When I looked into the concept of 'multiverses', I began wondering exactly what scientists think they are talking about. For instance, do they actually believe that at the outer bounds of our Universe there is another one? ....
It seems as if astrophysicists have come to that same unexplainable open end as atomic physicists. We wanted to find the most fundamental particle in the Universe (which is, in some ways, synonymous with the quest to determine a 'Theory of Everything', which the concept of 'multiverses' seeks to explain), so we looked deeper...then we looked deeper...and deeper...until we found that when you start getting down to the those fundamental particles, you begin to find that there is no objective answer, really....
I guess, my critique of the multiverse theory is that it cleverly diverts us from answers by making a broad assumption about things that cannot be tested. The same thing occurs when scientists trying to explain how life began on Earth fall to the idea that "aliens planted us here" or "we came from Mars". All they are doing is coming up with a fantastic story which moves the problem from a place we can study to a place we can't....
All in all, the 'multiverse' theory is certainly fascinating...I just question the value, really. What does it actually tell us about our Universe? Not much. If anything, its value is in finding some vaguely believable way to describe the much older notion that there are things in this Universe which just never seem to make sense without a little imagination.