From: nicolaas.vroom@pandora.be   
      
   Op maandag 12 juli 2021 om 19:18:57 UTC+2 schreef Nicolaas Vroom:   
   > Op woensdag 7 juli 2021 om 19:20:49 UTC+2 schreef Phillip Helbig:   
   > > Because, for practical reasons, the metre is now defined as the   
   > > distance light travels in a certain time. That is our definition,   
      
   > [[Mod. note -- An old nautical saying is "never go to sea with two   
   > chronometers; always take one or three".   
      
   In process control the best way to implement redundancy is:   
   triple redundancy.   
      
   > In this context, that means   
   > that people doing precision timing & clock development often use an   
   > an ensemble of co-located clocks (typically 5-10 are used), all of similar   
   > construction and method-of-operation, so that they can inter-compare the   
   > clocks. Since all the clocks in the ensemble are co-located, they should   
   > all record the same elapsed-time readings; more accurately, any differences   
   > in their elapsed-time readings can be ascribed to clock drifts (errors).   
   > Inter-comparing the clocks can thus give a statistical estimate of the   
   > clocks' accuracy   If any clock is an outlier   
   > in the ensemble, it's flagged as not-working-properly (a.k.a "broken").   
      
   I fully agree with you. But the experiment we are discussing here   
   is slightly different.   
   Starting point is the text by Tom Roberts:   
   > Your premise is wrong -- we do not use the speed of light to determine   
   > the unit of time. The second is defined as the duration of 9,192,631,770   
   > cycles of the hyperfine ground-state transition of Cs-133.   
      
   That means first we use this clock to measure 1 second.   
   This defines two moments t1 (start pulse) and t2 (stop pulse)   
   Secondly we use these two events to transmit a light ray at t1 at position p1   
   and mark the position p2 (along a rod) of the light ray at t2.   
   As described by Phillip Helbig.   
   The length between p2 and p1 defines the standard distance of 299792458 m.   
   The problem is that it is very difficult to establish the position p2 of the   
   light ray at t2.   
   What you need? is a clock at p2 and when that clock reaches 9,192,631,770   
   cycles the light signal should arrive from p1 simultaneous.   
   IMO this does not work because exactly where should you place this clock?   
   I hope that someone comes up with better detailed standard description how to   
   perform this experiment accurate, such that others can perform the same.   
      
   Using such a standard experiment we can now perform many experiments:   
   1) at the same location and observe if all the distances are the same.   
   2) at different locations and observe if all the distances are the same.   
   In case 1, in principle, all people should measure the same distance but   
   I expect they will not. The major reason is inaccuracy inherent in the   
   experiment.   
   In case 2, all people don't have to measure the same distance. The major   
   reason is that the speed of light is not the same in all directions,   
   caused by gravity considerations.   
      
   Nicolaas Vroom   
      
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