Parallel Worlds Science Fiction

Parallel Worlds Science Fiction are stories about traveling to parallel worlds or universes. The parallel world can be vastly different from our own, or very recognizable. While Parallel Worlds and Alternate History stories frequently overlap, generally, Parallel Worlds differ from Alternate History because a parallel world exists alongside our own. There are also some tie ins to Time Travel subgenre as well, with the parallel world conceit used to explain the grandfather conundrum (if you go back into the past and kill your grandfather, why you might still exist, the answer being that such an action kills your grandfather in a parallel world while you exist in a world your grandfather didn't die).

There are an infinite number of parallel universes--at least theoretically. This idea is based on probability, think about flipping a coin. For example, in the animated series Futurama, the episode "The Farnsworth Parabox" the Planet Express team enters a parallel world where the key difference is that coin flips have opposite outcomes. The concept can be extrapolated out infinitely, every time something happens, something else could have happened and did happen, just in a parallel world.

You can view the crowd-ranked "Popular" Parallel Science FIction Book list and vote and/submit entries to it.

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Level of Real Science
Low. While some scientists may reasonably postulate the existence of parallel worlds within a grand multiverse, they do not believe that travel between them is possible. With little real-world science applicable to the existence and travel between parallel worlds, this sub-genre has weak scientific explanations, like wormholes and hyperspace.
Level of Grand Ideas/Social Implications
High. Unless the story is a comedy or a pulp, chances are the level of grand ideas is high. Parallel Worlds stories have been used for social commentary and historical speculation since its inception.
Level of Characterization
Moderate. Characterization is a large component of world-building for Parallel Worlds Sci Fi. Characters are how readers are transported and connected to these fictional parallel worlds so characters have to be three dimensional otherwise readers will not be invested and will not be able to follow the story. That being said, a Parallel Worlds/Pulp Sci Fi crossover is not likely to have original characters.
Level of Plot Complexity
Moderate. In its more simplistic understanding, Parallel Worlds Sci Fi has two types of plots: someone from our world is transplanted to another world and goes on adventures, or a communication or visitor from another world has some kind of impact on our world.
Level of Violence
ariable. There is lots of freedom for writers of the Parallel Worlds sub-genre--it is truly a genre of anything can happen. As such, violence can be graphic or nonexistent.

Related Science Fiction subgenres

Alternate History. Frequently, a parallel world is much like our own, but its timeline is really an alternate history. Also see our Best Alternate History list
Time Travel. If time travel is possible, so too should travel to parallel worlds. Both of these sub-genres have similar tropes like wormholes to explain how characters are able to traverse time and space. Pulp Science Fiction. The pulp writers grabbed hold of the parallel worlds concept and used it for many sensational stories.

Popular Parallel Worlds Science Fiction Books

1 What Mad Universe

By Fredric Brown. A Sci Fi pulp magazine editor is transported to a parallel universe where Earth is at war with aliens, among other things.
2 Crosstime Traffic

By Harry Turtledove. A series of books where the technology to access parallel universes with alternate histories has been developed and is monopolized by the company Crosstime Traffic.
3 Wildside

By Steven Gould. High school students pass through a portal to a primeval Earth where humans have never existed.
4 Einstein's Bridge

By John Cramer. A Hard Sci Fi take on the Parallel Worlds story.
5 The Architect of Sleep

By Stephen Boyett. A parallel world where evolution has taken a weird path.
6 Yellow Blue Tibia

By Adam Roberts. A meta-fictional novel where there are multiple parallel worlds and aliens.
7 His Dark Materials

By Philip Pullman A trilogy of young-adult books, where there is a world that we recognize and a fantastical world.
8 The Sundered Worlds

By Michael Moorcock. A novel that introduces the concept of the multiverse.
9 The Number of the Beast

By Robert A. Heinlein. A story that is a bit parody and a bit homage of the early pulp novels told in a diary format by characters who can traverse six dimensions.
10 Worlds of the Impirium

By Keith Laumer. A story that is a bit parody and a bit homage of the early pulp novels told in a diary format by characters who can traverse six dimensions.
11 The Dark Tower

By Steven King. For a fantasy-ish recommendation, which features a whole many worlds concept.