A. Einstein, "Relativity", Chapter 22:

"A curvature of rays of light can only take place when the velocity of
propagation of light VARIES with position."

So, according to Einstein, an observer positioned in a gravitational
field will measure a VARIABLE, not constant velocity of light. The
observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Einsteinians never discuss this problem voluntarily but, when pressed,
they produce a combination of words more or less like this: The
velocity of light is constant only locally, non-locally it is variable.
The meaning of this combination of words, especially when applied to
Einstein's assertion, is a grand secret between Einsteinians.

Pentcho Valev

Pentcho Valev wrote:

Einsteinians never discuss this problem voluntarily

Patent nonsense. It's in every GR textbook. But if all you read is pop
science books then of course you wouldn't know that.

--
Jan Bielawski

"JanPB" wrote in message
oups.com...
[snip crap]
Empirical idiot.

Androcles

Pentcho Valev wrote:

"A curvature of rays of light can only take place when the velocity of
propagation of light VARIES with position."

even I've heard of the Shapiro delay, and I've never even done any GR.

It's also been measured to quite a few decimal place, see
http://relativity.livingreviews.org/...-4/node10.html
section 3.4.2 for example.

br

Pentcho Valev wrote:
A. Einstein, "Relativity", Chapter 22:

"A curvature of rays of light can only take place when the velocity of
propagation of light VARIES with position."

So, according to Einstein, an observer positioned in a gravitational
field will measure a VARIABLE, not constant velocity of light. The
observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Einsteinians never discuss this problem voluntarily but, when pressed,
they produce a combination of words more or less like this: The
velocity of light is constant only locally, non-locally it is variable.
The meaning of this combination of words, especially when applied to
Einstein's assertion, is a grand secret between Einsteinians.

Pentcho Valev


Valev confuses *velocity* of light with *speed* of light!

Pentcho Valev wrote:
A. Einstein, "Relativity", Chapter 22:

"A curvature of rays of light can only take place when the velocity of
propagation of light VARIES with position."

So, according to Einstein, an observer positioned in a gravitational
field will measure a VARIABLE, not constant velocity of light. The
observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Einsteinians never discuss this problem voluntarily but, when pressed,
they produce a combination of words more or less like this: The
velocity of light is constant only locally, non-locally it is variable.
The meaning of this combination of words, especially when applied to
Einstein's assertion, is a grand secret between Einsteinians.

This is all quite well known, has been for decades, and is no dirty
little secret. (If it were proprietary, then why did you find it in a
book written by Einstein targeted at the general public?)

Even in special relativity it's necessary for the speed of light to
vary between frames of reference having a relative velocity. The speed
of light is invariant locally. WITHIN any INERTIAL reference frame, c
will always measure out to 3.0 x 10^8 m/s.

-Mark Martin

Sam Wormley wrote:

Valev confuses *velocity* of light with *speed* of light!

Indeed!

Since Einstein died in 1955, and the Shapiro delay was only predicted
in 1964, then he couldn't have been referring to that.

br

Dr Photon wrote:
Since Einstein died in 1955, and the Shapiro delay was only predicted
in 1964, then he couldn't have been referring to that.

Sure he could -- Einstein was extremely well-versed in the basis of GR,
and he most definitely knew that the speed of light can vary when
measured over non-local paths. Shapiro's contribution was to realize
that this esoteric aspect of GR could actually be measured, and he went
on to measure it.


Tom Roberts

Pentcho Valev wrote:
A. Einstein, "Relativity", Chapter 22:
"A curvature of rays of light can only take place when the velocity of
propagation of light VARIES with position."

So, according to Einstein, an observer positioned in a gravitational
field will measure a VARIABLE, not constant velocity of light.

No, he did NOT say that. He said what he said. shrug

But indeed, when an observer measures (say) the deflection of stars'
images during an eclipse, that observer can conclude that the presence
of the sun's gravitation did affect the propagation of light from those
stars, and that means a position-dependent variation in speed
(necessarily over the different non-local paths from star to observer).


The
observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Hmmm. For the case of observing stars' images before, during, and after
an eclipse, the change in frequency is higher order in (extremely) small
quantities than the deflection. I'm pretty sure it is well below
realistic experimental resolutions.


Einsteinians never discuss this problem voluntarily

This is not a "problem", it is merely your personal misconceptions and
errors.


Sam Wormley wrote:
Valev confuses *velocity* of light with *speed* of light!

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. While
Valev is indeed confused, I don't think this is relevant.


Tom Roberts

On Thu, 01 Sep 2005 11:41:07 -0500, Tom Roberts wrote:

Pentcho Valev wrote:

[ some of Pentcho's garbage snipped, along with Tom's reasonable
responses ]

The observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Hmmm. For the case of observing stars' images before, during, and
after an eclipse, the change in frequency is higher order in
(extremely) small quantities than the deflection. I'm pretty sure it
is well below realistic experimental resolutions.

If the Sun is stationary relative to us (bad assumption but let's make
it anyway) then shouldn't there be _no_ frequency shift induced in the
light as a result of its passing near the Sun? (Assume the Moon is
massless or else so light we can ignore it -- "Styrofoam Moon".)

After all, a particular number of wave crests went into the Sun's gravity
well, the same number came out, and whether the light went near the Sun or
not makes no difference to how many seconds of time our clocks tick off.
So, there can't be any redshift/blueshift from that cause, _if_ the Sun
is stationary relative to us. (I stated that rather loosely; I hope it's
clear what I meant.)

On the other hand, if the Sun is moving transverse to our line of
sight, then ... uh ... wouldn't the light "steal" a little energy from
the Sun if it passes by the backside, and wouldn't it "give up" a
little energy if it passes by the front side, with the Sun being slowed
or accelerated slightly as a result? That would imply that stars on the
edge of the sun which is "in front of" our orbital path around the Sun
should be slightly blueshifted, and light which is "in back of" our
orbital path should be slightly redshifted, as a result of its trek close
to the Sun.

Right...?

Viewed differently, on the backside, the 3-d path is "getting shorter" as
the Sun moves out of the way, so the number of wavecrests "in transit"
must be decreasing, which implies there's a blueshift. On the front side,
the path is "getting longer" as the Sun moves into our line of sight, so
the number of wavecrests "in transit" along that line is increasing, and
there must be redshift. Rather pleasingly, both these rather fuzzy mental
models arrive at the same conclusion -- maybe it's even correct...


--
Nospam becomes physicsinsights to fix the email