From: tjoberts137@sbcglobal.net   
      
   On 9/17/23 1:24 AM, Luigi Fortunati wrote:   
   > If clocks A and B are stopped, they remain synchronized.   
      
   No. A stopped "clock" is not a clock, so "synchronized" is meaningless.   
   Fortunately you did not attempt to use this silliness.   
      
   You omitted important information about the physical situation. I   
   presume you mean clock B is located on the ground next to a rotating   
   carousel, and clock A is fixed to the carousel on its rim, so the two   
   clocks repeatedly meet, once per rotation of the carousel. For   
   simplicity, I also presume the ground is an inertial frame. (Your   
   animation confirms most of this.)   
      
   > If clock B stands still and clock A moves (land reference), every   
   > time they meet clock A lags behind.   
      
   Yes, between meetings clock A experiences less elapsed proper time   
   than does clock B. This is just a demonstration of the twin paradox.   
      
   > If clock A stands still and clock B moves (reference of the   
   > carousel), every time they meet clock B lags behind.   
      
   No! The elapsed proper time between meetings for each clock is an   
   invariant. So it does not matter which coordinates one uses as a   
   reference, clock A always has less elapsed proper time between meetings   
   than does clock B.   
      
   You seem to have fallen into the trap of believing that "moving clocks   
   run slow". That oft-repeated sound bite is FALSE in several different ways:   
      1. The moving clock ITSELF does not "run slow", because all   
         clocks ALWAYS tick at their usual rate [#]. It's just that   
         it is OBSERVED to run slow by an inertial frame relative to   
         which it is moving.   
      2. This only applies to a moving clock being observed by an   
         inertial frame. For a non-inertial observer, that sound   
         bite may or may not apply (it takes a real calculation).   
      
   	[#] If this were not true, Einstein's first postulate   
   	of SR could not be valid.   
      
   Your animation is woefully incorrect.   
      
   [[to the moderator]]   
   This is not the Sagnac effect, this is merely the fact that different   
   paths between a given pair of endpoints can have different path lengths   
   (aka elapsed proper time for timelike paths).   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)