On Friday, March 9, 2018 at 9:10:22 PM UTC-5, 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. > *Don't you read? I stated that I never made the assumption Russell attributed to me. What I did conjecture is that geodesic motion is an assumption of GR. Is it? 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. 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]. 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.
