String theories are strange. They require a spacetime of ten dimensions, at a minimum, or they won’t be mathematically consistent. This invites a rather obvious follow-up question: where are the extra dimensions? It could be the case that they are compactified, that they wrap in on themselves at shorter length scales than we are currently capable of investigating, like very tiny donuts.
String theories with different compactifications can be related through string dualities: they describe the fundamental space of the world in different ways but still give rise to the same observable physics. This has led some to conclude that the spacetime we observe must be an emergent phenomenon in string theory.
In this talk, I demonstrate that spacetime functionalism, which is supposed to give an account of the emergence of spacetime, instead implies that it is fundamental, in the context of string theory.