A parallel universe, also called an alternate universe, world, or dimension, is a tool used in stories to imagine a universe that exists alongside another. This idea helps writers explore different story possibilities. All possible parallel universes that make up reality are often referred to as the "multiverse."

This tool helps stories in several ways. It allows stories to include events that might break the rules of how the world works. It also lets characters meet and interact with different versions of themselves or others from their own universe, which helps characters grow. Additionally, it provides a starting point for stories that imagine different versions of history or other imaginative ideas.

History

One of the earliest examples of parallel universes in science fiction is Murray Leinster's short story "Sidewise in Time," published in 1934. While this story was not the first to use the idea of parallel universes, it helped make the concept more widely known.

The idea of parallel universes became popular in superhero fiction when issue 123 of The Flash, titled "Flash of Two Worlds," was released in 1961. In this story, two versions of the Flash—Barry Allen from Earth-One and Jay Garrick from Earth-Two—meet. This event introduced the concept of the DC Comics multiverse.

In the late 2010s and early 2020s, the multiverse appeared often in popular media, especially in superhero films. Examples include the Marvel Cinematic Universe (MCU), the animated Spider-Verse franchise, and the 2022 film Everything Everywhere All at Once. Some filmmakers and critics, such as MCU director Joe Russo, have noted concerns that movie studios might use multiverse stories to take advantage of already popular characters and ideas, which could harm originality and creativity in filmmaking.

Associated genres

Isekai is a type of Japanese fantasy story found in books, comics, cartoons, and video games. These stories are about a regular person who is moved to or stuck in another world. This other world may already exist in the main character's world as a fictional place, or the character may not know about it at all.

Fan fiction

In fan fiction, parallel universes are often used as a setting for stories that are different from the original fictional universe the fan work is based on. These stories are typically called "alternate universe" works, or "AU" for short. Common reasons for writing these stories include exploring different story ideas not shown in the original media or changing parts of the story that fans did not like.