🚀 go-pugleaf

On Apr 1, 12:52 am, Tom Roberts <tjroberts...@sbcglobal.net> wrote in
sci.physics:
> Anon wrote:
> > Because as you get closer to a massive body light is slowed down, this bends
> > the rays of light towards the massive object. The same is true of other
> > massive objects. That is what Einstein said.
>
> As I said before, Einstein said that in 1911, early on the
> then-unfinished journey to General Relativity. GR itself does not really
> have this property.

Einstein said so in 1920 Roberts Roberts:

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."

http://groups.google.com/group/sci.physics.relativity/browse_frm/thread/7c24a5fbab3bd2aa?
Tom Roberts, Sep 1, 2005: "AFAIK Einstein basically thought in German,
which does not have different words for "speed" and "velocity" ("die
Geschwindigkeit" is used for both). Certainly his "velocity of
propagation" could be phrased as "speed of propagation" without
changing the underlying physics."

> In a suitable approximation, and speaking rather loosely, it's not
> wrong. But without approximation, or to speak more accurately, one must
> discuss geodesic deviation, not "light slowed down". This bending of
> light rays near a massive object is a manifestation of the geometry of
> spacetime, not any change or variation in light -- light always follows
> a null geodesic path, and the only issue is where those paths lead, and
> their relation to each other.

http://groups.google.com/group/sci.physics.relativity/browse_frm/thread/ac686b4b365dee16?
Pentcho Valev wrote:
> CAN THE SPEED OF LIGHT EXCEED 300000 km/s IN A GRAVITATIONAL FIELD?
Tom Roberts, Nov 8, 2005: "Sure, depending on the physical conditions
of the measurement. It can also be less than "300000 km/s" (by which I
assume you really mean the standard value for c). And this can happen
even for an accelerated observer in a region without any significant
gravitation (e.g. in Minkowski spacetime)."

Pentcho Valev
pvalev@yahoo.com