If parallel universes do exist, then many theories suggest that we are ‘stuck’ in this one. The existence of a multiverse is a hotly debated topic among scientists, and some people think that because it’s such a radical idea which probably can’t be proved or disproved, that the subject should just be dropped!
I guess you can see parallel universes as a geometrical problem, in that the universe is 3-dimensional and we simply can’t see a 4th dimension (like a stickman/woman on a piece of paper, their world is 2D, nothing has any thickness and there’s no way to know a 3rd dimension even exists). We know that dense objects can distort spacetime, so one possibility is that black holes could create some sort of link.
Some people think the weird stuff we see at a quantum level is the result of an ‘exchange’ between parallel universes, so there’s another idea.
Like most awesome questions, the answer is “dunno; maybe with black holes or maybe with quantum stuff”! Ha!
As for showing us all we ever need to know.. well it would show us every possible way that things could have turned out at *this moment*, but since we’re not talking about time travel then I suppose some things still may be unknown, because there’s not been enough time for that particular outcome to happen.