Re: speed of light

Moorad Alexanian (
Sat, 13 Nov 1999 15:16:09 -0500

Dear George,

I am not sure I follow your argument. The meter is defined as the distance
light travels in vacuum in 1/299,792,458 seconds. If clocks can be taken
back into time and there is no time dilation or contraction, wouldn't a
meter have different lengths and wouldn't it be shorter in the past if the
speed of light in vacuum is reduced?

Always enjoy your posts,


-----Original Message-----
From: George Murphy <"">
To: <>
Cc: <>; <>;
Date: Saturday, November 13, 1999 7:52 AM
Subject: Re: speed of light

> wrote:
>> You all may be interested to know that John D. Barrow (who with F. J.
>> wrote, _The Anthropic Principle_ in 1986) wrote a feature article in _New
>> Scientist_ (July 24, 1999) entitled "Is nothing sacred?"
>> The lead-in to the article states, "Call it heresy, but all the big
>> cosmological problems will simply melt away, if you break one rule, says
>> D. Barrow--the rule that says the speed of light never varies."
>> In one place Barrow writes, "The simplicity of this new model [the
>> light speed hypothesis] and the strikinng nature of its predictions
>> that we should invstigate it more seriously."
> Yes, it's a possibility that has to be considered. But in the
>space-time way of understanding special relativity, c is simply a factor
for the
>conversion of units used for distances in spacelike directions (meters) &
those in
>timelike directions (seconds). The use of those different units (&
therefore of a
>value of c differing from 1) is due to historical convention, not basic
physics. The
>value of c therefore plays the same type of role as the mechanical
equivalent of heat.
> While we usually call the quantity c which occurs in the Lorentz
>"the speed of light" & that was its historical origin, the 2 quantities are
>distinct. What special relativity requires is that there be an absolute
speed. Whether
>or not light travels at that speed (& it doesn't if the photon has a rest
mass) is
>another matter.
> It isn't hard to formulate a relatvistic theory in which "the speed of
>isn't constant - e.g., with a nonzero photon mass. A theory in which the
>between seconds and meters varied would be - I think - a lot harder to
formulate in a
>way which agreed with what we know about relativity.
> George
>George L. Murphy