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Newsgroups: sci.physics.relativity
Subject: Re: E = 3/4 mc? or E = mc?? The forgotten Hassenohrl 1905 work.
From: nospam@de-ster.demon.nl (J. J. Lodder)
Reply-To: jjlxa31@xs4all.nl (J. J. Lodder)
Date: Thu, 5 Dec 2024 19:42:24 +0100
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Paul B. Andersen <relativity@paulba.no> wrote:

> Den 04.12.2024 21:17, skrev J. J. Lodder:
> > ProkaryoticCaspaseHomolog <tomyee3@gmail.com> wrote:
> >>
> >> The mere fact that theory and over a century of experimental
> >> validation have led to the speed of light being adopted as a constant
> >> does not invalidate experiments intended to verify to increasing
> >> levels of precision the correctness of the assumptions that led to
> >> it adoption as a constant.
> > 
> > So you haven't understood what it is all about.
> > I rest my case,
> > 
> > Jan
> 
> The meter is defined as:
> 
> 1 metre = (1 sec/?299792458? m/s)
> 
> 1 second = 9192631770 ??_Cs
> 
> Note that neither the definition of second nor the definition
> of metre depend on the speed of light.
> 
> The constant ?299792458? m/s is equal to the defined speed of light,
> but in the definition of the metre it is a constant.
> 
> That means that it possible to measure the speed of light
> even if it is different from the defined value.

> The point is that the metre isn't define by the speed of light,
> but by the constant 299792458? m/s.

So you didn't get the point either.
(also suffering from a naive empirist bias, I guess)

The point is not about pottering around with lasers and all that,
it is about correctly interpreting what you are doing.
To do that you need to understand the physics of it.

In fact, the kind of experiments that used to be called
'speed of light measurements' (so before 1983)
are still being done routinely today, at places like NIST, or BIPM.
The difference is that nowadays, precisely the same kind of measurements
are called 'calibration of a (secudary) meter standard',
or 'calibration of a frequency standard'.  [1]

> So if the speed of light, measured with instruments with better 
> precision than they had in 1983 is found to be 299792458?.000001 m/s,
> then that only means that the real speed of light (measured with
> SI metre and SI second) is different from the defined one.

So this is completely, absolutely, and totally wrong.
Such a result does not mean that the speed of light
is off its defined value,
it means that your meter standard is off,
and that you must use your measurement result to recalibrate it.
(so that the speed of light comes out to its defined value)

In other words, it means that you can nowadays
calibrate a frequency standard, aka secundary meter standard
to better accuracy than was possible 1n 1983.
This is no doubt true,
but it cannot possibly change the (defined!) speed of light.

In still other words, there is no such thing as an independent SI meter.
The SI meter is that meter, and only that meter,
that makes the speed of light equal to 299792458? m/s (exactly)

Jan

-- 
Aber das ist Falsch! Sogar ganz Falsch!! (Wolfgang Pauli)


[1] They publish 'prefered values' for the frequencies
of a number of standard laser lines.