On Mon, Jun 2, 2025 at 12:44 AM Brent Meeker <[email protected]> wrote:
* >>> That's not what Noether's theorem says. Time symmetry means that if >> you put a time shift in the equations of evolution, then equations remain >> valid. * >> > > >>*That's what I said! * > *If there's a symmetry then there's a corresponding conservation law, > equations remain valid because something has been conserved, and in the > case of time it is energy. * > > *>What I was objecting to is you wrote, "... if energy is conserved then > the universe should look the same from one time to another..." which is the > converse of your (correct) statement below. This is an interesting point. > Expansion of the universe is a failure of time symmetry that allows, but > does not imply, failure of energy conservation.* > *OK, we are in agreement. * *> And I also said that if all you know is that there is a conservation law > then Noether's theorem can tell you nothing. It only works one way. * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* iww > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAJPayv3fTRGhhLBhH-1D57rV-jrHF%2Bf8DP4Dfe%2BwbnGowv4NGw%40mail.gmail.com.
