From: helbig@asclothestro.multivax.de   
      
   In article <614a76af.436387578@news.aioe.org>, eric@flesch.org (Eric   
   Flesch) writes:   
      
   > On 01 Sep 2021, nospam@de-ster.demon.nl (J. J. Lodder) wrote:   
   > >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.   ...   
   >   
   > I just wanted to thank the OP for his excellent precis.  It has   
   > bothered me for a long time that with defining our length scale in   
   > reference to c-dependent physical outputs, that we've given up an   
   > absolute length scale as a basis of measurement.  That is, we've   
   > assumed c to be ever unchanging WRT a physical rod.  If that   
   > assumption is wrong, we've disabled our ability to find out.  We have   
   > put blinkers on ourselves.  It can't be right to do that.   
      
   What is to prevent you from measuring the speed of light in the same way   
   it was measured before the redefinition of the metre?  If you actually   
   find it to vary, no reasonable person will say that that is wrong since   
   the speed of light is defined to be a constant.  Nature doesn't care how   
   we define our units.   
      
   > In all the sciences, only astronomy looks directly backwards into   
   > time.  We assume that there is no overhead in doing so.  And yet there   
   > is the redshift which we interpret as physical recession.  But who can   
   > say what exactly separates the present from the past?  The redshift   
   > may be a symptom of something else as yet unmodelled.   
      
   There is no shortage of alternative theories.  There is no shortage of   
   criticism of them.  If you have a good idea, publish it, and let it be   
   debated.   
      
   ANYTHING may be a symptom of something else as yet unmodelled.  But   
   there seems to be no reason to doubt the cosmological redshift.   
      
   > Normally if we set up an apparatus or a software system and switch it   
   > on, then if its particles/data are seen to be expanding and   
   > accelerating all around, we adjudge that the system is mis-calibrated.   
      
   For a normal system in the lab, yes.  For the Universe, no.  It follows   
   from GR that it can be static only if infinitely fine-tuned.  We have no   
   reason to doubt the validity of GR on large scales.   
      
   > So we look for how to calibrate it.  Our "accelerating expansion"   
   > universe may simply be uncalibrated, and a new parameter needed to   
   > calibrate it.   
      
   Again, publish a hypothesis and let it be debated.   
      
   > I greatly hope that we haven't already blinkered   
   > ourselves in such a way as to make that calibration impossible.   
      
   I don't think so, but in any case it doesn't have anything to do with   
   the definition of the metre or the constancy of the speed of light, at   
   least not at this level.  (Note that some people have investigated   
   cosmological models with a varying speed of light.)   
      
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