The hypothetical group of all the possible universes in existence. "Our universe is a very small part of the multiverse." http://en.wiktionary.org/wiki/Multiverse Hypothetical enlargement of the cosmos in which our Universe is but one of an enormous number of separate and distinct Universes. http://nedwww.ipac.caltech.edu/level5/Glossary/Glossary_M.html a theory that there is a mirror universe and when one makes a decision in this universe, an alternate 'you' in the other universe makes the opposite decision http://dictionary.reference.com/search?q=parallel+universe&r=66 A multiverse (or meta-universe) is the hypothetical set of multiple possible universes (including our universe) that together comprise all of physical reality. The different universes within a multiverse are sometimes called parallel universes. The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes, depend on the specific multiverse hypothesis considered. Multiverses have been hypothesized in cosmology, physics, astronomy, philosophy, theology, and fiction, particularly in science fiction and fantasy. The specific term "multiverse," which was coined by William James,[1] was popularized by science fiction author Michael Moorcock. In these contexts, parallel universes are also called "alternative universes," "quantum universes," "parallel worlds," "alternate realities," "alternative timelines," etc. The possibility of many universes raises various scientific, philosophical, and theological questions. http://en.wikipedia.org/wiki/Multiverse

"Parallel universe may refer to: Scientific articles: - Multiverse, the hypothetical set of multiple possible universes. - Many-worlds interpretation, of quantum physics. - Parallel Universes (documentary) - a BBC/Horizon documentary film Fiction & other Non-scientific articles: - Parallel universe (fiction), alternative universes, worlds, realities and dimensions in fiction. - Alternative universe (fan fiction), fiction by fan authors that deliberately alters facts of the canonical universe they're writing about. - List of fiction employing parallel universes. - Parallel Universe (album), by 4 Hero. - Parallel Universe, Leiahdorus second album. - "Parallel Universe" (song), a song by the Red Hot Chili Peppers. - "Parallel Universe" (Red Dwarf episode), an episode of Red Dwarf. - Parallel Universe (company), a film company - Multiverse (DC Comics), the multiverse within the fictional setting used by DC Comics. - Multiverse (Marvel Comics), the multiverse within the fictional setting used by Marvel Comics. - Mirror Universe (Star Trek), a fictional parallel universe in which several Star Trek television episodes take place." Source and further information: http://en.wikipedia.org/wiki/Parallel_universe

another universe existing beside our own where reality may be similar to this universe or vastly different. parallel universe theories have been explored in books, films and television for decades. a perfect example is in the star trek television show, where captain kirk and a few of his crew are in a transporter malfunction that switches them with their alternate selves. they find themselves in a "Mirror universe" where the federation is an evil dictatorship, promotions are over your superiors dead body "literally" and spock has a devilish goatee. another example is the marvel comics series "What if" which features a look at alternate/ parallel universes which hav diverged from the mainstream continuity. like "what if someone other than peter parker had been biten by the redioactive spider?" where flash thompson, betty brant and john jameson each had a shot at becoming spider man. "what if Uncle Ben had Lived?" "What if the Fantastic Four had different super-powers?" where ben grim had dragon like wings, sue storm was elastic, johnny storm was a bionic man and reed richards was a disembodied brain with psionic abilities. "What if Rick Jones had become the Hulk?" also in the stormwatch and authority comicbook series' parallel universes play prominently in many stories. in the television series sliders each episode took the four "sliders" to another parallel earth, which was different in some major way from their own. for example a earth where penicillin and other antibiotics were never discovered, resulting in illness being rampent and people liking like "bubble boy" obsessively protected from all germ transmission. or a world where England won the Revolutionary War, a world where 99.99% of all men died from a bio-weapon and the the few who survived are kept in breeding harems in a world dominated by women. in the s. m. sterling Dominion series we see a parallel earth vastly different from ours where eventually the human race is replaced with the genetically enhanced Draka and there Homo servus slave race engineered to be incapible of rebellion. http://en.wikipedia.org/wiki/Draka or in the steve gould novel "Wildside" where a group of teens explore through a portal into a parallel earth untouched by man, where global worming never happoned, sabretooth tigers and passenger pidgins still live and all the resources the human race have used up over the last few thousand years are there for the taking all over again if the heroes can;t protect the portal from the rogue agent who wants to steal it from them.