This from EarthSky:
Many universes? Until recent decades, most astronomers would have told you that, by definition, the word universe means all there is. That word was used to describe all space, time, matter, physical laws and constants. But now a new word – multiverse – has entered the language of scientists.
Not all scientists agree, but some – including Stephen Hawking, for example, and Alan Guth of MIT – believe there’s scientific justification for a multiverse, many universes springing into being, possibly existing simultaneously, each possibly with its own physics. If true, then our universe of stars and galaxies is just a small part of this vast assemblage of many universes.
There is a growing interest in parallel universes, rather than just one universe, and not just one big bang, but several. This is discussed in http://earthsky.org/space/bumping-up...llel-universe?