On Sun, Jun 1, 2025 at 8:35 PM 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. * > * > In your interpretation any process that conserved energy would leave > the system unchanged* > *And I also said that if all you know is that there is a conservation law then Noether's theorem can you 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>* ugg > > On 6/1/2025 4:38 AM, John Clark wrote: > > On Sun, Jun 1, 2025 at 3:16 AM Alan Grayson <[email protected]> > wrote: > > *> But the question persists; when photons redden as the universe expands, >> where does the lost energy go? AG* > > > *The energy doesn't go anywhere, it's just destroyed, energy is not > conserved at the cosmic level. Noether's theorem says if there's a > symmetry, then there's a corresponding conservation law (but the reverse > does not necessarily hold, if there is a conservation law there may or may > not be a corresponding symmetry). * > > *In the case of energy Noether says the corresponding symmetry is time, at > the cosmic scale if energy is conserved then the universe should look the > same from one time to another, but if the universe is expanding it doesn't > look the same from one time to another, and if the universe is accelerating > then time is even less symmetrical. So energy is not conserved globally, > however it's still true that at the local level if things are at thermal > equilibrium then the amount of energy entering a finite volume of space > will equal the amount of energy leaving that volume.* > > > > -- > > -- 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/CAJPayv0rzESU%2Bbm0%2BKOAZpJ8Jvmnrxz%2B02f35PDzKyhRYBGQxQ%40mail.gmail.com.
