If you want a rigorously defined and clear version of many worlds, I recommend http://arxiv.org/pdf/0903.2211.pdf http://arxiv.org/pdf/0903.2211.pdf It uses th

If you want a rigorously defined and clear version of many worlds, I recommend http://arxiv.org/pdf/0903.2211.pdf http://arxiv.org/pdf/0903.2211.pdf It uses the (uncollapsed) wave function to have a mass density on physical space. There are many realities, if you like, implied, but they all move about in a self-consistent way. The analogy is that it is as if two tv channels were overlying each other. You can follow each separately if you watch the evolution, but at any one time it would look a bit like a mess. The problem with just having the wavefunction and nothing else is that it is not at all clear what the probabilities would be about. You need something that the theory describes that makes contact with our 3 dimensional experience.