From: tjroberts137@sbcglobal.net   
      
   On 7/31/19 11:23 PM, Nicolaas Vroom wrote:   
   >> I comparing performance of an hourly glass   
      
   An hourglass is NOT a clock. Hourglass+earth is the clock, and if you   
   change the relationship between the hourglass and the earth you have a   
   completely different clock. Of course no hourglass is accurate enough to   
   demonstrate any relativistic effects. Ditto for a pendulum or   
   grandfather clock.   
      
   > Consider you have two identical clocks and one clock is moved (is=20   
   > influenced by an external force). The question is: does this have=20   
   > consequence for the performance of the moving clock versus the not=20   
   > moving clock. For a clock based on light signals the answer is yes,=20   
   > because the path length of the photons will become longer.   
      
   No! You keep making the same mistake: not specifying the inertial frame   
   used for reference.   
      
   If you want to discuss a clock's tick rate, you must use its own rest   
   frame. For a light clock, in its rest frame the light path lengths are   
   constant; regardless of which frame it is at rest in, its tick rate does   
   not change (remember the speed of light is also the same in all inertial   
   frames).   
      
   If you want to discuss a clock's tick rate as measured in some inertial   
   frame other than its rest frame, you MUST say so. For any good clock, it   
   is only when measured from an inertial frame relative to which it is   
   moving that the observed tick rate changes.   
      
   	Or when observed from a different altitude in a   
   	gravitational field.   
      
   As I keep saying, discussing relativity requires precision in thought   
   and word. Your statements repeatedly fall short of what is required, and   
   you MUST improve the precision of your thinking in order to understand th=   
   is.   
      
   > For an hourly glass the answer is also yes. The issue is gravity.=20   
   > Dropping an hourly glass a couple of times (or shaking carefully)=20   
   > will increase the path length.   
      
   Dropping an hourglass changes its relationship to the earth and you have   
   a completely different clock. This is useless.   
      
   > I don't know how constant clocks based on radioactive decay are,   
      
   There are measurements of "time dilation" using radioactive ions in a   
   beam moving at an appreciable fraction of c, but I have lost the   
   references. Here are references for a "clock" made from the decay rate   
   of muons:   
      
        Bailey et al., =E2=80=9CMeasurements of relativistic time dilation   
        for positive and negative muons in a circular orbit,=E2=80=9D Nature   
        268 (July 28, 1977) pg 301.   
        Bailey et al., Nuclear Physics B 150 pg 1=E2=80=9379 (1979).   
      
   They stored muons in a storage ring and measured their lifetime. The   
   measured decay rate is consistent with the prediction of SR.   
      
   When combined with measurements of the muon lifetime at rest this   
   becomes a highly relativistic twin scenario (v ~0.9994 c), for which the   
   stored muons are the traveling twin and return to a given point in the   
   lab every few microseconds. While being stored in the ring they were   
   subject to a proper acceleration of approximately 10^18 g (1 g =3D 9.8 m/=   
   s2).   
      
   Tom Roberts   
      
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