Results in Einstein's theory are deduced from two incompatible principles: the principle of constancy of the speed of light (speed of photons is independent of speed of the light source) and the principle of variability of the speed of light (speed of photons does depend on speed of the light source). This sounds strange but only at first sight. In 1911 Einstein shows that in a gravitational field the speed of light is VARIABLE and gives the respective equation: c'=c(1+V/c^2), where c=300000km/s is the initial speed of light relative to the light source and V is the gravitational potential. But if the speed of light is variable in a gravitational field, the application of the equivalence principle would show that in the absence of a gravitational field the speed of light is also variable and obeys the equation c'=c+v, where v is the relative speed of the light source and the observer.

Einstein's 1911 equation c'=c(1+V/c^2) is consistent with the gravitational redshift factor 1+V/c^2 and therefore this factor is a corollary of the principle of VARIABILITY of the speed of light. In my view, any other result or prediction in Einstein's theory should undergo a similar test. Otherwise confusion would last forever.

Pentcho Valev
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