Let us try to focus. First a parallel universe would have to be existent independently of the mind of the self - it would have to be more than imagination. Second when and if discovered to exist it would require analysis to be sure of compatibility - the real possibility must be considered that some parallel universes would be antagonistic to this one and going there may cause 'all hell to break loose'. Third: Once discovered and defined method of transport would have to be found - not likely that we would find 'Stargates' as in the Sci-Fi series SG-1 left by a group of so-called 'Ancients';
BUT according to some philosophical systems such as Platos
there are a priori ideal forms that are there for us to discover. In that case the discovery and proof of a parallel dimension might in itself open the gate to the discovery that allows entry into that parallel dimension. As
Einstein's E=MC2 allowed for the unleashing of nuclear power
some other mathematical formula may allow the opening of Stargates to other universes. To date all we have is Quantum
Mechanics {Quantum Physics} which does in fact indicate the very real possibility of a parallel universe.

Or as stated at the beginning of this thread:

Some physicists now accept the possibility of parallel universes.

Supposedly there is proof of this. Here is a quote from an article by John Brandon {Published April 05, 2010}
titled "Freaky Physics Proves Parallel Universes Exist":

"Look past the details of a wonky discovery by a group of California scientists -- that a quantum state is now observable with the human eye -- and consider its implications: Time travel may be feasible. Doc Brown would be proud.
The strange discovery by quantum physicists at the University of California Santa Barbara means that an object you can see in front of you may exist simultaneously in a parallel universe -- a multi-state condition that has scientists theorizing that traveling through time may be much more than just the plaything of science fiction writers.
And it's all because of a tiny bit of metal -- a "paddle" about the width of a human hair, an item that is incredibly small but still something you can see with the naked eye.
UC Santa Barbara's Andrew Cleland cooled that paddle in a refrigerator, dimmed the lights and, under a special bell jar, sucked out all the air to eliminate vibrations. He then plucked it like a tuning fork and noted that it moved and stood still at the same time.
That sounds contradictory, and it's nearly impossible to understand if your last name isn't Einstein. But it actually happened. It's a freaky fact that's at the heart of quantum mechanics......"

-It is a question of fully understanding the meaning of dimension.