The theme of a closed loop in Time appears in sf in two distinct senses. A classic form of Time Paradox (which see) comes into being when the chain of causality eats its own tail to leave a circular sequence of events with no logical starting point, as in Robert A Heinlein's two famous examples: "By His Bootstraps" (October 1941 Astounding as by Anson MacDonald) and "All You Zombies –" (March 1959 F&SF). The present entry discusses the form of time loop in which, typically, periods of time are repeated and re-experienced by a character's consciousness: there is often some hope of breaking out of the useless cycle of repetition.
This is not so in Anthony Armstrong's early comic-fantasy example "The Prince's Birthday Present" (in The Prince Who Hiccupped and Other Tales, coll 1932), whose ungrateful recipient of three wishes – multiplied by recursive wishing to an indefinite number – is finally unwise enough to ask that he may relive the last, particularly enjoyable half-hour; the replay of course includes this fatal wish. A Mad Scientist entraps his victim and indeed the whole world in a reiterated New Year's Eve in the Shadow radio segment "The Man Who Murdered Time" (1 January 1939). One of the many temporal complications of Keith Laumer's Dinosaur Beach (1971) sees the protagonist enter a closed time loop where an older and wiser version of himself insists that (as he had been uselessly told by his predecessor, and so on back through an unknown number of cycles) the new arrival must kill his elder self to break the loop. Richard A Lupoff's "12:01 PM" (December 1973 F&SF) traps its protagonist in the same repeated hour, always resetting to the time of the title with even death offering no release; this became a short Oscar-nominated film, 12:01 PM (1991) directed by Jonathan Heap, and a longer made-for-tv feature: 12:01 (1993) directed by Jack Sholder (again see 12:01 PM). In Philip K Dick's "A Little Something For Us Tempunauts" (in Final Stage, anth 1974; rev 1975; ed Barry N Malzberg and Edward L Ferman), the cycle may be ultimately inescapable; there is a grim suspicion that the US chrononauts' suicidal attempt to disrupt the obscurely sensed time-loop has in fact brought it into being. The cast of Jack Skillingstead's Life on the Preservation (2013) is trapped in the domed City of Seattle, forever recycling the same day.
When memories of past circuits of a time loop are permitted, there is the possibility of transforming the imprisoning circularity into an upward spiral, a learning curve. Successive dreams in Ole Luk-Oie's The Defence of Duffer's Drift (1904 chap) as by Backsight Forethought reiterate a Boer War skirmish with steadily increasing understanding and improvement of small-unit tactics against a larger force. Ken Grimwood's Replay (1987) offers its protagonist the repeated opportunity to relive the "same" life with knowledge of past iterations, and the film Groundhog Day (1993) does similarly with a single recurring day: escape from the loop requires learning to steer a perfect course through replayed time. (This film's similarity to "12:01 PM" and 12:01 PM above is sufficiently strong that Lupoff and his director seriously contemplated legal action.) Further stories dealing with the repeated replay of a single day are "Doubled and Redoubled" (February 1941 Unknown) by Malcolm Jameson, "Friday, the Nineteenth" (Summer 1950 F&SF) by Elisabeth Sanxay Holding (1889-1955) and One Fine Day (1981) by Leon Arden – who did in fact sue the makers of Groundhog Day over similarities, though without success. The same general structure, in a Military SF context of progressively learning to be a better soldier with each iteration, is central to the film Edge of Tomorrow (2014). Other relevant Cinema productions include Los Cronocrímenes (2007; vt Timecrimes), Triangle (2009), Source Code (2011) About Time (2013) and Palm Springs (2020).
A further notable novel example of learning better from time-loop experiences is Kate Atkinson's Life After Life (2013), with its repeated rewinds and replays of a life to the point where premature death can be sidestepped. Roger Zelazny's "Divine Madness" (Summer 1966 Magazine of Horror) has something of the same quality, with recurring Time in Reverse episodes that eventually backtrack to the desired Jonbar Point and allow history to be steered into a better course. This trope is anticipated in fantasy by James Branch Cabell's The High Place (1923), whose Antihero reverts to childhood with full memory of his many appalling crimes, all of which he cheerfully commits again until he nears the turning point that leads to final catastrophe: only then does he piously embrace reform.
A frequent sf conceit is that the entire cosmos follows a recurring time loop: this is a central tenet of the Religion of Ritornel in Charles Harness's The Ring of Ritornel (1968), though the book ends with a strong suggestion that this past cycle will now be broken. The City in Diana Wynne Jones's A Tale of Time City (1987) exists outside Time but follows its course in an endless loop, as though time were a circular railway track; the same author's Archer's Goon (1984) features a more mundane city which – for complex reasons and for the most part unknowingly – has lived twice through the same thirteen-year period. [DRL]
see also: Donnie Darko; Robinson Crusoe on Mars (1964); Tenet; Trinity.
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