I thought I knew where this story was going — to a place of comfort, thinking that somewhere there’s a universe where things worked out differently. Borges has other plans, and the end of this story was a doozy.

Mr. Smyth teaches eleventh-grade physics, and this week they’re learning about the Many-Worlds Theory. They’re discussing the multiverse, the idea that every choice a person could make leads to another version of the universe, another version of themselves.