Thanks to the Marvel Cinematic Universe, the idea of other universes, timelines, and dimensions has become mainstream. We've all become well-versed in the possibility of other worlds out there. But how realistic is the idea? Some serious thinkers believe that the sort of universe in the MCU is possible. M Theory is a subset of string theory that seeks to explain all of the other possible dimensions and what is possible. Spoiler alert, there are 11 dimensions.