Parallel universe (fiction)

A parallel universe is a world or universe that exists outside of our own, but is similar to it in some ways. The trope of parallel universes is often used in fiction.

Examples

In 1884, Edwin A. Abbott wrote a novel called Flatland, about a world of flat, 2D shapes that discover a world of round, 3D shapes.

In 1905, H. G. Wells wrote a book called A Modern Utopia. In the book, two people from Earth go to a new world which is a utopia. Each of them has a doppelgänger there. Wells also wrote books where time travel changed history and created different worlds.

In 1934, Murray Leinster wrote a science fiction short story called "Sidewise in Time." In it, time changes—so that people from our world switch places with other people from other worlds— whose history is different from what they know. Some people go to a world where the Roman Empire still exists. There’s a world where the Vikings took over North America. One person ends up in a world where the Confederate States of America won the American Civil War.

In 1961, DC Comics published a comic book called “Flash of Two Worlds,” where the Flash runs so fast that he teleports to another world. Because of this, the original version of Flash, named Jay Garrick, and the new version of Flash, named Barry Allen, meet each other. Barry Allen’s world is called Earth-One, and Jay Garrick’s is called Earth-Two.

In 1967, Star Trek had an episode called "Mirror, Mirror," in which Captain Kirk switches places with another version of himself from a Mirror Universe where he and all his crew (except Spock) are evil.

In the 1970s, a show called “The Tomorrow People” involved time travel being used to change history and create new worlds.

Terry Pratchett’s Discworld books are set in a parallel universe. In “Lords and Ladies,” the characters talk about the idea of a multiverse.

The 1993 movie Super Mario Bros features Mario and Luigi traveling to a world where the dinosaurs never went extinct.

The 2009 movie Star Trek is about Spock and his enemy going back in time, changing the past, and creating a new universe.

In the television show Once Upon a Time, all fairy tales are true, but they happened in their world called The Enchanted Forest. The only people from our world who can go to the Enchanted Forest are people who write stories about what happens in it for people in the real world to read. It later turns out that not only are all fairy tales true, but all fictional stories are true. So if there’s an Italian version of Snow White and a French version of Snow White, then each one is real and exists as its world. The TV show featured iconic stories, including Frankenstein, Dr. Jekyll and Mr. Hyde, Twenty Thousand Leagues Under the Sea and Moby-Dick. When Emma Swan wishes she were never the Chosen One creates a new world—where she never existed, called The Wish Realm.

Since then, the Arrowverse superhero television shows and the Marvel Cinematic Universe have both used parallel universes as key plotlines.