On 26 May 2015 at 10:39, meekerdb <meeke...@verizon.net> wrote: > On 5/25/2015 10:45 AM, John Clark wrote: > > On Sat, May 23, 2015 , Pierz <pier...@gmail.com> wrote: > > >> > Bruno *did* acknowledge that his theory predicts that the laws of >> physics are invariant across space and time, because they are supposed to >> arise out of pure arithmetic >> > > We know from pure mathematics (by way of Noether's theorem discovered in > 1915) that if the fundamental laws of physics do not change with time then > the conservation of mass/energy must exist. And Noether also tells us that > if the fundamental laws of physics do not change from one place to another > then the law of conservation of momentum must exist. By the way, I don't > think Emmy Noether received the credit she deserved for this enormously > important discovery. > > > And to expand on that point, note that if we find a law of physics that > depends explicitly on time or location, we would be reluctant to consider > it fundamental and we would look for some more fundamental law that > explained its dependence. Incidentally, what Noether proved is that for > each symmetry in the Lagrangian of a physical system there is a > corresponding conserved quantity and vice versa. So for an expanding > universe, one that has no time-like Killing vector field, there is no > conserved mass/energy. John Baez (Joan's cousin) has a good essay on this > online. >
Yes, the fact that energy isn't conserved in the actual universe has long been a source of (minor) amusement to me. But generally, as Brent says, given some apparent assymmetry the natural tendency of science is to look for some law in which things *are* conserved and try to explain why they aren't in this particular case - graduating from a flat Earth that isn't at the centre of the universe is an example of this. (This hasn't yet happened for matter and antimatter, or indeed something and nothing, but we live in hope). -- 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 post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
