Is it possible to live another life in a parallel universe or omniverse? When you experience a déjà vu, are you drawing this experience from a parallel universe?
A parallel universe or alternative reality is a hypothetical self-contained separate reality coexisting with one's own. A specific group of parallel universes is called a 'multiverse', although this term can also be used to describe the possible parallel universes that constitute reality. While the terms 'parallel universe' and 'alternative reality' are generally synonymous and can be used interchangeably in most cases, there is sometimes an additional connotation implied with the term 'alternative reality' that implies that the reality is a variant of our own. The term 'parallel universe' is more general, without any connotations 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 relativistic limitations and the speed of light can be exceeded – would in general count as a parallel universe but not an alternative reality. The correct quantum mechanical definition of parallel universes is "universes that are separated from each other by a single quantum event."
Parallel universes are considered parallel because there is no way of reaching them. All other dimensions are not parallel, but more than likely most of them are. An Einstein Rosen bridge, or Wormhole, can take you to a different dimension. Note that the journey through space-time continuum could backwards age you, or wipe you from existence. More than likely, if you managed to get to the alternate dimension, then you would have no memory of how you got there. The dangers of time-space travel are still being investigated, and possibilities are growing.
Typically, parallel universes fall into two classifications. The first may be more accurately called a "diverging universe" whereby two versions of Earth share a common history up to a point of divergence. At this point, the outcome of some even happens differently on the two Earths and the histories continue to become more different as time elapses since that point. The second type is where despite certain, often large, difference between the two Earths history and/or culture, they maintain strong similarities. In such cases, it is common that every person in one universe will have a counterpart in the other universe with the same name, ancestry, appearance, and frequently occupation but often a very different personality.
We could all be living multiple parallel lives, because as scientists explore the outer reaches of physics and the cosmos, they're beginning to believe that parallel universes do exist and that they might determine the fate of humanity. The word "Universe" is supposed to mean everything that exists. Today, we're almost certain that our Universe is not all there is. There really could be parallel Earths, parallel you's, and parallel me's. It's hard not to wonder what our alter egos might be like, whether they are living out our most cherished dreams. But don't forget this possibility you could already be living the dream of another you from a parallel universe.
Scientists now believe there may really be a parallel universe - in fact, there may be an infinite number of parallel universes, and we just happen to live in one of them. These other universes contain space, time and strange forms of exotic matter. Some of them may even contain you, in a slightly different form. Astonishingly, scientists believe that these parallel universes exist less than one millimetre away from us. In fact, our gravity is just a weak signal leaking out of another universe into ours.