Re: E = 3/4 mc? or E = mc?? The forgotten Hassenohrl 1905 work.

Paul B. Andersen <relativity@paulba.no> wrote:

Den 05.12.2024 19:42, skrev J. J. Lodder:

Paul B. Andersen <relativity@paulba.no> wrote:>

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.

 
Note: measured with SI metre and SI second.
 

 
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)

 
The 1983 definition of the speed of light is:
  c = 299792458 m/s
 
The 1983 definition of second is:
  1 second = 9192631770 ??Cs
 
The 1983 definition of meter is:
  1 metre = 1 second/299792458 m/s
 
The 2019 definition of meter is:
  1 metre = 9192631770 ??Cs/299792458 m/s
 
If the speed of light is measured _with the meter and second
defined above_ it is obviously possible to get a result slightly
different from the defined speed of light.
 
So I was not "completely, absolutely, and totally wrong".

You were, and it would seem that you still are.
You cannot measure the speed of light because it has a defined value.
If you would think that what you are doing is a speed of light
measurement you don't understand what you are doing.

Are you are saying that if we got the result 299792458.000001 m/s
then the metre would have to be recalibrated to:
1 metre = 9192631770 ??Cs/299792458.000001 m/s ?

Of course not.
All it would mean is that you have made some systematic error
with your particular implementattion of the SI meter.

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.

 
Or are you saying that we would have to recalibrate the meter to:
1 metre = 9192631770.0000306 ??Cs/299792458 m/s ?

Neither.  The SI meter is a secondary standard that must be calibrated
such that the speed of light comes to 299792458 m/s.

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
 

 
You wrote:

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'.

 
Is any such recalibration of the meter ever done?

Of course, routinely, on a day to day basis.
Guess there are whole departments devoted to it.
(it is a subtle art)
The results are published nowadays as a list of frequencies
of prefered optical frequency standards.
(measuring the frequency of an optical frequency standard
 and calibrating a secondary meter standard are just two different ways
 of saying the same thing)
And remember, there is no longer such a thing as -the- meter.
It is a secondary unit, and any convenient secondary standard will do.

And which "frequency standard" are you referring to?

Any optical frequency standard of known frequency
defines a secondary meter standard.
(because given the frequency, you know the wavelength,
 so you can measure lengths by interferometry)

A commonly used one is a certain stabilised He-Ne laser.
(of specified construction)

The definition of a second?

Of course not, that is fixed. (for the time being)
It is the frequency that all other frequencies must relate to.
It will be replaced in the not to far future
by an optical frequency standard. (yet to be chosen)

Finaly, you really need to get yourself out of the conceptual knot
that you have tied yourself in.
Something is either defined, or it can be measured.
It can't possibly be both,

Jan