From: nospam@de-ster.demon.nl   
      
   Jos Bergervoet  wrote:   
      
   > On 21/10/15 9:47 PM, J. J. Lodder wrote:   
   > > Nicolaas Vroom  wrote:   
   > > [repost of another vanished posting, some minor edits]   
   > >> Op woensdag 1 september 2021 om 21:27:09 UTC+2 schreef J. J. Lodder:   
   > >>> The assertion was that you can at least in principle use laboratory   
   > >>> measurements of the speed of light to see if it varies.   
   > >>>   
   > >>> To see that you can't you need to have at least a vague idea   
   > >>> of how such measurements are done.   
   > >>> A) you build a stable light source.   
   > >>> B) you set up a fixed resonator for it to create a standing wave.   
   > >>> C) using the tricks of the trade you determine   
   > >>> how many wavelength there are in it.   
   > >>> D) idem, and far more difficult, you measure the frequency   
   > >>> of your light source, wrt to an atomic clock.   
   > >>> (frequency dividing, multiplexing, counting etc. very hard)   
   > >>> E) Knowing wavelength and frequency give you speed of light.   
   > >>   
   > >> IMO item B seems to me very tricky.   
   > >> To get an idea about how a resonator works follow this link:   
   > >> https://en.wikipedia.org/wiki/Resonator#Explanation   
   > >   
   > > Yes, it is a poor way to go about it.   
   >   
   > And anyhow, the above says that D) is in fact far more difficult.   
   > What would actually be the first divider? Are there injection-locked   
   > dividing lasers nowadays?   
      
   Nowadays the easiest way of doing it is with optical frequency combs.   
   No point in me repeating Google on this,   
      
   Jan   
      
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