Penny: What's a Multiverse? Sheldon: GET HER OUT OF HERE!
Charlie Jade: the Alphaverse (a Crapsack Worldand a Dystopia) is running out of clean water from its excessive pollution. So they use a portal to steal water from the utopian Gammaverse. Charlie Jade ends up in the world in between — the Betaverse, a.k.a. our world — when things go wrong with the portal. Later on he finds out that the hallucinations he's had through his life are actually the result of his ability to travel between the verses, and he returns home before deciding he liked the Betaverse better than Alphaverse. Long story short, the whole series is based around this trope, including the cliffhanger season finale (from which the show didn't get renewed) that would have revealed a fourth universe.
Community delved into the multiverse in Episode three, season three "Remedial Chaos Theory" where Jeff decides to roll a die in order to decide who has to get up to collect the pizza; in doing so, he creates six different timelines with vastly different outcomes. The die returns in the final episode of season four where they each face off with the victims of the die's worst timeline, the gang's "evil counterparts."
Doctor Who is a bit tricky. There are alternate timeline-style universes, like the fascist universe of "Inferno", or Pete's World from "Rise of the Cybermen"/"The Age of Steel"; post-the Last Great Time War, it's potentially multiverse-destabilizing for a TARDIS to hop between such universes. There are also pocket dimensions linked to the main universe, such as E-Space or the Land of Fiction.
Rejected in Farscape where it's explained there's only one of you with many potential alternate realities, which only become real when you start moving down one of them.
The Flash (2014) introduced the idea of a DC multiverse, which can be viewed whenever Barry travels from one universe to another. So far, there is no official name for this multiverse. Two types of Earths are featured, those that are home to the CW, CBS and Netflix's DC superheroes, and those featuring characters who migrate to the featured Earths.
Earths Featured on the CW, CBS & Netflix Include:
The Arrowverse, named after the universe that began with an adaptation of The Green Arrow's origin story. In-Universe, it was given the nickname of Earth-1. That universe contains:
Supergirl (2015) has its own Earth, Earth-38, which has been visited by the Barry Allen of Earth-1 three times, usually during Crisis Crossover time.
Notably, at least two of the same alien races exist in both Earth-1 and Earth-38: Dominators (they invade Earth-1 in a crossover event and one is seen in Supergirl) and Thanagarians (mentioned in both Legends of Tomorrow and Supergirl).
The Flash (1990) is also confirmed to have its own Earth (Earth-90) within the multiverse, where the conceit of this Earth is "What if superheroes were active in the 1990s instead of the 2010s?" This Earth is identical to Earth-1, but several events and incidents from Earth-1 (especially The Flash (2014)) are depicted with the influence from a Barry Allen active as the Flash in the 1990s instead of the 2010s (such as the Trickster's initial crime spree in the 90s). Barry Allen from Earth-1 has briefly glimpsed this universe, but has not visited it yet.
Two Unnumbered Earths were retroactively added to the Arrowverse, and are each home to Black Lightning and Smallville's version of Superman. Both appear in 2019's adaptation of Crisis on Infinite Earths.
Earths Occasionally Seen on Various DC Shows
Earth-2 is another universe, and was connected to Earth-1 in a freak accident involving a wormhole. It appeared prominently in season two of The Flash and has been visited by various characters of Earth-1 and Earth-3 several times.
A fact about this multiverse is that temporal changes on one Earth don't affect others, even if there were interactions between them. This comes to light, when Harry and Jesse return to post-Flashpoint Earth-1 and start noticing differences from what they remember during their last visit.
Another Earth-2 is featured in Smallville, where its conceit is "What if Clark Kent was raised by the Luthors instead of the Kents?"
Earth-3, first mentioned in the Flash season 2 finale and briefly visited in season 3. This is where the real Jay Garrick is from.
Earth-15 is offhandedly mentioned to be a lifeless world.
Earth-19 is where Harrison "H.R." Wells is from. Apparently, that world has been invaded by another Earth at some point (the invasion was repelled at great cost), resulting in laws that punish attempts to travel to or from Earth-19 with death. The only ones allowed to travel this way are Collectors, whose job is to track down and capture violators. This world's Flash appears to be the Accelerated Man.
Earth-22 is a post-apocalyptic wasteland that appears to be a mix of Mad Max and Fallout, with Wells 2.0 being an Aussie cyborg.
Likewise, we're not told much about Earth-47, but its H. Lothario Wells is a "genius, billionaire, playboy philanthropist" with a dash of Hugh Heffner.
It was briefly assumed that the number of Earths is finite — 52 to be exact. Well, 53, actually, but nobody wants to talk about Earth-X, as it's a world where the Nazis won World War II. This is primarily where Freedom Fighters: The Ray is set, although the protagonist is actually from Earth-1.
The 2019-2020 Crisis on Infinite EarthsCrisis Crossover destroyed and recreated the multiverse. A number of alternate universes are the settings of past DC shows and movies and were remade as original, others were repurposed as settings for newer shows:
Furthermore, Earth-1 (Arrow, The Flash (2014), et al.), Earth-38 (Supergirl (2015)) and the Earth of Black Lightning (2018) were merged into a single universe called Earth-Prime. The inhabitants of Earth-Prime are unaware of the continued existence of the rest of the universes, believing their universe to be the only surviving one.
In the middle of the first season, Fringe suggests a multiverse through the ZFT Manifesto. In the season finale Olivia goes there and meets Walter's old partner William Bell — in his office in the Alternative World's still-standing World Trade Center.
The Alternative Universe is further explored in Seasons 3 and 4, as both universes first suspect each other of trying to destroy the other and then team up to fight a common enemy. Two possible futures of the Prime Universe incorporated similar conditions as the Alternate Universe, in keeping with the idea that the evolution and decay of the Alternate Universe was slightly ahead of the Prime Universe. The show conveniently applied a red/blue color scheme to differentiate the "Red-Verse" and "Blue-Verse." The most prominent difference is the color of the Statue of Liberty: green in Prime and bronze in Alternate. This was frequently used to show which universe was being shown. Other differences between the universes are also shown, such as in the episode Olivia travels to the other Earth for the first time, is that the Twin Towers are still standing in New York City, suggesting the 9/11 terrorist attacks didn't happen, another episode has a theater marque in the 80s in the other universe label Eric Stoltz as starring as Marty in Back to the Future, and another states that there are diseases that there are vaccines for in the regular universe (which mirrors ours) that don't exist in the other one and, thus, are still plaguing at least America.
Kamen Rider is an odd handling of this: The Showa era shows all seem to take place in the same world, since veteran Riders would show up to help out the new guys, while the Heisei era shows all seem to be their own self-contained universenote Though Kamen Rider Agito is a little confusing; check its page for details. Then along comes Kamen Rider Decade, which portrays every series as its own separate universe, with their own Alternate Universes. In the final episode, a villain forcibly merges the universes together, then in the Grand Finale movie Decade performs a Heroic Sacrifice to preserve the memories of the Riders, and from that point on all Riders seem to exist in a shared universe as evidenced by the annual crossovers, not to mention the Super Hero Taisen movies where the Riders team up with the Super Sentai and Metal Heroes.
And speaking of Super Sentai, it's no less confusing. While it was stablished that Taiyou Sentai Sun Vulcan is a continuation of Denshi Sentai Denziman Showa era Sentai relegated any crossovers to side material of dubious canonicity, with the only evidence in-show that almost all shows were in the same universe being the first episode of Kousoku Sentai Turboranger. Then however, Kaizoku Sentai Gokaiger stablished all series take place in the same world, and it seemed to be like that ever since, with the exception of Uchu Sentai Kyuranger, whch is explicitly shown to be in its own universe. But then comes comes Kikai Sentai Zenkaiger, which stablishes all previous shows take place in their own worlds. Most people agree to not think too hard of it.
For the longest time, some fans speculated that, unless specifically stated otherwise, most of the shows in the franchise take place on alternate worlds. This is bolstered by in-universe retcons, such as the first 3 series featuring dinosaurs (Zyuranger,Abaranger, and Kyoryuger) depicting different ways of how the dinosaurs died out and the like. The same theory postulates however that there's a universe specifically for the various crossover movies and specials, which Gokaiger also takes place in, in which the various retcons and continuity gaffs don't exist and everything slots together neatly. This has never been explicitly stated by Toei or the production staff before Zenkaiger, though. Jonathean Tzachor, showrunner of various seasons of Power Rangers, is apparently a proponent of this theory and believes that every Power Rangers series takes place in its own universe as well, though that's not the official stance of the people higher up than he was who have controlled the direction of the franchise outside of RPM,Dino Charge, the MMPR movie, the 2017 movie, and possibly Beast Morphers.
In Lexx there are only the Light Universe and the Dark Zone. And the Dream Zone. And the Other Zone.
Nowhere Boys: In season 2, the multiverse is shown as being a part of Negative Space, a world between worlds. A Guardian protects the multiverse. A creature known as the Entity later begins destroying the worlds of the multiverse, but everything is restored when the Nowhere Gang defeat it.
Once Upon a Time and Once Upon a Time in Wonderland: Most of OUAT takes place in Storybrooke, a town created by magic that exists in the Land Without Magic, which is our "real world". The curse that created Storybrooke also trapped many people from The Enchanted Forest there, characters from various fairy tales and other stories. Other worlds include Neverland, Wonderland (in which Spin-Off series Once Upon a Time in Wonderland takes place), Oz, the Land Without Color (a Deliberately Monochrome world where Dr. Frankenstein is from), a Victorian England where Alice is from, a 1920s England where Cruella de Vil is from, The Underworld, The Land of Untold Stories (a universe that serves as a dumping ground for characters from stories that never finished), the Wish!Universe (a genie-created reality where Regina was defeated before casting the Dark Curse), and the Dark Realm (domain of the Black Fairy). Then Season 7 further complicates things by revealing that there are variations on the Enchanted Forest, to reflect the different versions of the stories told in our world.
Red Dwarf has an infinite number of parallel universes, and our heroes have crossed over occasionally:
"Parallel Universe" features a dimension where everyone throughout history is gender-flipped.
"Dimension Jump" introduces Ace Rimmer, Rimmer's counterpart from a dimension where he actually successfully became a Space Corps test pilot after being held back a year in primary school and resolving to do better. An alternate Lister also appears in the same dimension, here a flight engineer who is married to Kristine Kochanski.
"Stoke Me A Clipper" brings back Ace, who has since become a sort of dimension-hopping superhero (and a Legacy Character, with enough predecessors for their coffins to form an entire planetary ring). We see him in one dimension rescuing the Princess Bonjella from Nazis.
"Ouroboros" introduces Kristine Kochanski as a new cast member, originally hailing from an alternate universe where she was the sole survivor of the radiation leak that wiped out the crew instead of Lister.
Series 12 finale "Skipper" sees Rimmer use a dimensional skipper to visit various alternate Red Dwarfs. These include a reality in which the crew are still alive and everything is just like it was before the radiation leak in the first episode, except for the characters being about thirty years older (then there's a radiation leak); a reality in which Lister is cultured and sophisticated, and whose pet rat has evolved into a race of rat people that has overrun the ship; a reality with multiple clones of Lister and a reality where the crew is alive, Lister is captain and Rimmer his successful first officer, among others.
The Red Dwarf novels also play with the Multiverse idea, with the second novel Better Than Life reveal that there are seven universes, each accessible through black holes and wormholes via a realm called the OmniZone. Our universe is the only one where time runs in the wrong direction. Each universe also contains its own alternative realities, which play a part in the following novels Last Human and Backwards (each of which follows a different continuity).
The Red Dwarf Smegazine had a comic strip focusing on Ace Rimmer as he crossed into different universes and helped out their inhabitants. These include a reality where he and the rest of the cast were genetically engineered superheroes, one where the native Rimmer became a football player (and Zero Gee Football never became popular), a reality where Rimmer has become the Prime Minister of the United Republic of Lesser Britain (and the most successful politician ever), and a reality where Ace has become a bionic madman intent on destroying the galaxy, with the rest of the crew being hillbillies.
The TV show Sliders did this, although the heroes had no control over where they ended up each week.
In Season 1 Episode 10 of Shadowhunters Clary travels to an alternate universe where Shadowhunters defeated demons hundreds of years ago, causing there to be no need for them, while downworlders went into hiding to blend in with Mundane's. Clary and all her Shadowhunter friends ended up growing up with Mundane lives.
Season 10 of Smallville introduces an alternate Universe dubbed "Earth-2" where Clark was adopted by Lionel Luthor instead of the Kents. This is first revealed when Clark Kent of Earth-1 accidentally activates the mirror box. This Clark is a murderer and tyrant, and murdered his adopted brother Lex Luthor. He is also sexually promiscous.
The follow-up Season 11 comics explored this concept even more, with a version of Bruce Wayne from Earth-13 who is a cross between Batman and Joker. The final storyline of the comics involves the Justice League defending the Multiverse from being destroyed by the Monitors.
Kirk, McCoy, and several others were transported to a Mirror Universe in the "Mirror, Mirror" episode of the original Star Trek, in which a dark Earth-based empire ruled the galaxy. This was very much an In Spite of a Nail universe, since everything was much the same except the moral/ethical bent of the Federation's counterpart and its citizens.
Years later, the cast of Star Trek: Deep Space Nine returned to this universe to discover that the revolution Kirk had encouraged its native Spock to foment had happened; unfortunately, its effects were not necessarily for the better.
Star Trek: Discovery revisits the Mirror Universe again during a four-episode arc of its first season, making explicit reference back to the events of "In a Mirror, Darkly."
The showrunners of the new TOS-based movie series cite this episode, suggesting that the new Trek Verse (also known as the Kelvin Timeline or the Abramsverse) exists alongside, rather than replacing, the old one. The Expanded Universe definitely embraces this (stories in the old Trek Verse continue to be told rather than everything having to be based on Star Trek (2009) and Star Trek Into Darkness only. Stories unrelated to the new movies' events might reference the mysterious disappearance of a certain famous Vulcan in passing.)
Discovery explicitly references the Abramsverse in season 3 during a discussion of the Temporal Wars, reinforcing its existence alongside the Prime Universe as canon.
Stargate SG-1 had a handful of episodes where characters traveled to alternate realities. The first season finale's storyline was kicked off when Daniel accidentally activated an alien artifact and went to a timeline where he had never joined the Stargate program. A later episode used the same artifact to help an Earth in an alternate timeline that was faced with looming invasion, and other ways of accessing alternate universes were later found as well.
The season 9 episode "Ripple Effect" has with dozens of alternate universe versions of SG-1 coming through the Stargate due to some technobabble involving a black hole (and the meddling of one of the alternate teams.)
Stargate Atlantis also has several episodes that make use of the multiverse. The first has McKay's sister write an equation that allows connections to alternate universes to be made. McKay uses it to try to make an unlimited power source. The McKay from the universe he connected to has to cross the barrier to tell him it's a bad idea. The same technology was later used by McKay's rival back on earth to try to combat global warming (it didn't work). And yet another McKay from a different universe uses the same technology to build a Universe Hopping Starship (again, it didn't work) which sent the team from this universe on a wild ride. One just has to wonder if McKay really knows what he's doing when it comes to the multiverse.
Supernatural: Not only is there a Heaven, Hell, and Purgatory aside from Earth, but there are also multiple alternate realities, including one where the Winchesters' life is a TV show, one where the Apocalypse wasn't stopped in time, and one populated entirely by monsters. Essentially, they exist because God was bored and wanted more "toys" to play with; in Season 15, essentially throwing a tantrum over the Winchesters refusing to keep playing his game, he starts destroying every reality.
In 3rd Rock from the Sun there is a two part episode where the aliens visit an alternate universe (because they are bored) where they settled in New York instead of Ohio.
Dick: You may see people you know too. But FYI they may have made different life choices. Harry: I see, in this universe Officer Don could be an old Vietnamese woman. Sally: No Harry, they have the same bodies. Dick is saying they'll all probably be gay.
