From: jos.bergervoet@xs4all.nl   
      
   On 21/09/26 9:47 AM, J. J. Lodder wrote:   
   > 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.   
      
   And you are more and more reverting to rhetoric instead of physics..   
      
   > 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.   
      
   A completely baseless claim. The first speed of light measurement   
   (Rømer) was actually done on an astronomical scale. Also, planned   
   experiments like LISA will be space-based and they certainly rely   
   very strongly on knowing the exact speed of light, even more so   
   then equivalent earth-based setups. Some of your arguments against   
   the measurability of c may be sound, but this singling out of some   
   rest frame isn't!   
      
   > By the relativity postulate the results must be the same   
   > for all inertial observers.   
      
   So then why would the lab-frame on Earth be the best?   
      
   > So we can tell those LGM what our length and time units are.   
   >   
   > Astronomically speaking, hence cosmologically   
   > you are completely powerless to begin with,   
      
   Only if we believe that previous, baseless claim!   
      
   --   
   Jos   
      
      
   [[Mod. note -- LISA does not rely on knowing the exact speed of light.   
   Instead, it relies on (among other things) knowing the inter-satellite   
   distances in *light-seconds*.  See section 7 of   
     https://www.livingreviews.org/lrr-2014-6   
   for details.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
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