From: nospam@de-ster.demon.nl
Phillip Helbig (undress to reply)
wrote:
> 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?
Nothing. As a matter of fact these measurement -are- done routinely
in standards laboratories.
Nowadays they serve to calibrate secondary meter standards.
> 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.
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.
Jan
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