From: nospam@de-ster.demon.nl   
      
   Phillip Helbig (undress to reply)    
   wrote:   
      
   > In article <1pbx48j.1xmowyy1fnnxmfN%nospam@de-ster.demon.nl>,   
   > nospam@de-ster.demon.nl (J. J. Lodder) writes:   
   >   
   > > Thomas Koenig  wrote:   
   > >   
   > > > Nicolaas Vroom  schrieb:   
   > > >   
   > > > > Ofcourse you could claim that the speed of light is constant.   
   > > >   
   > > > The way that the SI units are defined now, the speed of light   
   > > > in vacuum is indeed constant.  If you measure anything else than   
   > > > 299792458 m/s, recalibrate your measurement devices.   
   > >   
   > > Nonsense.   
   > > In the SI as it stands it is impossible in principle   
   > > to measure the speed of light,   
   >   
   > Because, for practical reasons, the metre is now defined as the   
   > distance light travels in a certain time.  That is our definition, which   
   > Nature doesn't know about.  We cannot magically influence Nature by   
   > changing definitions.   
      
   Nature doesn't know about our definitions,   
   but we had better chose our definitions   
   in ways that agree with what nature is like.   
   To the best of our knowledge we live in a spacetime   
   that is characterised by an absolute velocity,   
   confusingly also called c.   
   If this is indeed the case we have to choose our length and time   
   units in accordance with this fundamental fact.   
   (like the SI already does)   
   If physical things (such as G or alpha for example) are indeed variable   
   we would otherwise obtain unphysical results,   
   such as deluding ourselves into a belief that c could be variable.   
      
   > With time, more and more SI units have been defined via fiat values of   
   > constants of Nature.  This is a purely practical matter, because we   
   > ASSUME that they do not change with time.  The definitions are also   
   > coupled with experiments which are relatively easy to reproduce.   
   >   
   > Back when the metre was defined as 1/10,000,000 of the distance from   
   > north pole to equator along the meridian through Paris, that did not   
   > somehow make it impossible to measure the change in the size of the   
   > Earth with time.   
      
   This meridian of the earth thing   
   was never more than a propaganda device.   
   For metrological reasons anno 1800 a length standard   
   could only be two scratches on a metal bar.   
   A reason had to be invented to declare a particular pair of scratches   
   on a particular better than all others. (to break all local chauvinisms)   
   As a matter of historical fact the earth was never remeasured   
   for obtaining a more accurate meter,   
      
   Jan   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)