The Universe Next Door... are we really part of a multiverse

Ive read several books on cosmology, string theory etc, etc, and the book that sticks in my mind the most is Marcus Chowns' "The Universe Next Door". It sticks in my mind firstly because its very easy to read yet still makes references to actual science and mathmatics. also because Marcus brings to light some very profound theories and scientific implications, such as, there is infinity versions of ourselves and because of this we are all, in a sense, imortal. This is based on mathmatics and science and seems to be very plausible and the principle is appararently actually used in quantum computers. Has anyone read this book or have any imput on the many worlds theory/principle (Max Tegmark).