Re: Constant 'c'?

George Murphy (
Wed, 05 Nov 1997 15:51:36 -0500

Moorad Alexanian wrote:

> In the case of length and energy, the numerical constants, 2.54 and 4.184,
> have no physical content and are only a historical curiosity. Note that one
> is dealing only with energy or only with length. On the other hand, the
> constant c is the speed of light in vacuum, a measurable quantity. By
> defining the value of c to have an exact number, 299792458, one is only
> defining the meter in terms of the unit of time, the second. But note that
> we are dealing with two different quantities---space and time, albeit,
> components of a 4-vector---which have different dimensions. If somewhere in
> the universe, the velocity of light is different, then by using our
> definition of the second and the meter, they would get a different length
> for the meter. The numbers 2.54 and 4.184 are the same anywhere in the universe.
> Moorad
> p.s. Perhaps we do need a referee to settle the issue.

Perhaps. But let me note one thing from an earlier post which
may have been overlooked. c in special relativity is really more
fundamental than "the speed of light". I.e., derivation of the Lorentz
transformation depends on there being a speed which is the same for all
inertial observers. Whether or not anything actually moves at that
speed is another question. & if photons have a rest mass (which must be
less than ~10^-58 g), light _doesn't_ move at speed c.
George Murphy