On Jun 21, 11:42 pm, harald wrote in sci.physics.relativity:
And here Kevin Brown explains the factor two much better:

http://www.mathpages.com/home/kmath115/kmath115.htm

Harald

http://www.mathpages.com/home/kmath115/kmath115.htm
"In the general theory of relativity the predicted frequency shift for
light in a gravitational field is the same as Einstein had predicted
in 1911. However, in the 1915 theory, the amount of deflection which a
ray of light is predicted to undergo when passing by a gravitating
body is twice as much as he had predicted in 1911."

The amount of deflection predicted in 1915 ("twice as much as he had
predicted in 1911") is INCOMPATIBLE with the 1911 frequency shift. See
also this:

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."

http://www.speed-light.info/speed_of_light_variable.htm
"Einstein wrote this paper in 1911 in German (download from:
http://www.physik.uni-augsburg.de/an...35_898-908.pdf
). It predated the full formal development of general relativity by
about four years. You can find an English translation of this paper in
the Dover book 'The Principle of Relativity' beginning on page 99; you
will find in section 3 of that paper Einstein's derivation of the
variable speed of light in a gravitational potential, eqn (3). The
result is: c'=c0(1+phi/c^2) where phi is the gravitational potential
relative to the point where the speed of light co is measured......You
can find a more sophisticated derivation later by Einstein (1955) from
the full theory of general relativity in the weak field
approximation....For the 1955 results but not in coordinates see page
93, eqn (6.28): c(r)=[1+2phi(r)/c^2]c. Namely the 1955 approximation
shows a variation in km/sec twice as much as first predicted in 1911."

The frequency shift predicted in 1911 (the prediction did not change
in 1915) is f'=f(1+phi/c^2); it was confirmed experimentally by Pound
and Rebka in 1960. Given the formula:

(frequency) = (speed of light)/(wavelength)

the equation f'=f(1+phi/c^2) is compatible with Einstein's 1911
equation c'=c(1+phi/c^2) given by Newton's emission theory of light
but incompatible with Einstein's 1915 equation c'=c(1+2phi/c^2). Two
conclusions:

(1) Einstein's 1915 theory is inconsistent: the predicted frequency
shift f'=f(1+phi/c^2) and the predicted shift in the speed of light
c'=c(1+2phi/c^2) cannot be reconciled within the formula:

(frequency) = (speed of light)/(wavelength)

(2) The Pound-Rebka experiment refutes the amount of deflection
predicted in 1915 ("twice as much as he had predicted in 1911") and
confirms the amount of deflection predicted by Newton's emission
theory of light.

Pentcho Valev