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, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime. 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.