On Sunday, April 21, 2019 at 6:59:25 PM UTC-5, agrays...@gmail.com wrote: > > > > On Sunday, April 21, 2019 at 5:54:33 PM UTC-6, Brent wrote: >> >> >> >> On 4/21/2019 2:20 AM, agrays...@gmail.com wrote: >> >> >> >> On Saturday, April 20, 2019 at 9:51:13 PM UTC-6, Brent wrote: >>> >>> >>> >>> On 4/20/2019 2:14 PM, agrays...@gmail.com wrote: >>> >>> The following (long!) video can also help (well, it did help me) >>>> >>>> https://www.youtube.com/watch?v=foRPKAKZWx8 >>>> >>>> >>>> Bruno >>>> >>> >>> *I've been viewing this video. I don't see how he established that the >>> metric tensor is a correction for curved spacetime. AG * >>> >>> >>> The metric tensor is the quantified embodiment of curved spacetime. But >>> How else would you define curvature, if not with the metric? >>> >>> Brent >>> >> >> *At 49:42 he defines the metric tensor. It has a Kronecker delta as the >> leading term. So all cross terms will be zero in its matrix representation. >> * >> >> >> But then he says that in a curved space g_mn must be something else, that >> does have cross terms. I don't find his presentation very enlightening. >> He ends up wit ds^2 = g_m_n dx^r dx^s He doesn't even have the indices >> match as in Einstein's summation forumula. >> >> Bren >> > > Thanks. I'm going on to Susskind's lectures on GR. AG > >> >> *Listen; this is pure mathematics. If what he calls the metric tensor is >> the general correction for curved spacetime, it can be proven >> mathematically, strictly by mathematics. What I see is a hand-waving >> argument at best! Ball in your court. AG * >> -- >> >> >> Theoretical physics is all hand-waving in a sense: One can take speaker X's formulation of GR in one vocabulary and speaker Y's formulation of GR in another vocabulary. and one is as good as the other it they produce the same predictions.
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