Background Independence in Physics

Gordon Belot

Any unified quantum theory of matter and gravity needs to incorporate into the fabric of physics the lessons implicit in general relativity. One of the most revolutionary features of general relativity is its background-independence: it treats space and time as actors in the drama, rather than as a fixed stage upon which the play is set. Opinions vary on how to make precise the notion of background-independence. I will discuss a few classic attempts which turn upon the notions of general covariance, absoluteness, and relationalism, and argue that none of them is adequate to our intuitions. I will then suggest a (deceptively simple) analysis of background independence: a theory is fully background-independent if according to it, no two physical possibilities correspond to the same spacetime geometry.

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