From: fortunati.luigi@gmail.com   
      
   Luigi Fortunati il 03/01/2024 03:49:09 ha scritto:   
   > Tom Roberts il 02/01/2024 09:17:26 ha scritto:   
   >> Note that "all physics is local" [Einstein and others], so these various   
   >> descriptions of accelerations of distant objects never appear in the   
   >> laws of physics.   
   >   
   > No distant objects.   
   >   
   > The two little men (at the center of the Earth and in the elevator in   
   > free fall) pass in front of each other in acceleration (when   
   > approaching) and in deceleration (when moving away) and, therefore,   
   > they are not far away at all: they are 'next to each other.   
   >   
   > During their meeting, they cannot perceive the force of gravity but   
   > they can easily measure their mutual gravitational acceleration (even   
   > in 4 or more dimensions).   
   >   
   > Luigi Fortunati   
   >   
   > [[Mod. note -- A corollary of what Tom Roberts wrote is that our modern   
   > conceptions of physics involve *local* equations.   
      
   If the two little men send each other radar signals, each of them   
   *measures* the acceleration of the approaching other with their own   
   light and their own watch, throughout the entire journey from the   
   surface of the Earth to its center.   
      
   Therefore, they are local measurements (carried out in your own   
   reference) and not at a distance.   
      
   And there is no clock synchronization to do: each of them only uses   
   their own.   
      
   Luigi Fortunati.   
      
      
   [[Mod. note -- Radar is not a local measurement: it sends a light/radio   
   signal out to a distant target, and some of that signal is reflected and   
   (a tiny fraction of it) returns to the sender.  "Local" means *everything*   
   (including any light/radio signals) fits in an elevator.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)