Max TegmarkMax Tegmark is a professor of physics at MIT specializing in cosmology. He has dramatically extended Hugh Everett, III's theory of many worlds to describe four possible levels of what Tegmark calls the "multiverse." Like many mathematical physicists, he thinks the universe "Is" mathematics. His popular 2014 book is called Our Mathematical Universe..
Tegmark thinks consciousness is a mathematical pattern.
The Four Levels of the MultiverseA Level I multiverse is based on the infinite nature of our universe (as was David Layzer's). They are both close to the "possible worlds" of philosopher David Lewis, who said any possible world must exist somewhere. There is room in an infinite universe for an infinite number of merely "observable" universes like ours, which has a finite distance to our "horizon," beyond which we will never see. Tegmark's Level I also depends on Alan Guth's theory of an inflationary origin of our universe and the so-called "eternal inflation" of other "universes." The law of physics and the natural constants are the same in all these Level I "universes." But different universes may have different histories. The idea of another universe with a "doppelganger" of Tegmark (or Layzer) who up until a certain moment in time is identical, but then does something different is mathematically absurd. A Level II multiverse changes the fundamental laws and constants of physics to be merely "effective laws" that can vary from place to place. Fine-tuning may provide evidence for Level II. A Level III multiverse is based on Hugh Everett's basic idea that the quantum wave function never collapses. Possibilities do not exist. Randomness is only an illusion. A Level IV multiverse includes universes that have different fundamental laws of physics. All the other "universes" in our Level I multiverse are completely and forever unobservable (by definition). All multiverses above Level I violate the cosmological principle, that laws of nature, physical constants are identical everywhere. Layzer's "strong cosmological principle" assumes that statistical properties are the same everywhere. "Eternal inflation" denies that. Definitions of Tegmark's Multiverse Terminology.