->''"Somewhere in the multiverse, there is a world I call 'Earth Prime'. Every Earth is a variation of this one, the original--and once I destroy ''it'', all reality will follow."''
-->--'''Owlman''', ''WesternAnimation/JusticeLeagueCrisisOnTwoEarths''

TheMultiverse is a weird thing. Depending on the genre of the work, it can mean a dozen different things. But most sci-fi has a pretty clear definition of what a "Multiverse" is. For every decision someone makes, the universe diverges into several parallel dimensions, one for every possible choice. As such, there are a nearly infinite number of universes where every conceivable version of you (or the lack thereof) exists.

This is a problem for {{Omnicidal Maniac}}s. How can one possibly destroy all of reality if, somewhere, there is ''another'' reality where they fail? The answer is to find Earth Prime: If you find and destroy the ''original'' universe that all others diverged from, you can [[RetGone retroactively destroy all of them]].

Not to be confused with [[DimensionalTraveler dimensional travelers]] who simply call the universe they're from "Earth Prime" to avoid confusion.

Related to ExpendableAlternateUniverse. Compare CosmicKeystone and NoOntologicalInertia. Of course, there are [[TimeyWimeyBall Time Travel Paradoxes]] and {{Logic Bomb}}s abound in this theory, so it definitely requires some WillingSuspensionOfDisbelief. Theoretically, the very act of doing that, would simply create ANOTHER infinite number of possibilities. Therefore, destroying everything ''should'' be impossible.

'''Warning''': May be some spoilers ahead.


[[folder: Anime ]]

* In Anime/YuGiOhArcV it is revealed that [[spoiler: there are alternative dimensions in the Yu-Gi-Oh! franchise; also, the Arc-V worlds called Standard, Fusion, Synchro and Xyz dimensions were once a single world - Original dimension - which split into these 4 ramifications but disappeared in the process.]]
* ''Anime/ReCreators'': According to Meteora, the real world gives birth to the worlds of fiction. If it were destroyed, all worlds connected to it will be destroyed as well.


[[folder: Comic Books ]]

* As of ''ComicBook/FiftyTwo'', the Creator/DCComics multiverse hinges on "New Earth" - not just a specific universe, but a specific planet in that universe. This becomes a plot point shortly afterwards in the ''ComicBook/SinestroCorpsWar'', where Sinestro wants to conquer Earth for this very reason.
** Interestingly, DC's comic multiverse has generally not run on the constant temporal divergence model; ''Comicbook/CrisisOnInfiniteEarths'' established that the universes of the pre-Crisis multiverse diverged at the Big Bang, making ''that'' the point to attack, while ''52'' established that the new multiverse began as 52 identical Earths that got cosmologically edited.
** Note that "Earth Prime" refers to another universe altogether that's like ours, where superheroes don't exist outside of comics. In some stories, it ''is'' "our" Earth for all intents and purposes. And it '''was''' actually destroyed in ''ComicBook/CrisisOnInfiniteEarths''. It came back as Earth-33 of the DC multiverse in ''Comicbook/TheMultiversity''.
---> '''[[WebVideo/AtopTheFourthWall Linkara]]:''' Yeah, that wave of antimatter that completely annihilated the universe was a bitch to clean up the next day, let me tell you!
** In ''Multiversity''[=/=]''Comicbook/TheNew52'' continuity the main Earth is sometimes called Prime Earth (as well as New Earth and Earth-0), Earth-Prime having been renamed as above. It's described in ''The Multiversity Guidebook'' as "the foundation stone of the multiversal structure".
* In the ''ComicBook/AllNewAllDifferentMarvel'' era, Earth-616 was reclassified as Prime Earth, due to it being the first Earth recreated by [[spoiler:the Beyonder-powered Reed Richards]]. This still doesn't give it any more cosmic significance though, it only means this is where the world displaced characters are most likely to end up (some people even kept referring to it by its old number).
** Not that the Marvel Universe was averse to the theory before that era either. The real world (our world) in that case would be Earth-1218, the problem is it's unreachable from the rest of the multiverse so nobody can tell what happened if it got destroyed. (An editor did claim it was destroyed in an [[Comicbook/SecretWars2015 Incursion]] and subsequently recreated, but how could that be tested?) To date when anybody claimed to find Earth-1218 in any Marvel media it ''always'' turned out to be just a CloseEnoughTimeline.
** However, according to the Maker (Reed Richards) in [[ComicBook/TheUltimates2015 The Ultimates 2]], 616 is unique because it is the "hub" the rest of the Multiverse revolves around. As a result the laws of reality are more flexible: science and magic are interchangeable, and higher levels of existence can be accessed more easily.
* The ''[[ComicBook/SonicTheHedgehog Sonic]]'' comic book has Mobius Prime, which all other parallel worlds (called Zones) are based off. Interestingly, despite the franchise starting with video games, Mobius Prime is the comic's Zone and not the one of the games. It's unknown how far this has stuck after the ContinuityReboot.


[[folder: Fan Fic ]]

* The ''Fanfic/PonyPOVSeries'' chapter "Applejack's Dream" establishes the existence of a "Heart World" from which the Pony POV Series world and all other AlternateTimelines diverged from and which anyone still connected to is affected by, implied to be the main series timeline. However, in an interesting twist, it is possible for a world to "break off" and continue on its own without any connection to the Heart World. The plot of that chapter involved preparing for the possibility that would happen so as to [[spoiler:prevent Applejack from going insane and turning into Nightmare Mirror in the event that it did.]] [[spoiler:This later bites Nightmare Eclipse in the flank when her plan has basically made her the Heart World Nightmare Eclipse, and tied all her other selves to her -- in other words, defeating her defeats ''all'' versions of her.]]


[[folder: Literature ]]

* Present in ''Literature/TheHitchhikersGuideToTheGalaxy1''. Vogon Jeltz, tasked with demolishing the Earth, is deemed unsuccessful by his superiors because he only demolished ''one'' Earth, whereas in fact there are millions of others still existing in alternate universes. At the end of ''Literature/MostlyHarmless'', [[spoiler: he finally succeeds in eliminating every single one.]]
* In Creator/GuyGavrielKay's ''Literature/TheFionavarTapestry'', Fionavar is a fantasy version of this; one world that all other ones spring from and depend on.
* In ''Literature/TheChroniclesOfAmber'', this is what makes Amber so special - it's the primal reality which defines the cosmos.
* Creator/WilliamShatner's ''Quest for Tomorrow'' series introduces this concept in the last novel prior to the reboot. In fact, the main characters' goal ''is'' to reboot their reality by altering the result of a coin flip in the prime reality. Unfortunately, Shatner abandons the series two books after the reboot.
* Creator/{{Stephen King}}'s ''Literature/{{Dark Tower}}'' books establish there are two - one where most of the action takes place, in which the Tower manifests as an actual tower; and the other, Keystone Earth, is explicitly our world, in which Stephen King is writing the adventures of the characters in the other universe. Should the Tower in either of these worlds be destroyed, all reality will topple.


[[folder: Live Action TV ]]

* After Season 2 of ''Series/TheFlash2014'' establishes the existence of TheMultiverse, the season finale has [[BigBad Zoom]] confirm that Earth-1 (the main setting of the Series/{{Arrowverse}}) is the center of it all, being the doorway to all the other Earths.


[[folder: Tabletop Games ]]

* In ''TabletopGame/MagicTheGathering'', the plane Dominaria is the Nexus of the Multiverse, situated at the center of the Multiverse. Events on Dominaria reverberate throughout the Multiverse; most notably during the Time Spiral arc where its imminent destruction would have destroyed the rest of the Multiverse with it, and even fixing it turned ''all'' [[DimensionalTraveller planeswalkers]] from PhysicalGods into merely gifted mages. Unusually for this trope, it's not Earth at all, but was a StandardFantasySetting until the plot turned it [[AfterTheEnd post apocalyptic]]. Nor was it always the Nexus; there are planes, such as Equilor, which are older than Dominaria.


[[folder: Western Animation ]]

* In the movie ''WesternAnimation/TurtlesForever'', when the Utrom Shredder realizes that there are literally hundreds of Franchise/TeenageMutantNinjaTurtles across the multiverse, he decides to destroy them all by defeating the versions from Turtle Prime; that is, those from [[ComicBook/TeenageMutantNinjaTurtlesMirage the first issue of the original Mirage comic]]. This was used again in the ''WesternAnimation/TeenageMutantNinjaTurtles2012'' episode "Trans-Dimensional Turtles" with [[spoiler: the 87 Krang's plan to destroy reality to get rid of the Turtles.]]
* ''WesternAnimation/JusticeLeagueCrisisOnTwoEarths'' has [[StrawNihilist Owlman]], who wants to [[EarthShatteringKaboom use]] [[SwordOfDamocles the QED]] on Earth Prime, thus wiping out all life. His main goal is to make the only choice that matters (in his own twisted mind), as there won't be an alternate version of him making the opposite choice (his problem with the multiverse). [[spoiler:When Batman foils his plan by sending him and the bomb to another reality, where Earth is a frozen wasteland, he intentionally gives Owlman a chance to stop the countdown. Realizing that, no matter what he does, another Owlman will do something else, he lets himself die.]]