On Friday, March 9, 2018 at 11:23:42 PM UTC-5, Brent wrote: > > > > On 3/9/2018 6:10 PM, John Clark wrote: > > On Fri, Mar 9, 2018 at 6:22 PM, Russell Standish <[email protected] > <javascript:>> wrote: > > Hi Russell > > *> Alan was claiming that motion of a free particle along a geodesic was >> an unjustified assumption in relativity.* > > But its not unjustified or an assumption if that's the way we observe > things move, and it is. > > I simply asked if geodesic motion is assumed by GR. I never alleged it was unjustified. And it could be an assumption if that's the way it is. AG
> *> If he were asking why is momentum conserved, then one could answer it >> along the lines of Vic Stenger's symmetries, utilising Noether's theorem.* > > > Yes but Noether's theorem couldn't be invoked and the conservation of > momentum produced from it unless there was a symmetry, in this case > the fact that the laws of physics are the same at all points in space. > Someone could then ask why that is, and at this time the best answer we > could give is that’s just what we observe. As far as I can see it is not a > logical necessity, physics could have been different from one place to > another but we see that is not the case. > > > If that were the case then we would look for some other variable(s) that > would account for the difference in order to arrive at a more comprehensive > theory that, with the new variable(s), made the theory the same both > places. The idea of physics as a fundamental theory is that it should be > the same at all times and places. So if it's not, we either look for a > better theory or (temporarily) give up and call the variations > "geography". As my friend Vic Stenger put it, physics assumes POVI, Point > Of View Invariance. > > Brent > > And Einstein said mass/energy tells spacetime how to curve and spacetime > tells mass/energy how to move, but if this were not true it would > contradict observations but not produce any logical self contradictions > that I know about. In physics if you keep asking recursive "why is that?” > questions eventually you'll come to a brute fact. Put it another way, I > don't think the laws of physics could be derived from pure logic alone > regardless of how intelligent you are, that's why we need observation. > > John K Clark > > > -- > 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] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > -- 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 post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
