From: nicolaas.vroom@pandora.be   
      
   On Tuesday, 6 August 2019 09:15:34 UTC+2, Tom Roberts  wrote:   
   > On 8/4/19 7:14 PM, Nicolaas Vroom wrote:   
   >   
   > > In the book 'Subtle is the Lord' by Abraham Pais at page 145 we can   
   > > read: "(g) Einstein rather casual mentioned that if two synchronous   
   > > clocks C1 and C2 are at the same initial position and if C2 leaves A   
   > > and moves along a closed orbit, then upon return to A, C2 will run   
   > > slow relative to C1, as often observed since in the laboratory.   
   > > [...]   
   >   
   > Einstein did not know better when he wrote, as this had not yet been   
   > fully understood. Pais is not a physicist and is writing for a general   
   > audience, so it is no surprise that he does not know better.   
   >   
   > 	The observation mentioned is really that C2 showed less   
   > 	elapsed proper time than C1; the tick rates of the two   
   > 	clocks were NOT compared, and "running slow" was NOT   
   > 	actually observed.   
   >   
   > This is merely another example of insufficiently precise wording: the   
   > notion that C2 "runs slow" compared to C1 implicitly assumes a) using   
   > the inertial frame of A (and C1), and b) the difference in final   
   > displayed times depends ONLY on the clocks' tick rates. But a) if you   
   > are talking about the tick rate of C2 you MUST use its own rest frame,   
   > and b) the final difference also CLEARLY depends on the clocks' paths.   
   >   
   > Bottom line: C2 does not "run slow". But C2 does run slow RELATIVE TO   
   > THE FRAME OF C1.   
      
   That means if Abraham Pais would have written:   
      "and if C2 leaves A   
      and moves along a closed orbit, then upon return to A, C2 will run   
      slow relative to THE FRAME of C1, as often observed since in the   
      laboratory. [...]"   
   then everything is okay?   
   Maybe that is what he (and Einstein) meant?   
      
   But is all off this that important?   
   Original both C1 and C2 are resident of the same frame (state).   
   When C2 leaves A a certain force is exerted on C2. In order to travel a   
   closed loop more forces are exerted on C2. At the end again a force is   
   exerted on C2 to bring him back in the frame of C1.   
   (What this implies is that C2 during his travelling, under going   
   accelerations, is not part of one particular frame at rest)   
   Finally what is observed, that C2 shows less counts than C1.   
   (relative to the frame of C1).   
   The cause of this lies in all these extra forces, (which physical affect   
   the internal operation of the clock) which results that the path length   
   of C2 travelled is much larger than C1.   
      
   Nicolaas Vroom   
      
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