Speaking somewhat loosely, the relationship between the local state of spacetime and its energy, the Lagrangian density, does not seem to depend on where you ar

Speaking somewhat loosely, the relationship between the local state of spacetime and its energy, the Lagrangian density, does not seem to depend on where you are or when you are. Emmy Noether gave us a straightforward proof that each such "differentiable symmetry" (in this case, translation invariance) implies that the state of spacetime maintains a corresponding "conserved current" (in this case, momentum and energy density).