From: tjroberts137@sbcglobal.net   
      
   On 6/24/18 10:12 AM, Nicolaas Vroom wrote:   
   > On Saturday, 23 June 2018 20:08:43 UTC+2, Tom Roberts  wrote:   
   >> In GR, the local laws of physics are the same everywhere,   
   >> including the laws that govern the ticking of watches. So the two   
   >> watches tick at the same rate (assuming they are identical).   
   >   
   > The question is what are the laws that govern the ticking of the watches?   
      
   It doesn't matter -- in GR, ALL the (local) laws of physics are the same   
   everywhere.   
      
   > IMO the most important step is to explain the experiments you perform   
   > accurately and the results of the experiments.   
      
   Yes. For any experiment comparing two clocks at different locations, or two   
   clocks moving differently, there are inevitably signals involved -- one does   
   NOT   
   compare two clocks, one compares one clock to signals from the other clock, or   
   one compares signals from both. In GR, after unwinding the effects of measuring   
   the signals, one finds that identical clocks ALWAYS tick at the same rate.   
      
   Note that a clock's tick rate can only be measured by a co-located and   
   co-moving   
   observer; anything else involves signals, not just the clock.   
      
   Tom Roberts   
      
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