[Xcelerate]

> but how can we know for sure that it's intrinsic randomness?

We can't be sure (even though Luboš Motl disagrees). The universe may not be intrinsically random if superdeterminism is true. However, this isn't a popular idea in physics; in fact Gerard t'Hooft is the only Nobel prize winner I can think of that supports this idea.

Local hidden variable theories have almost all been ruled out by experiment in the last few decades (the same kind of theory Einstein was trying to find). There's still some loopholes, but, eh...

Colbeck and Renner have written a pretty powerful paper that given the assumption that measurements can be chosen freely, no extension of QM can have improved predictive power than the current theory of QM, regardless of whether this randomness "comes" from somewhere. Here's the paper: http://arxiv.org/abs/1005.5173