alternate universe

A parallel universe, also known as an alternate universe or alternate reality, is a hypothetical self-contained reality co-existing with one's own. A specific group of parallel universes are called a "multiverse", although this term can also be used to describe the possible parallel universes that constitute reality. While the three terms are generally synonymous and can be used interchangeably in most cases, there is sometimes an additional connotation implied with the term "alternate universe/reality" that implies that the reality is a variant of our own, with some overlap with the similarly-named Alternate history. The term "parallel universe" is more general, without implying a relationship, or lack of relationship, with our own universe. A universe where the very laws of nature are different – for example, one in which there are no Laws of Motion – would in general count as a parallel universe but not an alternative reality and a concept between both fantasy world and earth.
The actual quantum-mechanical hypothesis of parallel universes is "universes that are separated from each other by a single quantum event."

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