History Main / TemporalMutability

* Just about all of these are [[DiscussedTrope discussed]] in Ray Bradbury's short story "A Sound of Thunder," involving time travel used to let rich folks hunt dinosaurs for amusement. They aren't sure exactly what rules time travel operates under, but discuss the prevailing theories: you can't change the past because you've already changed it, you can only change the past in minor ways, you can only change the past in direct and predictable ways, or the simple act of stepping on a butterfly in the past leads to chain reaction of events that completely alters the present in ways no one can foresee. [[spoiler: Turns out, in the end, Temporal Chaos Theory is correct.]]

* Literature/TimeScout presents Enforced Immutability that approaches Rubber Band. You can change anything so long as it doesn't matter in any way. If it does matter, you can't change it. Something will happen. Usually to you. Things that ''can'' be changed are enforced by uptime laws. And taxed accordingly. Reality seems to agree with humans on "what matters" to a degree that is almost comedic: if you tried to kill someone important to history, your gun would jam. If it's someone who never made the history books, go crazy! You would think that to the universe, to physics, it's ''all'' just atoms, but it seems reality cares a great deal about the "important" people and events in history enough to step in.

#'''[[ForWantOfANail Temporal Chaos Theory]]:''' The [[ButterflyOfDoom Butterfly Effect]] is in full force. Simply by ''being'' in the past in the first place, you alter the past, both overtly and in ways too subtle to notice. And these changes [[ForWantOfANail inevitably snowball]], eventually rendering the Present or Future ([[InSpiteOfANail almost]]) [[AlternateHistory completely unrecognizable]]. And sometimes, the universe hates you, [[ButterflyOfDoom so every change to the past only makes the present]] ''[[ButterflyOfDoom worse]]''. It bears mentioning that over short enough time periods, settings that fall under Temporal Chaos Theory may not be distinct from those that fall under Temporal Balancing Act.

* This is how it ''used'' to work in Franchise/MarvelComics, particularly around the Stan Lee editorial era, flowing into the Wolfman era. It kind of stopped somewhere in the 90s.

* ''Series/DoctorWho'', being the ''TropeNamer'', flirts with both this and Enforced Immutability (see above). Basically, the rules of time travel are fixed and immutable... within a single story. The writers don't even pretend it's consistent beyond that. This gets a lampshade in [[Recap/DoctorWho50thASTheDayOfTheDoctor "The Day of the Doctor"]] when Ten is terrified at the idea of changing history, only for Eleven to blow him off since they do it all the time.

* ''Film/BackToTheFuture'' used the Overwriting the Timeline version of this, with {{Delayed Ripple Effect}}s.

* '''Overwriting the timeline:''' The old timeline ceases to exist, and is replaced by the new series of events resulting from your time travel (implying that Time itself exists in a sort of [[SanDimasTime Meta-Time]]). The change to the timeline may be instantaneous, or it may cause a DelayedRippleEffect, allowing you to race against SanDimasTime to SetRightWhatOnceWentWrong before you find yourself RetGone. You may find yourself [[RippleEffectProofMemory the only person who realizes the past has changed]]. Overwriting the timeline is also prone to causing {{Temporal Paradox}}es. Progress can be tracked with a RippleEffectIndicator if one is available. Not to mention the realization that since you have erased a whole timeline, [[TheTimeTravellersDilemma anywhere from a few dozen to a few billion people will never have existed in the first place, so you effectively killed them all and erased their existence.]] NiceJobBreakingItHero.

#'''Enforced Immutability:''' In theory, the past could be changed, but some force stymies anyone who tries. Maybe the TimePolice or ClockRoaches menace anyone who violates the Temporal [[ObstructiveCodeOfConduct Prime Directive]], or maybe the past can only be visited via IntangibleTimeTravel.

#'''Enforced Immutability:''' In theory, the past could be changed, but some force stymies anyone who tries. Maybe TimePolice or ClockRoaches menace anyone who violates the Temporal [[ObstructiveCodeOfConduct Prime Directive]], or maybe the past can only be visited via IntangibleTimeTravel.

#'''Temporal Balancing Act:''' There's no rubber band, so there's nothing to prevent you from making major, permanent changes to the past if you want to. But at the same time, it's possible for a conscientious time traveler like yourself to leave the past exactly as you found it. Or to change the past, then change your mind and [[SetRightWhatOnceWentWrong go back again and un-change the past]]. Or to [[TrickedOutTime intentionally arrange]] a StableTimeLoop.

#'''[[ForWantOfANail Temporal Chaos Theory]]:''' The Butterfly Effect is in full force. Simply by ''being'' in the past in the first place, you alter the past, both overtly and in ways too subtle to notice. And these changes [[ForWantOfANail inevitably snowball]], eventually rendering the Present or Future ([[InSpiteOfANail almost]]) [[AlternateHistory completely unrecognizable]]. And sometimes, the universe hates you, [[ButterflyOfDoom so every change to the past only makes the present]] ''[[ButterflyOfDoom worse]]''. It bears mentioning that over short enough time periods, settings that fall under Temporal Chaos Theory may not be distinct from those that fall under Temporal Balancing Act.

* '''Branching timelines:''' Your time-traveling causes a new timeline to split off the original, and both timelines exist (can be [[RubberBandHistory temporarily]] or permanently if it happens to be AnotherDimension identical to your own but shifted in time) as {{Alternate Universe}}s of each other. Depending on the setting, you [[TheMultiverse may]] or may not be able to return to your native timeline after you've caused it to split. Thus, there's no danger of [[RetGone accidentally erasing yourself from existence]] — at worst, [[ExpendableAlternateUniverse you'll prevent one alt-timeline's equivalent of you from existing]]. On the other hand you can't truly SetRightWhatOnceWentWrong, either: for every timeline that you fix, there's another that you don't.

* In the ''[[WesternAnimation/WhatIf2021 What If...?]]'' episode [[Recap/WhatIfS1E4WhatIfDoctorStrangeLostHisHeartInsteadOfHisHands "What If… Doctor Strange Lost His Heart Instead of His Hands?"]], an {{alternate|Self}} Strange uses the Time Stone over and over to try undoing his beloved Christine's death, only to find out she will always die no matter what.

* ''WesternAnimation/SpiderManAcrossTheSpiderVerse'' introduces the concept of "canon events": events in every corner of the multiverse that define the Spider-Man of that dimension. In every case shown to Miles, this event is a personal tragedy for that Spider-Man, including (but not limited to) Uncle Ben's death. Aside from preventing denizens of the multiverse from ending up in the wrong dimension, the duty of [[ComicBook/SpiderMan2099 Miguel O'Hara]]'s Spider-Society is to ensure these canon events are not altered, lest such an alteration threatens to completely destroy that dimension.

* In the fourth ''VideoGame/{{Deponia}}'' game, Deponia Doomsday what kind of time travel rules you'r trip follows depends on what model of time machine you are using, one guy at a bar for time travelers is mocked for owning a deterministic model because it [[YouAlreadyChangedThePast doesn't allow any changes to the timeline]], at one point you have to use it to go back to a location you visited some time ago and set things up the way they were when you first visited to solve a puzzle.

* In the fourth ''VideoGame/Deponia'' game, Deponia Doomsday what kind of time travel rules you'r trip follows depends on what model of time machine you are using, one guy at a bar for time travelers is mocked for owning a deterministic model because it [[YouAlreadyChangedThePast doesn't allow any changes to the timeline]], at one point you have to use it to go back to a location you visited some time ago and set things up the way they were when you first visited to solve a puzzle.

* [[Wiki/SCPFoundation SCP]]-2003: a time machine created by the Foundation in order to study the future and promote the development of a positive future for humanity. Unfortunately, one thing they've found is there are individuals whose presence and actions affect causality disproportionately, even to completely unconnected events happening thousands of kilometers away. For example, Scenario XE has the birth of a boy in Turkmenistan and the election of the Prime Minister of New Zealand on the same day in 2049 cause a chain of events leading to a society-destroying nuclear war between Israel and Greater Indonesia in 2058. Other futures have included things like the sun spontaneously becoming a black hole or a gamma ray burst destroying all life. These futures are unstable and can be changed with the most mundane of actions, and there's no telling what the results may be.

* In Pokemon this is generally how Time Travel works as seen in ''VideoGame/PokemonLegendsArceus'' with how [[spoiler: due to time traveling because of Arceus the Protagonist sees and is indirectly the cause of Sinnoh (Hisui) being named Sinnoh, the destruction of The Temple of Arceus/creation of Spear Pillar, and Giritina’s HeelFaceTurn]]

* In the [[VideoGame/SamAndMaxFreelancePolice Sam & Max]] episode, "Chariots of the Dogs", Bosco accidentally goes back in time and changes his history. When Sam and Max go back in time to stabilize the past they in addition cause Bosco to never been born. They fix it all by the end.

* ''Webcomic/MSPaintMasterpieces'': Time travel itself is an act which changes the future. If you go forwards in time, you vanish from the present while travelling and so arrive in a future shaped by your absence. If you go backwards, your appearance in the past changes causality and erases the future you returned from. Two possible futures are shown in the comic: the first is one in which the Dr Wily attacks time and time again until his execution; this timeline is erased when he travels forward in time, arriving in a new timeline in which he vanished for 37 years before suddenly reappearing. Wily then returns to the present, erasing this second possible future which relied upon his absence, and the events of the comic continue down a new ''third'' timeline.

See also [[http://jbr.me.uk/chrono.html this page]], for a more in-depth discussion.

* According to Music/InsaneClownPosse's [[http://en.wikipedia.org/wiki/Dark_Carnival_%28Insane_Clown_Posse%29 "Dark Carnival" mythos]], there is a place where one can play with a jack-in-the-box and see what the afterlife holds for them. However, this is not set in stone; the fate revealed by the Riddle Box can be changed via doing enough good deeds. [[TimeyWimeyBall Other aspects of the Dark Carnival would probably fit into other categories on this page, though]], which is understandable as it is a MetaphysicalPlace to begin with.

** The author also invokes the TimeTravelersDilemma, given this version of the trope, as altering the timeline means, effectively, killing billions of humans, reasonably pointing out that the only way this can be acceptable is if the GodzillaThreshold has been reached.

* The ''Series/LegendsOfTomorrow'' spin-off appears to go back to the RubberBandHistory option with the oft-repeated phrase "time wants to happen". Apparently, one has to try ''really'' hard to make a major change to the timeline, since it will always try to "snap back" to the proper course. It also doesn't help that the [[TimePolice Time Masters]] are there to ensure no undue changes to the timeline (FridgeLogic ensues when you start wondering why they allow speedsters to do it at will). Near the end of season 1, [[spoiler:the device that allows the Time Masters to monitor the timeline is destroyed, rendering them impotent. Savage uses the opportunity to try to destroy the timeline with three {{Doomsday Device}}s at different points in time, which, as he claims, will roll the timeline back to Ancient Egypt, allowing him to start over]]. Also, Rip claims he tried to save his family multiple times, only for something to always prevent him from doing that ([[spoiler:he later finds out it was the Time Masters' doing]]).

* In ''VideoGame/TheLegendOfZeldaOcarinaOfTime'', time-travel shenanigans (or, rather, mental time travel shenanigans) cause the timeline to split into three branches, with one point of divergence known [[note]]the ending, where Zelda sends Link's mind back in time to prevent his removing the Master Sword from its pedestal[[/note]], and the other previously [[EpilepticTrees only theorized]][[note]]the final boss fight, depending on if Link wins or loses[[/note]].

** ComicBook/RipHunter states that the future is in flux but major events in the past (called "solidified time") are immutable. This strange time scheme hinging on the present is particularly odd when you consider Booster is ''from the future himself'' making the present ''his past'', and Rip spent most of his time in the future ([[spoiler:and is also Booster's future son.]])

** Before the revival and the Time War, Enforced Immutability was implied via the Time Lords. These days, the term "fixed point" is used to describe events which are basically historical lynch pins: you can ''technically'' change them, but you shouldn't seeing as the universe will [[TimeCrash fall apart]]. They also had the Reapers (beyond creepy monsters from outside time who came to "sterilise the wounds" if things got too messed up, but you had to [[UpToEleven really]] screw history up to get them.

* In ''WesternAnimation/{{Gargoyles}},'' the Phoenix Gate allows the user to travel through time, but every attempt to change things runs into YouAlreadyChangedThePast, resulting in the world as we always knew it and letting us know that ''this'' is why it was always that way. There at one point was a degree of "Enforced Immutability:" When Golaith saves a character who vanished and was thought dead and tries to allow him to return to his old life, increasingly improbable DiabolusExMachina events happen to said character to make his death a certainty. Eventually, Goliath realizes that the universe just won't let him send that character home, and brings that character to the present. And now we know why he disappeared in the first place: he was brought to the present by Goliath!

* In ''Franchise/Pokémon'' this is generally how Time Travel works whenever seen, best illustrated in ''VideoGame/PokémonLegends:Arceus'' with how [[spoiler: due to time traveling because of Arceus the Protagonist sees and is indirectly the cause of Sinnoh (Hisui) being named Sinnoh, the destruction of The Temple of Arceus/Creation of Spear Pillar, and Giratina’s HeelFaceTurn]]

* In ''Franchise/Pokémon'' this is generally how Time Travel works whenever seen, best illustrated in ''VideoGame/PokémonLegends:Arceus'' with how [[spoiler: due to time traveling because of Arceus the Protagonist sees and is indirectly the cause of Sinnoh (Hisui) being named Sinnoh, the destruction of The Temple of Arceus/Creation of Spear Pillar, and Giratina’s Heel-FaceTurn