On Wednesday, March 7, 2018 at 2:17:15 AM UTC-5, Russell Standish wrote: > > On Tue, Mar 06, 2018 at 09:18:46PM -0800, [email protected] > <javascript:> wrote: > > > > > > They follow from the principle of conservation of momentum, also > > > sometimes known as Newton's first law. > > > > > > > Can you elaborate on that? Is there always motion even if time > > doesn't exist? Motion in space or spacetime AG > > Clearly, with motion in flat space, conservation of momentum > implies that motion will be along a straight line. If the direction of > movement changed, that is automatically a change of momentum. > > In curved space, the corresponding curve must be a geodesic - there > are no such things as straight lines in curved space. IIRC, the > equivalent expression of conservation of momentum is that the > covariant derivative of the mass-energy tensor must vanish. There is a > discussion on page 386 of Misner, Thorne & Wheeler's epic book > gravitation... > > You can also come to the same conclusion using an extremum principle > such as Laplace's principle of least action, but for sheer intuition, > the above explanation works best for me.
*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* -- 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.
