From: nospam@de-ster.demon.nl   
      
   Nicolaas Vroom  wrote:   
      
   > Op woensdag 7 juli 2021 om 19:20:49 UTC+2 schreef Phillip Helbig:   
   > > In article <1pbx48j.1xmowyy1fnnxmfN%nos...@de-ster.demon.nl>,   
   > > nos...@de-ster.demon.nl (J. J. Lodder) writes:   
   > > > Thomas Koenig  wrote:   
   > > > > The way that the SI units are defined now, the speed of light   
   > > > > in vacuum is indeed constant. If you measure anything else than   
   > > > > 299792458 m/s, recalibrate your measurement devices.   
   > > >   
   > > > Nonsense.   
   > > > In the SI as it stands it is impossible in principle   
   > > > to measure the speed of light,   
   > > Because, for practical reasons, the metre is now defined as the   
   > > distance light travels in a certain time. That is our definition,   
   > Etc,   
   >   
   > You can do that, but now you create a new issue:   
   >   How is this CERTAIN TIME defined and more important measured in   
   >   detail in practice.   
      
   The practical answer is that the 'certain time' is effectively infinite.   
   Precision light speed measurements were done with standing waves.   
   (when these were still done, nowadays meter standard calibrations)   
      
   > That is a very important issue because we can all measure the same   
   > time, but when we compare all the distances measured,   
   > (which should be identical) they are not.   
   > That means at the most 1 person measures the distance of 299792458   
   > meters correct assuming we all measure 1 second.   
   >   
   > It is the same as the above ambiguous advice:   
   >       "YOU should recalibrate your measurement device."   
   > But if my measurement also is different from all of the others   
   > how much should I adapt my time measurement device?   
   >   
   > The above raised issue about CERTAIN TIME becomes even more important   
   > if you want to measure the speed of a cosmic ray (etc).   
      
   You calibrate the wavelength of your stabilised laser,   
   somebody else calibrates his, and when you communicate   
   your results should agree, within statistical errors.   
      
   > [[Mod. note -- An old nautical saying is "never go to sea with two   
   > chronometers; always take one or three".   
      
   Indeed.  [OT amusement, if moderators permit]   
   Naval chronometers could have sudden jumps   
   in their going rates for various reasons.   
   Take one, and you hope for the best.   
   Take two and you go crazy when they start to diverge.   
   (which one is right, so where am I ????)   
   Take three and you can hope to identify the faulty one.   
      
   These were quite practical matters,   
   literally matters of life or death.   
   Having rounded Cape of Good Hope or Cape Horn   
   they sailed East resp. West in the Roaring Forties,   
   and turned North to arrive where they wanted to go.   
   Turn to late, resp to early, would get them shipwrecked   
   on the Australian, resp. Chilean coasts,   
      
   Jan   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)