Calling them universes is problematic because everyone thinks of bubbles next to each other. That's not what many worlds says at all. Think of a Stern Gerlach e

Calling them universes is problematic because everyone thinks of bubbles next to each other. That's not what many worlds says at all. Think of a Stern Gerlach experiment with the particle spin up or spin down. The wave function after traversing the magnet has two distinct humps. With classical observers, the universe goes one way or the other. Many worlds theory says that there is no classical observer, so the wave function of the whole universe ends up with two humps. If you squint and look at it funny you can call each hump its own world. Thus the name.