Time Travel, while regarded by many as theoretically impossible, still represents one of science fiction's most popular literary themes. The notion of being able to touch the future or affect the events of the past has fascinated mankind for many thousands of years, going as far back as the ancient prophets of Egypt and the oracles of Greece. In fact, speculations about temporal shifts and time paradoxes have occupied scientists, philosophers and poets for centuries, fueling countless stories, articles and debates on that arcane subject. But the concept of shuttling back and forth in time (at will) is a modern one, with its many aspects and conventions tied to a very simple principle. If time is a fourth dimension, along which the other three dimensions travel from second to second, then time travel is a means whereby a human being (or alien) can project his consciousness or body into the past or future. Best illustrated by one of the earliest excursions into the genre, Charles Dickens' A Christmas Carol (1843) provides the perfect template for time-travel stories. When the miserly Scrooge is taken by spirits on a journey into his past and possible future, he is both an observer and participant in the events. The ghosts (specifically the Ghost of Christmas Yet to Come) give him a chance to reshape that future by changing key elements in his present life, or face a cold, lonely death. Later temporal excusions, utilizing sleep-induced suspension, cryonics, specialized machines, dreams or other involuntary twists of fate, would provide dozens of other protagonists with similar dilemmas.
Like Scrooge, early time travelers did not make use of mechanical devices or other elaborate means of temporal displacement. They simply fell asleep and were later revived from that natural state in some future world. In L.S. Mercier's L'an deux mille quatre cent quarante (1771; translated as Memoirs of the Year Two Thousand Five Hundred, 1772), the protagonist falls into a deep sleep and awakens seven hundred years later in Utopia. Similarly, Washington Irving's "Rip Van Winkle" (1819) and the anonymous hero of William Henry Hudson's A Crystal Age (1887) both discover their extra long cat-naps have transported them into the future. Other early stories, including Edward Bellamy's Looking Backward (1888), Edwin Lester Arnold's Wonderful Adventures of Phra the Phoenician (1890), Alvarado Fuller's A.D. 2000 (1890), George Allan England's Darkness and Dawn (1914), and Victor Rousseau's The Apostle of the Cylinder (1917), used this ploy to place enlightened representatives of their society in Utopian or Dystopian worlds. Most of these tales had very little to do with actual time-travel because the journeys themselves were limited to a one-way trip; but the stories did provide their authors with a literary means for making spectulative commentary about the future and the nature of contemporary society itself.
In Louis Boussenard's Dix mille ans dans un bloc de glace (1889; translated as 10,000 Years in a Block of Ice, 1898), the "deep sleep" actually resembled a primitive form of cryonic suspension, which would later be established as its own sub-genre. Although the notion was first pioneered by W. Clark Russell in The Frozen Pirate (1887), H.G. Wells actually created the first machine for suspended animation, in When the Sleeper Awakes (1898), to freeze his travelers for the long journey in time. Philip Francis Nowlan used this concept to introduce Anthony "Buck" Rogers to the 25th century in "Armageddon 2419" (Amazing, 1928). More recent efforts to utilize cryonics for time travel include Edmund Hamilton's The Star of Life (1959), Rex Gordon's First Through Time (1962), Roger Zelazny's "The Graveyard Heart" (1964), Frederick Pohl's Age of Pussyfoot (1968), Mack Reynold's Looking Backward, from the Year 2000 (1973), and Larry Niven's A World Out of Time (1976). Wilson Tucker's The Year of the Quiet Sun (1970), the most realistic of these attempts, describes in intricate detail the efforts to send one man into the near future. Other stories, in which protagonists have attempted to slow (or retard) their aging while the rest of humanity (and time) races by, owe a tremendous debt of gratitude to another one of Wells' inventions, "The New Accelerator" (1901). Among the many contemporary tales that challenge the very nature of how man perceives the passage of time are Arthur C. Clarke's "All the Time in the World" (1952), Eric Frank Russell's "The Waitabits" (1955), John D. McDonald's The Girl, The Gold Watch, & Everything (1962), Brian Aldiss' Cryptozoic (1967), and Philip K. Dick's Counter-Clock World (1967) and Ubik (1969).
One-way trips into the past, though somewhat rare and less easy to explain in rational terms, also seemed to occupy many early writers. The narrator, in the anonymous "Missing One's Coach" (1838), discovers that he has passed through a temporal shift and wound up in eighth-century Britain. The morphine-addicted hero of Edgar Allan Poe's "A Tale of the Ragged Mountains" (1843) also finds himself trapped in a past epoch with no means of return to his own time. A much more thorough treatment was given to the notion by Mark Twain in A Connecticut Yankee in King Arthur's Court (1889). His nineteenth century hero, saved from execution by his special knowledge of solar eclipses, proceeds to change the medieval world of Camelot by introducing many of his century's inventions. Regrettably, this tinkering with the past produces a time paradox that must be resolved in a destructive climax, which ultimately eliminates all his work. A similar fate befalls the protagonist in Jack London's Before Adam (1906), whose consciousness projected into the mind of prehistoric man brings about certain anachronistic changes. Through the use of forbidden drugs, Wallace Cook's hero is Marooned in 1492 (1905), while H. Rider Haggard's white hunter Allan Quartermain is thrown back into the body of a paleolithic man in The Ancient Allan (1920) and Allan & The Ice Gods (1927). The protagonist in F. Scott Fitzgerald's The Great Gatsby (1925) believes that he can recapture a particular moment in time in order to change its tragic outcome, but all of the money in the world cannot save him from his untimely fate. Like Gatsby, Olaf Stapledon's last species of man, in his monumental saga Last & First Man (1930), believe they can recapture their lost humanity by traveling back nearly a billion and a half years from the future. Successors of Twain, London, Haggard, and Stapledon would use this formula time and again to "move" their characters backwards in time through some temporal shift. Like the involuntary time travelers in L. Sprague de Camp's Lest Darkness Fall (1941), John Taine's The Time Stream (1946) and Robin Carson's Pawn of Time (1957), most would plunge into worlds that were not of their own making but try nonetheless to use their superior technology to hold back the advance of chaos.
When H.G. Wells created a device for travelling in time, with The Time Machine (originally published as "The Chronic Argonauts" in Science Schools Journal, 1888; expanded and revised in 1895), man was suddenly able to control his journeys backward and forward. By taking his anonymous time traveler on a trip into the distant future, then returning him safely to the present, Wells established the pattern for most modern time-travel stories. (But he was really not the first to create a time machine. Several years earlier, Edward Page Mitchell sketched out plans for a device to travel into the past. In his "Clock That Went Backward" (1881), two boys discover a broken clock which, when wound backwards, transports them to sixteenth-century Holland.) Though it would take another thirty years, or so, for the notion to finally take root, Wells' invention not only gave time travelers mobility but also changed the way in which many other writers would approach the subject. Pulp writer Raymond Cummings was the first to expand upon Wells' theories with The Man Who Mastered Time (Argosy, 1924), The Shadow Girl (Argosy, 1929) and The Exile of Time (Argosy, 1931). Murray Leinster took the notion one step further by creating "The Fourth Dimensional Demonstrator" (1935), a machine that duplicates matter by simply bringing the same object (from the past) forward.
The popularity of stories utilizing time machines grew very quickly during the golden age of the pulp magazines, as a great many writers realized the potential of Wells' marvelous invention. Like their nineteenth century counterparts, they were more interested in using the time machine as a plot device for placing their protagonists in unusual worlds than in documenting its technological features. For example, the travelers in John W. Campbell's "Twilight" (1932) and "Night" (1935) confront a distant future in which man has long since ceased to exit, while P. Schuyler Miller's hero finds himself millions of years in the past, witnessing an alien invasion in "The Sands of Time" (1937). Other stories, notably Henry Kuttner's "The Time Trap" (1938), Pohl and Kornbluth's "Trouble in Time" (1939), and Poul Anderson's "The Man Who Came Early" (1956) and Theodore L. Thomas' "The Doctor" (1967), sought to place modern man in bygone eras. L. Sprague de Camp and Willy Ley both dealt more realistically with the notion of time travel in their respective articles "Language for Time Travellers" (1938) and "Geography for Time Travellers" (1939), by pointing out some of the difficulties which might be faced. And those themes were explored nicely in Anthony Boucher's "Barrier" (1942) and David I. Masson's "A Two-Timer" (1966).
C.L. Moore, writing under the pseudonym of Lawrence O'Donnell, first suggested in "Vintage Season" (1946) that time travel might be used by the tourist industry, offering visitors from a distant future the one safe spot where they can watch the atomic war begin. Since then, sightseeing or eavesdropping on past events have featured prominently in numerous time-travel stories, including T. L. Sherred's "E for Effort" (1947), Isaac Asimov's "The Dead Past" (1956), Harry Harrison's "Famous First Words" (1965), and John Brunner's The Productions of Time (1967). The Crucifixion of Christ seems to be one of the more popular destinations for time travelers, as evidenced by Arthur Porges' "The Rescuer" (1962), Michael Moorcock's Behold the Man (1965), Gary Kilworth's "Let's Go to Golgotha" (1975), and Gore Vidal's Live From Golgotha (1992), while Ian Watson's "The Very Slow Time Machine" (1978) makes it possible for the Messiah to be projected into the future. Other famous historical figures to appear in time-travel stories include Leonard da Vinci in Manly Wade Wellman's Twice in Time (1957) and Kit Reed's "Mister Da V" (1962); Abraham Lincoln in Robert Silverberg's "Assassin" (1957) and Wilson Tucker's The Lincoln Hunters (1957); Albert Einstein, Adolf Hitler, and Franklin Roosevelt in James Hogan's The Proteus Operation (1986); Socrates and Pizarro in Silverberg's "Enter a Soldier" (1989), and many, many others.
The dangerous possibility of accidentally changing some past event (and thereby causing a rift in the space-time continuum) also gave rise to a variety of time-travel stories which dealt with paradoxes. In "The Brooklyn Project" (Planet Stories, 1948), William Tenn's time machine precipitates changes in the present by its mere presence in the past. In Ray Bradbury's "A Sound of Thunder" (1952), a dinosaur hunter unwittingly steps on a butterfly in prehistoric times and changes his own future world. In Robert Silverberg's Up the Line (1968), sightseers converge at the Crucifixion, even though the Gospels never described such a multitude. Both Arthur C. Clarke's "Time's Arrow" (1950) and Ross Rocklynne's "Time Wants a Skeleton" (1968) reveal modern artifacts in million-year-old rock. Occasionally, paradoxes occurred when time travelers came face-to-face with themselves. In Ralph Milne Farley's "The Man Who Met Himself" (1935), Robert Heinlein's "By His Bootstraps" (1941) and "All You Zombies" (1959), William Tenn's "Me, Myself and I" (1947), E.C. Tubb's "Thirty-Seven Times" (1957) and David Gerrold's The Man Who Folded Himself (1973), the heroes keep running into other versions of themselves. Some travelers in time actually try to alter the past with their own actions. The hero, in Silverberg's "Assassin," (1957) tries to prevent Lincoln's assassination, while the time traveler, in Maurice Vaisberg's "The Sun Stood Still" (1958), attempts to kill Joshua at the battle of Jericho. Similarly, the crazed director, in Harry Harrison's The Technicolor Time Machine (1967), decides to shoot his latest epic (about the Viking discovery of North America) on location in the past; but when the Vikings fail to appear, he imports them thus setting into motion the actual events. In "Delenda Est" (1955), Poul Anderson's hapless agents discover that Rome has fallen centuries earlier because Scipio Africanus never lived to challenge Hannibal at Zama. The most popular time paradox deals with a man who returns in time to kill his own grandfather, and was first introduced to readers in Nathan Schachner's "Ancestral Voices" (1933). Since then, many time-travel stories have wrestled with that perplexing problem, including David Daniel's "The Branches of Time" (1935), Robert Sheckley's "A Thief in Time" (1954) and "Slaves of Time" (1974).
Since small changes in the past can produce major changes in the future, some writers have introduced guardians to protect and maintain the integrity of historical events. Jack Williamson first suggested the notion of "time police" in The Legion of Time (1938), in which conflicting realities battle throughout time for the right to exist. H. Beam Piper introduced his own version with the "Paratime Police" in a series of stories, beginning with "Police Operation" (1948), "Last Enemy" (1950), "Temple Trouble" (1951), "Time Crime" (1952), and Lord Kelvan of Otherwhen (1965). Similar tales have followed, notably Charles Harness' The Paradox Men (1949), Poul Anderson's "time patrolmen" (in The Guardians of Time, 1960, and The Corridors of Time, 1965), Larry Maddock's "Agent of T.E.R.R.A." and Keith Laumer's Dinosaur Beach (1971). John Varley's future travelers in Air Raid (later released as Millennium, 1982) have tampered so much with the past that they must suffer through "timequakes" which will one day destroy their world. Invariably, though, problems develop between the alternate realities that erupt into full scale wars. Simon Hawke's Time Wars series, beginning with The Ivanhoe Gambit (1984) through the twelfth book The Six-Gun Solution (1991), introduced Lucas Priest and his band of time-warriors, while Robert Adams' Castaways in Time (1984) fight to preserve the past with their advanced weapons. The notion of time travel has consistently fascinated writers throughout the ages, but few have actually studied the dynamics of the trip or analyzed the phenomenon in depth. Larry Niven's essay "The Theory and Practice of Time Travel," included in All the Myriad Ways (1971), offers an interesting introduction to the problems of time travel, while Paul A. Carter's The Creation of Tomorrow (1977) provides the best survey on the subject in science fiction magazines. Copyright 1995 by John L. Flynn THIS ARTICLE WAS ORIGINALLY PUBLISHED IN 1995 IN THE ENCYCLOPEDIA GALACTICA.