What worries a physicist about the quantum

The Edge.org has its annual question for intellectuals. Lee Smolin writes:

But there is another possibility: that quantum mechanics does not provide an explanation for what happens in individual phenomena because it is incomplete, because it simply leaves out aspects of nature needed for a true description. This is what Einstein believed and it is also what de Broglie and Schroedinger, who made key steps formulating the theory, believed. This is what I believe and my lifelong worry has been how to discover that more complete theory.

A completion of quantum mechanics which allows a full description of individual phenomena is called a hidden variables theory. Several have been invented; one which has been much studied was invented by de Broglie in 1928 and reinvented by David Bohm in the 1950s. This shows its possible, now what we need to do is find the right theory. The best way to do that would be to discover a theory that agreed with all past tests of quantum mechanics but disagreed about the outcomes of experiments with large, complex quantum devices now under development.

We know that such a theory must be radically non-local, in the sense that once two particles interact and separate, their properties are entangled even if they travel far from each other. This implies that information as to the precise outcomes of experiments they may be each subject to has to be able to travel faster than light.

This means that a complete theory of quantum phenomena must contain a theory of space and time. As a result I've long believed that the task of completing quantum mechanics and the challenge of unifying quantum mechanics with spacetime are one and the same problem. I also see the problem of extending our understanding of physics at the cosmological scale to be the same as discovering the world behind quantum mechanics.

This belief in a theory of nonlocal hidden variables is irrational. There is not a shred of theoretical or experimental evidence for it. All attmpts at such a theories have been miserable failures.