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122-410: Time travel is the hypothetical activity of traveling into the past or future . Time travel is a concept in philosophy and fiction , particularly science fiction . In fiction , time travel is typically achieved through the use of a device known as a time machine . The idea of a time machine was popularized by H. G. Wells 's 1895 novel The Time Machine . It is uncertain whether time travel to

244-665: A Sura of the Quran , Sura Al-Kahf . The version recalls a group of young monotheists escaping from persecution within a cave and emerging hundreds of years later. This narrative describes divine protection and time suspension. Another similar story in the Islamic tradition is of Uzair (usually identified with the Biblical Ezra ) whose grief at the Destruction of Jerusalem by the Babylonians

366-761: A computer -like screen , computer viruses , video chat , tanning beds , home treadmills , and more. In 1963, the time travel-themed Doctor Who premiered on BBC Television. The original series ran until 1989 and was revived in 2005. It has been extremely popular worldwide and has greatly influenced later TV science fiction. Other programs in the 1960s included The Outer Limits (1963–1965), Lost in Space (1965–1968), and The Prisoner (1967). Star Trek (the original series), created by Gene Roddenberry , premiered in 1966 on NBC Television and ran for three seasons. It combined elements of space opera and Space Western . Only mildly successful at first,

488-428: A space opera , went on to become a worldwide popular culture phenomenon , and the second-highest-grossing film series of all time. Since the 1980s, science fiction films , along with fantasy , horror , and superhero films, have dominated Hollywood's big-budget productions. Science fiction films often " cross-over " with other genres, including film noir ( Blade Runner - 1982), family film ( E.T.

610-420: A statistical law, so decreasing entropy and non-increasing entropy are not impossible, just improbable. Additionally, entropy statistically increases in systems which are isolated, so non-isolated systems, such as an object, that interact with the outside world, can become less worn and decrease in entropy, and it's possible for an object whose world-line forms a closed loop to be always in the same condition in

732-439: A " sense of wonder ". According to Isaac Asimov , "Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology ." Robert A. Heinlein wrote that "A handy short definition of almost all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on

854-421: A certain point (the train station). Alternatively, the sentence, "He ran past us at full speed," utilizes the concept of the past to describe the position of someone ("He") that is further than the speaker. The "past" is also used to define a time that is a certain number of minute before or after a particular hour , as in "We left the party at half-past twelve." People also use "past" to refer to being beyond

976-643: A cylinder is infinitely long and spins fast enough about its long axis, then a spaceship flying around the cylinder on a spiral path could travel back in time (or forward, depending on the direction of its spiral). However, the density and speed required is so great that ordinary matter is not strong enough to construct it. Physicist Ronald Mallett is attempting to recreate the conditions of a rotating black hole with ring lasers, in order to bend spacetime and allow for time travel. A more fundamental objection to time travel schemes based on rotating cylinders or cosmic strings has been put forward by Stephen Hawking, who proved

1098-468: A definitive judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory. The theory of general relativity describes the universe under a system of field equations that determine the metric , or distance function, of spacetime. There exist exact solutions to these equations that include closed time-like curves , which are world lines that intersect themselves; some point in

1220-499: A different universe than the one they came from; it's been argued that since the traveler arrives in a different universe's history and not their own history, this is not "genuine" time travel. The accepted many-worlds interpretation suggests that all possible quantum events can occur in mutually exclusive histories. However, some variations allow different universes to interact. This concept is most often used in science-fiction, but some physicists such as David Deutsch have suggested that

1342-448: A finite cylinder might produce closed timelike curves if the rotation rate were fast enough, 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." This result comes from Hawking's 1992 paper on the chronology protection conjecture , which Hawking states as "The laws of physics do not allow

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1464-535: A great and influential film. In 1954, Godzilla , directed by Ishirō Honda , began the kaiju subgenre of science fiction film, which feature large creatures of any form, usually attacking a major city or engaging other monsters in battle . 1968's 2001: A Space Odyssey , directed by Stanley Kubrick and based on the work of Arthur C. Clarke , rose above the mostly B-movie offerings up to that time both in scope and quality, and influenced later science fiction films. That same year, Planet of

1586-669: A journey to the Moon and how the Earth 's motion is seen from there. Kepler has been called the "father of science fiction". Following the 17th-century development of the novel as a literary form , Mary Shelley 's Frankenstein (1818) and The Last Man (1826) helped define the form of the science fiction novel. Brian Aldiss has argued that Frankenstein was the first work of science fiction. Edgar Allan Poe wrote several stories considered to be science fiction, including " The Unparalleled Adventure of One Hans Pfaall " (1835), which featured

1708-436: A large gravity well such as a black hole . A time machine that utilizes this principle might be, for instance, a spherical shell with a diameter of five meters and the mass of Jupiter . A person at its center will travel forward in time at a rate four times slower than that of distant observers. Squeezing the mass of a large planet into such a small structure is not expected to be within humanity's technological capabilities in

1830-492: A man planting a carob tree and asked him about it. The man explained that the tree would take 70 years to bear fruit, and that he was planting it not for himself but for the generations to follow him. Later that day, Honi sat down to rest but fell asleep for 70 years; when he awoke, he saw a man picking fruit from a fully mature carob tree. Asked whether he had planted it, the man replied that he had not, but that his grandfather had planted it for him. In Christian tradition, there

1952-423: A new timeline. Early science fiction stories feature characters who sleep for years and awaken in a changed society, or are transported to the past through supernatural means. Among them L'An 2440, rêve s'il en fût jamais ( The Year 2440: A Dream If Ever There Was One , 1770) by Louis-Sébastien Mercier , Rip Van Winkle (1819) by Washington Irving , Looking Backward (1888) by Edward Bellamy , and When

2074-415: 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 M. Steinberg , a quantum optics expert at

2196-457: A particular biological age or phase of being, as in, "The boy was past the age of needing a babysitter," or, "I'm past caring about that problem." The "past" is commonly used to refer to history, either generally or with regards to specific time periods or events, as in, "Past monarchs had absolute power to determine the law in contrast to many European Kings and Queens of today." Nineteenth-century British author Charles Dickens created one of

2318-457: A region of spacetime that is warped a certain way, and hence time travelers would not be able to travel back to earlier regions in spacetime, before this region existed. Stephen Hawking stated that this would explain why the world has not already been overrun by "tourists from the future". 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

2440-452: A scientific basis for the possibility of backward time travel in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed. These semiclassical arguments led Stephen Hawking to formulate the chronology protection conjecture , suggesting that the fundamental laws of nature prevent time travel, but physicists cannot come to

2562-402: 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. A variation of Hugh Everett 's many-worlds interpretation (MWI) of quantum mechanics provides a resolution to the grandfather paradox that involves the time traveler arriving in

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2684-409: A small amount of proper time passes for them, while a large amount of proper time passes elsewhere. This can be achieved by traveling at relativistic speeds or through the effects of gravity . For two identical clocks moving relative to each other without accelerating, each clock measures the other to be ticking slower. This is possible due to the relativity of simultaneity . However, the symmetry

2806-493: 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. Another approach involves a dense spinning cylinder usually referred to as a Tipler cylinder , a GR solution discovered by Willem Jacob van Stockum in 1936 and Kornel Lanczos in 1924, but not recognized as allowing closed timelike curves until an analysis by Frank Tipler in 1974. If

2928-470: A theorem showing that according to general relativity it is impossible to build a time machine of a special type (a "time machine with the compactly generated Cauchy horizon") in a region where the weak energy condition is satisfied, meaning that the region contains no matter with negative energy density ( exotic matter ). Solutions such as Tipler's assume cylinders of infinite length, which are easier to analyze mathematically, and although Tipler suggested that

3050-464: A thorough understanding of the nature and significance of the scientific method ." American science fiction author and editor Lester del Rey wrote, "Even the devoted aficionado or fan—has a hard time trying to explain what science fiction is," and the lack of a "full satisfactory definition" is because "there are no easily delineated limits to science fiction." Another definition comes from The Literature Book by DK and is, "scenarios that are at

3172-551: A time traveler should end up in a different history than the one he started from. On the other hand, Stephen Hawking has argued that even if the MWI is correct, we should expect each time traveler to experience a single self-consistent history, so that time travelers remain within their own world rather than traveling to a different one. The physicist Allen Everett argued that Deutsch's approach "involves modifying fundamental principles of quantum mechanics; it certainly goes beyond simply adopting

3294-495: A total estimated readership of at least 1 million), making it the world's most popular science fiction periodical . In 1984, William Gibson 's first novel, Neuromancer , helped popularize cyberpunk and the word " cyberspace ", a term he originally coined in his 1982 short story Burning Chrome . In 1986, Shards of Honor by Lois McMaster Bujold began her Vorkosigan Saga . 1992's Snow Crash by Neal Stephenson predicted immense social upheaval due to

3416-427: A traversable wormhole would require the existence of a substance with negative energy , often referred to as " exotic matter ". More technically, the wormhole spacetime requires a distribution of energy that violates various energy conditions , such as the null energy condition along with the weak, strong, and dominant energy conditions. However, it is known that quantum effects can lead to small measurable violations of

3538-516: A trip to the Moon . Jules Verne was noted for his attention to detail and scientific accuracy, especially in Twenty Thousand Leagues Under the Seas (1870). In 1887, the novel El anacronópete by Spanish author Enrique Gaspar y Rimbau introduced the first time machine . An early French/Belgian science fiction writer was J.-H. Rosny aîné (1856–1940). Rosny's masterpiece

3660-416: A vacuum. His experiment involved slow light as well as passing light through a vacuum. He generated two single photons , passing one through rubidium atoms that had been cooled with a laser (thus slowing the light) and passing one through a vacuum. Both times, apparently, the precursors preceded the photons' main bodies, and the precursor traveled at c in a vacuum. According to Du, this implies that there

3782-575: A very palatable form... New adventures pictured for us in the scientifiction of today are not at all impossible of realization tomorrow... Many great science stories destined to be of historical interest are still to be written... Posterity will point to them as having blazed a new trail, not only in literature and fiction, but progress as well. In 1928, E. E. "Doc" Smith 's first published work, The Skylark of Space , written in collaboration with Lee Hawkins Garby , appeared in Amazing Stories . It

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3904-623: A world of harmony and conformity within a united totalitarian state . It influenced the emergence of dystopia as a literary genre . In 1926, Hugo Gernsback published the first American science fiction magazine , Amazing Stories . In its first issue he wrote: By 'scientifiction' I mean the Jules Verne, H. G. Wells and Edgar Allan Poe type of story—a charming romance intermingled with scientific fact and prophetic vision... Not only do these amazing tales make tremendously interesting reading—they are always instructive. They supply knowledge... in

4026-477: 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. 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

4148-470: Is Les Navigateurs de l'Infini ( The Navigators of Infinity ) (1925) in which the word astronaut, "astronautique", was used for the first time. Many critics consider H. G. Wells one of science fiction's most important authors, or even "the Shakespeare of science fiction". His works include The Time Machine (1895), The Island of Doctor Moreau (1896), The Invisible Man (1897), and The War of

4270-704: Is a genre of speculative fiction , which typically deals with imaginative and futuristic concepts such as advanced science and technology , space exploration , time travel , parallel universes , and extraterrestrial life . It often explores human responses to changes in science and technology. Science fiction is related to fantasy , horror , and superhero fiction and contains many subgenres . Its exact definition has long been disputed among authors, critics, scholars, and readers. Subgenres include hard science fiction , which emphasizes scientific accuracy, and soft science fiction , focusing on social sciences. Other notable subgenres are cyberpunk , which explores

4392-576: Is a similar, story of "the Seven Sleepers of Ephesus ", which recounts a group of early Christians who hid in a cave circa 250 AD, to escape the persecution of Christians during the reign of the Roman emperor Decius . They fell into a sleep and woke some 200 years later during the reign of Theodosius II , to discover that the Empire had become Christian. This Christian story is recounted by Islam and appears in

4514-452: Is broken if one clock accelerates, allowing for less proper time to pass for one clock than the other. The twin paradox describes this: one twin remains on Earth, while the other undergoes acceleration to relativistic speed as they travel into space, turn around, and travel back to Earth; the traveling twin ages less than the twin who stayed on Earth, because of the time dilation experienced during their acceleration. General relativity treats

4636-452: Is disputed. Presentism is a school of philosophy that holds that the future and the past exist only as changes that occurred or will occur to the present, and they have no real existence of their own. In this view, time travel is impossible because there is no future or past to travel to. Keller and Nelson have argued that even if past and future objects do not exist, there can still be definite truths about past and future events, and thus it

4758-500: Is highly unlikely to be possible. Any theory that would allow time travel would introduce potential problems of causality . The classic example of a problem involving causality is the " grandfather paradox ," which postulates travelling to the past and intervening in the conception of one's ancestors (causing the death of an ancestor before conception being frequently cited). Some physicists, such as Novikov and Deutsch, suggested that these sorts of temporal paradoxes can be avoided through

4880-442: Is impossible for the time traveler to "change" history in any way. The time traveler's actions may be the cause of events in their own past though, which leads to the potential for circular causation , sometimes called a predestination paradox, ontological paradox, or bootstrap paradox. The term bootstrap paradox was popularized by Robert A. Heinlein 's story " By His Bootstraps ". The Novikov self-consistency principle proposes that

5002-511: Is no possibility of light traveling faster than c and, thus, no possibility of violating causality. Many have argued that the absence of time travelers from the future demonstrates that such technology will never be developed, suggesting that it is impossible. This is analogous to the Fermi paradox related to the absence of evidence of extraterrestrial life. As the absence of extraterrestrial visitors does not categorically prove they do not exist, so

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5124-434: Is not feasible with current technology. As for backward time travel, it is possible to find solutions in general relativity that allow for it, such as a rotating black hole . Traveling to an arbitrary point in spacetime has very limited support in theoretical physics , and is usually connected only with quantum mechanics or wormholes . Some ancient myths depict a character skipping forward in time. In Hindu mythology,

5246-407: Is not on the action having been completed by the present moment, but rather on its having taken place actively over a time period before another moment in the past. The verb tense used in the sentence "She had been walking in the park regularly before I met her" is past perfect continuous because it describes an action ("walking") that was actively happening before a time when something else in the past

5368-429: Is observed when one correlates measurements of idler photons to the corresponding signal photons. However, since interference can be observed only 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, only by gathering classical information from the entire system; thus causality

5490-619: Is often called the first great space opera . The same year, Philip Francis Nowlan 's original Buck Rogers story, Armageddon 2419 , also appeared in Amazing Stories . This was followed by a Buck Rogers comic strip , the first serious science fiction comic . Last and First Men: A Story of the Near and Far Future is a " future history " science fiction novel written in 1930 by the British author Olaf Stapledon . A work of unprecedented scale in

5612-503: Is one of the most influential examples of social science fiction , feminist science fiction , and anthropological science fiction . In 1979, Science Fiction World began publication in the People's Republic of China . It dominates the Chinese science fiction magazine market , at one time claiming a circulation of 300,000 copies per issue and an estimated 3–5 readers per copy (giving it

5734-431: Is possible that a future truth about a time traveler deciding to travel back to the present date could explain the time traveler's actual appearance in the present; these views are contested by some authors. A common objection to the idea of traveling back in time is put forth in the grandfather paradox or the argument of auto-infanticide. If one were able to go back in time, inconsistencies and contradictions would ensue if

5856-487: Is preserved. The experiment of Lijun Wang might also show causality violation since it made it possible to send packages of waves through a bulb of caesium gas in such a way that the package appeared to exit the bulb 62 nanoseconds before its entry, but a wave package is not a single well-defined object but rather a sum of multiple waves of different frequencies (see Fourier analysis ), and the package can appear to move faster than light or even backward in time even if none of

5978-495: Is sent, in all reference frames. The signal could be said to have moved backward in time. This hypothetical scenario is sometimes referred to as a tachyonic antitelephone . 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

6100-465: Is still being researched. Wormholes are a hypothetical warped spacetime permitted by the Einstein field equations of general relativity. 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

6222-436: Is used to describe actions that were already completed by a specific point in the past. For example, "she had walked" describes an action that took place in the past and was also completed in the past. The past perfects continuous tense refers to an action that was happening up until a particular point in the past but was completed. It is different from the past perfect tense because the emphasis of past perfect continuous verbs

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6344-411: Is walking" refers to a girl who is currently walking (present tense), while "she walked" refers to a girl who was walking before now (past tense). The past continuous tense refers to actions that continued for a period of time, as in the sentence "she was walking," which describes an action that was still happening in a prior window of time to which a speaker is presently referring. The past perfect tense

6466-572: The Manyoshu , tells of a young fisherman named Urashima-no-ko ( 浦嶋子 ) who visits an undersea palace. After three days, he returns home to his village and finds himself 300 years in the future, where he has been forgotten, his house is in ruins, and his family has died. One story in Judaism concerns Honi HaMe'agel , a miracle-working sage of the 1st century BC, who was a historical character to whom various myths were attached. While traveling one day, Honi saw

6588-646: The Vishnu Purana mentions the story of King Raivata Kakudmi , who travels to heaven to meet the creator Brahma and is surprised to learn when he returns to Earth that many ages have passed. The Buddhist Pāli Canon mentions the relativity of time. The Payasi Sutta tells of one of the Buddha 's chief disciples, Kumara Kassapa , who explains to the skeptic Payasi that time in the Heavens passes differently than on Earth. The Japanese tale of " Urashima Tarō ", first described in

6710-596: The Bohm interpretation presume that some information is being exchanged between particles instantaneously in order to maintain correlations between particles. This effect was referred to as " spooky action at a distance " by Einstein. Nevertheless, the fact that causality is preserved in quantum mechanics is a rigorous result in modern quantum field theories , and therefore modern theories do not allow for time travel or FTL communication . In any specific instance where FTL has been claimed, more detailed analysis has proven that to get

6832-448: The Novikov self-consistency principle or a variation of the many-worlds interpretation with interacting worlds. Time travel to the past is theoretically possible in certain general relativity spacetime geometries that permit traveling faster than the speed of light , such as cosmic strings , traversable wormholes , and Alcubierre drives . The theory of general relativity does suggest

6954-477: The Russian writer and paleontologist Ivan Yefremov presented a view of a future interstellar communist civilization and is considered one of the most important Soviet science fiction novels. In 1959, Robert A. Heinlein 's Starship Troopers marked a departure from his earlier juvenile stories and novels. It is one of the first and most influential examples of military science fiction , and introduced

7076-516: 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 speed of the center of the train exceeds the speed of any of the individual cars. Shengwang Du claims in a peer-reviewed journal to have observed single photons' precursors , saying that they travel no faster than c in

7198-447: The information revolution . In 2007, Liu Cixin 's novel, The Three-Body Problem , was published in China. It was translated into English by Ken Liu and published by Tor Books in 2014, and won the 2015 Hugo Award for Best Novel , making Liu the first Asian writer to win the award. Emerging themes in late 20th and early 21st century science fiction include environmental issues ,

7320-615: The "World of the Ancients" ( Qin dynasty ) to retrieve a magical bell and then travels forward to the "World of the Future" ( Song dynasty ) to find an emperor who has been exiled in time. However, the time travel is taking place inside an illusory dream world created by the villain to distract and entrap him. Samuel Madden 's Memoirs of the Twentieth Century (1733) is a series of letters from British ambassadors in 1997 and 1998 to diplomats in

7442-550: The Apes (the original), directed by Franklin J. Schaffner and based on the 1963 French novel La Planète des Singes by Pierre Boulle , was released to popular and critical acclaim, its vivid depiction of a post-apocalyptic world in which intelligent apes dominate humans . In 1977, George Lucas began the Star Wars film series with the film now identified as " Star Wars: Episode IV – A New Hope . " The series, often called

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7564-575: The Extra-Terrestrial - 1983), war ( Enemy Mine - 1985), comedy ( Spaceballs - 1987, Galaxy Quest - 1999), animation ( WALL-E – 2008, Big Hero 6 – 2014), Western ( Serenity – 2005), action ( Edge of Tomorrow – 2014, The Matrix – 1999), adventure ( Jupiter Ascending – 2015, Interstellar – 2014), mystery ( Minority Report – 2002), thriller ( Ex Machina – 2014), drama ( Melancholia – 2011, Predestination – 2014), and romance ( Eternal Sunshine of

7686-579: The MWI". Everett also argues that even if Deutsch's approach is correct, it would imply that any macroscopic object composed of multiple particles would be split apart when traveling back in time through a wormhole, with different particles emerging in different worlds. Certain experiments carried out give the impression of reversed causality , but fail to show it under closer examination. The delayed-choice quantum eraser experiment performed by Marlan Scully involves pairs of entangled photons that are divided into "signal photons" and "idler photons", with

7808-569: The Sleeper Awakes (1899) by H. G. Wells. Prolonged sleep is used as a means of time travel in these stories. The date of the earliest work about backwards time travel is uncertain. The Chinese novel A Supplement to the Journey to the West ( c.  1640 ) by Dong Yue features magical mirrors and jade gateways that connect various points in time. The protagonist Sun Wukong travels back in time to

7930-457: The Spotless Mind – 2004, Her – 2013). Science fiction and television have consistently been in a close relationship. Television or television-like technologies frequently appeared in science fiction long before television itself became widely available in the late 1940s and early 1950s. The first known science fiction television program was a thirty-five-minute adapted excerpt of

8052-548: The States and Empires of the Moon (1657) and The States and Empires of the Sun (1662), Margaret Cavendish 's " The Blazing World " (1666), Jonathan Swift 's Gulliver's Travels (1726), Ludvig Holberg 's Nicolai Klimii Iter Subterraneum (1741) and Voltaire 's Micromégas (1752). Isaac Asimov and Carl Sagan considered Somnium the first science fiction story; it depicts

8174-510: The Worlds (1898). His science fiction imagined alien invasion , biological engineering , invisibility , and time travel . In his non-fiction futurologist works he predicted the advent of airplanes , military tanks , nuclear weapons , satellite television , space travel , and something resembling the World Wide Web . Edgar Rice Burroughs 's A Princess of Mars , published in 1912,

8296-421: The absence of time travelers fails to prove time travel is physically impossible; it might be that time travel is physically possible but is never developed or is cautiously used. Carl Sagan once suggested the possibility that time travelers could be here but are disguising their existence or are not recognized as time travelers. Some versions of general relativity suggest that time travel might only be possible in

8418-422: The appearance of closed timelike curves." When a signal is sent from one location and received at another location, then as long as the signal is moving at the speed of light or slower, the mathematics of simultaneity in the theory of relativity show that all reference frames agree that the transmission-event happened before the reception-event. When the signal travels faster than light, it is received before it

8540-846: The best-known fictional personifications of the "past" in his short book, " A Christmas Carol ." In the story, the Ghost of Christmas Past is an apparition that shows the main character, a cold-hearted and tight-fisted man named Ebenezer Scrooge , vignettes from his childhood and early adult life to teach him that joy does not necessarily come from wealth. The past is the object of study within such fields as time , life , history , nostalgia , archaeology , archaeoastronomy , chronology , geology , historical geology , historical linguistics , ontology , paleontology , paleobotany , paleoethnobotany , palaeogeography , paleoclimatology , etymology and physical cosmology . Science fiction Science fiction (sometimes shortened to SF or sci-fi )

8662-410: The case that backward time travel could be possible but that it would be impossible to actually change the past in any way, an idea similar to the proposed Novikov self-consistency principle in physics. According to the philosophical theory of compossibility , what can happen, for example in the context of time travel, must be weighed against the context of everything relating to the situation. If

8784-510: The causal future of the world line is also in its causal past, a situation that can be described as time travel. Such a solution was first proposed by Kurt Gödel , a solution known as the Gödel metric , but his (and others') solution requires the universe to have physical characteristics that it does not appear to have, such as rotation and lack of Hubble expansion . Whether general relativity forbids closed time-like curves for all realistic conditions

8906-413: The concept of powered armor exoskeletons . The German space opera series Perry Rhodan , written by various authors, started in 1961 with an account of the first Moon landing and has since expanded in space to multiple universes , and in time by billions of years. It has become the most popular science fiction book series of all time. In the 1960s and 1970s, New Wave science fiction

9028-506: The creation of microrobots and micromachinery , nanotechnology , smartdust , virtual reality , and artificial intelligence (including swarm intelligence ), as well as developing the ideas of "necroevolution" and the creation of artificial worlds. In 1965, Dune by Frank Herbert featured a much more complex and detailed imagined future society than had previously in most science fiction. In 1967 Anne McCaffrey began her Dragonriders of Pern science fantasy series. Two of

9150-473: The effects of acceleration and the effects of gravity as equivalent , and shows that time dilation also occurs in gravity wells , with a clock deeper in the well ticking more slowly; this effect is 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

9272-439: The episodes, ran from 1959 to 1964. It featured fantasy , suspense , and horror as well as science fiction, with each episode being a complete story. Critics have ranked it as one of the best TV programs of any genre . The animated series The Jetsons , while intended as comedy and only running for one season (1962–1963), predicted many inventions now in common use: flat-screen televisions , newspapers on

9394-426: The famous and easy-to-replicate observation of atmospheric muon decay . The theory of relativity states that the speed of light is invariant for all observers in any frame of reference ; that is, it is always the same. Time dilation is a direct consequence of the invariance of the speed of light. Time dilation may be regarded in a limited sense as "time travel into the future": a person may use time dilation so that

9516-527: The field came to associate the term with low-budget, low-tech " B-movies " and with low-quality pulp science fiction . By the 1970s, critics within the field, such as Damon Knight and Terry Carr , were using "sci fi" to distinguish hack-work from serious science fiction. Peter Nicholls writes that "SF" (or "sf") is "the preferred abbreviation within the community of sf writers and readers." Robert Heinlein found even "science fiction" insufficient for certain types of works in this genre, and suggested

9638-469: The film Somewhere in Time as an example of such an ontological paradox, where a watch is given to a person, and 60 years later the same watch is brought back in time and given to the same character. Ross states that entropy of the watch will increase, and the watch carried back in time will be more worn with each repetition of its history. The second law of thermodynamics is understood by modern physicists to be

9760-743: The first science fiction novel . Some of the stories from The Arabian Nights , along with the 10th-century The Tale of the Bamboo Cutter and Ibn al-Nafis 's 13th-century Theologus Autodidactus , are also argued to contain elements of science fiction. Written during the Scientific Revolution and later the Age of Enlightenment are considered true science-fantasy books. Francis Bacon 's New Atlantis (1627), Johannes Kepler 's Somnium (1634), Athanasius Kircher 's Itinerarium extaticum (1656), Cyrano de Bergerac 's Comical History of

9882-480: The first story to feature an alternate history created as a result of time travel. One of the first stories to feature time travel by means of a machine is " The Clock that Went Backward " by Edward Page Mitchell , which appeared in the New York Sun in 1881. However, the mechanism borders on fantasy. An unusual clock, when wound, runs backwards and transports people nearby back in time. The author does not explain

10004-467: The first time-machine story, but I'm not sure that a clock quite counts". H. G. Wells ' The Time Machine (1895) popularized the concept of time travel by mechanical means. 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 were possible. In technical papers, physicists discuss

10126-530: The first to toy with the rich idea of time-travel in the form of an artifact sent backward from the future to be discovered in the present". In the science fiction anthology Far Boundaries (1951), editor August Derleth claims that an early short story about time travel is An Anachronism; or, Missing One's Coach , written for the Dublin Literary Magazine by an anonymous author in the June 1838 issue . While

10248-640: The first true science fiction novel . Jules Verne and H.G. Wells are pivotal figures in the genre's development. In the 20th century, expanded with the introduction of space operas , dystopian literature, pulp magazines , and the Golden Age of Science Fiction . Science fiction has been called the "literature of ideas ", and continues to evolve, incorporating diverse voices and themes, influencing not just literature but film, TV, and culture at large. Besides providing entertainment it can also criticize present-day society and explore alternatives, and inspiration

10370-480: The genre, it describes the history of humanity from the present onwards across two billion years. In 1937, John W. Campbell became editor of Astounding Science Fiction , an event that is sometimes considered the beginning of the Golden Age of Science Fiction , which was characterized by stories celebrating scientific achievement and progress . The "Golden Age" is often said to have ended in 1946, but sometimes

10492-431: The idea of absolute time , while his contemporary Gottfried Wilhelm Leibniz maintained that time is only a relation between events and it cannot be expressed independently. The latter approach eventually gave rise to the spacetime of relativity . Many philosophers have argued that relativity implies eternalism , the idea that the past and future exist in a real sense, not only as changes that occurred or will occur to

10614-472: The implications of the Internet and the expanding information universe, questions about biotechnology , nanotechnology , and post-scarcity societies . Recent trends and subgenres include steampunk , biopunk , and mundane science fiction . The first, or at least one of the first, recorded science fiction film is 1902's A Trip to the Moon , directed by French filmmaker Georges Méliès . It

10736-405: The interface between technology and society, and climate fiction , addressing environmental issues. Precedents for science fiction are argued to exist as far back as antiquity, but the modern genre primarily arose in the 19th and early 20th centuries when popular writers began looking to technological progress and speculation. Mary Shelley 's Frankenstein , written in 1818, is often credited as

10858-527: The intersection of other more concrete subgenres. Damon Knight summed up the difficulty, saying "Science fiction is what we point to when we say it." Forrest J Ackerman has been credited with first using the term "sci-fi" (analogous to the then-trendy " hi-fi ") in about 1954. The first known use in print was a description of Donovan's Brain by movie critic Jesse Zunser in January 1954. As science fiction entered popular culture , writers and fans active in

10980-415: The late 1940s and the 1950s are included. In 1942, Isaac Asimov started his Foundation series , which chronicles the rise and fall of galactic empires and introduced psychohistory . The series was later awarded a one-time Hugo Award for "Best All-Time Series". Theodore Sturgeon 's More Than Human (1953) explored possible future human evolution . In 1957, Andromeda: A Space-Age Tale by

11102-409: The local laws of physics in a region of spacetime containing time travelers cannot be any different from the local laws of physics in any other region of spacetime. The philosopher Kelley L. Ross argues in "Time Travel Paradoxes" that in a scenario involving a physical object whose world-line or history forms a closed loop in time there can be a violation of the second law of thermodynamics . Ross uses

11224-661: The narrator waits under a tree for a coach to take him out of Newcastle upon Tyne , he is transported back in time over a thousand years. He encounters the Venerable Bede in a monastery and explains to him the developments of the coming centuries. However, the story never makes it clear whether these events are real or a dream. Another early work about time travel is The Forebears of Kalimeros: Alexander, son of Philip of Macedon by Alexander Veltman published in 1836. Charles Dickens 's A Christmas Carol (1843) has early depictions of mystical time travel in both directions, as

11346-413: The near future. With current technologies, it is only possible to cause a human traveler to age less than companions on Earth by a few milliseconds after a few hundred days of space travel. Philosophers have discussed the philosophy of space and time since at least the time of ancient Greece ; for example, Parmenides presented the view that time is an illusion. Centuries later, Isaac Newton supported

11468-472: The novellas included in the first novel, Dragonflight , made McCaffrey the first woman to win a Hugo or Nebula Award . In 1968, Philip K. Dick 's Do Androids Dream of Electric Sheep? was published. It is the literary source of the Blade Runner movie franchise . In 1969, The Left Hand of Darkness by Ursula K. Le Guin was set on a planet in which the inhabitants have no fixed gender . It

11590-458: The null energy condition, and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics. Although early calculations suggested that a very large amount of negative energy would be required, later calculations showed that the amount of negative energy can be made arbitrarily small. In 1993, Matt Visser argued that the two mouths of

11712-414: The offices of those who have previously served in an organization, group, or event such as, "past president," or, "past champions." "Past" can also refer to something or someone being at or in a position that is further than a particular point. For instance, in the sentence, "I live on Fielding Road, just past the train station," the word "past" is used to describe a location (the speaker's residence) beyond

11834-406: The origin or properties of the clock. Enrique Gaspar y Rimbau 's El Anacronópete (1887) may have been the first story to feature a vessel engineered to travel through time. Andrew Sawyer has commented that the story "does seem to be the first literary description of a time machine noted so far", adding that "Edward Page Mitchell's story The Clock That Went Backward (1881) is usually described as

11956-405: The 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; 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 backward in time. According to current theories on the nature of wormholes, construction of

12078-430: The past is a certain way, it's not possible for it to be any other way. What can happen when a time traveler visits the past is limited to what did happen, in order to prevent logical contradictions. The Novikov self-consistency principle , named after Igor Dmitrievich Novikov , states that any actions taken by a time traveler or by an object that travels back in time were part of history all along, and therefore it

12200-416: The past would be physically possible. Such travel, if at all feasible, may give rise to questions of causality . Forward time travel, outside the usual sense of the perception of time , is an extensively observed phenomenon and is well understood within the framework of special relativity and general relativity . However, making one body advance or delay more than a few milliseconds compared to another body

12322-450: The past, conveying the political and religious conditions of the future. Because the narrator receives these letters from his guardian angel , Paul Alkon suggests in his book Origins of Futuristic Fiction that "the first time-traveler in English literature is a guardian angel". Madden does not explain how the angel obtains these documents, but Alkon asserts that Madden "deserves recognition as

12444-603: The play RUR , written by the Czech playwright Karel Čapek , broadcast live from the BBC's Alexandra Palace studios on 11 February 1938. The first popular science fiction program on American television was the children's adventure serial Captain Video and His Video Rangers , which ran from June 1949 to April 1955. The Twilight Zone (the original series), produced and narrated by Rod Serling , who also wrote or co-wrote most of

12566-485: 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 these methods, time dilation causes the end of the wormhole that has been moved to have aged less, or become "younger", than the stationary end as seen by an external observer; however, time connects differently through

12688-444: The possibility of closed timelike curves , which are world lines that form closed loops in spacetime, allowing objects to return to their own past. There are known to be solutions to the equations of general relativity that describe spacetimes which contain closed timelike curves, such as Gödel spacetime , but the physical plausibility of these solutions is uncertain. Many in the scientific community believe that backward time travel

12810-529: 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. Some versions of the many-worlds interpretation can be used to suggest that future humans have traveled back in time, but have traveled back to the meeting time and place in a parallel universe . There is a great deal of observable evidence for time dilation in special relativity and gravitational time dilation in general relativity, for example in

12932-540: The present time. Events such as Perth's Destination Day , MIT 's Time Traveler Convention and Stephen Hawking's Reception For Time Travellers heavily publicized permanent "advertisements" of a meeting time and place for future time travelers to meet. In 1982, a group in Baltimore , Maryland , identifying itself as the Krononauts, hosted an event of this type welcoming visitors from the future. These experiments only stood

13054-435: The present. Philosopher of science Dean Rickles disagrees with some qualifications, but notes that "the consensus among philosophers seems to be that special and general relativity are incompatible with presentism". Some philosophers view time as a dimension equal to spatial dimensions, that future events are "already there" in the same sense different places exist, and that there is no objective flow of time; however, this view

13176-461: The protagonist is transported to the prehistoric past by the magic of a "lame demon" (a French pun on Boitard's name), where he encounters a Plesiosaur and an apelike ancestor and is able to interact with ancient creatures. Edward Everett Hale 's "Hands Off" (1881) tells the story of an unnamed being, possibly the soul of a person who has recently died, who interferes with ancient Egyptian history by preventing Joseph 's enslavement. This may have been

13298-476: The protagonist, Ebenezer Scrooge, is transported to Christmases past and future. Other stories employ the same template, where a character naturally goes to sleep, and upon waking up finds themself in a different time. A clearer example of backward time travel is found in the 1861 book Paris avant les hommes ( Paris before Men ) by the French botanist and geologist Pierre Boitard , published posthumously. In this story,

13420-492: The pure waves in the sum do so. This effect cannot be used to send any matter, energy, or information faster than light, so this experiment is understood not to violate causality either. 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 traveled "instantaneously" between

13542-660: The same point of its history. In 2005, Daniel Greenberger and Karl Svozil proposed that quantum theory gives a model for time travel where the past must be self-consistent. Past In English grammar , actions are classified according to one of the following twelve verb tenses: past (past, uses of English verb forms , past perfect , or past perfect continuous ), present ( present , present continuous , present perfect , or present perfect continuous ), or future ( future , future continuous , future perfect , or future perfect continuous ). The past tense refers to actions that have already happened. For example, "she

13664-479: The signal photons emerging from one of two locations and their position later measured as in the double-slit experiment . 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

13786-515: The term speculative fiction to be used instead for those that are more "serious" or "thoughtful". Some scholars assert that science fiction had its beginnings in ancient times , when the line between myth and fact was blurred. Written in the 2nd century CE by the satirist Lucian , A True Story contains many themes and tropes characteristic of modern science fiction, including travel to other worlds, extraterrestrial lifeforms , interplanetary warfare, and artificial life . Some consider it

13908-470: The time of writing technologically impossible, extrapolating from present-day science...[,]...or that deal with some form of speculative science-based conceit, such as a society (on Earth or another planet) that has developed in wholly different ways from our own." There is a tendency among science fiction enthusiasts as their own arbiter in deciding what exactly constitutes science fiction. David Seed says it may be more useful to talk about science fiction as

14030-454: The time traveler were to change anything; there is a contradiction if the past becomes different from the way it is . The paradox is commonly described with a person who travels to the past and kills their own grandfather, prevents the existence of their father or mother, and therefore their own existence. Philosophers question whether these paradoxes prove time travel impossible. Some philosophers answer these paradoxes by arguing that it might be

14152-414: 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. This means that an observer entering the "younger" end would exit the "older" end at a time when it was the same age as the "younger" end, effectively going back in time as seen by an observer from

14274-474: Was happening (when "I met her"). Depending on its usage in a sentence, "past" can be described using a variety of terms. Synonyms for "past" as an adjective include, "former," "bygone," "earlier," "preceding," and "previous." Synonyms for "past" as a noun include, "history, "background," "life story," and "biography." Synonyms of "past" as a preposition include, "in front of," "beyond," "by," and "in excess of." The word "past" can also be used to describe

14396-404: Was influential on later filmmakers , bringing a different kind of creativity and fantasy . Méliès's innovative editing and special effects techniques were widely imitated and became important elements of the cinematic medium . 1927's Metropolis , directed by Fritz Lang , is the first feature-length science fiction film. Though not well received in its time, it is now considered

14518-480: Was known for its embrace of a high degree of experimentation, both in form and in content, and a highbrow and self-consciously " literary " or " artistic " sensibility . In 1961, Solaris by Stanisław Lem was published in Poland . The novel dealt with the theme of human limitations as its characters attempted to study a seemingly intelligent ocean on a newly discovered planet . Lem's work anticipated

14640-401: Was older than he was. Time travel themes in science fiction and the media can be grouped into three categories: immutable timeline; mutable timeline; and alternate histories, as in the interacting- many-worlds interpretation . The non-scientific term 'timeline' is often used to refer to all physical events in history, so that where events are changed, the time traveler is described as creating

14762-405: Was so great that God took his soul and brought him back to life after Jerusalem was reconstructed. He rode on his revived donkey and entered his native place. But the people did not recognize him, nor did his household, except the maid, who was now an old blind woman. He prayed to God to cure her blindness and she could see again. He meets his son who recognized him by a mole between his shoulders and

14884-408: Was the first of his three- decade -long planetary romance series of Barsoom novels , which were set on Mars and featured John Carter as the hero . These novels were predecessors to YA novels , and drew inspiration from European science fiction and American Western novels . In 1924, We by Russian writer Yevgeny Zamyatin , one of the first dystopian novels, was published. It describes

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