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Temporal Paradox
aka: Time Paradox

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"History abhors a paradox."
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A contradiction of causality within the timeline brought about by Time Travel. Theorized to be dangerous to the fabric of reality, and known to be dangerous to the brains of anyone who tries to get their head around them. So don't. It's usually what The Professor worries about during a Time Travel story.

Punishments for creating a paradox vary. You might instantly vanish from history or cause your time-travelling self to be erased; you might be immune but find the world around you different; you might destroy reality itself; heck, you might even accidentally unleash killer flying time monkeys.

This is all fictional, of course. In reality, a confirmed paradox would disallow time travel to work at all. You see, a logical paradox is not a thing. It is a sign in a human-created model that either you have attempted something impossible or that you have incomplete understanding of how something works. Here's the thing: all our notions of causality are based on the fact that time only moves in the one direction and a paradox exploits this cause and effect relationship. Once you throw Time Travel into the equation and have time move in a different way, it's really anyone's guess what will happen. Not that this prevents authors from abusing the concept as a sort of universe-wide Logic Bomb.

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There are many kinds of paradoxes that can be created by poorly thought-out time travel, but it usually fits one of these two major categories:

Grandfather Paradox

This paradox gets its name for a very simple question: "what would happen to you if you went back in time and killed your grandfather before he had offspring?" (Parodied by Futurama; see example in Stable Time Loop)

More generally, this means doing something that makes your time travel impossible or unnecessary. For instance, if success in the time travel endeavor means that the condition you set out to change never happens, then you won't ever have had any reason to come back and try to change it. Thus, without your intervention, it will happen after all, meaning you then must go back to change it, meaning you don't have to, meaning you have to, and so on, ad infinitum.

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Most cases of Mental Time Travel sidestep or ignore the grandfather paradox.

Ontological Paradox

The kind of paradox that occurs in a Stable Time Loop if you're not very careful about what you're doing, involving events that are their own causes. While not a paradox in the strictest sense - events remain self-consistent - it does violate normal expectations in surprising waysnote . Common variations include:

The Object Loop

An object from the future is sent into the past, takes The Slow Path back to the future, and then gets sent back into the past again, in the same way, for the same purpose. For example, you travel to the past and sell a pair of antique glasses you got from a friend, who inherited them from his grandfather, who bought them from you, the time traveler. This time loop results in several important physics problems, such as:

Where did the glasses come from in the first place? The glasses have literally sprung into existence from nothing, appearing to violate the law of conservation of energy/mass. This is sometimes called a "closed timelike curve" in hard SF.

How does the object escape erosion or other forms of damage? Since its origin point is also its end point, the object cannot (relative to itself) loop endlessly as it would experience infinite decay (relative to itself) and therefore would not exist to be sent to the past, preventing the loop from occurring at all. Thus, to exist the object must (improbably) escape all forms of damage/erosion/entropy between its arrival and departure; technically, this isn't impossible, but its improbability makes object loops very weird from a quantum mechanics perspective.

In one common variation, information loops, rather than physical objects: for instance, an engineer from the future gives the formula for transparent aluminum to its historical "inventor", becoming the creator of a metal that has always existed. This version may avoid the problem of decay, provided that the information is correctly transmitted and recorded. The actual effect of this variation is that no one invented the object, or no one discovered the formula/concept. It's just there.

The object could also be repaired, or otherwise reset to a certain state, at some point during its existence; this would be the closest to creation the object experiences. This is a variant of an information loop, in that the object contains or suggests information (what it should be like) that is used (along with whatever remains of the damaged object) to create the like-new object.

The Reverse Grandfather Paradox

When time travel is involved, cause and effect tend to get muddled. Say you remember being involved in an accident as a child, and would have died if not for the intervention of a mysterious stranger who showed up, saved your life and then vanished without a trace. Later, you become a time traveler and find yourself at the scene of the accident, and there's a little kid who needs saving. That's right: you happen to be the mysterious rescuer. Instead of accidentally making your time travel unnecessary or impossible by meddling with the past, your meddling somehow made it required or possible in the first place. But then the question becomes how you originally (an increasingly meaningless concept in this context) survived to time-travel and save yourself.

Thus, an ontological paradox occurs, which is not actually a paradox in the logical sense, but a confusing and counter-intuitive result of time travel. This also precludes a multiverse explanation, since both child and rescuer-adult occupy the same timeline and universe, if the child has a childhood-memory of being rescued by the adult-self.

Normally, as written, the temporal paradox never turns out to be as dangerous as The Professor imagined it would be, or it turns out the characters were "supposed to do it" in the original timeline. The latter ontological paradox is also known as a predestination paradox, and the resultant philosophical questions are rarely thought about in the series.

If two time periods are featured, the effects of a paradox will usually be visible in the future only "after" the cause has happened in the past (see Meanwhile, in the Future...).

Interestingly, series rarely have the same result to paradoxes even in the same show.

The most common effect of a paradox, on TV at least, is to trigger the Reset Button and unmake the entire episode's consequences.

Theoretically, a paradox that consists of two mutually-exclusive events can have one of two results: either the fabric of reality rips itself apart trying to determine which reality is the 'correct' one, or — according to Multiverse Theory — it's discovered that causing a paradox is a technical impossibility, as each supposed 'paradox' merely creates two 'alternate' timelines — one for 'Situation A' and another for 'Situation B'.

(Of course, Multiverse Theory also holds that time-travel is hypothetically possible — since every choice made, and every action taken, and every word ever written, creates a series of 'alternate universes', each being slightly different to account for the results of the choice/action/word, we would just need a consistent way to travel 'between' the various 'multiverses' thus created.) On the flip side, it also means that it's impossible to completely Set Right What Once Went Wrong, as the "original" timeline will always be unchanged.

Compare Timey-Wimey Ball, Stable Time Loop. If time is somehow dangerous besides from paradox, it's Time Is Dangerous.


Example subpages:

Grandfather paradox examples:

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    Anime and Manga 
  • Akira Toriyama follows the multiverse approach in Dragon Ball Z: Future Trunks travels back in time to change the past, although he knows that this will not affect his own past or future (since each timeline exists as a separate dimension, changes made in one time line will not affect the others). Because Cell was also traveling around, but then Trunks prevents Cell's trip, fans have theorized that there are at least five time lines: the time line chronicled by the anime and manga (Line 1), the time line Trunks-who-participates-in-the-Cell-Games (this is Future Trunks, mentioned above) originates from (Line 2), and the time line Cell-who-killed-Trunks-to-steal-the-time-machine-and-terrorized-the-main-series-time-line originates from (Line 3), plus two theoretical/implied time lines. The first implied time line is the one visited by the Trunks native to Line 3, the Trunks killed by Cell so that he could go back to Line 1. This time line would proceed identically as Line 1 up to the point of Cell's discovery; after that, all fans have been able to guess is that the androids were somehow defeated. The commonly-accepted (suggested by the Daizenshuu guidebooks) theory is that Bulma built the deactivation switch (just like she did in Line 1) but Kuririn didn't destroy it, and Trunks took it back to Line 3 to use on the androids there. (Of course, it was the very discovery of Cell that lead Trunks and Kuririn back to Dr. Gero's lab in order to get the blueprints Bulma used to build the switch... so maybe Piccolo defeated them...?) The other theoretical time line is one Cell would have visited, if the Trunks native to Line 2 didn't kill him, using the strength gained from his training in Line 1. This line would proceed identically to Line 1 up until Cell's discovery, as well, so the Trunks visiting this time line probably won't be strong enough to defeat Cell, if he comes from a time line where Cell is waiting to kill him if he kills the androids and...
  • Haruhi Suzumiya: Every instance of time travel in the stories (and there are many) invariably generates paradoxes like these. Characters go back in time to save themselves, information comes out of nowhere, etc., etc. Of course, no explanation is ever given in the books.
  • Your Name gets into one of these once the time travel aspect is revealed. Taki and Mitsuha have spent the last few weeks randomly swapping bodies, until it abruptly stops happening. Taki tries to find Mitsuha, only to discover that they're three years out of synch — he's in 2016 while she died in 2013 when her town was destroyed by a fragmenting meteor. Armed with this knowledge, Taki tries to force one more mind-swap. He succeeds and, working with Mitsuha and her friends, they ultimately manage to evacuate the town to safety, saving all. This has absolutely no effect on Taki or any of the other events of the movie, except for the ending, where a now-living Mitsuha finally meets Taki face-to-face in 2022.

    Comic Books 
  • The Marvel Universe has a simple solution for this in the novel trilogy Time's Arrow. There are a large—but not infinite—number of alternate universes, that deal with what ifs. If someone in those timelines goes back in time to change something, it will create a new timeline that's an offshoot of one's own from that point. No going back and killing Hitler, Cyclops notes when told this—the idea being that if you do so, your own timeline will be unaffected. Oddly, this doesn't seem to be the case in the comic universe.
    • Except when it is that way. You don't think that any two comic writers actually agree on how this stuff works, do you? That said, the Earth X series (including Universe X and Paradise X) suggests a couple of different versions of this. In the end, it is fundamentally, philosophically important that the idea that alternate universes branch off only as a result of time travel is true.
      • This is generally accepted; however, it has been shown that Doctor Doom has invented technology that allows this rule to be broken in PAD's X-Factor run.
    • This is the reason time traveling villain Kang the Conqueror keeps multiplying, often despite his own wishes.
    • One run of Thunderbolts ended with the present-Thunderbolts meeting the past versions of themselves. Fixer killed his own past self, and the universe promptly began collapsing. Fixer resolved it by having himself de-aged and his memories erased, in order to replace himself in the past. He thereby condemned himself to live in an infinite loop, reliving the same period of time over and over for eternity.
    • One exception, however, are the Space Phantoms, servants of time-traveling The Avengers villain Immortus, who learned the hard way how dangerous this sort of thing is. Apparently, the Phantoms learned time travel before they learned space travel, and when a civil war broke out between them, each side tried using time travel to change the outcomes of important battles. If a side did so successfully, the other side would try to undo it, again and again, until finally, the constant meddling with the temporal flow destroyed their world, leaving them a Dying Race trapped in the dimension of Limbo who are little more than slaves to Immortus' will.
  • Grant Morrison's legendarily complex and metafictional series The Invisibles hinges itself on contradiction, and details several brainbending temporal paradoxes. It would perhaps be remiss to go into any of them here in any great detail. Basically, if you like that sort of thing, go read The Invisibles.
  • Shakara: The fellow members of The Hierarchy that the Overlord was planning on betraying go back in time to stop him before he can carry out his plan. He compliments their ingenuity but mocks their attempt, pointing out that this would only create a temporal paradox that would result in an alternate timeline, it wouldn't stop what they've already seen him do in the future. However, even that rests on the assumption that he could be killed to begin with.
  • Mighty Morphin' Power Rangers: Shattered Grid has a very painful one. In the very first part, Lord Drakkon kills Tommy Oliver to recharge the Green Crystal. However, since Tommy is massive integral to the Power Rangers timeline (as he would become the White Ranger, Red Zeo Ranger, first Red Turbo Ranger and the Black Dino Thunder Ranger), the Morphin' Grid decides to fix this little problem by dividing every Ranger era into its own separate universe just to prevent this.

    Fanfiction 
  • In the Facing the Future Series, Sam decides to try getting ghost powers for herself when she discovers that her future self just so happens to have ghost powers just like Danny does.

    Film 
  • Interstellar features a semi-temporal paradox, baring a similarity to the Reverse Grandfather Paradox. All of the scenarios in the Paradox are initiated by Cooper and TARS manipulating space-time inside the Tesseract.
  • Pretty much every film in the Planet of the Apes franchise.
  • In the Back to the Future movies, Doc Brown is very concerned with temporal paradoxes.
    • However, the effects of time travel are different in the various movies. For instance: in the first movie, Marty's accidental stopping his parents getting together was starting to delete him from existence; in the second movie, Biff interferes with his past, and the changed present has Biff saying he sent Marty to a school in Switzerland, yet this never affects the time-travelling Marty.
    • Fanon has justified this in various ways; for example, saying the time traveller is only affected by his own changes to the timeline, or by saying that he will be unaffected as long as there's somewhere in the timeline for him to "slot in" - changes to his situation in the new timeline are shrugged off, as long as he exists somewhere.
    • The documentaries on the DVD set mention how the justification was that there's some entity that regulates time itself. The partial deletion over time of Marty, why both Jennifers fainted when they met each other, and why even with relatively major changes to the timeline, Marty's family, home, and association with Doc Brown and Jennifer remain largely the same. They wanted to explore this aspect, but couldn't find a way to incorporate it into the films without it being obtrusive. The Other Wiki has more information here.
      • One possibility is that there are two Martys, just as there were in 2015 and when he returned to 1955.
    • Much stranger is how Biff, when he returned to 2015, returns to the version where he is a loser, instead of the one where he is rich. The only clear reason for this was so that Marty and Doc could get the DeLorean back.
  • The Lake House is a story about a mailbox that delivers letters from Kate to Alex two years ago and vice versa. Alex dies in a car accident on Valentines Day. Two years later, when Kate realizes that, she sends a message to Alex two years ago telling him not to be there, and he survives. It should be noted that the Korean movie this movie is based on dealt with the paradox differently: The female character sends the warning back in time, but the male character remains dead. Meanwhile, the insertion of the warning splits off an alternate universe where the male character survives, and the movie ends with the male character meeting the female character, just as the female character is moving into the house, before she's even gotten the first letter. It's okay, though. The guy has quite a story to tell her. Since the movie ends there, by the way, it's unknown whether the female character would have ever started the letter-exchanging if the guy hadn't...ugh, it's all sort of vague, really.
  • The horror film Triangle has loads upon loads. How it works, nobody knows, as even Phelous can tell you.
  • Frequency depicts basically the same situation as The Lake Housedue to abnormal sunspot activity, a police officer and his long-deceased father are able to communicate across a 30-year gulf of time over the same CB radio set. The son first saves his father from dying in a firefighting mishap, only to discover that he died of lung cancer a few years later anyway. But he then manages to convince him to quit smoking.
  • Donnie Darko: After sleepwalking away from the place where he was supposed to die, the eponymous character is caught in an unstable time loop that he must close. When he moves himself and the jet engine that should have killed him back into the past, he closes the loop by dying in the way that he should have from the beginning, negating everything in the time loop. This causes everything that was changed by his time travel to exist outside of the normal timeline without affecting it. Maybe. It's pointed out in the movie, more explicitly in the extended cut, that the cause of the time loop only happened because of the time loop; in the final timeline the jet engine falls into the past and kills him for no reason whatsoever. In-universe speculation is that a deity or other being outside time caused it for reasons of their own.
  • The whole plot of the movie The Butterfly Effect revolves around the main character's ability to travel back in time and change parts of his life. Every change causes his brain to physically rewire itself with the new memories, though, and this causes intense pain for him.
  • Meet the Robinsons. Let's see. If Goob made the catch and won, getting himself adopted and never becoming the Bowler Hat Guy, Lewis would never have learned that Goob became that person, and never bothered to prevent it. Yeah. And he wouldn't known not to create Doris.
  • Averted in The Time Machine (2002), where the time traveler attempts to save his fiancee, but she always dies on the same night no matter what he does. He travels into the future to find out why. In the far, far future, he learns from a more evolved human that if he saved her he would not have the motivation to build his time machine. Apparently, a paradox is allowed if it doesn't prevent the time travel device's creation, though.
  • In Wishmaster, the main character gets one wish from the evil djinn, after which it will be freed to work its evil upon the world unfettered. She wishes that a particular forklift operator had not been drinking on the job a few days before. Since he wasn't drinking on the job, he didn't drop a particular crate. Since he didn't drop the crate, the statue inside never broke. Since the statue never broke, the gem inside was never uncovered. And since the gem inside was never uncovered, the djinn trapped inside it was never released. But wait! Since the djinn inside it was never released, that means he never granted the protagonist's wish! And if he never granted the wish, then he was released after all! But then...

    Literature 
  • Lazarus Long, protagonist of Robert A. Heinlein's Time Enough for Love creates a time machine and argues that it would not be possible for him to change the past, because in doing so he would also change the future—in the essence, negating his own existence, or at least the details of it—and making his own journey into the past improbable at best, if not impossible.
  • David Weber's The Apocalypse Troll has the characters discussing the theories about time travel — one (it's not possible) has been disproved by the fact that one character just did, to arrive in the time of the discussion; the other two, that the future will be altered by what she did or that her presence has caused an alternate world to split off, can't be proved or disproved by anything they can do now. They end up assuming the alternate world and thereafter ignore the question.
  • The Time Scout novels avoid Temporal Paradox by the timeline including built-in safeguards; safeguards which are dangerous to time travelers. The most prominent are first, that you can't change anything that's important to the timeline—some improbable accident will occur to prevent it, no matter what you try—which is dangerous, as although some people, objects and events are obviously important to the timeline, there are even more that aren't obviously important, but just as crucial; and second, that if a time traveler ever arrives at a time where they already exist, the most recent version dies instantly to prevent them from doing anything to their past selves that would undermine their current presence.
  • The Dark Tower
  • The Caretaker Trilogy has an interesting take on this: there are no alternate universes, and while changing the future/past is possible, doing anything that would create a paradox is impossible simply because it would create a paradox. It's said that there is some natural "force" that prevents paradoxes from occurring. Exactly how that works is not explained, because the protagonist apparently doesn't have the necessary education to understand the specifics.
  • Time travel is forbidden in The Dresden Files because it might end up destroying the fabric of reality. Characters capable of seeing the future can't be specific about their visions for the same reason.
    • The Gatekeeper, specifically, has a vision of something major in the Dresdenverse, and alerts Harry to it, in the most vague, roundabout way. Bob later explains he did this to avoid the entire universe going kaput. He also mentions that no one has ever caused a temporal paradox before, and you can tell by the way the universe keeps existing.
  • Some argue that René Barjavel's Le Voyageur imprudent is the first ever example of the grandfather paradox.
  • In The Anubis Gates by Tim Powers, main character Brendon Doyle, a modern expert on the poet William Ashbless, ends up back in the 1800's during Ashbless' lifetime. When Doyle ends up BECOMING Ashbless thanks to a body-snatching werewolf (don't ask), he publishes the poems from memory—which leaves us with the problem of how the poems were written in the first place. In fact, it actually freaks Doyle out, but he concludes that as long as the poems exist, history will continue in its proper order, so he shouldn't sweat too much over it.
  • Distilled to its purest form in Fredric Brown's short story Experiment.
  • Gregory Benford's Timescape describes a unique, quantum-mechanical approach to Grandfather Paradoxes. If a time-travelling signal were to prevent its own transmission, the signal and everything involved in triggering it would be in an indeterminate state where it neither does, nor doesn't, occur — like Schrödinger's Cat before the box is opened.
  • The Hitchhiker's Guide to the Galaxy universe is full of this, particularly in the third book. A correction-fluid manufacturer tries to get an endorsement from a tragic poet and ends up preventing the tragedy that inspired him. A landmark cathedral is torn down to make way for a refinery, but in order to open on time they had to start construction so far back in time that said cathedral was never built.
    • Worst of all are aorist rods, which provided power to the present by depleting the power reserves of the past ... when it was discovered those bastards in the future were doing the exact same thing, the rods and all knowledge of their manufacture was destroyed to stop what was already happening now from occurring in the future.
  • In Dragonlance, Raistlin kills Fistandantilus and usurps his soul, and then goes forth to succeed where Fistandantilus failed in traveling into the realm of the Gods. Since it was Fistandantilus' drifting soul that resulted from that first failure which saved Raistlin's life during his Test in the first place, I think we can all say that Raistlin pretty much screwed causality in the ear.
  • It gets weird in the Doctor Who – Expanded Universe, which features Faction Paradox, a villain group whose hat is temporal paradoxes. In fact, part of their initiation ritual involves traveling back in time and killing off your own ancestors. Yes, really.
    • At one point, they infected the Third/Fourth Doctor with Faction biodata during a regeneration that wasn't supposed to happen (when he was shot on Dust, instead of the canon radiation poisoning on Metebelis Three), causing the Eighth Doctor to disrupt his own timeline so that the Third Doctor was shot on Dust, permitting the Faction to infect him with the biodata, which caused him to tinker with the past so he could be infected with the biodata... BOOM!
    • And that's before you enter the Eleven-Day Empire, a place literally made of nonexistent time. Or the Grandfather Paradox, the Anthropomorphic Personification of all potential evil and despair in the Universe. Or the part where Gallifrey's history is repeatedly raped into oblivion.
    • The entire story line of Clara is this, as The Doctor didn't die on Trenzalore, which means that she never jumped into his time stream, which means that the two previous Claras that died were never born, and The Doctor has no reason to ever go looking for the original Clara.
  • In Marion G. Harmon's Wearing the Cape, the Teatime Anarachist explains the rather unusual rules that do seem to eliminate the problem: there is a privileged Now, where his and everyone else's actions are real and affect things and can't be changed — because they slip into the Past, which he can't change. The Future, on the other hand, is only the most possible future. He can interact with it and bring things back, but acts in the Now can still alter it.

    Tabletop Games 
  • In the RPG Feng Shui there are no temporal paradoxes, because history rewrites itself to accommodate changes in the timeline. For instance, if Donald Fong goes back in time and kills his great-great-grandfather, when he returns to the present, he'll find that everyone now knows him as Donald Wong, a person with a very similar life to Donald Fong. He'll remember his old life as Donald Fong, but everyone else will always have known him as Donald Wong. In extreme cases - such as when someone controls enough feng shui sites to cause a critical shift (i.e. they change reality) - people can get written out of the timeline entirely; they still exist, but they have no past in the current timeline, because their version of history simply doesn't exist anymore.
  • The German RPG The Dark Eye takes a similar approach in declaring time a dynamic, "healing" weave. An example to solve the grandfather paradox is to have the person get stranded in time, get a life, meet a woman, marry and have kids and thus becoming his own grandfather.

    Visual Novels 
  • The actual objective of Servant Archer/Heroic Spirit Emiya in Fate/stay night. He tries to kill his younger self (the protagonist, Emiya Shirou) to force a contradiction within Gaia, which he hopes will cause his whole existence to be erased to keep reality from breaking from the impossibility of the event. He himself admits that this would have a very low chance of happening, considering that by meeting Archer, Shirou is already set on not becoming Heroic Spirit Emiya, so the death of a "different" Emiya Shirou shouldn't affect Heroic Spirit Emiya in the slightest.
    • Besides, it's said that the Heroic Spirits are removed from the time axis and await their summonings in the Seat of Heroic Spirits. So, even in the case that Shirou actually did want to become a Heroic Spirit, as Archer is no longer bound by the rules of time, Shirou's death would not form a paradox and free him from his destiny. Archer's whole objective in UBW was both to attempt this plan anyway in the off-chance that it actually succeeded, and to make sure his past self didn't have to see his ideals betray him like he did.

    Webcomics 
  • Schlock Mercenary:
    • Paradox is notably averted in every instance of time travel, where it's put forth that causality is never sacrificed. If a time traveler were to go back and kill his/her grandfather, even though another one of them wouldn't be born as a result, they've already caused the event, so they'll still exist. Changes due to time travel are likened to "overwriting" the original timeline (though it's also worth mentioning that, within the Schlockiverse, time travel is normally impossible).
    • The comic itself likens it to the most common time travel power in video games: "Load Game".
    • And in the storyline where the figured out that time would keep going: Petey and Kevyn ended up with two copies of a VDA probe, in the process of trying to figure out if they could change the past. (Short reason why- they wanted to prevent the activation of a device that was currently in the process of destroying the Galaxy.) Kevyn ends up shooting the version of the probe that hadn't been sent yet, arguing that even if they repair it, it wouldn't be identical enough to cause the "identity crisis" in the onboard AI that caused them to discover the duplication to begin with, thereby showing that "the future" could be change, without voiding their personal past. So, go ahead and send someone back far enough, make the change, and don't worry about disappearing in a puff of logic.
      Petey: Okay, confession time... when you fired, I was genuinely frightened for the first time in this whole affair.
      Kevyn: You call that a confession? Here's a real confession: So was I. But hey, now we know it works, right?
  • Evil Katarakis of Starslip Crisis hasn't thought his brilliant plan all the way through:
    Imagine... enjoying your favourite sandwich... then going back and stealing the sandwich from yourself before you eat it! So you get two sandwiches.
    • Deep Time isn't exactly the best off, either: one member spent spare weekends going back in time to kill Hitler, then back again to stop himself from killing Hitler. Another spends forty years on dead-end research, then tells a third agent to stop him from wasting his life on the matter. In yet another case, accidentally blowing up a planet causes an entire Deep Time spaceship to spontaneously fall apart.
      • At one point, people in the present protect themselves against attackers from the future by identifying the future guys' ancestors, and making sure they're on all the ships that the future guys are attacking.
  • Chuck Goodrich of The Adventures of Dr. McNinja traveled back from the future to stop a Zombie Apocalypse. Then another of him showed up in order to stop a Robot Uprising. And then more and more.
  • The high cost to reality is invoked and elegantly resolved in this Penny Arcade strip.
  • In American Barbarian, Rick refuses to do anything that would prevent their births.
  • In Homestuck, most of the technology that can teleport an object thorough time and space are designed to prevent these paradoxes; appearifying an object that would cause a paradox instead creates a copy made of paradox ghost slime, which quickly collapses in a puddle of goo. It is possible to cause a grandfather paradox, but this creates a doomed Alternate Timeline marked for deletion - even if someone travels back to the main timeline somehow, they're still doomed to die.
    • Except for Davesprite, who seems to have dodged Fate's bullet by merging with a pre-existing entity in the main timeline, i.e. the kernelsprite.
  • Faulty Logic: Fox built a time machine for the sole purpose of traveling back in time to prevent himself from building a time machine, because he knew he would build a time machine and misuse it.
  • In the Oglaf strip "Chronotherapy", a healer goes back in time to cure a plague before it devastates the kingdom, then goes to the queen to claim the Standard Hero Reward she promised him. Since the plague never happened, the queen never hired him, so she doesn't know what he's talking about.

    Western Animation 
  • The Danny Phantom movie The Ultimate Enemy is one big temporal paradox. In the original timeline, Danny's family and friends are killed, he goes mad with grief and kills himself (people with a Split Personality can do that and survive), and his evil self terrorizes the world for ten years. Thanks to Danny and some timely interference by the Dungeon Master, this timeline was erased, but his evil self was in the past when it was erased, so he still exists even with the events that caused his existence never happening. His evil self even pointed out the paradox. "You don't get it, do you? I'm still here. I still exist. That means you still turn into me." The Observants mention something about him still being there because "he exists outside of time."
  • Naturally enough, Bill & Ted's Excellent Adventures often courted this trope. One obvious example is the episode in which Bill and Ted neglect to buy Bill's father an antique railroad watch as a birthday present, to replace the one he lost as a child. Ted's initial plan is actually perfectly sound: take the original watch from Bill's father when he 'loses' it in the past, then give it to him in the present. This plan fails however, so they travel even further back in time to obtain the watch before Bill's father inherits it. Of course, this should mean that Bill's father wouldn't miss the watch in the first place, but the episode simply ignores this.
  • In Invader Zim, an entire episode (Bad Bad Rubber Piggy) has one scene that demonstrates this perfectly: After GIR finds out that Zim intends to send a robot back to the past to destroy Dib, it leads to this classic line of dialogue:
    GIR: Wait... if you destroy Dib in the past, then he won't ever be your enemy, so you won't have to send a robot back, so then he will be your enemy, so then you WILL have to send a robot BACK... (head explodes)
  • Super Friends. In the Challenge episode, "Secret Origins Of The Super Friends," the Legion of Doom tries to change history by messing with the origins of Superman, Wonder Woman, and Green Lantern. Okay, but seeing as how much of Super Friends is based on Pre-Crisis on Infinite Earths lore and hence Luthor's baldness and Start of Darkness were both accidentally caused by Superman when he was Superboy, how can Luthor— and as its founder, the Legion of Doom itself—exist if Superboy was never there to cause what happened to Luthor? Likewise, given his origins even Pre-Crisis involved someone copying Superman, how does Bizarro continue to exist as well? This also applies, to a lesser extent, to the others. Sinestro's crimes were exposed by Hal Jordan; maybe eventually, someone else would have, but it was Hal's newbie attitude that caused him to question an otherwise model Green Lantern; shift the timeframe and he maybe never meets the LoD. Most Cheetah origins have Wonder Woman involved in some way, at least some as Cheetah feeling challenged by her existence. Also, take Luthor grabbing Abin Sur's ring. That might get the Guardians' attention. Also, without those three, and especially Big S, would the SF have even formed, and since the LoD formed out of fear of this group…the list goes crazy on. Ah, everyone know time travelers are surrounded by a temporal bubble that prevents them from being affected by their own alterations in the timesteam. The real question is: if the Legion of Doom could see through time to spy on the "secret origins" of the heroes, how do they not know the entire Justice League's secret identities?
  • Starlight Glimmer's revenge plot in My Little Pony: Friendship Is Magic results in this: she travels back in time to prevent the Sonic Rainboom that gave the Mane Six their Cutie Marks...to get revenge on them for foiling her actions in Our Town in the season premier, meaning she'd negate her own reason for going back in time in the first place. Though her and Twilight seem to be immune to the timeline changes. Unlike many events, this actually does cause serious issues: each change to the past she makes causes a Bad Future worse and worse than the last note 
  • Thankfully averted in DuckTales (2017). One episode has Dewey being dropped into the past with a younger Donald and Della Duck. At the end of their adventure, Dewey tries to warn Delila her terrible fate, but both ducks stop him.
    Dewey: Okay, but a gotta warn you what's gonna happen to you in the future!
    (Donald and Della's eyes go wide, quickly clamp his beak shut)
    Donald: No! Keep your mouth shut!
    Della: No! Can't warn us about the future! You'll disrupt the timestream!
    Donald: Have you watched any movies?!
  • In the rather Timey-Wimey Ball finale of Samurai Jack, Ashi is Aku's biological daughter, and after she uses her powers to transport her and Jack into the past to kill Aku (right after Jack's past self is sent into the future) she pops out of existence because if Aku is dead then Ashi was never conceived. But if Ashi doesn't exist, then who transports Jack back in time to kill Aku?

Ontological paradox examples:

    Anime and Manga 
  • In The Disappearance of Haruhi Suzumiya, while traveling in the past Kyon is stabbed by Ryoko Asakura. As he lies bleeding out on the ground, what appears to be a Kyon from the future comes with a Yuki and a Mikuru also from the future and rescues him. So, basically, Kyon only lived because he lived long enough to go and come back to save himself. He lived because he lived. My head hurts...
    • Don't forget the information paradox with the knowledge of Mikuru's mole. Kyon didn't know Mikuru had the star-shaped mole until future!Mikuru showed it to him. Mikuru herself didn't know until Kyon told her about it. When future!Mikuru realizes this, she is understandably upset, thinking she messed something up.
    • Or the "Endless Eight" story arc, which finds the central characters reliving the same eight day cycle 15,498 times (quite unbeknownst to anyone but Yuki). They finally break the cycle when Kyon suggests a suitable ending to their summer vacation to Haruhi.
  • Transformers Armada, in the "Drift" episode. Starscream is blasted with the Requiem Blaster, then Highwire somehow apparently warps the kids back in time, but in an Alternate Universe, where both the Autobots and Decepticons are imprisoned and slowly being digested within Unicron. Before he expires, Hot Shot reveals that the Minicons are actually Unicron's cells, and the Transformers were being used by them. Then the kids travel further back in time to when the Minicons were created. Here they tell them to escape from Cybertron, eventually resulting in them coming to Earth and all subsequent events in the story. Then, back in the present, Perceptor stops Thrust from blasting Starscream. Therefore, the kids had to go back in time to trigger the sequence of events that led them to Cybertron and ultimately the time travel event itself.
  • Dragon Ball Z: In Dragon Ball Z: Bardock – The Father of Goku, Bardock attempts to stop Freeza from destroying Planet Vegeta to prevent the creation of a Super Saiyan. He fails. In the Episode of Bardock spinoff it turns out that Bardock wasn't killed in the explosion but was sent back in time to before the Saiyans discovered Planet Plant. He fights Chilled, Freeza's ancestor, and during the fight he becomes a Super Saiyan. This means that Bardock is the Super Saiyan of legend, and that Chilled was the one who passed the legend down to King Cold and Freeza. That in turn means that Freeza destroyed Planet Vegeta because Bardock became a Super Saiyan when he fought Chilled.
  • The sundial watch in Humanity Has Declined exists in a cycle of being stolen and given away between "Grandfather" and "Watashi", with no original in sight. Particularly noticeable since the other paradoxes all turned into dogs.
  • Tsubasa -RESERVoir CHRoNiCLE- has several such paradoxes. One of the most noticeable is Real!Syaoran, who is a living, breathing time paradox, what with being he's the son of his own clone. It's implied that the timestream was desperately trying to hold itself together, resulting in a few Stable Time Loops to patch up other paradoxes, resulting in Real!Syaoran's existence. When everything is sorted out in the end and the multiverse is repaired, Clone!Syaoran and Clone!Sakura are RetGonned from existence, and Real!Syaoran almost ceases to exist because if his clone never existed, then neither could he, and he only ever really existed in the first place because he went and broke causality. The same thing goes for Watanuki, who only started existing to fill out a hole that Syaoran went and made in the multiverse by time-traveling. Now they've both got to pay for the repairs, so Real!Syaoran exchanges his ability to stay in one world for very long for his right to continue existing, while Watanuki instead trades his ability to go anywhere ever except Yuuko's shop.
  • In Rokujyouma no Shinryakusha!?, Theia gets the school Drama club to do a play she wrote about an ancient legend on her homeworld. Kotarou ends up with the starring role of the Blue Knight. This involves not only memorizing his lines, but actual training in ancient sword styles. When he ends up on said homeworld millennia ago, He takes on the Blue Knight's role for real in an attempt to avoid a paradox, using the same skills and even lines he learned for the play.
    • And again, Kiriha takes Kotarou out on a date like the one she went with a boy she fell in love with ten years ago. Later, Kotarou ends up ten years in the past(on his way back from the previous adventure) and meets a girl he is unaware is actually a young Kiriha. He ends up taking her on the date Kiraha would revisit years later because that's the closest thing to a date he's ever been on.

    Comic Books 
  • Booster Gold only becomes Booster Gold because as Michael Carter, a janitor in a 25th-century superhero museum, he steals a timesphere belonging to the time master Rip Hunter. It later transpires that Booster will father Rip Hunter and teach him everything he knows about time travel. So if he hadn't stolen the timesphere, the timesphere wouldn't have been there to steal in the first place. Augh. To complicate matters, Rip has to train Booster to be a time master so that Booster can have trained him to be one when he was a little boy.
  • In Pre-Crisis Superman comics, all time travel works this way, which is why Superman's ability to time travel by exceeding the speed of light is not a Game-Breaker; he can travel back to the past, but he can't successfully change anything. The Movie ignores this.
  • In All-New, All-Different Avengers, the team makes sure to prevent this: Kang ends up knocking the Sam Wilson Captain America and Jane Foster Thor three days into the future, making sure that Thor lost the hammer. Cap gets Jane back to the hammer where it fell three days prior and use it to return to the present, then proceed to weaponize Temporal Paradox to drive Kang out. At Iron Man's suggestion, Thor drops the present day hammer in a spot so that she can find it once more without construction crews finding it and trying (and failing) to move it.

    Comic Strips 
  • Unsuccessfully invoked and thereby subverted in Calvin and Hobbes: Calvin tries to travel two hours into the future so that he won't have to write the story they're supposed to be writing for school. But the future Calvin doesn't have it, because he was to busy time travelling to the future to actually write it. Then they both travel to one hour ago because they decide that that Calvin should have written it... but he refuses on the grounds that whatever they threaten to do to him, they'll be doing it to themselves. In the end, the two Calvins return to the future empty-handed, only two find that the two Hobbeses have written the story for them. When Calvin starts reading it out loud at school, it turns out to be a story about his foolish time-travel while the tiger(s) save(s) the day.

    The timeline of this whole thing is a little paradoxical, but at least the object/information obtained has an origin.

    Fanfiction 
  • Eggman Generations has Eggman consider this when his younger self, as per the ending of Sonic Generations, consider going into teaching rather than world conquest. Despite this, Eggman notes that the decision hasn't affected his own existence.
  • Link saving himself in The Legend Of Zelda: The Return.

    Film 
  • In Back to the Future, Chuck Berry steals Johnny B. Goode from Marty (after hearing an incomplete performance over a 1950s payphone, no less), who learnt it from Berry in the first place.
  • Another Sandra Bullock film, Premonition, mixes this trope with You Can't Fight Fate: Linda's attempts to prevent her husband's death cause it, but she does get pregnant before he dies, and prevents herself from going crazy and getting committed, which she could not have done had she not had the premonitions of the future.
  • Referenced in Déjà Vu by agent Carlin right before they send a note back in time:
    Technician: It would have gone faster if you had written it [the note] yourself
    Carlin: Yeah, then I recognize my own hand writing and the universe explodes.
  • The Terminator: Fathering the guy who will send you back in time counts, too. Also, where did the message about how "the future is not set" originate? Chronologically, Kyle first gave it to Sarah in 1984 as a message Future-John had sent with him when he sent him back in time. Then Sarah decides to teach it to present-John when he is a child so that he will have the message to send. So she gives the message to John, who gives it to Kyle, who goes back in time and gives it to her, who gives it to John, who gives it to Kyle, who goes back in time and gives it to her, who oh look I've gone cross-eyed.
  • In Minority Report, Precogs can predict murders before they happen (hours for crimes of passion, days when premeditated). The protagonist finds himself being accused of a premeditated murder of a man he has never met. He naturally assumes himself to have been framed. To this end, he studies the visions of the Precogs to track down this individual. It is these acts which make the murder premeditated, since he's actively trying to find this guy and will supposedly end up killing him. This leads to the Fridge Logic problem with the entire movie: how the hell could Burgess have arranged such a thing? The last time he used the Precogs to do such a thing, he did it in a wholly logical way. His framing of Anderton is wholly illogical, since there's no apparent source for the vision and no way it could have happened naturally. The setup is entirely dependent on events that never would have come to pass without Anderton having been present to see the precogs' vision; their prediction itself is the very cause of what they predicted.
    • The precogs, or more accurately Agatha, the skilled one, might have constructed the vision themselves, in order to bring about the events of the movie and end their torture: dreaming of nothing but murder all the time.
  • Timecrimes could have been renamed Ontological Paradox: The Movie. The protagonist travels backwards in time, and ultimately ends up responsible for the events that caused him to travel back in time.
  • In The Time Machine (2002), the uber-Morlock explains, "You built your time machine because of Emma's death. If she had lived it would never have existed, so how could you use your time machine to go back and save her?"
  • Summer Time Machine Blues is a Japanese film that starts with a group of high school students on a hot summer day stumbling upon a time machine and using it to prevent the remote control for their air conditioner from fizzling out due to a spilled coke can. Hilarity Ensues.
  • Star Trek IV: The Voyage Home:
    • An Object Loop gets lampshaded when Kirk pawns his reading glasses in 20th Century San Francisco.
    Spock: Excuse me, Admiral. But weren't those a birthday gift from Dr. McCoy?
    Kirk: And they will be again. That's the beauty of it.
    • Except there's no reason to think there IS an Object Loop occurring, other than Kirk's offhand comment, since the glasses he sold could have easily simply been lost and destroyed over time while the version that existed at that time continued on into the future to become the pair that Kirk sold in the past.
    • There's also an Information Loop, in the form of Scotty providing the formula for "transparent aluminum" to a 20th century scientist, who, it is implied, will go on to "invent" it. The novelization explicitly states that the scientist they give the secret to IS the historical inventor of transparent aluminum, which was only the beginning of his accomplishments, and Scotty observes that it might be ESSENTIAL that they give it to him. In the film it's merely hinted at: McCoy complains about giving the scientist the formula and Scotty replies "How do we know he wasnae the one who invented it?"
  • Willow contains a predestination paradox (if you assume, as the film does, that prophecy really is knowledge of the future): Bavmorda's attempts to destroy Elora are the very thing that causes her own destruction, which she would not have attempted to do EXCEPT for foreknowledge that Elora was going to cause her destruction.
  • Predestination, being an adaptation of the below-mentioned —All You Zombies—, has the temporal police protagonist being his/her own father/mother/recruiter, and the very person s/he is hunting, as s/he sleeps with his/her future self, has a baby who is abducted, ends up meeting his/her recruiter at a bar to join the temporal police, runs into his/her past self on a mission, impregnates her/him with... her/himself, who is taken from her/him after birth and left at an orphanage, then goes to hunt the so called 'Fizzle Bomber', only to eventually find that said criminal is his/her future self, having gone mad.

    Literature 
  • Chronos, the Incarnation of Time from Piers Anthony's Incarnations of Immortality, is immune to this, to an extent. He cannot be balked by paradox, he remembers the original and the new timeline, though no one else does. The limit is that he cannot interfere with his own workings (the "Three Person Limit"). He can exist once, go back in time and change things, but he cannot go back in time and stop himself from changing things, thus the three person limit.
  • The ultimate time paradox story is Heinlein's —All You Zombies—, in which the protagonist turns out to be hisheritthey's own mother, father, son, daughter, grandmother, grandfather, grandson, granddaughter, great-grandmother, great-grandfather, great-grandson, great-granddaughter, great-great-grandmother, great-great-grandfather, and so on, ad infinitum. Also hisheritthey's own recruiting officer to the Temporal Bureau.
    • Another Heinlein story, By His Bootstraps, takes things nearly as far. Among other hijinks, the main character gets a book from the future, which he copies into another one (the same one, when it's new?) when it becomes too old and is falling apart. A good way to avoid an object-based ontological paradox.
  • Averted — by the characters, no less — in Isaac Asimov's short story The Red Queen's Race. They wind up creating a Stable Time Loop instead. A scientist conducts an experiment to send modern scientific texts back in time, translated into ancient Greek. His translator, fearing a Temporal Paradox, only translates the parts that would account for the oddly anachronistic scientific advances already in our ancient history, like Hero's steam engine or the infamous Baghdad Battery.
  • In Artemis Fowl and the Time Paradox, Opal Koboi from the past travels to the present, and possesses Artemis' mother, making her appear ill. This forces present day Artemis to travel back in time to get the cure from the past Artemis. Opal then uses Artemis returning to the present to return to a few days before the present to make Artemis' mother ill in the first place. Ironically, this is all so she can aquire the secret of time travel.
    • Not to mention, Artemis had foggy memories of the past. When he went back in time, he left a note for Mulch to open the trunk Artemis and Holly were locked in. Also, the Mulch and Artemis of the past had their minds wiped, and since Artemis' wipe was a blanket wipe, there were still several remaining facts about fairies. By travelling back in time, Artemis caused himself to discover the fairy race. Whoa.
  • Played with in the latest Thursday Next book, where they find that despite the existence of the Chronoguard, no one has actually invented time travel yet, so they assume that the technology much have been sent from the future and eventually they'll find the spot on the timeline where someone invented it to close the gap. As one character describes it, it's like they're running the technology "off of borrowed credit." This causes trouble however, when the Chronoguard begins to realize that no one in the timeline ever invented time travel. The resulting paradox causes the system to unravel and gets rid of any further possibility of Time Travel in the series (although it seems everyone in the populace has a Ripple Effect-Proof Memory).
  • In Harry Potter and the Prisoner of Azkaban, Harry and Hermione travel back in time for a number of reasons. During this time travel, Harry manages to save himself from dementors using an Expecto Patronum charm. The event is noted to have happened earlier in the book with Harry only glimpsing his mysterious saviour and thinking it looked a lot like his dad. Note that they are unaware of their problems they went back to fix being solved until after they travel back in time, thus making this not an example of the first.
  • In Flatterland (a Spin-Offspring sequal to Flatland), Victoria Line and the Space Hopper end up trapped in a black hole. They're rescued by slightly older versions of themselves with a portable white hole, producing both a reverse grandfather paradox and an object loop.
  • There's a human version of the object loop in Pyramids, with Dios (who frequently makes reference to a lack of memory very far back) being transported backwards through time to the beginning of Djelibeybi. There's also some Reverse-Grandfather involved, considering he persuaded the original founder of Djelibeybi to begin the Pyramid tradition, which in turn allowed Dios to live long enough to go back in time to persuade the founder and so on...
  • In Harry Harrison's The Stainless Steel Rat Saves the World, Jim comes home to find that sending He (that's the villain's name) to the time when Earth was about to be destroyed led him to launch the Time War, yet the Time War is the reason Jim got involved in the first place.
    Jim: The way I see it, He just bounces in a circle in time forever. Running from me, chasing me, running from me. . . . Arrrgh! When was he born? Where does he come from?
    Coypu: Those terms are meaningless in this sort of temporal relationship. He exists only within this time loop. If you wish to say it, though it is most imprecise, it would be fair to state that he was never born. The situation exists apart from time as we normally know it.
  • Played for Laughs in Xanthippic Dialogues, where a footnote explains that the really great poets' influence stretched backwards in time, which is how you can find shakespearean quotations in plays from the fifth century BC.

    Webcomics 
  • At the climax of the Doc Gets Rad chapter of The Adventures of Dr. McNinja, villain Sparklelord is sent back in time to the moment when he originally entered from Another Dimension. This version apparently overwrites the original copy of him, but without any accumulated memories, thus condemning him to repeat the same sequence of events for eternity. So there is an infinite quantity of him entering the loop, but nothing coming out... huh? Presumably, the only reason the universe doesn't implode is that the comic runs on the Rule of Cool.
  • Trying to understand a complicated series of events in Irregular Webcomic! seems to lead to this conclusion. Two characters are captured for Organ Theft purposes. Their future selves come to save them, but end up being captured as well. The original pair having their organs stolen survive by stealing the organs from their future selves, but eventually come across their original organs, and put those in them as well so that when their organs are stolen, only the spares are taken. It's all very complicated. Of course the characters end playing a part in destroying the universe by destroying the only time machine in existence instead of using it to become their future selves.
  • In this Faulty Logic comic the main character builds a time machine to steal ideas for comics from his future self, only to have them stolen by his past self several seconds later. In essence, these ideas only exist for several seconds, over and over again.
  • Homestuck contains probably the mother of all ontological paradoxes: The Heroes create their parents from their own genetic material, and then create themselves from their parents material, then send the parents and children back in time to become themselves. There's even a term for this: Paradox Cloning, when a person is cloned from themself.
    • It should be noted that those examples happen all the time. Locally to John's session a group of previous players make contact because one of the players, Terezi, found money that was sent to her on her orders. They only look for this money because later John and his group will send an omnipotent demon into the previous playing session. This previous group of players, once aware of the humans, use internet messaging to talk to them all over the course of their lives, usually in heavily non-linear fashions that create stable time loops either way.
      • Worth noting that Terezi told Dave to wire her past self money so that she would discover him and be able to tell him to wire her the money.
    • For a more minor example, at one point Jade complains to John that her pumpkins keep disappearing so John sends her some pumpkin seeds for her birthday. However, these get sent back in time, and it is receiving that present that inspires Jade to start gardening in the first place.
    • For another, we have one of John's conversations with Karkat, who is trolling him backwards through time. Karkat claims that John told him that humans hatch as slugs instead of being born, and John tells him that's completely false but thanks him for the pranking idea. Sure enough, in John's next conversation with Karkat, he tells him exactly that and Karkat believes him.
    • For another, much later on Karkat opens a memo only to be distracted by himself from ten minutes into the future angrily responding to it. Throughout the course of this conversation present Karkat becomes characteristically enraged and when it's over goes to take it out on himself from ten minutes ago, starting it all over again. Future Karkat even lampshades this, stating that the whole bad mood basically sprung from nowhere and wondering whether it's even real. Yeah, Homestuck likes to play around with time a lot.
    • There's even a whole class of artifact whose defining feature is being an ontological paradox. A juju is a supernatural artifact whose origin is impossible to trace specifically because it exists in a Stable Time Loop. One in-universe theory supposes that they are spontaneously created ex nihilio by Paradox Space. Lil' Cal is a juju, one whose Stable Time Loop encompasses at least three separate universes.
  • S.S.D.D, Doctor Cook claims that he got on the Maytec board of directors using stock market information from a PDA that was accidentally sent back in time. But then he locked up the present day version of the PDA and made sure it was never sent back, he noted that the future version didn't disappear or anything.
    • Also the Anarchists were prevented from stealing the Wildfire time machine and using it to build the Inglourious fifty years earlier. Unfortunately they still have it, centuries before it wasn't built.
  • From Bob and George, this ontological paradox shows the time-traveling X and Bass giving Dr. Light and Dr. Wily the ideas to create them in the first place.
  • In Educomix, two objects—Jessica's mask and Dave's fez—literally come from nowhere, having been given to their original owners by people from the future. This causes a "Time Fart", which drains energy from other universes to keep the paradox in place.
  • In 8-Bit Theater, Thief comes up with a plan by watching a future Red Mage carry it out. Red Mage immediately wonders about the paradoxical implications.
    • Later, Thief steals his class change from his future self, only to later lose it when his past self steals it from him. This class change has no origin.
    • Red Mage also accuses Chaos of having an unworkable plan because of a variant on this. Chaos intends to destroy all of space and time which would destroy all the events leading up to his being summoned to destroy all of space and time. (Reaction: I'd better not create a temporal paradox! I'd hate it if everything were destroyed the way I wanted it to be destroyed!)
  • In Wicked Powered, much like the "All You Zombies" example, the main character becomes both of his own parents through time travel, gender-bending, and amnesia. His DNA therefore has no origin, and he is immortal because of this.
  • In Jack, Drip unwittingly gets a chance at one, but he blows it and closes a Stable Time Loop instead. The Devil offers to trade Drip the scarf his mother wore in life in exchange for the murder of a married couple. Drip obliges and goes to kill their infant son, too, but the Devil tells him not to; instead, Drip decides to leave some disturbing imagery for the police by leaving the baby among the scattered carnage of what's left of the wife. It's not until Drip sets him down that he realizes that the people he brutally murdered were his mother and father, the crying baby looking up at him is his infant self. Drip is horrified to realize that not only did he actually kill his parents, he's also the reason he was sent to live with the grandmother who's been sexually abusing him all his life (and, having died and ended up in the area of Hell that Drip rules, is still doing it). The Devil points out that time works funny in Hell; Drip could have prevented it all if he had just chosen not to murder two strangers for a scarf.

    Web Original 
  • Tom Francis' "Exploded" (featured in the Machine of Death anthology) uses the "information" variant. Two guys invent a machine that predicts how one can die. While one can postpone one's predicted death, one cannot avert it entirely. The invention makes both men fantastically wealthy, and miserable. Late in the story, the machine's information is explicitly described as coming from the future.
    Narrator: But Pete kept saying something over and over to me that to this day I don't quite get: "It's a function of the future," he said, "not the past." He said it didn't matter what he did to it before it was built, because its predictions were somehow independent of anything that had already happened.
  • The Reversed Grandfather Paradox is lampshaded for all it's worth in Red vs. Blue when Church is send back in time and attempts to prevent the accident that started the entire time travel problem.
    • Captain Flowers dying from a heart attack in his sleep? He died from the heart medicine Church gave him to prevent that.
    • The tank's AI named Sheila?
    Tank: "Welcome to the 'M808V Main Battle Tank', you may call me 'Philis'."
    Church: "What? Your name is Sheila!"
    Tank: Name overwritten. You may now call me Sheila."
    • Sheila killing Church because of the friendly fire setting? Guess who changed the default setting.

    Western Animation 
  • In the first Futurama movie, the "paradox-free time travel" isn't quite paradox-free: there remains an ontological paradox surrounding the origin of the name "Lars," as future-Fry chose that name when he realized that the injuries he sustained when Bender attempted to kill him made him Lars. From whence did the name come?
    • Well, if we just accept that there is no 'beginning' to the Lars and Fry cycle, then it all works out nicely. Fry says "Ow, my larynx", but it comes out as "Lars", at which point he realises "Oh hey, I look and sound like Lars now, I guess I am Lars!"
    • Additionally, the temporal tattoo is an ontological paradox. At the end of the movie, Bender peels it off Lars's ass, takes it back in time, and puts it on the present Fry's ass. Thus, it was never actually created, and just loops through time eternally with no beginning or end.
    • Fry's genetic material. Being his own paternal grandfather, the question is where exactly the information carried on his y-chromosome originated.
    • One episode had Leela being the campaign manager of a Senator who had traveled back in time to become the president of the world in order to prevent an apocalypse. He wins the election, but unfortunately invokes a paradox, which is explained by Bender. Since he changed the past, that would mean that he wouldn't have traveled back in time in the first place. The Senator disappears via Reset Button, and Nixon is reelected.
      • Not only that, he went back in time using the same method as in the aforementioned movie. So much for "paradox-free" time travel.
      • This brings along Fridge Horror, since this means that in about 20 years, there will be an apocalypse led by robots.
      • This same paradox occurs in "The Why of Fry" with the Scootie Puff, Sr. but there it works out just fine (Fry tells Nibbler in the past to give him a better escape craft during the Infosphere mission, the Nibblonians give him one, and he escapes before the quantum interface bomb sends the Infosphere to the other dimension, which is not what happened the first time and invalidates the event that made it possible for him to go back in time in the first place).
    • Most if not all of the above is due to said "Paradox-Free" time travel actually being "Paradox-correcting" time travel: paradoxes come into existence repeatedly, but radiate enough doom that the universe actively kills them before they can do any damage. The only time this backfired on the universe was when the army of Benders was "corrected" all at the same time.
  • Gargoyles: Time travel always creates a Stable Time Loop:
    • David Xanatos planned out his fortune by time-travel. While in the past, he had a mundane coin and a note sent to his future self. The coin becomes a rare object worth a few thousand and the note contains instructions on how to invest the money.
    • The Archmage goes back in time, rescues his past self from falling into a chasm, then schools him on how to acquire the objects that gave him the power to, among other things, go back in time and rescue his past self from falling into a chasm, then school him—
    • The Phoenix Gate. It goes through all the events of the series until, to get it away from Puck, Goliath sends it to the distant past where it eventually gets discovered in the first place. The loop is looped.
  • This happens in the My Little Pony: Friendship Is Magic episode "It's About Time". Twilight Sparkle meets her future self, who tells her that she was able to get here because of the time spells located in the Star Swirl the Bearded wing of the Canterlot Archives. Later in the episode, she goes there (for entirely different reasons) and ends up using a time spell...to go back and tell herself about the time spells. Hmm, now where did she learn about the location in the first place?
    • The whole episode is this. Past Twilight is so bewildered and amazed by the concept of time travel that she can't shut up, and future Twilight doesn't manage to tell her what the actual thing she's supposed to be averting is before she gets sucked back to the future: all past Twilight knows is that future Twilight was from the following Tuesday. So she spends the week panicking about it, ends up with all the injuries future Twilight had when she visited, and by Monday night concludes the only way to stop whatever will happen by Tuesday from happening is to stop time. So she goes to the archives, but as Tuesday morning arrives, nothing happens, but she finds the time spell and goes back in time to warn herself not to worry about the future...
  • The Star Trek: The Animated Series "Yesteryear" revolves around a Reverse Grandfather Paradox in which Spock prevents his own death as a child. He doesn't do it quite right this time around, resulting in a slightly revised timeline when he gets home. Originally, his pet had lived. This time, he arrives a moment late, and the pet dies.
  • In the Transformers: Generation 1 episode War Dawn, the Aerialbots are sent back in time trying to destroy the Decepticons time machine. This put them back at the start of the war, right at the start of one of the very first Decepticon attacks. While they try to stay out of the way, the end up saving a insignificant, not important dock worker. As it turns out that insignificant dock worker was the un-upgraded Optimus Prime, both giving the Autobots a leader and keeping the Decepticons from winning an important first battle, getting an advantage over the Autobots and likely winning the war. It was Optimus who had the Aerialbots created in the first place.
  • In the Kim Possible three-parter "A Sitch in Time", future-Shego gives present-Shego a plan to use the Time Monkey to take over the world. Coming up with this sort of plan on her own initiative isn't really like her — but she didn't have to, she just had to remember what she'd been told and go back in time to repeat it to herself.
  • In the Milo Murphys Law episode, "Missing Milo", Milo, Cavendish and Dakota get stopped from running into a group of mutant pistachio monsters when a peach gets thrown at Cavendish which is then pocketed by Dakota; later after time traveling to 15 minutes in the past and seeing their past selves about to run into the mutants, Dakota hands the peach to Cavendish who uses it to stop themselves. This then leads to the two of them having a looping conversation about where the peach came from.
    Cavendish: Wait a moment, where did you get that peach?
    Dakota: Someone threw it at you earlier.
    Cavendish: But that someone was me.
    Dakota: I know.
    Cavendish: But where did I get it?
    Dakota: From me.
    Cavendish: But where did you get it.
    Dakota: Someone threw it at you earlier.
    (repeats)
  • This possibly happening is why Della and Donald refuse to let Dewey (Della's son and Donald's nephew) warn them about the future in the Ducktales 2017 episode "Last Christmas".
    Donald: NO! KEEP YOUR MOUTH SHUT!
    Della: You can't warn us about our future, you'll disrupt the time stream!
    Donald: Haven't you ever seen any movie?!

Unclassed, multiple or confused Examples

    Comic Books 
  • The fear of this appears to be the reason why Doctor Strange, having traveled to the distant past and witnessing the Fantastic Four having traveled to the same time and place for their own reason, is very reluctant to reveal himself to them. He has befriended them in the present, or rather his present, but the FF are from an earlier point in time and haven't met him yet.

    Fanfiction 
  • Improperly invoked in Light and Dark The Adventures of Dark Yagami, after Blud learns that Matt survived a car crash with "Yotsuba", he decides to write Matt's name in his Death Note in the future to kill him in the past. This results in the past changing, with Matt dying and Yotsuba surviving. Dark claims the reason why Blud is telling him and Light this now, rather than at the point in the future when he writes the name is "Its one of those time parradoks that they have in Back to the Future".
    • Dark's exact words are "Oh I didn't tell you my death note can also kill people in the past and I am going to write his name in it in the future to kill him in the past and stop him stealing the death note." Hope that clears up any confusion. It doesn't help that the flashback scenes go from "Present Day" to "Meanwhile in the Past" to "Back in the Future"
  • In Megaman Star Force Orion, Amaya and Taisaka decide to go back in time to prevent Kiri from making contact with the Ice Goddess Talisman. With the help of the UMA Fire, they reach the year in which Kiri is exiled from her home. Fire then brings them 2 years forward in time, and Taisaka and Amaya meet Tagekai, who reveals that Taisaka was originally a member of Tri-Clan. This causes Taisaka to break down as Amaya abandons Taisaka, soon meeting Takeshi's former self. Takeshi later reveals he has memories of everything that occurred as he was 66, as he is trapped in that age. Taisaka changes herself by telling her younger self not to fight Tagekai which causes her to become exiled. Amaya and Taisaka bring Kiri to the Omnikron Temple, and Amaya meets Eidaya, explaining everything. This creates a major time paradox, which causes the already fragile sands of time to become even more fragile. Soon Amaya returns to the past, meeting his father, who realizes that Amaya is Amaya, and he travels after him. As Amaya tries to fix things in Tri-Clan, Takeshi reveals he killed Taisaka, and Daisuke King, a Time Traveling Kamen Rider, shows up and brings Amaya to the present. He warns Amaya that Ryo is about to be killed by a Shinigami named Albano, and if this were to happen, the future would be corrupt, as Takeshi would cease to exist in the present. At the same time, Amaya's father plans to force time into 11:60 PM on December 24th. Finally, Taisaka travels to the present from the past, creating a temporal corruption where memory demons overcome the present world and attempt to end the world. Time is eventually reset with the use of the Stolen Pocketwatch from the very first episode.
  • With the Tenth Doctor traveling with Holmes and Watson in Children of Time, temporal paradoxes are a concern, as the Victorian duo do have fates to fulfill in their own time. The season finale revolves around this, specifically, what happens when something that should not have happened does.
  • In the Pony POV Series, there's actually a character who is more or less the embodiment of this trope. Nightmare Eclipse is a potential future Twilight Sparkle in the Bad Future where Discord won. She caused a Grandfather Paradox by resetting the timeline so Discord never won in the first place. However, she decided to become a Nightmare and kill Discord in revenge for the hell she put him through, forgetting her reasons for resetting things to begin with and trapping him in a "Groundhog Day" Loop. However, she then proceeds to be the cause of an Ontological Paradox, manipulating events so Twilight will become her and reset the timeline, fusing with Eclipse and repeating the cycle next loop. Her doing this results in Apple Pie nicknaming her Nightmare Paradox.
  • ''The Last Great Time War'', a Doctor Who fanfiction, has a multiverse-wide war of paradoxes.

    Film 
  • Millennium concludes with a massive paradox barrelling its destructive way into the future whose time travel efforts caused it.
  • Played with in Primer. As one of the characters says, "The last revision is apparently the one that counts." We find characters gradually losing their worries about causality; they wind up going back in time to relive the events of that same week in their original place — apparently intending to do everything right this time. It appears that causing a paradox causes some kind of mild brain trauma to the time traveler involved. But then there's that other version of yourself that you drugged up and locked in the basement so you could replace him...
  • Déjà Vu contradicted itself on terms of this. First, it is implied that anything changed in past changes the present, as Doug causes the death of his partner, that was thought caused by the ferry explosion. Later, it is implied that the past has already been changed, as the message "U CAN SAVE HER" in Claire's house was written by him, but in the end, it is contradicted, because if he prevented the explosion, he could never have been assigned to the case, and thus could never do the time travelling, and so on...
  • French-Canadian movie based from a cult tv show Dans une galaxie près de chez vous 2 featured a spatio-dimensional rip (shaped like a zipper) who goes to present Earth. The Capitain was able to chuck down a DVD with their plea (NOT to destroy the ozone layer) recorded on it. It backfired when the video got featured on YouTube and ridiculed as "Star Wars Twit" (Being bad at pronounciation dosen't help). Nevertheless, it might have pushed a younger version of the Capitain to go into space, directly and indirectly setting the events of the show into place.
  • Austin Powers: The Spy Who Shagged Me shows Austin briefly attempting to reason why no time paradox has occurred due to him and Dr. Evil time traveling to a date where they logically shouldn't be. Basil Exposition puts his mind at ease
    Basil: "I advise that you not worry about that sort of thing and.. just enjoy yourself (faces audience) that goes for you all too."
    Austin: (also facing audience) "Yes"
  • The reason the universe is ending in Star Crossed is because of all the various paradoxes created by the Federation, from Jim Kirk to Captain Janeway.

    Literature 
  • In Strange Attractors by William Sleator, almost any time travel to the past causes instability in the universe. As those instabilities add up, the entire universe can "go chaotic", essentially becoming a huge mass of paradoxes. The only noticeable effect of this is that electrical lighting flickers. In fact the timeline in the series is so fragile you can cause paradoxes by going so much as five minutes into the future.
  • In Ted Chiang's short story The Merchant and the Alchemist's Gate, the titular gate can transport anyone exactly twenty years into the future, or twenty years back. This leads to increasingly more improbable shenanigans, starting with a Stable Time Loop involving a treasure map, and reaching its arguable peak when a character's wife meets her husband's younger self in the past, takes him to the bedroom, and upon descovering his lack of the, er, skills that the husband has in the present, teaches him how to please a woman, over the course of weeks. It's also implied that the husband married her in the present because, when he saw her, she reminded him of the middle-aged woman who took his virginity.
  • In L. Sprague de Camp's short story "A Gun for Dinosaur," four characters (two hunters and two guides) travel to the Cretaceous period for a dinosaur-hunting safari. One of the hunters, Holtzinger, is killed by a tyrannosaur, and the other, James, is blamed for his death because he recklessly fired the shots that woke the dinosaur up. Later, James, swearing revenge, tries to go back to just before the expedition arrived so he can kill the guides once they emerge from the time machine. Instead, the space-time continuum snaps him back to the present to prevent a paradox, killing him messily.
  • The novel Ice And Blood manages to produce a very strange reverse grandfather paradox. ZJ is a depressed, bipolar paranoid schizophrenic who has no memories of his childhood. He hates his life enough to deliberately break into a lab where time travel technology exists, he goes back to the past, and he kills his parents in the hopes he'll stop existing. Instead the violent and bloody deaths they suffer triggers his past self's mental illness. The obvious problem with this is that there's no guarantee that ZJ would suffer the exact same breakdown and block out his memories every time, nor is there any logical reason that depressed ZJ would ever go this route again when suicide would be significantly easier for him. It just doesn't work from a logic standpoint. (It's still a good read if you apply enough MST3K Mantra to it.)

    Tabletop Games 
  • In the Time Travel RPG Continuum, if a time traveler creates a paradox, they accumulate "frag," and if they accumulate too much, it eventually causes them to unravel. What's more, unchecked temporal paradoxes will eventually lead to the unraveling of reality itself. (On the other hand, the game totally mindscrews you with the fact it manages to be utterly fatalistic about it: the fact the universe itself exists, even if there is a paradox in existence, means that — at some point — the temporal paradox will be/does get/has been fixed, by the Continuum. It's just a matter of who or what becomes collateral damage in the process of fixing it.) Much of the game centers around the players, who are part of "The Continuum", trying to fix paradoxes deliberately created by time travelers (known as "narcissists") who don't believe the official line on paradoxes and who want to mess with the timeline for their own personal gain.
    • Similarly, the expansion sourcebook (currently trapped in Development Hell) Narcissist has a different take on this — the original time traveler entered the "main" timeline's past and introduced time travel sometime around 14000 BC. Said time travel directly resulted in a singularity around 2400 AD, which then used its super-powerful minds and infinite resources to make sure that said time traveler never leaves our timeline (which would require a portal made out of X number of Temporal Paradoxes), and that time travelers don't cause the timeline to deviate from the history that led to the singularity. In alternate timelines away from "the swarm" — agents of the Singularity, named that because there's a lot of them, but they're disorganized idiots — paradoxes don't exist: "frag" exists in the main timeline specifically due to the singularity's agents constantly trying to time-Mind Rape anyone attempting to change history.
  • Time Travel is rare in Warhammer 40,000, but the Warp does strange things sometimes, which may result in a ship setting out to answer what turns out to be its own distress signal. In another example, one kleptomaniac Ork Warboss was sent back through time via warp-storm, met up with his past self, and killed his temporal doppelganger so he could have two copies of his favorite gun. The resulting confusion stopped the Waaagh! in its tracks.
  • Averted in Genius: The Transgression. As the game puts it, it turns out the universe doesn't particularly care if your grandmother gets shot and there's no shooter — barring external intervention, you pop out of existence if you pull the trigger and the bullet hits home. This can have some interesting consequences, as the angry young lad seeking to avert a massacre in his country's history did not discover...
  • In Time and Temp, a paradox would Ret Gone all of existence. Office temps (hence the name of the game) are used as field agents to prevent this, because they're otherwise unimportant enough to minimize the risk of personal Grandfather Paradox - though their potential for incompetence is at odds with this.
  • The GURPS Sourcebook GURPS Infinite Worlds includes a chapter exploring time travel and paradoxes.

    Visual Novels 
  • Time Hollow avoids these, for the most part, by having a few people remember all alterations - as such, you can't hit the "prevent myself from adjusting time" snag by fixing the thing you wanted to change. There is, however, of all things, a cat that ends up in a near-ontological paradox avoided only by the fact that it's locked in time and cannot age.

    Webcomics 
  • Super Stupor's Clockstopper can change history with his "Time Punch". (And he'd rather be surfing TVTropes than fighting crime.)
  • Breakpoint City has several examples. Some are played straight, some are... not. A few have been explained away as due to alternate universes, therefore probably not a paradox, but you never know.
  • This is confusing. How is a flashback to the childhoods of the Cheer! girls even possible? Weren't they, you know, boys? Just how much of the past did Miranda rewrite to cover up Anne's mistakes? Is it like what happens when a misfile occurs? Argh...maybe it's best to pretend this isn't canon, especially seeing as there are lots of people who still remember.
    • Well, three of the girls do not remember ever being anything but girls, so presumably their memories were altered. As for Jo...
  • In the Surreptitious Machinations arc of General Protection Fault, Empress Trudy travels back in time to give her younger self the necessary information on what she must do to take over the world. Near the end of the arc, Nick and Ki's son Todd reveals that the entire Bad Future he and Empress Trudy came from was the product of a temporal paradox, since it could not have happened without Empress Trudy advising her younger self, which would not be possible if it did not previously exist. It is heavily implied that Pandemonium was responsible for the existence of the alternate future in the first place. As a result of the future being changed, Todd, the Empress and all other objects from the alternate future fade from existence, but the Empress teleports to a different time just before she fades, and the Gamester finds and recruits Todd.
  • This Rock, Paper, Cynic comic. A man uses an axe to murder someone and get at a time machine. He then briefly experiments with it before realizing that he doesn't know where his alternate self that should exist is. Then, by intention or accident, he goes back to the moment first chronicled in the comic, where he becomes the man his past self killed to get at the time machine.
  • Subnormality has The Mission, which holds a Reverse Grandfather Paradox - the traveler spread the teachings of the holy book he adored, but it turns out HE was the propogator of that holy book. So where did those teachings originate?
  • In Dragon Mango you have to ride the rollercoaster-- because you're already getting off.
  • In Sailor Moon Cosmos Arc, because of the Chibiusa of the 21st century traveling through time and being present in the final battle, she was reincarnated along with the other senshi. However, because the other senshi were revived in the 30th century, the Chibiusa that was born to Usagi and Mamoru never ended up traveling in time, therefore, unlike the other senshi, has no memories of her past life and has never awakened as a senshi. It's because of an unconscious wish Usagi had that Chibiusa would never awaken as a senshi. There is one more twist to this: the memories of the time-traveling Chibiusa were sealed inside the Pink Moon Crystal, so when she broke her brainwashing and started receiving her powers, she finally gained the memories of her past self.

    Web Original 
  • The end of The Onion article "Pistorius Case Takes Dramatic Turn As Altered Plane Of Reality Results In Paralympian Shooting John Lennon": At press time in November of 1986, South African officials reported they have apprehended a newborn Oscar Pistorius for the murder of John Lennon, thereby preventing the deaths of both Reeva Steenkamp and John Lennon at the hands of a 26-year-old Oscar Pistorius, and thereby making Pistorius a free man.

    Western Animation 
  • The Fairly OddParents! special, "The Secret Origin of Denzel Crocker". Timmy goes back in time to find out why Crocker was so miserable and to try to fix it. He finds out that as a child, Crocker himself had fairy godparents—and that they were Cosmo and Wanda, something that they don't remember—and figures out that he must've done something to lose his fairies. He tries to warn the young Crocker, but inadvertently ends up being the one who reveals the secret (with some help from both '70s Cosmo and modern Cosmo's stupidity). Furthermore, as Jorgen shows up to erase everyone's memories of there being fairies, young Crocker manages to get his hands on the DNA tracker that AJ had built so that they'd know when Crocker was around, and managed to get Cosmo's DNA to use in it, and managed to covertly write a memo on the back of it that fairy godparents exist without Jorgen noticing, allowing him to keep that knowledge after his memory of fairies was erased...which means that if Timmy had never interfered, Crocker would be neither miserable nor fairy-obsessed. However, whereas when Timmy left for the past, Crocker was using a very primitive and likely useless "fairy finder", the Crocker in the present that Timmy returned to was using the tracker that AJ had built, implying that he had created an alternate timeline, and leaving one to wonder what happened in the original timeline. Of course, considering it's explicitly stated in The Movie that few kids keep their fairies past their first year, much less until adulthood when they would leave anyway, we can guess...
    • Well the original timeline seems to be that 70's Cosmo is that cause of Crocker losing him and Wanda. Timmy then stops this incident only for present day Cosmo to turn on the mic while Timmy is talking and cause the incident to happen anyway. While this doesn't explain how Crocker knew about the existence of fairies after his mind was wiped in the original timeline, since we don't see the original incident play out, we can just assume any number of reasons for that. (Perhaps he managed to write a note in that timeline too.)
    • There was also a Historical In-Joke to imply that it was an alternate timeline.
  • Justice League
    • Lord Chronos was at first a meek scientist who invented time travel. He used it to steal things from history that would not affect the timeline. Then his wife nagged him about his lack of imagination, and one trip to the Wild West later he decided that stealing the most famous items from history and setting himself up as master of space and time was the better way to go. Reality itself falls apart, so he decides to go to the beginning of time and do it all over again. Batman and Green Lantern manage to reset history. Batman also manages to create a close And I Must Scream moment by trapping him in an eternal loop of his wife's naggery.
    • Time travel itself seems perfectly fine: Superman went to the future and the past, the Justice League went to WWII, one of the team is from the future, and the list goes on. Vandal Savage notes that his time machine couldn't send him back to a period where he already existed, which may be with good reason: in that episode, time was falling apart only when Batman was with his very old self.


Alternative Title(s): Time Paradox

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