On Friday, December 22, 2017 at 7:45:42 AM UTC, Brent wrote: > > > > On 12/21/2017 11:06 PM, agrays...@gmail.com <javascript:> wrote: > > > > On Friday, December 22, 2017 at 4:46:10 AM UTC, Brent wrote: >> >> >> >> On 12/21/2017 4:22 PM, agrays...@gmail.com wrote: >> >> >> >> On Thursday, December 21, 2017 at 11:03:53 PM UTC, Brent wrote: >>> >>> >>> >>> On 12/21/2017 2:04 PM, agrays...@gmail.com wrote: >>> >>> >>> >>> On Tuesday, December 19, 2017 at 8:51:51 PM UTC, Brent wrote: >>>> >>>> >>>> >>>> On 12/18/2017 11:44 PM, agrays...@gmail.com wrote: >>>> >>>> Invariants are always the important things in physics because they are >>>>> what we can have intersubjective agreement on. >>>>> >>>>> Brent >>>>> >>>> >>>> *IIUC, the field equations are covariant, which means coordinate system >>>> independent. * >>>> >>>> >>>> Right. Covariant means that something that changes in such a way that >>>> invariant things remain the same. So vectors components transform >>>> covariantly so that they keep the vector physically the same. >>>> >>>> *Isn't Newton's Law of Gravitation also coordinate independent? That >>>> is, if we use Newton to calculate the planetary orbits, won't we get the >>>> same results in different coordinate systems? * >>>> >>>> Right. >>>> >>> >>> >>> * If Newton's Law of Gravitation is covariant -- that is, coordinate >>> frame independent -- I'd expect it to to be invariant between inertial >>> frames, but I don't believe it is. That is, I don't think a LT between >>> inertial frames will leave the form of the law unchanged. How do you >>> resolve this problem? TIA, AG * >>> >>> >>> Don't use a Lorentz transform between frames in a Galilean invariant >>> theory. >>> >> >> *OK, So why didn't Einstein do what he did for classical mechanics which >> is not Lorentz invariant, and directly modify Newton's Law of Gravitation? >> AG* >> >> >> (a) I don't read minds, and especially not Einstein's and (b) I don't >> know what "directly modify" means. >> >> Brent >> > > *He changed (= directly modified) the laws of mechanics to make them > Lorentz invariant. So why can't that be done for Newton's Law of > Gravitation? Does that law work for any inertial frame? AG* > > > Newton's gravity is a field theory. It implies an infinite speed of > changes in the gravitational field. That wasn't consistent with > relativity. What you're calling "directly modified" was just local > mechanics, not fields. > > Brent >
*When you think about it, it's apriori highly improbable that Newtonian gravity would work as well as it does, say for planetary orbits, given the substantial light times between the Sun and the planets, and between the planets. AG * -- 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 https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
