[azalemeth]

There's also the problem of fine tuning -- why is the fine structure constant roughly 1/137? If it were different from its current value by a tiny amount, the universe as we know it wouldn't exist. Is the anthropocentric principal the only explanation we have -- it has the value it has because it produces a universe in which we're able to observe it?

And I guess less formally there's also the problem of complexity: condensed matter physics exists because trying to solve the standard model for a solid directly is both incredibly infeasible (think "cost of flipping bits in the calculation far extends that of all matter in the observable universe") and fails to capture the emergent phenomena in a natural way.

[robertlagrant]

The other theory is there are infinite universes somehow being created all the time by every choice. Which to my mind isn't very Occam's Razor-ish. But it does exist as a theory.

[mr_mitm]

You mean the Many-Worlds interpretation? That's not every choice, but every quantum measurement. And it's not necessarily an infinite number. And it's not a theory, but an interpretation. And it's actually very Occam's Razor-ish (at least that's what proponents claim), because it needs less postulates than the standard Copenhagen interpretation. The many worlds are a consequence, not a postulate.

[naasking]

It's the multiverse theory, typically discussed under the framework of string theory.