The multiverse theory seems to me to come from two different ideas and or observations and I think either one is just dandy. Today, there is a debate about whether light is a particle or a wave, or some fancy combination of both. By particle, I mean individual "photons" of light and when I say wave, I mean the electromagnetic wave that propagates all around us allowing us to see. So, which is it? Well if you use what is called the "Double-Slit Experiment," you can demonstrate that light acts like a wave. By shining a laser at a double slit, you set up an interference pattern on a screen beyond the slit like so:


The second idea is much simpler and I don't think there are any proofs yet for this. It is merely that every choice that anybody in any time has ever had to make has spawned a parallel universe; one where you did the alternative to whatever choice you eventually made. One where you went with brown socks and then destroyed the world and one where you stuck with white socks and had a good day at school. Get the drift? Good. It makes for fascinating discussions about science, psychology, morality, and Western civilization. For your viewing pleasure, I have drawn the first four dimensions and then what the multiverse would be like. Think of the sphere as one time unit. (The fourth dimension having popularly been accepted as time.)

Somewhere, and most likely not to far away down that imaginary line of universes, is a planet Earth where the sci-fi TV show Firefly did not get canceled. It got signed for five or six or even more seasons and went on to great things. I am going to go to this universe someday and bring back the DVD sets of these seasons, so that this world doesn't have to suffer the stupidity of certain network executives and their shortsightedness by canceling the show before it even had a chance.
(Yes, you read all that sci-babble for that. Sorry)
p.s. Even more astonishing, though I didn't include any numbers in my picture, is that these parallel universes don't necessarily have to be at the same time in...well time. You could go to a universe that is our exact universe except at an earlier or later time frame. How cool would that be?