Re: a relativity question

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

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.