Science fiction movies and comic books made a lot of money by imaging parallel universes. You know... the idea that there are multiple Earths, many with a Clark Kent (and so a Superman)?
Sean Carroll says it's more than imagination. Carroll is a theoretical physicist at Cal Tech, and he says new versions of us are splitting into separate universes all the time.
The one on THIS Earth wrote a soon-to-be-published book, . It lays out his theory, and the general crisis he sees in physics and how it is understood and taught. The author visits with enough information to blow many minds.