Theoretical physicists talk about parallel or multiple universes a lot these days. The interesting video below explains that there are three main kinds of theories under discussion.
My favorite version is #1. It’s the kind of scenario described by the physicist Lee Smolin in a wonderful book called The Life of the Cosmos. Smolin suggested that we live in a universe that is fit for life (molecules stick together, for example) because a black hole in universe X will tend to generate a new universe Y that is similar to universe X, but not exactly the same (like parents have offspring who are similar but not the same). So there tend to be universes that are like the one we happen to live in, with lots of black holes and natural laws compatible with life. Cosmology meets the theory of evolution and explains why our universe is such a nice place to hang out.
If you’re interested, check out other videos on Henry Reich’s MinutePhysics channel: