What defines quantum physics? The mathematical formalism is very well defined, but we don’t know which physical principles enforce those mathematics (whereas we know, for instance, that the formalism of special relativity is enforced by the constancy of the speed of light). In a sense, we are still stuck in the “shut-up-and-calculate” mood.

A definition of quantum physics in terms of physical principles would not only be a great advance in the task of communicating science to the non-expert: even among the experts, there has been a growing desire to define "quantum" in physical terms. Several such principles have been proposed in the past few years. Some have come pretty close to matching the predictions of quantum theory, but it is known that none of them is exact.

The new principle that we propose to study in this project is based on reversing a common observation: we don't see quantum phenomena in our everyday life. We suggest that this may not only be a fact to be noted, but the very definition of the quantum world: maybe, if physics were only slightly different, we could see non-classical behavior even at the macroscopic level. The non-classical behavior that we shall focus upon is the violation of Bell inequalities, which has recently received a strong confirmation in three independent “loophole-free” experiments.