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A time loop or temporal loop is a common plot device in science fiction (especially in universes where time travel is commonplace) where a certain length of time (such as a few hours, or a few days) repeats over and over. When the time loop "resets", the memories of most characters are reset, and behave as though they're not aware of the loop. The plot is advanced by having one or more central characters retain their memory or become aware of the loop through déjà vu.
One well-known example of this is in the 1993 film Groundhog Day, in which the main character is the only one affected by the time loop. Stories with time loops commonly center on correcting past mistakes or on getting a character to recognize some key truth; escape from the loop may then follow.
The closed loop in time, in which an event becomes its own cause, is the simplest narrative form of the time-paradox story, seized upon by several of the contestants invited by the editor of Amazing Stories to find a clever ending for Ralph Milne Farley's "The Time-Wise Guy" (1940). More notable examples include Ross Rocklynne's "Time Wants a Skeleton" (1941), Bester's "The Push of a Finger" (1942), P. Schuyler Miller's "As Never Was" (1952) and Mack Reynolds's "Compounded Interest" (1956). Greater ingenuity is exercised when these loops become more complicated, forming convoluted sealed knots. Two classic exercises in this vein were written by Robert A. Heinlein, "By His Bootstraps" (1941) as Anson MacDonald and "—All You Zombies—" (1959), the latter being a story whose central character moves back and forth in time and undergoes a sex-change in order to become his own mother and father.
Types of Time Loops 
Physical Time Loop 
In a physical time loop (rarely seen in the media), the spacetime loops around to form several closed timelike curves. Since the time in that region is looped, a person could escape it only by leaving the affected area. Also, there would be an infinite number of copies of any matter in the area, unless an object left the loop. In that case, there would only be as many copies of that object as many times it completed the loop. This type of time loop cannot be ended or destroyed.
Conscious Time Loop 
In a conscious time loop, everyone's consciousness loops through time. In such a time loop, causality could easily be violated.
In popular culture 
||This article may contain excessive, poor, or irrelevant examples. (November 2012)|
The following television series featured time loops as a main theme or at least fairly frequently:
- Continuum - A police officer and eight criminals from 2077 are sent back to 2012 when the criminals are attempting to escape execution; there is growing evidence to suggest that the time-travel used has created a time loop where their actions in 2012 will create the circumstances that created the world they left in 2077.
- Fringe has several time loops through the shows running time. Most prominatly the episode ("White tulip").
- Day Break - A police officer relives the same day over and over, and has to figure out how to save himself and those close to him from a host of threats.
- Doctor Who makes frequent use of time travel. A number of episodes involve or make mention of a time loop (also referred to as a "chronic hysteresis").
- Higurashi no Naku Koro ni - The story is shown in chapters, each one a variation of the same time period.
- Lexx - Stanley Tweedle, Zev, Kai and 790 travel the span of two universes on a Manhattan-sized living insect ship, in an effort to discover a way to defeat a villain called "His Divine Shadow".
- The Tatami Galaxy - An unnamed student relives the first two years of his college career repeatedly, choosing a different club to join at the beginning each time, unaware consciously of the time loop.
- Tru Calling - A university graduate working in the city morgue is able to repeat the same day over again to prevent murders or other disasters.
- Steins;Gate - A self-proclaimed mad scientist accidentally discovers time travel and uses his unique ability to retain memories across world lines to attempt to change the world.
Time loops have been featured in individual episodes of many TV series, including: Angel ("Time Bomb"), The Angry Beavers, Blood Ties, Buffy the Vampire Slayer ("Life Serial"), Cardcaptor Sakura, Charmed, Crime Traveller, Family Guy, Farscape, Futurama, Haven ("Audrey Parker's Day Off"), Justice League Unlimited, Lois & Clark: The New Adventures of Superman, Lost ("Flashes Before Your Eyes"), My Little Pony: Friendship is Magic, The Outer Limits ("Déjà Vu", "The Refuge"), Phineas and Ferb ("Phineas and Ferb's Quantum Boogaloo"), Red Dwarf ("White Hole"), Silver Surfer, Smallville, South Park ("Cancelled"), Stargate SG-1 ("Window of Opportunity"),Star Trek: Enterprise ("Future Tense"), Star Trek: The Next Generation ("Cause and Effect", "Time Squared"), Star Trek: Voyager ("Coda"), The Suite Life on Deck, Supernatural, The Twilight Zone ("Shadow Play"), The Twilight Zone (2002 TV series), The X-Files ("Monday"), and Xena: Warrior Princess ("Been There, Done That").
- 12:01 PM and 12:01 - two films (a 1990 short and a 1993 full-length), based upon Richard A. Lupoff's short story of the same name.
- 1408 - A jaded writer is trapped in a hotel room that physically and psychologically torments him, and prevents his escape. Although the main storyline of the film is not a time loop, this device does appear as one of the many horrors inflicted by the room.
- Bless the Child, a 2003 Hong Kong film
- Blind Chance - Krzystof Kieslowski's 1987 film following three different possibilities, all spouting from chance. Precursor to Tykwer's Run Lola Run.
- Christmas Do-Over - A shallow ad executive finds himself reliving Christmas day over and over.
- Christmas Every Day - A 13-year-old boy relives Christmas day again and again.
- Galaxy Quest - Jason Nesmith (Tim Allen), actor of a show in which he is Commander of a space ship, finds that the show is believed to be real to some extraterrestrials involved in a galactic war. Hoping to save them and his friends, who include actress Gwen (Sigourney Weaver) and actors Alex (Alan Rickman) and Fred (Tony Shalhoub), he activates the Omega 13, a time machine that sends its user 13 seconds into the past, which is all the time he needs to defeat their enemy in one desperate, brave move.
- Groundhog Day - A jaded weather man relives the same day, Groundhog Day, over and over, while stuck in a small town, Punxsutawney, Pennsylvania, due to a winter storm.
- Il Mare and its Hollywood remake, The Lake House - these two films share time-loop like features.
- The Last Day of Summer - A boy relives his last day of summer after being repeatedly hit on the head.
- Limbo 2004 - An attorney finds himself stuck in Limbo, neither alive or dead. He is in a unique time loop that lasts 1 hour and does not move him back to the same place when time resets.
- Mickey's Once Upon a Christmas - retells Christmas Every Day with Huey, Dewey, and Louie.
- Nirvana - time loop happens to a fictional person in a virtual reality game.
- Pleasantville - Pleasantville is a town in a TV show, so its events will loop as long as it is syndicated. It also has a spatial loop: the end of Main Street is also where it begins.
- Pokémon: Giratina and the Sky Warrior - Dialga traps Giratina in a time loop, preventing it from leaving the Reverse World.
- Primer - Film deals with a time loop that is described as being like a cul-de-sac with an "A end" and a "B end"; one character, Abe, tries to re-enact a violent incident at a party, again and again, so that he will be seen as the hero.
- Source Code - A film in which the protagonist repeatedly lives out the last eight minutes of a victim of a terrorist bombing in order to try to ascertain who the bomber is and to prevent them from detonating a dirty bomb in central Chicago.
- Timecrimes (Originally Los Cronocrímenes), is a 2007 time loop film from Spain.
- Triangle (2009) - this film involves a young woman trapped in a loop. There are copies of people and items, seemingly allowing many variations on the loop happening at the same time.
- Urusei Yatsura 2: Beautiful Dreamer - The day before Tomobiki High School's student fair is looped repeatedly.
- Strange Life of Ivan Osokin (1915 (Russian); 1947 (English)) by P. D. Ouspensky. Unsuccessful struggle of Ivan Osokin to correct his mistakes when given a chance to relive his past.
- "12:01 PM", an influential 1973 short story by Richard A. Lupoff, adapted many times for film and television (see above).
- All You Need Is Kill (2004 (Japanese); 2009 (English)), a novel by Hiroshi Sakurazaka, featuring a soldier who relives an unwinnable battle endlessly, until he wins it.
- Before I Fall is a 2010 novel by Lauren Oliver, in which a teenage girl who dies in a car crash relives her last day seven times.
- The Dark Tower, a series of seven novels by Stephen King featuring many elements of time travel, including a time loop.
- The Day Room, a short play by Don DeLillo, features actors in a play who perform the roles of doctors, nurses, and patients in a "day room" of the Arno Klein Psychiatric Wing. However, the play is performed at unannounced locations and times.
- In a story in The Decameron, a dead man (Guido degli Anastagi) is ordered to catch his dead recalcitrant beloved and tear her apart, every Friday.
- The Details of Nikita Vorontsov's Life (1984) by Arkady Strugatsky.
- "Doubled and Redoubled", a short story by Malcolm Jameson that appeared in the February, 1941 issue of Unknown. Accidentally cursed by a witch, the protagonist repeats a "perfect" day, including a lucky bet, a promotion, a heroically foiled bank robbery, and a successful wedding proposal. This story was a precedent to Groundhog Day and 12:01 PM.
- HELP! I'm Trapped In the First Day of School! (1994) by Todd Strasser. A boy keeps repeating his first day of school.
- I Am the Cheese (1977). Technically not a true time loop novel, but the young main character, who is revealed to be insane, acts out the same week over and over.
- "A Little Something for Us Tempunauts", a 1975 short story by Philip K. Dick.
- In Lord Sunday (2010), the last of the The Keys to the Kingdom, a series of seven young adult fantasy novels by Garth Nix, the main character's mother is stuck within a time-loop.
- Lost in a Good Book (2002), the second of the Thursday Next novels by Jasper Fforde. The title character travels back in time to save her husband from being eradicated and experiences a time loop before returning to her present-day 1985.
- The Man Who Folded Himself (1973), by David Gerrold - A young man in possession of a time machine enjoys hedonistic adventures with a future version of himself who is one day (or more) older.
- Mathematicians in Love, a 2006 novel by Rudy Rucker.
- The Neverending Story, a book by Michael Ende - a time loop is deliberately set in motion at one point to force Bastian's hand. (Original German title: Die unendliche Geschichte: Von A bis Z) (1979).
- The Plot to Save Socrates, a 2006 novel by Paul Levinson.
- In The Rashness of Haruhi Suzumiya there is a chapter Endless Eight in which Haruhi Suzumiya creates a time loop because she never wants their vacation to end.
- Replay, a Ken Grimwood novel (1987) in which the main character suddenly shifts to much earlier in his life, then relives shorter and shorter periods.
- "That Feeling, You Can Only Say What It Is in French", 1998 short story by Stephen King.
- "This is Death," a story by Donald E. Westlake in which a man relives his suicide for eternity.
Video Games 
- The Legend of Zelda: Majora's Mask, a Nintendo 64 video game in which the main protagonist, Link, has three days to prevent the end of the world, in which a time-loop occurs until he is able to stop the world-ending event.
- Ephemeral Fantasia, a PlayStation 2 RPG where the main character, a minstrel named Mouse, is trapped in a five-day time loop by an evil king, and must defeat him to stop the loop.
- Call of Duty: Black Ops II, In "Zombies" mode, The main characters on the maps Green Run and Die Rise, Are stuck in a time loop where if they die they restart the cycle. Samuel is the only one who even slightly remembers what happened before they all die, stating; "Have we...been here before?" Also in "Mob of The Dead, The cast, Finn O'Leary, Salvatore "Sal" DaLuca, Albert "The Weasel" Arlington, and Billy Handsome, are stuck in a time loop where they build a plane to escape and crash on the Golden Gate Bridge, where after a round, four electric chairs land on a platform where a sign says: "No One Escapes Alive" When you sit in one the cycle starts over, Unless you do the "Pop Goes The Weasel" Achievement/Trophy (25G/Bronze Trophy) In which you either kill Weasel or let him kill you. (Kill Weasel: The cycle continues/ Let him kill you: The cycle is broken..)
See also 
- Time loop logic
- Butterfly effect
- Eternal return
- Grandfather paradox
- List of television series that include time travel
- Ontological paradox
- Predestination paradox
- Time slip
- Time travel
- Time travel television series
- Edwards, Malcolm; Stableford, Brian (1995). "Time Paradoxes". In John Clute, Peter Nicholls. The Encyclopedia of Science Fiction (Updated ed.). New York: St Martin's Griffin. pp. 1225–1226. ISBN 0-312-09618-6.
- DeLillo, Don (1987). The Day Room. New York: Knopf.
- Peter Stockwell. The Poetics of Science Fiction. p. 143. ISBN 0-582-36993-2, 9780582369931 Check