Some interpretations of time travel also suggest that an attempt to travel backwards in time might take one to a parallel universe whose history would begin to diverge from the traveler's original history after the moment the traveler arrived in the past. 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.
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", 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."
Louis-Sébastien Mercier's L'An 2440, rêve s'il en fût jamais ("The Year 2440: A Dream If Ever There Were 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.
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. 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.
Charles Dickens' 1843 book A Christmas Carol is considered by some 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.
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. Another clear early example of time travel in fiction is the short story The Clock That Went BackwardPDF (35.7 K
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.
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. 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.
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.
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