History Main / GrandfatherParadox

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. [[LogicBomb Are you confused yet?]]

* Happens literally in René Barjavel's novel ''Le Voyageur imprudent'' (translated as ''Future Times Three'') written in 1943 (hence the first novel to enunciate the grandfather paradox) where the time-traveler (Pierre Saint-Menoux) tries to assassinate Napoleon Bonaparte before his rise to power: [[spoiler:at the last moment, a soldier jumps to take the bullet and save Bonaparte. This soldier is of course the time-traveler ancestor. The time-traveler is then wiped out from existence]]. There is even an appendix explaining the paradox at length [[spoiler: (including the fact that, for the time-traveller, there is no real ending - he is constantly oscillating between existing and non-existing. The ending of the novel however makes it clear he does not exist any more - his fiancée is celibate, and the man he helped build the time machine in the first place is fruitlessly trying to make it work)]]

* In ''VideoGame/TheForgottenCity'', you are summoned into ancient Roman times by a man, who asks you to prevent the Golden Rule from being broken in the neat future. He points out if you do successfully prevent the Golden Rule from being broken, he won't have a reason to perform the ritual to summon you to his time, creating a paradox and returning you to present time. If you kill him right then and there, he'll be unable to perform the ritual, returning you to back to your time (but with the worst ending). [[spoiler: Two other endings still require his death, and one ending has you abolish the Golden Rule, so he doesn't have to summon you to prevent a rule that doesn't exist from being broken.]]

'''Twilight:''' Suppose you travelled back in time to a point before you, and your parents, were born, and you killed your maternal grandmother...\\
'''Rarity:''' Why would I ever want to do that? My grandmother is a delightful lady. Even if she does insist on wearing those dreadful frocks with such old fashioned sleeves.\\
'''Twilight:''' But hypothetically -- suppose you did -- by accident --\\
'''Rarity:''' I would have trouble -- she's a tough old mare.\\
'''Twilight:''' Yes, but, ''theoretically'' you could do it -- when she was young. But then she would never give birth to your mother, so you would never be born -- so you could never go back in time to kill her -- it's a paradox -- see!

* ''Series/{{Outlander}}'': Claire, who has time traveled from the 20th century to the 18th century, has to stop Jamie from killing her future husband Frank's ancestor Black Jack Randall for at least a year, to give him time to father a child with Mary Hawkins. Jamie holds off so that Claire, [[spoiler: who is pregnant]], will have someone to go back to if she chooses to go back to the future. [[spoiler: Then it turns out that Black Jack isn't Frank's direct ancestor, rather, it's his brother Alex. However Black Jack married Mary Hawkins after Alex died to GiveTheBabyAFather.]]

* ''Series/{{Outlander}}'': Claire, who has time traveled from the 20th century to the 18th century, has to stop Jamie from killing her future husband Frank's ancestor Black Jack Randall for at least a year, to give him time to father a child with Mary Hawkins. Jamie holds off so that Claire, [[spoiler: who is pregnant]], will have someone to go back t if she chooses to go back to the future. [[spoiler: Then it turns out that Black Jack isn't Frank's direct ancestor, rather, it's his brother Alex. However Black Jack married Mary Hawkins after Alex died to GiveTheBabyAFather.]]

-->'''GIR:''' Wait, if you destroyed Dib in the past, then he won't ever be your enemy, ''(short circuits)'' then you won't have to send a robot back to destroy him...and then he ''WILL'' be your enemy, so you ''WILL'' have to send a robot back--''([[YourHeadAsplode head explodes]])''

* In ''WesternAnimation/ThePenguinsOfMadagascar'' "It's About Time", Kowalski invents a time machine called the Chronotron. However, a Kowalski from the near-future appears before Private and tells him the Chronotron will cause TheEndOfTheWorldAsWeKnowIt, and as NeverTheSelvesShallMeet is in effect, he needs Private to stop his past self and destroy the machine. ''However'', another Kowalski appears before Skipper and tells him that the Chronotron must remain because it's key to the universe's survival (because without it he can't go back in time) and needs his help to keep it safe. As it turns out, present Kowalski seeing his two future selves is what causes the RealityBreakingParadox, which results in rampant LampshadeHanging of the StableTimeLoop in effect. [[spoiler:Ultimately, Rico solves the problem by throwing the Chronotron into the time-space continuum rift after the other two Kowalskis have used it to destroy the former and shut the latter. Kowalski-B thus becomes the Kowalski they know.]]

-->'''Kowalski:'' I never should have created this Chronotron. I had no idea. But Private! He understands! I'll go back in time and talk to Private! He'll stop me before any of this happens!\\

** [[Recap/DoctorWhoS29E13LastOfTheTimeLords "Last of the Time Lords"]]: The Master constructs a Paradox Machine specifically to evade the consequences of this paradox, [[spoiler:as his army of homicidal laser balls happen to be the descendants of humans, from the end of the universe.]]

** [[spoiler: Since it was with Ashi's powers that they returned to the past, if she was never born then how did Jack get back to kill Aku in the first place?]]

* ''Series/LegendsOfTomorrow'': While the series lets people change history [[TimeyWimeyBall in all sorts of wonky ways]], the forces of the universe won't allow Constantine to deliberately [[RetGone prevent his own existence]] by giving his father a "back alley vasectomy". Every time he tries, he stops existing for a few seconds and immediately falls flat on his ass when he reappears.

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

** In ''Discworld/{{Eric}}'', the wizard Rincewind is time-traveling and says that since he's gone back to the beginning of time due to someone using him as a genie wishing to live forever (i.e. beginning to end of time), and he says that he would have to wait around for a while until he could kill his grandfather which is "the only aspect of time travel that really appealed to him".
** Averted in ''Discworld/NightWatch'', where Vimes' mentor is murdered while he's in the past; [[YouWillBeBeethoven he ends up taking over his identity,]] [[StableTimeLoop teaching his younger self everything that his mentor taught him.]]
** Also a DiscussedTrope in ''Discworld/TheLastContinent'' when Ponder Stibbons tries to explain the idea to Archchancellor Ridcully, but runs up against the latter's LiteralMinded {{Metaphorgotten}} tendencies. "Why would I want to kill my grandfather? I rather liked the old boy."

* ''Fanfic/MyFamilyAndOtherEquestrians'': Blade Star has been sent back in time to near the events of the season 2 finale of ''WesternAnimation/MyLittlePonyFriendshipIsMagic'', thanks to a [[Series/DoctorWho Weeping Angel]]. How does he decide to get back? By causing a Grandfather Paradox. If he were to do something at that moment in the past, it would have a ripple effect on his own future, causing everything to change since Blade Star's arrival in Equestria. This would mean that the timeline in which Apple Bloom and Blade Star went to Time Turner's shop and encountered the Weeping Angel would not happen, or at least, happen differently. He would change the past, but therefore have never existed to come back and change the past in the first place. He then concludes that the Weeping Angel itself would become a paradox, as it fed off of something that had no time energy because it didn't exist. In LaymansTerms, he would potentially be brought back to his point of origin, and the angel would be caught in the paradox.\\\
Blade Star then decides to confront Queen Chrysalis and expose her to the ponies earlier than in canon, severely injuring her in the process. The paradox this causes is so huge that Discord has to come in and fix the mess, stating that this was simply way too much chaos for one being, [[EvenEvilHasStandards even by his standards]].

* ''WesternAnimation/{{Sixteen}}'': Jude Lazowski misinterprets this in "Bicker Me Not," where after Jonesy accidentally breaks up George and Gracie Bickerson (an elderly couple that's been married for fifty years), Jude reveals that his own grandparents got married fifty years previously (he never clarifies if they were his mom's parents or his dad's parents). However, Jude never met them, "on account of the fact that they were political rebels who went into hiding" before he was born--after the rest of the gang points out that (assuming Jude's grandparents are still alive) they're probably around the same age as the Bickersons, Jude begins to think that George and Gracie are actually his grandparents. This is what leads to Jude misinterpreting the titular paradox: if George and Gracie break up (in the current timeline) and don't get back together, [[CessationOfExistence he'll eventually cease to exist]].

* While ''Series/LegendsOfTomorrow'' lets people change history [[TimeyWimeyBall in all sorts of wonky ways]], the forces of the universe won't allow Constantine to deliberately [[RetGone prevent his own existence]] by giving his father a "back alley vasectomy". Every time he tries, he spontaneously teleports a few feet away, flat on his ass. Rather than a Grandfather Paradox, though, this is referred to as:
-->"Ball Kick Paradox. You can't kick your own dad in the junk, because you'd erase yourself from the timeline, and there'd be no one to kick your dad in the junk."
** It is specifically stated that if you remained in the Time Stream, you would be immune to the results of a paradox. In the last episode of season 4, Zari intends to do this since she just started a relationship with Nate, but needed to have her brother, the original intendent, receive the Wind Totem. She leaves the Waverider to revive Nate. Because of this, when Nate hugs her, her brother replaces her mid-hug, and no one present sees anything odd or different.

* Happens literally in René Barjavel novel ''Le Voyageur imprudent'' (''The imprudent Traveller'') written in 1943 (hence the first novel to enunciate the grandfather paradox) where the time-traveler (Pierre Saint-Menoux) tries to assassinate Napoleon Bonaparte before his rise to power: [[spoiler:at the last moment, a soldier jumps to take the bullet and save Bonaparte. This soldier is of course the time-traveler ancestor. The time-traveler is then wiped out from existence]]. There is even an appendix explaining the paradox at length [[spoiler: (including the fact that, for the time-traveller, there is no real ending - he is constantly oscillating between existing and non-existing. The ending of the novel however makes it clear he does not exist any more - his fiancée is celibate, and the man he helped build the time machine in the first place is fruitlessly trying to make it work)]]