We talked about the many-worlds hypothesis in my quantum mechanics class today — the idea that there are multiple universes that exist in superposition with each other, overlapping intangibly. It’s a fascinating philosophical idea proposed to explain some of the reasons quantum mechanics is unexplainable (such as random wavefunction collapse), and basically states that any time a random quantum mechanical process is observed, all possible outcomes occur and then branch off, creating new individual “worlds” where each outcome occurred uniquely.
Anyway, it’s really interesting and totally untestable. My professor doesn’t think the idea holds water, however, because if you do believe in the many-words interpretation, you also by definition believe that there’s another universe (or even an infinite number of universes) in which you simultaneously do not believe the many-worlds interpretation. And then you’re just contradicting yourself.