Modular spacetime
String theory is canonically accompanied with a space-time interpretation which determines S-matrix-like observables, and connects to the standard physics at low energies in the guise of local effective fi eld theory. We have recently introduced metastring theory as a reformulation of string theory which does not rely on an a priori spacetime interpretation or a presumption of locality found in local effective field theory. In this essay, we focus on the concept of modular spacetime as the natural quantum gravitational notion of spacetime that emerges from metastring theory.