On the (In?)Stability of Spacetime Inextendibility

Leibnizian metaphysics underpins the near universally held view that spacetime must be inextendible – that it must be “as large as it can be” in a sense. But here we demonstrate a surprising fact within the context of general relativity: the property of inextendibility turns out to be “unstable” when attention is restricted to certain collections of “physically reasonable” spacetimes.