From: tjroberts137@sbcglobal.net   
      
   On 10/8/18 12:37 PM, Phillip Helbig (undress to reply) wrote:   
   > In article , Nicolaas   
   > Vroom  wrote:   
   >> My whole point is that when a clock (Using lightsignals) undergoes   
   >> acceleration (its speeds increases) its behaviour changes. These changes   
   >> are different, and are a function, of how the clock is build.   
   >   
   > If I enclose a spring-driven pocket watch, an atomic clock, a quartz-battery   
   > clock, a grandfather clock and so on in a box and accelerate it, the   
   > decelerate it and examine them (or accelerate myself to catch up to it and   
   > enter it while moving), do you expect them to read differently, assuming   
   > that they were synchronized at the beginning (and, as per a   
   > Gedankenexperiment, all completely accurate when at rest)?  One could argue   
   > that a grandfather clock is driven by gravity and thus, due to the   
   > equivalence principle, would be affected by acceleration, but what about the   
   > other three?  What about two partially-silvered mirrors with a light pulse   
   > bouncing between them which beeps when a photomultiplier behind one of the   
   > mirrors is activated?   
      
   A grandfather clock is not really a clock, it is just a pendulum and a   
   counter; the actual clock is that PLUS THE EARTH. So it cannot possibly   
   be put into the box (and if you imagine a huge-enough box then it will   
   not be pointlike).   
      
   Given that all of the (other) clocks are pointlike, as well as the box   
   [#], then GR certainly predicts they all read the same. I see no reason   
   to doubt this prediction -- after all, it is based purely on geometry,   
   not on any construction details of the clocks.   
      
   As my earlier discussion showed, this applies only to the accuracy with   
   which the clocks and box [#] can be considered to be pointlike (not   
   being pointlike affects the geometry). And of course the gedanken is   
   limited to accelerations that do not break any of the clocks.   
      
   	[#] The box must be pointlike, or clocks higher in the   
   	acceleration's equivalent "gravitational field" will not   
   	remain in sync with clocks that are lower. This is also   
   	geometry.   
      
   Note that arguments about "nothing being truly pointlike" are valid   
   MATHEMATICALLY, but in physics such approximations are used all the   
   time, when the error involved is smaller than the measurement   
   resolution.   
      
   	(I'm willing to discuss the geometry of GR; I'm not interested   
   	 in construction details of clocks.)   
      
   Tom Roberts   
      
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