# virus: Re : The Speed of Light

Fri, 15 Nov 1996 15:53:54 +0000

John Schneider wrote :-

>
> Question: how long is a meter? Do we know the length of a meter
> as well as we know the speed of light? The above value suggests
> that we know how long a meter is on the order of 1 in a million.
> But the meter was always defined to be the length of some metal
> bar in Paris. How crude! Here's a better approach: define the
> speed of light to be a constant: call it 299792458 m/s. All
> physical theories (that we have thought of that work) employ the
> notion of it being constant, and experimental measurements based
> on whatever we have called the 'meter' have suggested that value.
> Let's define that constant. (Just like we define the constant
> 3.14159265359...... to be the 'pi')
>
> So, having defined the speed of light to be 299792458 m/s, let's
> also define the 'second' in terms of another very precise number
> (related to radioactive cesium clocks), and finally let's define
> the meter to be "the length of path in vacuum travelled by light
> in 1/299792458 second". This way, anybody can find out how long
> the meter really is, with very tiny uncertainty, on the order of
> one in a billion. Progress! We certainly could not have found
> that bar's length with such precision.
>

The International System of Units (SI) is based on the recommendations
of the Eleventh General Conference of Weights & Measures of October
1960. The definition of the metre that John suggested is in fact the
exact SI definition (bar none). However the "second" (s) is defined
independently of the metre as follows :-

"the duration of 9,192,631,770 periods of the radiation corresponding
to the transition between the two hyperfine levels of the ground
state of the caesium-133 atom"

The speed of light (c) is now considered to be exactly 299,792,458 m/s.

>
> Anyway, when we argue long enough about anything, we always seem
> to have to rely on what Richard calls a level-3 argument: it is
> more useful to treat the speed of light as a constant, since
> theories based on that assumption seem to work remarkably well.
> If someone can write down a new theory with a variable speed
> for light that works as well as relativity or quantum mechanics
> (which does treat c as constant in its equations), then perhaps
> I'll become interested. I'm not counting on that happening in
>

I'm no physicist but...

If c was a variable then the formula E = m c^2 would mean that energy (E)
was variable and thus annihilating the First Law of Thermodynamics.

That would be an object reality anarchist's dream.

---------------------------------
Hakeeb A. Nandalal