I read The Fabric of Reality many years ago.
I read The Fabric of Reality many years ago. Deutsch makes a compelling case for the multiverse in a variety of ways and had me convinced at one time, but like many proponents of the multiverse he pretends that the only alternative is “wavefunction collapse”. That is a strawman argument. Sum over histories does not require that all the paths be followed. Indeed, that is not what we actually measure. We only measure one path. You need to invoke not only multiple paths but multiple scientists measuring those paths, one for each path, in order to support the multiverse. As I argued in the article, the alternative is a dual state model where you have one universe, one particle, one path in the guiding function and a wavefunction as well. You cannot distinguish mathematically the predictions of a nonlocal hidden state theory from a no-hidden state multiverse theory.