This is an good visualization of the theory. (The original video I posted got removed at the source, so I replaced it with this one. Not bad, but longer.)
The multiverse theory is fascinating. We have good reason to believe there are literally thousands of other universes besides our own, in-which the laws of nature, the physics of those worlds, may be very different from our own. Read The Case for Parallel Universes.
One of my favorite science writers, Alan Lightman, sees the multiverse theory as generating a crisis of faith in science. Why? Because the search for universal laws of nature, the idea that the universe can be reduced to a set of basic universal principles that apply in all instances, is the sine qua non of all the sciences. But if there are other universes, with different natural laws, then the dream of science, in some since, is a leap of faith. We can only know our own world and the one set of physical laws that govern it. And that’s it. Our search for ultimate scientific truths, in other words, that tie all of nature and reality together, our attempt to Knock on Heaven’s door, is a grand illusion.