Parallel universe
Parallel universe may refer to:

Science
Many-worlds interpretation of quantum mechanics, which implies the existence of parallel universes
Multiverse, the sum of all universes, e.g. everything that exists

Philosophy
Possible world, a construct in metaphysics to bring rigor to talk of logical possibility
Modal realism, an account of possible worlds according to which they are all just as real as the actual world
Extended modal realism, the view that all worlds, possible as well as impossible, are as real as the actual world

Arts and media
Parallel universes in fiction, a hypothetical self-contained plane of existence, co-existing with one's own
List of fiction employing parallel universes
Alternate history, a genre of fiction in which historical events differ from reality
Alternative universe (fan fiction), fiction by fan authors that departs from the fictional universe of the source work

Literature, film, and television
"Parallel Universe" (Red Dwarf), a 1988 TV episode
Parallel Universes (film), a 2001 British TV documentary
Mirror Universe (Star Trek), a fictional parallel universe in the Star Trek franchise

Music
Parallel Universe (4hero album) or the title song, 1994
Parallel Universe (Garnet Crow album), 2010
Parallel Universe, an album by  Plain White T's, 2018
"Parallel Universe" (song), by the Red Hot Chili Peppers, 1999
Parallel Dimensions (album), by Perseo Miranda, 2008

See also
Metaverse, a collective virtual shared space
Alternate reality (disambiguation)
Multiverse (disambiguation)
Parallel World (disambiguation)