via Futurology.comOne very prominent mind twister in both science fiction and real-life science is the concept of parallel universes. This is hardly surprising, since the idea of multiple copies of yourself existing at the same time is both existentially disturbing and thrilling.
I think it depends on how you define "parallel universe" and what school of thought you subscribe to. String theorist Brian Greene (of Columbia University) says that if you're an advocate of multiple big-bang multiverses, you'd have to leave your existing universe to visit another one... Which is about as possible as traveling back in time to BEFORE the big bang happened (read: not likely).
If you're a subscriber to the quantum mechanics school of thought, there's no need to leave your current universe as you're already inhabiting multiple alternate universes at the same time.
Michio Kaku believes that our universe will end up in a "big freeze" and that we'll be able to devise technology that'll allow us to travel between these realities.
All in all, NOBODY really understands how this works, not least of all because such a theory is completely un-testable at this point. It's definitely something being looked at and thought about though, as you can see in the videos below:
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