Alternate Universe

"John Oliver: You've stated you believe there could be an infinite number of parallel universes. Does that mean there is a universe out there where I am smarter than you? Stephen Hawking: Yes, and also a universe where you are funny."

- Last Week Tonight

A story in which the characters we know are seen in a reality that's somehow different, often disturbingly so. If they can access multiple alternative realities, that's The Multiverse.

Sometimes everyone has an Evil Twin. Other times, everyone has a twin that's just a little different. Allows the goodies to be baddies for an episode, or for half of the cast to be killed—but not really. Sometimes it's just part of Side-Story Bonus Art.

Given a long enough run, any series based on Superhero comic books will run into these.

If the writers want to depict an Alternate Universe, but the show's genre would not usually allow an Alternate Universe per se, the depiction may be accomplished via an extended Dream Sequence.

Not to be confused with Alternate Continuity, Alternate Reality Episode, Alternate Universe Fic or a Constructed World.

May be meta-caused by aforementioned Alternate Continuity; as well as by any of the three varieties of Discontinuity (Canon Discontinuity, Fanon Discontinuity, or Negative Continuity). In-Universe, though, there may be a specific Point of Divergence which caused events to run differently.

Specific variations:
 * Alternate History—Some major event changed, like Germany wins WWII.
 * Another Dimension—Different worlds don't have to resemble each other, Alternate Universe is a subtrope of this.
 * Bizarro Universe—A lot of things in that world are reversed from the usual context, good is evil or vice versa, etc.
 * For Want of a Nail—One small change caused a huge difference between the universes.
 * In Spite of a Nail—Tiny changes have made the world almost the same but the differences are critical (or wildly different, but the cast is still the same and still together.)
 * Mirror Universe—Often a subset of Bizarro Universe, Good and Evil are reversed, but otherwise most of the things are the same.
 * The Multiverse—The people involved have the capacity to cross over to more than one additional universe.
 * Elseworld—Famous character placed into a situation which potentially is wildly different.
 * Wonderful Life—You get to see how the world would have turned out if you were never born.
 * Alternate Tooniverse—An animated counterpart to reality.

Another type of Alternate Universe is that which doesn't take any of the characters, but instead takes concepts, or machines. Such Alternate Universes are uncommon, but exist. Gundam is the perfect example, with no less than seven separate universes, all of them rehashing essentially the same plots and concepts—in particular, the conflict between those living in space and those living on Earth. With giant robots.

Anime & Manga

 * During the Third Impact sequence of Neon Genesis Evangelion, Shinji is shown an alternate universe mirroring a stereotypical love comedy anime (which has since become an official Evangelion Elseworld).
 * Every path in the multi-route TYPE-MOON games is a potential outcome of the main scenario, which makes it rather difficult to establish the rules of the 'verse due to the plot differences in each route; according to Word of God, all of them are canon.
 * In the fourth Suzumiya Haruhi novel, The Disappearance of Haruhi Suzumiya, Kyon suddenly finds himself in a world without supernatural powers, with what SOS members remain leading normal, human lives.
 * It is, however, quite important to the plot that it actually
 * Tengen Toppa Gurren Lagann has one of these in Episode 26 with
 * In a different vein, the new Parallel Works music videos leading up to the movie seem to be using these.
 * The series also has a High School AU manga.
 * One fan also seems to make an excellent example with an AU universe comic about TTGL worthy of the series.
 * With the exception of the second season (a sequel to the first) and the seventh season (a sequel to the sixth), each of the seven seasons of Digimon exists in an alternate universe from the rest. The only constants are the titular Mons and the world from which they come, and even the exact traits of the latter differ from season to season.
 * In the third season, we learn that in their universe, the first two seasons were just a cartoon show, like in the real world. This only occurs in the English dub, though. To be more precise, Digimon Adventure and Digimon Adventure 02 may be cartoon shows in Digimon Tamers, but they do exist in their own reality. This is most clearly evidenced by Ryo Akiyama being a Canon Immigrant from the Digimon Adventure universe. Unfortunately, he is only clearly seen in a series of games that never made it out of Japan.
 * Notably, Ryo only solidly connects the Adventure and Tamers universes. However since recently, Tai, Davis, Takato, Takuya, and Marcus all made a cameo in the third arc of the sixth series, and were described as ''heroes that saved their own worlds", it is confirmed (despite the existence of some continuity errors) that each anime series has it's own continuity.
 * In the Kyoto Animation adaptation of Key's Visual Novel Clannad, Tomoyo's arc, which was never completed properly, was showcased in an AU OVA entitled Another World: Tomoyo Arc, where Tomoya never met Nagisa and Tomoyo is the winning girl.
 * In July 2009, Kyo Ani will be releasing the final DVD of Clannad: After Story that contains an extra OVA episode entitled Another World: Kyou Arc. Kyou finally gets her arc!
 * A major plot twist in Rave Master involved this trope:.
 * As it was written by the same mangaka as Rave Master, Fairy Tail had to have one of these as well, in the form of Edolas. It makes for an interesting plot twist, and despite its relative lack of plot significance, it doesn't feel tacked on at all. Although it does explain a good few things, like Happy and Carla's origin, and why.
 * Steel Ball Run is an Alternate Universe to JoJo's Bizarre Adventure, created in-continuity after
 * The Kirby anime is meant to be an alternate universe from the games, something many fans miss.
 * Tsubasa Chronicles has many different worlds, and the four protagonists actually come from different worlds.
 * The Hetalia Bloodbath 2010 event:  It Makes Sense in Context.
 * And that's not counting the High School AU or the Nyotalia-verse.

Comic Books

 * The DCU has had many different Earths before the Crisis on Infinite Earths, the Reset Button event from the mid to late 80's, and many Elseworld stories, including one where Superman turns out like [[media:1141875127011.jpg|this]].
 * By far the most important AU in the DC Multiverse was Earth-Two, home of the Justice Society of America, who would cross over with the Justice League on Earth-One once a year.
 * After Infinite Crisis, the Multiverse was restored, with 52 separate realities, most of them containing the Elseworld stories. So we got to see Superman fight Communist Superman at last.
 * Marvel has explicitly adopted a Multiverse as part of their canon, with "out of continuity" storylines assumed (or explicitly stated) to have happened on an alternate Earth (or alternate-wherever). The "main continuity" of most Marvel titles is labelled as taking place on "Earth-616".
 * Galactus is the sole known survivor from the previous Big Bang-Big Crunch universe cycle, making him technically a native of an alternate universe.
 * And then there's Age of Apocalypse storyline. Although it was initially an alternate present for Marvel's baseline universe "Earth-616", it became an alternate reality when Jean Grey split it off into a separate universe during the events of X-Men Omega.
 * The comic Exiles explores this idea to its fullest, having the main characters hop between different Marvel AU's and fixing problems.
 * According to Earth X every time you alter history through time travel you create an alternate universe.
 * The Adventures of Luther Arkwright is based on the premise of an infinite multiverse of parallel universes or realities which differ with each other in many things. For example, one of the main places where the action in the comic book takes place is a 20th century world where Great Britain is still ruled by a puritan government and a descendant of Oliver Cromwell. In addition, New York is New Amsterdam and the other great powers are the empires of Russia and Germany.
 * The Star Wars Infinities comics. Yavin goes up in smoke? Vader in white armor? Sweeeet....
 * And
 * Even Archie Comics do this sort of thing, a recent, notable example being the new Life With Archie series. The storyline where Archie marries Betty is treated as a different universe from where Archie marries Veronica. The former also happens to feature a character traveling between universes!
 * Let's not forget how its done in their Sonic the Hedgehog, where universes are known as "Zones". Beginning with the Mirror Universe with Scourge the Hedgehog, and continuing with Blaze the Cat and her "Sol Zone". And did I mention, in one "zone", Sonic is a cop who patrols between zones?
 * Man-Thing's swamp is home to a plot-friendly conflux of universes, including Howard the Duck's home dimension.
 * Zot It is left ambiguous which Earth is the real Earth, but it is hinted that Zot's world is merely our Earth with all the bad parts taken out. It becomes more evident when it is revealed that the year is always 1965.
 * Sinister Dexter introduced an alternate universe, which fans dubbed the Doppelverse, around the time it got serious. The Point of Divergence is that in the Doppelverse, the title characters were killed while still a pair of punk kids, with the result that most of their enemies are still alive and can come back to make trouble.

Fanfiction

 * Axis Powers Hetalia fanfic Gankona, Unnachgiebig, Unit&agrave; is set in an alternate universe where the countries have more power and are able to bend the rules more than in canon. Romano proves this by overseeing a polyamorous marriage between Germany, Italy, and Japan.
 * Due to the reality bending nature of AT-field in Aeon Natum Engel, there was a brief glimpse of Episode 2 of the original Neon Genesis Evangelion, where Unit 01 got his head pierced with blood flying everywhere. The fic itself may or may not get into this after a certain Rocks Fall Everybody Dies ending.
 * Two of these exist in Phoenix's SSBB Case Files, aptly named Alternate Turnabout and Alternate Turnabout 2. The first has Larry Butz working as a defense attorney, with Adrian Andrews at his side, while 2 features Franziska von Karma and assistant Dick Gumshoe working for the Wright and Co. Law Office.
 * This trope is likely to be used by any Intercontinuity Crossover fanfic in which the melded continuities would otherwise contradict one another.
 * With Strings Attached is set on another planet in an alternate universe. Additionally, the four visit three other universes (including one set in a 1950s New York, more or less); the Fans are watching from their universe; the Dalns gods inhabit yet another universe; and Jeft comes from still another.
 * The Son of the Emperor mixes the real world with the world of My Little Pony Friendship Is Magic. This results in an Alternate Universe where the ponies grow to the size of horses and have been used for centuries in warfare, mytical creatures like griffons are commonplace and magic exists.
 * Just One, Big, Happy Kingdom is a Merlin fanfic in which an eighty-year-old Merlin decides to teach his younger self a lesson by putting him in a mirror universe ("Not-Camelot") and put Not-Merlin in the normal Camelot. It's one of those mirror everybody-is-his-opposite universes.
 * NIGHTWALKER: STRANGE PATHS is a Nightwalker fic which basically has Riho as a 300 or so year old vampire and Shido who starts out as a human detective.
 * The Pony POV Series has such a thing. It's explained that all the worlds diverged from the Heart World (implied to be the actual shows' timeline) and are effected by changes there, but can break off and continue on their own in the event the change in the Heart World is so great said universe can no longer harbor the connection. The ones the series itself focuses on are it's main timeline and the Discorded Timeline, a Villain World ruled by Discord, but we also see a lot of alternate timelines which Princess Luna refers to as "possibilities and impossibilities". Applejack gets to see quite a few of them on two seperate occasions, the one that means the most to her being the Orangejack universe, where she never left Manehatten. There's also a universe were Rainbow Dash turned into Nightmare Manacle, another where Pinkie Pie turned into Nightmare Granfalloon, and another were the mane cast are the Mighty Morphing Power Ponies fighting a Goldar version of Gilda. Oh and
 * Streets of Rage Saga, a 10-story saga based on the Streets of Rage game series (both the canon trilogy and several fan-made games and remakes based on said trilogy), takes place in a setting based on but highly different from the canon. Just a few brief examples, with the canon information in parentheses: Axel lost his father in a fire that was set by the man who would later become The Dragon for the first story's Big Bad (in canon, no mention is made of Axel's family members); Blaze comes from a Doomed Hometown that was razed by The Syndicate (in canon, the only back-story on her is that she was a rookie cop who quit alongside Axel and Adam because of the force's corruption); and Mr. X is a U.S. senator with the full name of George Xetheus (in canon, his real name wasn't divulged and his role as a Corrupt Corporate Executive was only hinted at in canon and expounded on in Bombergames' remake).
 * This trope runs rampant in the Undertale fandom, to the point where the most common Fandom Specific Plots are "lets do an Alternate Universe Fic where the characters are some High Concept" and "let's do a crossover between AUs".
 * This is often common in Real Person Fic, where various of celebrities from one line of fame are placed in different line.
 * For example, Astral Journey: It's Complicated has Brandy Norwood, Mariah Carey, Celine Dion, Melanie Chisholm, Emma Bunton and Geri Halliwell as football (soccer) players.

Film

 * The One is a cross between this and Conservation of Ninjitsu. The villain is traveling around to the various universes killing all the alternate versions of himself so he'll have all the power that would otherwise be spread out between them. Since the hero is one of the alternates, he winds up with bigger and bigger slices of the power pie as well, making for a battle royale when it's down to just the two of them.
 * Super Mario Bros. The Movie posits a "sub-dimension" created through the impact of the meteorite into earth that caused the extinction of the dinosaurs. The dinosaurs continued to evolve in this sub-dimension in the city of "Dinohattan", a city mirroring New York city.

Literature
"Ridcully: You'd think I'd think of me, wouldn't you? What a bastard!"
 * The Wonderful Wizard of Oz was loosely translated into Russian. The translator modified the story as he as saw fit. When the story became popular, he wrote a series of books based on his translation of the first Oz book. Those books went in a different direction than the Oz books written by Baum, effectively making an alternate Oz universe.
 * While The Wicked Years may technically follow some of the events in the Oz books and movies, the vast difference between it and the Oz canon makes them another alternate universe.
 * Anti-Ice by Stephen Baxter, in which the discovery of an Applied Phlebotinum with properties similar to anti-matter dramatically accelerates the Industrial Age. The book begins with the Crimean War ending with the destruction of Sevastopol by a single anti-ice shell, and includes a Jules Verne-like trip to the Moon.
 * In Teresa Edgerton's Celydonn trilogy, the Inner Celydonn plays this role to Celydonn proper, so that, for example, the version of Tir Gwyngelli known in traveller's tales really exists as the home of The Fair Folk.
 * Robert A. Heinlein's The Number of the Beast and The Cat Who Walked Through Walls are based on this, exploring various fictional universes created not only by Heinlein but also others, especially Oz.
 * Created by Hex the magic AI as an emergency dumping-ground for a thaumic overload, an orange-sized spherical universe is kept on Rincewind's desk at Discworld's Unseen University. Most of the UU faculty think this narrativium-deprived alternate reality is a silly waste of time; even so, the Archchancellor occasionally (meaning, whenever a new Science of Discworld book is published) tasks his wizards to offset interlopers' tampering with the pocket universe's history. Silly or not, it is University property.
 * Alternate Universe theory crops up elsewhere in Discworld, too, such as in Lords and Ladies, where Ridcully, upon being told that there's a universe somewhere where he married his childhood sweetheart, gets annoyed that he wasn't invited to the wedding:


 * In Dragonlance, Raistlin succeeds in becoming a god and killing every other god as well as all life in Krynn. Then Caramon time travels back to prevent him from succeeding.
 * The Alternate Universe part comes from the suggestion that there are universes where Caramon didn't succeed.
 * The Myriad Universes Star Trek novella collections have the "for want of a nail" version of this trope. The Mirror Universe short story collections, on the other hand, are very different to the main universe.
 * The Man in the High Castle by Philip K. Dick contains an alternate 1960s California controlled by the Japanese after a defeat of the allies during WWII. There is mention of another alternate reality, apparently revealed to an author who writes a book about such an alternate in which the US does not lose WWII. This is slowly revealed not to be "our" alternate, but one dreamed up by the writer, and of no special significance. The book was written using the I-Ching as a guide to the character's actions.
 * In The Edge, the Weird is a mirror universe to our world, mirrored so that Florida is in the west and California in the east. None of the characters are duplicated, though.
 * Robert J. Sawyer's trilogy, "Hominids", "Humans", "Hybrids", is all about an alternate universe where Neanderthals didn't go extinct, but homo sapiens did.
 * Michael Kurland has a few examples involving world-hopping, including The Unicorn Girl and The Whenabouts Of Burr.

Live Action TV

 * Dark Shadows may well have brought this trope to television for the first time.
 * Andromeda did several episodes exploring Alternate Universes in various ways: as a Near-Death Experience, and as a result of one character's ability to view potential futures. The most noteworthy was "The Unconquerable Man", which was an entire Clip Show playing out events from the show's history with a different lead character.
 * Birthdayverse in Angel
 * Illyria mentions being able to live seven different lives at once in different universes back in her days, including a universe made entirely of shrimp. She tired of that one quickly.
 * The Wishverse in Buffy the Vampire Slayer (and the asylum-universe of "Normal Again")
 * These eventually became a running gag on the show, with Anya often mentioning universes she could potentially send people to: the universe of infinite Wednesdays, the universe without shrimp, the universe of nothing but shrimp...
 * At, first, "Superstar" appears to take place in an alternate reality where Jonathan is the eponymous Marty Stu, but it later turns out that he cast a spell that altered reality itself!
 * There's also the universe as it was Before Dawn and Post-Dawn.
 * Charmed employs a literal Mirror Universe, which could be accessed through a mirror.
 * A mirror universe in Red Dwarf uses the same joke.
 * "Ace" Rimmer (what a guy!) on Red Dwarf came from an Alternate Universe, and travelled between dimensions. The Red Dwarf crew themselves had previously travelled into an Alternate Universe in the episode "Parallel Universe". Some episodes have featured similar alternate versions of characters and events, but were a result of time travel rather than passing into another Universe (notably "Timeslides" and "Inquisitor").
 * The books delve into this too. While multiple universes are established in Better Than Life, they really come into play in Last Human and Backwards. Last Human occurs when the crew return from Backwards Earth to the wrong universe and try to track down Lister's other self. In Backwards, Ace Rimmer is given a backstory behind Project: Wildfire and turns up to save the crew. Bonus points for the fact that both books, having each been written by Grant and Naylor separately, take place in alternate universes to each other.
 * Lois and Clark had an Alternate Universe in which Lois was lost in a jungle and Clark had not made himself into Superman.
 * This does allow the protagonists to discredit the Big Bad, who tries to expose Superman's secret identity. It's kinda hard to argue that Clark Kent is Superman, when both of them are standing right there.
 * Nate experienced an Alternate Universe during a Near-Death Experience in an episode of Six Feet Under.
 * The series Sliders used this as its central premise.
 * "Mirror, Mirror" in Star Trek: The Original Series—the Mirror Universe was used often in Star Trek: Deep Space Nine.
 * And the mirror universe provided the means for arguably the best episode of Enterprise. Hooray for mirror Hoshi!!
 * Star Trek: Voyager didn't make use of the Mirror Universe, but in "Living Witness", a historian hundreds of years in Voyager's future has created a "historically accurate" holo-program depicting the crew as murderous thugs who started a war on his planet. It's up to the Emergency Medical Hologram (the only surviving witness) to put things right... which isn't easy, as he's being portrayed as a Mad Doctor. Star Trek: The Next Generation also didn't have the mirror universe, although it did have alternate universe stories (as the term "mirror universe" in Star Trek refers specifically to that featured in The Original Series and Deep Space Nine).
 * The Mirror Universe was touched upon in the Next Generation Expanded Universe novel Dark Mirror.
 * "Parallels" in Star Trek: The Next Generation -- "I do remember. I just remember it differently."
 * Xena: Warrior Princess, Hercules: The Legendary Journeys use a mostly standard Mirror Universe: Good characters become Evil, shaven characters become bearded etc. But regular Iolaus is a good, shaven, competent warrior and regular Joxer is good, shaven and incompetent; in the Mirror-verse, they are both good and shaven, but Iolaus is incompetent and Joxer is competent.
 * There are some weird rules for the two universes. If a person (or a god) dies in one universe, he also dies in the other. Unless they happen to be not in their universe at the moment. This happened to who was trapped in an "in-between" world when . Also happened to, as his double  was killed while in this "in-between" world.
 * Smallville had an interesting subversion: Clark wakes up in a mental asylum; apparently, he started having delusions of superdom in high school, and his "saving" of Lex in the first episode actually cost Lex his legs. Oh, and Chloe is a freaking nutcase. Of course, it was all a delusion caused by an escaped Phantom that attacked him in his barn and invaded his mind. John Jones (the Martian Manhunter) helped him escape by entering the illusion (as another inmate), and capturing the creature in a Kryptonian crystal.
 * Season 10 had an Alternate Universe as a major plot line, Clark discovers a kryptonian artifact called a "mirror box" and when activated it takes him to world where the Kents never adopted him, instead he was raised by Lionel and goes by the name "Clark Luthor". Clark Luthor himself is brought to Clark Kent's world and causes no end of trouble before the original Clark manages to switch them back. Then it turns out the alternate Lionel managed to come through to the main world with Clark, taking the place of the original Lionel (who was dead) with a story that he'd faked his death. Then Clark Luthor uses his mirror box to come back and send our Clark to his world, where he helps the alternate Jonathan reconnect with Martha, and convinces Clark Luthor to try and use his powers for good, rather than live in Lionel's shadow.
 * In Seinfeld episode #137 "The Bizarro Jerry", Elaine is in a similar social circle where the Kramer equivalent is neat, George's is responsible, etc.
 * In NCIS, a generally reality based show, features a series of clips from Alternate Universe based on a series of What-If moments. What if Kate hadn't died?  What if Gibbs also hadn't killed Pedro Hernandez?   What if Shannon and Kelly hadn't died? (Warning: major Tear Jerker behind those spoilers.
 * Stargate SG-1 has had many different alternate universes. Oftentimes, the "alternate" Sam Carter is not in the military and is engaged/married to the "alternate" Jack O'Neill. Alternately Daniel Jackson was never part of the Stargate Program. More often or not, when this is used, Earth is under imminent Goa'uld attack.
 * Atlantis also does this, though the details vary, and the universes aren't usually quite the Crapsack World versions that SG-1 is fond of.
 * In the one in the episode McKay and Mrs. Miller, Rodney is a really nice guy with lots of friends and Sheppard is a member of Mensa, greatly annoying everyone with his egoism. In our universe, Rodney is the egoist one, Sheppard is a nice guy who took a Mensa test but turned down the offer to join.
 * And another is shown in the penultimate episode Vegas. There, Sheppard is a homicide detective with massive gambling debts. He couldn't be included in the team because the stunt he pulled off in Afghanistan got him dishonorably discharged instead of getting Reassigned to Antarctica in time for the pilot. Rodney is more likeable (though one scene suggests that he's simply better at keeping a lid on his ego) and the Wraith already made an attempt at culling Earth just to be repelled by the control chair in Area 51. Oh, and Todd got so delirious from starvation he's speaking in rhymes.
 * The Rodney from Vegas also mentioned that he once traveled to yet another universe and met an alternate Sheppard who was similar to the main Sheppard.
 * VR.5's Missing Episode, "Parallel Lives" had Duncan wake up one morning to find himself in a universe where Sydney, rather than her sister, had died in a car crash years earlier (of course, it eventually turned out that neither sister had actually died; both the car crash and the parallel universe were complex VR hoaxes. The episode was intended to test the viability of replacing the central character for the second season, a possibility which became moot when the series was not renewed).
 * A slightly different take on this was done in "Author Author" in Star Trek: Voyager, in which the Doctor created a holodeck program peopled by altered versions of the Voyager crew.
 * Doctor Who:
 * "Inferno" an alternate totalitarian Britain (branching off with the 'defence of the republic act, 1943'), which is in a still greater rush to get free power from tapping the magma of the Earth. It is destroyed, with the Doctor able to just avert the similar events happening a few hours later in his 'home' alternate. Not bad at all.
 * "Rise of the Cybermen"/"Age of Steel" has the TARDIS fall through a crack in time and land in a universe where the Cybermen were being created on Earth. Mickey explicitly references how common the trope is in comics. This universe crossed over again in "Army of Ghosts"/"Doomsday" and its effects continued to be felt in Torchwood's "Cyberwoman" episode. And in the finale of Series 4 of Doctor Who.
 * In "Turn Left", Donna Noble has an entire alternate universe built around her, where she never met the Doctor, and he consequently dies after the events of "The Runaway Bride." Suffice it to say, It Got Worse. Much, much worse. In fact, the universe without the Doctor is pretty much a terrible place to be.
 * Sci-fi series Lexx made this its staple. The first season of the show involved the characters jumping through an inter-universe rift twice, and in the second season once at the beginning, before the entire Light Zone was wiped out in the second Season Finale, forcing the Lexx (and a large amount of particle matter from the zone) to get forced back out into the other universe.
 * Homaged in Mystery Science Theater 3000, "Last of the Wild Horses", where Dr. Forester and TV's Frank get to quip at the movie, and evil Mike and Bots watch on from Deep 13.
 * An Alternate Universe is seen in the Supernatural episode "What Is And What Should Never Be", but it's really all in Dean's head and everything is his perception—he's an utter bastard, Mary's perfect, Sam's a bit wussy and his soulmatey girlfriend looks like the reaper from the premiere. In his fantasy, his mother Mary and Sam's girlfriend Jessica were never killed by Azazel, so the Winchester family live perfectly normal lives and his Dad died peacefully.
 * Another Alternate Universe, or rather a series of them, pops up in the episode "Mystery Spot" thanks to a repeating time loop in which Dean keeps dying. The iteration before the final time loop lasts months instead of the standard day, resulting in a dark, isolated Sam.
 * Most recently in the episode "It's a Terrible Life" where Dean is a Marketing Director for a firm and Sam is a techie in the same building with no memory of their hunter life beforehand apart from a few dreams. It's revealed that this was all a test from an angel to discover whether Dean would still revert back to his hunter ways being told it's in his blood and he will always find a way to be a hunter. This is also a play on the Wonderful Life trope.
 * Yet another AU episode took place in the sixth season, where the brothers are sent to a universe where Supernatural is just a TV show filmed in Canada, in which Sam and Dean are played by Jared Padalecki and Jensen Ackles, and there is no magic, demons, angels, monsters, or any supernatural beings at all.
 * And then there's "My Heart Will Go On", in which the Titanic never sank, somehow causing the Winchesters to own a Mustang, Bobby to be married, and Celine Dion to be a lounge singer in Quebec.
 * Kamen Rider Decade uses Alternate Universes for its main premise. The main cast travels through various alternate universes which are modified versions of the previous Kamen Rider shows.
 * Kamen Rider Dragon Knight uses the concept of alternate universes, accessible through mirrors. The Earth Kamen Riders are chosen because they are genetic doubles of the original Kamen Riders from the alternate universe of Ventara.
 * Season 6 of Lost features an alternate universe where 815 never crashed, and many other details are different. Word of God has it that neither timeline should be called "alternate" or "parallel" as those words imply that one is more real than the other. Flash-sideways has been decided to be the proper term. People in the flash-sideways actually retain memories from the other timeline, with Desmond seemingly able to switch between both willingly.
 * The Alternate Universe on Fringe is a world where pockets of time and space become unstable due to.
 * In the AU, there are many details that differ from the characters' home universe, such as Martin Luther King Jr. being on the American $20 bill and the World Trade Centers still standing and
 * Did we mention ZEPPELINS? I feel like we should do a quick mention of ZEPPELINS, based on the frequency with which ZEPPELINS appear in the Alternate Universe.
 * Wizards of Waverly Place had an episode where Alex goes through a mirror and enters a parallel universe where nearly everything is about her and in her favor.
 * The Community episode "Remedial Chaos Theory" features the group rolling a die to choose who will go to the door to get the pizza. Abed warns that this will create 6 (actually 7) alternate universes. Everyone else of course dismisses this, but we the audience get to watch each one unfold. The differences ranges from different characters hooking up, mental break downs occurring, everyone having an awesome night, and everything going to shit.

Multiple Media

 * Bionicle has the Olmak, also called the Mask of Dimensional Gates. Does exactly that. Its wearer, Brutaka, has used it both to teleport and to send enemies to a dimension they probably won't return from. He tried to send his former friend Axonn into the Zone of Darkness (a pitch-black dimension with only flat, featureless plain with gravity), and also used his (then damaged) mask to teleport Takanuva to Karda Nui to warn the heroes of a great danger. However, the mask malfunctioned, and sent Takanuva into both Alternate History and a Bizarro Universe. After finally finding the another Olmak in one of those universes, Takanuva entered inter-dimensional space and got to his intended destination. This is a Multiverse with a twist, as "our" dimension is explicitly called "the real universe", the rest are only pocket dimensions that shows how things would've turned out if they were done differently. Brutaka's mask was destroyed eventually, but the lunatic villain Vezon managed to get his hands on another one... and it ended up fusing to his face. Now he is a living dimensional gate, and has already visited several other universes (among them a few of those that Takanuva got lost in).

Tabletop Games

 * TORG features several different dimensions/realities, each corresponding to a different genre (such as Aysle, a traditional world of Medieval European Fantasy; the Cyberpapacy, a Cyberpunk world run by a Corrupt Church; the Space Opera-influenced dimension of the Space Gods; Orrorsh, a Lovecraftian Cosmic Horror Story in a Heart of Darkness style British colonial jungle setting; the Nile Empire, a world of Pulp Action Adventure; the Living Land, with sentient dinosaurs; and others), all cooperating to invade Earth.
 * Part of what made TORG such an interesting game is that it was based on distinctly different rules for how reality worked, depending on the context of the home dimension. The Nile Empire, for example, had no room for moral ambiguities: every character was either Good or Evil, though they could change from one to the other under the right circumstances. Characters could engage in literal 'reality duels' with opponents from different dimensions, and the High Lords could do the same with entire areas of real estate.
 * The GURPS Infinite Worlds setting involves the PCs as agents travelling through alternate universes. Officially all GURPS settings are universes within the Infinite Worlds. This includes assorted Alternate Histories (GURPS Technomancer, GURPS Reign of Steel), several universes where All Myths Are True (GURPS Camelot, GURPS Atlantis), multiple worlds with superheros (GURPS Supers, GURPS International Super Teams), and even universes inexplicably modeled on the popular fiction of the baseline universe (GURPS Conan, GURPS Discworld)!
 * The enemy timeline in Infinite Worlds is Centrum, a scientific state that wants what is best for all, and for this to continue (discovering where this one branched off is a surprise)... others in the Alternate Worlds books have included Gernsback (named for the Golden Age SF editor), where Nikola Tesla's inventions shaped the development of science; Excalli, where the dominant empire is an Aztec-derived one; Roma Aeterna, where the Empire of Rome simply carried on, with the adoption of science; an alternate where China continued to trade overseas; and several versions of the usual "Nazis triumphant" parallel. Oh, and the United States of Lizardia, where dinosaurs evolved into sentient beings but somehow ended up recapitulating human history along the way.
 * The two Dungeons & Dragons campaign settings of Greyhawk and Mystara are both alternate universes to Earth and each other, though this is rarely referenced in game materials and comes mostly from Word of God.
 * Greyhawk exists in a Multiverse (along with Dragonlance and the Forgotten Realms), but it's not made up of alternate universes. Rather, it's the term used for the system of heavens and hells, elemental planes, the Astral Plane, and so on; the different campaign settings are planets in the same universe.
 * The entry for 1357 DR in The Grand History of the Realms notes that in that year, on an alternate Material Plane world known as Earth, Ed of the Greenwood gathered together various books and maps given to him by Elminster of Shadowdale, and made the first publication of the Forgotten Realms campaign setting.
 * Mystara somehow exists in a different multiversal set-up from the other campaign settings. In addition to Earth, it also crossed over with another universe with futuristic technology; a starship from that universe crashed on Mystara and its radioactive engine became a major source of arcane power.
 * The point here is that, unlike most other official Dungeons & Dragons settings, Mystara and Greyhawk share background elements pulled from early games (such as the aforementioned starship crash, the Barony of Blackmoor, and connections to Earth), but in slightly different formats.
 * Gothic Earth, a spinoff of the Ravenloft product line, is an Alternate Universe version of our own planet in which supernatural horrors lurk beneath the facade of Victorian-era society. Also, some characters from classic fiction in our world are real there.
 * Urban Arcana's worlds on the other side of Shadow could be this, but the nature of Shadow makes travel between universes... tricky. As in, 'you can't go back'. One of the adventures includes a character from the other side that have figured out how you can travel between the Earth of UA and his world. This character, and his organization, also appeared in Planescape...
 * Wizards of the Coast long ago published a set of generic supplements for handling deities in roleplaying games, called The Primal Order. One of the books in this series, Chessboards, covered in exquisite detail how to design and manage an entire multiverse complete with cosmology.
 * This trope is a common excuse for game masters to use, when importing player characters from one tabletop role-playing campaign to another.

Video Games

 * The Super Robot Wars games are set in an Alternate universes for each of the series portrayed in it(the alternate, of course, being that they're all happening at the same time in the same place). Each game or series is, additionally, an alternate universe from each other. Then there is the Original Generation universe, which contains all the original characters and mecha from the other games and then some, which also has its own Mirror Universe, the Shadow-Mirror universe, which is itself the Original Generation version of the Shadow-Mirror universe from Super Robot Wars Advance. Confused yet? We haven't even gotten to the Endless Frontier!
 * In Super Robot Wars L, Macross Frontier, Voltes V, and Iczer One all come from one universe and end up somehow Folding into another, which is where all the other series take place.
 * Nearly every character from Kingdom Hearts is an alternate version of his/her Disney or Final Fantasy counterpart (otherwise the game would run into some serious continuity problems). This is implicitly stated in the Tron world.
 * The two Sonic Rush games feature a parallel universe. The first game takes place in Sonic's universe, which is slowly merging with Blaze's. The second game takes place in Blaze's universe... which is apparently a giant ocean.
 * Kirby and the Amazing Mirror takes place in another literal mirror universe (akin to the Charmed and Red Dwarf ones above), parallel to Dreamland and containing mirror versions of Meta Knight and Kirby.
 * In Tsukihime and the Nasuverse, Alternate Universes are pretty much canon. As such, that means there may be at least five separate continuities for Tsukihime, and three for Fate/Stay Night, not to mention all the bad endings. Which ending the sequels use varies quite a bit.
 * Chrono Cross had alternate universes replacing time travel as the main hook.
 * The Mega Man series has two universes: the main one (Classic, X, Zero, ZX and Legends), and the alternate one (Battle Network and Star Force). The difference between these two timelines is that the latter has internet technology prosper instead of robotics (as was the case in the former).
 * In a strange way, the alternate universe also rewrites most of the robot masters who were Megaman's enemies into potential allies, the most notable being Gutsman and Searchman, both whom are enemies in the mainline series, but consistent allies in the alternate timeline.
 * The World Ends With You has Another Day. This takes place in a world where Neku and his friends, Shuto is The Hero with Neku as The Lancer, Tin Pin Slammer is Serious Business, Eri's parents decided to call her Shiki for some reason, and Neku is less emo.
 * And, mind-bogglingly, despite what the game says, it actually has some bearing on the main plot. flees to that universe after . Whereupon he challenges Another Day!Neku to a Boss Rush to kill time.
 * It also seems to cross over into The Multiverse with certain people as they can go to other dimensions, and even meet themselves if they aren't careful.
 * The Resistance games take place in a setting where after World War I Germany's economy wasn't totally devastated, therefore Adolf Hitler never rises to power and there was no World War II. Instead, creatures known as Chimera take over the entirety of Europe and by the sequel have wiped out the US.
 * Based on what has thus far been fan-translated of Magical Girl Lyrical Nanoha A's: The Battle of Aces, it takes place in an AU where
 * The DLC for Dragon Age entitled The Darkspawn Chronicles pitches the idea of a world where The Hero died near the beginning of the game, thus leaving Alistair to save the day.
 * In the second installment of the "Timeline" mod trilogy for Half-Life, Gordon Freeman is transported to a parallel Earth where the US never rebelled (the major superpowers are the British Empire, the Soviets and the Japanese), and an ice age began some 300 years earlier, threatening human survival. That world's Gordon Freeman has failed, so our world's equivalent is sent to stop the Xen invasion there (as well as an invasion of time-travelling Nazis from our dimension).
 * The original Crazy Taxi has "Another Day" mode. Where in the normal mode most customers want to travel in a certain direction which leads to the cabbie going in a counter-clockwise direction around the circuit, in "Another Day", the customers usually want to travel to a destination in the opposite direction, causing the cabbie to go in a clockwise direction around the circuit.
 * The main plot behind Little Busters! can be described as this.
 * The areas Yaschas Massif and Academia in Final Fantasy XIII-2 have alternate versions that appear after solving paradoxes in the timeline, and are marked with an X in the year name (ex. 01X AF). You can still go back to the original universe, though.
 * The plot of the Portal 2 PeTI DLC involves this. Earth-Prime's version of Aperture is nearly broke, so they decided to cut test chamber construction costs by sneaking the designs into alternate versions of Aperture, letting them build it, then stealing them back. You can either play the part of a test chamber designer with the new level editor, or a test subject traveling between universes to test the new chambers. You end up running into various versions of Cave Johnson, all of whom are still running tests and crazy to some extent (save for the one who stopped the resonance cascade experiments after buying Black Mesa).
 * The Dawn of Victory mod for Sins of a Solar Empire has its premise based on an Alternate History where the course of World War Two is changed by the arrival of a powerful alien race known as the Scinfaxi (inspired by Harry Turtledove's Worldwar series). After losing much territory to the invaders, the main world powers manage to develop nuclear weapons and beat them back to the Southern Hemisphere. They then rebuild and consolidate their power. Eventually, the Northern Hemisphere is divided between the Soviet Union, the Greater German Reich, and the Democratic Federation. They manage to develop interstellar flight and settle other worlds. After the Scinfaxi resume their advance, the human powers evacuate the remaining population from Earth and nuke the entire planet from orbit. Fast-forward a few centuries. The three main human nations (as well as many smaller states) are spread out over many star systems and vying for domination. Meanwhile, the Scinfaxi (a vast interstellar empire) are preparing to strike again.

Web Animation

 * The 150th Strong Bad Email had Strong Bad visiting many of the website's alternate universes.
 * The world of Vytal in RWBY: two moons in the sky, active magic with technology, humanity all but trapped in five city-states and beseiged by hordes of monsters...

Web Comics

 * In El Goonish Shive, the Word of God said that at least four dimensions have meddled with the "main" one. Most of them are Alternate Universes, each with its own version of Tedd or other main characters.
 * Supernormal Step takes place on an AU Earth with magic and fantasy creatures. It is one of many dimensions, and two of the main characters are actually from our normal, boring one.
 * Minions At Work: Invoked here.
 * Bob and George has an infinite number of them, and Bob visits quite a few. The title characters themselves are from a different universe than the one where most of the action takes place.
 * Dinosaur Comics has an alternate universe where everyone has goatees, a Shout-Out to the Star Trek: The Original Series episode "Mirror Mirror," in which the Spock counterpart wore a goatee. Anytime you see an alternate universe counterpart with a goatee, chances are it's a Shout-Out to "Mirror Mirror."
 * In What Birds Know, a mysterious tower acts as a gateway between the normal world and a bizarre version where people lay eggs, among other oddities.
 * Fall City Blues revolves around two versions of the same person forced to live together when their alternate universes were merged to save space.
 * Bittersweet Candy Bowl, According to the commentary, the chapter "Another Path" was originally intended to be set in an alternate universe where . The final version has it as a daydream of Paulo's.
 * Maze of Many in Goblins allows characters from multiple realities to exist in the same place simultaneously.
 * Jix had a story that took place in an alternate reality where Remula had taken over the Earth and it was discovered later that the original Lauren had actually be transported to that universe when she caught up to her counterpart.
 * In Dragon City, Erin's friend Natasha reveals herself to an alternate universe counterpart despite Erin having blue scales and Natasha having brown.
 * Actually, as Natasha (the brown Erin) points out, due to genetics, Erin was more likely to be brown than blue and that the blue Erin is a genetic fluke.
 * Yes, Erin IS that vain to have made friends with her other world counterpart.
 * Very briefly done in vexxarr.
 * Sluggy Freelance is almost the Sliders of web comics. Among the worlds its characters have visited are:
 * A sci-fi dimension heavy on tropes from Star Trek and Alien,
 * A "Dimension of Pain" inhabited by demons,
 * A rather saccharine dimension where everyone is always nice and friendly to each other, there's no beer, and the main source of food is rice cakes,
 * A dimension where everyone has purple hair and speaks Portuguese,
 * An anime-parody dimension where battles between good and evil were regularly fought out by giant robots, in which the entire universe is actually a power source for a giant waffle iron (don't ask),
 * A dimension that has been invaded by Aylee's race, and
 * A dimension that has been overrun by mutants, with the only survivors holed up in the Orwellian 4U City, which keeps its inhabitants drugged into submission.
 * John Ringo's Hell's Faire features several Sluggy Freelance strips as if they were created within the novel's setting. This was possibly a favor in return for the shout outs to Sluggy Freelance in the third and fourth books of the series.
 * Dumbing of Age is an alternate universe to Shortpacked and the other series in Dave Willis' Walkyverse. It reboots the story by placing it back in college (most of the Walky cast graduated from college in 2001) removing the science fiction elements completely, and using a Sliding Time Scale so the characters will never graduate. Shortpacked is still running alongside it, though, ensuring the walkyverse will continue.
 * In Bobwhite, Cleo freaks out over the many-worlds hypothesis and its implications on fast food. In this universe, she never orders burritos because they're gross... which means that in some other universe she always orders burritos. But why?
 * In Goblins, a dungeon called the Maze of Many serves as a point where the dimensions in the multiverse are drawn together. Adventurers who attempt to conquer the dungeon are required to compete against multiple versions of themselves, each from a different reality, being allowed infinite retries until each has completed the dungeon once and each reality is 'satisfied'.
 * In Homestuck, initiating  creates one of these by resetting the conditions of the game, including the players and their universe.   This has happened twice so far: once to Earth, and once to.

Web Original

 * Tasakeru takes place in an alternate universe where humans have never existed.
 * Survival of the Fittest has had several small-scale AU RPs. These range from simple 'What-If' scenarios (What If the students had been rescued on Day 3, What If SOTF really was a TV show, etc) to radically different concepts such as Mech SOTF and SOTF with zombies.
 * Fairly recently, a spin-off site effectively dedicated to Alternate Universe versions of Survival of the Fittest was created, with the pilot in an interesting Continuity Nod, being an alternate version of Battle Royale, the concept which SotF was based off.
 * The Mini site also now hosts SOTF: Evolution, which is like normal SOTF, only with 20 characters instead of the Loads and Loads of Characters the main site has, and with Super Serum induced mutations instead of designated weapons.
 * Fate Nuovo Guerra takes one of Fate Stay Night's bad endings and runs with it as their Backstory. The Fifth Grail War results in the destruction of Fuyuki City, prompting the Einzberns to start a new Grail War elsewhere.
 * A popular fad on YTMND is to take pre-existing memes and create Alternate Universe counterparts, usually under the PTKFGS moniker ("Punch The Keys, For God's Sake!", another one of Sean Connery's lines from the famous scene in Finding Forrester that named the website), although even more Alternate Universe versions exist, usually as either "Yes Yes" or the elusive "Fourth Corner", where no-one can really agree on a final name for the latter.

Western Animation

 * "Life, the Negaverse, and Everything" in Darkwing Duck—a mirror universe set up to explain the origin of Negaduck (not to be confused with the self-proclaimed Negaduck whom Megavolt accidentally created in another episode by dividing Darkwing into good and evil clones) The portal to the Negaverse was lost at the end of this episode, in a traditional Status Quo Is God ending.
 * Futurama:
 * In "The Farnsworth Parabox", Farnsworth creates a box leading to an alternate universe where coin tosses have different outcomes. There are also lots of other boxes, leading to other alternate universes, each linking to each other.
 * In "I Dated A Robot", Fry goes to the edge of the universe and sees alternate versions of himself and his friends, all wearing cowboy hats.
 * In "The Beast With A Billion Backs", a portal opens to an alternate universe, home to only one sentient being: Yivo, the infinitely huge, love-lorn ball of Naughty Tentacles.
 * In "The Late Phillip J. Fry", after Farnsworth, Bender, and Fry go to the edge of the universe, a new, identical universe starts, and then that universe ends, so they end up in a third identical universe.
 * Invader Zim seems like it may take place in one, but then again, it may just be Twenty Minutes Into the Future.
 * Justice League had several—the retro-styled world of the Justice Guild, the dark dystopia of the Justice Lords, the Vandal Savage-ruled world created through time travel, and others.
 * Notably, the Justice Lords Universe depicted Arkham Asylum, and Gotham City for that matter, as very bright, Metropolis-esque places, in one of the few instances of the city being shown during the day.
 * Superman: The Animated Series also featured a universe where Lois died, prompting Superman to team up with Luthor and take over Metropolis.
 * The various incarnations of the Transformers franchise have done this quite a bit, with alternate timelines galore.
 * Perhaps most notably is "Shattered Glass", the 2008 BotCon event featuring heroic Decepticons and evil Autobots. With goatees. And eyepatches.
 * The goatees are a Shout-Out to the Star Trek: The Original Series episode "Mirror Mirror," in which the Spock counterpart wore a goatee. The eyepatches are from the Doctor Who episode "Inferno," in which the fascist counterpart to one of the recurring characters wore an eyepatch.
 * In an episode of Rugrats, Tommy and Chuckie think they're in a "Mirrorland."
 * An episode of G.I. Joe featured a timeline where Cobra had succeeded in taking over the world.
 * In The Secret Saturdays, the whole family (except the female lead's brother) has a twin in an alternate universe, who all try to take out the heroes as Psycho Rangers.
 * Star Trek: The Animated Series
 * "The Magicks of Megas-Tu" has the crew discover a world where much of their equipment doesn't work, but Functional Magic is commonplace. Oddly, Spock adapts quickly.
 * Presumably he Sufficiently Analyzed it first.
 * "The Counter-Clock Incident". In the other universe, time runs in reverse, and the only way to travel between universes is to go through a dead star/nova at Warp 36.