I haven't read that particular book, but I'm familiar with the theory. The idea has been around since the 50's. It seems a bit much to manufacture an infinite number of universes to satisfy a theory. It's fascinating to think about, it fits the behavior of subatomic entities, but to me, it's just too far fetched. And besides, there are several other competing theories. So, take your pick, I suppose.Well, I suppose we do not really have to call them separate universes. The fact remains is that there are "shadow" particles which sometimes interferes with particles that we see, and sometimes interfere with them.