The theory goes that there are only a certain number of combinations of particles possible. There's only so many possible combinations, and in a large enough universe, all those bits are inevitably going to wind up in the same place and create another you. Scientists don't actually know how big the universe is. If it happens to be infinite, which some think it is, then the fact that you have a cosmic twin is downright certain. It's not likely that you'll ever cross paths. Science's prediction is that your doppelganger lives about 10 to the 10^28 meters away. In movies, you always see that fight between the devil and angel versions of the characters. What if there really is a good and bad version of you?