From time to time the Magic Grandmother of Philosophy flies down from the sky and touches physics with her magic wand and it the field becomes slightly different. Philosophy is the careful examination of the concepts we use to think with. It can spark revolutions in thought. I've noticed it's not uncommon for people who have changed foundations in physics to have been educated in philosophy and even to have taught philosophy or held philosophy chairs at their universities for at least part of their careers. Wikipedia is wonderful for details like this. Maybe their experience in philosophy helped them, at a crucial moment, to ask a deeper question---which turned out (that time) to be the right one to ask. I think of Ernst Mach asking what acceleration might be relative to, how could you tell, and what caused objects to resist acceleration. He held a philosophy chair at the U. of Vienna for part of his life. People who critically explore the concepts that other people take for granted. Emmy Noether wondering where conservation laws come from. Maybe she wasn't officially a philosopher but wouldn't you say she thought like one? So I want to say the obvious thing, at least I guess it's obvious: the boundary of physics is not fixed, it's mixed. There is no clear impermeable demarcation between it and neighboring lines of investigation. I was struck by the philosophical novelty of this paper: http://arxiv.org/abs/1306.5206 The boundary is mixed Eugenio Bianchi, Hal M. Haggard, Carlo Rovelli In this case (of a revolutionary gambit that might or might not succeed) the philosophical opening moves, I think, go like this: with GENERAL COVARIANCE you can't have TIME until you have a solution to the equation, which is to say a geometric PROCESS. Time should hatch from the process. And the word "STATE" has too much the favor of "state at a particular time". State is a cognate of "status" or "standing". So maybe the Hilbert space should not be a space of states but a space of processes. And suddenly we have a new format for quantum field theory and quantum statistical mechanics---a new format that is general covariant.