Parallel universe
In science fiction a parallel universe is a separate reality from the universe the show normally occupies. Usually, events in the parallel universe unfold in a slightly different manner than in the "primary" universe.
In Star Trek
The most often seen parallel universe is the one from the TOS episode "Mirror, Mirror". In this universe, the Federation is an evil "Terran Empire". Every person in the standard universe had an "evil twin" in the parallel one. This universe later appeared in DS9 and Star Trek: Enterprise.
In Stargate
In the Stargate universe, there are many parallel universes. Some of the alternates have Earth under Goa'uld control.
One point of contact between the universes is the Quantum Mirror. In the episode "There But For the Grace of God" , an alternate Daniel Jackson escaped from his Earth which was being over-run by Goa'uld. In another episode, "Point of View", an alternate Samantha Carter who was a civilian scientist married to O'Neill escapes the Goa'uld through the Quantum Mirror, but the alternate Carter starts to suffer from entropic cascade due to the two Carters being so different.
Another gateway between universes was the Stargate itself. In "Ripple Effect," multiple SG-1 teams arrive in one universe due to a black hole affecting the wormhole.
In 2008, the Atlantis-1 team went aboard a reality jumping Daedalus which was just going into random realities. they eventually managed to get back to their own reality and escape[1].
Real life
There is no supporting evidence for the existence of parallel universes in the real world. Usually the phrase is used as a figure of speech. For example, someone daydreaming is often said to be off in his own little universe. However, there are certain deluded crackpots who insist that someone using that phrase must be speaking literally. More specifically, George Lucas has stated the Star Wars Extended Universe is a parallel universe and Trektards insist he must be using the Star Trek definition of the term rather than as a metaphor the way a normal person would.
- ↑ SGA: The Daedalus Variations