From: tjroberts137@sbcglobal.net   
      
   On 5/31/22 2:54 AM, Luigi Fortunati wrote:   
   > In accelerated reference frames, the clocks do not stay synchronized   
   > with each other.   
      
   Hmmm. Clocks that are at the same "altitude" relative to the   
   acceleration do remain synchronized.   
      
   Note also that "accelerated frame" is an oxymoron -- "frame" implies a   
   set of four mutually-orthogonal coordinate axes, which can occur ONLY   
   for inertial coordinates.   
      
   > Yet on Earth, which is an accelerated reference frame,   
      
   No, it is not. On the surface of the earth, a "small" region of   
   spacetime can be considered to be equivalent to an accelerated system in   
   flat spacetime, but larger regions on the surface are nowhere close to   
   an accelerated system in flat spacetime. Here "small" depends on one's   
   measurement accuracy.   
      
   > all the clocks that are at the same altitude remain perfectly   
   > synchronized with each other wherever they are, why?   
      
   Because in weak gravity, "gravitational time dilation" depends on the   
   gravitational potential, which primarily depends on altitude (as in an   
   accelerated system in flat spacetime). This is only approximate: when   
   measured very accurately, the potential at a given altitude depends on   
   the density of the material below, and on the positions of sun, moon,   
   and planets above -- at 15,000 feet above earth's geoid, the potential   
   over Pike's Peak is measurably different from that over Death Valley.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
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