I'm listening once again to an audio book by Brian Greene on infinite universes. I think that I mentioned it before, but one of the concepts is so cool to me.
Here's the gist: given a finite number of types of particles and energy states, there are a finite number of combinations that can occur. That number is enormous - but finite. If the universe is infinite, or if there are an infinite number of finite universes, then there will be an infinite number of identical combinations of particles/states. Bored? Okay, here's what that means - right now, there could be an infinite number of yous reading this exact post thinking about an infinite number of yous reading this exact post. That's pretty amazing to me. There are also an infinite number of alternatives in which one or more things is slightly different - one or more decisions that were made differently in your life, for example. Also, an infinite number of alternatives in which things are dramatically different - like, an identical world, except no you. Or, no us...or no life...or no Earth...or no solar system...and on, and on.