Diff gauge symmetry

Diff gauge symmetry, or diffeomorphism invariance, is a fundamental principle in general relativity stating that the laws of physics remain unchanged regardless of how we smoothly reshape or coordinate our spacetime description. Think of it like choosing different map projections: the actual terrain doesn’t change, only our view of it. This symmetry ensures that gravity is described in a way that does not depend on specific coordinate choices, emphasizing that spacetime itself is dynamic and flexible, and the physical content remains consistent under different smooth transformations of coordinates.