Re: c in m/s (was A. Einstein and science-fairs)

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Others had probably said this; I did not read all  messages of this
thread. There is nothing wrong in saying, for example, that "as far
as this class is concerned one meter is defined as the distance between
the two scratches ..., one second is defined by our astronomical clock ..,
and one kilogram ....". In other words we can start by treating m, s
and kg as independently defined references.  The ultimate issues of
accuracy should be addressed at some point, but not in the introductory
chapter. At that stage conceptual simplicity is much more important than
the ultimate accuracy. One has to be very sophisticated to understand
recent (since 1950's) evolutionary steps in the definitions of m or s.
In a first physics course a ruler, a stopwatch and a set of labeled pieces
of brass are as good today as they were a century ago.
Ludwik Kowalski

Cliff Parker wrote:

> Since when does nature respond to our declarations.  I am not suggesting that it is
> likely that she has altered the speed of light but one could always check.  I have a
> problem with the idea expressed previously that the speed of light is something that
> is defined and therefore can not be measured.  God does not check our definitions or
> declarations to see how fast light should travel today.
>
> As to the second part of your comment.  What would happen if someday we detected a
> change in the speed of light based on an accepted definition of time and an accepted
> definition of length (of course that length would have to be something other than the
> meter)?  Which would be wrong the clock, the measure of length or the accepted speed
> of light?