Our Mathematical Universe: My Quest for the Ultimate Nature of Reality by Max Tegmark.

Abstract

Max Tegmark is a well-known physicist who has authored or co-authored more than 200 papers on the subjects he writes about in Our Mathematical Universe (OMU). In the opening chapters of OMU he takes us on a journey with often humorous anecdotes into our universe as if it were only one of an infinite number of parallel universes—a subject I wrote about in 1988 (Wolf 1988)—that I believe the author says consists of what he labels as external reality (ER). After taking us on this journey into our own known universe, he points out why it is that we don’t see these other universes in our everyday reality we experience as “out there.” It is due to a discovery he made (but was scooped by other physicists) called decoherence theory (for those of you a little more adept at quantum physics, this theory shows how density matrices get stripped of their off-diagonal terms when interactions with the environment are taken into account) that shows how ordinary but often invisible and uncontrollable environmental processes (like cosmic rays and neutrinos) as well as ordinary processes such as air movement and heat tend to spoil the many interference effects that parallel universes would indicate as present in our everyday world. This doesn’t throw away the existence of parallel universes; it just makes them hard to see. Nevertheless they are there.