From: nospam@de-ster.demon.nl   
      
   Phillip Helbig (undress to reply)    
   wrote:   
      
   > In article <1pfxkcn.125esf5v7jrgeN%nospam@de-ster.demon.nl>,   
   > nospam@de-ster.demon.nl (J. J. Lodder) writes:   
   >   
   > > > If you actually find it to vary, no reasonable person will say that t=   
   > hat   
   > > > is wrong since the speed of light is defined to be a constant.   
   > >   
   > > That is precisely what reasonable people will say.   
   > > They will ask: varies -with respect to what-?   
   > > All that might be observed experimentally   
   > > is that the meter, as defined by clock and c,   
   > > varies wrt to the meter defined in some other way.   
   > > (platinum bar? seconds pendulum? some optical wavelength?)   
   > >   
   > > Instead of people saying that the speed of light   
   > > has been observed to be variable   
   > > they will ask what the 'right' length unit is.   
   >   
   > Except that (as in varying-speed-of-light cosmological models) it might   
   > vary with respect to ALL possible standards, in which case it wouldn't   
   > make sense to define any sort of length with respect to that speed, just   
   > as one doesn't define any length with respect to the speed of someone   
   > riding a bike, say.   
      
   I'm sorry to say, but you are moving goalposts.   
   Paper is cheap, and people can write all kinds of ds^2 = ...   
   It is then up to those authors to explain what their models   
   mean in terms of observation and measurement.   
      
   We were discussing the measurability of the speed of light,   
   and perhaps of changes in it.   
   (or equivalently, calibration of length standards)   
   By the very nature of these experiments they can only be done   
   with any accuracy in the rest frame of standards laboratories.   
   By the relativity postulate the results must be the same   
   for all inertial observers.   
   So we can tell those LGM what our length and time units are.   
      
   Astronomically speaking, hence cosmologically   
   you are completely powerless to begin with,   
   for all astronomical distances can be known only   
   in terms of (light)seconds.   
   They are all based on the AU, which can only be measured accurately   
   in terms of (light)seconds.   
   To such an extent even that it became necessary   
   to give the AU a defined value in terms of meters, hence seconds.   
      
   So, if you leave the context of precision laboratory measurement   
   it is completely unclear to me what you are trying to argue,   
      
   Jan   
      
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