This document discusses the relationship between physics at different scales and theories of space-time and gravitation. It describes how quantum field theory describes small structures while general relativity describes large structures and gravitation. String theory attempts to unify these descriptions by proposing fundamental strings that can appear as different particles. Recent work has found mathematical connections between topological string theory, which counts curves on Calabi-Yau manifolds, and the physics of melting crystals, providing support that string theory can describe quantum fluctuations of space-time known as the "quantum foam".