In order for the gravitational time dilation (fabricated by Einstein in 1911) and the gravitational redshift to be compatible, light in a gravitational field must behave in an idiotic way: Its speed must DECREASE as the light falls towards the source of gravity. That is, the acceleration of falling photons is NEGATIVE - in the gravitational field of the Earth it must be -2g. This idiotic negative acceleration of photons, -2g, was essentially a fudge factor Einstein and his mathematical friends had to introduce in 1915 (otherwise general relativity would not have been able to "predict" the gravitational redshift originally predicted by Newton's emission theory of light):

"Specifically, Einstein wrote in 1911 that the speed of light at a place with the gravitational potential j would be c0(1 + j/c0^2), where c0 is the nominal speed of light in the absence of gravity. In geometrical units we define c0 = 1, so Einstein's 1911 formula can be written simply as c = 1 + j. However, this formula for the speed of light - indeed, this whole approach to gravity - turned out to be incorrect. [...] ...the circumferential speed of light differs from the radial speed. The former is given by the same formula as in Einstein's 1911 paper, but the latter differs from the 1911 formula by a factor of 2 on the "potential" term. [...] ...we have c_r = 1 + 2j, which corresponds to Einstein's 1911 equation, except that we have a factor of 2 instead of 1 on the potential term. Thus, as j becomes increasingly negative (i.e., as the magnitude of the potential increases), the radial "speed of light" c_r defined in terms of the Schwarzschild parameters t and r is reduced to less than the nominal value of c." http://www.mathpages.com/rr/s6-01/6-01.htm

Nothing in general relativity is deduced from postulates. The "theory" is a malleable combination of ad hoc equations and fudge factors able to "predict" anything.

Pentcho Valev