Speed of Light a constant?

[AA]

I'm a bit perplexed by the value of c being considered a constant beyond
the Milky way, and possibly within. Could someone enlighten my thoughts
on this issue.

It has been shown that light will change course due to gravatational
wells around a star, and a slight change in direction will occur thus
leading the postulation that the photon has some very small mass. If
one considers intergalactic travel of light, wouldn't light also be
effected in the third dimention; speed. I would think that light would
not only change direction, but also velocity as it enters and exits the
galactic garvitational wells that exist.

Thank You,
Kevin Longbrake
Student

[Uncle Al]

AA wrote:
>
> I'm a bit perplexed by the value of c being considered a constant beyond
> the Milky way, and possibly within. Could someone enlighten my thoughts
> on this issue.
>
> It has been shown that light will change course due to gravatational
> wells around a star, and a slight change in direction will occur thus
> leading the postulation that the photon has some very small mass. If
> one considers intergalactic travel of light, wouldn't light also be
> effected in the third dimention; speed. I would think that light would
> not only change direction, but also velocity as it enters and exits the
> galactic garvitational wells that exist.

Photon velocity (vector) changes, photon speed (scalar) does not. All
inertial observers observe an identical lightspeed. Lorentz
invariance demands it.

http://arXiv.org/abs/gr-qc/9909014
Amer. J. Phys. 71 770 (2003)
Phys. Rev. Lett. 92 121101 (2004)
falling light

Physics Today 57(7) 40 (2004)
http://physicstoday.org/vol-57/iss-7/p40.shtml
No aether

http://fsweb.berry.edu/academic/mans/clane/
http://physicsweb.org/articles/world/17/3/7
No Lorentz violation

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf

[Phillip Helbig---remove CLOTHES to reply]

In article <eO0Ug.3487$Cq3.921@tornado.ohiordc.rr.com>, "AA" <aa@aa.com>
writes:

> I'm a bit perplexed by the value of c being considered a constant beyond
> the Milky way, and possibly within. Could someone enlighten my thoughts
> on this issue.
>
> It has been shown that light will change course due to gravatational
> wells around a star, and a slight change in direction will occur thus
> leading the postulation that the photon has some very small mass. If
> one considers intergalactic travel of light, wouldn't light also be
> effected in the third dimention; speed. I would think that light would
> not only change direction, but also velocity as it enters and exits the
> galactic garvitational wells that exist.

The LOCALLY MEASURED speed of light is constant. The rest-mass of the
photon is 0, despite the gravitational bending of light. There IS a
delay effect, though, called the Shapiro delay. It has been measured.
It is generally thought of not as a slowing of the speed of light, but
rather as a stretching of space.

[harry]

"Phillip Helbig---remove CLOTHES to reply" <helbig@astro.multiCLOTHESvax.de>
wrote in message news:efrk3i$fii$1@online.de...
> In article <eO0Ug.3487$Cq3.921@tornado.ohiordc.rr.com>, "AA" <aa@aa.com>
> writes:
>
>> I'm a bit perplexed by the value of c being considered a constant beyond
>> the Milky way, and possibly within. Could someone enlighten my thoughts
>> on this issue.
>>
>> It has been shown that light will change course due to gravatational
>> wells around a star, and a slight change in direction will occur thus
>> leading the postulation that the photon has some very small mass. If
>> one considers intergalactic travel of light, wouldn't light also be
>> effected in the third dimention; speed. I would think that light would
>> not only change direction, but also velocity as it enters and exits the
>> galactic garvitational wells that exist.
>
> The LOCALLY MEASURED speed of light is constant. The rest-mass of the
> photon is 0, despite the gravitational bending of light. There IS a
> delay effect, though, called the Shapiro delay. It has been measured.
> It is generally thought of not as a slowing of the speed of light, but
> rather as a stretching of space.

Indeed, as Helbig stressed, the essential point is that the speed of light
is c in any LOCAL measurement system. Not all textbooks make this
sufficiently clear. Another essential point is that using a Newtonian
reasoning of "falling particles" you would get a speeding-up effect, while
in reality there is a "Shapiro DELAY" effect.

For non-local considerations it can be handy as well as enlightening to use
one single inertial reference system far away from stars in free space and
in which the star is approximately at rest. When you use such a reference
system the speed of light near the sun as well as on earth is reduced and is
a function of gravitational potential. See also:
http://www.physlink.com/Education/AskExperts/ae13.cfm

You can see Einstein's 1916 Huygens light bending approach in:
http://www.alberteinstein.info/gallery/gtext3.html (near the end, p.198).

Cheers,
Harald

[markwh04@yahoo.com]

Uncle Al wrote:
> Photon velocity (vector) changes, photon speed (scalar) does not. All
> inertial observers observe an identical lightspeed. Lorentz
> invariance demands it.

Well, there's the catch-22. What constitutes a locally inertial frame
is determined by the metric; i.e. a frame locally inertial at point x
is one whose coordinate charge has {mn,r} = 0 at x.

A fluctuation in the metric also entails a fluctuation in the field of
locally inertial frames. Thus, if L is inertial at x under the metric
g, then under the metric g + dg, L is slightly accelerating at x.

Consequently, the determination of light speed, itself, acquires an
effective fluctuation dependent on dg; and an uncertainty dependent on
whatever uncertainty may exist in g.

There is a different conclusion that also arises out of this
consideration. In quantum field theory, one learns that the field
vacuum for an inertial frame isn't even seen as a pure quantum state,
at all, in an accelerating frame, but as a thermal state. A thermal
mixture is an *incoherent*, *classical* mixture of states, not a
quantum superposition and resides in an entirely different sector from
the pure states associated with the accelerating frame's 'vacuum".

Though these objects are global, one might envision there to be a local
approximation of them such that a *local* frame that is inertial at a
given point x will yield something like an approximate vacuum which,
when seen from the point of view of a frame that is non-inertial at x
will appear as a thermal state that resides in an inequivalent sector
of state space.

The fluctuation in the metric g -> g + dg pushes the inertial frames in
too accelerating frames. Consequently, the vacuua of g are seen as
slightly thermalized, slightly classically-mixed, states when the
metric is at g + dg.

Because of this, the states which reside in the background metric g can
*not* coherently superpose with those that reside in the background
metric g + dg. The corresponding result in quantum theory would be that
the two coherent states |g> and |g + dg> that represent these metrics
would, themselves, reside in different sectors.

The fluctuation g -> g + dg therefore can NOT be seen as a quantum
fluctuation at all and cannot participate in coherent superpositions!
The field, itself, is essentially classical.

These are also conclusions that had been arrived at by independent
means by Sardanashvily, who is fairly well-known for his "gauge
gravitation" programme; and who copublished "Gauge Gravitation Theory"
along with Zakharov in 1992.

The conclusion they drew was in reference to the breaking of the world
symmetry from a local GL(4) group to the local Lorentz group that the
presence of fermions engenders. The quotient GL(4)/Lorentz plays an
analogous role that it would in the symmetry breaking of the Higgs
phenomena. Each sector comprises a separate vacuum phase (and separate
sector in state space). Fluctuations of the associated "Goldstone"
fields are essentially classical and can only be regarded as quantum
fluctuations in a "quasi-particle" approximation.

The fields which embody the GL(4) -> Lorentz symmetry breaking are none
other than the tetrad fields h, out of which the metric g is
constructed.

It also dovetails consistently with the argument posed by Jacobson
(1995, his paper that derives GR from the laws of thermodynamics as a
consequence of the Bekenstein bound), who points out that gravitation
should no more be quantized as a fundamental field to yield gravitons,
than the "sound" field in a solid should. Instead, the gravitons are to
be regarded as analogous to phonons, rather than fundamental quantum
particles in their own right.