There are many open-questions in all the theories I've heard of. If you search for a Penrose video or two you will find one where he discusses the problems he has with string theory and, in particular, the Multi-verse idea (which is an outgrowth of string theory, specifically, I think). I've posted a few of his video interviews in the past.
The problem with STRING THEORY (and thus, I believe, with Multiverse which, as I said, apparently relies on String Theory) is that the universes are so separated that there not only is no obvious way to test for it - it appears to be IMPOSSIBLE to ever prove it, at all, as a precondition of string theory!
BTW, there are MANY unresolved issues in physics. I thought we were talking about possible theories for the origin of the universe ... which is pretty much tantamount to origin of the Big Bang, at this point (aka, what came BEFORE the "Bang").
I don't think Copenhagen Theory addresses the origin question, does it?
Again, I am not a physicist, just a lay person interested in the topic quite a bit and for some time.
Penrose admits that his "theory" is more of a hypothesis at this time, and needs someone else to work out the math (he is in his nineties now). What it DOES have going for it, is that if there were "prior" universes as he hypothesizes, they WOULD be expected to leave a clear signal in our own "Big Bang". And so, indeed, when the microwave background radiation was recently measured:
The background was NOT uniform. What does that matter?
(1) String/Multiverse says it should have been uniform.
(2) Penrose's hypothesis says it would NOT be uniform, as prior gravition in any previous universe would affect the starting conditions IN ACCORD WITH HIS HYPOTHESIS.
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