From: richalivingston@gmail.com   
      
   On Sunday, September 11, 2022 at 6:38:33 PM UTC-5, Luigi Fortunati wrote:   
   > Stefan Ram venerd=EC 09/09/2022 alle ore 08:30:00 ha scritto:   
   > > I currently can't go on websites, but maybe what is intended   
   > > is this: a particle is placed on a geodesic compatible with   
   > > that particle. The particle now can move on the geodesic,   
   > > but how does it know in which direction as the geodesic has   
   > > no preferred direction?   
   > >   
   > > The answer might be: While a geodesic has no preferred   
   > > direction, the time coordinate has.   
   > The time coordinate is part of the geodesic.   
   >   
   > If the time coordinate has a preferred direction, the geodesic also has   
   > a preferred direction.   
   ...   
      
   This is somewhat over simplified, but you can think of the g_00 metric   
   component   
   as similar to a potential, in that it multiplies the particle energy rather   
   than   
   adds/subtracts like a true potential.  Never the less, the "potential"   
   decreases   
   as you get closer to the gravitating mass, and thus objects feel a "force"   
   in that direction.   
      
   When you really understand how it works, you will find that the curvature   
   of the metric that causes gravitational acceleration is the time metric,   
   g_00, that varies with radius.  Ultimately this is what causes the acceleration   
   to be toward the large mass.   
      
   The radial metric, g_11, also varies with radius, but this is not an intrinsic   
   curvature that causes an acceleration.  It does affect orbits, particularly   
   close to the event horizon, and is the reason there are no stable orbits   
   w/in 1.5 Schwarzshild radii of the event horizon.   
      
   Rich L.   
      
   [[Mod. note --   
   For massive particles the innermost stable *circular* orbit in   
   Schwarzschild is a bit farther out, at r=6M.  There are circular orbits   
   inside r=6M, but they're unstable.   
      
   For massless particles (photons et al), there's only one circular orbit,   
   at r=3M.  It's unstable.   
   -- jt]]   
      
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