From: nospam@de-ster.demon.nl   
      
   Phillip Helbig (undress to reply)    
   wrote:   
      
   > In article <1pbx3kk.jywko91341fc9N%nospam@de-ster.demon.nl>,   
   > nospam@de-ster.demon.nl (J. J. Lodder) writes:   
   >   
   > > Tom Roberts  wrote:   
   > >   
   > > > On 6/29/21 1:41 AM, J. J. Lodder wrote:   
   > > > > [...] The speed of light cannot 'really' be variable. [...]   
   > > >   
   > > > You make far too many assumptions to be reasonable.   
   > > >   
   > > > Certainly the (vacuum) speed of light COULD vary, it's just that in t=   
   > he   
   > > > world we inhabit, with current technology, it is observed to not vary   
   > > > significantly (when measured using standard clocks and rulers at rest=   
   >  in   
   > > > some locally inertial frame).   
   > >   
   > > That's where you are mistaken.   
   > > There is no such thing as a god-given 'standard clock'   
   > > or 'standard ruler'.   
   > >   
   > > > But it certainly is possible that in the   
   > > > future we will develop technology with greatly improved resolution an=   
   > d   
   > > > discover that it actually does vary in the world we inhabit.   
   > >   
   > > A meaningless statement.   
   > > If variation is found we will have to discover (or decide!)   
   > > what it is that varies.   
   > > (speed?, rulers?, clocks?, all three?, some 'fundamental' 'constant'?)   
   > >   
   > > > It is also possible we will never find it varies -- science is a JOUR=   
   > NEY,   
   > > > not a destination.   
   > >   
   > > Empty ideology.   
   > > This is not a matter that can be settled   
   > > by means of naive empiricism,   
   > > by just 'measuring' the 'speed of light',   
   >   
   > One could measure the speed of light via several different types of   
   > rulers and clocks, or by measuring wavelength and frequency, or   
   > whatever, in the lab.  It is theoretically possible that the speed of   
   > light could change with time and that we could measure it.   
      
   That is utterly and thoroughly wrong.   
   You can potter about with all kinds of measuring equipment,   
   and you might see that things vary.   
   That you have measured the speed of light to be varying   
   must be a theoretical assumption.   
   Your units could be changing instead.   
   (as a result of something else changing, alpha for example)   
      
   > The fact that the speed of light is now a defined quantity does not   
   > somehow magically make it impossible to make a measurement which was   
   > possible with the original SI definitions.   
      
   You can still do exactly the same measurements.   
   (and in fact these are done routinely)   
   Only the interpretation has changed.   
   What used to be called 'a speed of light measurement'   
   is nowadays called 'the calibration of a (secondary) meter standard'.   
      
   > Obviously, if such a change were detected, then it would be a good idea   
   > to change the definition of the metre.   
      
   You would need a lot of much better ideas than that,   
   such as reinventing spacetime,   
      
   Jan   
      
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