The idea of a Multiverse is pretty widely accepted in pop culture now, but that hasn’t always been the case. DC first helped to craft the idea of a shared universe when they debuted the Justice Society of America in 1940. The team and comic took a number of previously standalone heroes and joined them together in a pioneering move. From there, the idea of mirror worlds was played with from time to time, but it wasn’t until the Silver Age that the concept of the Multiverse was born.

In 1960, DC and writer Gardner Fox premiered the idea of parallel Earths with the story “Flash of Two Worlds!” The comic saw Barry Allen and Jay Garrick meet, and the concept of multiple Earths was born. The Flash TV series has not only paid tribute to the comic, but introduced the idea of parallel Earths to the Arrowverse beginning last season. Since then, the gang have regularly traveled to other worlds and met up with various doppelgangers, mirroring the same surge in the comics. In an effort to understand the various worlds we’ve seen so far, and imagine the ones that could appear, here’s a quick guide to the most important Earths of the Multiverse.

Earths We’ve Seen So Far

Earth Two in the Speed Force on the Flash

Earth One

While technically every Earth views themselves as Earth One, this is the Earth that our main group of characters exist within. It’s here that Teams Arrow and Flash, along with the Legends of Tomorrow live. It’s also presumably the home to the worlds of the Constantine and Vixen series. While the events of the latter have been referenced on Arrow, the former is only assumed as Matt Ryan plays the character in all appearances. It could easily be set in an alternate Earth, but we’re yet to be informed of that. The one main omission is the events of Supergirl happen on a separate Earth (more on that below). There’s no word yet on where the CW’s Black Lightning will fall.

Earth Two

Earth Two is the first parallel world that our heroes discovered, and served as the primary focus for season 2. It’s not only the home to nerdy Barry, Detective Iris West, and a fully villainous Killer Frost, but also where Zoom originates. Harrison “Harry” Wells, our second Wells and the slightly less nefarious one, and his daughter Jesse Quick, hail from this world. It also served as the regular source of many of season 2’s metas, like Killer Shark.

Earth Three

Earth Three hasn’t been visited much, but its main resident is Jay Garrick's Flash. Here, Barry’s father is the Golden Age version of the Flash, and regularly tackles villains like the Trickster, sporting a look similar to the Joker. It’s also where Hunter Zolomon kidnapped Garrick and stole his helmet and identity for a time while he was posing as the Flash on Earth Two.

Earth Three on the Flash

Earth Nineteen

Earth Nineteen is where the current Harrison Wells, dubbed H.R., comes from. In reality, he’s sci-fi writer Randolf Morgan, and uses his genius friend’s identity as a front. He intercepts Harry’s cryptogram and joins Team Flash on Earth One, but not without some blowback. Gypsy, who shares Cisco’s powers, is also from Earth Nineteen, where she serves as a law-enforcing Collector. Earth Nineteen was previously the location of an invasion by an unnamed Earth, which caused crossing dimensions to become a treasonous act.

Earth Thirty-Eight

Finally, there’s Earth Thirty-Eight, the home of Supergirl and her collection of friends, allies and enemies. Barry’s crossed over to this Earth a few times, and Supergirl has come to Earth One as well. No word yet on where they’ll meet to battle the Music Meister, as it could be an entirely new dimension. As the sole show to operate on a different Earth, many are hoping Supergirl will join the main continuity in a Crisis on Infinite Earths-style event that could merge all of the various Earths like the comic book event did in the ‘80s.

Earths We Could See In The Future

Crisis on Infinite Earths Multiverse

Earth-Two

The comic book version of Earth-Two (which adds a hyphen) is the home to the Golden Age heroes of DC Comics. Here, the Jay Garrick Flash and Alan Scott Green Lantern are just some of the members of the Justice Society of America. Since a version of the JSA already exists on Earth One in the Arrowverse, this version of Earth-Two could see Golden Age takes on many of our heroes in a future episode. It could also be that Earth Three, home of the show’s Jay Garrick, also features some of these characters. Hopefully, we’ll get a chance to explore it more soon.

Earth-Three

Though the name would be change, Earth-Three from the comics would make for a great series of episodes for an Arrowverse crossover. It’s home to the Crime Syndicate of America, an evil version of the Justice League. A number of villains are also heroes, so this seems primed to make an exciting multi-episode arc where our heroes must confront villainous versions of themselves and work alongside altruistic takes on their greatest foes.

Earth-Four

Before Crisis on Infinite Earths, Earth-Four was the home to characters that DC acquired from Charlton Comics. Eventually, heroes like Blue Beetle and the Question would join the main DC continuity, but a version of this Earth would be a great way to introduce some of these characters to the CW. They could also serve as the answer to the Golden Age JSA. The Charlton Comic characters were also the inspiration for the Watchmen, and while we doubt they’ll ever show up on TV, we can certainly dream.

Worlds shatter in Crisis on Infinite Earths comics.

Earth-Prime

Over the years, Earth-Prime has gained its own superheroes, but it started out as the home of our reality. In the comics, characters would regularly cross over and interact with comic book versions of DC’s editor and writers. Supernatural was once known for its hilarious meta episodes where it sent up TV and the series itself. We’d love to see The Flash pull a similar move by sending the team to ‘our’ world, we’re they’re simply characters on a CW show.

Earth-C

Earth-C is (sadly) one of the least likely to appear on the show as it’s the home to Captain Carrot and His Amazing Zoo Crew. As a world full of anthropomorphic animals, this could make for a fun, surreal episode that’s either animated or done in claymation (à la the Community Christmas special). Perhaps after Mr. Mxyzptlk shows up on Supergirl, he can stop by The Flash and transport the gang to this alternate dimension.

Over the years, DC has actually created dozens of parallel Earths, and it looks as though The Flash is set to do the very same thing. This aspect of the show is unlikely to die, and the writers and producers are only going to get more confident about how zany the adventures are. While some of these Earths may seem like a long shot, we wouldn’t be surprised if some of the more bizarre versions (like Earth-Zero, an all-Bizarro world) begin popping up on the Arrowverse. When they do, we’ll be here to help you make sense of it all.

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Which other Earths from the comics do you hope to see on The Flash? Which parallel Arrowverse worlds have been your favorite so far? Let us know in the comments!

The Flash journeys to Earth Two next week for ‘Attack on Gorilla City’ at 8 p.m. on the CW.