Chapter 15: Introduction

Abstract

Publisher Summary The nature of space and time is a traditional philosophical subject. Whether space is an independently existing substance and whether time is a measure of change in material processes or something that exists and flows even if there are no material processes going on are questions that go back to the very beginning of natural philosophy. Despite this longevity, no consensus has been reached, and these issues are still exercising the minds of both scientists and philosophers. The past few decades have even seen an upsurge of interest. This is because of a number of factors. Among these figures, the revival of the substantivalism versus relationalism debate as a consequence of the foundational studies of general relativity, especially the renewed attention for Einstein's notorious hole argument. The diffeomorphism invariance of the equations of general relativity appears to indicate that prima facie different models of the theory that are related to each other by diffeomorphisms actually represent the same physical situation. The only difference between any two such models is in the manifold points where events take place. If the verdict of physical sameness is accepted, the implication is that only physical objects and fields and their coincidence relations are relevant for the specification of the state of the universe. The identity of the spacetime points at which events take place plays no role. This suggests that it may be unnecessary to accept these points as independent parts of the ontological furniture of the world.