Structure, Individuality, and Quantum Gravity

Abstract

Afterreviewingvariousinterpretationsofstructuralrealism,Iadoptadefinitionthatallowsboth relations between things that are already individuated (which I call ‘relations between things’) and relations that individuate previously un-individuated entities (‘things between relations’). Since both spacetime points in general relativity and elementary particles in quantum theory fall into the latter category, I propose a principle of maximal permutability as a criterion for the fundamental entities of any future theory of ‘quantum gravity’; i.e. a theory yielding both general relativity and quantum field theory in appropriate limits. Then I review of a number of current candidates for such a theory. First I look at the effective field theory and asymptotic quantization approaches to general relativity, and then at string theory. Next, a discussion of some issues common to all approaches to quantum gravity based on the full general theory of relativity argues that processes, rather than states should be taken as fundamental in any such theory. A brief discussion of the canonical approach is followed by a ey of causal set theory. The chapter ends by suggesting a new approach to the question of which spacetime structures should be quantized.