Introduction

Michael Redhead began his Tarner Lectures by allowing that ‘many physicists would dismiss the sort of question that philosophers of physics tackle as irrelevant to what they see themselves as doing’ (1995, p. 1). He argued that, on the contrary, philosophy has much to offer physics: presenting examples and arguments from many parts of physics and philosophy, he led his audience towards his ultimate conclusion that physics and metaphysics enjoy a symbiotic relationship.

By way of tribute to Michael we would like to undertake a related project: convincing philosophers of physics themselves that the philosophy of space and time has something to offer contemporary physics. We are going to discuss the relationship between the interpretative problems of quantum gravity, and those of general relativity. We will argue that classical and quantum theories of gravity resuscitate venerable philosophical questions about the nature of space, time, and change; and that the resolution of some of the difficulties facing physicists working on quantum theories of gravity appears to require philosophical as well as scientific creativity. These problems have received little attention from philosophers. Indeed, scant attention has been paid to recent attempts to quantize gravity. As a result, most philosophers have been unaware of the problem of time in quantum gravity, and its relationship to the knot of philosophical and technical problems surrounding the general covariance of general relativity – so that it has been all too easy to dismiss this latter set of problems as philosophical contrivances. Consequently, philosophical discussion of space and time has suffered.

This point is best illustrated by attending to the contrast between what philosophers and physicists have to say about the significance of Einstein's hole argument.