" The Machine Empire traps Earth in a time loop; a recent brainwashing experience allows Tommy Oliver to be partly aware of the day repeating itself. The crew are exposed to a white hole- the opposite of a black hole- which spews time into the universe, causing them to repeat various events as well as experiencing time out of order. Red vs. Blue "Have We Met?" "Same Old, Same Old" 7 Days "Déjà Vu All Over Again" "The Forever War" Run Frank Run! Frank Parker must save Talmadge. The clock is ticking, he's far away, traveling on foot, but thankfully, if at first he doesn't succeed (and indeed he doesn't), he gets to try, try again. Silver Surfer finds Adam Warlock trapped in a time loop where he defends his homeworld from the Kree. After leaving it they find that Warlock's true homeworld was destroyed long ago, so he returns to the time loop. Having indirectly caused the death of Lana Lang, Clark Kent turns back time to avert the events that led to her death (Although the new timeline results in Jonathan Kent dying instead) Silver Surfer Smallville "Reckoning" South Park "Cancelled" "Go God Go XII" The time loop is inescapable only because the person remembering it is incapable of understanding the problem. The episodes "The Gamekeeper" and "Avatar" also feature time repeatedly "resetting" itself, but they both take place within virtual reality universes, whereas "Window of Opportunity" takes place in the real world and is the only instance of the term "time loop" being used in the series, Earth and sixteen other worlds within a certain distance of the original machine apparently repeating the same eight hours for over three months. Stargate SG-1 "Window of Opportunity" Star Trek: Enterprise Star Trek: The Next Generation "Future Tense" "Cause and Effect" A localized time loop only loops for the main characters and those involved directly in the loop. The loop is caused by the destruction of the Enterprise, which in turn resets the loop. Once the ship's destruction is averted, the loop breaks, and the characters discover that quite some time has passed while they were trapped in the localized loop. The Enterprise is destroyed and Captain Jean-Luc Picard is sent back in time to the moments before the ship was destroyed, but Picard is able to break the loop that would have led to him becoming his future self. Captain Kathryn Janeway apparently experiences multiple timelines resulting in her death, but the 'loop' is revealed to be an illusion generated by a life-form trying to trick Janeway into 'accepting' her death Corinne Baxter has what she considers the worst day of her life and repeats it over and over until she looks at it optimistically. "Time Squared" Star Trek: Voyager "Coda" Strange Days at Blake Holsey High The Suite Life on Deck "Thursday" "International Dateline" The time loop is caused by a lightning bolt that strikes while the boat passes the international dateline sending the S.S. Tipton back in a time loop that only Cody Martin Realizes, so he takes advantage to try and kiss Bailey Pickett, his crush. In the end, he doesn't manage to kiss her. The time loop is caused whenever Dean Winchester is killed. The time loop was created by a Trickster to teach Dean's brother Sam a lesson. Supernatural "Mystery Spot (3.11)" Totally Spies! The Twilight Zone The Twilight Zone (2002 TV series) "Deja Cruise" "Shadow Play" "Rewind [1] " Jonah is given a gift of a personal tape recorder that rewinds time and allows the holder to create a 5 minute Time Loop. Time loop 160 "Universal Remote" "First Kiss" Alex Russo wants her brother, Justin, to get his first kiss. During the kiss, something wrong happens, so Alex set the time back so Justin could do it right. A woman has to repeat the same day over and over, each ending with someone dead after a bank heist. She confronts Scully and Mulder on several occasions to try and stop the time loop, and Mulder gets the sense of Deja Vu. Weird Science Wizards of Waverly Place The X-Files "Monday" Xena: Warrior Princess "Been there, Done that" Audio Drama • In one episode of The Shadow, "The Man Who Killed Time", the antagonist creates a time loop. Music videos • • • • • • "Redundant" (1997) by Green Day "Feel It" (1997) by Neneh Cherry "Looking For Love" (1998) by Karen Ramirez "Otherside" (1999) by Red Hot Chili Peppers "7 Days" (2000) from Born to Do It by Craig David "Stuck in a Moment You Can't Get Out Of" (2000) from All That You Can't Leave Behind by U2 • The North American music video features the end of an American football game replayed repeatedly as a place kicker misses a field goal. • The European music video shows Bono being thrown from a van repeated times. "Grounded" (2001) from Finelines by My Vitriol "Come Into My World" (2002) from "Fever" by Kylie Minogue "Ocean Avenue" (2004) from Ocean Avenue by Yellowcard "In My Arms" (2005) by Mylo "If I Surrender" (2007) by The Color Fred "Time After Time" (2008) by Elliot Minor • • • • • • • "Hey" (2009) by Mitchel Musso • "The Island (Pendulum song)" (2010) by Pendulum (band) • "Luv Delux" (2009) by Cinnamon Chasers Film • 12:01 PM and 12:01 - two films (a 1990 short and a 1993 full-length), based upon Richard A. Lupoff's short story of the same name. • 1408 - A jaded writer is trapped in a hotel room that physically and psychologically torments him, unable to escape. Although the main storyline of the film is not a time loop, this device does appear as one of the many horrors inflicted by the room. At several points in the story, he thinks he has managed to leave the room, only to discover later he has been inside it all along. • 50 First Dates - A girl repeats the same day in her mind over and over as the rest of the world keeps going. • Bless the Child, a 2003 Hong Kong film • Blind Chance - Krzystof Kieslowski's 1987 film following three different possibilities, all spouting from chance. Precursor to Tykwer's Run Lola Run. • Christmas Do-Over - A shallow ad executive finds himself reliving Christmas day over and over. • Christmas Every Day - A 13-year-old boy relives Christmas day again and again. Time loop • Donnie Darko - A 16-year-old boy is visited by a strange entity from the future who guides him into ending a time loop and thus preventing the destruction of our universe. • È già ieri - A man relives a day again and again • Groundhog Day - A jaded weather man relives the same day, Groundhog Day, over and over, while stuck in a small town due to the weather. • Il Mare and its Hollywood remake, The Lake House - these two films share time-loop like features: Two characters exist in different time frames, and affect each other's lives. The ending of the film is a causality paradox, which if followed through would cause the timeloop to repeat. • The Last Day of Summer - A boy relives his last day of summer after being repeatedly hit on the head. • Limbo 2004 - An attorney finds himself stuck in Limbo, neither alive or dead. He is in a unique time loop that lasts 1 hour and does not move him back to the same place when time resets. Then he finds others who are stuck in the same loop as him. • Mickey's Once Upon a Christmas - retells Christmas Every Day with Huey, Dewey, and Louie. • Mirror for a Hero [2] - a 1987 Russian film. Besides Groundhog Day's idea of living a perfect day it has a bundle of time, person and society related ideas. • Nirvana - time loop happens to a fictional person in a virtual reality game. • Pokémon: Giratina and the Sky Warrior - Dialga traps Giratina in a time loop, preventing it from leaving the Reverse World. The time loop is broken when Giratina is brought out of the Reverse World via artificial means. • Primer - Film deals with a time loop that is described as being like a cul-de-sac with an "A end" and a "B end". • Source Code - A film in which the protagonist repeatedly lives out the last eight minutes of a victim of a terrorist bomb in order to try to ascertain who the bomber is and to prevent them from detonating a dirty bomb in central Chicago. • Timecrimes (Originally Los Cronocrímenes), is a 2007 time loop film from Spain. • Triangle (2009) - this film involves a young woman trapped in a loop. There are copies of people and items, seemingly allowing many variations on the loop happening at the same time. • Urusei Yatsura 2: Beautiful Dreamer - The day before Tomobiki High School's student fair is looped repeatedly. 161 Literature • "Doubled and Redoubled", a short story by Malcolm Jameson that appeared in the February, 1941 issue of Unknown. Accidentally cursed by a witch, the protagonist repeats a "perfect" day, including a lucky bet, a promotion, a heroically foiled bank robbery, and a successful wedding proposal. This story was a precedent to Groundhog day and 12:01 PM.[3] • "Escapement", a 1956 short story by J. G. Ballard. • "12:01 PM", a 1973 short story by Richard A. Lupoff. • The Dark Tower, a series of seven novels by Stephen King featuring many elements of time travel, including a time loop. • In a story in The Decameron, a dead man (Guido degli Anastagi) is ordered to catch his dead recalcitrant beloved and tear her apart, every Friday. • The Details of Nikita Vorontsov's Life by Arkady Strugatsky. • "Genevieve Undead" by Jack Yeovil. While not a true time loop due to time still carrying on as normal outside the estate and the loop changing slightly with each playthrough it is still endless repetition for those who are caught in the curse. • HELP! I'm Trapped In the First Day of School! by Todd Strasser. A boy keeps repeating his first day of school. A later book in the series features the same character being trapped in the first day of summer camp. • I Am the Cheese. Technically not a true time loop novel, but the young main character, who is revealed to be insane, acts out the same week over and over. Time loop • In Lord Sunday, the last of the The Keys to the Kingdom, a series of seven young adult fantasy novels by Garth Nix, the main character's mother is stuck within a time-loop. • "A Little Something for Us Tempunauts", a 1975 short story by Philip K. Dick. • Lost in a Good Book, the second of the Thursday Next novels by Jasper Fforde. The title character travels back in time to save her husband from being eradicated and experiences a time loop before returning to her present-day 1985. (Time loops are also mentioned as a form of incarceration and punishment, confining the prisoner to a dull place such as a laundromat or in the line to checkout at a store over a span of a few minutes repeated for the duration of the sentence. Aornis Hades is incarcerated in an 8 minute loop in the checkout of a TJMaxx, Temporal J. Maximum security prison, never quite being allowed to checkout. Her enloopment could be lengthened as a reward or shortened as further punishment.) • Mathematicians in Love, a novel by Rudy Rucker. • The Neverending Story, a book by Michael Ende - a time loop is deliberately set in motion at one point to force Bastian's hand. • The Plot to Save Socrates, a novel by Paul Levinson • In The Rashness of Haruhi Suzumiya there is a chapter Endless Eight in which Haruhi Suzumiya creates a time loop because she never wants their vacation to end. • Replay, a Ken Grimwood novel in which the main character suddenly shifts to much earlier in his life, then relives shorter and shorter periods. • Tales from the Time Loop, a book by David Icke. • "That Feeling, You Can Only Say What It Is in French", short story by Stephen King. • Time Trap and Back To The Time Trap by Keith Laumer. • The Tunnel Under The World, a short story by Frederik Pohl. in which the citizens of a town are seen to relive the same day over and over, seemingly unaware that they are doing so. At one point however a chance event results in one man retaining his memory of the previous day, allowing him to observe that history seems to be repeating; the rest of the story is concerned with his attempts to solve the mystery, which is resolved in a bizarre ending. • All You Need is Kill, a novel by Hiroshi Sakurazaka, featuring a soldier who relives an unwinnable battle endlessly, until he wins it. • Several stories from the Ijon Tichy series by Stanisław Lem. • Before I Fall is a novel by Lauren Oliver, in which a teenage girl that dies in a car crash relives her last day seven times, unraveling the mystery of her death in the process. 162 Comic books • Kid Gravity - Kid Gravity changes the clock to suit himself, but it causes a time loop. He ends up fixing it. As always, he gets in trouble for his wrongdoing. • JoJo's Bizarre Adventure - At the end of the fourth part of the manga, Kira Yoshikage gains a time looping power named Another One Bites the Dust. The originality of it is that Yoshikage doesn't manipulate the power by himself (he knows that time loops can occur, but he doesn't know how many times it has happened and what has happened before). • Nth Man: The Ultimate Ninja - At the end of the series, both John Doe the Nth Man and Alphie O'Meagan realise that they are trapped in a time loop because of Alphie's manipulation of the Time stream. • Fred's Bed- In the 2011 Beano Annual story he sets his alarm clock backwards to have extra helpings of cake. • The Bogies In a 2009 issue of The Dandy, Dr Goo spits out the tea that Snot Bothered had made him, which lands on the controls to send them going back in time. However, each time they spend too much time talking about what's just happened rather than stopping him to spit it out sending them in a loop. This goes on forever. Time loop 163 Video games • BlazBlue: Calamity Trigger - The "multiple endings" are rather possibilities, after which time loops back again to the beginning. As an Observer, the only one aware of the looping is Rachel Alucard. • Breakdown - In one section of the game the main character experiences an illusion that causes him to repeat the last few seconds of what just happened. • Dragon Warrior VII - One town in this game is placed under a curse so that the same day is repeated, with only the heroes, not native to the town being cursed, knowing that there is a time loop. • Ephemeral Fantasia - The game centers around a five-day time loop, about which only the hero is aware. • Fate/hollow ataraxia - The main characters Shiro and Bazett are trapped in a four-day time loop. • Final Fantasy - Garland, once loyal knight of the Kingdom Coneria (Cornelia), is sent back 2000 years into the past. There he became Chaos, the Master of Evil, and sent the Four Fiends of the Elements ahead 2000 years into the future, where they would send him back in time. Garland/Chaos theorized that in 2000 years the time loop would close and he would cease to exist, which he thought would make him immortal. • Futurama - The central characters, Fry, Leela, and Bender travel back in time to stop an unfortunate sell by Mom and Professor Farnsworth. Only after the three are killed, does the Professor (of the past) still make the sale successful, thereby repeating the events of the game for the Fry, Leela, and Bender of the past (who remained unharmed and unaware of the events) to live out, creating an endless loop. • GrimGrimoire - The main character is stuck in a time loop and has 5 days to try to stop a disaster. • Higurashi no Naku Koro ni - Each chapter is a different iteration of the same month, with only one character being aware that she is living in a time loop, although some of the other characters begin to recall events from past time loops. • The Legend of Zelda: Majora's Mask - The entire game is set around a three-day time loop, which the main character and protagonist, Link, can reset at any time he needs to. • Little Busters! - The entire visual novel takes place within an artificial world—set at high school—that loops on itself every few months. The protagonists are unaware of the loop, but each time they return they are stronger and smarter, until finally hero and heroine fully regain their memories and are to ready to face the challenges of the real world. • Prince of Persia: The Sands of Time - The player is given the "Dagger of Time", allowing them to continuously relive the previous ten seconds of game-play for a set amount of times, or until the player is satisfied with the way he or she played those ten seconds. The Prince is also sent back to the night before he stole the dagger, with the dagger of time in his possession, near the end of the game. • Shadow of Memories aka Shadow of Destiny - The game begins with the death of the player, which the player then needs to prevent. • Timesplitters: Future Perfect includes many scenarios where the player works with past and future versions of himself that he meets through time loops. • Escape from Monkey Island (2000) - In one portion of the game, the player has to repeat the actions of the second Guybrush encountered earlier. If not performed identically (because at this point in time, the player is now the earlier second Guybrush), the player is returned to the start of the swamp. • Wild Arms: The Vth Vanguard (2006) - One of the characters, Avril Vent Fleur is obligated to relieve a 12,000 year old time loop in order to save Filgaia, the planet where the game takes place. Although she is unaware of the loop at first, she gains back her memories near the end and decides to return to the past to prepare for the future events. Otherwise, breaking the loop will result in a time paradox. This is one instance where only the character's consciousness travels through time, not the body. • Flower, Sun, and Rain - In this game, "searcher" Sumio Mondo is assigned the task of defusing a bomb on an airplane. When he tries to make it to the airport, he is blocked by outside forces, and the plane explodes. Upon waking in the morning, he discovers that he is back in the previous day, with the bomb still waiting on the airplane. Time loop • Xenosaga - One of the series villains, Wilhelm, makes use of Zarathustra to create what he calls an Eternal Recurrence to prevent the universe to collapse, effectively creating a time loop, which the heroes tries to prevent in the end of the third episode of the saga. • WWE SmackDown vs. Raw 2011 - In a portion of the "Vs. Undertaker" Road to WrestleMania story, the player has to win a 2-on-1 match against Mark Henry and Big Show. During the match, an evil laugh can be heard and a flash of light is shown, automatically restarting the match and restoring Henry and Show. The time loop ends when your character/wrestler has either Henry or Show on the outside, counting them out during the 10-count and winning the match. 164 References [1] http:/ / www. imdb. com/ title/ tt0734799/ [2] http:/ / www. imdb. com/ title/ tt0094371/ [3] Peter Stockwell. The poetics of science fiction. p. 143. ISBN 0-582-36993-2, 9780582369931. Temporal paradox Temporal paradox (also known as time paradox and time travel paradox) is a theoretical paradoxical situation that happens because of time travel. A time traveler goes to the past, and does something that would prevent him from time travel in the first place. If he does not go back in time, he does not do anything that would prevent his traveling to the past, so time travel would be possible for him. However, if he goes back in time and does something that would prevent the time travel, he will not go back in time. Thus each possibility seems to imply its own negation - a type of logical paradox. A typical example of this kind is the grandfather paradox, where a person goes back in time to kill their grandfather before he had any biological descendant. If they succeed, one of their parents would never exist and they themselves would never exist either. This would make it impossible for them to go back in time in the first place, making them unable to kill their grandfather, who would continue to produce offspring and restart the situation. But if they fail, their grandfather would be alive and produce offspring, one of whom would eventually conceive the time traveler and the whole scenario would start over. Solution Temporal paradox has been used to argue that time travel must be impossible, because it is capable of resulting in a paradox. Kip Thorne, however, said that none of the supposed paradoxes formulated in time travel stories can actually be formulated at a precise physical level: that is, any situation in a time travel story turns out to permit many consistent solutions. Time line protection hypothesis This theory states that a time traveler, no matter what he had done, would not be able to create a time paradox. A person traveling back in time to terminate his grandfather, could have appeared in a wrong place, or had his gun jammed, thereby allowing his grandfather to have descendants. The natural law would prevent the traveler to alter the time travel he had done in the first place. Prior to 1986, DC published a number of Superman stories where he tried to alter the past, only to be defeated by the past protecting itself. (In one, Superboy tries to prevent the assassination of Lincoln, only to come upon Lex Luthor who is also time traveling. Luthor exposes Superboy to red kryptonite and this piece totally paralyzes Superboy. The effect does not wear off until the dying president is carried out of Ford's Theater. ) Temporal paradox The animated television series Futurama shows a more lighthearted side of the paradox. In the episode "Roswell That Ends Well", the main character, Philip J. Fry, travels back in time with his friends to 1947 in Roswell, New Mexico. Remembering that his grandfather works at the base, and told that killing the man would nullify his own existence, Fry becomes obsessed with protecting him. Fry's efforts prove counterproductive: he locks the man in a shack to protect him, failing to realize that an atomic bomb is being tested on the grounds. When he does not disappear, he assumes that the man could not have been his grandfather and thus proceeds (unknowingly) to sleep with and (accidentally) impregnate a beautiful woman, who apparently is the younger version of his grandmother, thereby becoming his own grandfather. In the 1972 Doctor Who adventure Day of the Daleks, Sir Reginald Styles is targeted by guerrillas from the 22nd century, who believe he's behind the deaths of VIP delegates. Because of those deaths, the Daleks were able to take over Earth in their time. However, a fellow guerrilla who was left behind was to blame, which was the true cause of their timeline ensuing. In the game "Ratchet and Clank Future: A Crack in Time", Alister Azimuth tries to fix his mistake of causing the fall of the Lombaxes, but if he was successful in traveling to the past, time would rip itself apart and the universe would collapse on itself. In the Machinima series Red vs. Blue, Church is sent back in time via the combined energy of a bomb and a weather machine. He attempts to fix past events, as well as preventing the explosion, but his attempts are ultimately responsible for most of the events that took place beforehand in the series, including his own death. In the Japanese manga Doraemon, the future grandson (Sewashi) of the lead character—Nobita—comes back in time to meet his grandfather in his primary school days intentionally to change the life he is in. Nobita questions the existence of his grandson that if he did marry Shizuka, the girl he likes (instead of the one he dislikes but conceived the father of his future grandson), what would happen to his grandson. His grandson, along with Doraemon, replies that there are multiple paths leading to the same future, and they will still exist even if Nobita married another girl. The plot never explicitly told of when the history was altered, but later events in the plot did show a future where Nobita married the girl he likes and lived a better, wealthier life and yet, future characters showed no signs of remembering the original history. However, when being asked of Doraemon's reason of being in the past, he replies that his role is to make sure Nobita marries the girl he likes, which mentally still reserves logic. In the television series Lost, Jack and Locke enter an underground research facility on the island in 2004, and watch an orientation film made by the mysterious DHARMA Initiative organisation in 1980. The film makes reference to an "incident" having occurred on the island at some point in the 1970s, necessitating the construction of the underground bunker, as a method of containing a limitless amount of electromagnetic energy, and preventing a global catastrophe. In the show's fifth season, some of the main characters begin moving erratically through time, before eventually becoming stuck in 1974. Three years later, these same characters unwittingly become the cause of the incident. In the game Legacy of Kain: Soul Reaver 2 when Raziel and Kain travel to Nosgoth's past, a paradox occurs when Kain saves Raziel by removing the Soul Reaver from Raziel's body. This ends the time loop that Raziel endures because the soul devouring entity within the Reaver was Raziel's own soul, which he could not consume. Raziel's fate was to be absorbed by the blade, and in not being absorbed Raziel now has free will and can not spin within the Wheel of Fate. History attempts to protects itself from the paradox by creating a new enemy for the vampire race, known as the Hildan, leading into to the events of Legacy of Kain Defiance. 165 Temporal paradox 166 Novikov self-consistency principle This Novikov self-consistency principle says that anything a time traveler does in the past must have been part of history all along, so although the time traveler can have a causal influence on events in the past, it is impossible for anything the time traveler does to "change" history. So, for example, any attempt by the time traveler to kill one of his ancestors before they became a parent would be guaranteed to fail for some reason or another (perhaps the gun would jam, or perhaps the traveler would just have a change of heart), so the grandfather paradox would be avoided. This theory, however, is capable of causing bootstrap paradox. An example of this is the Artemis Fowl series. In book 6, Artemis travels back in time, accidentally causing his younger self to eventually discover the fairys, setting the events of book one in motion. He also allowed mastermind Opal Koboi from the past to take over the house by travelling in same time stream that Artemis travelled back in. The book shows that if Artemis hadn't travelled back in the first place, he wouldn't have discovered the faires and never have been able to go back at all. Multiple universes hypothesis This theory states that there are infinite number of universes, all-together known as multiverse. If a person is about to travel back in time, he will end up in a parallel universe. So if he kills "his" grandfather, a paradox would not occur because the grandfather that he had killed is the grandfather who lives in the universe he currently is in. An example of this occurs in the Japanese anime series Dragonball Z in which Trunks, the son of Vegeta and Bulma, comes from the future. In the present, Trunks was not even born. He warns of the arrival of androids which are more powerful than even Goku and Vegeta, and forewarns the death of Goku in his past. However, by giving the medicine which can cure Goku and undertaking extensive training, Trunks and the Z Fighters manage to defeat the androids as well as Cell. When Trunks returns to his present, though, his universe is still the same with Goku and other Z-fighters still dead, the only difference being that at that point of time, Trunks, because of his training with the Z-fighters, had become strong enough to defeat the androids and Cell of his own time. Another example is in the manga/anime series Reborn!. A special weapon called the Ten-Year Bazooka (because anyone hit by it will be swapped with themselves from 10 years in the future for 5 minutes) allows Tsuna and his Guardians, as well as some of his other friends to travel into the future. However, due to a special device invented by Irie Shouichi, they are kept there for an extended period of time. They learn that this was because they possessed the Vongola Rings, which the Tsuna in that time period destroyed to avoid conflicts with rival mafia families. They learn that the rings power is necessary to defeat Byakuran, a man who, due to Shouichi's time-traveling, realized that he himself, and not merely a parallel version of himself, was present in all other multiple universes, referred to as parallel worlds. This allowed him to use knowledge far beyond what was present in any single one of those worlds, allowing him to take over all of them except for the future in which Tsuna traveled to. However, by defeating him in that universe, Tsuna killed all other instances of Byakuran in the other universes as well, as they were metaphysically the same person. Despite this, however, the universe in which Byakuran was defeated is still shown to exist. Branching universe hypothesis This theory says that to travel back in time would cause time to branch. An example of this occurs in The Legend of Zelda. Toward the middle of The Legend of Zelda: Ocarina of Time, the protagonist, Link, is sealed in slumber for seven years. When he awakens, he finds the world in a ruined state. At the end of the game, the antagonist, Ganon, is defeated and sealed within the Sacred Realm. Princess Zelda then sends Link into the past to right the wrongs Ganon created. By doing so, he creates two worlds, one in which Ganon is sealed away in the Sacred Realm, and one in which Ganon was merely imprisoned by the King. Additional evidence is stated by Eiji Aonuma when conversing on timeline placement of The Legend of Zelda: The Wind Waker and The Legend of Zelda: Twilight Princess, where he says that the games are parallel. Temporal paradox This was also in a DC anthology, which included among other series, one comic with Superman. In the comic, Superman attempts to change many of the world's great events, including Lincoln's assassination. When he comes back to his own time, nothing had changed. However, he discovers a parallel version of the world with the altered history. 167 Timeline corruption hypothesis Another idea is that any change in the timeline, even without personal interaction, while allowable, would cause a "butterfly effect" in the timeline. All history after the time traveler visited would be affected by minute changes the traveler had made in the past, and the history, depending on how severe the time traveller's actions were, would sooner or later be completely changed. This has been coined the "timeline corruption hypothesis." The 2004 film The Butterfly Effect and the Multiverser RPG system prefer this view. There's also the Ray Bradbury science fiction short story "A Sound of Thunder", in which the butterfly effect is caused by a real butterfly. Note that the timeline corruption hypothesis is not intended to solve the temporal paradox. It seems to be part of the multiple universes hypothesis, in which a change in the timeline creates a new universe. The most well-known example of this theory is the 1985 film Back to the Future, in which the protagonist Marty McFly goes back in time and interferes with his parents' first romantic encounter, thus erasing his own existence (as well as that of his siblings). However, the effect only happens gradually, exemplified by a family photo in his possession: each of his siblings begins to disappear limb by limb, starting with the oldest and working down to him (the youngest of the three). This allows Marty to correct the error and restore the timeline, albeit with a few minor changes that are due to his interference. This effect has one contradiction - If a person, somehow, causes himself to not be born in the past, then he would not have been able to do the thing that caused him to not be born for he would have not existed, thus causing time to corrupt. This theory also figures prominently in the 1989 sequel Back to the Future Part 2 in which McFly's enemy, the now-elderly Biff Tannen, travels from 2015 back to 1955 to give his younger self a copy of a sports almanac with the final scores of professional sports games from 1950 to 2000. The younger Biff uses this information to change history, so when Doc and McFly return to 1985 from their own mission in 2015, they find Hill Valley drastically changed. Marty proposes going back to 2015 to stop Biff from going back to 1955, but Doc explains that it would do no good since they were on a different timeline and 2015 would also be different. The only way to restore the timeline is to return to 1955 and take the almanac away from Biff so he will not use it to change history. Note that this does not create a bootstrap paradox because Biff, from timeline A, traveled back in time and created timeline B, thus there is a clear(ish) logical reason as to where the almanac came from. This idea also appears in a Family Guy episode, in which Peter goes back in time with the help of "Death" so that he can relive his teen life. When he arrives in the past, rather than spending time with his present-day wife, Lois, Peter ignores her. His actions cause a corruption in the timeline, and when Peter returns to the present day, all of reality is radically different. In the Simpsons' Halloween show Treehouse of Horror V, there is TIME AND PUNISHMENT where Homer attempting to fix the toaster,accidentally creates a time machine and travels to the age of dinosaurs, inadvertantly altering his time far for the worse. His attempts to rectify matters alter time over & over in amazing ways. The timeline corruption hypothesis is also used in the Red Dwarf episode, "Tikka to Ride", when the Red Dwarf crew travels back in time (with Lister's intention of ordering 500 curries) and accidentally kills Lee Harvey Oswald, saving Kennedy's life. Three years later, in an alternate reality, it is revealed that through a series of chain events, the USSR won the Space Race and put the first man on the moon, meaning that the Dwarfers never travelled into deep space in the first place, trapped in an alternate 1966. The Dwarfers manage to correct this by trying to make Oswald shoot from a different floor, before making an impeached Kennedy assassinate himself, as the man on the grassy knoll. Temporal paradox Philip K. Dick also explored timeline corruption paradoxes. In the story "Orpheus with Clay Feet", Slade, a character from the future, goes on a time travel vacation to the past where he can visit famous science fiction writer Jack Dowland and become his muse. Slade, however, fails to inspire Dowland as he had hoped, and Dowland never becomes the master he should have been. Timeline corruption is an important motif in Star Trek: Enterprise. Captain Archer and the Enterprise crew become embroiled in an ongoing Temporal Cold War with the Suliban Cabal, a race of hostile aliens from the future who deliberately manipulate the timeline for their own ends. One of the results was that Earth's early 20th-Century history was changed so that the Nazis controlled much of Europe and proceeded to invade North America. Of course, the humans had to find a way to stop the Suliban and restore the timeline. Similar events occur in other Star Trek series. In the videogame World of Warcraft, the Bronze Dragonflight (tasked with the safety of the timelines) frequently asks the heroes (players) to help them fight the Infinite Dragonflight, who would want to change important events of the past. Although this may vary depending on the point of the view of the player, most of the events are negative ones - Thrall's escape from his prison, leading to the formation of the new Horde, enemies of the Alliance; the opening of the Dark Portal, in which a corrupted Medivh opens up a link with the world of Draenor, starting the orcish invasions of Azeroth and ensuing wars; and the Culling of Stratholme, a defining moment in which Prince Arthas's fall to madness leads to the rise of the undead Scourge and his eventual merge with the Lich King - but they insist that the outcome of preventing such events would be "much worse". The videogame series Command & Conquer contains a miniseries called Red Alert, whose three games depict what "happened" when Albert Einstein traveled back in time to prevent Hitler from rising to power. This resulted in the Nazi regime never coming to power, allowing the Soviet Union to become a formidable threat to the Allied Nations; instead of just tension during the Cold War, the Soviets launched a full-scale invasion against the United States. Later in the series, the Soviets steal the time-travelling technology for themselves to kill Einstein, preventing his technology from helping the Allies; however, this leads to Japan's Empire of the Rising Sun emerging as a new superpower. In the videogame The Journeyman Project, a Temporal Distortion Wave threatens to alter the present. The player is tasked with retrieving a CD-ROM disk that has the correct timeline stored on it. Upon returning to the present from the far distant past, it is revealed that the timeline has indeed been corrupted by four key events in the recent past. This idea of avoiding corrupted timelines is seen throughout the Journeyman Project Trilogy. Although, it is only a story element in the later games as opposed to a major gameplay moment. 168 Temporal merging hypothesis This is the opposite of the multiple universes hypothesis, in that each action committed in time travel actually overlaps one reality with another. For instance, if a time traveler were to meet his double from another time, the double would merge with the time traveler, making the traveler a part of the time he is visiting. The same would hold true for events. Two events would merge into the nearest event which does not produce a paradox (a dead grandfather in one universe but not in another would either create a dead grandfather in both universes, but alter the person's heritage so as to allow this, merge both timelines so that the person would fade from all timelines upon return, or produce a mean between life and death such as a coma). An example of this is seen in the film The One, in which a character travels across time or dimensions, destroying copies of himself to cause them to merge — thus increasing power for the original character. A similar idea is seen in Margaret Peterson Haddix's book series, The Missing, in which any records of original time are kept in tracers, and those traveling back in time can merge with their own tracers. Temporal paradox 169 Choice timeline hypothesis In the choice timeline hypothesis, history changes the instant the time traveler decides to travel back in time, thereby rendering his actions in that regard pre-destined. This theory is the most consistent with our understanding of the dimension of time. Bill & Ted's Excellent Adventure, as well as its sequel and television spin-offs (Bill & Ted's Excellent Adventures both animated and live-action), feature numerous uses of this hypothesis. Bill and Ted, constantly realizing that their plans are foiled by the lack of a certain item, decide to later travel back in time and deliver themselves the necessary item, often indicating a specific place in which the item will appear. Upon searching the location, the item is invariably there. Can-Not Because Has-Not This theory states that the present is not the forefront of time, and so we are our future selves' past. Thus, if sometime in the future a time travel device were created, someone from the future would have already brought it back to us, thus establishing itself as "already" existing in our time as a result - and likely copied and recopied. Since our present selves are still wondering about time travel, this theory states that we will never be able to build a time machine, because if we are still wondering, then no one from the future has built a time machine and brought it back with them to us, and if no one in the future has built a time machine, then we in the future will not build a time machine, and no one can ever build a time machine because no one in the future has built one. This theory is demonstrated in an episode of the TV show Big Bang Theory where Leonard and Sheldon sign a roommate agreement that states if either one of them ever invents time travel their first trip back would be to their present location 5 seconds after the signing of the contract, they are subsequently disappointed when the 5 seconds pass and nothing happens. This theory, however, creates a Causality Loop. Also if it is that any time machine made will allow only one way travel, i.e. into the future, or if it is that we can go into the future, but while returning, we can only return to the present (i.e. not set the dial to go back more than we used to go into the future, or before the time machine is invented), this theory fails. Wormholes, which are suggested to allow backwards time travel, demonstrate this, as you cannot go further back in time than when the wormhole was created. There are also other possibilities: someone in the future will build a time machine and many people will use it to travel back in the past, but we do not know this because: "no one can travel so far in the past to reach our time" or "no one has revealed that time-traveling is possible" or "no one that revealed that time-traveling is possible, was trusted" or "anyone with the knowledge to sufficiently understand temporal mechanics enough to build such a device, will also be enlightened enough not to interfere with the known written past" or "the time machine will be destroyed if you go back before it is created." Self-Healing hypothesis This theory states that time would heal itself from the paradox. A person is about to alter an event in the present by traveling back to the past and altering the events that cause the events in the present day to happen. Then there will be another set of events that will cause the present-day events to happen, and so there will be reason for him to travel back in time, and thus the paradox would never happen. An example of this can be seen in the film The Time Machine, where the main character creates a time machine to save his dead fiancé, but upon doing so, she is killed another way. When traveling to the future, he finally finds out that if she did not die he would never create the time machine. Thus it is impossible to save her. Even though this does not create a physical paradox, it creates a mental one in which the time traveler, who still builds the time machine for the same reason, remembers a different cause for that reason. Another example is the TV series Doraemon, where in one episode the main character travels back in time to save someone from being hit by a car. Doraemon then states that 'if history is altered, it will always repeat itself to make up for the event that did not occur'. However he also states that 'the event might happen on another person, or be a Temporal paradox completely different event altogether', raising the question how did the time traveler know about what was supposed to happen in the first place? This theory also happens in the TV series Lost when Desmond Hume, who can see into the future, sees Charlie Pace die when struck by lightning. Desmond saves him by building a big metal pole to absorb the shock instead. When Charlie doesn't die this way, Desmond sees him dying by trying to save Claire from drowning, trying to get Claire a bird, and while getting shot with an arrow from a trap in the jungle- all from which he is saved. Eventually Charlie accepts his fate and drowns in the DHARMA Initiative facility "the Looking Glass". 170 Destruction resolution This theory states that any paradox would cause the destruction of a universe, or at least the part of the time & space affected by the paradox. In this hypothesis, if a person travels back to kill his grandfather before one of his parents is conceived, then it will cause himself to disappear. History would erase all traces of the person's existence, and the death of the grandfather would be caused by another reason. Thus, the paradox would never occur from the historical viewpoint. A variation of this example occurs in the Season 3 finale of FRINGE when Peter Bishop uses the Doomsday machine. When he tells both Walter and Walternate he punched holes in both universes in the past and created a bridge between universes in order to repair the damage, Peter disappears because his actions caused the younger versions of himself in both of the new timelines to die in 1985. Temporal Modification Negation Theory This theory is partially similar to other theories on time travel. While stating that if time travel is possible it would be impossible to violate the grandfather paradox, it goes further to state that any action taken that itself negates the time travel event cannot occur. The consequences of such an event would in some way negate that event, by either voiding the memory of what one is doing before doing it, by preventing the action in some way, or even by destroying the universe among other possible consequences. It states, therefore, that to successfully change the past one must do so incidentally, though one might be able to change this fact slightly. If one were to go back and place a note in someplace one knew one's future self would find it and then subsequently stop an assassination one might be able to tweak this theory. If the specified note said to go back into time, stop the assassination, copy this note, and place it in the same spot it originally was, one might be able to intentionally stop the assassination. For example, if one tried to stop the murder of one's parents, he would fail. On the other hand, if one traveled back and did something to some random person that as a result prevented the death of someone else's parents, then such an event would be successful, because the reason for the journey, and therefore the journey itself, remain unchanged preventing a paradox. In addition, if this event had some colossal change in the history of mankind, and such an event would not void the ability or purpose of the journey back, it would occur, and would hold. In such a case, the memory of the event would immediately be modified in the mind of the time traveler. An example of this would be for someone to travel back to observe life in Austria in 1887 and while there shoot five people, one of whom was Hitler's parent. Hitler would therefore never have existed, but since this would not prevent the invention of the means for time travel, or the purpose of the trip, such a change would hold. Also for it to hold, every element that influenced the trip must remain unchanged. This would void someone convincing another party to travel back to kill the people without knowing who they are and making the time line stick, because by being successful, they would void the first party's influence and therefore the second party's actions. Temporal paradox 171 Changes allowed, without resolution to paradoxes Another theory, though much less commonly utilized, is one in which the altering of an event in the past would always be allowed, even if such alteration would logically cause a paradox. Ad exemplum, a time traveler who embarks on a trip to the past would be able to kill his grandfather, even though such an act would prevent one of his parents from being born and thus prevent the time traveler himself from being born, without causing the resulting paradox to change any other part of the past. Though, with this theory, the time traveler, who would still remember having a grandfather and even parents, would appear to have not been born. This seems to generate a problem resembling the bootstrap paradox. Doomed Timeline Theory This theory involves the universe incorporating a "fail-safe" by destroying any instance or timeline that deviates from a main timeline to prevent multiple universes from existing. Basically, any time travel deviating from a stable time-loop, paradoxical or not, is doomed to be destroyed. For instance, if a man goes back in time to prevent someone who's dead in the future from dying, succeeding will lead to that timeline ceasing to exist. Multiple examples of this can be found in Andrew Hussie's webcomic Homestuck. Dave Strider, who's role as the Knight of Time allows him to utilize time travel on a frequent basis, has to be wary of keeping time loops stable. For instance, if he goes back in time to save himself, his past self will eventually become his future self that goes back in time to save himself. Any deviation from this will result in the creation of an alternate Dave. All alternate Daves are destined to die, and in this way, any alternate reality versions of the characters or universes are automatically destined to be destroyed. Grandfather paradox The grandfather paradox is a proposed paradox of time travel first described (in this exact form) by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent (Future Times Three).[1] The paradox is this: suppose a man traveled back in time and killed his biological grandfather before the latter met the traveler's grandmother. As a result, one of the traveler's parents (and by extension the traveler himself) would never have been conceived. This would imply that he could not have travelled back in time after all, which means the grandfather would still be alive, and the traveller would have been conceived allowing him to travel back in time and kill his grandfather. Thus each possibility seems to imply its own negation, a type of logical paradox. Despite the name, the grandfather paradox does not exclusively regard the impossibility of one's own birth. Rather, it regards any action that makes impossible the ability to travel back in time in the first place. The paradox's namesake example is merely the most commonly thought of when one considers the whole range of possible actions. Another example would be using scientific knowledge to invent a time machine, then going back in time and (whether through murder or otherwise) impeding a scientist's work that would eventually lead to the very information that you used to invent the time machine. An equivalent paradox is known (in philosophy) as autoinfanticide, going back in time and killing oneself as a baby.[2] The grandfather paradox has been used to argue that backwards time travel must be impossible. However, a number of hypotheses have been postulated to avoid the paradox, such as the idea that the past is unchangeable, so the grandfather must have already survived the attempted killing (as stated earlier); or the time traveller creates an alternate time line in which the traveller never was born. Grandfather paradox 172 Scientific theories Novikov self-consistency principle The Novikov self-consistency principle and Kip S. Thorne expresses one view on how backwards time travel could be possible without a danger of paradoxes. According to this hypothesis, the only possible time lines are those entirely self-consistent—so anything a time traveler does in the past must have been part of history all along, and the time traveler can never do anything to prevent the trip back in time from happening, since this would represent an inconsistency. Nicholas J. J. Smith argues, for example, that if some time traveler killed the child who lived in his old address, this would ipso facto necessitate that the child was not the time traveler's younger self (and not anyone's younger self.) Parallel universes There could be "an ensemble of parallel universes" such that when the traveller kills the grandfather, the act took place in (or resulted in the creation of) a parallel universe where the traveler's counterpart never exists as a result. However, his prior existence in the original universe is unaltered. Succinctly, this explanation states that: if time travel is possible, then multiple versions of the future exist in parallel universes. This theory would also apply if a person went back in time to shoot himself, because in the past he would be dead as in the future he would be alive and well. Examples of parallel universes postulated in physics are: • In quantum mechanics, the many-worlds interpretation suggests that every seemingly random quantum event with a non-zero probability actually occurs in all possible ways in different "worlds", so that history is constantly branching into different alternatives. The physicist David Deutsch has argued that if backwards time travel is possible, it should result in the traveler ending up in a different branch of history than the one he departed from.[3] See also quantum suicide and immortality. • M-theory is put forward as a hypothetical master theory that unifies the six superstring theories, although at present it is largely incomplete. One possible consequence of ideas drawn from M-theory is that multiple universes in the form of 3-dimensional membranes known as branes could exist side-by-side in a fourth large spatial dimension (which is distinct from the concept of time as a fourth dimension) - see Brane cosmology. However, there is currently no argument from physics that there would be one brane for each physically possible version of history as in the many-worlds interpretation, nor is there any argument that time travel would take one to a different brane. Nonexistence theory According to this theory, if one were to do something in the past that would cause their nonexistence, upon returning to the future, they would find themselves in a world where the effects of (and chain reactions thereof) their actions are not present, as the person never existed. Through this theory, they would still exist, though. A famous example of this theory is It's A Wonderful Life. Theories in science fiction Parallel universes resolution The idea of preventing paradoxes by supposing that the time traveler is taken to a parallel universe while his original history remains intact, which is discussed above in the context of science, is also common in science fiction—see Time travel as a means of creating historical divergences. Grandfather paradox 173 Restricted action resolution Another resolution, of which the Novikov self-consistency principle can be taken as an example, holds that if one were to travel back in time, the laws of nature (or other intervening cause) would simply forbid the traveler from doing anything that could later result in their time travel not occurring. For example, a shot fired at the traveler's grandfather misses, or the gun jams or misfires, or the grandfather is injured but not killed, or the person killed turns out to be not the real grandfather—or some other event prevents the attempt from succeeding. No action the traveler takes to affect or change history can ever succeed, as some form of "bad luck" or coincidence always prevents the outcome. In effect, the traveler cannot change history. Often in fiction, the time traveler does not merely fail to prevent the actions, but in fact precipitates them (see predestination paradox), usually by accident. This theory might lead to concerns about the existence of free will (in this model, free will may be an illusion, or at least not unlimited). This theory also assumes that causality must be constant: i.e. that nothing can occur in the absence of cause, whereas some theories hold that an event may remain constant even if its initial cause was subsequently eliminated. Closely related but distinct is the notion of the time line as self-healing. The time-traveller's actions are like throwing a stone in a large lake; the ripples spread, but are soon swamped by the effect of the existing waves. For instance, a time traveller could assassinate a politician who led his country into a disastrous war, but the politician's followers would then use his murder as a pretext for the war, and the emotional effect of that would cancel out the loss of the politician's charisma. Or the traveller could prevent a car crash from killing a loved one, only to have the loved one killed by a mugger, or fall down the stairs, choke on a meal, killed by a stray bullet, etc. In the 2002 film The Time Machine, this scenario is shown where the main character builds a time machine to save his fiance from being killed by a mugger, only for her to die in a car crash instead; as he learns from a trip to the future, he cannot save her with the machine or he would never have been inspired to build the machine so that he could go back and save her in the first place. In some stories it is only the event that precipitated the time traveler's decision to travel back in time that cannot be substantially changed, in others all attempted changes "heal" in this way, and in still others the universe can heal most changes but not sufficiently drastic ones. This is also the explanation advanced by the Doctor Who role-playing game, which supposes that Time is like a stream; you can dam it, divert it, or block it, but the overall direction resumes after a period of conflict. It also may not be clear whether the time traveler altered the past or precipitated the future he remembers, such as a time traveler who goes back in time to persuade an artist— whose single surviving work is famous— to hide the rest of the works to protect them. If, on returning to his time, he finds that these works are now well-known, he knows he has changed the past. On the other hand, he may return to a future exactly as he remembers, except that a week after his return, the works are found. Were they actually destroyed, as he believed when he traveled in time, and has he preserved them? Or was their disappearance occasioned by the artist's hiding them at his urging, and the skill with which they were hidden, and so the long time to find them, stemmed from his urgency? Destruction resolution Some science fiction stories suggest that any paradox would destroy the universe, or at least the parts of space and time affected by the paradox. The plots of such stories tend to revolve around preventing paradoxes, such as the final episode of Star Trek: The Next Generation. A less destructive alternative of this theory suggests the death of the time traveller whether the history is altered or not; an example would be in the first part of the Back to the Future trilogy, where the lead character's alteration of history results in a risk of his own disappearance, and he has to fix the alteration to preserve his own existence. In this theory, killing one's grandfather would result in the disappearance of oneself, history would erase all traces of the person's existence, and the death of the grandfather would be caused by another means (say, another existing person firing the gun); thus, the paradox would never occur from a historical viewpoint. Grandfather paradox 174 Temporal Modification Negation Theory While stating that if time travel is possible it would be impossible to violate the grandfather paradox, it goes further to state that any action taken that itself negates the time travel event cannot occur. The consequences of such an event would in some way negate that event, be it by either voiding the memory of what one is doing before doing it, by preventing the action in some way, or even by destroying the universe among other possible consequences. It states therefore that to successfully change the past one must do so incidentally. For example, if one tried to stop the murder of one's parents, he would fail. On the other hand, if one traveled back and did something else that as a result prevented the death of someone else's parents, then such an event would be successful, because the reason for the journey and therefore the journey itself remains unchanged preventing a paradox. In addition, if this event had some colossal change in the history of mankind, and such an event would not void the ability or purpose of the journey back, it would occur, and would hold. In such a case, the memory of the event would immediately be modified in the mind of the time traveler. An example of this would be for someone to travel back to observe life in Austria in 1887 and while there shoot five people, one of which was one of Hitler's parents. Hitler would therefore never have existed, but since this would not prevent the invention of the means for time travel, or the purpose of the trip, then such a change would hold. But for it to hold, every element that influenced the trip must remain unchanged. The Third Reich would not exist and the world we know today would be completely different. This would void someone convincing another party to travel back to kill the people without knowing who they are and making the time line stick, because by being successful, they would void the first party's influence and therefore the second party's actions. These issues are treated humorously in an episode of Futurama in which Fry travels back in time and inadvertently causes his grandfather's death before he marries his grandmother. His distraught grandmother then seduces him, and on returning to his own time, Fry learns that he is his own grandfather. Other considerations Consideration of the grandfather paradox has led some to the idea that time travel is by its very nature paradoxical and therefore logically impossible, on the same order as round squares. For example, the philosopher Bradley Dowden made this sort of argument in the textbook Logical Reasoning, where he wrote: “ Nobody has ever built a time machine that could take a person back to an earlier time. Nobody should be seriously trying to build one, either, because a good argument exists for why the machine can never be built. The argument goes like this: suppose you did have a time machine right now, and you could step into it and travel back to some earlier time. Your actions in that time might then prevent your grandparents from ever having met one another. This would make you not born, and thus not step into the time machine. So, the claim that there could be a time machine is self-contradictory. ” However, some philosophers and scientists believe that time travel into the past need not be logically impossible provided that there is no possibility of changing the past, as suggested, for example, by the Novikov self-consistency principle. Bradley Dowden himself revised the view above after being convinced of this in an exchange with the philosopher Norman Swartz.[4] Consideration of the possibility of backwards time travel in a hypothetical universe described by a Gödel metric led famed logician Kurt Gödel to assert that time might itself be a sort of illusion.[5][6] He seems to have been suggesting something along the lines of the block time view in which time does not really "flow" but is just another dimension like space, with all events at all times being fixed within this 4-dimensional "block". Grandfather paradox 175 References [1] Barjavel, René (1943). Le voyageur imprudent ("The imprudent traveller").; actually, the book refers to an ancestor of the time traveler not his grandfather. [2] Horwich, Paul (1987). Asymmetries in Time. Cambridge, MIT Press. pp. 116. When the term was coined by Paul Horwich, he used the term autofanticide. [3] Deutsch, David (1991). "Quantum mechanics near closed timelike curves". Physical Review D 44 (10): 3197–3217. Bibcode 1991PhRvD..44.3197D. doi:10.1103/PhysRevD.44.3197. [4] "Dowden-Swartz Exchange" (http:/ / www. sfu. ca/ philosophy/ swartz/ time_travel1. htm). . [5] Yourgrau, Palle (2004). A World Without Time: The Forgotten Legacy Of Godel And Einstein. Basic Books. ISBN 0-465-09293-4. [6] Holt, Jim (2005-02-21). "Time Bandits" (http:/ / www. newyorker. com/ printables/ critics/ 050228crat_atlarge). The New Yorker. . Retrieved 2006-10-19. Ontological paradox The bootstrap paradox is a paradox of time travel in which information or objects can exist without having been created. After information or an object is sent back in time, it is recovered in the present and becomes the very object/information that was initially brought back in time in the first place. Numerous science fiction stories are based on this paradox, which has also been the subject of serious physics articles.[1] The term "bootstrap paradox" refers to the expression "pulling yourself up by your bootstraps"; the use of the term for the time-travel paradox was popularized by Robert A. Heinlein's story By His Bootstraps (see below). Definition Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is to posit that these changes already are contained self-consistently in the past timeline. A time traveler attempting to alter the past in this model, intentionally or not, would only be fulfilling his or her role in creating history, not changing it. The Novikov self-consistency principle proposes that contradictory causal loops cannot form, but that consistent ones can. However, a scenario can occur where items or information are passed from the future to the past, which then become the same items or information that are subsequently passed back. This not only creates a loop, but a situation where these items have no discernible origin. Physical items are even more problematic than pieces of information, since they should ordinarily age and increase in entropy according to the Second law of thermodynamics. But if they age by any nonzero amount at each cycle, they cannot be the same item to be sent back in time, creating a contradiction. Another problem is the "reverse grandfather paradox", where whatever is sent to the past allows the time travel in the first place (such as saving your past self's life, or sending vital information about the time travel mechanism). The paradox raises the ontological questions of where, when and by whom the items were created or the information derived. Time loop logic operates on similar principles, sending the solutions to computation problems back in time to be checked for correctness without ever being computed "originally". Whether or not a scenario described in this paradox would actually be possible, even if time travel itself were possible, is not presently known. The bootstrap paradox is similar to, but distinct from, the predestination paradox, in which individuals or information travel back in time and ultimately trigger events they already experienced in their own present. In the latter case, no information or matter 'appears out of thin air'. Ontological paradox 176 Examples Involving information • On his 30th birthday, a man who wishes to build a time machine is visited by a future version of himself. This future self explains to him that he should not worry about designing the time machine, as he has done it in the future. The man receives the schematics from his future self and starts building the time machine. Time passes until he finally completes the time machine. He then uses it to travel back in time to his 30th birthday, where he gives the schematics to his past self, closing the loop. • A professor travels forward in time, and reads in a physics journal about a new equation that was recently derived. She travels back to her own time, and relates it to one of her students who writes it up, and the article is published in the same journal which the professor reads in the future. • A man builds a time machine. He goes into the future and steals a valuable gadget. He then returns and reveals the gadget to the world, claiming it as his own. Eventually, a copy of the device ends up being the item the man originally steals. In other words, the device is a copy of itself and it is not possible to state where the original came from. • A young physicist receives an old, disintegrating notebook containing information about future events sent by her future self via a time machine; before the book deteriorates so badly as to be unusable, she copies the information in it into a new notebook. Over the years the predictions of the notebook come true, allowing her to become wealthy enough to fund her own research, which results in the development of a time machine, which she uses to send the now old, tattered, disintegrating notebook back to her former self. The notebook is not a paradox (it has an end and a beginning; the beginning where she receives it and the end where she threw it out after she copied the information), but the information is: It's impossible to state where it came from. The professor has transferred the information that she wrote herself, so there was no original notebook. Involving physical items • A woman is locked outside her house because she's lost her keys. Another woman approaches her with the keys. When the woman enters the house five minutes later, she encounters a time machine which transports her and her keys back in time five minutes, allowing her to give them to herself and close the loop. [The woman would have to take the keys she left inside back in time, otherwise the keys given to her would age by a non-zero amount.] Involving people • A man travels back in time and falls in love with and marries a woman, whom he later learns was his own mother, who then gives birth to him. He is therefore his own father and, because of this, also his own grandfather, great-grandfather, great-great grandfather, great-great-great grandfather and so on, making his ancestry infinite, and also giving him no origin for his paternal genetic material. Examples from fiction The term bootstrap paradox comes from Robert A. Heinlein's story "By His Bootstraps", in which the protagonist is asked to go through a time portal by a mysterious stranger, a second stranger tries to stop him, and all three get into a fight which results in the protagonist being pushed through anyway. Ultimately, it is revealed that all three are the same person: the first visitor is his future self and the second an even older future self trying to prevent the loop from occurring. The bootstrap paradox here is in where and how the loop started in the first place. Heinlein's "—All You Zombies—" involves an even more convoluted time loop involving kidnapping, seduction, child abandonment and sex reassignment surgery, resulting in the protagonist creating the circumstances where he becomes his own mother, father, son, daughter, forever-lost lover and kidnapper. Ontological paradox One of the most noted examples of the bootstrap paradox in fiction occurs in the film Somewhere in Time, based on the Richard Matheson novel Bid Time Return. In the film, Christopher Reeve's character is given a pocket watch by an old lady. He then goes back in time and gives the pocket watch to the old lady's younger self, played by Jane Seymour, which prompts her to seek him out years in the future and give him the watch, resulting in the watch having no apparent origin. The bootstrap paradox occurs several times in the Terminator franchise, perhaps most notably in the creation of the main villain Skynet. In the first film, the Terminator cyborg sent back in time to kill Sarah Connor is destroyed, but its components are salvaged to form the basis of Skynet, the artificially intelligent computer network that will, in the future, send it back in time on its murderous mission. The knowledge of how to create an artificially intelligent machine therefore has no ultimate source. The current series of Doctor Who features many examples of the bootstrap paradox, most constructed by writer and later showrunner Steven Moffat. For example, in Moffat's 2007 episode "Blink", the Doctor records a message on film in 1969 in the form of half a conversation. The other half is filled in when Sally Sparrow views the film on DVD in 2007, which her friend Lawrence Nightingale transcribes. The full transcript, including the Doctor's portion, is eventually handed to the Doctor in 2008, but before he is sent back to 1969 from his subjective viewpoint, so he can use it in creating the message later. The contents of the conversation form a bootstrap paradox. In the movie Back to the Future, Marty McFly learns the Chuck Berry song Johnny B. Goode in the 1980s, but Berry presumably first hears it via telephone during McFly's 1955 performance of it at his parents' prom. The song thus has no origin. In the popular internet show Red vs. Blue: The Blood Gulch Chronicles, the blue team tank introduces herself as Sheila. However when Church goes back in time to "fix" the tank before it can kill him, the tank calls herself F.I.L.L.S. (pronounced Phyllis) and changes her name only after Church mistakenly calls her Shelia. Therefore the name Sheila has no apparent origin. 177 References [1] Matt Visser (1995). Lorentzian wormholes (http:/ / books. google. com/ books?id=Zo_vAAAAMAAJ& q=Bootstrap+ paradox& dq=Bootstrap+ paradox& hl=en& ei=aHunTrGLMqTn0QG7q5inDg& sa=X& oi=book_result& ct=result& resnum=1& ved=0CC0Q6AEwAA). . "Bootstrap paradoxes A second class of logical paradoxes ..." Predestination paradox 178 Predestination paradox A predestination paradox (also called causal loop, causality loop, and, less frequently, closed loop or closed time loop) is a paradox of time travel that is often used as a convention in science fiction. It exists when a time traveler is caught in a loop of events that "predestines" or "predates" them to travel back in time. Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is by saying that whatever has happened must happen. A time traveler attempting to alter the past in this model, intentionally or not, would only be fulfilling their role in creating history as we know it, not changing it. Or that the time-traveler's personal knowledge of history already includes their future travels to their own experience of the past. In layman's terms, it means this: the time traveller is in the past, which means they were in the past before. Therefore, their presence is vital to the future, and they do something that causes the future to occur in the same way that their knowledge of the future has already happened. It is very closely related to the ontological paradox and usually occurs at the same time. Examples A dual example of a predestination paradox is depicted in the classic Ancient Greek play 'Oedipus': Laius hears a prophecy that his son will kill him and marry his wife. Fearing the prophecy, Laius pierces newborn Oedipus' feet and leaves him out to die, but a herdsman finds him and takes him away from Thebes. Oedipus, not knowing he was adopted, leaves home in fear of the same prophecy that he would kill his father and marry his mother. Laius, meanwhile, ventures out to find a solution to the Sphinx's riddle. As prophesied, Oedipus crossed paths with a wealthy man leading to a fight in which Oedipus slays him. Unbeknownst to Oedipus the man is Laius. Oedipus then defeats the Sphinx by solving a mysterious riddle to become king. He marries the widow queen Jocasta not knowing she is his mother. A typical example of a predestination paradox (used in The Twilight Zone episode "No Time Like the Past") is as follows: A man travels back in time. While trying to prevent a school fire he had read about in a historical account he had brought with him, he accidentally causes it. An example of a predestination paradox in the television show Family Guy (Season 9, Episode 16): Stewie and Brian travel back in time using Stewie's time machine. They are warped outside the space-time continuum, before the Big Bang. To return home, Stewie overloads the return pad and they are boosted back into the space-time continuum by an explosion. Stewie later studies the radiation footprints of the Big Bang and the explosion of his return pad. He discovers that they match, and he concludes that he is actually the creator of the universe. He explains his theory to Brian, who replies with "That doesn't make any sense; you were born into the universe. How could you create it?" Stewie explains that it is a temporal causality loop, which is an example of a predestination paradox. A variation on the predestination paradoxes which involves information, rather than objects, traveling through time is similar to the self-fulfilling prophecy: A man receives information about his own future, telling him that he will die from a heart attack. He resolves to get fit so as to avoid that fate, but in doing so overexerts himself, causing him to suffer the heart attack that kills him. Here is a peculiar example from Barry Dainton's Time and Space: Many years from now, a transgalactic civilization has discovered time travel. A deep-thinking temporal engineer wonders what would happen if a time machine were sent back to the singularity from which the Predestination paradox big bang emerged. His calculations yield an interesting result: the singularity would be destabilized, producing an explosion resembling the big bang. Needless to say, a time machine was quickly sent on its way.[1] In all five examples, causality is turned on its head, as the flanking events are both causes and effects of each other, and this is where the paradox lies. In the third example, the paradox lies in the temporal causality loop. So, if Stewie had never traveled back in time, the universe would not exist. Since it would not have existed, it could not have created Stewie, so Stewie would not have existed. One example of a predestination paradox that is not simultaneously an ontological paradox is: In 1850, Bob's horse was spooked by something, and almost took Bob over a cliff, had it not been for a strange man stopping the horse. This strange man was later honored by having a statue of him erected. Two hundred years later, Bob goes back in time to sight-see, and sees someone's horse about to go over a cliff. He rushes to his aid and saves his life. In The Big Loop the Big Bang owes its causation to the temporal engineers. Interestingly enough, it seems the engineers could have chosen not to send the time machine back (after all, they knew what the result would be), thereby failing to cause the Big Bang. But the Big Bang failing to happen is obviously impossible because the universe does exist, so perhaps in the situation where the engineers decide not to send a time machine to the Big Bang's singularity, some other cause will turn out to have been responsible. In another example, on the show Mucha Lucha in the episode "Woulda Coulda Hasbeena", Senior Hasbeena goes back in time to stop a flash from blinding him in an important wrestling match, when the three main protagonists try to stop him due to dangerous possible outcomes he unleashes a disco ball move thereby blinding himself in the past causing the future he knows to that day. Another example is in "The Legend of Zelda: Ocarina of Time", when the player travels to the future and meets a man in a windmill, who tells him about a mean Ocarina kid who played a song that sped up his windmill and dried up the well. He then teaches Link the song, who plays it in the past, causing him to learn the song in the future. This also an example of a Bootstrap Paradox, as the song itself was never written, but taught back and forth between Link and the man in the windmill. In most examples of the predestination paradox, the person travels back in time and ends up fulfilling their role in an event that has already occurred. In a self-fulfilling prophecy, the person is fulfilling their role in an event that has yet to occur, and it is usually information that travels in time (for example, in the form of a prophecy) rather than a person. In either situation, the attempts to avert the course of past or future history both fail. 179 Examples from fiction Time travel Many fictional works have dealt with various circumstances that can logically arise from time travel, usually dealing with paradoxes. The predestination paradox is a common literary device in such fiction. • In Robert Heinlein's "—All You Zombies—", a young man (later revealed to be intersex) is taken back in time and tricked into impregnating his younger, female self (before he underwent a sex change); he then turns out to be the offspring of that union, with the paradoxical result that he is his own mother and father. As the story unfolds, all the major characters are revealed to be the same person, at different stages of her/his life. In another of his stories, "By His Bootstraps", the protagonist in a series of twists, interacts with future versions of himself. • The Man Who Folded Himself is a 1973 science fiction novel by David Gerrold that deals with time travel and the predestination paradox, much like Heinlein's. The protagonist, Daniel Eakins, inherits a time belt from his "uncle" that allows him to travel in time. This results in a series of time paradoxes, which are only resolved by the existence of multiple universes and multiple histories. Eakins, who repeatedly encounters alternate versions of Predestination paradox himself, finds himself in progressively more bizarre situations. The character spends much of his own contorted lifetime at an extended party with dozens of versions of himself at different ages, before understanding the true nature of the gathering, and his true identity. Much of the book deals with the psychological, physical, and personal challenges that manifest when time travel is possible for a single individual at the touch of a button. Eakins repeatedly meets himself; has sex with himself; and ultimately cohabitates with an opposite-sex version of himself. Eventually, that relationship ends up with a male child who he finally realizes is him, and he is now his own "uncle". • In the SpongeBob SquarePants episode SB-129m, Squidward, inspired by 'jellyfishing', teaches prehistoric SpongeBob and Patrick to catch a jelly in a net. This means that Squidward invented Jellyfishing. • In the video game Timesplitters: Future Perfect the main protagonist, Sergeant Cortez, often helps himself solve puzzles, and protects himself during hard situations. • In Flatterland, Vikki Line and the Space Hopper fall into a black hole, are rescued by future versions of themselves, and then go back in time to rescue themselves. • In the American Dad! episode "Fart-Break Hotel", Steve becomes drawn to a Patrick Nagel painting of a woman. A hotel concierge explains to Steve that the painting was made in 1981, meaning Steve would have to travel back in time to meet the woman. After successfully traveling back in time, Steve meets Nagel, who drugs his champagne, causing Steve to pass out. When he wakes up, he finds himself naked on a bed and sees the painting of the woman. However, Nagel explains that he painted Steve, meaning Steve was the woman in the painting he had become attracted to. • In the film 12 Monkeys, James Cole travels into the past to stop an attack attributed to the elusive "Army of the Twelve Monkeys", which leads indirectly to the formation of the group. The fatal shooting at the end of the movie is witnessed by his childhood version and leads to the nightmares that haunt him throughout his life. • In The Twilight Zone 2002-2003 revival, in the episode, Cradle of Darkness, Andrea (played by Katherine Heigl) goes back in time to assassinate Adolf Hitler while he is a baby. She kills the baby (whom she presumes to be actual Adolf Hitler, though the viewer might note it seems like a very normal baby, perhaps not very dark hair), but the nanny (discovering the death) replaces the baby with a street gypsy's baby (the mother being a very crazy looking woman who has black hair resembling the Hitler we know), and she presents this baby to the father as his own. The father proceeds to introduce this son to his guests as "Adolf", presumably the Adolf Hitler known to history in the first place. • In Bill and Ted's Bogus Journey the antagonist, unhappy with the future, sends evil robots back in time to kill Bill and Ted. When his robots are defeated, he goes back himself and takes control of the world's satellites so the whole world can see them defeated. Instead, the whole world watches them play their music, cementing their place in history. In Bill and Ted's Excellent Adventure we see that the band could not have formed if not for Rufus appearing from the future to help them with their history project. • The episode "Roswell That Ends Well" of the animated television series Futurama puts a more humorous spin on the paradox. In the episode, the main characters go back in time to 1947 in Roswell, New Mexico, sparking the Roswell UFO Incident. Meanwhile, Fry, told that the death of his grandfather Enos would nullify his own existence, becomes obsessed with protecting the man. He shuts Enos in a deserted house in the desert in order to protect him, failing to realize that the house is in a nuclear testing site. The resulting atomic test kills Enos, but Fry does not disappear. Fry later comforts Enos' fiancée, no longer believing her to be his future grandmother. He has sex with her, only to realize afterward that she is his grandmother and therefore he is his own grandfather. • The video game Prince of Persia: Warrior Within, the Prince is chased by the Dahaka, whose purpose is to preserve the time-line by erasing the Prince from it. Unable to fight the monster, the Prince travels to the Island of Time to kill the Empress of Time, who created the time-manipulating sands from the first game. He hopes to prevent the sands from being created, since it was the sands that put him in his current predicament. However, the 180 Predestination paradox Prince realizes too late that killing the Empress is what creates the sands, and hence he becomes the architect of his own fate. A secondary paradox is the Sand Wraith, who seems to stalk the Prince throughout the first half of the game, even trying to kill him at one point. The wraith is killed by the Dahaka shortly before the Prince kills the Empress. After killing the Empress, the Prince realizes that he can change his fate by using the Mask of the Wraith, which transforms him into the Sand Wraith and sends him back in time a short distance. He learns that the wraith (who he now understands to be his future self) was trying to protect him, rather than attack him. Upon reaching the point at which the Dahaka is supposed to kill him, the Prince uses his knowledge of the encounter to have his younger self die instead, ending the mask's power and creating a grandfather paradox as well. • The film Donnie Darko incorporates an example of fictional predestination paradox. Donnie avoids death by a jet engine that appears out of nowhere, only to later, because of information he has learned since, send the engine back in time himself so that he may die by it. He thereby negates all activity that occurred between the appearance of the engine and him sending it back, including his learning of the reason that he must die. This is explained through use of a tangent universe and a physical and temporal theory. • In Harry Potter and The Prisoner of Azkaban, Harry is saved from the Dementors by a stag patronus. At that time, he thought it was his dead father's spirit of some sort watching over him. After traveling back in time, he realizes he was the one who produced the patronus- after watching himself being attacked and seeing that no one had produced the stag patronus- he himself casts the spell, producing the stag patronus he had seen earlier. [2] Similarly, in the film, Harry and his friends are alerted to the presence of the Minister for Magic when a rock hits Harry in the head; but after traveling back in time, Hermione recognizes the same rock and throws it at Harry herself. • In the Legacy of Kain video game series, more specifically Soul Reaver, Soul Reaver 2, and Defiance, the predestination is evident in the Soul Reaver as well as Raziel, whose soul is contained inside. Through the storyline of the 3 games it is learned that Raziel's soul must become part of the Reaver, despite the fact that it has been a part of the weapon the whole time. Defiance ends in Raziel being stabbed by the Reaver, allowing his soul to be transferred to it, however because of the purification his soul had gone through earlier the cycle is broken rather than beginning again. • In the Terminator films, Skynet, a computer program that controls nearly the whole world in the future, sends a machine to the past in order to kill John Connor, the future leader of the human resistance, at different points of his life: once before he is conceived (by killing his mother, Sarah Connor), again when he is 10 years old (in Terminator 2: Judgment Day) and a final time a few days before Judgment Day happens (Terminator 3: Rise of the Machines). In the second film Dr. Dyson (Joe Morton), the lead scientist for the Skynet project, explains that the surviving arm and CPU chip of the original Terminator was analyzed and found that the technology was so advanced, they (humans) would have never invented the technology themselves and was used to create Skynet in the first place. However, all the components and research were destroyed in an attempt to prevent Skynet, but in (Terminator 3: Rise of the Machines) Skynet is built anyway without any information or components from the future, implying that it was inevitable. In a not yet made movie, the humans somehow successfully invaded the complex in which the time machine is placed, manage to send someone else to the past so that the Connors can be protected, which is what starts the series. In The Terminator, the machines send the T-800 and the humans send Kyle Reese: Kyle will be John Connor's father (that is, if Skynet had not have happened, Kyle Reese would have no reason to go back in time to protect Sarah, and thus John Connor would not have been born). • In the episode "He's Our You" of the television series Lost, several characters travel back into the 1970s. One of them, Sayid Jarrah, encounters the younger version of Benjamin Linus, the leader of the Others, and a man who has committed various acts such as betraying the Dharma Initiative and causing their complete genocide by the Others, the manipulation and deceit towards various people on the show and caused much strife to Sayid personally including recruiting him to become an assassin during his wife's funeral. When Sayid meets Ben's younger version he believes that it is his destiny to kill him and prevent all of the bad things he does from ever 181 Predestination paradox happening. However when he does this by shooting him, Ben is taken to the Others where they state that they could heal him in a mysterious temple but, "his innocence would be lost" and he would "always be one of them." By trying to prevent Ben from doing the things he did, Sayid actually caused him to become the evil manipulator that he is and caused all of the evil acts he committed. • In Artemis Fowl: The Time Paradox, Artemis's mother contracts the deadly magical disease, Spelltropy. To save his mother, he travels into the past to save the Silky Sifaka lemur, which he kills at age 10 by handing to the Extinctionists. In the past, Artemis the elder meets Opal Koboi, who follows Artemis into the future. In the present, Opal gives Artemis's mother Spelltropy-like symptoms, which causes Artemis to time-travel in the first place. • In the 2008 episode of Doctor Who: "The Doctor's Daughter", the TARDIS takes the Doctor, Donna, and Martha to find the source of the Doctor's Daughter's signal. However, the TARDIS arrives early, which leads the Doctor to the accidental creation of his daughter, thus activating the signal. In the 2010 episode "The Big Bang", the Doctor is released from the Pandorica by Rory Williams, using the sonic screwdriver supplied by the Doctor after his release. In the 2011 episode "Let's Kill Hitler", Mels, a friend who Amy and Rory name their daughter Melody after, turns out to be a pre-regeneration version of River Song, who in the prior episode, "A Good Man Goes To War", was established to be an alias used by their daughter as an adult, an alias she adopts shortly after regenerating and hearing the Doctor, Amy, and Rory refer to her as such, having known her only by her alias until recently. • In Red vs Blue, when the character Church is thrown back in time in Episode 50, he tries to prevent certain things from happening, in the process leading to everything becoming the way it was: kicking dirt on a switch hoping it to be replaced, instead it was kept and later got stuck; giving his captain painkillers to prevent a heart attack, but killing him because the captain is allergic to aspirin; trying to make the tank not kill him by disabling the friendly-fire protocol, which later proves his death; telling the tank and robot that they should not leave and build a robot army, thereby giving them the idea to do it; trying to shoot O'Malley with the rocket launcher only to shoot Tucker because of the launcher's highly defective targeting system and his inability to aim. • In the PlayStation 2 video game Shadow Hearts: Covenant Karin Koenig, one of the main protagonists, falls in love with Yuri Hyuga. She is gently rejected because Yuri still has feelings for the exorcist Alice Elliot, who died in the previous game. Unrequited love does not stop her from fighting alongside Yuri, though, until at the end of the game when she is flung into the past and meets Yuri's father. There you finally see a picture she is given earlier in the game by Yuri's aunt that shows his father, mother and Yuri as a child. It's obvious the woman in the picture is Karin, thus making her Yuri's mother. She ends up being the only one staying in the past because she knows she is to become Yuri's mother and assumes the alias "Anne". She also takes back a cross Yuri gave to her, which is the same cross that belongs to his mother. The cross becomes an Ontological paradox. • The Black Sabbath song "Iron Man" tells the story of a man who time travels into the future of the world, and sees the apocalypse. In the process of returning to the present, he is turned into steel by a magnetic field. He is rendered mute, unable verbally to warn people of his time of the impending destruction. His attempts to communicate are ignored and mocked. This causes Iron Man to become angry, and have his revenge on mankind, causing the destruction seen in his vision. • In The Penguins of Madagascar, the episode "It's About Time" sees Kowalski constructing a time machine called the "Chronotron". A future Kowalski tells Private to convince his present self not to complete it. After he decides to destroy the Chronotron, another Kowalski from the future tells Skipper to convince him to save the Chronotron. When the present Kowalski spots his future selves, a vortex appears. The present Kowalski activates the Chronotron and goes back in time to talk to Private. When Private points out that if Kowalski had not invented the Chronotron then he would not have gone back in the first place to tell himself not to make it, the future Kowalski then goes back in time to talk to Skipper. Rico then throws the Chronotron into the vortex, sealing it. While a baffled Kowalski tries rationalizing that such a simple thing defies all laws of the universe, Skipper 182 Predestination paradox simply states that Rico is a maverick who makes his own rules, and tells Kowalski to invent something that will not destroy the world. • In the Red Dwarf episode "Timeslides", Dave Lister travels back in time using a mutated photograph of a pub in Liverpool where his band once played a gig to give his teenage self the idea of inventing the Tension Sheet (a stress relief tool invented by Fred 'Thickie' Holden, a former classmate of Arnold Rimmer, which earned him millions). This causes him to become rich and famous in the past and never get stuck on Red Dwarf. Arnold Rimmer, in an attempt to experience fame and fortune for himself, travels back even further in time to his school days, to give his own younger self the idea of inventing the Tension Sheet instead. Unfortunately for Rimmer, while he is giving young Rimmer the idea, the conversation is overheard by Thickie Holden (who sleeps in the next bed) and he is able to patent the idea before young Rimmer can, therefore putting everything back to how it was at the start of the episode. • In the PC game Fallout 2, there is a side quest where the protagonist enters a time travel device and travels back in time to Vault 13, prior to the events of Fallout 1. During this time travel period, the hero sabotages the vault's water chip, thus starting the series of events of the first game and ultimately the birth of our hero. After sabotaging the water chip the game informs us that the hero "feels better about his future". • In the British Television show Misfits, The group repeatedly encounters a man they call Superhoodie, who seems to know a lot about them. He's almost always seen whenever they have to deal with a dangerous situation and helps them out of it. The character Alisha Bailey eventually discovers he's really a future version of their friend Simon Bellamy and begins a relationship with him. He's shot and killed while trying to protect Alisha from a man who believes he's in a violent video game. He requests she doesn't tell his past self who he is and she agrees. Alisha, because of future Simon, begins respecting present day Simon and the two become closer. Alisha is killed by Rachel, a woman who the Misfits killed, but was returned in ghost form by a medium named Jonas to exact revenge on them. As Alisha dies in Simon's arms, she tells him Superhoodie's true identity. Later, Simon acquires a one-way time travel ability from a power dealer named Seth, traveling back and becoming Superhoodie. Rudy Wade, a member of the group, mentions that the paradox will continue and they'll probably just keep going in circles. • In The Transformers episode "The Key to Vector Sigma", Optimus Prime assists in the creation of the Aerialbots who, in the later episode "War Dawn", are sent back in time and become instrumental in the creation of Optimus Prime, thus ensuring their own creation in the future. • In Sam & Max Season Two there exist 2 examples of this paradox: • In "Ice Station Santa", Sam and Max must save their future selves from being killed. In "What's New, Beelzebub?" they are saved by their past selves; this creates a never ending cycle of "save and later be saved; the savers are later saved". • In "Chariots of the Dogs", Sam and Max are given an egg by their future selves from "What's New, Beelzebub?" who they also give a remote control too. Later, in What's new Beelzebub S&M give their past selves the egg and get the remote from them which, once again, creates a never ending cycle. However it is still unknown how the egg got into the hands of the Future S&M's in the first place. • In the Chinese novel Bu Bu Jing Xin, centering the rivalry of Kangxi Emperor's sons for the throne during the 18th century Qing Dynasty, which will results the monarch's fourth son Yinzhen as Yongzheng Emperor. Its main character, Ma'ertai Ruoxi (Zhang Xiao), a time traveler from the 21st century, aware the princes' feud would leads to a tragic outcome. However, she is romantically entangled with the three of them, unawares that her relationship with them would inadvertently leading history to be unfold as written in the future instead of changing it. • In the Rampage of Haruhi Suzumiya, the fifth in a series of light novels by Nagaru Tanigawa, is about Haruhi, a girl who can unconsciously change the universe to her tastes (like a deity) and wishes that the summer holidays would never end. As a result, the summer loops over 15,527 times before her friend Kyon realises what is happening. He tries to break the time loop many times by trying to stop her leaving a restaurant to go home at the 183 Predestination paradox end of the day. He eventually succeeds by convincing Haruhi to come to a study session, as neither of them have done their homework yet. Although this was only a 30 page chapter in the book, the much-anticipated second season aired what was essentially the same episode eight times, with minor differences in camera angles, the characters' clothes etc. This caused a lot of tension for fans and caused many of them to drop the series. • In the 20th episode of the second season of My Little Pony: Friendship Is Magic, the main character Twilight Sparkle receives a warning from her future self, and drives herself crazy in an attempt to avoid an unspecified upcoming catastrophic disaster, which the future Twilight couldn't explain exactly. Later it comes out that there is no such disaster, and that her future self just tried to tell her not to worry too much about the future, which accidentally caused her worrying about the future. 184 Prophecies Prior to the use of time travel as a plot device, the self-fulfilling prophecy variant was more common. In Revenge of the Sith, Anakin Skywalker has visions of his wife dying in childbirth. In his attempt to gain enough power to save her, he falls to the dark side of the force and becomes Darth Vader. His wife is heartbroken upon learning this and argues with him. In his anger, he uses his power to hurt her, which eventually leads her to die in childbirth. Shakespeare's Macbeth is a classic example of this. The three Witches give Macbeth a prophecy that he will eventually become king, but the offspring of his best friend will rule after him. Macbeth kills his king and his friend Banquo. In addition to these prophecies, other prophecies foretelling his downfall are given, such as that he will not be attacked until a forest moves to his castle, and that no man ever born of a woman can kill him. In the end, fate is what drives the House of Macbeth mad and ultimately kills them, as Macbeth is killed by a man who was never 'born' as the man was torn from his mother's womb by caesarean section. In the movie Minority Report, murders are prevented through the efforts of three psychic mutants who can see crimes before they are committed. When police chief John Anderton is implicated in a murder-to-be, he sets out on a crusade to figure out why he would kill a man he has yet to meet. Many of the signposts on his journey to meet fate were predicted exactly as they occur, and his search leads him inexorably to the scene of the crime, where he cannot stop himself from killing the other man. In the end, the prediction itself is what had set the chain of events in motion. In Lost, Desmond Hume's future flashes regarding Charlie's deaths eventually lead to his death. Desmond has a vision in which Charlie pushes a button below a flashing light which allows the other castaways to be rescued just before he drowns. However when the event occurs, events happen slightly differently than in Desmond's vision and it is suggested that Charlie may have been able to save himself without jeopardizing the hopes of rescue, if he had not believed his death was crucial in the rescue of the other castaways. Yet there are examples of prophecies that happen slowly, if at all. In Red Dwarf: "Stasis Leak", when Lister travels back in time to meet with Kochanski to marry her, he finds out from his future self from 5 years later that he is going to pass through a wormhole and end up in a parallel universe version of Earth in 1985 but after 8 whole series, this has never happened (although similar events happen in "Backwards"). In the Harry Potter Universe by J. K. Rowling a prophecy by Sybill Trelawney is overheard by Severus Snape about the birth of a wizard "with the power to vanquish" Voldemort. This prophecy was only partially overheard by Severus Snape, who relayed what he heard to Voldemort. To stop the prophecy from coming true, Voldemort attempted to kill Harry while he was an infant, but his curse backfired on him, separating his soul from his body for 13 years, and transferring some of his powers, as well as a part of his severed soul, to Harry. Dumbledore tells Harry several times that the prophecy is only true because the Dark Lord believes it. Harry is free to turn his back on it, but the fact that Voldemort will never turn his back on it, and therefore never rest until he has killed Harry, makes it inevitable that Harry will have to kill Voldemort, or vice versa. Moreover Harry wished to finish Voldemort only because Voldemort killed his parents following the prophecy. Predestination paradox 185 References [1] Dainton, Barry (1958). Time and Space. Montreal, California: McGill-Queen's University Press. p. 126. ISBN 0-7735-2306-5 [2] Silberstein, Michael (2004). "Space, Time, and Magic". In Baggett, David and Shawn E. Klein. Harry Potter and Philosophy. United States: Open Court Publishing. p. 198. • Gerrold, David (1973). The Man Who Folded Himself. Random House. ISBN 1-932100-04-0. List of time travel science fiction Time travel is a common and important element of science fiction, depicted in a variety of media. Time travel in novels and short stories Time travel is a recurrent theme in science fiction literature. There are thousands of books that incorporate time travel. Below are examples of texts that are repeatedly recognized as works of science fiction (as the genre has been defined in this article) that integrate time travel. Date 1733 Title Memoirs of the Twentieth Century Missing One's Coach: An Anachronism Author Description Samuel Madden A guardian angel travels to 1728 with letters from 1997 and '98 1838 Anonymous Dublin University Magazine Traveler picked up by a stagecoach but is suddenly transported back over a thousand years. 1843 A Christmas Carol Charles Dickens Ghosts accompanies Scrooge into the past to show his life, then the future to show the consequences of his heartlessness if he does not change his ways. Pierre Boitard Magic of a “lame demon” allows main character to interact with prehistoric life. A clock that has the power to take people back in time. 1861 Paris Before Men 1881 The Clock That Went Backward Edward Page Mitchell Enrique Gaspar y Rimbau Edward Bellamy William Morris H.G. Wells 1887 El Anacronopete First to introduce a time machine, originally written as a zarzuela in 1881, released as a novel in 1887. Julian West towards the end of the 19th century, falls into a deep, hypnosis-induced sleep and wakes up 113 years later. Describes a time travel encounter between the medieval and modern worlds. Inventor takes another with him in a time machine, before deciding to leave to a time where he will fit in more. 19th century citizen goes to King Arthur's time (528 AD). 1887 Looking Backward: 2000-1887 1888 1888 A Dream of John Ball The Chronic Argonauts 1889 A Connecticut Yankee in King Arthur's Court Tourmalin's Time Cheques Mark Twain 1891 Thomas A. Gutherie H.G. Wells Time travel and the paradoxes that can result from it. 1895 The Time Machine Inventor creates a time machine and travels to the year 802,701 A.D., where he finds humanity have evolved into two races, Morlocks and Eloi. Enoch is transported 100 years into the future (1997) to see if he became a great writer or not - a Faustian-like pact with the Devil is involved. Anthony Rogers is transported to the year 2419 by a strange cave gas. Later became the comic strip Buck Rogers. 1919 Enoch Soames Max Beerbohm 1928/ 1929 Armageddon 2419 A.D. Philip Francis Nowlan List of time travel science fiction 186 T. S. Eliot Begins with "Time present and time past// Are both perhaps present in time future..." Child goes back into Derbyshire of the Babbington Plot and Mary Queen Of Scots. Circular paradox-character is brought to the future where he later operates a time machine to bring himself to the future Justice Society of America use a time ray to travel 500 yrs in to the Future and get an effective bombing defence to protect America. C. S. Lewis C.L. Moore Merlin travels through time to dispel a N.I.C.E. dystopia in post war England. Time travellers from the future experience vintage seasons in the past. Villain Per Degaton murders a scientist who has invented a time machine and tries to use it to change history, causing modern technology from the Present, meaning he can then conquer America with technology protected from thee effects. Ray Bradbury Changes in the past affect the future; part of the genealogy of the term Butterfly effect A time traveller from an alternate reality appears at the Battle of Gettysburg and alters his own future into ours. An experiment involving the time travel of a small brass cube results in disaster.[1] Use time machines to transfer goods between centuries Historian returns to mid-20th century to study artist whose works he finds himself having to create, so the past is a product of the future's interest in the past. Series of 11 novels related to the Time Patrol, an organization which protects the past. Man learns how to travel through time Time travellers from the future disrupt life in a small town life by treating it as a quaint place for sightseeing. A novel in the Welsh Language where the narrator travels to Wales on two occasions in the year 2033 and encounters contrasting future scenarios each time. After thirty years trapped in suspended animation, a man uses a time machine to go back and exact revenge on his friend and fiance for stealing his business. Tale of Armageddon and the devil A soldier comes back from the future to warn against the path toward global conflict. Everett Barthold travels through time to find an ancestor look-a-like that can be used to defraud an insurance company. Comedy in which a professor travels back in time to kill someone by killing their grandparent, but the results confound him. Explores many time travel scenarios in a short story format. Circular paradox-the hero is both his own mother and his own father, in addition he manipulates his younger self using a time machine to make his own birth happen. Boy Scouts find an abandoned time machine and visit the year 4000 AD. (First of a 23-story Time Machine series appearing 1959-1989 in Boys' Life.) 1936 Burnt Norton 1939 A Traveller in Time Alison Uttley 1941 By His Bootstraps Robert A. Heinlein 1942 All-Star Comics #10 1945 1946 1947 That Hideous Strength Vintage Season All-Star Comics #35 1952 A Sound of Thunder 1953 Bring the Jubilee Ward Moore 1954 Experiment Fredric Brown 1955 1955 The End of Eternity The Discovery of Morniel Mathaway Isaac Asimov William Tenn 19551995 1956 1956 Time Patrol, plus 10 others Poul Anderson Extempore Pawley's Peepholes Damon Knight John Wyndham 1957 Wythnos yng Nghymru Fydd (A Islwyn Ffowc Week in the Wales of the Future) Elis 1957 The Door Into Summer Robert A. Heinlein Damon Knight Harlan Ellison 1957 1957 The Last Word Soldier From Tomorrow 1957 Double Indemnity Robert Sheckley Alfred Bester 1958 The Men Who Murdered Mohammed 1959 —All You Zombies— Robert A. Heinlein 1959 The Day We Explored the Future Donald Keith List of time travel science fiction 187 Alan Garner Colin and Susan go back in time in the caves of Alderley Edge in Cheshire crystal bracelet, magic great wolf included. A couple of teenagers use their professor's time machine to study the history of the US. 1960 The Weirdstone of Brisingamen 1961 Danny Dunn, Time Traveler Raymond Abrashkin and Jay Williams Stan Lee and Jack Kirby 1962 Fantastic Four vol 1 #19 The Fantastic Four travel to Ancient Egypt, and meet Pharaoh Rama-Tut, who is really another time traveller, from the 31st century. First appearance of Marvel Comics time-travelling villain Kang. George Bletzo mistakenly call his own phone number and talks to his own person in a few months into the future. Predestination in play. More than 530 original novels and novelisations based on the popular TV show. Ensign Joe Rate, "captain of a wooden ship in a predominantly atomic navy," is transported, with his ship and crew, first back to the time of the Vikings, then to the time of the Romans. Teenage girl finds ancient mirror buried in sand, looks into it, is transported back in time to the Roman empire- where she is mistaken for a runaway slave. A man inadvertently destroys the world in order to travel back eighteen minutes in time. A time machine is used by an oppressive government for deporting political prisoners a billion years in the past, to the Pre-Cambrian era. A man is randomly traveling through time in his life jumping from one event to another in no particular order. Time travel as guided tours to past historical events. 1963 The Other End of the Line Walter Tevis 1964–present Doctor Who various authors 1965 The Ship that Sailed the Time Stream G. C. Edmondson 1966 The Green Bronze Mirror Lynne Ellison 1966 The Man From When Dannie Plachta 1968 Hawksbill Station Robert Silverberg Kurt Vonnegut 1969 Slaughterhouse-Five 1969 Up the Line Robert Silverberg Daphne du Maurier Michael Moorcock D.G. Compton Jack Finney Wilson Tucker 1969 The House on the Strand Drug-induced trip back to 14th century Cornish Village 1969 Behold the Man A man travels in a time machine to 28 AD, hoping to meet the historical Jesus. 1970 1970 1970 Chronocules Time and Again The Year of the Quiet Sun A millionaire establishes a research village to experiment with time travel Uses hypnosis to travel through time The government uses a forward-traveling time machine to survey the future and adjust its policies accordingly. Four scientists/anthropologists travel from 2070 A.D. to 12,000 B.C. 1972 Time's Last Gift Philip Jose Farmer Robert A. Heinlein David Gerrold 1973 Time Enough for Love Lazarus Long travels in time to 1916 and falls in love with his own mother. 1973 The Man Who Folded Himself Main character receives a belt that allows him to travel through time. Complications ensue. A young man sees an old photograph of a woman, and through hypnosis travels back in time from 1980 to 1912 to meet her. Basis of the 1980 film "Somewhere in Time" Marc Despard graduates from an involuntary time traveler to a deliberate time travel, picking up many fellow travelers along the way. A half finished Tipler cylinder is discovered by a future human explorer. When the leader decides to complete it, his civilization is destroyed by a nova. 1975 Bid Time Return Richard Matheson 1977 Time Storm Gordon R. Dickson Larry Niven 1977 Rotating Cylinders and the Possibility of Global Causality Violation List of time travel science fiction 188 Ian D. Watson "you must travel through time by an equal amount of accumulate hindward potential" H.G. Wells builds a time machine, which is stolen by Jack the Ripper so he can escape the authorities and continue his killing spree What happened when H.G. Wells' time machine returned from the future. A man uses time travel to experience the sensation of death. 1978 The Very Slow Time Machine 1979 Time After Time Karl Alexander 1979 1979 Morlock Night Closing the Timelid K.W. Jeter Orson Scott Card Gregory Benford 1980 Timescape Use of tachyons to warn scientists of the past about an upcoming disaster 1980 Thrice Upon a Time James P. Hogan Messages are sent back through time which deletes the timeline in which it exists Harry Harrison Time machine misuse. U.S. Government aids the Confederacy with submachine guns Dana, an African American woman, is inexplicably transported from 1976 Los Angeles to early 19th century Maryland. She meets her ancestors: Rufus, a white slave holder, and Alice, an African-American woman who was born free but forced into slavery later in life. 1980 A Rebel in Time 1980 Kindred Octavia Butler 1980 The Restaurant at the End of the Universe Douglas Adams Milliway's is "located" in the very last future time of the Universe and requires time travels to reach it and then return back to your own time. Due to time travel effects you can now deposit a penny in a bank account to get lots of money to pay for your bill, and you can book a table after you return home from the restaurant. David J. Lake H.G. Wells' time traveller confronts the Morlocks again, this time equipped with a camera and revolver. Time travellers from the late 21st/early 22nd century go through a one-way time portal to the Earth's Pliocene period, already controlled by humanoid extraterrestrials. 1980 The Man Who Loved Morlocks 1981 The Many-Colored Land, first book of the Saga of the Pliocene Exile series Life, the Universe and Everything Julian May 1982 Douglas Adams Time travel paradoxes are described in a funny way such as moving back and forward through the history and so affecting it, as in the case of an ancient poet Lallafa. John Varley In the far distant future, a time-travel team is preparing to snatch the passengers of a plane collision, leaving prefabricated smoking bodies behind for the rescue teams to find. Basis of the 1989 film. In 1983, a millionaire discovers time-travel gates, and organizes a trip to the past to attend a lecture by S. T. Coleridge in 1810. A professor hired by the millionaire is trapped in 19th century London. Spock is aboard a Klingon ship when it travels back in time to Seattle in 1867. He discovers a Klingon plot to destroy the Federation by assassinating an ancestor of his mother, a prominent local businessman who will later be instrumental in repelling an invasion by the alien Karsids. In an effort to prevent the Vietnam War, a man travels back in time to prevent the assassination of John F. Kennedy. A girl, Vivian Smith, is kidnapped while being evacuated from London during World War II, and is caught up in a struggle to preserve history. A man in 1988 suffers a heart attack and finds himself back in his life in 1963. A time traveler from Nazi Germany interferes with the life of a young woman in the future. A great warrior, the Shrike, is sent from the future for an unknown reason. Main characters will travel through time in a very complex timeline. 1983 Millennium 1983 The Anubis Gates Tim Powers 1985 Star Trek: Ishmael Barbara Hambly 1986 Running Against Time Stanley Shapiro 1987 A Tale of Time City Diana Wynne Jones Ken Grimwood Dean Koontz 1988 1988 Replay Lightning 1989 Hyperion Dan Simmons List of time travel science fiction 189 Harry Turtledove Jack Finney Connie Willis During American Civil War, South African white supremacists give the Confederacy AK-47s Use of hypnosis to travel through time Travel through time from 2048 to 14th century. Time travel limited by the Laws of Physics. 1992 The Guns of the South 1992 1992 From Time to Time Doomsday Book 1992 Outlander Diana Gabaldon Travel through time from 1940s to 1740s. Woman time travels through standing stones in Scotland. Diana Gabaldon Time-travel romance, the second of a trilogy (after Outlander, 1991). 1960s to 18th century. Diana Gabaldon Time-travel romance, the third of the Outlander series. Time travel from the 20th century to 18th century. Leo Frankowski 20th Century Polish Engineer is transported back to 13th century Poland 10 years before the Mongol invasion. Greg Egan After the invention of a method for sending messages back in time, history of the future becomes common knowledge, and every person knows their own fate. Authorised sequel to H.G. Wells' The Time Machine. 1992 Dragonfly in Amber 1993 Voyager 1993 The Cross Time Engineer 1995 The Hundred-Light-Year-Diary 1995 1996 The Time Ships Drums of Autumn Stephen Baxter Diana Gabaldon Time-travel romance, the fourth of the Outlander series. Time travel from the 20th century to 18th century. Kurt Vonnegut People in 2001 are transported back to 1991 to relive their lives 1996 1996 Timequake The Dechronization of Sam Magruder Pastwatch: The Redemption of Christopher Columbus Animorphs George Gaylord A scientist working in the year 2162 is thrown back in time 80 million years to Simpson the Jurassic period. Orson Scott Card Researchers travel back in time to see Christopher Columbus's arrival in the new world in order to know the historical truth. 1996 1996 K. A. Applegate In book 11, the Animorphs and Visser 3 are sent back a few hours to the Amazon by a Saurio Rip, with the plot used again in Altermorph 1. The same concept is uses to sent the animorphs back to time to 65 million B.C. in Megamorph 2. In the Andalite Chronicles, Elfangor discovers a technology known as the Time Matrix, seen again in Megamorph 3. Stephen Fry Connie Willis Gary Paulsen Two men in the present attempt to prevent the birth of Adolf Hitler. Time traveler from 2048 travels back to the 19th century A boy gets transported to a weird world by a blue light, only to discover that it is the dark future of planet Earth A modern day boy switches places with a Shakespearean actor who needs to be cured by modern medicine so as to return to his own age and help Shakespeare to greater success on the stage. People from three atemporal time tribes must unite to save the crystallization and fracturing of all of history. Historians travel to and become stuck in the Middle Ages. 1997 1997 1998 Making History To Say Nothing of the Dog The Transall Saga 1999 King of Shadows Susan Cooper 1999 All of an Instant Richard Garfinkle Michael Crichton 1999 Timeline 1999 Harry Potter and the Prisoner of J. K. Rowling Azkaban Hogwarts student Hermione Granger acquires a Time-Turner, a magical necklace that allows her to travel back in time on a daily basis in order to take an unusually large courseload. The device is later used to manipulate the events of a single night to aid a wrongly accused convict's escape. 2001 The Fiery Cross Diana Gabaldon Time-travel romance, the fifth of the Outlander series. Time travel from the 20th century to 18th century. Robert Charles Wilson Monuments from the future appear in the early 21st century, precipitating a global political collapse. 2001 The Chronoliths List of time travel science fiction 190 Terry Pratchett Stephen King Unfreezing and freezing of time using a small mechanism An airplane accidentally flies through a rip in space/time and appears in the "used time" of yesterday Shorts stories of lateral time movement and alternate universes ForeWord Magazine Silver Medal Winner for Sci-Fi Book of The Year, 2002 - Sequels: Nexus Point, Touchstone, Anvil of Fate - The first ever experiment in Time travel sets off a "Time War" where opposing sides struggle to alter key events on the Meridians of Time. Five book series: Meridian, Nexus Point, Touchstone, Anvil of Fate, Golem 7. Character interacts with a younger version of himself Time travel with the twin perspectives of a man who travels back in time for relationship stability A huge storm traps a girl who is accused of being a thief and takes her into the future Takes place on Mars. A man has a virus that puts him to sleep every 15 years and he wakes 10 younger. West-Virginian town is taken back to the Thirty Years War in Germany and gives them insight to the future Two characters, Mikuru Asahina and Fujiwara, are time travelers from the future and many parts of the storyline involve time traveling. Man with a rare genetic disorder unpredictably travels in time, living his life out of sequence A naval task-force from 2019 is accidentally sent back to the battle of Midway. Describes the First Crusade and the beginning of the Knights Templar in the future Loops in a man's life told through a narrative that goes from future to present A human, a dragon and an orc travel back in time to help save Azeroth from the Burning Legion. 2001 1990 Thief of Time Four Past Midnight: "The Langoliers" Paratime Meridian 2001 2002 H. Beam Piper John Schettler 2002 2002 Night Watch Counting Up, Counting Down Terry Pratchett Harry Turtledove Malorie Blackman John Barnes 2002 Thief! 2002 Kaleidoscope Century 2002 1633 Eric Flint 2003-ongoing Haruhi Suzumiya Nagaru Tanigawa Audrey Niffenegger John Birmingham Romain Sardou 2003 The Time Traveler's Wife 2004 Axis of Time 2004 The Spark of God (orig. title: L'Éclat de Dieu) Pen Pal Warcraft: War of the Ancients Trilogy A Breath of Snow and Ashes 2004 2004–2005 Lou Antonelli Richard A. Knaak 2005 Diana Gabaldon Time-travel romance, the sixth of the Outlander series. Time travel from the 20th century to 18th century. S.M. Stirling Nantucket is transported 3000 years back in time because of a space disturbance Multibillionaire clones a mammoth and sends it back in time. A Time Rover from 2057 returns to 1888 London in search of a missing time tourist only to be caught in the Jack the Ripper murders and the history-changing plots of a mysterious group of shape-shifters called Transitives. Time travelers from 2042 to prevent Socrates from consuming hemlock Fifth book in the Artemis Fowl series. Artemis must pair up with his old comrade Captain Holly Short, to track down the missing demon, before the spell that holds a demon island Hybras in limbo dissolves completely and the lost demon colony returns violently to Earth. Artemis also ends up saving Holly by manipulating time. Characters participate in "Party Crashing" which can, under certain conditions, cause time travel. A research assistant stumbles across a forward-traveling time machine. 2005 Island in the Sea of Time 2005 2006 Mammoth Sojourn John Varley Jana G. Oliver 2006 2006 The Plot to Save Socrates Artemis Fowl: The Lost Colony Paul Levinson Eoin Colfer 2007 Rant: An Oral Biography of Buster Casey The Accidental Time Machine Chuck Palahniuk Joe Haldeman 2007 List of time travel science fiction 191 Spider Robinson 3 books (Mindkiller-1982, Time Pressure-1988, LifeHouse-1997) chronicling the story of visitors from earth's future visiting the past to essentially harvest souls. A Time Rover from 2057 is sent to 1888 London to find Harter Defoe, the first time traveler who slowly going insane. Abandoned in a Victorian insane asylum, memories erased, a Time Rover from 2057 must find a way to thwart a plot from the future that will remake British history. Sixth book in the Artemis Fowl series. After Angeline Fowl contracts spelltropy, Artemis travels back in time eight years to when he was ten years old to find a lemur that can help cure his mother. The plot twist in the end of the book creates a circular timeline that started the series. Thirteen year olds Jonah and Chip find out that they are missing children from time and go on a journey along with Jonah's sister Katherine to uncover many secrets. In the near future, an authoritarian regime discovers a time-travel device invented before the technology existed to make it work. The reconnaissance team from that future kidnaps Max Burkowski, the inventor’s son, and Brother Frank Bootsma from the Vatican Observatory, who says that he has been abducted for a related reason. While they struggle to find a way back home, the story unfolds and reunfolds as things that happened in the past change, and things that happened in the future change back again. Time Hack (also available as The Day Time was Hacked) has a fresh outlook on what it means to visit the past, and perfectly blends Cold War paranoia with new-age digital terrorism. Mackenbach weaves at least five different narratives masterfully into a well-balanced story. Time Hack is the film edition of "The Day Time Was Hacked". 2007 The Lifehouse Trilogy 2007 Virtual Evil Jana G. Oliver 2008 Madman's Dance Jana G. Oliver 2008 Artemis Fowl: The Time Paradox Eoin Colfer 2008 Found Margaret Peterson Haddix [2] Carel Mackenbach 2009 The Day Time Was Hacked 2009 Time Hack [3] Carel Mackenbach 2009 An Echo in the Bone Diana Gabaldon Time-travel romance, the seventh of the Outlander series. Time travel from the 20th century to 18th century. Margaret Peterson Haddix Duane Swierczynski Margaret Peterson Haddix Connie Willis Jonah, Katherine, Chip and Alex are sent back to 1483 to learn that Chip is actually King Edward V and Alex is his brother Richard, Duke of York. 2009 Sent 2010 Expiration Date Hardboiled pulp tale of an ex-journalist who discovers pills in his grandfather's medicine cabinet that transport him back in time to the 1970s. Jonah and Katherine go on yet another mission to return a missing kid named Andrea(really Virginia Dare) to her time in the Roanoke Colony. 2010 Sabotaged 2010 Blackout and All Clear Time travelers from 2048 go to the London Blitz during WWII to observe and end up being part of it. Novel published in two parts. The sequel to 'The Fourth World' has the kids from Area 51 caught up in an accident that sends them a million years into the future. In search of his father, a time machine mechanic adventures through time accompanied by TAMMY and his ontologically valid dog, Ed, all while documenting his travels in a manual for future travellers. Various methods of time travel are explored in these poems and short stories. Thrall, an orc shaman, travels through time and alternative reality in order to find his inner strength. Follows the story of two teenagers who are transported back in time to medieval Wales. 2010 The Million Year Journey Laurence Moroney Charles Yu 2010 How to Live Safely in a Science Fictional Universe 2011 2011 Everything Is Actual World of Warcraft: Thrall: Twilight of the Aspects The After Cilmeri Series: Footsteps in Time, Prince of Time, and Daughter of Time Eric Hoffman Christie Golden 2011 Sarah Woodbury List of time travel science fiction 192 Stephen King A man travels through a time portal to 1958, intending to stop Oswald from shooting John F. Kennedy. A young man is transported from 2010 to 1929 and tasked by a disillusioned archangel with correcting historical errors. Part of the Alien Characters series of children's stories. Alien Tim helps people by going back in time to prevent accidents. When Alien William has thousands of time crossing Alien Tims in his city every lunch time he decides to find a way to prevent him from 'helping'. Alien Tim becomes a regular character later in the series which means many of the later stories touch on time travel. A boy from a distant planet living on Earth frantically searches for his missing parents with the help of seven unique friends, battling many deadly obstacles and one terrifying enemy along the way. 2011 11/22/63 2011 Angels and their Hourglasses J.M. Surra 2011 Alien Tim Neil A Hogan 2012 Patalosh: The Time Travelers [4] Z Altug and Tracy Gensler Time travel in science fiction films Time travel is a common theme and plot device in science fiction films. Below are examples of science fiction films that incorporate time travel. Year 1949 Title A Connecticut Yankee in King Arthur's Court The Time Machine Director Tay Garnett Description Based on Mark Twain's classic in which a mechanic (Bing Crosby) is knocked out and wakes up in the land of King Arthur. Loose adaption of H. G. Wells's classic in which a time traveler enters a future where the world is broken up into two classes, the peaceful Eloi and the malevolent masters of the world, the Morlocks. The hero is haunted by a memory from his childhood, which turns out to be himself as an adult. (La Jetée - a movie short - was the basis of the full-length feature 12 Monkeys). A time travel experiment that was supposed to produce a window into different times is actually a portal. Based on the BBC TV series. In this, the Doctor is an inventor not an alien. His TARDIS device takes the Doctor and companions to the future of an alien world. Based on the BBC TV series. In this the Doctor is an inventor not an alien. His TARDIS device takes the Doctor and companions to a future London devastated by war. George Taylor (played by Charlton Heston) travels to a future Earth inhabited by intelligent talking apes. Another astronaut, Brent, travels to the future Earth ruled by apes. His search for Taylor leads to an underground city of nuclear mutants. Three apes escape Earth's destruction by salvaging and repairing the astronaut Taylor's spaceship and piloting it through a time warp back to 1973. A man travels to various times and places from his life in addition to another planet. Due to an impending disaster that threatens to destroy mankind, a time machine is built by a group of young scientists to transport themselves into the future to rebuild civilization. Engineer Shurik has invented a time machine in his apartment. By accident, he sends two people back into the time of Ivan IV while the real Ivan IV is sent by the same machine into Shurik's apartment. Superman circles the Earth at tremendous speeds allowing him to travel back in time to just before an earthquake created by Lex Luthor. Using a time machine, Jack the Ripper and H. G. Wells travel from 1893 London to 1979 San Francisco. 1960 George Pal 1962 La jetée Chris Marker 1964 The Time Travelers Ib Melchior 1965 Dr. Who and the Daleks Gordon Flemyng 1966 Daleks – Invasion Earth: 2150 A.D. Planet of the Apes Gordon Flemyng 1968 Franklin J. Schaffner Ted Post 1970 Beneath the Planet of the Apes Escape from the Planet of the Apes Slaughterhouse-Five Idaho Transfer 1971 Don Taylor 1972 1973 George Roy Hill Peter Fonda 1973 Ivan Vasilievich: Back to the Future Leonid Gaidai 1978 Superman Richard Donner 1979 Time After Time Nicholas Meyer List of time travel science fiction 193 Don Taylor Jeannot Szwarc A storm at sea transports a nuclear warship back in time from the 1980s to the 1940s. A young man sees an old photograph of a woman, and through hypnosis travels back in time from 1980 to 1912 to meet her. Based on Matheson's 1975 novel "Bid Time Return" A young boy unwittingly joins a band of dwarves as they travel through time hunting treasure. The hero travels by means of "time cannons". 1980 1980 The Final Countdown Somewhere in Time 1981 Time Bandits Terry Gilliam 1982 Timerider: The Adventure of Lyle Swann Twilight Zone: The Movie William Dear 1983 John Landis, Steven Spielberg, Joe Dante and George Miller James Cameron Big-screen adaptations of three classic episodes from the popular 1950s and 1960s Rod Serling television series, plus a new segment featuring a bigot who is transported into the lives of past victims of racism. 1984 The Terminator A cyborg (played by Arnold Schwarzenegger) is sent back in time from 2029 to 1984 to destroy humanity by killing the future mother of its future savior. In 1943, an anti-radar experiment accidentally sends two sailors forward in time to 1984. Nancy Allen and Michael Pare star in this film. The school janitor Mario (Massimo Troisi) and the teacher Saverio (Roberto Benigni) have an automobile breakdown, decide to spend the night in an inn, and the next morning they awake in the Florence of the 16th century. Time travel is achieved by means of a flux capacitor. Marty McFly intervenes in his parents' first meeting, preventing them from falling in love, and placing his own existence in danger. Jack Deth is a kind of cop/bounty hunter in a future dystopic Los Angeles. Michael and Ellie break into a military junkyard to find a science project. They find an orb that dangerously bends time and have to stop it to save the world. Peggy Sue Bodell faints at her high school reunion. When she wakes up, she finds herself in her own past, just before she finished school. To save Earth, Admiral James T. Kirk and his crew travel back in time to retrieve the beings who can communicate with an alien probe (humpback whales). Five cowboys of the 1880s are sent forward through time 100 years and fight crime. In 1978, a boy winds up 8 years into the future, and discovers an alien spaceship brought him there. A Russian dystopian comedy. Uncle Vova asks a person from the planet Alpha to move him and Fiddler back in time to save two aliens who got imprisoned because of the main hero's actions. The villain uses a camcorder-like gadget that shows the past, and an inventor opens up wormholes to other timestreams allowing the heroine (a young Courteney Cox) to save her parents from dying. A professor who's lost his family finds evidence of a time traveller in Old West memorabilia. Sequel to Back to the Future, Part II follows Marty McFly and Doc Brown as they go to the year 2015 to prevent Marty's kids from ruining the McFly family's reputation. Along the way, an old Biff Tannen steals the DeLorean so he can give a sports almanac to himself in the past, and win millions of dollars gambling. This creates a hellish alternate 1985 that it's up to Marty and the Doc to correct. 1984 The Philadelphia Experiment Non ci resta che piangere Stewart Raffill 1984 Roberto Benigni and Massimo Troisi Robert Zemeckis 1985 Back to the Future 1985 1985 Trancers My Science Project Charles Band Jonathan R. Betuel Francis Ford Coppola Leonard Nimoy 1986 Peggy Sue Got Married 1986 Star Trek IV: The Voyage Home Outlaws Flight of the Navigator 1986 1986 Nicholas Corea Randal Kleiser 1986 Kin-dza-dza Georgi Daneliya 1987 Masters of the Universe David Odell 1987 Timestalkers Michael Schulz 1989 Back to the Future Part II Robert Zemeckis List of time travel science fiction 194 Stephen Herek Two teenagers (Alex Winter and Keanu Reeves) will not graduate from high school unless they pull on A on their history project. A time traveler (George Carlin) visits them to help because their success on this report is vital as it ensures they will stay together to create a Utopian future. As Bill and Ted travel through time, they encounter historical figures including Socrates, Joan of Arc, and Billy the Kid. Time travelers from the far future steal people already destined to die, such as in plane crashes, in order to restock humankind in their own desolate future. Based on the 1983 John Varley novel. A warlock in the 17th century who has been sentenced to death for witch craft is transported to the 20th century, followed by a witch hunter who must stop the warlock finding the Grand Grimoire. A scientist creates a weapon that causes your enemy to disappear but has a side effect of causing shifts in time. The scientist is transported back in time to 1817 and he meets Doctor Frankenstein and his monster as well as Mary Shelley who in this film wrote her novel based on true events. Sequel to Back to the Future Part II. In the final installment of the trilogy, Marty McFly goes back to 1885 to stop an outlaw from killing Doc Brown in a duel, and bring him back home to 1985. Sequel to The Terminator. 1989 Bill & Ted's Excellent Adventure 1989 Millennium Michael Anderson 1989 Warlock Steve Miner 1990 Frankenstein Unbound Roger Corman 1990 Back to the Future Part III Robert Zemeckis 1991 Terminator 2: Judgment James Cameron Day Bill and Ted's Bogus Journey Army of Darkness Peter Hewitt 1992 Sequel to Bill and Ted's Excellent Adventure. Two evil robot versions of Bill and Ted are sent back in time to kill them. Central character Ash (Bruce Campbell), a supermarket employee, is sent back in time by a specific book to the 14th century. The rich in a future where time travel has been invented snatch people from history a moment before their death in order to use the bodies as hosts for their own minds after death. Ben Wilson and daughter Hillary are visited by a strange group of travelers looking for lodging. The travelers are from the future, intending to witness an impending catastrophe. The turtles go back in time to feudal Japan to retrieve a kidnapped April. 1992 Sam Raimi 1992 Freejack Geoff Murphy 1992 Timescape (or: Grand Tour: Disaster in Time) Teenage Mutant Ninja Turtles III Les Visiteurs David Twohy 1993 Stuart Gillard 1993 Jean-Marie Poire A 12th-century knight and his servant travel in time to the end of the 20th century and find themselves adrift in modern society. Barry Thomas is the average office worker. He becomes attracted to Lisa Fredericks who works in the same company. After work, Barry witnesses the murder of Lisa and goes to a bar to get drunk. Later that night, there is a storm and Barry gets a shock from a lamp's faulty power wire at exactly 12:01 am. The next morning, he realizes that everything is happening exactly as it did the previous day. The next morning the day is repeated again. It is now Barry's job--being the only person alive who is aware of this time loop--to stop the murder of Lisa, and stop the time loop or be caught in time forever. Weatherman Phil Connors is trapped in February 2 in the town of Punxsutawney, Pennsylvania when he finds the same day repeating over and over. An amateur inventor goes through time with an airplane to stop a villain from changing history for profit. USS Enterprise Captains James T. Kirk and Jean-Luc Picard meet through the effects of an energy ribbon. Includes a prohibition against changing the past. The Time Enforcement Commission (TEC) is created to prevent alterations to the past. This causes a dilemma for the hero, Max Walker, who has to prevent time-travelers from altering time, but is tempted to do so to prevent his wife's death. 1993 12:01 Jack Sholder 1993 Groundhog Day Harold Ramis 1994 Time Chasers David Giancola 1994 Star Trek Generations David Carson 1994 Timecop Peter Hyams List of time travel science fiction 195 Terry Gilliam James Cole tries to change the past but fails. It therefore runs on the principle of a fixed timeline (the Novikov self-consistency principle). This film involves the Doctor in his eighth incarnation and has a showdown with the Master. The USS Enterprise follows the Borg back in time to stop them from altering history and preventing Earth's first warp flight and first contact with the Vulcans. Dr. Evil is back and has invented a time machine that allows him to go back to the 1960s so he can steal Austin Powers' mojo. A reporter, learning of time travelers visiting 20th century disasters, tries to change the history they know by averting upcoming disasters. A music group finds a time portal while on their way to Los Angeles and find themsevles in a desert town in the year 1959 under the control of a gang with a corrupted sheriff as an ally. The group learns about the fate of a local chef at a diner and tries to prevent certain disaster despite threats against them from both the sheriff and the gang. An accidental cross-time radio link connects father and son across 30 years. The son tries to save his father's life, but then must fix the consequences. Two people separated in time are somehow able to talk to each other using an amateur radio. The people in question are two students in the same school, one in 1979, the other in 2000. A 40 year old image consultant (Bruce Willis) finds himself being visited by his 10 year old self. The two protagonists both live in a lake house two years apart in time, but are able to communicate through a mysterious post box. This movie inspired the 2006 American film The Lake House. A teenager travels through time using wormholes, a man in a bunny suit, and the modern ritual of sleeping on golf courses. A medieval knight and his serf travel to 21st century Chicago, meeting the knight's descendant. But they must travel back to their time to ensure her birth. A Duke time travels from 1876 to the present and falls in love with a career woman in New York. The film focuses on Celebi who travels to the future and returns with a boy named Sam when being chased by a hunter. 1995 12 Monkeys 1996 Doctor Who Geoffrey Sax 1996 Star Trek: First Contact Jonathan Frakes 1999 Austin Powers: The Spy Jay Roach Who Shagged Me The Time Shifters Mario Azzopardi 1999 1999 (UK) 2000 (USA) 2000 S Club 7: Back to the 50's Andrew Margetson Frequency Gregory Hoblit 2000 Ditto Kim Jeong-gwon 2000 Disney's The Kid Jon Turteltaub 2000 Il Mare Lee Hyun-seung 2001 Donnie Darko Richard Kelly 2001 Just Visiting Jean Marie-Poire 2001 Kate & Leopold James Mangold 2001 Pokémon 4Ever Kunihiko Yuyama Jim Malone Takashi Yamazaki Simon Wells 2002 Returner The human race is on the edge of annihilation after decades of war with an alien force. In an outpost in Tibet, mankind’s last hope of survival is a time travel device. Remake of 1960s version of the film, directed by H.G. Wells' great-grandson, has little in common with H. G. Wells’s original novel. A Bible professor from 1890 comes forward in time to the present via a time machine and cannot believe the things that he sees. Upon learning that his father has been kidnapped, Austin Powers must travel to 1975 and defeat the villain Goldmember - who is working with Dr. Evil. In Israel, a student in archaeology is seeking a video camera hidden 2000 years ago by a mysterious time traveler. Eddie Hitler builds a time traveling toilet which he calls the TURDIS 2002 The Time Machine 2002 Time Changer Rich Christiano 2002 Austin Powers in Goldmember Das Jesus Video Jay Roach 2002 Sebastian Niemann Rick Mayall 2003 Bottom Live 2003: Weapons Grade Y-Fronts Tour Timeline 2003 Richard Donner Film adaptation of the book by Michael Crichton. List of time travel science fiction 196 Jonathan Mostow Sequel to The Terminator and Terminator 2: Judgement Day. 2003 Terminator 3: Rise of the Machines Harry Potter and the Prisoner of Azkaban 2004 Alfonso Cuarón Hermione Granger receives a Time-Turner from Professor McGonagall, so she can attend more classes than time would normally allow. She and Harry later use the Time-Turner to save Sirius Black and Buckbeak. Time travelers spend as much time in the time machine as they want to go back, and can only travel as far back as to when the machine was first turned on. A college psychology student (Ashton Kutcher) learns he can temporarily travel to his past and change it. The time traveling in this film involves a process initiated by reading childhood journals. A 13 year old girl makes a birthday wish and wakes up as a 30 year old woman. Distraught over his drug-addicted girlfriend, Cody (Sarah Lind), who's overdosed and fallen into a coma, small-time dope peddler Art (Jay Baruchel) uses a time machine to journey into the past in a desperate gamble to change her future. A amnesiac Persian Gulf War veteran (Adrien Brody) is subjected to an experimental treatment which moves him forward 15 years. For an extraordinary price, Time Safaris, Inc. will take clients through a wormhole to a time in pre-history to hunt dinosaur game. Based loosely on the 1952 short story by Ray Bradbury, with the Butterfly Effect portrayed as much more pronounced. Five college boys in a sci-fi club break their air-conditioner's remote control. In the sweltering clubhouse, a time machine appears and they go back in time to retrieve a functioning controller, but this causes complications. 2004 Primer Shane Carruth 2004 The Butterfly Effect Eric Bess & J. Mackye Gruber 2004 2005 13 Going on 30 Fetching Cody Gary Winick David Ray 2005 The Jacket John Maybury 2005 A Sound of Thunder Peter Hyams 2005 Summer Time Machine Blues Katsuyuki Motohiro 2006 The Lake House Alejandro Agresti Time travel romance where two people living in the same house at a lake at different times are able to exchange letters through its mailbox and fall in love. Frank Coraci Mamoru Hosoda Adam Sandler is given a remote that lets him fast forward, pause, and rewind his life. A teenage girl discovers that she can leap through time. 2006 2006 Click The Girl Who Leapt Through Time Déjà Vu 2006 Tony Scott Denzel Washington is an ATF agent investigating a terrorist act who is invited to assist in a government time travel surveillance project. Alien scammers discover the code for time travel tattooed on Philip J. Fry's buttocks, and use it to send Bender back in time to steal priceless artifacts. Young Lewis is taken to the year 2037 by his future son Wilbur to stop a "Bowler Hat Guy" who has stolen Lewis' memory scanning machine. House wife (Sandra Bullock) learns that her husband died in a car crash the previous day, but, wakes up next morning to find him well and alive, and awakens the next day to a time when it has been a few weeks since he had died. 2007 Bender's Big Score Dwayne Carey-Hill Steve Anderson 2007 Disney's Meet the Robinsons Premonition 2007 Mennan Yapo 2008 2008 Timecrimes Minutemen Nacho Vigalondo A man who accidentally travels back to the past and meets himself there. Lev L. Spiro Three high-school outcasts use a time machine that one invented to save their fellow classmates from embarrassing moments. Their time-travel creates a black hole, which could destroy the world. Ba'al changes the timeline so that SG-1 or the Stargate program never existed. Three people were unaffected by the change but are unable to do anything until Ba'al and the system lords arrive. Spock's attempt to prevent a supernova fails, resulting in the destruction of the Romulan homeworld. The captain of a Romulan mining ship blames Spock, and both the Romulans and Spock fall through a black hole to the past, creating an alternate reality. A romantic drama about a Chicago librarian (Eric Bana) with a gene that causes him to involuntarily time travel, and the complications it creates for his marriage. Based on the Audrey Niffenegger novel. 2008 Stargate: Continuum Martin Wood 2009 Star Trek J. J. Abrams 2009 The Time Traveler's Wife Robert Schwentke List of time travel science fiction 197 Gareth Carrivick Two geeks and a cynic attempt to navigate a time-travel conundrum in the middle of a British pub. Faris plays a girl from the Future who sets the adventure in motion. 2009 Frequently Asked Questions About Time Travel Disney's A Christmas Carol The Disappearance of Haruhi Suzumiya 2009 Robert Zemeckis Miserly moneylender Ebenezer Scrooge is visited by the ghosts of Christmas Past, Present and Future, in order to change his ways. Kyon is the only one who knows two of his classmates are missing and everything is different. To restore his life, he gathers several keys to power an alien device and travel back three years. Four friends spend a crazy, drunken night in a hot tub at a ski resort only to travel back in time to 1986. They are each presented with an opportunity to alter their futures. The film stars John Cusack, Rob Corddry, Craig Robinson, and Clark Duke. Disney's adaption of the video game of the same name. A dagger is used to turn back the clock, it has a grip made of crystal through which a special "Sand of Time" has to flow in order to create the time transition effect. The Prince has to prevent someone from alternating history. 2010 Tatsuya Ishihara 2010 Hot Tub Time Machine Steve Pink 2010 Prince of Persia: The Sands of Time Mike Newell 2010 Yu-Gi-Oh! 3D: Bonds Beyond Time Kenichi Takeshita Series protagonist Yusei Fudo encounters Turbo Duelist Paradox, who is from the future, and who believes the only way to prevent his future from happening is to stop Duel Monsters from existing. Ernie Barbarash James is a guy from the year 2032 who comes back in time with a custom-made watch that is a time machine. He travels back in time to fix his life but fails. While visiting Paris with his fiancee, an American writer discovers a way to travel back to the 1920s, allowing him to mingle with and draw inspiration from historical greats such as Ernest Hemingway, F. Scott Fitzgerald, and Gertrude Stein. 2011 Ticking Clock 2011 Midnight in Paris Woody Allen Time travel in science fiction television series Time travel is a recurrent theme in science fiction television programs. In some television series, time travel creates the premise and direction for the plot and/or setting of the show. Two model examples of television shows that utilize time travel in this way are Doctor Who and Quantum Leap. There are other television programs that incorporate time travel in only one, or some of their episodes. The table below encompasses television shows that fall into the first of these two categories. Shows that fall into the second category may be found in List of television series that include time travel. Start date 1951 End Date 1956 Title Author Description Captain Z-Ro Roy Steffens Scientist Captain Z-Ro, working in his remote laboratory, safeguarded mankind and history from impending harm. He had a time machine, the ZX-99, both to view history and to send someone back in time. A Time Lord known as "the Doctor" travels through time and space in a TARDIS (Time And Relative Dimension In Space). 1963 - Doctor Who 1966 1967 The Time Tunnel Irwin Allen The year is 1968, and Doug Phillips and Tony Newman are working on a top secret project beneath the Arizona desert called "tic-toc". The project has been 10 years in the making, and a visiting senator wants to see if this project really works, or he will cut the funding for it. To prove that it can work, Tony Newman turns on the time tunnel and goes back to the year 1912, and is on board the Titanic, which would sink hours later. Doug Phillips goes into the tunnel to help Tony, and both are stuck hapless in time. They are catapulted each week to a new adventure in history. Two astronauts who break the speed of light, accidentally travel back in time to prehistoric Earth. When they realise that they are unable to return, they make friends with the cave-people they encounter. Eventually, they are able to return, but inadvertently bring some of the cave-people with them who then have to learn how to get along in the 1960s. 1966 1967 It's About Time Sherwood Schwartz List of time travel science fiction 198 11th Century wizard accidentally ensorcels his way into the 20th. Humorous mistakes are made. Two time traveling children visit both the past and future. Two time traveling inter-dimensional agents protect and guard the order of time in this British drama. 1970 1971 Catweazle Richard Carpenter John Cooper Peter J. Hammond (dir.s Shaun O'Riordan & David Foster) 1970 1979 1971 1982 Timeslip Sapphire & Steel 1982 1983 Voyagers! James D. Parriott A member of a league of time travelers and a boy travel through time repairing errors in world history. After a family traderdy a young girl is transpoeerted into the past. 1988 Moondial (TV serial) 1991 Bill & Ted's Excellent Adventures Back to the Future: The Animated Series Quantum Leap Helen Cresswell 1990 Animated spin off of the movies Bill & Ted's Excellent Adventure and Bill & Ted's Bogus Journey 1991 1992 Bob Gale Follows on from Back to the Future III. 1989 1993 Donald P. Bellisario Dr. Sam Beckett helped to develop Quantum Leap, a project that would allow a person to time travel back to any point since that person was born. Beckett ended up being the test subject, and while he could remember only certain details, he traded places with a person in the past. Others in the past saw the other person instead of Beckett. In the present, an observer named Al, who Beckett could see as a hologram, gave Beckett advice. This usually involved having Beckett correct some problem in the other person's life. Live action spin off of the movies Bill & Ted's Excellent Adventure and Bill & Ted's Bogus Journey 1992 1993 Bill & Ted's Excellent Adventures Time Trax Harve Bennett Jeffrey M. Hayes Grant Rosenberg 1993 1994 A police officer from the 22nd century makes his way back to our time to track down fugitives from the future. 1993 1999 Goodnight Sweetheart Crime Traveller Laurence Marks An accidental time traveller, Gary Sparrow, who leads a double life after discovering a time and Maurice Gran portal allowing him to travel between 1990s London and wartime London of 1939–1945. Anthony Horowitz Jeff Slade uses a time machine created by colleague Holly Turner's father to solve crimes. The machine operates seemingly-randomly, sending the user(s) back in time a time that can be a matter of minutes, or several days. NSA Agent Frank B. Parker can travel back 7 days in a time machine powered by alien technology. Four policemen travel from the year 3000 to the year 2000 to arrest fugitives. 1997 1997 1998 2001 Seven Days Christopher & Zachary Crowe 2000 2001 Mirai Sentai Timeranger Samurai Jack Genndy Tartakovsky Dave Wesson 2001 2004 An ancient demon throws the hero Samurai Jack into the future, in order to allow himself enough time to conquer the world. Time cops from the year 1,000,000,000 A.D. travel back in time to keep famous historical figures from diverting the course of history. Various species from the 30th century are having a "Temporal Cold war" that is interfering with life in the 22nd century, which affects the lives of the USS Enterprise (NX-01) and its crew. 2001 2003 Time Squad 2001 2005 Star Trek: Enterprise List of time travel science fiction 199 Joel Larsen, a 34 year old man, gets a second chance to get his life right, thanks to a freakish accident that catapults him back to 1981, as a 14 year old. He is electrocuted, then wakes up in his teenage body, but with all his adult memories intact. Blessed with adult wisdom, though hampered by adolescent urges, Joel sets out to right the wrongs that will befall his family. Astronauts are sent back in time after witnessing the end of the Earth from space. A young woman receives request from corpses to stop their untimely deaths and wakes up then the day before, in order to attempt to save them. A family attempts to repair their spaceship after being stranded in the past, or modern day, while maintaining the appearance of being normal people. On their journeys through the Stargate SG-1 experiences timetravel both to the past and future. Both John Sheppard and Dr. Elizabeth Weir experiences timetravel when dealing with various ancient devices among others the Stargate. Desmond Hume, former Royal Scots Regimen, is caused by electromagnetic radiation to become "unstuck in time." His consciousness switches between 2004 (the present) and 1996. Benjamin Linus, former leader of the island natives, travels ten months into the future after moving the island. In Season 5, the characters on the island skip through time to different periods of the island's past and future. A children's cartoon where using books three children travel through time and space. Hiro Nakamura and Peter Petrelli can travel in time and space. This is the foundation for the plot of both series one and series two, in which apocalyptic disasters happen and the characters travel back and forth in an attempt to prevent them. A police officer who must learn to adapt to the way things were done in the 70s after being thrown back in time by an accident. (A U.S. version of the series Life on Mars aired in 2008-2009.) 2002 2003 Do Over Rick Wiener and Kenny Schwarz 2002 2003 2004 2005 Odyssey 5 Tru Calling David Carson Jon Harmon Feldman 2004 2006 Phil of the Future Tim Maile & Douglas Tuber Stargate: SG-1 Peter DeLuise 1997 2007 2004 2009 Stargate: Atlantis Martin Wood 2004 2010 Lost Damon Lindelof & Carlton Cuse 2005 2006 2007 2010 Time Warp Trio Heroes Peter K. Hirsch Tim Kring 2006 2007 Life on Mars Matthew Graham Ashley Pharoah Tony Jordan Chris Chibnall 2006 2007 Transformers: Cybertron Torchwood Russell T Davies Chris Chibnall Jane Espenson John Fay The Autobot Vector Prime is a defender of spacetime, he saved your friends human using your power over time, did before of destroy them, by Megatron Humans and aliens alike from different periods in time start to come through to our world by means of a rift in the space/time continuum. (Spin-off from Doctor Who.) 2006 - 2007 - Primeval Portals to different time periods start opening up and creatures from the past and future start to come through. Kevin Falls Matt McGuinness Tom Szentgyorgyi Dan Vasser is the main protagonist of the series, who finds himself jumping through time, unable to stop or control the jumps. Olivia "Livia" Beale is also a traveler from 1948 who jumps into the future. After not being able to jump home, she was stuck in Dan's present and adapted to life there, where she began a legal career and fell in love with Dan, only to finally jump back home while on the plane. For unknown reasons, she now jumps to the same times that Dan visits, and offers him advice and assistance in his missions. In one episode, Phineas and Ferb "fix" an old model of a time machine at a museum which allows them to travel back to the age of the dinosaurs, and eventually back to the future again. In another episode, they used this same time machine again to travel into the future. This time, a much more complicated series of events followed, where their future sister follows them back through time and accidentally disrupts the normal course of various events, setting off a chain reaction that turns the future into a dystopian society. 2007 2007 Journeyman 2007 - Phineas and Ferb Dan Povenmire and Jeff Marsh List of time travel science fiction 200 The protagonists must work with and fight creatures known as Imagin who come from a possible future and have come back in time to kill the key figure to the Junction Point: a human whose sole existence ensures that the Imagin's future cannot exist. The Imagin grant wishes to weak-willed humans to travel farther back in time along that person's memories in order to find the Junction Point by destroying anyone and anything in their way to change the future. 2007 2008 Kamen Rider Den-O 2008 2010 Ashes to Ashes Matthew Graham Ashley Pharoah Julie Rutterford Mark Greig Jack Lothian Spin off series from "Life on Mars" set in 1980s 2008 2009 Kamen Rider Kiva Parallel storylines taking place in 1986 and 2008 are told, with two of the protagonists from the 2008 timeline going back in time to 1986. The latter time traveler goes back in time to attempt to prevent his birth such that his love may live, but instead ensures that his existence remains by saving his father from being killed by the series' antagonist. A female Terminator from the year 2027 comes back in time to 1999 to protect a young John Connor. They then use the time displacement equipment to move forward in time by 8 years to hide John. Various other Terminators are sent back in time on varying missions. Jana Sinyor Erica Strange, a woman who begins seeing a counselor to deal with regrets in her life, only to discover the counselor (Michael Riley) has the ability to send her back in time to actually change these events. A T-rex named Buddy travels with his adopted Pteranodon family on the Dinosaur Train. The Dinosaur Train has the ability to visit the entire Mesozoic Era, the “Age of Dinosaurs,” passing through magical Time Tunnels to meet the dinosaurs in the Triassic, Jurassic, and Cretaceous time periods. FBI agent Mark Benford and the rest of the world fall victim to an incident that renders the entire population of Earth unconscious for two minutes seventeen seconds on October 6, 2009. During the "Black Out", as it is called, the consciousness of the entire planet shifts forward six months into the future to the date April 29, 2010, where they witness their potential futures that could occur that day. Dr. Victor Frankenstein has since completely mastered immortality and now has also created an infinite number of Einstein-Rosen Bridge "wormholes" portals or "Frankenholes" between his small Eastern European village (which is teeming with monsters and supernatural forces) and every time period from the past and the future. This allows historical figures and celebrities seeking the doctor's services to find him. Although many classic Horror monsters are present, the series' focus is mainly on Dr. Frankenstein and his family. A mysterious girl named Homura Akemi is revealed to have made a contract with a being known as Kyubei to go back in time and save the titular character. When Earth is threatened with extinction in 2149, some humans travel back 85 million years in hopes of preventing disaster later. In a TV special, Hoops and Yoyo accidentally travel through a wormhole and meet Santa Claus when he was still Kris Kringle. 2008 2009 Terminator The Sarah Connor Chronicles Being Erica 2009 - 2009 - Dinosaur Train Craig Bartlett 2009 2010 FlashForward Brannon Braga and David S. Goyer 2010 - Mary Shelley's Frankenhole Dino Stamotopolous 2011 2011 Puella Magi Madoka Magica Terra Nova Gen Urobuchi 2011 - 2011 - Hoops & Yoyo Ruin Christmas Time travel in video games List of time travel science fiction 201 Title Teenage Mutant Ninja Turtles: Turtles in Time Date 1991 Description As the TMNT reach the Technodrome, Shredder sends the m through a time warp through the past (Age of Dinosaurs, a pirate ship in 1530 AD, a train in the American West in 1885 AD) and the future (New York City in 2020 AD and a Star Base in 2100 AD) before they can go back to their present in 1991. In order to prevent Purple Tentacle from growing a pair of arms and subsequently enslaving humanity, students Bernard, Laverne and Hoagie attempt to travel one day back in time in Dr. Edison's Chron-o-Johns, time machines housed in portable toilets. During the trip, the machines malfunction and strand Hoagie and Laverne 200 years into the past and future respectively. Players control each character in his/her own time zone (past, present, future), meeting historical figures and progenitors/descendants of some characters; the goal is to return Hoagie and Laverne to the present and prevent Purple Tentacle's world domination. A group of heroes from different eras travel back and forth through time in an attempt to prevent the end of the world in the year 1999. Crash Bandicoot is sent to various points in time to retrieve relics. Maniac 1993 Mansion: Day of the Tentacle Chrono Trigger 1995 Crash Bandicoot: Warped Vigilante 8: 2nd Offense 1998 1999 A car combat game and Sequil to Vigilante 8 Time Travel plays a big role in this games storyline. as well as one character "Agent Chase" using a weapon that momentarily freezes time for anything his weapon hits. the future vehicles and time travel systems used in the game appear to be very much inspired by Back to the Future. At the series' core is the struggle of human beings against the TimeSplitters, a race of aliens that attempt to exterminate humanity by altering its past. The first game in the series took the perspective of several characters fighting off the TimeSplitters in their own eras. The second game added two central protagonists, Sgt. Cortez and Corporal Hart, soldiers from 2401 who traveled to different eras to fight the TimeSplitters. Future Perfect placed a heavier emphasis on a linear story, cinematic cutscenes and character-based humor, and follows Cortez as he teams up with characters against the TimeSplitters and a new, human antagonist, mad scientist Jacob Crow. The ending of Future Perfect implies a definite conclusion to the plot, although a fourth game has been in development hell since 2007. The protagonist, Eike Kusch, is murdered at the start of the game by a knife stab on the back. He is saved from death by an unknown entity who gives him a time travel device, called a digipad, that can be used to send Eike back to a pre-determined point in time, allowing him to take actions in order to prevent his death. After being sent back 30 minutes, Eike succeeds in preventing his stabbing, only to find that he is killed in some different manner, starting the time-travel cycle again. During the course of the game, Eike travels to several time periods as far back as medieval times, gradually uncovering the connection behind the attempts on his life, the mysterious being who saves him and his own past. The game features several possible endings, depending on the player's actions and choices that alter the timeline. Scientists from the near future have begun work on creating a viable time machine. The project results in the creation of two devices, the Alpha Suit, a less advanced prototype jump suit, and the Beta Suit, a more advanced, so-called military grade model with features the Alpha Suit lacks such as combat-related timeshifting abilities and an integrated artificial intelligence to prevent the creation of temporal paradoxes. The director of the project, Dr. Aiden Krone, takes the Alpha Suit and travels into the past. Once there he alters the timeline, placing himself as the ruler of the Krone Magistrate that controls a dystopic world. The protagonist, a fellow scientist whose name is never spoken (never mentioned in the game or manual), then takes the Beta Suit and follows Dr. Krone back to the year 1939 (in an alternate timestream) to a place called Alpha District. During the trip parts of the Beta suit are damaged, forcing the protagonist to assist the Occupant Rebellion against Dr. Krone in hopes of salvaging parts from the Alpha suit. TimeSplitters series 2000–2005 Shadow of Memories (US: Shadow of Destiny) 2001 Timeshift 2007 "World of Warcraft" 2007–present Beginning with the Burning Crusade expansion in 2007, The Caverns of Time hosted dungeons and raids in which players traveled back in time to prevent Azeroth's timeline from being negatively changed. The original 3 dungeons/raids from the Burning Crusade expansion include Escape from Durnholde Keep (level 66+ 5-player dungeon), Opening the Dark Portal (level 68+ 5-player dungeon), and Battle for Mount Hyjal (level 70+ 25-player raid). The Wrath of the Lich King expansion added The Culling of Stratholme (level 80 5-man dungeon). The Cataclysm expansion added End Time (level 85 5-man dungeon), Well of Eternity (level 85 5-man dungeon), Hour of Twilight (level 85 5-man dungeon), and Dragon Soul (level 85 10/25-player raid) as post-release content in its patch 4.3. List of time travel science fiction 202 Prior to the release of the Burning Crusade expansion, players were able to enter The Caverns of Time through terrain exploits. The caverns at the time were incomplete, having no direct access to the instances which were to be added later on. Anonymous players have stated that their access to the game was temporarily suspended for entering the caverns via terrain exploits. Many quests are available to players which bring their character's mind and/or body back in time. "Braid (video game)" 2008 Braid is a platformer art game where the player manipulates time in a variety of creative ways to solve puzzles. Braid's story also deals with the subject of time travel in a way similar to the relationship portrayed in Eternal Sunshine of the Spotless Mind "Professor Layton and the Unwound Future" "Back to the Future: The Game" JP: 2008, US: The Third in the Professor Layton series, set between London Present and 10 years later. Layton receives a letter 2010 from Luke ten years in the future. and it is connected by a failed time Machine Demonstration and the missing Prime Minister of the UK 2010 The game takes place six months after the events of the film Back to the Future Part III and sees Marty McFly, the protagonist of the series, trying to adjust to a life without his best friend, scientist Doctor Emmett "Doc" Brown, whose belongings are being sold off by the bank following his disappearance to an unknown time period. Out of nowhere, an intact duplicate of the destroyed DeLorean time machine appears in front of Marty, and hints and notes inside instruct him to come to Doc's rescue, who is stranded in the year 1931, during the time of Prohibition. The game's series follows the events of Marty and Doc trying to repair hellish timelines created by their past attempts. RTS tme travel game - if you lose a skirmish you can travel back to before it happened and avoid or fix it. But so can your opponents. [5] "Achron" 2010 References • Odgers, Sally O. (1999). "Twilight Times Feature: SF? Fantasy? What's the difference?" [6]. Twilight Times. Retrieved 2007-01-29. • Goldschlager, Amy; Avon Eos. "Science Fiction & Fantasy:" [7]. The Science Fiction and Fantasy Homepage. Retrieved 2007-01-29. • "The Internet Movie Database" [8]. Retrieved 2007-01-30. • "The Ultimate Science Fiction Webguide" [9]. Magic Dragon Multimedia. 2004. Retrieved 2007-01-30. • "Scifipedia" [10]. Scifi.com. 2007-01-10. Retrieved 2007-01-30. • timelinks - the big list of time travel video, time travel movies, & time travel TV [11] - over 600 movies and television • UltimateTimeTravel - the best source on the web for finding time travel books, time travel movies, and time travel computer games [12] • SciFan: Time Travel - Time Control - Time Warp [13] - list of over 2400 books featuring time travel • Aparta Krystian. Conventional Models of Time and Their Extensions in Science Fiction [14] Master's thesis exploring conceptual blending in time travel. • "J.M. Surra Book Releases" [15]. 2011. Retrieved 2012-01-11. List of time travel science fiction 203 Footnotes [1] http:/ / www. gutenberg. org/ files/ 29948/ 29948-h/ 29948-h. htm [2] http:/ / www. amazon. com/ Day-Time-Was-Hacked/ dp/ 1439227853/ ref=sr_1_1?s=books& ie=UTF8& qid=1329085246& sr=1-1 [3] http:/ / www. amazon. com/ Time-Hack-Carel-Mackenbach/ dp/ 1456562703/ ref=sr_1_1?s=books& ie=UTF8& qid=1329084887& sr=1-1 [4] http:/ / www. amazon. com/ gp/ product/ 1463521332 [5] http:/ / www. achrongame. com/ site/ [6] http:/ / www. twilighttimes. com/ Odgers4a. html [7] http:/ / www. sfsite. com/ columns/ amy26. htm [8] http:/ / www. imdb. com/ [9] http:/ / www. magicdragon. com/ UltimateSF/ SF-Index. html [10] http:/ / scifipedia. scifi. com/ index. php/ Category:Time_Travel [11] http:/ / www. aetherco. com/ timelinks/ timevideo-thebiglist. html [12] http:/ / www. UltimateTimeTravel. com [13] http:/ / www. scifan. com/ themes/ themes. asp?TH_themeid=4& Items= [14] http:/ / www. timetravel. 110mb. com [15] http:/ / www. jmsurra. com/ Book_Releases. html Article Sources and Contributors 204 Article Sources and Contributors Time travel  Source: http://en.wikipedia.org/w/index.php?oldid=495473628  Contributors: -dave-, 12va34, 209.239.196.xxx, 21655, 23skidoo, 28421u2232nfenfcenc, 2D, 2over0, 5 albert square, 64.34.161.xxx, 99Timetravel99, A Nobody, A. Parrot, A5b, ABF, AMglobal, AarCart, Aarktica, Abcdef20, Abomasnow, Abyss42, Acdx, Acebulf, Actcohen, Adam Keller, Adam R. Dennison, Adam78, Adashiel, Addshore, Adhawk, Adiazpaz, AdjustShift, Adlez123, Adonis Albattross, Aerion, Afabbro, Age Happens, AgentPeppermint, Agnt9, Ahoerstemeier, Aillema, Aim Here, Aitias, Ajoykt, Aktron, AlMac, Alan d, Alansohn, AlecStewart, Alecmconroy, Alegoo92, Alekroy, Alex Bakharev, Alex.muller, Alfakim, Alfie66, Ali Abbasi7, AliceTaniyama, AlistairMcMillan, Allen3, Allstarecho, Amatulic, Amit.3ku, Anaxandra, Andareed, AndieM, Andres, Andrewlp1991, Andrewpmk, Andy Leighton, Andy120290, Andy5421, Andycjp, Angr, Angrybob945, Animum, Anomo, AnonMoos, Anonymous Dissident, Antandrus, Antixt, Antonio Lopez, Apostrophe, Apparition11, Applejuicefool, Appraiser, Arbinado, Arcann, Arcturus, ArielGold, Arjun01, Arjunm, ArmadilloFromHell, Arrt-932, Artcomic, Articulatefacts, Ashenai, Astrid jamison, AstroHurricane001, Atimetraveler, AugustinMa, Auric, Avono, Avsa, Awsomelawngnome, Az2yusuf, Azxsdcvf, BBSM, BD2412, Backto1992, Baconmaster117, Bakabaka, Balyg, Banno, Bantomx, Barkingdoc, BarretB, Basispitch, Baxxterr, Bcarstens, BeastieLips, Belfunk, BenBaker, Benji64, Benscripps, Bentley4, Bento00, Bertus, Bevo, Bewildebeast, Beyond My Ken, Billy212, Billy213, Billy500, Bisqwit, Bkell, Blake-, Blanchardb, Blueyoshi321, Bmader, Bmckeag, Bmicomp, Boaz1998, Bob Castle, Bobbaxter, Bobbb7, Bobo192, Bogey97, Bongwarrior, Booblo, BookGuru, Bougerox134, Boyd.ocon, BoyliciousDarian, Braddie, Branddobbe, Brandmeister, Brandon, Brinklej, Brossow, BruceGrubb, Bryan Derksen, Bt8257, Btljs, Bubba hotep, Bugnot, BuickCenturyDriver, BurnDownBabylon, Bwithh, C1k3, CQJ, CWenger, CWii, CalebNoble, Calor, Caltas, Calumrulz, CameronKidd, Camw, Can't sleep, clown will eat me, Canadian-Bacon, Canis Lupus, Capitalist, Capricorn42, CaptainWesker, Carbuncle, Carmichael, Catastic14, Catbar, Catgut, CatherineMunro, CattleGirl, Cbingel, CedricVonck, Cghobbs, Chairman S., Chardish, CharlotteWebb, CharmedFreak123, Cheaposgrungy, Cheat2win, Chensiyuan, ChicXulub, Chillum, Chowells, Chrestomanci the Enchanter, ChrisBaker, ChrisHodgesUK, Christiaan Roorda, Christian Roess, Christian75, Christopher Thomas, Christopher1968, Christy than, Chuq, Chzz, CinnamonCinder, Ckatz, ClimbRider, Cmdrjameson, Coffeepusher, Cometstyles, Comicist, CommandantNick, CommonsDelinker, Como se what?, ConicProjection, Connelly, Conversion script, Coocooforcocopuffs, Corpx, Corruptcopper, Coyoty, Crazycomputers, Cromulent Kwyjibo, Cronokiller, Crowley, Cspj12, Cst17, Cteckerman, Curps, Cutesmartguy, Cybercobra, Cynthia Sue Larson, Cyp, D. Recorder, D.M. from Ukraine, DDeRosia82, DMC88, DVD R W, DVdm, Dachshund, DaiTengu, Daman4562, Damian Yerrick, DanielLC, Danieljackson, Danner578, Dantopia, Daram.G, Darklilac, Darksyde, Dave6, David Gerard, DavidWBrooks, Davidstrauss, Dawn Bard, Dayewalker, Dekisugi, Delldot, DennyColt, Dependent Variable, Desmond71, Detinycyrus, Dfrg.msc, Diannaa, Dinesh smita, Discospinster, Dj05ny, Dlohcierekim, Dlrohrer2003, Dmondom, Docbillnet, Doctor Whom, Doctor den, DoctorHarris21, Doczilla, Dogaru Florin, DoktorDec, Dommccas, Doulos Christos, Dph1210, Dr Greg, Dr. Reiter, Dr. Sunglasses, DragonflySixtyseven, Drcool70, DreamHaze, Driscolj, Drlight11, Drpickem, Drumfreak66, Dtr1001, Dudegalea, Dudley1980, Dustimagic, Dylan Lake, Dzusin, Długosz, E smith2000, EJF, ESkog, Eartheaven1, Ebajorek, Ebygum, Eclecticology, Ed Addis, Ed.capistrano, EdBever, Edward, Eean, Eeekster, Egil, Ehrenkater, Ejosse1, Ekpyrotic Architect, Electric-adam, Elipongo, Ellmist, Emo muffins15, Ems57fcva, Endomion, Enormousdude, Enviroboy, Epaphroditus Ph. M., Epbr123, EpiVictor, Eric119, Erik J, Erik9, Erri4a, Escape Orbit, Evb-wiki, Everyking, Excirial, Explicit, Ezhiki, FF2010, Facts707, Falcon8765, Falcon9x5, Familyguy001, Farmercarlos, Fatman1152, Favonian, Fayenatic london, Fconaway, Feedmecereal, Feelin420247, Feezo, Fennec, Fifth Rider, Filz Patrick Dureza, Finngall, Fintler, Firebladed, Firetrap9254, FlamingSilmaril, Flip, Florentino floro, Fluffernutter, Flyer22, Fortdj33, Forteanajones, FrankP, FranksValli, Fratrep, Frazzydee, Fred Hartzell, Free-mind, Freethinker716, Frozennacho57, Frumphammer, Frymaster, Fueldoctor, Fuhghettaboutit, Fullstop, FunPika, Funandtrvl, FunnyMan3595, Furrykef, FutureEvanGreene, Fuzzie, Fuzzypeanut, Fvw, G Rose, GHcool, GHe, GM11, Gamebrain, Garda40, Gary King, GaryOAKSTERX, Gaurav, GeneralCheese, Gentaur, GeoGreg, Geof, GeorgeHarnish, Gfoley4, Gggh, Ghughesarch, Giftlite, Giggett, Gilliam, Gimboid13, Gjd001, Gladen, Glen, Gogeba, Gogo Dodo, Golbez, Goodgirl 2011, Goodnightmush, Grafikm fr, Graham87, Grahammorehead, Grandia01, Green Phantom, GreenDay, Gregbard, Gregkaye, GregorB, Grenavitar, Grim23, Grondilu, Grstain, Grunt, Gscshoyru, Gunmetal, Gurch, GutoAndreollo, Gwernol, Gzkn, Gökhan, Hadal, Hallows AG, Hamsterlopithecus, Hanul12, Haoie, Hardlysocial, Harry Potter, HarryDav1, HastyDeparture, Headbomb, Heiar7, Heimstern, HereToHelp, Heron, HighPriest15, Hillman, Hiphats, History2007, Histrion, Hitzoidlerberg, Hmitt, Holetel, Hoplite516, Hotel Caliphate, HovisM, Howcheng, Hu, Hughtcool, HumphreyW, Husond, Hyphz, Hypnosifl, Hypotime, I b pip, IG-2000, II MusLiM HyBRiD II, Ibagli, Icairns, Icweiner, Idaltu, Ifnord, Iheartghs, Infomaniax, Inimish, Inky, Inter16, Interchange88, Inversetime, Invincible Ninja, Iridescent, Irishguy, Isopropyl, ItsTheFace, Itsjesus, Ivancurtisivancurtis, Iwoopyourass, Ixfd64, J.delanoy, J157, JARIAN, JForget, JFreeman, JHMM13, JLM, Jabir99, Jacobolus, Jaffo Gonzales, Jag123, Jagged, Jagged 85, Jagsandkamels, JamesMLane, Jamesfryar, Jamesontai, Jan1nad, Jason Gieles, Jason Potter, JasonAQuest, Jasonuhl, Javierito92, Jaxl, JayKeaton, Jaydec, Jdude3, Jeepday, Jeff Fries, Jeffrey Mall, Jeh, Jeoth, Jerry, Jersey Devil, Jeyjey654, Jfreyre, Jiebie, Jim1138, JimVC3, JimWae, JimmyBlackwing, Jimw338, Jj137, Jkominek, Jman36, Jmr213, JoanneB, Joao, Joebwan, Joecool94, Joeyvigil, John Foxwhitener, John Quincy Adding Machine, John Vandenberg, JohnBlackburne, JohnOwens, Johnbender, Johndburger, Johnleemk, Johnnybender2, Jolb, Jon the Geek, Jonathanbender, Jonathanbender3, Jonathunder, Jonjonson, Jonnyf88, JorisvS, Joshlight, JoshuaZ, Jossi, Jpgordon, Jt10258, Jusdafax, JustAGal, Kaiba, Kaijan, Kainaw, Kalban, Karada, Karl Palmen, Karthick 1984m, Katanada, Keeves, KefkaTheClown, Keilana, Kencrapalot, Ketlan, Kevin B12, Kevin Rector, Khaosworks, Khatru2, Khunglongcon, Killiondude, Kimagain, Kirill Lokshin, Kizor, KnowledgeOfSelf, Knowledgeum, Koldito, Kombatgod, Korako, Krackenback, Krisscheibe, KuroiShiroi, Kurt Parker, Kuru, Kurykh, Kusunose, Kyle Barbour, Kyphe, Kzollman, L Kensington, LAgurl, LC, LFaraone, LOL, La Pianista, Lambiam, Lanchedgehog, Languagehat, Latitude0116, LeCire, LeaveSleaves, Lectonar, Lefty, Legija, LegoABC, Leoboswell, LeonWhite, Les boys, Leuko, Lexor, Liftarn, Lightmouse, Lightning jim, LikeLakers2, Linas, Lindowman, Little Mountain 5, LittleOldMe, Lloyd Nixon, Loadmaster, Localhost00, Lokicarbis, Longhair, Looxix, Lord Galen, Lord Voldemort, Lord of Light, Losan33, Love's Labour Lost, LtNOWIS, LuK3, Luk, Luke.J.D., LukeCopenspire, Lyght, Lyle Swann, M623d, MER-C, MPerel, MRISLAND, MSGJ, MSJapan, Macusernick, MadIce, MakeRocketGoNow, Makewater, Mallocks, Mandarax, Manikandan.k, Mannafredo, Marc Venot, Marcok, Marct3176, Marcus Brute, Marijuanarchy, Mark91, Marshall Williams2, Martarius, Martijn Hoekstra, Martin bennett76, MartinHarper, Martyson21, Marvelvsdc, Master Deusoma, MasterXiam, Materialscientist, Mathias-S, Matniz, MattGiuca, Mattbuck, Matticus78, Matu94, Maurice Carbonaro, Maury Markowitz, Maximaximax, Mayur, Mbell, McAusten, Mckaysalisbury, Mderezynski, Me300, MeEnjoyYourself, Meaghan, Meelar, Mehk, MeltBanana, Mentifisto, Mercurywoodrose, MetaManFromTomorrow, Mhbizzle101, Mhoward2291, Michael Atma, Michaelbusch, MichiHenning, Mickeyd24, Mifter, Mikaey, Mike Field, Mike Garcia, Mike Peel, Mike R, Mike Rosoft, MikeAltieri, MikeLynch, Mikebach, MikeyChalupaUSN, Minna Sora no Shita, Miranda, Miss Madeline, Misterdan, Misza13, Mitsukai, Mjfan12346, Mm40, Mmxx, MoisesMB, Monedula, Mononomic, Monterey Bay, Moriori, Mountainsdenver, Mr spock4113, MrBeck, MrWhipple, Mrabcx, Mrlynam, Mrmmattson, Mufka, Mushroom, Musicbuff, Myasuda, Mygerardromance, Mysid, NCase, NHRHS2010, NMChico24, Nabla, Nagelfar, Nathanrdotcom, NawlinWiki, Ncurses, Nescio, Netalarm, Netkinetic, NewEnglandYankee, Newportm, Nights Shadow, Nihiltres, Nilfanion, Nima Baghaei, Nitku, Nn123645, Nobaddude, Noctibus, Nommonomanac, NorwegianBlue, Noster se solus, Nova77, Novaprospekt, Novium, Nubz0rs, Nuclear man, Nxsty, OMGsplosion, ONEder Boy, Obankston, Oda Mari, Oddrick, Off2riorob, OffsBlink, Ohanian, Ohnoitsjamie, Old Moonraker, Old Space Timer, OleMaster, Oliverjrhodes, Omicronpersei8, Omnieiunium, OnePt618, OrbitOne, Orisohana, Orphan Wiki, Ortund, Oswald bastable, Ottershrew, Owner213, Oxymoron83, PBP, PL290, Paki.tv, Paranoid, Parsiferon, Partheemail, Pascal666, Patkplc, Patriarch, Patstuart, PaulHammond, Pentrant, Pepper loves grusly, Pepso, Peregrine981, Persian Poet Gal, Peruvianllama, Peterbd, Peterdjones, Petrb, Pharos, Phil Boswell, Phil-mcracken, PhilHibbs, PhilKnight, Philip Trueman, PhysicsForBreakfast, Piano non troppo, Pie4all88, Pinethicket, Pingveno, Pinkflowers246, Pixel, Platform H, Pleasantville, Pmcray, PoccilScript, Ponder, PonyToast, Poor Yorick, Porcatus, Prashanthns, Psegura41190, Psychoj867, Ptrslv72, Pwalt15, Pwningmason, Q0, Qazqwert, Qst, QuaestorXVII, Quarl, Quench123, QuiteUnusual, Qwertyuioptt-2008, Qwyrxian, Qxz, ROVER13, RSStockdale, RadicalBender, Radon210, Raiders321654987, RainbowOfLight, Raja99, Randytsx, Ravn, Rawr, Ray Dassen, Razasyed, Razorflame, Reconsider the static, Red Shotgun, RedRollerskate, RedSpruce, Redmtndew42, Redoc, RetroBob, Reuvenk, RexNL, Rexxtaylor, ReyBrujo, Rfc1394, Rhue of Landorin, Riana, Ricardo630, Rich Farmbrough, Richard BaltoCo, RickK, Rickyrab, Ridwan93, Rising*From*Ashes, Rjbrock, Rjd0060, Rjwilmsi, Roadrunner, Robchurch, Robin klein, Robint22, Ron Ritzman, Ronhjones, Rory096, RoryReloaded, Rosenkreuz, Rossodio, RoyBoy, Rpresser, Rracecarr, Rrburke, Rror, Rsand726, Rsm99833, Rt66lt, RyanGerbil10, Rypcord, Ryururu, SJP, Salsb, Salvio giuliano, Sam Korn, Sanchom, Sango123, Saraal, SarahLawrence Scott, SarekOfVulcan, Sasoriza, Savidan, Sawjan, Scarian, Sceptre, Scetoaux, SchuminWeb, Scooter, Scorpionman, Scottchavez, Seador, SeanDuggan, Seanmckaveney, Seans Potato Business, Sebastian789, Seidenstud, Semperlibre, Sephiroth13, Seqsea, Serealnome, Setheron, Sethomas, Sexydave, Sexzguy, Shadow Android, Shadowdancer, Shadowjams, Shadowlynk, Shadowx180, Shaker 2000, Shalom Yechiel, Shaneisthesickest, Shanes, Shankara1000, Shawncorey, Shawnisking, Sheba189, ShelfSkewed, Shikhars23, Shivjha20081, Shizane, Shoy, Shubinator, Sibi antony, Sigil7, Signinstranger, Sikory, Silversnake020, Silversurfer4646, SimonP, Sjakkalle, Skater, SkepticMuhs, Skizzik, Skorp, SkyMachine, Slady, Slash, Slightsmile, Sloq, Smoove Z, SnappingTurtle, Snigbrook, Snowolf, SoLando, Sommerfeld, Sonjaaa, Soojmagooj, Sp00n17, Sp33dyphil, SpaceFlight89, Spacey, Sparkchu, Sparkit, Special-T, Spellcast, Splash, Split Infinity, Squiggle, StAkAr Karnak, Stanley011, Stannered, Starrydust, Stephen, Stephen Gilbert, Stephenb, Stephenchou0722, Steve Quinn, Steven J. Anderson, Steven Zhang, StevenMcFlyJr, Steveo2, Stevertigo, Stilanas, Stormie, Streetwise1, Stuart.Jamieson, Stux, Suffusion of Yellow, SunnySideOfStreet, Supergeniusbigtime, Supersaiyanplough, Surv1v4l1st, Swilliams1989, Swwright, Symbolt, SyntaxError55, TJDay, Takuya Kanbara, Tangotango, Tarquin, Tasc, TassadarAlpha, Tassedethe, Tavilach, Tawker, Tbhotch, TeaDrinker, Techman224, Tempshill, TenPoundHammer, TerryE, Teslasheir, Texture, Tham153, Thatdog, The Grim Voice, The Knowledge-seeker, The Minister of War, The Moose, The Thing That Should Not Be, The ansible, The snare, The sock that should not be, The stuart, TheFeds, TheKMan, ThePatchedFool, TheProject, TheRenegade, TheWeakWilled, Thedarkfreak, Theeothersteve, Theironwop, Theroadislong, This lousy T-shirt, Thiseye, Thisnamestaken, Thruston, Thug outlaw69, Thumperward, ThunderbirdJP, Tide rolls, TigerShark, Tim Starling, Timeship, Timetraveler2, Timetravellers01, Timventura, Titoxd, Titus III, Tmxxine, Tnxman307, Tobby72, Tohd8BohaithuGh1, Tom Atwood, Tom harrison, Tomta1, Toniblack82, Tony Fox, TonyMath, Travelbird, TravisTX, TreasuryTag, Tregoweth, Trick, Trusilver, Truthhere, TsiyonNassi, Tsuchiya Hikaru, Ttob, Tulkolahten, Turnip Wars, Tvoz, TyA, Uaxuctum, UberScienceNerd, UkPaolo, Ukexpat, Uncle Dick, Underdog, Universe Daily, Usa8000, Useight, UtherSRG, Utmost97, Vary, Vasuman, Vcorani, Vehement, Velella, Versus22, Vid2vid, Vints, Virtualquark, VladimirKorablin, Vodex, Vrenator, Vsf3000, Vsmith, WCFrancis, WDavis1911, WFNelson, WX 0, WacoJacko, Waggers, Waldir, Waltgith, Walton One, Wandering Ghost, Warfreak, Wayne Slam, Web129, Wellthatisgr8, Weregerbil, Wereon, West Brom 4ever, Whatisupmay, WheehW, WhiteDragon, Whizmd, Wiki alf, WikiAuthor, WikiLeon, Wikiecam, Wikimaster77, Wikipelli, Will-B, Willfein, William Avery, Wimt, Winterheart, Wisemannn, WiteoutKing, Wiwaxia, Wjejskenewr, Wknight94, WolFox, Woohookitty, Worldwidereach, Worloq, Wotnow, Written, Wwoods, Wxlfsr, WyvernOne, XJamRastafire, Xeno, Xezbeth, Yafujifide, Yamamoto Ichiro, Yamara, Yamla, Yani, Yserarau, Yvwv, ZAMBAM13, ZZzcastroz, Zac Effron, Zachlipton, Zane043, Zapvet, Zarxos, Zedmelon, Zepheus, Zerokitsune, Zginder, Zhou Yu, Zoicon5, Zsinj, Zyadamin1, Zymphor, Zythe, 3061 anonymous edits Multiverse  Source: http://en.wikipedia.org/w/index.php?oldid=494857121  Contributors: 09dhummel, 123465421jhytwretpo98721654, 213.253.39.xxx, APL, Aaron Bowen, AbstractClass, Addihockey10, Admiral Roo, Adrigon, Aitias, Ajcheema, Akash pagla, Alansohn, Albertmin, Alex earlier account, Allen234, Alxeedo, Amnuel, Anarchia, Androo, Angela, Annaalexandrae, Anonymous Dissident, Another disinterested reader, Ant, Anthony on Stilts, Anville, Apeloverage, Apostrophe, Araignee, Arion 3x3, Armeria, Arthena, AstroWiki, Athanatsius, Athenean, AxG, B4hand, Bacabed, Barbara Shack, Bartledan, Beardo, BenBaker, BenRG, BenRayfield, Bernard Marx, Beyond My Ken, Bfinn, BigBang616, Blehfu, BlueNight, BobKawanaka, Bobo192, Boing! said Zebedee, BorealisXIV, Boud, BrianY, Brighterorange, Bryan Derksen, Bubba73, CHBMch05, CRGreathouse, CSTAR, Caledones, Casimir9999, Cassowary, Cfortunato, CharlesC, Chasrob, Article Sources and Contributors Chimesmonster, Chris the speller, Chrisdann, Christinedoby, Chunminghan, Ciphergoth, Cloudblazer, Clq, Conversion script, Css, Curst Saden, DCNanney, DV8 2XL, DVdm, Dan, Daniel Newman, Danogo, Darklilac, DarthSidious, Dazedbythebell, Dbachmann, Dcoetzee, Ddddurga, Delirium, Derek Ross, Deville, Dianelos, Dillee1, Discrepancy, Djf2564, Dlarmore, Dmitrybrant, Doczilla, Dominik92, Dorftrottel, Drbogdan, Dream of Nyx, EdBever, EdgarCarpenter, Editorius, Eequor, Ehheh, Electricnet, Emperorbma, Eog1916, Eridani, ErkinBatu, Escape Orbit, ExternalGazer, Fabartus, Fairandbalanced, Falcorian, FeanorStar7, Fermion, Firsfron, Fishal, Foosher, Freakofnurture, Future kosmos, GateKeeper, Gating, Gco, Gdm, GentlemanGhost, Geoffr, GeorgiaSLee, Geshel, Giftlite, Gil987, Gioto, Glastohead, Gracefool, Graeme Bartlett, GreenUniverse, Greenguy1090, Grunt, Gtrmp, Ha33 blondechick, Hac13, Hadal, Handsaw, Hanjunjade, Hannes Karnoefel, Hans Adler, Hathaldir, Hawkaris, Haxwell, Headbomb, Hemlock Martinis, Hephaestos, HieronymousCrowley, Hiplibrarianship, Hrafn, Ht686rg90, Hu, Hyblackeagle22, IRWolfie-, Ictlogist, Ilmari Karonen, Imad marie, In another mutiverse, IomPsinso, Iridescent, Ito123456789, J04n, JHunterJ, Jagged 85, Jamelan, JamesAM, Jeff3000, JeffStickney, JeffreyN, Jenattiyeh, Jeraphine Gryphon, Jerome Charles Potts, Jesse V., JoanneB, Joecab, Johnbmckenna, Johnpseudo, Johnstone, Joke137, Joncolvin, Joseph Solis in Australia, JoshuaZ, K a r n a, K00bine, K0hlrabi, K1234567890y, KGasso, Keeganp, KelleyCook, Khaosworks, Kilo39, Kingpin13, Kintetsubuffalo, Kitch, Kmarinas86, Knowledge Seeker, Kookyunii, Kozuch, Krawi, Kriak, Kriss12, KronicTOOL, Kurrupt3d, Kurtilein, Lambiam, Latka, Lefty, LinkinPark, Livajo, Longhandle1137, Lotje, MJMyers2, Machine Elf 1735, MadIce, Magioladitis, MakeRocketGoNow, Makyen, Malcolmxl5, Martarius, Martg76, Masqline, Masterpiece2000, MattB2, Mbroderick271, McSly, Mchmike, Mel Etitis, Meneth, Metamagician3000, Miami33139, Michael C Price, Michael Hardy, Mike Peel, Mike Rosoft, Mike18xx, Mirage GSM, Mjkrol, Modemac, Modster, Moogsi, Moosester, Morwen, Mpfrank, Mporter, MrH3MinuteMile, Mshonle, MuZemike, Multisport3, Naiveandsilly, Nakon, Naroood, Neparis, Nerudography, Netdragon, Netkinetic, NewEnglandYankee, Newone, Nfenn, Noah Salzman, Noetica, OCCullens, Obey, Ohnoitsjamie, Old Moonraker, Olivier, Ollj, Osprey9713, Ott, Parsifal, Parsiferon, Parthdu, Pascal666, Pass a Method, Patrick, Paul August, Pcarbonn, Peter.thelander, Peterdjones, Petersam, Pfahlstrom, Philip Stevens, Phoenix2, Pitamakan, Pne, PointedEars, PoisonGM, Police officer, Poor Yorick, Portillo, Projectyugo, Pwqn, Quafman, RA0808, Radon210, Rafi5749, Ran4, Rbj, Rchamberlain, Red Echidna, Reedy, Renamed user 4, Reuben, Richard D. LeCour, Richard-r-v, Richardvanas1, Rickard Vogelberg, RickardV, Rickybaksh, Riction, Riemann Zeta, Riraito, Rjwilmsi, Rnm102696, Robma, Roboshed, Rory096, Roy7, RoyBoy, Rrburke, Rursus, Salix alba, Sam, Sam Hocevar, Sanspeur, Sapphic, Saswann, Scarian, Scwlong, Sedecrem, SeniorInt, Shadowblade, ShakingSpirit, ShaunMacPherson, Shiritai, Silicianer, Silver Spoon, Siroxo, Sjorford, Skakkle, SkyMachine, Slightsmile, Slivester, Smjg, Smurfsider, SnowFire, Soilguy5, Sophus Bie, Spartan, Spikehay, Spydra, Stemonitis, Steve Quinn, Steven Avraham Rosten, Stoned philosophaster, Stupidjassi, Sunwukongmonkeygod, SwisterTwister, Taigei, Tarotcards, Teflon Don, Terraflorin, Thanos6, Thanose, Thatguyflint, The Anome, The Anonymous One, TheGrimReaper NS, ThisIsRealPuma, Three887, Tide rolls, Tim Shuba, Tim Starling, Titanium Dragon, Tlogmer, Tomisti, Troublemane, Trusilver, Tverbeek, Twoshotted, UBeR, UberScienceNerd, Uruk2008, Vald, Valoem, Vampus, Vanished User 0001, VanishedUser314159, Vinay Jha, Vyznev Xnebara, WAS 4.250, Waza, Wednesday Next, Wereon, Wesley J M, Whosasking, Wikianon, WikipedianMarlith, Wikipelli, Winterus, Wmpearl, Wylfing, XDanielx, Xammer, Xiner, Yboc2000, Z E U S, Zaian, Zetawoof, Zhonghuo, Zippedmartin, Zntrip, Zx-man, ²¹², 767 anonymous edits Many-worlds interpretation  Source: http://en.wikipedia.org/w/index.php?oldid=494924774  Contributors: 213.253.39.xxx, 24.93.53.xxx, 5Q5, AIMW32, Aarchiba, Acsenray, Aero66, Alexnye, Alfio, Altenmann, Andy Fugard, Ar-wiki, Arkuat, Arnero, AshLin, AussieScribe, AxelBoldt, Aymatth2, Barbara Shack, BarretB, Batmanand, Bboyneko, Ben Standeven, BenRG, Bevo, Bfinn, Birge, Bkell, Brian Olsen, Brian Wowk, Brusegadi, Bstepp99, CSTAR, CYD, Carnildo, Charles Matthews, Chatfecter, ChicXulub, Chris Howard, Cj67, Ckatz, Ckoenigsberg, Coastal593, Cogiati, Conversion script, CosineKitty, Count Iblis, Courcelles, Ctkohl, Cyclonenim, Czj, D6, DJIndica, DV8 2XL, DVdm, Dan100, Dandv, Danski14, Darius Bacon, Dave Kielpinski, David R. Ingham, DavidBoden, Dc987, DenisDiderot, Derek Ross, Dicklyon, Diza, Djr32, Don4of4, Dr. Sunglasses, Draeco, Dragon's Blood, Dreftymac, Duendeverde, Duke159, Dule1101, ELDRAS, EMC125, Ebonmuse, Eclecticology, Ehaque, El C, ElBenevolente, Eli the Barrow-boy, Emersoni, EoGuy, Eqb1987, Eridani, Eve Hall, Evercat, Eyu100, Eyv, Fabartus, Fairandbalanced, Falcorian, Feelingsman22, Firsfron, FiveColourMap, Fourthords, Freakofnurture, Fredkinfollower, Fredrik, FvdP, Gabbe, Gahr gardner, Gaius Cornelius, Geewee, General Epitaph, Geoffrey.landis, George Richard Leeming, Giftlite, Graham87, GregWooledge, Gregbard, Gregz08, Grendelkhan, Grok42, Gtrmp, HappyCamper, Harizotoh9, Haxwell, Hdeasy, Headbomb, HisSpaceResearch, Hpa, Hrimpurstala, Hunter2005, Huntingg, Hypnosifl, Ilmari Karonen, Imaginaryoctopus, Incompetence, Inwind, Ixfd64, J.delanoy, JForget, JakeVortex, Jamesabloom, Jcorgan, Jdcaust, JohnSankey, JohnSawyer, JohnnyMrNinja, Joke137, Joseph Solis in Australia, Josh Grosse, Jrockley, Jusses2, Kartasto, Kazzie1995, Kevin aylward, Khaosworks, Kkmurray, Korg, Kromozone, L Kensington, LC, Lambiam, Laplace's Demon, Latitude0116, Ld100, Leibniz, Lethe, Lhollo, Light current, Likebox, LilHelpa, Linas, Longi 93, Lumidek, MER-C, Mac Dreamstate, Machine Elf 1735, MadIce, Mandarax, Maury Markowitz, Mbell, McGinnis, Measles, Mgiganteus1, Michael C Price, Michael D. Wolok, Michael Hardy, MichelCPrice, Mmm, Modalizer, Mukake, Mustbe, Nate Silva, Nchaimov, NeilN, Neuromath, Nixer, Nnh, Nobody60, Nti2005, Oliver Pereira, Pablo-flores, Parsiferon, Pauli133, Pavel Vozenilek, Peterbyrne, Peterdjones, Pfalstad, Phatius McBluff, Phys, Pink!Teen, Piotrus, Plexos, Plumbago, Pnrj, Proxima Centauri, Quadell, QuaestorXVII, Quantholic, Quantum Person, RUBEN TESOLIN, Radioflux, Rekcana, Rememberway, Resuna, Rex the first, Rgonsalv, Rholton, Rich Farmbrough, Richj, Rjwilmsi, Roadrunner, Ryan Roos, Ryanaxp, SDC, SHCarter, Salmar, Sam Hocevar, SamRushing, Sanchoquixote, Santa Sangre, Sapphic, Sarge009, Saswann, Savidan, Schaefer, SchreiberBike, Senjuto, Shantrika, Sheliak, Silly rabbit, Skew-t, SlimVirgin, Sm8900, Stannered, Startswithj, Stephen B Streater, Stevertigo, SunCreator, Surajt88, Taketa, Targeran, Tarotcards, Teapeat, Teo64x, Terse, The Anome, Theodork, Thingg, Thruston, Tianasez, Timo Honkasalo, Timwi, Togo, Torchiest, Txomin, Unara, Vanhoabui, Vespristiano, Vincej, Vyznev Xnebara, WaysToEscape, Whitneyz32, Will314159, WillWare, Willempramschot, William M. Connolley, Wmahan, Wolfkeeper, Woohookitty, Wragge, Wwoods, Xnquist, Zahd, ZoneSeek, ‫ 533 ,ﺯﺭﺷﮏ ,0102 ﺍﯾﻠﯿﺎ‬anonymous edits Novikov self-consistency principle  Source: http://en.wikipedia.org/w/index.php?oldid=492338885  Contributors: 134.132.115.xxx, 6birc, Ajarmitage, Andyroo316, Arabani, Arthur Rubin, AxelBoldt, Bando26, Bfinn, Bisected8, Bobrayner, Bredd13, Brooksindy, Bryan Derksen, Bryce, Bulmabriefs144, Burnside65, CamLewis, Chetvorno, Chinju, Ckatz, Comicist, Corkscrewkitty, Daguerio, David Latapie, Davidhorman, Demophon, Derek Ross, Doczilla, Długosz, Eisblume, Equendil, Eric Sandholm, Felicity4711, Foobaz, Gioto, Gregbard, Grenavitar, Headbomb, Hypnosifl, Iamthedeus, Ickle Ronnie, Imfromthepast, Intgr, Itinerant1, Jaydec, John Darrow, Kgagne, Khaosworks, LilHelpa, Macslacker, Mattrix, Matzeachmann, MegX, Michael Hardy, MileyDavidA, N4nojohn, Nexus501, Numenorean7, NurMisur, Oerjan, Onionmon, Oren0, OrinR, PMLawrence, Peterdjones, Petter Strandmark, Piet Delport, ProfessorPaul, RJFJR, Raidr, Rando991, RedSpruce, Renamed user 212, Rjwilmsi, Rogerd, Ruakh, Sabik, Saeed.Veradi, Salasks, Shrug-shrug, Slowmover, Spaceman0, Spoon!, Stephen, Surajt88, Susurrus, T.O. Rainy Day, TSBoncompte, Tarquin, Timwi, Uusijani, Val42, Vampus, VolatileChemical, Whitepaw, Zedmelon, 131 anonymous edits Wormhole  Source: http://en.wikipedia.org/w/index.php?oldid=495146534  Contributors: 1959pond, 1narendran, 218, 42Bakchoi, 4RM0, A. Parrot, Abb615, Achyuth Murlei, Acid-Burn, Acroterion, AdjustShift, Ae7flux, AerobicFox, Alain r, Alansohn, Alba, AlexUT, AlexiusHoratius, Alexlax08, Allen McC., Altman, Altmany, American Eagle, Anand Karia, Anchpop, Ancientanubis, Andrea105, AndrewH, Aragorn2, ArasTCP2, Archanamiya, Ardonik, Areldyb, Argo Navis, Arichnad, Arretu, Ashmoo, Ask123, AstroHurricane001, Atlan, Autonova, Axl, Axlroseslashes, Az1568, Ba22a, Badgernet, BaseLine, Beardo, Ben Standeven, Bender235, Benji64, Bentley4, Betacommand, Biblbroks, Bicknell660, BierHerr, BillFlis, Bkell, Bkonrad, Blabla34, Blocpark, Bluemoose, Bnetter, Boardup2010, Bobo192, Boing! said Zebedee, Bowlhover, Brandx0, BrownHairedGirl, Bryan Derksen, Bugnot, Buran, CBM, Calmer Waters, Caltas, Can't sleep, clown will eat me, CanadianLinuxUser, Capefeather, Casper2k3, Catgut, Causa sui, CesarB, CheesyBurito, Chocolate Panic!, Chris Howard, ChrisCork, ChrisHamburg, Christopher Parham, Christopher Thomas, Chronolegion, Cit helper, Cjlongfellow, Colin012, Commander Odball, CommonsDelinker, Conversion script, Courcelles, Crabnebula, Crash Underride, Crux007, Cryonic07, Curlymeatball38, Cwilliamsdog, D, DBigXray, DSRH, DV8 2XL, DVdm, DaBenCCC, Dahk, Danhomer, Dar book, Darigan, Darkhelmet322, Darthjarek, David spector, David xie, Dbulldog, Deniska.G, Denorios, DerHexer, Deville, Diannaa, Diego.andree, Discospinster, Djramone, Doczilla, Download, Dr. Reiter, Drplat, Dstary, Dust Filter, Dycedarg, Dysepsion, ESkog, EVula, Eaglizard, Efghij, Ekwos, El C, ElTyrant, Elano, Eleassar, Eluchil404, Enviroboy, Eran, Ericbg05, ErkDemon, Esurnir, Evalowyn, Eve Hall, Exvicious, Ezelenyv, Fangfufu, Fastfission, Favonian, Firefork, Fixup, Fl, Flyer22, Foobar, Foobaz, Fosnez, Fplay, Francisco Albani, Freebirth Toad, Froid, GDonato, GHe, Gaius Cornelius, Gandalf61, Gary King, Gdtc6, Gemini4t, Gene s, General Geers, GenkiNeko, Geoffrey.landis, Gerrardkaka, Gfoley4, Giftlite, Gilliam, Gioto, Glenn, Gmusser, Gogo Dodo, GoingBatty, Grayfell, GregManninLB, GregorB, Grendelkhan, Gurch, Gwib, Gwr2004, HOLYCOWITSME126, Hadal, Hairy Dude, Hall Monitor, Hans Dunkelberg, Hbackman, Headbomb, Heapchk, Hellbus, Henning Makholm, Herbee, HiDrNick, Highlander, Hiided, Hillman, Hueydoc, HumbleAbelard, Hurricane111, Hydra351, Hypnosifl, I am The Inventor, I dream of horses, I80and, IVAN3MAN, Icalanise, Inquisitus, Iridescent, Ixfd64, J.delanoy, JCRules, JFreeman, JJ Harrison, JaGa, Jamesm69, Jasonbook99, JavierMC, Jayc, Jdeuxf, Jdevola, Jean-François Clet, Jeffrey Mall, Jeltz, JephSullivan, Jkasd, Jlacount, John Doe or Jane Doe, Johnbod, Joshlmay, Joyous!, Jusdafax, JustAddPeter, Jyaus, Kablammo, KaiShengHu, Kaini, Kaisershatner, Karol Langner, Kashami, Katieh5584, Kev, Khaosworks, Kheg k, KirtZJ, Kkkdddiii, Klotus7, Kmarinas86, KnowledgeOfSelf, Koavf, Korkscrew, Koweja, Kukini, Kurykh, Kusma, Kwg06516, L Kensington, Landon1980, Lantonov, Lethe, Lightdarkness, Lights, LilHelpa, Looxix, Loren.wilton, Lozeldafan, Lstrings, Luna Santin, MC707, MCTales, Mac Davis, Macy, Mad2Physicist, MadIce, Magikarp 123, Magioladitis, Magnum17x, Magnus.de, MakeChooChooGoNow, Malcolm Farmer, Mandarax, Mani1, Mansouryar, Marisusis, Markdarb, Martarius, Martinp23, Mastertek, Maurice Carbonaro, Maximus Rex, Mbell, McGeddon, MeekSaffron, Meier99, Mephiles602, Mgiganteus1, Mhazard9, Michael Hardy, Michaelas10, Mika1h, Mimihitam, Mindeye, Mitchello, Mkrajenke, Moeron, Morad Abdi, Mpatel, Mprm86, Mrfencey, Mscuthbert, Mutt454, Myasuda, Mygerardromance, MystRivenExile, Naerii, Nakon, Natl1, NatureA16, NawlinWiki, Nellis, Nepenthes, Nerrolken, Neschek, Neurolysis, Night Gyr, Nishantp, Nivix, Noclevername, Nostrum, Nothingofwater, Notjake13, Nuno Tavares, Obolisk0430, Ohms law, Ohnoitsjamie, OlEnglish, Oleg Alexandrov, OneDoubleO, OpinionPerson, Orochi nem0, Orthologist, Oxymoron83, PS2pcGAMER, PainMan, Paine Ellsworth, Palfrey, Panzi, Passive, Paul August, Permenent, Pervect, Peter Fritz, Philbog, Philip Stevens, PhuryPrime, Physicist, Physics16, Piano non troppo, Pianocompose, Pie4all88, Pinethicket, PizzaBox, PlanetStar, Pleasantville, Pmronchi, Poeloq, Polisher of Cobwebs, Portillo, Prickus, Pszeszczep666, Pt, Puffin, Pulu, Qmwnebrvtcyxuz, Quantumobserver, Qwfp, RMHED, Radix, Raidr, Ramirez Sanchez, Razorthe6249th, Rbrwr, ReginaLynn, Regulus000, Remi0o, Renny Bright, RexNL, Rhwawn, Rich Farmbrough, Richbank, Rjwilmsi, Roachmeister, Roadrunner, Rob.derosa, Roboarmy, Roguelazer, Ronark, RoyBoy, Ryulong, S Schaffter, S2000magician, SDaniel, Saberwyn, Sam Hocevar, Sam Vimes, Samrolken, Sapeli, Sarwicked, ScAvenger lv, Sceptre, Scharks, Schmiteye, Schmock, Schrei, Scoobystones, Sdriscoll, Seador, Seaphoto, Seishin17, Seth Ilys, Sgkay, Shanti95, Shauntp, Shell Kinney, Shiftmain7, Shinchan777, Shoeofdeath, Shriram, Silverthorn, Simplemindedted, Sivazh, Sky Attacker, Skysmith, Slightsmile, Smalljim, Smartyhall, Snowdog, Solidsnake 8608, Sord halo, Spencerian, Spherion89, Stabbycat, Stakle4, Stan Shebs, Steve Quinn, Stevertigo, Storm Rider, Stultiwikia, Stwalkerster, Suki77, Superwj5, Suruena, SwitchUK, T3h 1337 b0y, Tarotcards, Tassedethe, Tavilis, Tedp, Tellyaddict, Templarion, Teo64x, That Guy, From That Show!, ThatGuy1212, The Anome, The Matrix Prime, The Thing That Should Not Be, The Wiki ghost, The751, TheGreenMartian, Thebusstop, Thefluffyturtle, Thiseye, ThomasK, Throwmeaway, Tiddly Tom, Tide rolls, Timyau1126, Tobyk777, Topbanana, Totorotroll, Tprentice, Trekphiler, Trusilver, Twang, Twinsday, Tyco.skinner, Ultra megatron, Unique and proud of it, Urvabara, Utcursch, VETrill, VIVEKKHANDELWAL100, Vald, VanishedUser314159, Veraladeramanera, Vicki Rosenzweig, Voorlandt, Vsmith, Vsst, WadeSimMiser, Waggers, Warfieldian, Warhorus, Wayfarer, Wayne Hardman, Wayne Slam, Weregerbil, West.andrew.g, WikHead, Wiki alf, Wikiborg, Will Neal, Windom, Winged Cat, Woohookitty, Work permit, Ww, Wwheaton, Wysprgr2005, Xanzzibar, Xaonon, Xasz, Xmnemonic, Xnuala, Youssefsan, ZICO, ZacharyLevinson, Zargulon, Zchenyu, 1087 anonymous edits Faster-than-light  Source: http://en.wikipedia.org/w/index.php?oldid=494988906  Contributors: 2D, 6birc, 8digits, ANTIcarrot, ATOE, Aarchiba, Aarghdvaark, Aiglard, Ajoykt, Akral, Alextrevelian 006, Alexwcovington, AllGloryToTheHypnotoad, AllanLee, Alodyne, Alphachimp, Alphius, Amakuru, Amalas, Anakin101, Andattaca2010, Andywebby, Angr, Animum, Anr, 205 Article Sources and Contributors Antandrus, Anthony Appleyard, AnthonyQBachler, Antixt, Anville, Anyeverybody, Arabani, ArmadniGeneral, Army1987, ArquiWHAT, Art LaPella, Artistarijit, Ashmoo, Asspladel, Atdotde, Ati3414, Auric, Autonova, Axl, Baffclan, Barticus88, Bastien Sens-Méyé, BatteryIncluded, Beanyfootymad, BenWilson, Bhig3, Bobo123456, Bobo192, Bopomofo, Boud, Bradkittenbrink, Brainssturm, Brandmeister, Brentonboy, Brian Sayrs, Bryan Derksen, Buddy13, Bueller 007, CanadianLinuxUser, Captain panda, Charles Matthews, CharlotteWebb, Children of the dragon, Chris the speller, Chrisempson, Christopher Thomas, Comet Tuttle, Conversion script, Coolleo277, Corambis, Count Iblis, Coyle33, Cracked acorns, Craigsjones, Crazz bug 5, Cryptic, Cuddlyopedia, Curps, Cwolfsheep, D.H, D4vr05, DVdm, Danski14, DariuszT, DarthVadre, Dbachmann, Dchristle, Ddvche, DeLarge, DeadEyeArrow, DeniseMToronto, Deville, Dfeldmann, Dingopup, Dirac66, Dispenser, Diza, DocWatson42, DocumentN, Dome1ioun1, Doogie2K, DrBob, Drbogdan, Dreadstar, Drernie, Drmies, Dyetsu, Długosz, Eaefremov, Ec5618, Eep², Einstein runner, Eisnel, El C, Eliezerke, EllsworthSK, Emurphy42, EncMstr, Ensnaregod, Epbr123, Epeefencer, ErkDemon, EvanTPeoples, Eve Hall, Evercat, Eyu100, Falcon8765, Fbs. 13, Fcn, Feezo, Firehawk1717, Foobaz, Foot, Fosnez, Francis Flinch, Fresheneesz, Fritz freiheit, Fru1tbat, Furby100, Fusion7, GNimtz, Gary King, Geeoharee, GenestealerUK, Geof, Geoffrey.landis, Giftlite, Gilliam, Gimmetrow, Gingekerr, Glenn, Googie k, Grapplequip, Gravitophoton, Green caterpillar, GregorB, Gregory9, Gregwmay, Guanghuilin, Hackwrench, Hairy Dude, Hanfiredfirst74, Haraldthi, Hcobb, Headbomb, Hellsheep, Hillman, Holetel2, Hraefen, Hstdgrypk, HumphreyW, Hydrox, Hypnosifl, IRWolfie-, Iamiyouareyou, Icairns, Icarus3, Icek, Ihope127, Intgr, Ixfd64, Izno, J.Dong820, J.delanoy, JIMCKEE, JNW, JRSpriggs, JWSchmidt, Ja 62, JarahE, Jatoo, Javalenok, JeffBurdges, Jeffme, Jeh, Jeremyl.lmsg, Jeroenr, Jetman123, Jheise, Jimfbleak, Jman1974, Jnivekk, Jo3sampl, John K, JohnBlackburne, JorisvS, Joshua Scott, Justaperson117, Justin Forbes, JustinWick, Jwhinson, Jwinius, KasugaHuang, Kemeab, Kenect2, Keraunos, Kilcoyne, Kim Dent-Brown, Kipton, Klubbit, Knotnic, Korporaal1, Kostatoronto3, Kronnang Dunn, Kumagoro-42, Kyle112, Lainagier, Larry V, Latitude0116, Latka, Ldussan, LeContexte, LeYaYa, Leflyman, Lenoil, Light current, Likebox, Locke Cole, Logicus, Loudenvier, LtNOWIS, LukeSurl, M-le-mot-dit, M1ss1ontomars2k4, MIKQ, MaizeAndBlue86, MakeRocketGoNow, Manscher, Mark J, Martin Hogbin, MarxistRevolutionary, Matthew, Mattymattyblack, Mbell, Mcfly, Measles, Meeso, Megasquid500, Member, Mephiles602, Michael C Price, Michael Hardy, Michael riber jorgensen, Michaelbusch, Michaelfloyd, Mike Peel, Mild Bill Hiccup, Mindmatrix, Minutes, Modster, Moroder, Mr.viktor.stepanov, Mufka, MuthuKutty, Myrin1, Nairebis, Namboodiriarun, Nashpur, Navigatr85, Nhandler, Nima Baghaei, Nistra, Nixer, Noclevername, O18, Odysseus94, Oklahoma3477, Oleg Alexandrov, Oliphaunt, Orc lover, Ownedroad9, Oxnard27, PS4FA, Paine Ellsworth, Pakaran, Palpatine, Parthdu, Pdcook, Peanutjake, Pedro, Pef333, Percy Snoodle, Petri Krohn, Phisolire, Phys, Physicks, Pingveno, Prickus, ProfessorToomin, Proxima Centauri, Psyfyman81, Puddytang, Quickcrazy78, Quidproquo2004, R'n'B, R.e.b., RPaschotta, Radon210, Railwayfan2005, Randyis, Rangi42, Rapierian, Rasmus Faber, Rastamees, Rattlesnake, Real NC, RenagadeX, Rep07, Revth, RexNL, Rich Farmbrough, Richard D. LeCour, Richard.decal, Rickyrab, Ripe, Rjwilmsi, Roadrunner, Robodude2000, Rockfang, Rockstone35, Roger wilco, Roger491127, Ron g, Rorrima, Rory096, Rotiro, Rwflammang, SHCarter, SWAdair, Sabre Knight, Sad squirrel, Sam Blacketer, Sambc, SamuelRiv, Sayden, Sbharris, Scwlong, SebastianHelm, Seleucus, Serpentduv, Sesshomaru, Sha-256, Shadowjams, Shattered, Shiftnoise, Signalhead, Sim, Simoes, Sinus, Siroxo, Skippydo, Skybon, Soap, Sopholatre, Spike Wilbury, Spinningspark, Starfyredragon, Starstriker7, Sted, Steve Quinn, Strait, Superborsuk, Suvadip 192, T57yh54t5gbhet, TJSwoboda, TMaster, Tealwisp, Teque5, Tercer, Terra Novus, Tesi1700, Tetrahedron93, Th1rt3en, The Final Dream, The Rambling Man, The Thing That Should Not Be, TheLivingHeiromartyr, Theroadislong, Think outside the box, This lousy T-shirt, Thorrstein, Timc, Timeshifter, Timwi, Titodutta, Toby Bartels, Tom Lougheed, TonyMath, Topbanana, Tornbl, TorontoFever, Tparameter, Tpbradbury, Tregoweth, Triwbe, Trovatore, Tyco.skinner, Uioplk, Unicorn234, Urhixidur, UtherSRG, VHrock96, Val42, Vampus, Vandalz0rs, Venny85, Verson, Vicki Rosenzweig, Visuall, Vranak, Vyznev Xnebara, W1k13rh3nry, WMC, Waldir, Waleswatcher, Waltpohl, Warut, WayneC, Weaponofjedi, WhisperToMe, Wiendietry, Wiki Raja, Wikipelli, Wildstarlights, Will Bradshaw, Wolfkeeper, Wolfrock, Wormcast, Wtmitchell, Wuffyz, X-Bahamut, Yawe, Yellowdesk, Yipdw, Zack, ZaphodWikibrox, Zgstehdyp, Ziiv, Ziofil, Zzuuzz, Еdit, ‫ 767 ,ﻫﻤﻨﺸﯿﻦ ﺑﻬﺎﺭ‬anonymous edits Chronology protection conjecture  Source: http://en.wikipedia.org/w/index.php?oldid=490148293  Contributors: Acdx, Agamemnon2, Branddobbe, Bryan Derksen, Burns flipper, Cructacean, David-Sarah Hopwood, Destynova, Doczilla, Giganut, Hairy Dude, Hillman, Hmonroe, Hypnosifl, Inging, Ironholds, Jag123, Khaosworks, Letranova, MadIce, Mdwh, Michael C Price, Mpatel, PaulLev, Pt, Raidr, Rclark7083, Stormie, Sudhakarang, Thanos6, The Anome, Tioover, Tmxxine, Topbanana, Work permit, Xmoogle, Ywong137, Zandperl, 31 anonymous edits Philosophy of space and time  Source: http://en.wikipedia.org/w/index.php?oldid=492093091  Contributors: 2over0, Aknegi88, AlMac, Alan Liefting, Allan Zade, Alro, Anarchia, Andres, Apyule, Arthur Rubin, Banno, Batmanand, BenFrantzDale, Bengalor, BrideOfKripkenstein, Can't sleep, clown will eat me, Clicketyclack, DV8 2XL, DabMachine, Dariusmartens, Dawn Bard, Deeptrivia, Dorikinusa, Dpv, Dr. Günter Bechly, Drkhan77, Dyanne Nova, Dypteran, EPM, Edward, El C, Elsehow, Enormousdude, Eric.cavalcanti, Fredrik, Fvw, Fyyer, Gary King, GeoGreg, Gerocus, Giftlite, GoingBatty, Gregbard, Gurch, Harald88, Hectorfazio, Henry Delforn (old), Heron, Hjelmerus, Hkfortytwo, Hyarmendacil, IZAK, Icairns, Irish09er, J8079s, JCNSmith, JFlav, JHunterJ, JaGa, Jagged 85, Japanese Searobin, Jheald, JimWae, JuliusJeff, Kaifer, Karol Langner, Keenan Pepper, Khazar, Kimse, Knucmo2, Komponisto, Loxley, Macmelvino, Malreux1, Matthew Kynaston, Maurice Carbonaro, Maximus Rex, Michael Hardy, MrOllie, Mushin, Neutrality, Olivier Mengué, OneMarkus, Overlord, Paradoctor, Peterdjones, Phe, Phys, Pjacobi, Pollinosisss, Postmodern Beatnik, R'n'B, Raoul NK, Reflexinio, Renamed user 4, Ricky81682, RobinK, Sam Hocevar, Shahidur Rahman Sikder, Shalom Yechiel, Shlomke, Sigil7, Skyy Train, Slash, Stephen Bain, Stijn Vermeeren, Syncategoremata, Tanzeelat, Thehotelambush, Timetraveler-33, Timothyyuen, Tomisti, Tstrobaugh, Uncle G, Vanished User 0001, Wgrey, Whizmd, WithSelet, Wnt, Xinyu, Yamara, Yone Fernandes, 166 anonymous edits Eternalism  Source: http://en.wikipedia.org/w/index.php?oldid=491839536  Contributors: Ahoerstemeier, Anarchia, Aurigans, Banno, Bryan Derksen, C mon, Canderson7, CesarB, Cessator, Dangerous3000, David Latapie, Derek Ross, Dori, Drkhan77, Dypteran, Dysprosia, Editor with a background in philosophy, Ereshkigal1984, Fairandbalanced, Falsetto, Filthish, Foelectric, Fram, Fruit.Smoothie, Fvw, Geometer, Gregbard, Happinessiseasy, Headbomb, Heron, Hypnosifl, Imagine Reason, Jeff Relf, JimWae, Jiohdi, KSchutte, Klimov, Kubrick, Lantonov, Lar, Livitup, Mackensen, MarXidad, Max David, Michael C Price, Michael Hardy, Modabid, MrMontag, NBeale, Neliobelmont, Neparis, Peterdjones, Postmodern Beatnik, RJFJR, Reidlophile, Rjwilmsi, RockMagnetist, Ron g, Sam Hocevar, Sburke, Sillyfolkboy, Slash, Stevenmitchell, The Anome, Tlogmer, Tmopkisn, Tom dl, UnderHigh, Vyznev Xnebara, Wereon, Woohookitty, Yamara, Zero Thrust, 87 anonymous edits Determinism  Source: http://en.wikipedia.org/w/index.php?oldid=493167379  Contributors: 1ForTheMoney, 1dragon, 50ideas, A45b22chp, Adam Conover, Adhib, Ahpook, Ale jrb, Alexander256, Alexjohnc3, Allens, Allforfree, Anarchia, Anarcho-capitalism, Andkore, Andre Engels, Andres, Andycjp, Anomalocaris, AntOnTrack, Arado, Architypist2, Archivingcontext, ArnoldReinhold, Asdfgh07, Atmapuri, BACbKA, BD2412, Bacab, Barabum, Bbobjs, Bedges McClaverty, Belovedfreak, Benandorsqueaks, Betacommand, Bilby, Bill Stock, Bkell, Bobo192, Brian0918, Brighterorange, Bryan Derksen, Btyner, Buckwheatandgrits, BuffaloBill90, Byelf2007, Cacycle, Caroldermoid, Cassowary, Cazort, Centrx, CesarB, Cesarconcepcion, Chaojoker, Chaos, Chealer, Chicnstew, Chill doubt, Chinesearabs, Chris kupka, ChrisCork, Circeus, Clivestaples, Cloudblazer, Cmsreview, Correogsk, Crosbiesmith, Curb Chain, D1152029, DYLAN LENNON, Dalmoz, Danmaz74, David R. Ingham, Deprifry, Dhammapal, Dicorpo, Diego Azeta, Dishcmds, Doctorage, Dpb2104, Dragon's Blood, Drpickem, Dsp13, E235, EIFY, Echoaa23, Edcolins, Edward, El C, ElizabethJM, Emufarmers, Equendil, Erkekjetter, Evercat, Exigentsky, Falcorian, Fenrisulfr, Fibo1123581321, FishFarmer, Flammifer, Florkle, Flyguy649, ForesticPig, Freakofnurture, Fredkinfollower, Fubarius, Funandtrvl, Future Perfect at Sunrise, Gabrielxz, Galwhaa, Gary King, Giftlite, Glenn, Go for it!, Godardesque, Gongshow, Goudron, GovStuff, GraemeL, Graham.Fountain, Gregbard, Griffin700, Grunt, Gugilymugily, Gurch, Gwen-chan, Gwernol, Hadal, Hamiltondaniel, HarryHenryGebel, Headbomb, Hogne, Ig0774, Incompetnce, Infinity0, Info D, Infovoria, Infrogmation, Innerear, Iridescent, Iulius, J Milburn, J.delanoy, JH-man, JWSchmidt, JaGa, Jak123, Jfp2006, Jim E. Black, JoeForest99, Joedahlquist, Jonathan Enderle, Jordgette, Jorfer, Joshuareid, Juan Ponderas, Jud Evans, Justin Satyr, K0hlrabi, KJS77, KSchutte, Kalogeropoulos, Karol Langner, Kbodouhi, Kenneth M Burke, KeyStroke, Kieff, Klubbit, Kman543210, Knightshade, Koltaaz, Korcevic, Kristofer0, Kzollman, Lambiam, Legare, Lester, Lestrade, Letranova, LieAfterLie, LilHelpa, Louis Waweru, LoveMonkey, Lucidish, Lumoslindsay, MSGJ, Machine Elf 1735, Makeemlighter, Malo, Marasmusine, Marc Girod, Matt Heard, Max David, Mcc1789, Meldor, MichaelExe, Mijcsmu, Minutes, Mitsube, Mladifilozof, Mmyotis, NBeale, Neelix, Nihiltres, Nike787, Nk, Nkf31, Nodem, PFR, Pacific PanDeist, Paradisevalleycampground, Patrick Grey Anderson, Patrick0Moran, Paul Murray, Pdcook, Pedant, Peterdjones, Pfhorrest, Pgk, Phil Sandifer, PhilKnight, Philosophus, Phlegat, Phuz, Pigman, Pinar, PinchasC, PitchBlack, Plumbago, Prumpf, PublicSquare, Qvamp, R Lowry, R'n'B, R6144, RL0919, Raghavb, Ramarama12, Ratzgame, Rbonvall, Rebent, Red8aron, Renamed user 4, Rfl, Richard001, Richfife, Rjstanford, Rjwilmsi, Robert P. O'Shea, Robertdorsky, Robin klein, Rodri316, Rootbeer, Rstevensonatwiki, SP-KP, Saeed.Veradi, Sammygod, Sardanaphalus, Scwlong, Sdorrance, Sehrgut, Serpent's Choice, Sethmahoney, Shadowmuse, Siddhant, Skeletoria, Slightsmile, Sloth monkey, Smeira, Smyth, Snalwibma, Snoyes, Sophist234, Spencer, Splash, Stancollins, Steohawk, Stephen Bain, Stephen Poppitt, Stevenmitchell, Stevertigo, Stijn Vermeeren, Surferhere, Sygmn, Tedickey, Tesseract2, The Anome, The Lizard Wizard, The One Philosopher, The Thing That Should Not Be, The world deserves the truth, Thepluralist, Thingg, Thorwald, TigerShark, Tired time, TonyMath, Toussaint, Triggtay, Troa, U of H Greek, Ubiq, Unijorn, UnitedStatesian, Vanished User 1004, Vegetator, Veilrap, Viriditas, Visualerror, Waggers, Wahabijaz, Walkiped, Wavelength, Weregerbil, Wetman, WhiteC, WikHead, Wilsonredd, Wisco, Wmahan, Wmpearl, Wolfdog, Xaosflux, Yair rand, Yamara, Yerpo, Zachlipton, 573 anonymous edits Free will  Source: http://en.wikipedia.org/w/index.php?oldid=495188899  Contributors: 1066william, 1dragon, 1skyboy, 2010philosopher, A Musing, A. Parrot, AC+79 3888, Aaron Schulz, AbsolutDan, Acroterion, Adriansrfr, Aeusoes1, Ahoerstemeier, Alienlifeformz, Alienus, An Eternal Now, Anarchia, Andre Engels, Andres, Andrew Lancaster, Andrewlp1991, Andyiou52345, Antique Rose, Antoni Barau, Apoc2400, ArchetypeRyan, ArnoldReinhold, Artoasis, Arunsingh16, Asbestos, Ash, Astronautics, Atlan, Avecmonami, Avicennasis, B4hand, BACbKA, BD2412, Babub, Baddox, Banedon, Banno, Bekus, Belovedfreak, Bender235, Better Than You At Everything, Bevo, Billy T2, Bkkbrad, Bkwillwm, Blaircjohnson, Bmorton3, Bobblewik, Bobdoyle, Bobo192, Borock, Brad101, Bratsche, Brighterorange, Brinticus, Brunoton, Bryan Derksen, Bukkake bud, Bummylikery, Cacycle, Cakeyice, Calwatch, Capricorn42, CarlKenner, Carloveldema, Carlstreator, Cascadiaa, Cat Cubed, Catgut, Cdg1072, Cfcapps, Chameleon, Charles Matthews, CharlesGillingham, Charlieleach, Chris 73, Christofurio, Christopherjfoster, Chun-hian, Ckatz, ClockworkSoul, Cmsreview, Codex Sinaiticus, Coelacan, Coleman Glenn, CommonsDelinker, Conti, Cosmic Latte, Crowley, Cutler, Cyrus XIII, DA3N, DARTH SIDIOUS 2, Damifb, Dan56, Dana boomer, Dane Sorensen, Dark Shikari, David A Bozzini, David Gerard, David Ludwig, Dbergan, DeXXus, Decltype, Defyn, Dekaels, Deleet, Denaar, Denisutku, Denny, Dferruolo, Dhammapal, Diberri, Dino, Discospinster, Dismas, Dispenser, Dobrich, Doctorage, Dodiad, Dp462090, DrKiernan, Dreadstar, Drilnoth, Dume7, Dysepsion, Dzhuo, E235, EPadmirateur, ESkog, EagleFan, Edhubbard, Ejectgoose, Ejmasi, El C, EliasAlucard, Emc2, Empty Buffer, EncMstr, Epolk, Equilibrial, Erianna, Erinmulcaire, Eu.stefan, Evercat, Everyking, Everything Else Is Taken, FF2010, Fairandbalanced, Fanboy, Felix Dance, Fintor, Flammifer, Flaviusvulso, Fnielsen, FocalPoint, Foolcontact, Fram, FrancisTyers, Frank Romein, FrankTobia, Fritzpoll, Frongle, FullMetal Falcon, GManNickG, Gabbe, Gaius Cornelius, Galoubet, Garamond Lethe, Gary D, Gary.goldberg.md, Gaytan, Gene Nygaard, Geneb1955, Ghaz, Gianfranco, Gibbzmann, Glane23, Go For It, Gregbard, Gsp, Haileywhat, Hamiltondaniel, Harnad, Harro5, Harry Stoteles, Headbomb, Heironymous Rowe, Hemanshu, Hensa, Herman88, Heron, Hesperian, Hgilbert, Hoverfish, Hu, Huadpe, Hut 8.5, IRWolfie-, Iamthedeus, Ichormosquito, IdahoEv, Ig0774, Ilickeggbeaters, ImperfectlyInformed, Infinity0, Innerear, Invisifan, Iridescent, Irishguy, Itschris, J.delanoy, JASpencer, JForget, JHunterJ, JWSchmidt, JaGa, Jackrm, Jacob.jose, Jacquerie27, James Orr, Jan van Male, Jarble, JasonCupertino, Jasperdoomen, Jauhienij, JayJasper, Jayron32, Jbricklin, Jcanfi2, Jdforrester, Jdonohue, Jeraphine Gryphon, JeremyA, Jerryfrancis, Jfbennett, Jfdwolff, Jgardner, Jguk, Jhbeck23, Jimfbleak, Jimothytrotter, Jimwilliams42, Jiohdi, Jj1236, Jobin RV, JocK, Joelr31, Johnrpenner, JorisvS, Jossi, Jusdafax, KHM03, KSchutte, Kaelus, Karol Langner, Kctucker, Kelson, KenBailey, Kevin aylward, Khatru2, Kia 80, Kinkreet, Kjells, Klenod, Kleuske, KneeLess, Knowledge for All, Koavf, Kozuch, Kp grewal, Krich, Kukini, Kumioko (renamed), Kusma, Kyle1278, Kzollman, La goutte de pluie, Lacatosias, Lambiam, Larklight, Ledouch vi britannia, 206 Article Sources and Contributors Leptictidium, Lestrade, Letranova, Levineps, Li3crmp, Lightlowemon, Lilac Soul, LittleHow, Livajo, Livedevilslivedevil, Llamabr, Loodog, Looie496, Lotje, Lova Falk, LoveMonkey, Loyan, Lucidish, Lupin, MJ94, MLearry, MPerel, Mac Davis, MadSurgeon, Magioladitis, Makeswell, Manasgarg, ManchesterPoet, Mandarax, Manis404, Marinus Bier, MarkCTest, MartinPoulter, Master Jay, Mathonius, Mattisse, Mauls, Maurice Carbonaro, Mav, Max Velmans, Mayooranathan, Mbell, Mboverload, MeUser42, Mel Etitis, Metron4, Michael Hardy, Mifter, MikalZiane, Mike R, Mike.lifeguard, MisfitToys, Mkmcconn, Modulatum, MonkeeSage, Mostly Zen, Moxy, Mporch, MrBoo, MrSteve, Mrh30, Msasscts, Myscience, NBeale, Nakon, Nancy Danielson, Narssarssuaq, Nathanielfirst, NatureA16, Neelix, Neilbeach, Neko-chan, Neo Deacon, Netoholic, Neuralwarp, Nicke Lilltroll, Nikodemos, Nirvana2013, Nk, No Account, Noel Streatfield, Nono64, Notjake13, Nsh, Oculi, Onealej, Opuntiaflower, OracleofTroy, Otashiro, Outriggr, Owl, Owlmonkey, PHV, Pacas, Paine Ellsworth, Paragon, Patrick Grey Anderson, Paul Stansifer, Pedant, Peterdjones, Pfhorrest, Pgan002, Phantomsteve, Phil Sandifer, Philosophygeek, Pigman, PinchasC, Pinethicket, Plabarca3, Playanaut, PokeHomsar, Pollinator, Pollinosisss, Poor Yorick, Populus, Porkchop117, Preda, Prodvocalist, Prunesqualer, PseudoSudo, Pukkie, Quangbao, Quizkajer, Quodvultdeus, R Lowry, R. S. Shaw, Radak, RainbowCrane, Raj2004, RedRollerskate, Redthoreau, Reiddp, Reidlophile, Reinyday, ReluctantPhilosopher, Renamed user 4, Rfl, Rholton, Rich Farmbrough, Richard001, Richardbrucebaxter, Rick Norwood, Rintrah, Rjanag, Rjwilmsi, Robert P. O'Shea, RobertG, Robin klein, Rogerd, Roisterer, Romarin, Ronhjones, Rootbeer, Rspeer, Rtyq2, Rubenarslan, Rursus, Ruud Koot, Rwtbrad1, Ryan250, SGBailey, Sabbut, Sadi Carnot, Sagaci, Sam Clark, Sam Spade, SandyGeorgia, Santa Sangre, Schneelocke, Sethmahoney, Sfahey, Shadowlynk, Shadowthedog, Shantavira, Shlomi Hillel, Shmilyshy, Shoaler, Sidmow, SirAglet, Sjakkalle, Sjö, Skomorokh, Skywalker, Sluzzelin, Smilesfozwood, SnowFire, Snoyes, Soewinhan, Solipsist, Somerset219, Soporaeternus, SpNeo, SpaceFlight89, Spellraiser, SpikeToronto, Spitfireatme, Srds, Srnec, Staffwaterboy, Sundar2000, SuperHamster, Surferhere, Suslindisambiguator, Susurrus, Swagology, Syamsu, Symane, TBT, TBadger, Tassedethe, Tesseract2, The Anome, The Rambling Man, The Thing That Should Not Be, TheZapster, Thejimbaker, Thingg, Thomas Aquinas, Timl2k4, Timwi, Tisthammerw, Tktktk, Toowise, Tpbradbury, Treisijs, Tsop, Twiin, Uber crowds, Ubiq, Unint, Untold knowledge, Val42, Vassyana, Vegetator, Vejlefjord, Versageek, Vesal, Visarga, Visualerror, Voluptuous Nature, Vsmith, W, Wanderer 034, Warut, Wavelength, Weregerbil, Wereon, Wiki Raja, Wikieditor1988, Wikipedical, William M. Connolley, Willjzuke, Willtron, Wjkiely, Wojtekr, Wolfdog, Woohookitty, Woz2, WraithM, Xdvr, Xxglennxx, Xzuiko, YH1975, Yamara, Yom, Ype, Zar, ZarkOmicron, Zenbullets, Zenohockey, Žiga, 789 anonymous edits Time travel in fiction  Source: http://en.wikipedia.org/w/index.php?oldid=490994303  Contributors: ***Ria777, AMglobal, AdmiralWinfield, Againme, AirLiner, AlMac, Alvestrand, Andareed, Andy120290, Andyroid, Angmering, Armando Alvarez, Art1991, Asnallar, Atomsmasher86, AtticusX, Auric, Awtaylor2, Axem Titanium, B-bones69, Basique, Bdushaw, BenoitRen, Beyond My Ken, BillFlis, Billdorr, Biontenagent2008, BookGuru, BreathingMeat, Brokenyin, Bronzethumb, Bryan Seecrets, Buckleycloud, Budzamom, BurnDownBabylon, CNash, CStyle, Cambalachero, Capt Jack Doicy, CaptainWesker, Centrx, Cerebellum, Ceyockey, CharlotteWebb, Chillum, Ckatz, Clarkbhm, Cmdrjameson, Coreman, Courcelles, CrazedNinja, Crouchbk, DJ Clayworth, DStoykov, DanDs, Danlev, Darktruth2, David Gerard, Decltype, Deor, Dharmabum420, Dhricenak, Doctor Nemesis, Doczilla, Drdrwilliams, Dreadstar, Duoduoduo, Dyslexic agnostic, EEMIV, Emil den kule, Error, Escape Orbit, Ethan, Expendable, Faizdanyal, Falconer, Farrahi, FigmentJedi, Fijiman, Fitch, Fritz Saalfeld, Frog47, Gaius Cornelius, Galactic war, Garethfc, Geoffrey.landis, GracieLizzie, Grstain, Gs68, GusF, Hahnchen, Haoie, Hegowski, Hegria66, Henry Merrivale, Hetar, Hiphats, HollyI, Hypnosifl, Igordebraga, Interiot, Inuyasha20985, IslandHopper973, J Greb, JBellis, JHMM13, JQF, Jack turnip, Jagged 85, JasonAQuest, Jc37, Jcbarr, Jeffro77, Jfire, Jigj119, Jogers, John Doe or Jane Doe, JohnI, Jojit fb, Jon Ascton, JoshuaZ, Julyda4th, K-UNIT, KC109, KF, Karam89, Keenan Pepper, Kelisi, Kgf0, Khaosworks, Kitia, Koncur, Kookyunii, Krellion, KrytenKoro, Kungfuadam, LDHLontz, Lady Aleena, Larry158, Lee J Haywood, Lenoxus, Liam Skoda, Loadmaster, Lord ignus, Lyle Swann, MER-C, Magiclite, MakeRocketGoNow, Mareino, Markcmarino, Masaruemoto, Matthew, Matthew Yeager, Maver1ck, Mboverload, McGeddon, Mcgyver5, MegX, Mermaid from the Baltic Sea, Miami33139, Michael Hardy, MichaelGranados, Michaelritchie200, Mike Klaassen, Mike Peel, Mikejstevenson, Milesnfowler, Minaker, MisterHand, Misza13, Mklobas, NaminesPetals, Nareek, NeilEvans, Nerrolken, Nhackler, Nickersonl, Niffweed17, Nikki311, Obankston, Otto4711, Paul S. Cilwa, PaulLev, PaxEquilibrium, Pegship, Peter S., Pikawil, Piotrus, Pippin Bear, Polygonfla, Prolog, Qzurr, R'n'B, Radagast83, Ragzouken, Ralkarna, Ravengambit, Rebelofnj, Red Polar Bear Ranger, RedOrange&Blue, Redeagle688, Rhindle The Red, Rholton, Rjwilmsi, Robertd, Robina Fox, Roger McCoy, Ronny corral, Rukario639, Saintgermain777, Salamurai, Scifireader, Scorpion48, Sdsouza, SeanDuggan, Shawn [email protected], Signinstranger, SimonLeeAuthor, Slashme, SleepyGuy, Sonic Shadow, Sonicsuns, Soxos, Sp33dyphil, StAkAr Karnak, Stu-Rat, Stymphal, Sunilrajguru, Superml, Symbolt, T-borg, TKD, Tabletop, The Tramp, The prophet wizard of the crayon cake, TheHYPO, Thetrick, Thiseye, Tidus the BlitzStar, TimeHorse, Timeflyer, Tobias Bergemann, Travis Wells, Trekphiler, Trish ferguson, Val42, Vchimpanzee, Vfcrescini, VolatileChemical, Vossman, Waldir, WeatherExperiment, Weregerbil, Wikibiohistory, Woodwynlane, Xander the shadow, Yamara, Yann, Yobmod, Zoicon5, Zvis, 382 anonymous edits Parallel universe  Source: http://en.wikipedia.org/w/index.php?oldid=494643049  Contributors: *Ulla*, 3family6, 5Q5, 78.26, A Softer Answer, Ad Nauseam, Agent 86, Ahjwiki, Ai4ijoel, Albert.a.jackson, Aldaron, AlexChurchill, Amoffit, Andrew K. Zimmerman, AndrewHowse, AndrewJD, Andymarczak, Animehorsegirl, AnonymousIdiot, Another disinterested reader, Apparition11, Archola, Arctic.gnome, Arjayay, Arpingstone, Aspects, Awbeal, Axem Titanium, BD2412, BPK2, Bacchus87, Barraki, Basique, Begoon, Berig, Bgmax2, Biosaber, Blake-, Bobblewik, Brandonrc2, Braxiatel, Brockert, Bryan Derksen, Bryanpeterson, Bud0011, BulletBillTime, CSTAR, Calibanu, Cantus, Cat's Tuxedo, Catapult, Celique, Centauri, Cezarika1, ChrisHodgesUK, Christopherlin, Chronolegion, Cjewell, Closedmouth, Closettrekker, Cokeandpoprocks, Colonies Chris, Comrade Graham, Cooksey, Courcelles, Coyoty, Cpt. Oats, Crystallina, CyberSkull, Cyklopas, Cyro, DFS454, DV8 2XL, DaichiS4815162342, Damian Yerrick, Daniel J. Leivick, DannyF, DannyZ, Dbachmann, Dca5347, Delirium, Dexter11235, Discospinster, Dodger, Dodopod, Dogaroon, Dpv, Drake Clawfang, Drew First, Dshfhgsfhadhdsf, DyslexicCrayon, E03bf085, Ebonmuse, El C, Eldarone, EliasHoweNash, Ellsworth, Energicko, Enviroboy, Epbr123, Evercat, Evertype, Everyking, Fabartus, Facts707, Faster than C, FaustX, Feydey, Firsfron, FixerMX, Foodmaster, Foosher, Fredrik, Fui in terra aliena, GMcGath, Gaius Cornelius, Gcapp1959, Gdm, Geniac, Goldfritha, Goniochromism, Griffin700, Ground Zero, Grovers, Grubber, Gwernol, Haem85, Hanjunjade, Harxor, Hibana, Hikui87, Hmains, Hochnebel, Horawiki, Hu, Hula Hup, Hypnosifl, IAmTheCoinMan, ISD, Iancarine, Igordebraga, Insanity Incarnate, Interlingua, Iridescent, JAF1970, JIGZ, JIP, JONJONAUG, JQF, Jack turnip, Jagged 85, Jahudson1, JamesAM, JamesB3, Jason Quinn, Jc37, Jenattiyeh, JerryFriedman, Joecab, John of Reading, JohnDBuell, JohnnyChicago, Joncolvin, JoshuaZ, Josiah Rowe, Junyi, Kaobear, Kate, Katsesama, Keeves, Ken Gallager, Kevinalewis, Khaim, Khaosworks, Khatru2, Khazar2, Khoikhoi, Kineticman, Knowledge Seeker, Koavf, Kookyunii, Koweja, Krazykillaz, Kryptonite Kid, Kwekubo, LOL, Lefty, Lemonv1, Lesfer, LeyteWolfer, Liftarn, Lightmouse, Lihaas, LilHelpa, Linas, Loremaster, Lost Banana, Lotje, Lowellian, Lupo, M4701, M4bwav, MECU, MK2, MSchmahl, MZMcBride, Machine Elf 1735, MadIce, MakeRocketGoNow, Makron1n, Mandarax, Marcok, Mark K. Jensen, Martarius, MathMartin, Matt Chase, Max Schwarz, Maxim, Maywee, Mbell, Mfu254, Mike Klaassen, Mild Bill Hiccup, Mintleaf, Miriemirie, MisterVodka, Mklobas, Modemac, Mohanprem, Monedula, Montgomery '39, Moorem92, Mphorsley, Mr d8a, Msavidge, Mwtoews, Myofilus, Mythsearcher, Nagelfar, Narsil, NawlinWiki, Nehrams2020, Netkinetic, New World Man, Noclevername, Nv8200p, Ohaider, Oliver Pereira, Olivier, Onionmon, Oreolvrs1987, Oxymoron83, Pablo-flores, Papa November, Pcarbonn, Pejhman, Peter Grey, Petrarch, Pfahlstrom, Philip Stevens, Philip Trueman, PigFlu Oink, Pikawil, Planck0, Prodego, Progressive19, Psychopoet406, Puneeeetjain, Recharge330, Redlock, RepublicanJacobite, Rgollum, Rhindle The Red, Rjwilmsi, RlyehRising, Robo37, Rohit Vaidya, Roygbiv666, Rscoular, Ryanbomber, Ryulong, Saccerzd, Sandstorrm, Saswann, Satansrubberduck, Scottinglis, Screenwriter72, Seaphoto, Sebras, Seisatsu, Semper discens, SeniorInt, Senjuto, Sfufan2005, Shadowjams, Shanthehan, ShaunMacPherson, Shsilver, Sidewinder468, Skier Dude, Sleetacon, SmartGuy Old, Smjg, Snowolf, Sodmy, Splash, Spug, Stephenb, Strannik, Streona, Susurrus, TAMilo, TBrandley, TMC1982, TPIRFanSteve, TTE, Tamfang, Tassedethe, Template namespace initialisation script, Tenebrae, Thanos777, That Guy, From That Show!, The Anonymous One, The Thing That Should Not Be, TheEditrix2, TheRealFennShysa, TheodoreLarson, Thinking of England, Thu, Thunderbird2, Tiinapayson, Tim!, Topbanana, Tphi, TracyRenee, Trainik, Trainra, Trausten2, Tree Biting Conspiracy, Tuur, Tyger63, UberMan5000, Uclafalcon, Utcursch, VKokielov, VanishedUser314159, Videmus Omnia, WBardwin, Waggers, Wapcaplet, Wayland, WebTV3, Webwarlock, Wednesday Next, Wereon, WhisperToMe, Whysanitynet, Wild ste, Woken Wanderer, Woohookitty, WpZurp, Wraithdart, X!, Xelanared, Yobmod, Yworo, Zanimum, Zomic13, Zythe, Zzombie, 608 anonymous edits Alternate history  Source: http://en.wikipedia.org/w/index.php?oldid=495482628  Contributors: -Midorihana-, 5Q5, ARTEST4ECHO, Aaron of mpls, Abelson, AccountName1222, Achmelvic, ActiveSelective, Adam Carr, Adam Keller, Adam keller, Againme, Ahasuerus, Airframe101, Airminded, Ajd, Akiyama, Al Lemos, AlMac, Alai, AlainV, Alan Millar, Alansohn, Alarob, AleatoricConsonance, Althist1, Andre Engels, Andreas Kaganov, Andrew Levine, Angusmclellan, AnkhMorpork, AnnaFrance, Anne McDermott, Anomalocaris, Ansh666, Antonrojo, Apenpaap, Apo-kalypso, Arado, Arcadina, Arnoox, Aroundthewayboy, Artemis-Arethusa, Arthur Frayn, Arvindn, Asteriks, Auric, AusJeb, Aymerik, BLineToWhen, BPK2, Barsoomian, BehemothCat, Beland, Belovedfreak, Betacommand, Binabik80, Bjones, Blackbird 4, Blackhawk66, Blue403, Bluejay Young, BoLingua, Bob on a Bike, Bobblewik, Bobo192, Bojan, BorgQueen, Bosco13, Bowlhover, Branddobbe, Brando130, Brion VIBBER, Briony Coote, Bryan Derksen, Bubbleboy987, CFLeon, Caiyu, Cal 1234, Calibanu, Calistemon1, Caltas, Can't sleep, clown will eat me, Cancun771, Carelmackenbach, Carey Evans, Cast, Catpedantic, Cevpar, Chad Gerson, Chairboy, ChairmanR, Chameleon, Charlene.fic, Chbarts, Cheesemonkey11, Chingo360, Chlewey, Chowbok, Chris Oakley, Chris the speller, Chrisch, Chzz, Cirt, Cjperritt, Cocytus, ConorGMoran, Conversion script, Courcelles, Czolgolz, DReifGalaxyM31, DagosNavy, Dale Arnett, DaleWatt, DanMS, Dana boomer, DarkHorizon, Davek121, Davichito, David Latapie, DavidA, Dawn Bard, Dca5347, Deadlyfish, Decumanus, Dekisugi, Demos99, Derekbd, Deville, Dialectric, Dimts, Djdaedalus, Dking, Dmacgr 22, Dmmaus, Doc W, DocWatson42, Dom Kaos, Donreed, Doshindude, DougWise, Download, Dpaajones, Dposte46, Dpr, Dreamafter, Dybryd, ESkog, Eaglestorm, Ed Poor, Edward, Eleos, Emperor, Emperor of Rockingham, Emurphy42, Erisie, Error, Espoo, Euchiasmus, EurekaLott, Evercat, Everyking, Everyme, Evil Monkey, Evil saltine, Fabartus, Fadethebutcher, Falcon8765, Fanx, Fearlessweaver, FilipeS, Fitch, FiveIronFlip, Flexxx, Flowerpotman, Fratrep, GABaker, GCarty, Gaius Cornelius, Galanx, Gerry Lynch, Gilemon, Gioto, Glen Finney, Goldfritha, Goltz20707, Gracenotes, Grahamdubya, GreatWhiteNortherner, Ground Zero, Growltiger, Grutness, Gryphon044, Gtrmp, Gun Powder Ma, Guy Harris, Gwalla, GwydionM, Hajor, Hannu, Harald Hansen, Harxor, Hede2000, Henry Dalton, Henrydms, Heron, Hexhand, Hillsc, Historyguy, Hmains, HodginsBackmaker, Hu, Hugo999, Hv, Hyperionsteel, Hypnosifl, I hate the system, IJzeren Jan, ISD, IainP, Iainscott, Ian Montgomerie, Ian Pitchford, Iceberg3k, Ich, Imperator3733, Ingolfson, Interlingua, InternetMeme, Isomorphic, J.delanoy, JAF1970, JCCyC, JCDenton2052, JForget, JLaTondre, JMLofficier, JTGILLICK, JaGa, Jagged 85, Jamelan, Jc37, Jcchat66, Jdelator, Jeff02, Jiang, JoDB, Joe Roe, JoePhoneMonkey, JoeSmack, John Reaves, Johnny Pez, Jok2000, Jolomo, JonnyLightning, Jor, JorgeGG, Josquius, Juliancolton, Junkyardprince, K7aay, KF, Kaisershatner, Kdau, Kevinalewis, Khaosworks, Khazar, Kidblast, Kingturtle, Kintetsubuffalo, Knucmo2, Krapitino, Kross, Kuralyov, Kusma, Kweeket, Kyng, LadyofShalott, Lapsus5, LarryGilbert, Lawrence Cohen, Lefty, Leifbk, Lenoxus, Leo Caesius, Leonard G., Lethargy, LiBai, Lightmouse, Ligulem, Ljhliesl, Loengard, Logotu, Lokicarbis, Lord Bodak, Lord Sander, Lord Voldemort, Lotje, Lowellian, Lucifer2000, Lycurgus, M-le-mot-dit, MER-C, Ma8thew, Mahanga, MakeRocketGoNow, Mapetite526, Marcok, MargyL, Master Scott Hall, Master of Tofu, Mathew5000, Maxxicum, Mbarry829, Mbell, McGrobbles, Mdiamante, Meco, Megarockman, Mellow honey, Mervyn, Mhacdebhandia, Michael C Price, Michael Hardy, Michaelritchie200, Mike Klaassen, Misterx2000, Modulatum, Moofoo, Mormegil, Morwen, Mswake, MtlWriterguy, MuscleJaw SobSki, Nakedbacon, Nemissimo, Nerrolken, Nihonjoe, Nilotp, Ningauble, Noah Salzman, Ntennis, NuclearWarfare, OAC, ONEder Boy, Ohnoitsjamie, Onomou, Onthegogo, OpenToppedBus, Orient, Orion11M87, Ossipewsk, OwenBlacker, PDH, Paul A, Paul Benjamin Austin, Paul Magnussen, Pavel Jelínek, PeterCanthropus, Petrovic-Njegos, Pfahlstrom, PhennPhawcks, Phgao, Phil Bridger, Phunting, Phuzion, Piecraft, Piotrus, Pjacobi, Plastikspork, Pmcalduff, Pne, Pollinator, Pperos, Punklesa22, Pylgrym, R'n'B, Rayc, Rboatright, Reargunner, Reconsider the static, Redddogg, Reddi, Reinhardheydt, RepublicanJacobite, Res2216firestar, Retired username, Rich Farmbrough, Richard Keatinge, Richard Weil, RickK, Rickyrab, Rjo, Rmhermen, RobinCarmody, Rodlox, Ronny corral, Rosenknospe, Rossrs, Rossumcapek, RoyalFool, Rusty2005, Ruthless Xero, SGCommand, Sam Hocevar, Samwaltz, Sarahjansen, SarekOfVulcan, Sasoriza, Saswann, Scorpion451, ScottieRoadPatriot, Sd-100, Sebjarod, Shanalk, Shooterwalker, Shsilver, Simonkaye, Simonw2000, Sitenl, Slatersteven, 207 Article Sources and Contributors Slightsmile, SlimVirgin, Snailwalker, Solipsist, Sonsani, Staecker, Stbalbach, StuffOfInterest, Supergodzilla2090, Surfren, T-Money, TMC1221, TallNapoleon, Tassedethe, Tavdy79, Teh Bomb Sophist, Ten-pint, TengriAsura, The Epopt, The Mink Ermine Fox, The Vegetarian Tiger, TheRingess, TheosThree, Theraven, Threadnecromancer, Tillman, Tim!, Time for action, Timwi, Tiyang, Tnxman307, Topbanana, TransUtopian, TreasuryTag, Triumphant, Trolleyfan, Twas Now, Two halves, TwoOneTwo, UK Bakosi, UKPotts, Uusitunnus, Varlaam, Vchimpanzee, Verbose, Verdi1, Verne Equinox, Vicki Rosenzweig, VolatileChemical, Vzbs34, Walter Kaufmann, Wayland, Westrim, WikipedianMarlith, Woohookitty, Wwoods, Xyphy, YUL89YYZ, Yerpo, Yonitdm, YoungFreud, Yug, Zachorious, Zaroff2, Zephyrus67, Zoe, Zoicon5, Zombie Hunter Smurf, 800 anonymous edits Time loop  Source: http://en.wikipedia.org/w/index.php?oldid=492164937  Contributors: -Ril-, 0dd1, A B VYAS, A Ramachandran, Acegikmo1, Alison9, Amberrock, Anchoress, Andareed, AndrewTJ31, Andycjp, Angie Y., Anirbans, Anthrcer, Aranel, Art1991, Artemisboy, Atomika, BTP51, Bando26, Bb1, Benlisquare, Bhuston, Blake, BlueAzure, Bob 32 116, Bongwarrior, Breakingspell, Brockhardon, C James L, Cambalachero, CatWatcher, Chandler Rulz, Chester Markel, Chexmix53, Chris the speller, Chrisrus, Christopher Thomas, Chzz, Conan-san, Custardninja, CyberSkull, Cyclonius, Cynthia Sue Larson, DBigXray, Damian Yerrick, Darac, DarkFireTaker, DarkfireTaimatsu, DavidK93, Davidhorman, Dayewalker, Dcflyer, Deadkid dk, Densus, Derktar, Destron Commander, Diego Moya, Doczilla, Doniago, Dr. Rondart, Earthbound77, Ebertek, Efrem7, Ehtz28, Eldar, Ella Press, Emijrp, Ergonaut2001, Figure19, FlogMachine, Fratrep, Frosted14, Gabknight2005, Ghelae, Ghughesarch, Gillespee, Greengobbie92, Groudon199, Gunnrwol, Haipa Doragon, Haon 2.0, Harryboyles, Hibana, Highway99, Horkana, Iknowyourider, IlGreven, Itgonrain, Iuio, JAF1970, JQF, Jackdavinci, JakeVortex, James086, Jh51681, John Abbe, Jok2000, JoshuaZ, Kanohara, Kariteh, Keeves, Kimagain, Kitch, Kreb Dragonrider, Krychek, Langis, Lathrop1885, Lenin and McCarthy, Letranova, LilHelpa, Lintpants, Listmeister, Loodog, Lordvolton, MakeRocketGoNow, Marcsin, Martarius, Master Deusoma, Matt3483, Maxl, MegX, MikeDX, Mikeymike2001, MileyDavidA, Milnivlek, Mister3, Mixen Dixon, Mkuehn10, Mouse Nightshirt, Munroe, NES Wii, Naddy, Netoholic, Nfitz, Nick R, Nono64, Ntsimp, Nusumareta, Nx, PaulLev, Penguin, Pixelface, Polymerbringer, Psi edit, R9tgokunks, RaHarakhte, Raul654, RedManiac2, Reddi, Remy B, Richard Arthur Norton (1958- ), Ringm, Rjwilmsi, Rodrigo-kun, Ropera, Sabalon, Salamurai, Salgueiro, Sampo Torgo, Samwaltz, Sandy13991, Scottclowe, Scottmage, Sean D Martin, Senator2029, Shay Guy, ShelfSkewed, Sipi1230, SirNeilGlen, SnappingTurtle, Socal gal at heart, Sommerfeld, SonicGamer, Soundwave, Spaceman0, Spannatabaspant, Subtlecoolness, TK421, Tassedethe, TheBlindGiants, Thiseye, Toad of Steel, TonyFleet, Toogs, TreasuryTag, Trivialist, Ttonyb1, Un1234l, Uncle G, Underwaterbuffalo, Uthbrian, Val42, Vortex Dragon, Vrenator, WCityMike, Waveformula, Wavy G, We hope, Wereon, Who me0000, WillMak050389, William Graham, Woohookitty, Wraithdart, Wuffyz, Zachs33, Zeldafan3242, Zephris, Zotel, Zythe, 323 anonymous edits Temporal paradox  Source: http://en.wikipedia.org/w/index.php?oldid=493756611  Contributors: Adfectio, Alexius08, Andyjoule, Annrules, Ashu qwert, Asqueella, Badtempered, Betty Logan, Blaziken rjcf, Brainblaster52, Brianann MacAmhlaidh, Bulmabriefs144, CKelly, Cesue, Cfclements, Chairsenses, Circeus, Clintville, Coolcatkim22, Crazzy349, DMW2123, DScott750, Damiantgordon, Darkhelmet322, Dayewalker, Dehydromon, DenisAdonis, Disavian, Doctorwhofan63, Drat, Ellissound, Emperor Niro, Eugene-elgato, Factomancer, Fishal, Florescent, Gaius Cornelius, GoingBatty, Gyrobo, Hebrides, Hellbaron, Hi878, HovisM, Hypnosifl, Iridescent, Ithizar, J.alex.johnson, J.delanoy, JChrisQuint, JamesAM, Jbrougham, Jeremjay24, Jibb34, Joe Sewell, JohnWrot, Jonadin93, Joshed100, JoshuaPearce, JuliusHG, Koavf, Lambiam, LeeHunter, LilHelpa, Madler, Marcus Brute, Martarius, Master Deusoma, Mattyhill, Maurice Carbonaro, Max mahito, Mindspillage, Minna Sora no Shita, Mwtoews, Mythsearcher, Neelix, Nightkey, Occultations, One-dimensional Tangent, OneWeirdDude, Paradoctor, Philip Trueman, Piecemealcranky, Pin Collector, Pollinosisss, Professional Waffle, ProtoBuster, Ptok Bentoniczny, Razasyed, Rjwilmsi, SKIPper76M, Sagaciousuk, Sameboat, Sasoriza, Saurabhmangal, Serendipodous, Signalhead, Sphilbrick, Spineywolf, StonedPerson, SuperDude007, Superk1a, SurrealWarrior, Sussexonian, The Rogue Penguin, The Thing That Should Not Be, TheRealFennShysa, ThomasO1989, Timc, Trysohard, Waldir, Whpq, WikHead, Wikieditor1988, XJ90, Zaxnort, 212 anonymous edits Grandfather paradox  Source: http://en.wikipedia.org/w/index.php?oldid=494204725  Contributors: ***Ria777, 041744, 1Winston, ATD, Abomasnow, Abrech, Abu badali, Acalamari, Acthompson, Adam keller, Adam9812, Addihockey10, AdjustShift, Adoniscik, Aerie124, Ahoerstemeier, Al E., Ale jrb, Alexius08, Amcfreely, AnonMoos, Antepenultimate, Arctic.gnome, Are You The Cow Of Pain?, Arichnad, Ashmoo, Atomsmasher86, Auric, AxelBoldt, Backstabb, Barkingdoc, Beam022, Ben 10, BerserkerBen, Bfinn, Bhig3, Bob A, Bolddeciever, Braindigitalis, Brianski, Bryan Derksen, Burnside65, CPRdave, Cactus Wren, Calabraxthis, Calamari, Calhobs23, Caltas, Cambalachero, CanadianLinuxUser, Candent shlimazel, Captain Wacky, Captain-tucker, Cat's Tuxedo, Chicagorob1, Chris 42, Cmdrjameson, Coanda-1910, ComaVN, Consumed Crustacean, Coollettuce, Coralmizu, Corvun, Cybercobra, DAGwyn, DHBoggs, DV8 2XL, Daniel J. Leivick, Darkwind, David Levy, Dayewalker, Dcamp314, Delicious carbuncle, Demon Lord 302, Deniskrasnov, Densus, Dermeister, Dfeldmann, Digamma, Doczilla, DoktorDec, Dominic subkey, Drat, Dstebbins, Dudegalea, Duggy 1138, EVula, Eeekster, Efflo74, El Cubano, Elwood00, EncMstr, Enigmatical, Enochjli642, Eugene-elgato, Everyking, Ewlyahoocom, Finog, Fiona CS, Foreverprovence, Furrykef, Fusionmix, Futuresuperstar scw, GUllman, Garda40, Gezman, Giant89, Giftlite, Gioto, Goldfritha, Gorank4, GrahamHardy, Graue, Greenodd, Gsp8181, Gunnar Guðvarðarson, Guthrie, Gvimalku, Gyohng, Halcyonhazard, Hello32020, Henryodell, Heslopian, Hibana, Histrion, HovisM, Hq3473, Ht686rg90, Hu, Hughesdavidw, Humanist92, Hydrargyrum, Hypnosifl, I.am.lost, Icyisamu, Igoldste, Imagine Wizard, Imagine me2, Ineedrevelation, Ixfd64, JIMfoamy1, Ja 62, Jakeyb33, Jamelan, JasonAQuest, Jitterro, John Darrow, John254, Jok2000, Jon Ascton, Jonny-mt, Josiah Rowe, Jpk, Jpmccord, Junyor, Jushi, JustAGal, K-twist808, K69, Kameraad Pjotr, Kanonkas, Karada, Karl E. V. Palmen, Katalaveno, Kdau, Kent28, Keraunos, Khaosworks, Kmarinas86, KnightRider, Koro Neil, KrytenKoro, Kwinki, Lab-oratory, Lambiam, Lashiec, Lazzzzze, Letranova, Ligulem, Lilwik, Loadmaster, Lord E, Luiz48, MJ94, Mablanco, Maian, Majorclanger, Mallanox, Man It's So Loud In Here, Marc Weil, Marc pasquin, Marisusis, Martarius, Matharvest, MattManic7325, Mattbuck, Mattmanp, Max Jetzer, Maximus Rex, Maxis ftw, Mbell, Midasminus, Mike Peel, Mike4ty4, Milesnfowler, Mkuehn10, Mnemo, Modus Ponens, Monkeycheetah, Montgomery '39, Morven, Morwen, Mr. Garrison, Mranostay, Mritaly1000, Mrmets26, Mthteh, Mustangwill, Mwboyer, Myscrnnm, Mythsearcher, Nakon, Nalvage, Nate1481, Nenva, Netsnipe, New Age Retro Hippie, Nhandler, Notshabti, Nyttend, Obi2Kenobi, OffsBlink, Olathe, OldRight, Oliver Pereira, OneWeirdDude, Oren0, Orville Eastland, OsirisV, Paliku, Paradoctor, Patar knight, Paul A, PaulLev, PcGnome, Peruvianllama, Petaseakittenarmy, Peter.C, Phil Boswell, Philip Trueman, Pictureuploader, Pikawil, Platypus222, Plrk, Prasadbeeraka, PsychoJosh, Puap, Pupster21, Quadratic, Quercusrobur, Qwyrxian, Raiki15, Razasyed, Reformparty82, RememberMe?, Rewop777, Rgrg, Rich Farmbrough, Richard001, Riffsyphon1024, Rjwilmsi, Rob T Firefly, Robertd, Robofish, Rphb, Rundquist, Ryan Postlethwaite, S Whistler, SDaniel, SJK, SYSS Mouse, Sam Hocevar, Sanchom, Saric, Sastra Manurung, Saswann, Schneelocke, SchuminWeb, Sega381, Segagman, Senjuto, Ser Amantio di Nicolao, Shaen, Shahid1618, ShaneCavanaugh, Shawn81, Shawnallen, Shell Kinney, Sherqnill, Shreevatsa, Signalhead, SimonLyall, Simonfielder, SingCal, Sith Lord 13, Skwinch, Smartyllama, Soccerluke22, Soumya92, SpaceFlight89, SpecialAgentUncleTito, St Fan, StAkAr Karnak, Staffwaterboy, StarDigian, Stardust8212, Steel, Stephen P. Merchant, Stephenb, Stephenchou0722, Stevertigo, Strength rune, Superbiate, Superm401, Swwright, THATSBETTER, TKD, Taragui, Tasc, TehPhil, Tempshill, TerrorBite, The Monster, The Rogue Penguin, TheAnimus, TheChancellor, Thegline, Thewiki userxd, Thinkr, Thrashmeister, Tkgd2007, Tony Sidaway, Tregoweth, Trer, Trovatore, Trusilver, Tyler8779, UTSRelativity, UltimatePyro, VanishedUser314159, VasilievVV, Vhbelvadi, Vicki Rosenzweig, Viewdrix, Vinodkotiya, Voidxor, Voldemore, WDavis1911, Waldir, Wampa Jabba, Wannablessedbe, Wayne Slam, WereSpielChequers, Wereon, Wikidmage, Wikieditor1988, Wikipelli, WillMak050389, Witteafval, Wraithdart, Writelf, Wulf eng, Wwcsa, Yobmod, Zafiroblue05, Zundark, 604 anonymous edits Ontological paradox  Source: http://en.wikipedia.org/w/index.php?oldid=403049078  Contributors: 18-Till-I-Die, 1ForTheMoney, 9258fahsflkh917fas, Aaron Bruce, Ahpook, Ajsh, Alexjohnc3, AndrewTJ31, Another Believer, Arielkoiman, AtaruMoroboshi, Auric, Autobogg, Bearcat, BillC, Bisqwit, Bolddeciever, Brandov, Bronzethumb, Bryan Derksen, Bstepp99, Btyner, Burnside65, Calhobs23, CatherS, ChibiKareshi, Chintan 1988, Chris the speller, ChrisCork, Clerks, Cljohnston108, Conspiration, Crissyman, Ctjf83, Daniel Benfield, David Gerard, Deadlyops, Diego, Diet, DiogenesNY, Doczilla, Dodger, DonQuixote, Dpmuk, Dream of Nyx, Droidguy1119, Drpickem, Dstebbins, Duggy 1138, Ehsteve23, Eliyak, Elsan, Emurphy42, EoGuy, Epbr123, Fiasco229, Frecklefoot, Frotz, Gamer 2k4, Geeked, Godsoflogic, Gundersen53, Gzuckier, Hamiltondaniel, Harry Mudd, Hhliao, Histrion, Hotwire379, Hu, Hvn0413, Imnotoneofyou, Int3gr4te, ItsZippy, JaGa, JackSparrow Ninja, James J. Rowland, JasonAQuest, Jasonfward, Jbgreen, Jcarroll, Jdkasper, Jhemmila, John Darrow, John0309, Jon1104, Joncnunn, Jourell, Ju gatsu mikka, Juansmith, Kamikaze28, Keeves, Keycard, Khaosworks, Khazar, Kizor, LFaraone, Lambiam, Lazyteen542, Lhopitalified, Lisa mynx, Loadmaster, Lowellian, Lrj27, Luigifan, Lukeluke112, Lyonsbane, MWielage, Madmardigan53, Magioladitis, Mandarax, Marcus Brute, Markcpeck, Martarius, Mattbuck, Mboverload, MichaelGranados, Michaelpremsrirat, MidNiteBlade, MightyJAK, MightyWarrior, Milesnfowler, MileyDavidA, Mini-Geek, Mithcoriel, Mrquizzical, Muchness, NYKevin, NeonNero, New User, NonNobisSolum, Nutster, ObiWanBillKenobi, Oceanwind, Off2Explore, Oknazevad, Onslaught262, Overlord11001001, OwenBlacker, Paddu, Paradoctor, Pigsonthewing, Pikawil, Plushpuffin, ProtegoMaxima, Pseudo-Dionysius, Psyblade42, Quigonkenny, R-RockMan.EXE, Rabbabodrool, Rainwarrior, Raven's Crux, Rev Sysyphus, Reywas92, Richard Arthur Norton (1958- ), Richard001, RichardKleiner, Richiau, Rjwilmsi, RonConescu, Ruby2010, SchfiftyThree, Sega381, Serendipodous, Sgeureka, ShadowUltra, ShaleZero, Shawn [email protected], Shay Guy, ShelfSkewed, SiegfreidZ, Squids and Chips, Stansfield, Steverapaport, Subtlecoolness, Supernerd170, TCHJ3K, Tad Lincoln, Tassedethe, Tavdy79, Tbmorgan74, TeamCoachingNetwork, The Big L, The Light6, The Rogue Penguin, The Yeti, TheDJ, TheFarix, Thisisausernameok, Titoxd, Toad of Steel, Tobetheman, Tonyrex, Traxs7, Tristanaustin, Trysohard, Tustin2121, Tzfat Mystic, UK Bakosi, Ulric1313, UltimatePyro, Uroshnor, Valley2city, Verin Sedai, VolatileChemical, Waldir, WaysToEscape, Wellspring, Westacular, Wikichao999, Wikieditor1988, Wikignome0529, Wild ste, Wlmg, Wolfram.Tungsten, Wuzzlewazzle, ZPM, ZZninepluralZalpha, Σ, 486 anonymous edits Predestination paradox  Source: http://en.wikipedia.org/w/index.php?oldid=494574687  Contributors: A plague of rainbows, ACSE, AMK152, AdmiralMemo, Adonator, Aitias, Alistair P, Alivine, Alvis, Amoffit, Andrei Cvhdsee Brazil, Angela, Angeldeb82, Anon126, Anville, Apetc, Arjayay, Astavats, AtticusX, Autobogg, BanyanTree, Bart133, Bartekmajewski, Beeblebrox, Bennydigital, BillC, Binadot, Binx, Bks1209, Blasfamous, BobThePirate, Bonalaw, Brian Olsen, Bryan Derksen, Btyner, Burnside65, Calhobs23, Cambalachero, Cameron Scott, Cat's Tuxedo, Chasingsol, Chookmeister, Chris1219, Clem cowsie, Clockwork Angel, Colonies Chris, Conti, Corvun, Crackpottheorist, DBrane, DabMachine, Daibhid C, Daniel Benfield, Dantheman531, Darksun, David Gerard, Dayewalker, Delicious carbuncle, Denny, Derktar, Desertmonk, DoctorWho42, DonQuixote, Download, Drat, Dreamafter, Dstebbins, Dudegalea, Dyolf Knip, Emurphy42, Eric Burns, Etacar11, Everyoneandeveryone, Evil saltine, ExoTiger, Festivewombat, FlashpointDFW, Flyte35, For An Angel, Frankie1969, Frecklefoot, Freedom Inc, Fuchsia Groan, Fudoreaper, Furrykef, GHcool, Geogh84, Glimmer721, GoingBatty, Golbez, Goldfritha, Gregbard, Gunny01, Hailinel, Hellbus, HelloAnnyong, Histrion, HovisM, Hu, Humuhumunuku, Ianblair23, Ichibun12, Igordebraga, Ikanreed, Incrediblehoke949, Intgr, Irandill, JAF1970, Jabberwockgee, Jagged 85, Jeff02, Jnork, Juranas, JustPhil, Katefan0, Kelly Martin, Ketans, Keycard, Khaosworks, Kitsunegami, Kizor, Koavf, KramarDanIkabu, Krj373, Kylu, LUCAS FOX, Lambiam, Lazzzzze, Leader Vladimir, Leaflord, Letranova, Libro0, Linhle, Lomedhi, Lonelydarksky, Lotiel, Luiz48, Lyle Swann, MacGyverMagic, Madchester, Maetah, Magioladitis, Maian, Marcus Brute, Marcus Qwertyus, Marcus2, Mark Lessig, Mark5677, Markcpeck, Martarius, Master Deusoma, MattGiuca, Mattbuck, Mattmanp, Max22, Maximoff77, MegX, Menelaos, Miami33139, Michael316, Mike Klaassen, Monobi, MoogleDan, Morwen, Moxmalin, Mr. XYZ, Msmarmalade, N W, Nationalparks, Nblschool, Ndanielm, NeoBatfreak, Nightscream, Nintendoman01, NoriMorishima, Notcarlos, Nuclearheadache, Nutster, ONEder Boy, Omega13a, P.D., Paddles, Paddu, Pagrashtak, Paliku, Paradoctor, Paradoxian, Paranoid, PaulHammond, Pavel Vozenilek, Phil Boswell, Phoenixrod, Phydend, Piisuke, Pikawil, Pokepal101, Polylerus, Pomte, Ponder, Progressive19, Protiek, Psychorob, Pudding30, Quarl, Quicksilvre, Radix Z, RainbowCrane, Random contributor, Razasyed, Relativity, Rfc1394, Rfl, Rich Farmbrough, Ricky81682, Ritchy, Rjanag, Rjwilmsi, Robert Brockway, Robertd, Ron Stoppable, Rotek, Rvgavan, Ryvius, SAMAS, SJK, Sabbut, Scott Sanchez, Scoutersig, Sega381, Senjuto, Shawn [email protected], Shirt58, Simon Solts, Simulcra, Skyfaller, Skzyp, Smokizzy, Socialist10196, Soylentyellow, Sparkiegeek, Sparky the Seventh Chaos, Spud007, SpuriousQ, StAkAr Karnak, Subscriber0100, 208 Article Sources and Contributors Sukima, Surajt88, TKD, TaintedMustard, Terrypin, The Rogue Penguin, The Young Avenger, TheDoctor10, TheFarix, Thinkpad, Tim!, Timwi, TransUtopian, Tregoweth, Ttfntata, Tycho, UK-Logician-2006, UPL2229, UTSRelativity, Ukexpat, Umofomia, Umpa-lumpa-tooka-dumpa-onyomama, Ungvichian, Vegaswiki, Viewdrix, Vzbs34, Waldir, Wgrey, WikidSmaht, Wikieditor1988, Wild ste, William M. Connolley, Wong, Woohookitty, Xiner, YouMoo!, Zedmelon, 592 anonymous edits List of time travel science fiction  Source: http://en.wikipedia.org/w/index.php?oldid=494496266  Contributors: Ackatsis, After Midnight, Akoroves, Alivine, Allecher, American Eagle, Andareed, Anderpda, Andersonspadawan, Andy5421, Antara-2009, Ar2285, Artemis-Arethusa, Asenine, Auric, Ayayla, BD2412, Beamjockey, Beanyk, Biglovinb, BillFlis, Blagole, Blocktek, Bobthesecond, Bogdangiusca, Bookmoser, Bookreviewer123, BountyCocaine, Cburns1010, Chaheel Riens, Chinese frustrum, Chris the speller, Cmarschal, Cnposner, Colonies Chris, Cw6165, Cymy, Dakovski, Damiantgordon, DanDud88, Danni243, David Gerard, De Administrando Imperio, Delverie, Dharma7, Digifiend, Diogeneselcinico42, Doc9871, DrHUSE, DragonZero, DragonflySixtyseven, Drchirag, Drpickem, Dumarestuk, Durin, Edwin de Kock, Egsan Bacon, Ellohir, Emperor, Enekororo, EoGuy, Ericrosenfield, Evans1982, Fabrictramp, Frankiepaquito, Fred Bradstadt, Frog47, Gaius Cornelius, Garrittg, Giggett, GoingBatty, Hal Raglan, Henry Merrivale, HisRuntyDogma, Hmains, Hu, HubHikari, InverseHypercube, J 1982, JHunterJ, JaGa, Jagged 85, Jamdav86, Jeff Leites, Jfire, Jmricker, JocK, Jogers, Johnny Mnemonic, Jpbowen, Jt10258, Kam Solusar, Kasper2006, Kavalino, Ken Gallager, Khazar, Khazar2, Kjp993, Koavf, Lacivi, LeoStarDragon1, Lesliejas, Lisatwo, Loadmaster, Lochii, LyleHoward, MageOfTheSouth, Magnius, Major Watt, MakeRocketGoNow, Mandarax, Manitou, Marjaliisa, Markjoseph125, Martarius, Matchups, MattButts, Metaprimer, Meyer, MiaowForever, Miskaton, Mklobas, Mmortal03, Monkey sandwich, Montana's Defender, Mplsray, Myscrnnm, N432138, Nhprman, Nightspore, Ntnon, Nwbeeson, ONEder Boy, Oldieslover55, Open2universe, PWilkinson, Panel Guy, Pascal.Tesson, Pernelldh, Petro1313, Piotrus, Pmokeefe, Pmoteles, Prolog, R'n'B, RFBailey, RSStockdale, Random Passer-by, Rayc, Reenem, RepublicanJacobite, Rgcarr, Rhindle The Red, RiFraS, Risker, Rjwilmsi, Robina Fox, RockMagnetist, Rohan1970, Rpielke, Ryulong, Saatyolcu, Salamurai, SamEtches, SanGavinoEN, Sentient alien gravy, Setsuya-san, Sf junglist, ShelfSkewed, Shreevatsa, Silverhill, Skynilix, Slatersteven, Someguy1221, Spacepotato, Spiessens, Stories, Supertask, Supt. of Printing, Symbolt, Tassedethe, Tedder, The Anome, TheRealFennShysa, Thricecube, TimNelson, Timefan, Timeflyer, Tinmanic, TomXP411, Trish ferguson, Ulric1313, Unohoo, Vchimpanzee, Vusys, Welsh, WikHead, WikiuserNI, Woohookitty, Yobmod, ZouBEini, 320 anonymous edits 209 Image Sources, Licenses and Contributors 210 Image Sources, Licenses and Contributors Image:Irvington statue of Rip van Winkle.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Irvington_statue_of_Rip_van_Winkle.jpg  License: unknown  Contributors: Daryl Samuel File:A Christmas Carol - Mr. Fezziwig's Ball.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:A_Christmas_Carol_-_Mr._Fezziwig's_Ball.jpg  License: Public Domain  Contributors: AndreasPraefcke, Droll (usurped), Interpretix, Man vyi, Martin H., Ranveig Image:Twin Paradox Minkowski Diagram.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Twin_Paradox_Minkowski_Diagram.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Acdx Image:Time dilation02.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Time_dilation02.gif  License: GNU Free Documentation License  Contributors: Cleonis Image:time-travel-illustration3.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Time-travel-illustration3.gif  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Grondilu File:time-travel-parallel-universe2.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Time-travel-parallel-universe2.gif  License: GNU Free Documentation License  Contributors: Grondilu (talk) Image:time-travel-causal-loop.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Time-travel-causal-loop.gif  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Grondilu (talk) Image:time-travel-continuous-version.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Time-travel-continuous-version.gif  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Grondilu (talk) File:Multiverse.png  Source: http://en.wikipedia.org/w/index.php?title=File:Multiverse.png  License: Creative Commons Zero  Contributors: User:Silver Spoon File:Multiverse - level II.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Multiverse_-_level_II.svg  License: Public Domain  Contributors: Original by K1234567890y Vectorisation by Lokal_Profil Image:MWI Schrodingers cat.png  Source: http://en.wikipedia.org/w/index.php?title=File:MWI_Schrodingers_cat.png  License: Creative Commons Attribution-Sharealike 3.0  Contributors: . Original uploader was Dc987 at en.wikipedia Image:Many-worlds-bloch.png  Source: http://en.wikipedia.org/w/index.php?title=File:Many-worlds-bloch.png  License: GNU Free Documentation License  Contributors: CSTAR Image:Splittings-1.png  Source: http://en.wikipedia.org/w/index.php?title=File:Splittings-1.png  License: GNU Free Documentation License  Contributors: en:User:Jecowa Image:Many-worlds.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Many-worlds.svg  License: GNU Free Documentation License  Contributors: Traced by User:Stannered Image:Paths-many-worlds.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Paths-many-worlds.svg  License: GNU Free Documentation License  Contributors: Traced by User:Stannered Image:Sobel North America.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Sobel_North_America.gif  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors: Psychonaut, Roke File:LorentzianWormhole.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:LorentzianWormhole.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: AllenMcC. File:FY221c15.png  Source: http://en.wikipedia.org/w/index.php?title=File:FY221c15.png  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors: Alain r, Kanonkas, MickOre, Nihonjoe, 5 anonymous edits File:Wurmloch.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wurmloch.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: CorvinZahn File:Willow path.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Willow_path.jpg  License: Public Domain  Contributors: Javaman2000 File:Iimatyas.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Iimatyas.jpg  License: Public Domain  Contributors: 17th century coin designer File:JuliusOttoGrimm-Sculpture.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:JuliusOttoGrimm-Sculpture.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Gerardus, Knoe, Mutter Erde, STBR, 1 anonymous edits File:Using Mobile Phone 0251.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Using_Mobile_Phone_0251.JPG  License: GNU Free Documentation License  Contributors: Biswarup Ganguly File:DeterminismXFreeWill.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:DeterminismXFreeWill.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Tesseract2 File:Gospers glider gun.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Gospers_glider_gun.gif  License: GNU Free Documentation License  Contributors: Kieff File:Double-slit experiment results Tanamura 2.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Double-slit_experiment_results_Tanamura_2.jpg  License: GNU Free Documentation License  Contributors: Belsazar, Glenn, Kdkeller, Pieter Kuiper, Quibik, Tano4595 File:HEUraniumC.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:HEUraniumC.jpg  License: Public Domain  Contributors: Original uploader was Zxctypo at en.wikipedia File:Toppledominos.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Toppledominos.jpg  License: GNU Free Documentation License  Contributors: BazookaJoe, Enoch Lai, Leevclarke, 2 anonymous edits File:DeterminismXFreeWill.svg  Source: http://en.wikipedia.org/w/index.php?title=File:DeterminismXFreeWill.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: DeterminismXFreeWill.jpg: Tesseract2 derivative work: Richardbrucebaxter (talk) File:Luther46c.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Luther46c.jpg  License: Public Domain  Contributors: Aavindraa, CTSWyneken, David Levy, Hahnchen, Ixfd64, Joakao, Rosenzweig, Schmelzle, Shakko, Shizhao, Wst, 1 anonymous edits File:FreewillConceptsBasedUponPhilosophyOfMindCausationViews.svg  Source: http://en.wikipedia.org/w/index.php?title=File:FreewillConceptsBasedUponPhilosophyOfMindCausationViews.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: Richardbrucebaxter. Original uploader was Richardbrucebaxter at en.wikipedia File:Thomas Hobbes (portrait).jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Thomas_Hobbes_(portrait).jpg  License: Public Domain  Contributors: Brainmachine, Daniel (de), Dcoetzee, Diomede, FranksValli, Kelson, Mathonius, Mattbr, PKM, Pieter Kuiper, QWerk, Sonphan10, Svencb, Victuallers, 1 anonymous edits File:Schopenhauer.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Schopenhauer.jpg  License: Public Domain  Contributors: Abigor, Agostino64, Bibi Saint-Pol, Gabor, Jcornelius, Mogelzahn, SSS, Thuresson, 3 anonymous edits File:Quantum Cloud, Bugsby's Reach - geograph.org.uk - 691469.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Quantum_Cloud,_Bugsby's_Reach_-_geograph.org.uk_-_691469.jpg  License: Creative Commons Attribution-Share Alike 2.0 Generic  Contributors: File:Flatland cover detail.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Flatland_cover_detail.jpg  License: Public Domain  Contributors: Fui in terra aliena File:H G Wells pre 1922.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:H_G_Wells_pre_1922.jpg  License: Public Domain  Contributors: Andreagrossmann, JasonAQuest, Lupo, 2 anonymous edits Image:Oz-and-surrounding-countrie.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Oz-and-surrounding-countrie.jpg  License: Public Domain  Contributors: AnonMoos, Ejdzej, Erica Letzerich, Man vyi Image:Šachovnice.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Šachovnice.jpg  License: Public Domain  Contributors: Butko, Maksim, Man vyi File:It's A Wonderful Life.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:It's_A_Wonderful_Life.jpg  License: Public Domain  Contributors: National Telefilm Associates File:Fatherland.png  Source: http://en.wikipedia.org/w/index.php?title=File:Fatherland.png  License: GNU Free Documentation License  Contributors: Original uploader was Briangotts at en.wikipedia License 211 License Creative Commons Attribution-Share Alike 3.0 Unported //creativecommons.org/licenses/by-sa/3.0/