On Thu, Dec 29, 2022 at 4:34 PM Brent Meeker <meekerbr...@gmail.com> wrote:
> On 12/28/2022 9:01 PM, Bruce Kellett wrote: > > On Thu, Dec 29, 2022 at 3:29 PM Brent Meeker <meekerbr...@gmail.com> > wrote: > >> Of course one reason there are "laws of physics" is what my late friend >> Vic Stenger called Point Of View Invariance. This was his generalization >> of Emmy Noether's theorem that showed every symmetry implied a conservation >> law. >> > > That is not strictly true. It is only continuous symmetries of the > Lagrangian that imply conservation laws -- not all symmetries. For example, > the symmetries of a square under rotation and reflection do not generate > any conservation laws. Neither do discrete symmetries like parity and > charge conjugation. > > So momentum is conserved because we want any law of physics to be >> invariant under translation of a different location. Energy is conserved >> because we want the laws of physics to be the same at different times, etc. >> > > It is not what we want, it is what we find. We find that nature is > invariant under these continuous transformations, so we build those > symmetries into our laws. > > > Vic called in POVI because he wanted to extend it to transformations in > abstract spaces, e.g. gauge invariance. Of course the invariance depends > on the "point of view" in a sense. Things didn't look at all space > translation invariant to Aristotle. Galileo said ignore that your ship is > moving along the shore, just look at the dynamics in the cabin. So we > discovered these symmetries by learning what ignore as well as what to > measure. > The real point is that the laws are discovered, not imposed. The fact that continuous symmetries correspond to conservation laws was discovered only very much later. Most of the history of physics is about discovering what works -- what the laws might be. POVI was thought of only very late in the game, and is not a fundamental insight. Bruce -- 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 everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLS7uHeH9BkzWHj_V_nL7j27qEdqpG%3D-274eDm1kgw_Ewg%40mail.gmail.com.
