Einstein shows how the speed of light varies with the gravitational
potential:
http://www.relativitybook.com/resources/Einstein_gravity.html
Albert Einstein: "If we call the velocity of light at the origin of co-
ordinates c0, then the velocity of light c at a place with the
gravitation potential phi will be given by the relation c=c0(1+phi/
c^2)."
Einsteiniana's zombies sing "Divine Einstein" and "Yes we all believe
in relativity, relativity, relativity". This is "perfectly valid and
makes good physical sense", explains Steve Carlip, "but a more modern
interpretation is that the speed of light is constant in general
relativity":
http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html
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."
Einsteiniana's zombies know nothing more consistent than Steve
Carlip's explanation. The ecstasy gets uncontrollable - zombies tumble
to the floor, start tearing their clothes and go into convulsions.
Pentcho Valev
pva...@yahoo.com