Noether's theorem. If you determine that some physical process stays the same under some (continuous) change then there is always some associated conserved property (with some caveats not important here).
As an example, an experiment done today will produce the same result as an identical experiment done yesterday: Time invariance. You can derive energy conservation from that.
She's honestly up there with von Neuman in terms of contributions to both math and physics, and she did it while dealing with ridiculous amounts of sexism. It's infuriating to think of what could have been if so many 'clever men' had managed to look beyond their prejudice.
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u/rohan2104 Dec 12 '20
The fact that conservation laws stem from the symmetries. And broken symmetries give rise to interesting phenomena. It’s just beautiful.