From: fortunati.luigi@gmail.com   
      
   Phillip Helbigundress to reply luned=EC 31/10/2022 alle ore 12:02:13 ha   
   scritto:   
   > In article , Luigi Fortunati   
   >  writes:   
   >   
   >> If we let all the elevators in the world move freely (unhindered), they   
   >> would head towards the center of the Earth where they would all meet.   
   >>   
   >> If we rested a body anywhere else, it would invariably accelerate   
   >> towards the center of the Earth, and only if we rested it in the center   
   >> of the Earth would it remain stationary in its place.   
   >>   
   >> So there is no doubt that the center of the Earth is not the same as   
   >> all the other points but it is very special, because it is a center of   
   >> gravity (and the other points don't).   
   >>   
   >> Also for General Relativity, is the center of the Earth different from   
   >> all other points?   
   >   
   > Not different from all other points, but different from all other points   
   > on Earth because, as you mentioned, it is the center of gravity.  But   
   > there is nothing special about the location per se, as one can change   
   > the center of gravity by, say, digging a hole and piling the dirt into a   
   > hill nearby.   
      
   It is not true that "there is nothing special about the location per   
   se" it is the location itself that is special.   
      
   And nothing changes if you move the privileged point by making a hole   
   and a small hill beyond: the privilege passes from one point to another   
   but does not disappear.   
      
   And what is this privilege?   
      
   If you are on Earth and you throw a stone anywhere, the stone does not   
   come back on its own.   
      
   But if you are in the center of the Earth and you throw a stone in any   
   direction, it will come back * by itself *, accelerating towards you.   
      
   That's what's special about the center of gravity location, that's its   
   privilege.   
      
   [[Mod. note -- I think Phillip Helbig's point is that if you change the   
   Earth's mass distribution a bit (e.g., by digging a hole and piling the   
   dirt into a hill nearby), that the center of gravity will change to   
   a different point.  If you are in the original (pre-digging) center   
   of the Earth-with-hole-and-pile-of-dirt and throw a stone, the stone   
   does *not* come back to you.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)