multiverse isn't really that cheap, the logic makes sense. a cheap theory would be http://en.wikipedia.org/wiki/Novikov...ency_principle
anyways, back to multiverse. level 1 for example, especially makes sense, in short it's saying given infinite space, beyond our cosmological scope, events can duplicate the exact same way as it did on earth, with slight differences, repeated with more slight differences elsewhere in the universe. This is straight math of probability really. it's level 3 that's used in many fictions, the many worlds interpretation, and the one most people associate with multiverse theory.