Re: a relativity question

[Jack Uretsky <jlu@HEP.ANL.GOV>]

Be not so arbitrary, John.  It is a matter of convention as to whether
"mass" means restmass or it means the energy of a system divided by c^2.
Using the latter definition, and delta E = mgh, one gets the correct
answer for the Pound-Rebka experiment and 1/2 the correct answer for the
bending of light by the sun (the other half we can ascribe to the
curvature of space).

Convention is like religion, you know.  Whatever gives you your jollies is
fine with me.
                                        Regards,
                                                Jack

On Tue, 26 Nov 2002, John Mallinckrodt wrote:

> Bob Sciamanda wrote:
>
> > Does not a photon change mass/energy/wavelength/color as it climbs the
> > gravitational potential hill of the earth?
>
> The mass doesn't change; it is always zero.  The energy changes in a
> way that depends on the choice of reference frame just like that of a
> ball or any other object.
>
> Just as we insist that the mass of a ball be judged by determining
> *its* energy in *its* rest frame (or by simply calculating sqrt(E^2 -
> (pc)^2)), we do the same for the photon.  In the case of a photon the
> concept of a "rest frame" is problematic, but we can still calculate
> the "rest energy" or "mass" and we find that it is always zero.
>
> The wavelength and color of the photon are merely additional
> reflections (like energy) of the arbitrary choice of reference frame
> and are not inherent to the photon itself.
>
> --
> John Mallinckrodt        mailto:ajm@csupomona.edu
> Cal Poly Pomona          http://www.csupomona.edu/~ajm
>
> This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.

--
        "What did Barrow's lectures contain?  Bourbaki writes with some
scorn that in his book in a hundred pages of the text there are about 180
drawings.  (Concerning Bourbaki's books it can be said that in a thousand
pages there is not one drawing, and it is not at all clear which is
worse.)"
                                        V. I. Arnol'd in
                                Huygens & Barrow, Newton & Hooke

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.