Underrated point. Conservation Laws emerge from symmetries via Noether's theorem. In particular, Conservation of Mass / Energy arises from Time Translation Symm

Underrated point. Conservation Laws emerge from symmetries via Noether's theorem. In particular, Conservation of Mass / Energy arises from Time Translation Symmetry. General Relativity doesn't have Time Translation Symmetry because the universe is expanding. Now the question is can we extract free energy from the expansion of spacetime and avoid the heat death of the universe?