I've read mostly non-mathematical accounts of this interpretation so forgive me if I'm not making any sense. I have the impression that a many worlds theory is an application of our laws of the universe, to the multiverse. To make a simple analogy, it would be conceivable (?) that in one world a photon always passes deterministically through either slit (they would never have to account for an interference pattern, but then again we never really observe it do we?) and its inhabitants would arrive at a completely different view of the world. Why are we to suppose that our account of quantum physics (minus the collapse postulate) is "universal" or "multiversal"? Or in other words in the context of many worlds how confident should we be that our laws are a reflection of reality at large? Is it not strange to admit that there may be worlds which obey different rules based on interpretations we made about our world's rules?