Originally Posted by MaartenVergu
The "singularity" is just where the current theory breaks down. We don't actually know what the state of the universe was at t=0 because relativity can't deal with that singularity. Perhaps when we get a theory of quantum gravity we'll have something that can describe the state of the universe at t=0. Maybe it will turn out that there was a time before that, or maybe it won't. We don't actually know yet.
But while there may be some things we don't know yet, there's a lot that we do
know. For instance, the state of the universe a nanosecond after
As for QM, while there's still work being done in quantum foundations, the Everett interpretation is pretty clear and mostly understood at the fundamental level, and it's consistent with everything we know. There's some question about where the probabilities arise in a deterministic theory (which Everett is, if you look at it from the entire wave function), but those questions seem to be mostly answered.