FACTOID # 11: Oklahoma has the highest rate of women in State or Federal correctional facilities.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
RELATED ARTICLES
People who viewed "Time travel" also viewed:
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Time travel
Unsolved problems in physics: Is time travel theoretically and practically possible? If so, how can paradoxes such as the grandfather paradox be avoided?

Time travel is the concept of moving between different moments in time in a manner analogous to moving between different points in space, either sending objects (or in some cases just information) backwards in time to a moment before the present, or sending objects forward from the present to the future without the need to experience the intervening period (at least not at the normal rate). Some interpretations of time travel also suggest that traveling backwards in time might take one to a parallel universe whose history could begin to diverge from the traveler's original history after the moment the traveler arrived in the past.[1] Although time travel has been a common plot device in fiction since the 19th century, and one-way travel into the future is arguably possible given the phenomenon of time dilation based on velocity in the theory of special relativity (exemplified by the twin paradox) as well as gravitational time dilation in the theory of general relativity, it is currently unknown whether the laws of physics would allow backwards time travel. Any technological device, whether fictional or hypothetical, that is used to achieve two-way time travel is known as a time machine. Image File history File links Question_book-3. ... Image File history File links No higher resolution available. ... This is a list of some of the unsolved problems in physics. ... Look up paradox in Wiktionary, the free dictionary. ... The grandfather paradox is a paradox of time travel, first described by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent (The Imprudent Traveller).[1] The paradox is this: Suppose a man traveled back in time and killed his biological grandfather before the latter met the... This article is about the concept of time. ... This article is about the idea of space. ... For other uses, see Multiverse (disambiguation). ... A plot device is an element introduced into a story to solely to advance or resolve the plot of the story. ... For other uses, see Fiction (disambiguation). ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In physics, the twin paradox refers to a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find they have aged less than an identical twin who stayed on Earth. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... A physical law or a law of nature is a scientific generalization based on empirical observations. ... A time machine is a device for traveling through time. ...

Contents

Origins of the concept

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. For example, 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.[2] 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",[3] 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."[2] Samuel Madden (1686-1765) was an Irish author. ... A guardian angel is a spirit who is believed to protect and to guide a particular person. ...


Louis-Sébastien Mercier's L'An 2440, rêve s'il en fut jamais ("The Year 2440: A Dream If Ever There Was One") is a utopian novel set in the year 2440. An extremely popular work (it went through twenty-five editions after its first appearance in 1771), the work 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." [Robert Darnton, The Forbidden Best-Sellers of Pre-Revolutionary France (New York: W.W. Norton, 1996), 120.] Louis-Sébastien Mercier (6 June 1740 - 25 April 1814) was a French dramatist and miscellaneous writer. ...


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 by an anonymous author in 1838, as a very early time travel story.[4] 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 — 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 where 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 of 1837), with his coach having just passed his spot on the road, leaving him stranded in Newcastle for another night.[5] To meet Wikipedias quality standards, this article or section may require cleanup. ... Anonymous redirects here. ... Stagecoach in Switzerland A stagecoach is a type of four-wheeled enclosed passenger and/or mail coach, strongly sprung and drawn by four horses, widely used before the introduction of railway transport. ... This article is about a city in the United Kingdom. ... For other uses, see Bede (disambiguation). ... This article concerns the buildings occupied by monastics. ...


Charles Dickens' 1843 book A Christmas Carol is considered by some[6] to be one of the first depictions of time travel, 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. Dickens redirects here. ... For other uses, see A Christmas Carol (disambiguation). ...


A clearer example of time travel is found in the popular 1861 book Paris avant les hommes (Paris before Men), published posthumously by the French botanist and geologist Pierre Boitard. 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.[7] Another clear early example of time travel in fiction is the short story The Clock That Went BackwardPDF (35.7 KB) by Edward Page Mitchell, 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. Pierre Boitard (1789–1859) was a French botanist and geologist. ... Families Cimoliasauridae Cryptoclididae Elasmosauridae Plesiosauridae Polycotylidae Plesiosaurs (pronounced ) (Greek: plesios meaning near or close to and sauros meaning lizard) were carnivorous aquatic (mostly marine) reptiles. ... “PDF” redirects here. ... b. ... The original New York Sun began publication September 3, 1833, as a morning newspaper, and an evening edition began in 1887. ... Samuel Langhorne Clemens (November 30, 1835 – April 21, 1910),[1] better known by the pen name Mark Twain, was an American humanist,[2] humorist, satirist, lecturer and writer. ... A Connecticut Yankee in King Arthurs Court is an 1889 novel by American humorist and writer Mark Twain. ... For other uses, see King Arthur (disambiguation). ...


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.[8] 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. Enrique Lucio Eugenio Gaspar y Rimbau (Madrid, March 2, 1842 – Olorón, September 7, 1902) was a Spanish diplomat and writer, who authored plays, zarzuelas (light operas), and novels. ... Herbert George Wells (September 21, 1866 – August 13, 1946), better known as H. G. Wells, was an English writer best known for such science fiction novels as The Time Machine, The War of the Worlds, The Invisible Man, The First Men in the Moon and The Island of Doctor Moreau. ... The Time Machine is a novel by H. G. Wells, first published in 1895, later made into two films of the same title. ... Zapped One day Sunny and his friend Nelson were trying to write a short story for English whilst listening to their favorite band D12. ...


Since that time, both science and fiction (see Time travel in fiction) have expanded on the concept of time travel, but whether it could be possible in reality is still an open question. Poster for Back to the Future (1985). ...


Time travel in 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.[9] 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, but the physical plausibility of these solutions is uncertain. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... For other uses of this term, see Spacetime (disambiguation). ... This article is about the idea of space. ... In a Lorentzian manifold, a closed timelike curve (CTC) is a worldline of a material particle in spacetime that is closed. ... A world line of an object or person is the sequence of events labeled with time and place, that marks the history of the object or person. ...


Physicists take for granted 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" (although according to relativity there is no single objective answer to how much time has 'really' passed between the departure and the return). On the other hand, many in the scientific community believe that backwards time travel is highly unlikely. Any theory which would allow time travel would require that issues 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, either by appealing to the Novikov self-consistency principle or to the notion of branching parallel universes (see the possibility of paradoxes below). For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... Causality describes the relationship between causes and effects, and is fundamental to all natural science, especially physics. ... The grandfather paradox is a paradox of time travel, first described by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent (The Imprudent Traveller).[1] The paradox is this: Suppose a man traveled back in time and killed his biological grandfather before the latter met the... This article or section does not cite its references or sources. ... For other uses, see Multiverse (disambiguation). ... Time travel is a concept that has long fascinated humanity—whether it is Merlin experiencing time backwards, or religious traditions like Mohammeds trip to Jerusalem and ascent to heaven, returning before a glass knocked over had spilt its contents. ...


Tourism in time

Stephen Hawking once suggested that the absence of tourists from the future constitutes 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 in fact developed (or was 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 right 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."[10] 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.[11] Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... A tourist boat travels the River Seine in Paris, France Tourism can be defined as the act of travel for the purpose of recreation, and the provision of services for this act. ... A graphical representation of the Arecibo message - Humanitys first attempt to use radio waves to communicate its existence to alien civilizations The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for or contact with... Insert non-formatted text here Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an American astronomer and astrobiologist and a highly successful popularizer of astronomy, astrophysics, and other natural sciences. ...


General relativity

However, the theory of general relativity does suggest scientific grounds for thinking backwards time travel could be possible in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed.[12] These semiclassical arguments led Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel,[13] 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.[14] For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... Semiclassical gravity is the approximation to the theory of quantum gravity in which one treats matter fields as being quantum and the gravitational field as being classical. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ... 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 (closed timelike curves) on all but sub-microscopic scales. ... Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ...


The "presentist" view

Presentism holds that neither the future nor the past exist—that the only things that exist are present things, and there are no non-present objects. Some have taken presentism to indicate that time travel is impossible for there is no future or past to travel to; however, recently some presentists have argued that although past and future objects do not exist, there can still be definite truths about past and future events, and that it is possible that a future truth about the time traveler deciding to return to the present date could explain the time traveler's actual presence in the present.[15] 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. In any case, the relativity of simultaneity in modern physics is generally understood to cast serious doubt on presentism and to favor the view known as four dimensionalism (closely related to the idea of block time) in which past, present and future events all coexist in a single spacetime In the philosophy of time, presentism is the belief that neither the future nor the past exists. ... For other uses, see Future (disambiguation). ... The past is the portion of the timeline that has already occurred; it is the opposite of the future. ... The relativity of simultaneity is the dependence of the notion of simultaneity on the observer. ... In the philosophy of time, four dimensionalism is the view that reality is a four-dimensional continuum composed of time and space (spacetime). ... Block time is one way of approaching the problem of the nature of time. ... For other uses of this term, see Spacetime (disambiguation). ...


Time travel to the past in physics

Time travel to the past is theoretically allowed using the following methods:[16]

Faster-than-light (also superluminal or FTL) communications and travel are staples of the science fiction genre. ... A cosmic string is a hypothetical 1-dimensional topological defect in the fabric of spacetime. ... This article is about the astronomical body. ... For other uses, see Wormhole (disambiguation). ... This article is about the Alcubierre metric. ...

The equivalence of time travel and faster-than-light 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 backwards 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 spacetime interval between the events is 'space-like', meaning that neither event lies in the future light cone of the other).[17] 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.[17] 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. Faster than the speed of light redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... An inertial frame of reference, or inertial reference frame, is one in which Newtons first and second laws of motion are valid. ... The relativity of simultaneity is the dependence of the notion of simultaneity on the observer. ... For other uses of this term, see Spacetime (disambiguation). ... In special relativity, a light cone is the pattern describing the temporal evolution of a flash of light in Minkowski spacetime. ... See also: Special relativity Postulates of special relativity 1. ... Causality describes the relationship between causes and effects, and is fundamental to all natural science, especially physics. ... The Minkowski diagram is a graphical tool used in special relativity to visualize spacetime with regard to an inertial reference frame. ...


It should be noted that according to special relativity it would take an infinite amount of energy to accelerate a slower-than-light object to faster-than-light speeds, and 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,[18] and there is no evidence for their existence. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... A tachyon (from the Greek ταχύς {takhús}, meaning swift) is a hypothetical particle that travels at superluminal velocity. ... Quantum field theory (QFT) is the quantum theory of fields. ...


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.[9]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.[9] Whether general relativity forbids closed time-like curves for all realistic conditions is unknown . General relativity (GR) or general relativity theory (GRT) is the theory of gravitation published by Albert Einstein in 1915. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ... From the point of view of general relativity, a closed timelike curve (CTC) is a closed worldline. ... Kurt Gödel (IPA: ) (April 28, 1906 Brünn, Austria-Hungary (now Brno, Czech Republic) – January 14, 1978 Princeton, New Jersey) was an Austrian American mathematician and philosopher. ... The Gödel solution is an exact solution of the Einstein field equation in which the stress-energy tensor contains two terms, the first representing the matter density of a homogeneous distribution of swirling dust particles, and the second associated with a nonzero cosmological constant (see lambdavacuum solution). ...


Using wormholes

Main article: Wormhole

Wormholes are a hypothetical warped spacetime which are also permitted by the Einstein field equations of general relativity,[19] although it would be impossible to travel through a wormhole unless it was what is known as a traversable wormhole. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... For other uses, see Wormhole (disambiguation). ... For other uses, see Wormhole (disambiguation). ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ... For other uses, see Wormhole (disambiguation). ...


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.[20] 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;[21] 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. Propulsion may refer to: Look up propulsion in Wiktionary, the free dictionary. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... Synchronization is coordination with respect to time. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ...


According to current theories on the nature of wormholes, construction of a traversable wormhole would require the existence of a substance known as "exotic matter" with negative energy. 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.[22] However, it is known that quantum effects can lead to small measurable violations of the null energy condition,[22] and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics.[23] 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.[24] Exotic matter is a hypothetical concept of particle physics. ... In relativistic classical field theories of gravitation, particularly general relativity, an energy condition is one of various alternative conditions which are not consequences of the field equation but which can be imposed on a spacetime model as an additional constraint. ... In physics, the Casimir effect is a physical force exerted between separate objects, which is due to neither charge, gravity, nor the exchange of particles, but instead is due to resonance of all-pervasive energy fields in the intervening space between the objects. ...


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.[25] 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.[26] Professor Matt Visser is a Mathematics Professor at Victoria University of Wellington. ... Causality describes the relationship between causes and effects, and is fundamental to all natural science, especially physics. ... A Roman ring, in theoretical physics, is a type of wormhole where the time difference across its mouths is such that it may not allow a closed timelike curve (CTC), or closed-time loop. If these wormholes and their mouths are arranged in a suitable configuration, a closed time loop...


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[27] in 1936 and Kornel Lanczos[28] in 1924, but not recognized as allowing closed timelike curves[29] until an analysis by Frank Tipler[30] in 1974. If a cylinder is long, and dense, 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. This article is in need of attention from an expert on the subject. ... Willem Jacob van Stockum (November 20, 1910-June 10, 1944) was a physicist who made an important contribution to the early development of general relativity. ... Cornelius Lanczos (Lánczos Kornél), born Kornél Löwy (February 2, 1893–June 25, 1974), was a Hungarian mathematician and physicist. ... Frank J. Tipler is a professor of mathematical physics at Tulane University, New Orleans, physicist, theologian and cornucopian philosopher. ... A cosmic string is a hypothetical 1-dimensional topological defect in the fabric of spacetime. ...


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.[citation needed] Robert Lull Forward commonly known as Robert L. Forward (August 15, 1932 - September 21, 2002) was a United States physicist and science fiction writer. ... For the indie-pop band, see The Magnetic Fields. ...


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 in any finite region that satisfies the weak energy condition, meaning that the region contains no exotic matter with negative energy. 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,[31] 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."[32] 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."[33] However, this theorem does not rule out the possibility of time travel in regions which contain exotic matter with negative energy (which would be necessary for traversable wormholes or the Alcubierre drive), and 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). In relativistic classical field theories of gravitation, particularly general relativity, an energy condition is one of various alternative conditions which are not consequences of the field equation but which can be imposed on a spacetime model as an additional constraint. ... Exotic matter is a hypothetical concept of particle physics. ... 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 (closed timelike curves) on all but sub-microscopic scales. ... In physics, a Cauchy horizon is a light_like boundary of the domain of validity of a Cauchy problem. ... This article is about the Alcubierre metric. ...


Time travel and the anthropic principle

It has been suggested by physicists such as Max Tegmark that the absence of time travel and the existence of causality might be due to the anthropic principle. The argument is that a universe which allows for time travel and closed time-like loops is one in which intelligence could not evolve because it would be impossible for a being to sort events into a past and future or to make predictions or comprehend the world around them (at least, not if the time travel occurs in such a way that it disrupts that evolutionary process).[citation needed] Max Tegmark Max Tegmark born 1967 in Sweden to Karin Tegmark and Harold S Shapiro, is a cosmologist formerly at the University of Pennsylvania and now at the Massachusetts Institute of Technology as an Associate Professor. ... Causality describes the relationship between causes and effects, and is fundamental to all natural science, especially physics. ... In physics and cosmology, the anthropic principle states that we should take into account the constraints that our existence as observers imposes on the sort of universe that we could observe. ...


Experiments carried out

Certain experiments carried out during the last ten years 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. Causality or causation denotes the relationship between one event (called cause) and another event (called effect) which is the consequence (result) of the first. ... A delayed choice quantum eraser is a combination between a quantum eraser experiment and Wheelers delayed choice experiment. ... Marlan Orvil Scully is a physicist best known for his work in theoretical quantum optics. ... It has been suggested that Quantum coherence be merged into this article or section. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... The double-slit experiment consists of letting light diffract through two slits producing fringes on a screen. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...


The experiment of Lijun Wang might also give the appearance of 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 backwards in time, so this experiment is understood not to violate causality either. Fourier analysis, named after Joseph Fouriers introduction of the Fourier series, is the decomposition of a function in terms of a sum of sinusoidal basis functions (vs. ...


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 (0.91 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.[34] Günter Nimtz of the Physics Institute at the University of Cologne (Universität zu Köln) in Germany has been conducting experiments that purport to show that under certain conditions, particles may travel faster than the speed of light (c). ...


Some physicists have attempted to perform experiments which would show genuine causality violations, but so far without success. The Space-time Twisting by Light (STL) experiment run by physicist Ronald Mallett is attempting 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 which 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). Ronald L. Mallett, Ph. ... The opal in this bracelet contains a natural periodic microstructure responsible for its iridescent color. ... Ronald L. Mallett, Ph. ...


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 or MIT's Time Traveler Convention heavily publicized permanent "advertisements" of a meeting time and place for future time travelers to meet. 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. Although it is theoretically possible that future humans have traveled back in time, but have traveled back to the meeting time and place in a parallel universe.[35] 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.[36][37] The Time Traveler Convention was a convention held at MIT on May 7, 2005, in the hopes of making contact with time travelers from the future. ... For other uses, see Multiverse (disambiguation). ... For other uses, see Wormhole (disambiguation). ...


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. Image File history File links Twin_paradox_Minkowski_diagram. ... Image File history File links Twin_paradox_Minkowski_diagram. ... In physics, the twin paradox refers to a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find they have aged less than an identical twin who stayed on Earth. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... This article or section is in need of attention from an expert on the subject. ...


This form of "travel into the future" is theoretically allowed using the following methods:[16]

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": The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ... This article is about Earth as a planet. ... In physics, the twin paradox refers to a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find they have aged less than an identical twin who stayed on Earth. ... General relativity (GR) or general relativity theory (GRT) is the theory of gravitation published by Albert Einstein in 1915. ... For other uses, see Black hole (disambiguation). ...

This article refers to the process of hibernation in biology. ... This article is about suspended animation in a medical context. ...

Time dilation

Transversal Time dilation
Main article: 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.[39] 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 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. Image File history File links This animated GIF is meant to be used as an illustration for the time dilation article. ... Image File history File links This animated GIF is meant to be used as an illustration for the time dilation article. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... “Einstein” redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... A gravity well is the scientific/science fictional term for the distortion in space-time caused by a massive body such as a planet. ... In special relativity the rest frame of a particle is the coordinate system (frame of reference) in which the particle is at rest. ... An inertial frame of reference, or inertial reference frame, is one in which Newtons first and second laws of motion are valid. ... In physics, the twin paradox refers to a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find they have aged less than an identical twin who stayed on Earth. ... GPS redirects here. ... For other uses, see Black hole (disambiguation). ...


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 at the bottom of a 5 meter tall funnel with the mass of Jupiter.[16] 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 a non-spherical object five meters in length is not expected to be within our technological capabilities in the near future. For other uses, see Jupiter (disambiguation). ...


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. Domains and Kingdoms Nanobes Acytota Cytota Bacteria Neomura Archaea Eukaryota Bikonta Apusozoa Rhizaria Excavata Archaeplastida Rhodophyta Glaucophyta Plantae Heterokontophyta Haptophyta Cryptophyta Alveolata Unikonta Amoebozoa Opisthokonta Choanozoa Fungi Animalia An ericoid mycorrhizal fungus Life on Earth redirects here. ... This article refers to the process of hibernation in biology. ... Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... This article is about suspended animation in a medical context. ...


Time dilation and suspended animation only allow "travel" to the future, never the past, so they do not violate causality, and arguably should not be considered time travel. Causality or causation denotes the relationship between one event (called cause) and another event (called effect) which is the consequence (result) of the first. ...


Other ideas about time travel from mainstream physics

The possibility of paradoxes

The Novikov self-consistency principle and recent calculations by Kip S. Thorne[citation needed] 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 generalised, 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.[citation needed] This article or section does not cite its references or sources. ... Kip Stephen Thorne (born June 1, 1940) is an American theoretical physicist, known for his prolific contributions in the field of gravitation physics and astrophysics. ... Consistency has three technical meanings: In mathematics and logic, as well as in theoretical physics, it refers to the proposition that a formal theory or a physical theory contains no contradictions. ...


Parallel universes might provide a way out of paradoxes. Everett's many-worlds interpretation of quantum mechanics suggests that all possible quantum events can occur in mutually exclusive histories.[40] 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 many-worlds interpretation is correct, then a time traveler should indeed end up in a different history than the one he started from.[1] On the other hand, Stephen Hawking has argued that even if the many-worlds interpretation is correct, we should expect each time traveler to experience a single self-consistent timeline, so that time travelers remain within their own world rather than traveling to a different one.[10] Hugh Everett III (November 11, 1930 – July 19, 1982) was an American physicist who first proposed the many-worlds interpretation(MWI) of quantum physics, which he called his relative state formulation. ... The many-worlds interpretation or MWI (also known as relative state formulation, theory of the universal wavefunction, many-universes interpretation, Oxford interpretation or many worlds), is an interpretation of quantum mechanics that claims to resolve all the paradoxes of quantum theory by allowing every possible outcome to every event to... David Deutsch (born 1953) is a physicist at Oxford University. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ...


Daniel Greenberger and Karl Svozil proposed that quantum theory gives a model for time travel without paradoxes.[41] 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. For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ...


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.[42] This effect was referred to as "spooky action at a distance" by Einstein. In quantum information, quantum teleportation, or entanglement-assisted teleportation, is a technique that transfers a quantum state to an arbitrarily distant location using a distributed entangled state and the transmission of some classical information. ... In quantum mechanics, the EPR paradox is a thought experiment which challenged long-held ideas about the relation between the observed values of physical quantities and the values that can be accounted for by a physical theory. ... It has been suggested that Quantum coherence be merged into this article or section. ... The Bohm interpretation of quantum mechanics, sometimes called the Bohmian Mechanics or Ontological interpretation is an interpretation postulated by David Bohm in 1952, which was an extension of the de Broglie-pilot-wave theory of 1927. ... In physics, action at a distance is the interaction of two objects which are separated in space with no known mediator of the interaction. ...


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. 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. Quantum field theory (QFT) is the quantum theory of fields. ... Superluminal communication is the term used to describe the hypothetical process by which one might send information at faster-than-light (FTL) speeds. ... In quantum information theory, a no-communication theorem is a result which gives conditions under which instantaneous transfer of information between two observers is impossible. ...


Ideas from fiction

Further information: Time travel in fiction

Poster for Back to the Future (1985). ...

Types of time travel

Time travel themes in science fiction and the media can generally be grouped into two main types and a third, less common type (based on effect—methods are extremely varied and numerous), each of which is further subdivided. These classifications do not address the issue of time travel itself, i.e. how to travel through time, but instead call to attention differing rules of the time line. Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ...

1. The time line is consistent and can never be changed.
1.1 One does not have full control of the time travel. One example of this is The Morphail Effect. This concept of time can be referred to as circular causation. For examples of circular causation, see Robert A. Heinlein's story By His Bootstraps.
1.2 The Novikov self-consistency principle applies (named after Dr. Igor Dmitrievich Novikov, Professor of Astrophysics at Copenhagen University). The principle states that if you travel in time, you cannot act in such a way so as to create a paradox.
1.3 Any event that appears to have changed a time line has instead created a new one. It has been suggested that travel to the past would create an entire new parallel universe where the traveler would be free from paradoxes since he/she is not from that universe[43].
1.3.1 Such an event can be the life line existence of a human (or other intelligence) such that manipulation of history ends up with there being more than one of the same individual, sometimes called time clones.
1.3.2 The new time line might be a copy of the old one with changes caused by the time traveler. For example there is the Accumulative Audience Paradox where multitudes of time traveler tourists wish to attend some event in the life of Jesus or some other historical figure, where history tells us there were no such multitudes. Each tourist arrives in a reality that is a copy of the original with the added people, and no way for the tourist to travel back to the original time line.
2. The time line is flexible and is subject to change.
2.1 The time line is extremely change resistant and requires great effort to change it. Small changes will only alter the immediate future and events will conspire to maintain constant events in the far future; only large changes will alter events in the distant future. (Example: The Saga of Darren Shan, where major events in the past cannot be changed, but minor events can be affected. This is explained as if you went back in time and killed Hitler, another Nazi would take his place and commit his same actions.)
2.2 The time line is easily changed. (Example: Doctor Who, where the time line is fluid and changes often naturally; even changes to the traveler's own timeline are possible, though it is suggested such an act would destroy most of the universe.)
3. The time line is consistent, but only insofar as its consistency can be verified.
3.1 The Novikov self-consistency principle applies, but if and only if it is verified to apply. Attempts to travel into the past to change events are possible, but provided that:
-They do not interfere with the occurrence of such an attempt in the present (as would be the case in the Grandfather Paradox), and
-The change is never ultimately verified to occur by the traveler (e.g. there is no possibility of returning to the present to witness the change).

There are also numerous science fiction stories allegedly about time travel that are not internally consistent, where the traveler makes all kinds of changes to some historical time, but we do not get to see any consequences of this in our present day.[citation needed] The Morphail Effect refers to the imminent Dr. Brannart Morphail, from Michael Moorcocks classic science fiction novel, Dancers at the End of Time. ... Robert Anson Heinlein (July 7, 1907 – May 8, 1988) was one of the most popular, influential, and controversial authors of hard science fiction. ... By His Bootstraps is a science fiction short story by Robert A. Heinlein that plays with some of the inherent paradoxes that would be caused by time travel. ... This article or section does not cite its references or sources. ... Igor Dmitrievich Novikov (И́горь Дми́триевич Но́виков) (born November 10, 1935) is a Russian theoretical astrophysicist and cosmologist. ... University of Copenhagen The University of Copenhagen (Danish: Københavns Universitet) is the oldest and largest university and research institution in Copenhagen, Denmark. ... This article is about Jesus of Nazareth. ... The Saga of Darren Shan (The Cirque Du Freak Series in the United States) is a young adult book series written by Darren Shan about the struggle of a young man who has become involved in the world of vampires. ... Hitler redirects here. ... National Socialism redirects here. ... This article is about the television series. ... This article or section does not cite its references or sources. ... The grandfather paradox is a paradox of time travel, first described by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent (The Imprudent Traveller).[1] The paradox is this: Suppose a man traveled back in time and killed his biological grandfather before the latter met the...


Immutable timelines

Time travel in a type 1 universe does not allow any paradoxes, although in 1.3, events can appear to be paradoxical. Look up paradox in Wiktionary, the free dictionary. ...


In 1.1, time travel is constrained to prevent paradox. If one attempts to make a paradox, one undergoes involuntary or uncontrolled time travel. Michael Moorcock uses a form of this principle and calls it The Morphail Effect. 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. Michael John Moorcock (born December 18, 1939, in London, England) is a prolific English writer primarily of science fiction and fantasy who has also published a number of literary novels. ... Connie Willis at Clarion West, 1998 Constance Elaine Trimmer Willis (born 31 December 1945) is an American science fiction writer. ...

Example: A man who travels into the past with intentions to kill Hitler finds himself on a Montana farm in late April 1945.

In 1.2, the Novikov self-consistency principle asserts that the existence of a method of time travel constrains events to remain self-consistent (i.e. no paradoxes). This will cause any attempt to violate such consistency to fail, even if 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. Two examples of this kind of universe is found in Timemaster, a novel by Dr. Robert Forward, and the 1980 Jeannot Szwarc film Somewhere In Time (based on Richard Matheson's novel Bid Time Return).
An example which could conceivably fall into either 1.1 or 1.2 can be seen in book and film versions of Harry Potter and the Prisoner of Azkaban. Harry went back in time with Hermione to change history. As they do so it becomes apparent that they are simply performing actions that were previously seen in the story, although neither the characters nor the reader were aware of the causes of those actions at the time. This is another example of the predestination paradox. It is arguable, however, that the mechanics of time travel actually prevented any paradoxes, firstly, by preventing them from realizing a priori that time travel was occurring and secondly, by enabling them to recall the precise action to take at the precise time and keep history consistent.

In 1.3, 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. Jeannot Szwarc (born 21 November 1939) is a French film director. ... This article is about the 1980 film. ... Richard Matheson (born February 20, 1926) is an American author and screenwriter, typically of fantasy, horror, or science fiction. ... Bid Time Return is a 1975 science fiction novel by Richard Matheson. ... HP3 redirects here. ... Harry James Potter is the title character and the main protagonist of J. K. Rowlings Harry Potter fantasy series. ... Hermione Jean Granger (first name pronounced ) is a fictional character in J.K. Rowlings Harry Potter series. ... A predestination paradox, also called either a causal loop, or a causality loop and (less frequently) either a closed loop or closed time loop, is a paradox of time travel that is often used as a convention in science fiction. ... David Gerrold, born Jerrold David Friedman (January 24, 1944), in Chicago, Illinois, is an award-winning science fiction author who started his career in 1966 as a college student by submitting an unsolicited story outline for the television series Star Trek. ... The Man Who Folded Himself is a 1973 science fiction novel by David Gerrold. ... The Time Ships is a 1995 science fiction novel by Stephen Baxter. ... Stephen Baxter (born in Liverpool, 13 November 1957) is a British hard science fiction author. ...


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 too 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 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. Thrice Upon A Time is a book by James_P._Hogan_(writer), first published in 1980. ... At the 63rd World Science Fiction Convention in Glasgow, August 2005 James Patrick Hogan (born June 27, 1941, London) is a science fiction author. ... The Back to the Future trilogy is a comedic science fiction film trilogy written by Bob Gale and Robert Zemeckis, directed by Zemeckis, and distributed by Universal Pictures. ... William Tenn is the pseudonym for the science fiction work of Philip Klass (born May 9, 1920). ...


In type 2.1, attempts are being made at changing the timeline, however, all that is accomplished in the first tries is that the way of how decisive events happen is changed; final conclusions in the bigger scheme cannot be brought to a different outcome. Example: In the Movie Deja Vu a paper note is being sent to the past with vital information to prevent the main plot incident. All that happens, though, is that an ATF agent gets killed, with the final disaster still not being prevented; also, the very same agent died in the previous version of the timeline as well, albeit under different circumstances. Finally though, the timeline is changed (Claire Kuchever is being saved from murder) by sending a human back into the past in order to prevent the murder of Claire and the main incident (a terrorist attack), which is arguably a "stronger" measure than simply sending back a paper note. Déjà Vu is a science fiction crime thriller directed by Tony Scott and produced by Jerry Bruckheimer. ...

Similar to the Back to the Future movie trilogy, there seems to be a ripple effect (changes from the past 'propagate' into the present, and people in the present have altered memory of events occurred after the changes made to the timeline)
The type of timetravel in Deja Vu fits the 2.1 Type very well: Sending the paper note seems to be too "weak" a measure to cause any permanent effect, but agent Carlin going back into the past has a final decisive impact.

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 1.2 scenario.[citation needed] This is sometimes referred to as the "Time Dilution Effect." The Back to the Future trilogy is a comedic science fiction film trilogy written by Bob Gale and Robert Zemeckis, directed by Zemeckis, and distributed by Universal Pictures. ... The ripple effect is an education-related term associated with the studies of Jacob Kounin. ... This article does not cite any references or sources. ...


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,[44] 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 papernote sent back to the past in the film Deja Vu, as described above: Was it a too "weak" change, or was it after all just (time-local; that is, in the past) bad circumstance which made it have no effect, but it might have worked if the paper note would have been sent back 1 hour earlier, or 1 hour later into the past? As the universe in Deja Vu seems to be not entirely self-preserving from paradoxes (some, arguably minute, paradoxes, do occur), both versions seem to be equally probable, to which the film gives no further clarification.


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 phonebooth which traveled through the 'circuits of history' in Bill and Ted's Excellent Adventure). 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 which he cannot interact with. A compact disc player or CD player is an electronic device to play audio from compact discs. ... The De Lorean DMC-12 is a sports car that was manufactured by the De Lorean Motor Company for the American market in 1981 and 1982 in Northern Ireland. ... This article is about the first film in the Back to the Future trilogy. ... A classic red telephone box. ... Bill & Teds Excellent Adventure Bill & Teds Excellent Adventure (1989) is a comedy/science fiction film based on the idea of time travel. ... Adam Richard Sandler (born September 9, 1966) is an American comedian, actor, musician, screenwriter, and film producer. ... Click is a 2006 comedy/drama/fantasy film directed by Frank Coraci and written by Steve Koren and Mark OKeefe. ...


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." 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. This method of gradual time travel fits best in quantum physics, but is not as popular in modern science fiction. 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 back in time, because he was born "at the wrong end of time" and has to live backwards from in front. "Some people call it having second sight", he says. The Time Machine is a novel by H. G. Wells, first published in 1895, later made into two films of the same title. ... H. G. Wells at the door of his house at Sandgate Herbert George Wells (September 21, 1866 - August 13, 1946) was an English writer best known for his science fiction novels such as The War of the Worlds and The Time Machine. ... The Reverend Charles Lutwidge Dodgson (IPA: ) (27 January 1832 – 14 January 1898), better known by the pen name Lewis Carroll (), was an English author, mathematician, logician, Anglican clergyman and photographer. ... Through the Looking Glass redirects here. ... Terence Hanbury White (May 29, 1906 - January 17, 1964) was a writer. ... The Once and Future King is an Arthurian fantasy novel written by T.H. White. ... Wikibooks [[wikibooks:|]] has more about this subject: The Sword in the Stone This article is about the novel. ...


Time travel, or space-time 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, according to the theory of special relativity, this argument is based on a false premise. Special relativity rejects the idea of absolute time and space; there can be no universal truth about the spatial distance between events which occurred at different times (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, because the distance depends on the observer's frame of reference.[45] For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In physics, the concept of absolute time and absolute space are hypothetical models in which time either runs at the same rate for all the observers in the universe or the rate of time of each observer can be scaled to the absolute time by multiplying the rate by a... This article or section is in need of attention from an expert on the subject. ...


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 Bombs" to propel an enemy several seconds into the future, during which time the movement of the Earth causes the unfortunate victim to re-materialize in space. 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 six (not four!) co-ordinates 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.[citation needed] 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 cleverly 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. Cover of the first issue of 2000 AD, 26 February 1977. ... The Door into Summer is a science fiction novel by Robert A. Heinlein, published in 1957. ... The term handwaving is an informal term that describes either the debate technique of failing to rigorously address an argument in an attempt to bypass the argument altogether, or a deliberate gesture and admission that one is intentionally glossing over detail for the sake of time or clarity. ... In physics, the world line of an object is the unique path of that object as it travels through 4-dimensional spacetime. ... The Number of the Beast is a science fiction novel by Robert A. Heinlein published in 1980. ... Piers Anthony Dillingham Jacob (born August 6, 1934 in Oxford, England) is an American writer in the science fiction and fantasy genres, publishing under the name Piers Anthony. ... Incarnations of Immortality is the name of a seven-book fantasy series by Piers Anthony. ... This article contains brief biographies for major characters from Piers Anthonys Incarnations of Immortality series. ... This article is about the television series. ... The current TARDIS prop. ...


See also

Speculations

The grandfather paradox is a paradox of time travel, first described by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent (The Imprudent Traveller).[1] The paradox is this: Suppose a man traveled back in time and killed his biological grandfather before the latter met the... A predestination paradox, also called either a causal loop, or a causality loop and (less frequently) either a closed loop or closed time loop, is a paradox of time travel that is often used as a convention in science fiction. ... A temporal paradox is an impossible situation in which a time traveler interferes with the timeline involved in his own existence. ... This article is in need of attention from an expert on the subject. ... Ronald L. Mallett, Ph. ...

Claims of time travel

For other uses, see Philadelphia Experiment (disambiguation). ... The Chronovisor was supposedly a machine for viewing past and future events. ... It has been suggested that Talmud Jmmanuel be merged into this article or section. ... Darren Arthur Daulton (born January 3, 1962 in Arkansas City, Kansas), nicknamed Dutch, is a former catcher in Major League Baseball best remembered for his years with the Philadelphia Phillies. ... John Titors military insignia John Titor is the name used on several bulletin boards during 2000 and 2001 of a poster claiming to be a time traveler from the year 2036. ... This article is about the military experiments. ... A time slip (also called a timeslip) is an alleged paranormal phenomenon in which a person, or group of people, travel in time, usually without the aid of a time machine. ...

Fiction, humor

There are very few or no other articles that link to this one. ... Poster for Back to the Future (1985). ... Thiotimoline is a fictitious chemical compound conceived by science fiction author Isaac Asimov and described in a spoof scientific paper entitled The Endochronic Properties of Resublimated Thiotimoline in 1948. ... A time 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. ... Chronodynamics is an invented system of time travel found in the fiction of James Boudreaux II. By adhereing to the principle of self-consistency, put forth by Igor D. Novikov, Chronodynamics offers a reasonable and logical alternative to paradoxes. ...

References

  1. ^ a b Deutsch, David (1991). "Quantum mechanics near closed timelike curves". Physical Review D 44: 3197-3217. 
  2. ^ a b Alkon, Paul K. (1987). Origins of Futuristic Fiction. The University of Georgia Press, 95-96. ISBN 0-8203-0932-X. 
  3. ^ Alkon, Paul K. (1987). Origins of Futuristic Fiction. The University of Georgia Press, 85. ISBN 0-8203-0932-X. 
  4. ^ Derleth, August (1951). Far Boundaries. Pellegrini & Cudahy, 3. 
  5. ^ Derleth, August (1951). Far Boundaries. Pellegrini & Cudahy, 11-38. 
  6. ^ Flynn, John L.. Time Travel Literature. Retrieved on 2006-10-28.
  7. ^ Rudwick, Martin J. S. (1992). Scenes From Deep Time. The University of Chicago Press, 166-169. ISBN 0-226-73105-7. 
  8. ^ Uribe, Augusto (June 1999). "The First Time Machine: Enrique Gaspar's Anacronópete". The New York Review of Science Fiction Vol. 11, No. 10 (130): 12. 
  9. ^ a b c Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton, p. 499. ISBN 0-393-31276-3. 
  10. ^ a b Hawking, Steven. Space and Time Warps (html). Retrieved on 2006-11-20.
  11. ^ NOVA Online - Sagan on Time Travel
  12. ^ http://arxiv.org/pdf/gr-qc/0204022
  13. ^ Hawking, Stephen (1992). "Chronology protection conjecture". Physical Review D 46. 
  14. ^ 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. 
  15. ^ Keller, Simon; Michael Nelson (September 2001). "Presentists should believe in time-travel". Australian Journal of Philosophy 79.3: 333-345. 
  16. ^ a b c Gott, J. Richard (2002). "Time Travel in Einstein's Universe".  p.33-130
  17. ^ a b Jarrell, Mark. The Special Theory of Relativity (PDF) 7-11. Retrieved on 2006-10-27.
  18. ^ Chase, Scott I.. Tachyons entry from Usenet Physics FAQ. Retrieved on 2006-10-27.
  19. ^ Visser, Matt (1996). Lorentzian Wormholes. Springer-Verlag, p. 100. ISBN 1-56396-653-0. 
  20. ^ Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton, p. 502. ISBN 0-393-31276-3. 
  21. ^ Thorne, Kip S. (1994). Black Holes and Time Warps. W. W. Norton, p. 504. ISBN 0-393-31276-3. 
  22. ^ a b Visser, Matt (1996). Lorentzian Wormholes. Springer-Verlag, p. 101. ISBN 1-56396-653-0. 
  23. ^ Cramer, John G.. NASA Goes FTL Part 1: Wormhole Physics. Retrieved on 2006-12-02.
  24. ^ Visser, Matt; Sayan Kar, Naresh Dadhich (2003). "Traversable wormholes with arbitrarily small energy condition violations". Physical Review Letters 90: 201102.1—201102.4.  arXiv:gr-qc/0301003
  25. ^ Visser, Matt (1993). "From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture". Physical Review D 47: 554—565.  arXiv:hep-th/9202090
  26. ^ Visser, Matt (1997). "Traversable wormholes: the Roman ring". Physical Review D 55: 5212—5214.  arXiv:gr-qc/9702043
  27. ^ van Stockum, Willem Jacob (1936). "The Gravitational Field of a Distribution of Particles Rotating about an Axis of Symmetry". 
  28. ^ Lanczos, Kornel (1924, republished in 1997). "On a Stationary Cosmology in the Sense of Einsteins Theory of Gravitation". General Relativity and Gravitation 29 (3): 363—399. Springland Netherlands. doi:10.1023/A:1010277120072 . 
  29. ^ Earman, John (1995). Bangs, Crunches, Whimpers, and Shrieks: Singularities and Acausalities in Relativistic Spacetimes. Oxford University Press, p. 21. ISBN 0-19-509591-X. 
  30. ^ Tipler, Frank J (1974). "Rotating Cylinders and the Possibility of Global Causality Violation". Physical Review D 9: 2203. 
  31. ^ Earman, John (1995). Bangs, Crunches, Whimpers, and Shrieks: Singularities and Acausalities in Relativistic Spacetimes. Oxford University Press, p. 169. ISBN 0-19-509591-X. 
  32. ^ 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. 
  33. ^ Hawking, Stephen (1992). "Chronology protection conjecture". Physical Review D 46: 603 - 611. 
  34. ^ Anderson, Mark (August 18-24, 2007), "Light seems to defy its own speed limit", New Scientist 195 (2617): 10, <http://www.eurekalert.org/pub_releases/2007-08/ns-lst081607.php> 
  35. ^ [gr-qc/0102010] Many worlds in one
  36. ^ Taking the Cosmic Shortcut - ABC Science Online
  37. ^ Transcript of interview with Dr. Marc Rayman at "Space Place"
  38. ^ "http://www.pbs.org/wgbh/nova/time/thinktime.html" . 
  39. ^ Physics for Scientists and Engineers with Modern Physics, Fifth Edition, p.1258.
  40. ^ Vaidman, Lev. Many-Worlds Interpretation of Quantum Mechanics. Retrieved on 2006-10-28.
  41. ^ Greenberger, Daniel M; Karl Svozil (2005). "Quantum Theory Looks at Time Travel".  arXiv:quant-ph/0506027
  42. ^ Goldstein, Sheldon. Bohmian Mechanics. Retrieved on 2006-10-30.
  43. ^ "Time Travel and Resolving Paradoxes in Fiction"
  44. ^ see this discussion between two philosophers, for example
  45. ^ Geroch, Robert (1978). General Relativity From A to B. The University of Chicago Press, 124. 

David Deutsch (born 1953) is a physicist at Oxford University. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 301st day of the year (302nd in leap years) in the Gregorian calendar. ... The New York Review of Science Fiction is a monthly, long-running science fiction critical journal edited by David G. Hartwell and others. ... Kip S. Thorne Professor Kip Stephen Thorne, Ph. ... This page is a candidate for speedy deletion. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 324th day of the year (325th in leap years) in the Gregorian calendar. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Kip S. Thorne Professor Kip Stephen Thorne, Ph. ... Igor Dmitriyevich Novikov (Russian: ) (born November 10, 1935 in Moscow) is a Russian (and former Soviet) theoretical astrophysicist and cosmologist. ... Timothy Ferris (born August 29, 1944) is the best-selling author of twelve books, including Coming of Age in the Milky Way, for which he was awarded the American Institute of Physics Prize, and a nomination for the Pulitzer Prize. ... Alan Lightman is a physicist, novelist, and essayist born in Memphis, Tennessee in 1948, son of Richard Lightman, a movie theater owner, and Jeanne Garretson, a dancing teacher and volunteer Braille typist. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 300th day of the year (301st in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 300th day of the year (301st in leap years) in the Gregorian calendar. ... Professor Matt Visser is a Mathematics Professor at Victoria University of Wellington. ... Kip S. Thorne Professor Kip Stephen Thorne, Ph. ... This page is a candidate for speedy deletion. ... Kip S. Thorne Professor Kip Stephen Thorne, Ph. ... This page is a candidate for speedy deletion. ... Professor Matt Visser is a Mathematics Professor at Victoria University of Wellington. ... John G. Cramer (born 1934) is a Professor of Physics at the University of Washington in Seattle, USA. When not teaching, he works with the STAR detector at the new Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, and the particle accelerator at CERN in Geneva, Switzerland. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 336th day of the year (337th in leap years) in the Gregorian calendar. ... Professor Matt Visser is a Mathematics Professor at Victoria University of Wellington. ... Physical Review Letters is one of the most prestigious journals in physics. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... Professor Matt Visser is a Mathematics Professor at Victoria University of Wellington. ... Physical Review is one of the oldest and most-respected scientific journals publishing research on all aspects of physics. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... Professor Matt Visser is a Mathematics Professor at Victoria University of Wellington. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... Willem Jacob van Stockum (November 20, 1910-June 10, 1944) was a physicist who made an important contribution to the early development of general relativity. ... Cornelius Lanczos (Lánczos Kornél), born Kornél Löwy (February 2, 1893–June 25, 1974), was a Hungarian mathematician and physicist. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Frank J. Tipler (born in 1947 in Andalusia, Alabama) is a professor of mathematical physics at Tulane University in New Orleans, Louisiana. ... Physical Review is one of the oldest and most-respected scientific journals publishing research on all aspects of physics. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Kip S. Thorne Professor Kip Stephen Thorne, Ph. ... Igor Dmitriyevich Novikov (Russian: ) (born November 10, 1935 in Moscow) is a Russian (and former Soviet) theoretical astrophysicist and cosmologist. ... Timothy Ferris (born August 29, 1944) is the best-selling author of twelve books, including Coming of Age in the Milky Way, for which he was awarded the American Institute of Physics Prize, and a nomination for the Pulitzer Prize. ... Alan Lightman is a physicist, novelist, and essayist born in Memphis, Tennessee in 1948, son of Richard Lightman, a movie theater owner, and Jeanne Garretson, a dancing teacher and volunteer Braille typist. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 301st day of the year (302nd in leap years) in the Gregorian calendar. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 303rd day of the year (304th in leap years) in the Gregorian calendar. ...

Further reading

  • 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. Time Travel in Einstein's Universe: The Physical Possibilities of Travel Through Time. 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. 
  • Nikolic, H. "Causal paradoxes: a conflict between relativity and the arrow of time".  arXiv:gr-qc/0403121
  • 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. "Constructing Time Machines". Int. J. Mod. Phys. A, Theoretical.  arXiv:gr-qc/0210048
  • Toomey, David (2007). The New Time Travelers: A Journey to the Frontiers of Physics. W.W. Norton & Company. ISBN 978-0-393-06013-3. 

For the member of the National Assembly for Wales, see Paul Davies (Welsh politician). ... For the member of the National Assembly for Wales, see Paul Davies (Welsh politician). ... Dr. John Gribbin (1946 - ) is a British science writer and a visiting Fellow in astronomy at the University of Sussex. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... Heinz Pagels (1939 – 1988) was an American physicist who headed the New York Academy of Sciences. ... Clifford A. Pickover is an author, editor, and columnist in the fields of science, mathematics, and science fiction. ... Jenny Randles is a British author and member of BUFORA who specialises in writing books on UFO and paranormal phenomena. ... arXiv (pronounced archive, as if the X were the Greek letter χ) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ...

External links

  • Black holes, Wormholes and Time Travel Freeview Lecture. A Royal Society Lecture by Paul Davies provided by the Vega Science Trust
  • SF Chronophysics, a discussion of Time Travel as it relates to science fiction
  • On the Net: Time Travel by James Patrick Kelly in Asimov's Science Fiction
  • Howstuffworks' article on "How Time Travel Will Work"
  • Time Travel in Flatland?
  • NOVA Online: Time Travel
  • Professor Predicts Human Time Travel This Century Ronald Mallett, Professor at the University of Connecticut, has used Einstein’s equations to design an experiment to observe a time traveling neutron in a circulating light beam. He published his research in Physics Letters.
  • Through The Looking Glass: Time-Travel in Brane Theory An interview with a University of Hawaii research team seeking reverse-time communications using sterile neutrinos
  • Time Traveler Convention, at MIT - "Technically, you would only need one..."
  • Time Machines in Physics - almost 200 citations from 1937 through 2001
  • Stanford Encyclopedia of Philosophy:
    • Time Machines
    • Time Travel and Modern Physics
  • Internet Encyclopedia of Philosophy:
    • Time
    • Time Travel
  • Aparta Krystian. Conventional Models of Time and Their Extensions in Science Fiction A master's thesis exploring conceptual blending in time travel.
  • Time travellers from the future 'could be here in weeks' Two mathematicians suggest that the Large Hadron Collider might create tiny wormholes that could allow time travel

Two-dimensional analogy of space-time curvature described in General Relativity. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ... Coordinate time is the interval of time independent of relativistic time dilation. ... In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ... Space-time theories of consciousness relate the geometrical features of conscious experience, such as viewing things in space-time at a point, to the geometrical properties of the universe itself. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... Reaction time (RT) is the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response. ... Although the sense of time is not associated with a specific sensory system, the work of psychologists and neuroscientists indicates that our brains do have a system governing the perception of time. ... The specious present is the time duration wherein ones perceptions are considered to be in the present. ... Future studies reflects on how today’s changes (or the lack thereof) become tomorrow’s reality. ... The Long Now Foundation, established in 1996, is a private organization that seeks to become the seed of a very long-term cultural institution. ... In sociology and anthropology, time discipline is the general name given to social and economic rules, conventions, customs, and expectations governing the measurement of time, the social currency and awareness of time measurements, and peoples expectations concerning the observance of these customs by others. ... Time use research is a developing interdisciplinary field of study dedicated to knowing how people allocate their time during an average day. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ... This article is about the idea of space. ... A duration is an amount of time or a particular time interval. ... For other uses, see Time capsule (disambiguation). ... The time signature (also known as meter signature) is a notational convention used in Western musical notation to specify how many beats are in each measure and what note value constitutes one beat. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... For other uses, see Carpe diem (disambiguation). ... Tempus fugit on a sundial Tempus fugit is a Latin expression meaning time flees, more commonly translated as time flies. It is frequently used as an inscription on clocks. ...


  Results from FactBites:
 
Time - Time Travel (2954 words)
Time travel is the concept of traveling forward and backward to different points in time, much as we do through space.
The assumption that time travel or superluminal communications is impossible allows one to derive interesting results such as the no cloning theorem, and how the rules of quantum mechanics work to preserve causality is an active area of research.
Time, and the apparent movement of time, is connected to the number 12 - which is 1+2 =3 - or third dimension.
Time travel - Wikipedia, the free encyclopedia (4328 words)
Time travel is the concept of moving backward or forward to different points in time, in a manner analogous to moving through space.
On the other hand, the direction of time (or the arrow of time) may not be a fundamental intrinsic property of time, but rather could be viewed as an emergent property traceable to the fact that we live in a universe in which the entropy increases with time.
Time travel themes in science fiction and the media can generally be grouped into two main types and a third, less common type (based on effect—methods are extremely varied and numerous), each of which is further subdivided.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m