🚀 go-pugleaf

On Mar 11, 5:27 am, Tom Roberts <tjroberts...@sbcglobal.net> wrote in
sci.physics:
> Tom wrote:
> > The speed of light varies depending on the strength of the
> > gravitational field. Einstein said that.
>
> He said that in 1911, early on the then-unfinished journey to General
> Relativity. GR itself does not really have this property -- the _LOCAL_
> speed of light is everywhere c. When measured over non-local paths the
> speed of light can vary, but there is no definite dependence on
> "strength of the gravitational field", it's rather that one must compute
> an integral over the path to obtain the theoretical value for such a
> speed measurement.
>
>         Yes, as one prolific idiot around here is fixated on,
>         in the APPROXIMATION of weak fields and restriction to
>         paths at fixed gravitational potential, for Newtonian
>         coordinates one can express the non-local COORDINATE
>         speed of light in terms of the gravitational potential.
>         In 1911 Einstein did not understand all the caveats
>         mentioned here, but certainly did by 1915; this idiot
>         still does not understand them.

The year is 1920 Roberts Roberts and Divine Albert still believes that
the speed of light "varies with position" in a gravitational field, as
Superior Brother Steve Carlip explains to you:

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html
Superior Brother Steve Carlip: "Einstein went on to discover a more
general theory of relativity which explained gravity in terms of
curved spacetime, and he talked about the speed of light changing in
this new theory.  In the 1920 book "Relativity: the special and
general theory" he wrote: ". . . according to the general theory of
relativity, the law of the constancy of the velocity of light in
vacuo, which constitutes one of the two fundamental assumptions in the
special theory of relativity [. . .] cannot claim any unlimited
validity.  A curvature of rays of light can only take place when the
velocity of propagation of light varies with position."  Since
Einstein talks of velocity (a vector quantity: speed with direction)
rather than speed alone, it is not clear that he meant the speed will
change, but the reference to special relativity suggests that he did
mean so.  THIS INTERPRETATION IS PERFECTLY VALID AND MAKES GOOD
PHYSICAL SENSE, but a more modern interpretation is that the speed of
light is constant in general relativity."

In a sense, Superior Brother Steve Carlip is less dishonest (or more
naive) than you Roberts Roberts.

Pentcho Valev
pvalev@yahoo.com