On Thursday, March 8, 2018 at 12:36:07 PM UTC-5, Brent wrote: > > > > On 3/8/2018 4:24 AM, [email protected] <javascript:> wrote: > > > > On Wednesday, March 7, 2018 at 11:04:09 PM UTC-5, Brent wrote: >> >> >> >> On 3/7/2018 5:39 AM, [email protected] wrote: >> >> *Thanks for your time and effort, but I don't think you understand my* >> *question. Suppose a test particle is restrained spatially, say in * >> *the Sun's gravitational field. When released, it starts to move (toward * >> *the Sun). How does GR explain this motion? By the advance of time? AG* >> >> >> Time was advancing all along. Your restraint was a force causing the >> particle to follow a non-geodesic path through space-time. When you >> released it, it then followed the "straightest path possible", i.e. a >> geodesic. >> >> Brent >> > > So time is the "culprit". What has this resumption of spatial motion > (along a geodesic in spacetime) have to do with conservation of momentum, > if at all ? TIA, AG > > > It's not a "resumption" of motion; it's just tilting the direction of > motion from being along your coordinate time line (which you think of as > 'not moving') to being along the geodesic (which you think of as > 'falling'). The 4-momentum of the system, including whatever device you > were using to keep the particle from falling is conserved. > > Didn't you say you had read Epstein? > > Brent >
I said I was reading Epstein. I have it with me while traveling. If 4 momentum is conserved, isn't that the same as saying motion on a geodesic is postulated? Incidentally, if one accepts GR as a "valid" model of gravity, doesn't that preclude any coupling between gravity and EM? 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 [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.
