History Main / GrandfatherParadox

* In the final episode of ''WesternAnimation/SamuraiJack'', Jack finally manages to travel back to his own time and kill Aku. Unfortunately, [[spoiler:since his love interest, Ashi, was Aku's daughter, she ends up ceasing to exist. Cruelly, [[DelayedRippleEffect she seems perfectly fine until their wedding day]], when she suddenly collapses, realizes Aku would have never fathered her, then vanishes in Jack's arms.]]

* Invoked in ''VideoGame/BioShockInfinite'' [[spoiler:ending: Elizabeth travels back in time and kills Booker, her own father, before her conception in every possible timeline, thus forcing the universe to block off all branching timelines where Booker becomes Comstock, kidnaps Booker-from-another-universe's daughter Anna, who grows up to become Elizabeth and develops reality-warping and time-traveling powers as a result of her dimension shift. That way, the only timelines that are left are the ones where Anna/Elizabeth grows up peacefully with a never-baptized Booker]].

* The Creator/CharlesStross novella ''Literature/{{Palimpsest}}'' has a twist: killing your own grandfather is the initiation rite for the TimePolice. The graduation ceremony is stepping back in time a few minutes and killing ''yourself''.

* The Creator/CharlesStross novella ''Palimpsest'' has a twist: killing your own grandfather is the initiation rite for the TimePolice. The graduation ceremony is stepping back in time a few minutes and killing ''yourself''.

* Creator/GregoryBenford'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.

* A different take, not involving relatives, is in ''A Dry, Quiet War'' by Tony Daniel. The protagonist returns to his home planet after fighting a war twelve billion years in the future at the end of time, apparently to hold back the spread of entropy so the universe has a chance to exist in the first place. He has a run-in with several deserters from that war who are terrorizing the place. If he does anything to harm them however, it changes the future and everything he's fought for has been for nothing.

* Discussed in Creator/OctaviaButler's novel ''Kindred'' when Dana finds herself pulled back in time to [[UsefulNotes/AntebellumAmerica the antebellum South]] whenever her ancestor Rufus is in mortal danger. As he comes to treat her more and more like one of the plantation slaves, only the threat of a paradox keeps her protecting his life. [[spoiler:Once Rufus has a child, that protection expires.]]
* Happens quite often in Stephen Baxter's Xeelee Sequence books, where entire wars are fought atemporally, causing battles to happen multiple times in different timelines with different outcomes, and where going back in time to give your own side intelligence about your enemy's future actions is a common tactic. Defied in one instance where a character receives information from a timeline that should no longer exist, but the information still remains. The explanation given was that time is flexible, and just because the one particular event that led to him getting that information now had never happened, in some other timeline he had gotten it a different way, and so he ended up still having it.

* A DiscussedTrope in ''A Quantum Murder'' by Creator/PeterFHamilton. The conclusion is you can due to the existence of [[TheMultiverse parallel realities]]. In short, you're conceived in one universe, then go back in time and kill your grandfather in another universe.

* A variation in ''Thus We Frustrate Charlemagne'' by Creator/RALafferty. By killing one messenger they can, in theory, open up scientific exchange between Charlemagne's kingdom and the more advanced Muslim Spain, thus ending the Dark Ages centuries earlier. They succeed, but don't realize they did. They attempt something similar and end up sending civilization back to the Stone Age.
* The Creator/RALafferty example is mentioned in ''The Last Day of Creation'' by Wolfgang Jeschke. The US government has invented time travel and wants to use it to solve the oil crisis. It's pointed out that if this works, no-one will remember it and it will look like the government is spending vast amounts of money for nothing, potentially shutting down the project. There's also the threat of starting a [[TerminatorTwosome temporal arms race]] which is exactly what does happen; eventually a DividedStatesOfAmerica is created that is too poor to continue the research, stranding the expedition in the past.

* In the [[https://www.tor.com/2011/08/31/wikihistory/ International Association of Time Travelers]] skit, which is mostly dedicated to [[HitlersTimeTravelExemptionAct going back in time and killing Hitler]], this ends up being the fate of [[spoiler:[=AsianAvenger=]]].

* Parodied in ''Series/TheXFiles'' in "Clyde Bruckman's Final Repose": the title character cites this as a reason why he shouldn't help Mulder and Scully catch a serial killer -- because one of the people he might save could be the grandmother of the person who'd invent a time machine that would mean Clyde's father never met his mother and therefore he'd never have been born. As his ability to see the future had made his life a misery, Clyde suddenly realizes that wouldn't be a bad thing after all.

So, then, killing your grandfather causes you to not exist, and since you don't exist, you never killed him. Which means he survives, so you exist, so you do go back to kill him. Which means he doesn't, so you don't; therefore he does, so you do, etc. Are you confused yet?

* The 2002 film version of ''Film/TheTimeMachine2002'' is [[TimeyWimeyBall inconsistent]] in how it deals with this. The first act demonstrates that it is actually impossible to create a paradox; Alexander builds his time machine so he can save his love Emma from dying, but no matter what he does, she always ends up dying in one way or another, because if she didn't, he wouldn't build the machine and save her. However, the third act throws this out the window when [[spoiler:Alexander travels from 802,701 to even further in the future, discovers that the Morlocks have conquered the Earth, and then goes back to 802,701 to destroy them so that they can't.]] By the first act's logic, it should be impossible for him to do this, since he's erasing the reason for his own actions, but it works perfectly anyway.

[[folder:Podcasts]]
* ''Podcast/Case63'': Dr Knight is a psychiatrist working with Peter, a patient who claims to be a time traveler from 40 years in the future. She doesn't believe him, thinking he's instead lying or delusional. In their very first session together, Dr Knight suggests that, if true, Peter's story could be verified by doing a DNA match with his currently-living mother. She expects his story to be {{conveniently unverifiable|CoverStory}}, assumes Peter will say no, they can't intervene in his parents' lives because that could stop them getting together, creating a Grandfather Paradox. But to Dr Knight's surprise, it's a SubvertedTrope--Peter ''encourages'' her to go talk to his parents, explaining that their origin story as a couple is actually a StableTimeLoop that hinges on Dr Knight's interference. This could also be considered an InvertedTrope, as time travel doesn't ''threaten'' Peter's existence, it ''causes'' it.
-->'''Dr Knight:''' But if I contacted your parents, that would alter the future in some way, right?\\
'''Peter:''' True.\\
'''Dr Knight:''' They wouldn't get to know each other and you wouldn't be born, we wouldn't be--\\
'''Peter:''' --we wouldn't be having this conversation.\\
'''Dr Knight:''' Correct.\\
'''Peter:''' In four weeks--not sure of the exact date--but precisely because of the fact that you ''will'' believe me, you will contact my parents. And this story of an American psychiatrist who called my parents talking about their time-traveling son who hasn't been born will seem so funny that my dad will go ''looking'' for my mom. They'll go out for some beers and they'll start to date. They'll become boyfriend and girlfriend, and I'll be born. All thanks to you, Doctor. I'll grow up listening to this story--the story of the American psychiatrist who brought my parents together.
[[/folder]]

--> '''Clover:''' You know how it’ll go. You don’t wish to invoke the … what is it now? The 'killing your own grand-dam' problem."\\

* ''TabletopGame/GeniusTheTransgression''[='=]s stance on the subject: "And yes, if you kill your own grandmother before your father is born, you will cease to exist. The universe, it turns out, doesn't care that much if your grandmother gets shot in the head and there's no shooter. You still go poof."

* One of the death scenes in ''VideoGame/TimeGal'' has [[PlayerCharacter Reika]] fire her gun into a bunch of cavemen — and promptly dematerialize because she just shot one of her ancestors.

* ''Podcast/Case63'': Dr Knight is a psychiatrist working with Peter, a patient who claims to be a time traveler from 40 years in the future. She doesn't believe him, thinking he's instead lying or delusional. In their very first session together, Dr Knight suggests that, if true, Peter's story could be verified by doing a DNA match with his currently-living mother. She expects his story to be {{conveniently unverifiable|CoverStory}}, assumes Peter will say no, they can't intervene in his parents' lives because that could stop them getting together, creating a Grandfather Paradox. But to Dr Knight's surprise, it's a SubvertedTrope--Peter ''encourages'' her to go talk to his parents, explaining that their origin story as a couple is actually a StableTimeLoop that hinges on Dr Knight's interference.

* Played with in ''Enter Nowhere'', in which a young woman about to rob a convenience store finds herself transported to an isolated cabin where two strangers are similarly stranded, and where a mysterious rifleman is creeping around in the woods. [[spoiler: The rifleman ''is'' her grandfather, who'd died in WWII without ever seeing his baby daughter, and the others are the still-pregnant mother she never knew and the son she won't live to see grow up. Inverted in that the grandfather actually kills ''her'' and causes her son to disappear in the process, leaving it up to her mom-to-be to save her own dad and thus, all four lives. Played straight in that it's implied the three were sent back in time to avert the grandfather's death because the convenience-store clerk has supernatural power and wanted to give them all another chance ... one meaning that, since her Mom survived to stop her from becoming a criminal, the robber wouldn't have confronted the clerk in the first place.]]

-->-- ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' fanfic ''[[http://www.fimfiction.net/story/282998/1/ Temporal Irregu-Rarity]]''

* Within the semi-canon/non-canon of Telltale's ''VideoGame/BackToTheFutureTheGame'', Marty does encounter his paternal grandfather and affects his own existence in time.

* Narrowly averted in ''[[VideoGame/TheLegendOfZeldaOracleGames The Legend of Zelda: Oracle of Ages]]''; Ralph attempts to destroy his own ancestor Queen Ambi (who is possessed by Veran), ''knowing'' that it will remove him from existence and [[HeroicSacrifice willing to take that consequence to protect the people of Labrynna]]. Subverted when [[CurbStompBattle she proves more than capable of defending herself]].

* A non-grandfather version appears in ''Webcomic/{{Oglaf}}''. A sorcerer is promised the StandardHeroReward for going back in time and curing a devastating plague before it starts, but when he returns, [[http://oglaf.com/chronotherapy/ the plague never happened, so the queen never made the promise]] (this strip is worksafe, [[{{NSFW}} the rest of the comic is not]]).

** [[TheArchmage Archmasters]] are explicitly allowed to use time travel to erase their lives from history. It doesn't annihilate them, simply because becoming an archmaster means they're partway through [[AscendToAHigherPlaneOfExistence Ascending to a Higher Plane of Existence]] and aren't bound to the material world, but it does, well, [[RetGone erase their lives from history]].
* {{Lampshaded}} in ''TabletopGame/MagicTheGathering''. In the ''Tarkir'' block, Sarkhan Vol travels back into the past of his own plane and alters the timeline so that the dragons never went extinct. One of many knock-on effects from this is that Sarkhan himself was never born in the new timeline. However, perhaps due to being a Planeswalker, he still exists as a self-described "orphan of time". For all intents and purposes, he simply popped into existence fully-formed when he returned to the present.

* The grandfather paradox is a major plot point in the third season of ''Series/TheUmbrellaAcademy2019''. After arriving back in the future, the Hargreeveses learn that they were never born in this timeline because something killed their mothers, and said ''something'' -- [[spoiler:Vanya empowering Harlan in 1963, and him growing up to psychically kill their moms by accident]] -- was the result of their actions. This causes a reality-breaking paradox known as the ''kugelblitz'', a "reverse black hole" that collapses reality unto itself.

* The Creator/RALafferty example is mentioned in ''The Last Day of Creation'' by Wolfgang Jeschke. The US government has invented time travel and wants to use it to solve the oil crisis. It's pointed out that if this works, no-one will remember it and it will look like the government is spending vast amounts of money for nothing. There's also the threat of starting a [[TerminatorTwosome temporal arms race]] which is exactly what does happen.

* In a variant of this, in the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' fan-comic "Twilight's Erasure", Cozy Glow from an AlternateTimeline erases [[RetGone pregnant Twilight's mother's baby in the past from the existence,]] which also not only makes present Twilight's presence become unnoticed by every pony, but also causes her to lose her talents and cutie mark, and eventually [[FountainOfYouth slowly regresses her.]]

* In a variant of this, in the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' fan-comic "Twilight's Erasure", Cozy Glow from an AlternateTimeline makes [[RetGone pregnant Twilight's mother's baby in the past disappear,]] which also not only makes present Twilight's presence become unnoticed by every pony, but also causes her to lose her talents and cutie mark, and eventually [[FountainOfYouth slowly regresses her.]]

* In a variant of this, in the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' fan-comic "Twilight's Erasure", Cozy Glow from an AlternateTimeline makes pregnant Twilight's mother's baby in the past disappear, which also not only makes present Twilight's presence become unnoticed by every pony, but also causes her to lose her talents and cutie mark, and eventually [[FountainOfYouth slowly regresses her.]]

* In a variant of this, in the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' fan-comic "Twilight's Erasure", Cozy Glow from an AlternateTimeline makes pregnant Twilight's mother's baby in the past disappear, which also not only makes present Twilight's presence become unnoticed by everypony, but also causes her to lose her talents and cutie mark, and eventually [[FountainOfYouth slowly regresses her.]]