A time loop or temporal loop is a common plot device in science fiction (especially in universes where time travel is commonplace) in which time runs normally for a set period (usually a day or a few hours) but then skips back like a broken record. When the time loop "resets", the memories of most characters are reset (i.e. they forget all that happened). 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 aware of 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.
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.
In a conscious time loop, everyone's consciousness loops through time. In such a time loop, causality could easily be violated.
The following series featured time loops as a main theme or at least fairly frequently:
Time loops have been featured in individual episodes of many TV series, including:
|Illyria's god-like powers become unstable and threaten to explode in a way that will destroy the continental shelf; her mystical energy causes her and Angel to jump back and forth through time and experience certain important events multiple times. Angel sees his friends and himself killed by Illyria, but Wesley finds a way to stop the catastrophe.
|The Angry Beavers
|"Same Time Last Week"
|The characters discover Pandora's Box, which ends the world whenever it is opened; due to the main character Vicki Nelson having been marked by a powerful demon, history is apparently 'reset' each time the box is opened to give the demon the chance to kill Vicki.
|Buffy the Vampire Slayer
|Three villains led by Warren Mears put Buffy into a time loop when she's working at the Magic Box. She has to face the same customer over and over until she's able to satisfy her.
|"Sakura's Never-Ending Day" ("Time and Again" in the Nelvana release)
|"Déjà Vu All Over Again"
|A demon tries to repeat the same day over and over again until he can find a strategy to defeat the sisters.
|"The Good, the Bad, and the Cursed"
|Breaking a time loop that others are stuck in is a major plot element, but the sisters and the audience only go through it once.
|"A Great Day"
|Although the main characters have the ability to relive a day ("Return to the past" or "RTTP") and be the only ones who retain their memories, throughout the entire series these are the only two episodes in which the same day is repeated multiple times.
|"The Rewinding Town"
|The Dead Zone
|"Run, Gary, Run"
|"I Do Over"
|The main character has to solve what is causing him to relive the same day repeatedly without the help of the geniuses in the town, and he finds that no matter what he changes throughout each repeated day, the end result is still the same. He then realizes that nothing simple he does will change anything, and that if he wants to stop reliving the same day, a drastic measure must be taken.
|The Fairly OddParents
|"Christmas Every Day"
|The main character wishes that it was Christmas every day.
|The main character wishes for a watch that allows him to reset a certain amount of time so that he can undo his mistakes.
|"The Big Bang Theory"
|It's the episode where Stewie and Brian Griffin was trapped outside the Space-Time Continuum. Stewie was forced to destroy his return pad so that they could return inside time and space. After their return, Stewie was amazed to see that the explosion made by his return pad matched the explosion of the Big Bang that created the universe. After seeing the explosions, Stewie concluded that he might have created the universe, Brian denied Stewie's conclusion and said that he is born IN the universe. Stewie explained that his creation of the universe is somehow like a Temporal Causality Loop ( he was created by the universe to create the universe ).
|"Back and Back and Back to the Future"
|John Crichton's exposure to the energy of a black hole causes him to experience time jumps where he sees the future.
|"The Late Philip J Fry"
|Fry, Bender and Professor Farnsworth use a forwards time machine and after travelling through multiple times in the future, fast forward to the end of the universe where they witness a second big bang and discover that when the universe ends, another universe exactly the same as the old one is created.
|"Audrey Parker's Day Off"
|Justice League Unlimited
|"The Once and Future Thing: Time Warped"
|The villain, Chronos, is trapped in a time loop at the conclusion of the episode and his actions thus undone. Title is a word play on The Once and Future King by T. H. White.
|Lois & Clark: The New Adventures of Superman
|"'Twas the Night Before Mxymas"
|A 4th season episode written by Tim Minear in which Mister Mxyzptlk, a Trickster being from the fifth dimension (Howie Mandel), plans to take away hope by repeating Christmas Eve day.
|"Flashes Before Your Eyes"
|This episode, the first to deal with the concept of time travel in the series, is centered on Desmond (Henry Ian Cusick), who experiences flashbacks and uncanny predictions. Hugo and Charlie think that Desmond can see into the future after he saves Claire from drowning. Desmond reveals that Charlie is destined to die.
|"Be Kind, Rewind"
|The Melancholy of Haruhi Suzumiya
|The "Endless Eight" arc
|Episodes where the characters relive the same two weeks of summer vacation, as the one behind it attempts to pack as much into these two weeks as possible, but is not satisfied, and thus the loop repeats
|Monty Python's Flying Circus
|Déjà vu (skit, a.k.a. "It's the Mind"), episode 16.
|My Little Pony: Friendship is Magic
|It's About Time
|Twilight Sparkle is visited by her future self, from a seemingly apocalyptic world due to her tattered jumpsuit and shocking appearance. Before she can convey an urgent warning, she is forced back to the future, and Twilight attempts to avert the apparent crisis, her paranoia leading to several injuries that match what her future self had possessed. After realizing there will be no disaster, she travels back in time to tell her past self not to bother worrying about an apocalypse, but being forced back into the present day before being able to mention not to worry, setting in motion a time loop.
|The Outer Limits
|Doctor Mark Crest (Kevin Nealon) is a scientist in charge of a teleportation experiment. He learns that he has an ally and an enemy, and as he experiences time loops, he realizes that each loop is growing shorter. He must stop the enemy who wants to use their experiment to create a weapon.
|The story is not precisely inside a time loop, but protagonist Raymond Dalton finds himself in a bizarre place, apparently a log cabin besieged by snow, where there are many other people who act out different types of personalities (religious fanatic, adulterer, and other types), over and over. He learns that they are in cryonic stasis and under the control of one of these strange people.
|Jane Vasco (Kristanna Loken) and her team encounter a Neuro (a mutant with supernormal mental powers) who can reset time to the beginning of the day.
|Pepper Ann is supposed to take a history test on Friday, but she didn't study for it, so she pretends to be sick. Unfortunately, the next day is Friday again, and the day keeps repeating.
|"The Day That Wouldn't End"
|Phineas and Ferb
|"Phineas and Ferb's Quantum Boogaloo"
|Phua Chu Kang
|"Power Rangers: Lightspeed Rescue"
|"Power Rangers: Zeo"
|"A Brief Mystery of Time"
|The Machine Empire traps Earth in a time loop; a recent brainwashing experience allows Tommy Oliver to be partly aware of the day repeating itself.
|The crew are exposed to a white hole - the opposite of a black hole - which spews time into the universe, causing them to repeat various events as well as experiencing time out of order.
|Red vs. Blue
|"Have We Met?"
|"Same Old, Same Old"
|"Déjà Vu All Over Again"
|Run Frank Run! Frank Parker must save Talmadge. The clock is ticking, he's far away, traveling on foot, but thankfully, if at first he doesn't succeed (and indeed he doesn't), he gets to try, try again.
|"The Forever War"
|Silver Surfer finds Adam Warlock trapped in a time loop where he defends his homeworld from the Kree. After leaving it they find that Warlock's true homeworld was destroyed long ago, so he returns to the time loop.
|Having indirectly caused the death of Lana Lang, Clark Kent turns back time to avert the events that led to her death (Although the new timeline results in Jonathan Kent dying instead)
|"Go God Go XII"
|The time loop is inescapable only because the person remembering it is incapable of understanding the problem.
|"Window of Opportunity"
|The episodes "The Gamekeeper" and "Avatar" also feature time repeatedly "resetting" itself, but they both take place within virtual reality universes, whereas "Window of Opportunity" takes place in the real world and is the only instance of the term "time loop" being used in the series, Earth and sixteen other worlds within a certain distance of the original machine apparently repeating the same eight hours for over three months.
|Star Trek: Enterprise
|Star Trek: The Next Generation
|"Cause and Effect"
|A localized time loop only loops for the main characters and those involved directly in the loop. The loop is caused by the destruction of the Enterprise, which in turn resets the loop. Once the ship's destruction is averted, the loop breaks, and the characters discover that quite some time has passed while they were trapped in the localized loop.
|The Enterprise is destroyed and Captain Jean-Luc Picard is sent back in time to the moments before the ship was destroyed, but Picard is able to break the loop that would have led to him becoming his future self.
|Star Trek: Voyager
|Captain Kathryn Janeway apparently experiences multiple timelines resulting in her death, but the 'loop' is revealed to be an illusion generated by a life-form trying to trick Janeway into 'accepting' her death
|Strange Days at Blake Holsey High
|Corinne Baxter has what she considers the worst day of her life and repeats it over and over until she looks at it optimistically.
|The Suite Life on Deck
|The time loop is caused by a lightning bolt that strikes while the boat passes the international dateline sending the S.S. Tipton back in a time loop that only Cody Martin Realizes, so he takes advantage to try and kiss Bailey Pickett, his crush. In the end, he doesn't manage to kiss her.
|"Mystery Spot (3.11)"
|The time loop is caused whenever Dean Winchester is killed. The time loop was created by a Trickster to teach Dean's brother Sam a lesson.
|The Twilight Zone
|The Twilight Zone (2002 TV series)
|A casino gambler is given a tape recorder that rewinds time and allows the holder to create a five-minute time loop; he uses it to win big money from the casino.
|Wizards of Waverly Place
|Alex Russo wants her brother, Justin, to get his first kiss. During the kiss, something wrong happens, so Alex set the time back so Justin could do it right.
|A woman has to repeat the same day over and over, each ending with someone dead after a bank heist. She confronts Scully and Mulder on several occasions to try to stop the time loop, and Mulder gets the sense of Déjà vu.
|Xena: Warrior Princess
|"Been there, Done that"
As future Picard arrives with Romulan and Klingon help at the final battle the other Picard is there. Realising that the temporal loop must be closed he asks the other Picard to go back in time to the exact time and place to prevent the ambassador's assimilation.
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