Schroedinger thought that was absurd, and created his famous cat-hostile thought experiment as a demonstration of how ridiculous the idea of superposition was: So then a cat could be both alive and dead at the same time, until you look? Then it suddenly becomes one or the other? Pffshhhh!

The "Many Worlds" interpretation, however, says that a photon travels every possible path, but in separate universes, each of which is just as real as the others. So a "superposition" is two or more universes that haven't been pried apart just yet. There's no collapse, but rather a split; after which one universe has one less cat than the other.

This theory, originated by Hugh Everett, has become the favored explanation among many of today's most prominent physicists, most notably Sean Carroll and David Deutsch.

Albert Einstein, when he wrote the famous quote "God does not play dice with the universe," was in a sense supporting the "Many Worlds" theory, which does away with randomness by postulating that everything possible happens, whether likely or not. Stephen Hawking has apparently also made statements which appear to support the theory.

In some popular books and movies, this theory is interpreted to mean "You can make your own reality." The theory, however, says no such thing; it merely says that subatomic events play out every which way, rather than just one way. Interpreting that to mean that you can have any reality you want is quite a stretch. Fun to think about, but not at all what the theory says. But oddly enough... (More)