Sheng exclaimed, "Indeed, you know about parallel worlds! During my travels, I learned of a legend of ten suns and twenty worlds. The sun you see daily might look the same to you, but they actually rotate from world to world. Similarly, these worlds look the same from the outside, but they're each different and independent."

"This is a little different from the parallel worlds theory that I've heard of. In my version, each choice you make can spawn two different worlds—for instance, a world in which I encounter you, and a world in which I don't—and perhaps even a world in which you're still alive. There's not just one world, but uncountably many worlds."

In this analogy, the universe...