On Apr 9, 10:33 pm, Tom Roberts wrote in sci.physics.relativity:
> bill wrote:
> > A person is located on a mountain top and is looking at a (very large)
> > clock (B) at sea-level.
> > He notices that clock B is ticking over at a slower rate than his own
> > clock (A) as theorized by Einstein in general theory and as ratified
> > by the Wallops Island experiment where a clock at sea-level, being
> > located in a strong gravitational tidal area, will tick over at a
> > slower rate than an identical clock on top of a mountain that is in a
> > weaker gravitational tidal area.
>
> Note that what you call "gravitational tidal area" is really called
> "Newtonian gravitational potential", valid in the Newtonian
> approximation to GR. Indeed, tidal forces/effects are not involved
> (tidal forces are second derivatives of the Newtonian potential).
>
> Note that while A SEES B tick at a slower rate, this does not imply
> that clock B actually ticks at a slower rate than clock A. Indeed, in GR
> this is modeled as an artifact of the COMPARISON [#], not as an effect
> or modification of the clocks themselves: both clocks tick at their
> usual (proper) rates, but their tick rates appear different when
> situated and compared as you describe.
>
> [#] This comparison is via EM signals in curved spacetime.
>
> > Is he entitled to be of the opinion that if he were to move to sea-
> > level his clock would be subjected to the same 'law' of physics thus
> > it will then be ticking over at a slower rate than it is before he
> > starts his descent?
>
> No. See above -- this is not an effect ON THE CLOCKS, but rather OF THE
> COMPARISON. Note that he is entitled to expect that if he carries his
> clock down and puts it right next to B that the two clocks will tick at
> the same rate.
>
> Your statements are expressed with the implicit assumption there there
> is some "global", "universal", or "absolute" way to determine a clock's
> tick rate. In GR there is no such thing -- all you can do is compare
> clocks to other clocks; the method of comparison can, and usually does,
> affect the result.
>
> Tom Roberts

Honest Roberts, your cleverer brothers Einsteinians expose the "artifact of the COMPARISON" in a somewhat clearer way:

http://www.people.fas.harvard.edu/~djmorin/book.html
Chapter 14: "The equivalence principle has a striking consequence concerning the behavior of clocks in a gravitational field. It implies that higher clocks run faster than lower clocks. If you put a watch on top of a tower, and then stand on the ground, you will see the watch on the tower tick faster than an identical watch on your wrist. When you take the watch down and compare it to the one on your wrist, it will show more time elapsed."

However, Honest Roberts, even your cleverer brothers Einsteinians would never answer the following question:

Is the "artifact of the COMPARISON" (that is, gravitational time dilation) consistent with Einsteiniana's dicovery that the speed of light is CONSTANT in a gravitational field, or is it consistent with Einsteiniana's discovery that the speed of light is VARIABLE in a gravitational field and obeys e.g. Einstein's 1911 equation c'=c(1+gh/c^2) given by Newton's emission theory of light?

Pentcho Valev
pvalev@yahoo.com

On Apr 10, 12:48 pm, "harry" wrote in sci.physics.relativity:
> "Pentcho Valev" wrote:
> : or is it consistent with
> : Einsteiniana's discovery that the speed of light is VARIABLE in a
> : gravitational field and obeys e.g. Einstein's 1911 equation c'=c(1+gh/
> : c^2) given by Newton's emission theory of light?
>
> You should instead refer to his corrected equations of 1916 - which are NOT
> given by Newton's theory.

In 1915 Einstein replaced c'=c(1+gh/c^2) with c'=c(1+2gh/c^2):

http://www.mathpages.com/rr/s6-01/6-01.htm
"In geometrical units we define c_0 = 1, so Einstein's 1911 formula can be written simply as c=1+phi. However, this formula for the speed of light (not to mention this whole approach to gravity) turned out to be incorrect, as Einstein realized during the years leading up to 1915 and the completion of the general theory. In fact, the general theory of relativity doesn't give any equation for the speed of light at a particular location, because the effect of gravity cannot be represented by a simple scalar field of c values. Instead, the "speed of light" at a each point depends on the direction of the light ray through that point, as well as on the choice of coordinate systems, so we can't generally talk about the value of c at a given point in a non-vanishing gravitational field. However, if we consider just radial light rays near a spherically symmetrical (and non- rotating) mass, and if we agree to use a specific set of coordinates, namely those in which the metric coefficients are independent of t, then we can read a formula analogous to Einstein's 1911 formula directly from the Schwarzschild metric. (...) In the Newtonian limit the classical gravitational potential at a distance r from mass m is phi=-m/r, so if we let c_r = dr/dt denote the radial speed of light in Schwarzschild coordinates, we have c_r =1+2phi, which corresponds to Einstein's 1911 equation, except that we have a factor of 2 instead of 1 on the potential term."

However the new equation, c'=c(1+2gh/c^2), was incompatible with the gravitational redshift factor experimentally confirmed by Pound and Rebka:

http://www.blazelabs.com/f-g-gcont.asp
"So, faced with this evidence most readers must be wondering why we learn about the importance of the constancy of speed of light. Did Einstein miss this? Sometimes I find out that what's written in our textbooks is just a biased version taken from the original work, so after searching within the original text of the theory of GR by Einstein, I found this quote: "In the second place our result shows that, 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 and to which we have already frequently referred, 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. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)." - Albert Einstein (1879-1955) - The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity-. Today we find that since the Special Theory of Relativity unfortunately became part of the so called mainstream science, it is considered a sacrilege to even suggest that the speed of light be anything other than a constant. This is somewhat surprising since even Einstein himself suggested in a paper "On the Influence of Gravitation on the Propagation of Light," Annalen der Physik, 35, 1911, that the speed of light might vary with the gravitational potential. Indeed, the variation of the speed of light in a vacuum or space is explicitly shown in Einstein's calculation for the angle at which light should bend upon the influence of gravity. One can find his calculation in his paper. The result is c'=c(1+V/c^2) where V is the gravitational potential relative to the point where the measurement is taken. 1+V/c^2 is also known as the GRAVITATIONAL REDSHIFT FACTOR."

Pentcho Valev
pvalev@yahoo.com

On Apr 10, 6:24 pm, John Polasek wrote in sci.physics.relativity:
> On Thu, 09 Apr 2009 23:31:56 -0500, Tom Roberts wrote:
> >bill wrote:
> >> On Apr 10, 5:33 am, Tom Roberts wrote:
> >>> Note that while A SEES B tick at a slower rate, this does not imply
> >>> that clock B actually ticks at a slower rate than clock A. Indeed, in GR
> >>> this is modeled as an artifact of the COMPARISON [#], not as an effect
> >>> or modification of the clocks themselves: both clocks tick at their
> >>> usual (proper) rates, but their tick rates appear different when
> >>> situated and compared as you describe.
>
> >> So a clock that is located at sea-level does not tick over at a slower
> >> rate than an identical clock on top of a mountain?
>
> >No. Because comparing either clock in the usual way to a frequency
> >standard shows that each is ticking at its usual rate. The COMPARISON
> >via EM signals shows the lower clock is ticking slower than the higher
> >clock, so this difference is an artifact of the comparison, not of
> >either clock.
>
> In order to support your rather surprising position, it would be
> helpful to hear your version describing the results of Pound-Rebka.
> Does it involve the concept of the wave losing energy on the way up?
> What really happened there if both clocks retained their original rate
> regardless of potential?
> It is a given that both clocks taken to the same place would match.
> But there's no really good unambiguous way to compare two clocks at
> different potentials. But it should be possible to hypothesize what
> happened in Pound-Rebka, step by step, that was clearly
> self-consistent. What is your version?

This is a dangerous question and Roberts would never give a straightforward answer. Still, quite surprisingly, some time ago Tom Roberts did find some courage and said that the Pound-Rebka result is consistent with Einstein's 1911 equation (an equation given by Newton's emission theory of light and showing how the speed of light varies with the gravitational potential):

http://groups.google.com/group/sci.physics.relativity/msg/1fb3e28be351d2bd

Pentcho Valev
pvalev@yahoo.com