Re: Fact
From: Paulps (paulps_at_freeuk.com)
Date: 03/04/05
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Date: Fri, 4 Mar 2005 16:24:45 -0000
"Tom Roberts" <tjroberts@lucent.com> wrote in message
news:d04nj6$5dl@netnews.proxy.lucent.com...
> Paulps wrote:
> > Some simple facts.
> > a) The speed of light (SOL) is constant in the medium of vacuum and as
such
> > is used as constant.
>
> OK. Remember that what is actually measured is the speed of light in
vacuum
> relative to the measuring apparatus. We find that no matter how the
apparatus is
> oriented, or how it moves relative to objects like the earth and sun, the
> measured value is constant (after accounting for any non-inertial motions
of the
> apparatus).
>
> BTW nobody else calls vacuum a "medium". Be aware that your nonstandard
usage
> will probably confuse others (and perhaps/probably yourself). Calling
vacuum a
> "medium" does not make it one.
>
I have taken note of this point
>
> > b) The SOL is independent of the velocity of the source with respect to
the
> > vacuum/medium.
>
> For an optical medium this is clear and observable[#]. For vacuum you need
to
> explain how "speed relative to vacuum" makes sense and can be measured (at
least
> in principle). This directly implies you must specify how to measure the
speed
> of an apparatus "relative to vacuum". That will be quite difficult, as all
> measurements of speed are relative to the measuring apparatus, and vacuum
has no
> apparatus....
>
See improved facts.
> [#] But, of course, nobody measures speeds relative to the medium.
> What is measured is either speed in the medium relative to the
> apparatus, or speed relative to the apparatus and speed of the
> medium relative to the apparatus. In this last case some theory
> is needed to convert the two measurements into a speed relative
> to the medium.
>
> With that last point of the footnote in mind, what you need to define and
> describe is a measurement of the speed of vacuum relative to an apparatus.
Good
> luck....
>
Thank you
> > c) The observer can from observation of the deviation frequency of light
> > with a known frequency, determine their velocity with respect to the
vacuum
> > that the light is constant in by a spectrophotometer and computation.
>
> This has the same difficulty mentioned above. In fact, as I mentioned
above,
> speed of light measurements in vacuum obtain the same value independent of
> motion of the apparatus. Measurements of frequency shifts depend on a
number of
> things, including gravitational potentials and relative velocity of
detector
> relative to source.
>
Point noted
> But none of that can be described as "relative to vacuum" -- in every case
there
> is a physical apparatus relative to which measurements are made.
>
Point noted See improved fact or later.
Paul.
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