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Noether's theorem

Noether's theorem is a central result in theoretical physics that shows that a conservation law can be derived from any continuous symmetry. For example, the laws of physics do not change from one moment to the next, which means that the laws are symmetric (i.e. invariant) with respect to time. If we imagine, for example, that the strength of gravity did change from one day to the next, then we could violate conservation of energy by raising a weight on a day when gravity was weak, and lowering on a day when gravity was strong, extracting more energy than we had originally put in.
Noether's theorem - Wikipedia, the free encyclopedia

physics, energy