sci.physics.particle

On Mar 16, 12:41 pm, The Speaking Clock
wrote:
> On 16 Mar, 20:30, BradGuth wrote:
>
>
>
> > On Mar 16, 9:14 am, Tom Roberts wrote:
>
> > > The Speaking Clock wrote:
> > > > On 15 Mar, 08:57, Pentcho Valev wrote:
> > > >> [... his usual nonsense]
>
> > > > Would the speed of light be a non wiggly constant at the very edge of
> > > > the universe - bending around it?
>
> > > The speed of light is a constant, c, for any LOCAL measurement anywhere
> > > in the universe. I guess that includes "non wiggly". It also includes
> > > essentially all measurements of light speed here on earth. At least that
> > > is what GR predicts, and there are no observations that contradict it.
>
> > > [Ignore Valev when he brings up Pound-Rebka and similar
> > > experiments -- they do not measure speed.]
>
> > > But if you want to see light "bending around the universe" then that
> > > would certainly require a non-local path, and there's no solid
> > > prediction of the result (given the uncertainties in the physical
> > > situation you have in mind).
>
> > > It is rather difficult to perform a non-local measurement of the speed
> > > of light, but it has been done by sending radar waves across the solar
> > > system to reflect back from mars and venus. By measuring the round-trip
> > > delay repeatedly over several years, and fitting to the planetary
> > > orbits, one can deduce the round-trip speed of light for these paths.
> > > That speed varies, depending on how close to the sun the path passes;
> > > look up "Shapiro time delay". The results are in excellent agreement
> > > with the predictions of GR.
>
> > > Some people claim this is due to the solar atmosphere.
> > > They are wrong: by doing this for multiple wavelengths the
> > > effect of the solar atmosphere can be identified, and is
> > > found to be negligible. Of course it would be highly
> > > unlikely that such a different effect could mimic the GR
> > > dependence on path. Indeed, measurements using pulsars
> > > agree with the GR predictions for paths that never go
> > > inside earth's orbit, and we know what the solar
> > > atmosphere is out here.
>
> > > Tom Roberts
>
> > But photons clearly represent mass, thus the solar atmosphere of
> > photons does offer mass for other passing photons to interact with.
> > . -BradGuth- Hide quoted text -
>
> > - Show quoted text -
>
> Photons are just light packets of energy with no mass. Mass and
> energy are interconnected, but if there is something for photons to
> interact with in a solar atmosphere then it is not mass. I'm a whelk
> and so I'd say that the universe is even stranger than the dreams of
> the most rabid string theorists, but mass is an outdated concept
> anyways. I mean - what the hell is mass?

I think of photons as zero mass dump trucks, each capable of hauling a
wee bit of mass.
. - Brad Guth