These days, thanks especially to Marvel Studios' Spider-Man: No Way Home and Doctor Strange in the Multiverse of Madness – not to mention the earlier Spider-Man: Into The Spider-Verse, or the CW’s 2019 crossover event 'Crisis on Infinite Earths' – it feels as if everything is part of one multiverse or another, but… how did that happen? Of all the stories superheroes can tell, how did we end up so obsessed with parallel realities?

In The Beginning…

Fittingly, given the subject matter, it’s difficult to pinpoint one particular origin for the multiverse. Both H.G. Wells’ 1905 book A Modern Utopia and his 1923 novella Men Like Gods touch on multiversal ideas, even if they fall short in the execution. (Both feature other planets that are, explicitly, not Earth.)

A better official starting point would be the pulp magazines of the '30s and ‘40s; it’s there that we can find the first recognizable parallel Earth stories.

In 1934, 'Sidewise in Time' by Murray Leinster appeared in the July issue of Astounding Stories, wherein parts of the Earth are replaced by their geographical equivalents from parallel Earths, much to the surprise of scientists. Seven years later, 'Elsewhen' by Robert A. Heinlein was published in the September 1941 issue of Astounding Science Fiction. It’s a story in which a philosophy professor and his students manage to travel to alternate timelines and experience their lives on those parallel Earths using, of all things, hypnosis; it’s also the closest thing to a multiverse story as we’d recognize it that had appeared to that point.

Of course, the term 'multiverse' wasn’t being used as a term back then. Although it had existed as a word since the end of the 19th century – philosopher William James wrote, “Visible nature is all plasticity and indifference, a multiverse, as one might call it, and not a universe,” back in 1895 – “multiverse” wouldn’t be given its current meaning until 1963, when novelist Michael Moorcock adopted it for his parallel-Earth novella The Sundered Worlds. By that point, though, fandom had already awoken to the power of a good parallel Earth story by a comic book published two years earlier.

Two Earths? What Are You Talking About?

It’s difficult to overstate the importance of 1961’s The Flash #123. Even at the time, readers knew that the story of Barry Allen accidentally traveling to another Earth and meeting Golden Age Flash Jay Garrick was something special. 'The Flash of Two Worlds' won a number of fan awards upon publication, including Best Story and Best Artist for Carmine Infantino in the Alley Awards. It’s unclear whether it was writer Gardner Fox or editor Julius Schwartz who initially had the idea to not only revive the original Flash, but also to place him on another Earth, but it was one that would go on to form a significant portion of DC’s mythology over the next quarter century and beyond.

Two years after Barry first met Jay – and around the same time that Michael Moorcock was writing the word 'multiverse' into The Sundered Worlds – the Justice League traveled across realities to meet the Justice Society. 1963’s Justice League of America #21 laid the groundwork for DC’s future event programming in a couple of ways; not only was it the first meeting between multiple superhero teams, but it was also the comic that instituted a classification system to keep track of the different Earths, as evidenced in the story’s title, 'Crisis on Earth-One!'

As with 'The Flash of Two Worlds,' the issue was enough of a hit that crossovers between parallel Earths became a regular part of the JLA’s DNA. Almost every successive crossover, taking place every summer as an annual tradition, would add a new parallel Earth with its own superpowered heroes or villains to contend with. The DC universe was expanding in ways that even its fans would have trouble keeping track of… which would, eventually, have significant consequences.

Marvel, meanwhile, initially didn’t really follow DC into the parallel Earth game. Sure, there was an occasional visit to a world just like the regular Marvel Earth – 1968’s Avengers Annual #2 is the first of those, with the contemporary Avengers facing an almost-but-not-quite version of the originals. Avengers #85 would be the first issue to introduce a recurring parallel Earth to the Marvel Universe three years later, with the Squadron Supreme showing up for the first time – but they were few and far between, and often referred to as alternate timelines instead of officially parallel Earths. Even a series like What If…?, which launched in 1976 and is, in theory, set entirely on parallel Earths, shied away from using the terminology on a regular basis.

That’s not to say that Marvel stayed entirely away from pushing the envelope on multiversal thinking. 1983’s Daredevils #6, published by subsidiary Marvel UK, introduced the first superhero team made up entirely of members from different Earths with the introduction of the Captain Britain Corps. That story was written by Alan Moore, a fan of the DC era that had introduced Earths-1 and -2, a fact reflected in his introducing a similar numbering system for Marvel’s multiverse… or, as he called it, the Omniverse (The primary Marvel comic book Earth is Earth-616, for those curious).

Moore’s use of Omniverse, perhaps coincidentally, shares a name with a theory invented by Marvel editor Mark Gruenwald for a fanzine he produced ahead of beginning his professional career. Omniverse: The Journal of Fictional Reality, as the name suggests, concerned itself with the fictional worlds of comic books, and how they interrelated. The Omniverse, Gruenwald suggested, was the collective term for multiple realities, and multiple multiverses, so that the Marvel and DC universes could co-exist and even crossover, for example, if the conditions proved favorable. (The first issue of Omniverse was published in 1977, a year after Superman versus the Amazing Spider-Man, so it wasn’t an entirely outrageous concept, it should be noted.)

The Wheel – It is relentless

1985 was when everything started to change on the multiversal front, at least in comics. Elsewhere, movies and TV shows were still for the most part staying away from the concept except for the occasional episode of a science fiction show, usually following guidelines laid down elsewhere. Even 'Mirror, Mirror,' the beloved 1967 Star Trek episode that introduces that show’s Mirror Universe, is basically the evil-Earth story of 1964’s Justice League of America #29 ('Crisis on Earth-Three!') on a different scale.

Despite setting the trend for more than two decades, DC was tiring of its many parallel-Earths. Believing them too confusing for new readers, Marv Wolfman – then the writer of DC’s biggest book, The New Teen Titans – came up with a bold suggestion: get rid of all but one Earth, and start DC’s mythology anew as something simpler and, not entirely coincidentally, more Marvel-like. Crisis on Infinite Earths did exactly what Wolfman intended: by the end of the 12-issue series in 1986, DC’s multiverse was no more, collapsed down to one reality, one Earth, and one coherent timeline. Well, as coherent as superhero timelines get, anyway.

The series was a hit and revitalized DC’s fortunes with both creators and fans. (That it was publishing titles like Alan Moore and Dave Gibbons’ Watchmen, Frank Miller and David Mazzucchelli’s Batman: Year One, and John Byrne’s Man of Steel at the time helped matters.) Even as this was happening, Marvel was moving in the opposite direction, finding new ways to embrace its own parallel Earths: a character from an alternate Earth joined the X-Men as a regular cast member; series like Quasar and Squadron Supreme – both written by Mark Gruenwald – made more regular use of Marvel’s alternate realities; and, to accommodate a publishing deal that brought the Image Comics founders back to Marvel, an entire parallel Earth was created to house the Heroes Reborn series.

Things arguably peaked for Marvel in 2001, when, even as the Ultimate imprint was telling stories set in yet another parallel Marvel dimension – one that would, of course, crossover with the regular Marvel world more than once – the company launched Exiles, a canny mix of Alan Moore’s Captain Britain Corps concept, the X-Men franchise, and What If’s central idea of visiting worlds just like the regular Marvel universe but slightly different. The series would last 100 issues, before going on to be relaunched on a number of different occasions.

As the 21st century got underway, the winds were shifting at DC again. To celebrate the 20th anniversary of Crisis on Infinite Earths, the company published Infinite Crisis, which teased the return of the multiverse, before delivering on that promise a year later with the weekly series 52… a title that referred to the number of Earths in DC’s new cosmology. A handful of years later, writer Jonathan Hickman took over Marvel’s Avengers franchise with a storyline that featured a collapsing multiverse and heroes forced to destroy other Earths in order to survive. This spin on DC’s Crisis was, ultimately, a fake-out, and Marvel’s multiverse was reborn again at the end of Hickman’s 2015 miniseries Secret Wars.

By that point, however, the multiverse had moved into another medium altogether.

Every choice that we make would create countless other possibilities

In retrospect, it was almost guaranteed that superhero multiverses would end up onscreen. As if their prevalence in superhero comics wasn’t reason enough, movies and television shows had been increasingly playing with the ideas of alternate Earths and the multiverse through the 1990s and early '00s, whether it was syndication favorite Sliders or the tangent horror world of Donnie Darko, as if to prepare audiences for what was to come. Pop culture was finally catching up with superheroes, just as superheroes were beginning to take over pop culture as a whole with the rise of superhero movies and TV series.

Inevitably, it was Warner Bros’ DC shows that got there first, for entirely practical reasons: with Supergirl originally airing on a different network from The Flash and Arrow, it only made sense to present it as happening on a different Earth – and, given the Flash’s history with the comic book multiverse, it made sense that he should be the character to crossover between universes in 2016’s 'Worlds Finest,' airing during the first season of Supergirl. The success of that episode led to 2018’s “Crisis on Earth-X” storyline, which ran through Supergirl, The Flash, Arrow, and Legends of Tomorrow, followed by 2019’s “Crisis on Infinite Earths,” which ran through the same four shows in addition to the newly launched Batwoman. It was, to some degree, an adaptation of the comic of the same name, if somewhat less ambitious in scale, even if it managed to bring the big screen Flash in for a brief cameo that hinted at how big the multiverse could be, given the chance.

While DC was helping television viewers understand the multiverse, Sony and Marvel was doing the same for moviegoers, courtesy of the stunning Spider-Man: Into the Spider-Verse. Inspired by a comic book “Spider-Verse” storyline, Into the Spider-Verse took advantage of the potential of parallel Earths in a way that few could have anticipated, creating different visual languages and aesthetics for each character even as they interacted, and bringing the energy of the comic book medium to movies in a way never-before-seen. Even if fans hadn’t been fans of alternate reality stories before the movie, they were almost guaranteed to be so afterwards.

That brings us to today, where the multiverse is at the center of onscreen superhero storytelling. The MCU is leaning heavily on the idea, thanks to Disney+’s Loki, and the most recent Spider-Man and Doctor Strange movies.

The multiverse is also as strong as ever in comics, whether it’s DC’s Dark Crisis event or Marvel’s Avengers Forever or Captain Carter series. There is, it appears, just something about superheroes that makes it seemingly impossible to keep them contained to just one world – or, for that matter, just one universe. But then, maybe that’s the kind of limitation best left to us mere mortals.

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Want to read some more cool analysis about overarching trends in superhero stories? Check out this Popverse piece on the future of Marvel Cinematic Universe films.