ABSTRACT
This chapter examines a purely metaphysical argument for spatial anti-realism; the claim that our universe is not in fact spatial, despite appearances that suggest the contrary. In The Case for Idealism Foster develops an argument intended to establish that the physical world is not be a part of what he calls 'ultimate reality', and the key step in reaching this conclusion is an argument for spatial anti-realism. Foster's argument poses a threat even for realists. Poincaré's conventionalism might easily be taken to have ontological implications: Physical space has the geometry specified by our best physical theory. Substantivalism, in its traditional guise, is the doctrine that space is an entity in its own right, possessing its own inherent structure. A nomologically deviant physical world is one in which nomological uniformity would be brought about by some alteration in the geometry of the world.
