I'm a bit late to the game on this one, but according to current physical theory, two universes that began identically would not stay identical due to quantum mechanical fluctuations.
Regarding hidden variables (by which I mean the possibility that Quantum events are actually determined by some unknown physics) several results restrict these theories. We know that they would have to be:
(a) non-local, communicate faster than light
(b) contextual, particles are aware of and contain information on the state of every other particle in the universe
(c) have essentially infinite complexity, each particle stores an infinite amount of data
Which I think is just as strange as quantum mechanics.