Yeesh, over a month and no one has read anything? I'm reading The Hidden Reality by Brian Greene. It's about parallel universes and the concept of a multiverse and how different variations of the idea factor into, or arise out of, different physics theories. He covers about ten different possibilities, also delving into the underlying theories (string theory, parts of quantum mechanics, and so on) as he does so. Greene does go a bit heavy on the string theory relative to other areas but I'll excuse him that because (a) some of the most interesting multiverse ideas come from that field and (b) he is working in that field so probably knows it better than some of the others.
The problem, as with any highly theoretical area of science, is how to test the hypotheses. Even Greene, who is working on, and an advocate for, string theory, concedes it may be a long time before we can validate even one of these theories. Still, it makes for some interesting speculation and along the way, he explains things like branes (an important element of current string theory and at least one cosmological theory) better than I've seen done before, at least to the extent that I can now grok them to some degree.
As you might guess, this is not a light read being theoretical physics by a theoretical physicist. Still, he does a decent job of explaining things in a way that an educated layperson should be able to follow.
