From: tjroberts137@sbcglobal.net   
      
   On 3/18/22 4:27 PM, Stefan Ram wrote:   
   > Richard Livingston  writes:   
   >> Simultaneity at a distance is not observable.   
   >   
   > In an inertial system: Place a detector D midway between A and B   
   > (using a yardstick). I assume that A, B and D are at rest. Generate   
   > two signals at A and B. If they arrive at D at the same time, they   
   > were sent at A and B at the same time. This would be a kind of   
   > observation, albeit delayed.   
      
   That is not observing simultaneity at A and B, it is observing   
   simultaneity at D. From that observation and the setup and the inertial   
   frame, we can INFER that the signals from A and B were sent at the same   
   time IN THAT INERTIAL FRAME. Inference is not observation.   
      
   Observation implies a physical quantity is being observed. Simultaneity   
   at different spatial points is not any kind of physical quantity, it is   
   a CONVENTION based on the time coordinate of a particular inertial   
   frame; such coordinate-dependent quantities cannot possibly be physical   
   quantities.   
      
   > [...]   
      
   Attempting to apply modern physical theories to our everyday experience   
   is hopeless, because there are too many approximations involved.   
      
   Similarly, attempting to discuss "collapse of the wave function" in   
   terms of simultaneity and SR is also hopeless, because such "collapse"   
   is not observable (one can observe the system transitioning between   
   states, but not any "collapse").   
      
   A major lesson of modern physics is to discuss only measurable   
   (observable) quantities [#]. Both "everyday lives" and "wavefunction   
   collapse" violate that dictum (in very different ways).   
      
   	[#] Interestingly, this applies to both QM and GR (for   
   	very different reasons).   
      
   Tom Roberts   
      
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