Review

Speculative physics, described without the least whiff of mathematics, but with frequent mentions of the fact that the mathematics is actually very difficult, and that much of it is brand new.

This is all about parallel universes, arising from string theory in about five different ways, from general relativity, from a particular interpretation of quantum mechanics, and from philosophy. Most of the string theory parallel universes seem to arise from the following argument:

• here’s a (mostly untestable) form of string theory.

• you can apply a certain mathematical transformation to certain equations in this theory.

• that transformation can be interpreted as representing a parallel universe.

• therefore, the theory is compatible with the existence of parallel universes.

• therefore, there might be parallel universes.

Anyway, it’s all vaguely interesting, but I didn’t come away feeling that I had learned much.

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