According to Einstein's relativity, in a gravitational field the speed of light varies in accordance with the formula:

c' = c(1 + 2φ/c^2)

where c is the speed of light in gravitation-free space and φ is the gravitational potential. The formula is obviously idiotic - it implies that, as photons fall in the gravitational field of the earth, they DECELERATE - their acceleration is negative, -2g. Needless to say, Einsteinians practice crimestop in this case - the formula is never discussed. There are exceptions but the full idiocy is not revealed - either the factor of two is omitted or the minus sign (deceleration) is implicitly replaced with a plus sign (acceleration):

http://www.youtube.com/watch?v=FJ2SVPahBzg
"Relativity 3 - gravity and light"

http://arxiv.org/pdf/gr-qc/9909014v1.pdf
Steve Carlip: "It is well known that the deflection of light is twice that predicted by Newtonian theory; in this sense, at least, light falls with twice the acceleration of ordinary "slow" matter."

Pentcho Valev