EINSTEINIANA: 1 = 0 = 2

Photons and cannonballs have an identical acceleration in a gravitational field, as predicted by Newton's emission theory of light. Einsteinians often admit that but, for the sake of confusion, introduce two additional accelerations for photons - zero acceleration and twice the acceleration of cannonballs:

http://www.damtp.cam.ac.uk/user/hsr1...notes12_02.pdf
Harvey Reall, University of Cambridge: "...light falls in the gravitational field in exactly the same way as a massive test particle."

http://sethi.lamar.edu/bahrim-cristi...t-lens_PPT.pdf
Dr. Cristian Bahrim: "If we accept the principle of equivalence, we must also accept that light falls in a gravitational field with the same acceleration as material bodies."

http://www.wfu.edu/~brehme/space.htm
Robert W. Brehme: "Light falls in a gravitational field just as do material objects."

http://www.amazon.com/Why-Does-mc2-S.../dp/0306817586
Why Does E=mc2?: (And Why Should We Care?), Brian Cox, Jeff Forshaw, p. 236: "If the light falls in strict accord with the principle of equivalence, then, as it falls, its energy should increase by exactly the same fraction that it increases for any other thing we could imagine dropping. We need to know what happens to the light as it gains energy. In other words, what can Pound and Rebka expect to see at the bottom of their laboratory when the dropped light arrives? There is only one way for the light to increase its energy. We know that it cannot speed up, because it is already traveling at the universal speed limit, but it can increase its frequency."

http://www.amazon.com/Brief-History-.../dp/0553380168
Stephen Hawking, A Brief History of Time, Chapter 6: "A cannonball fired upward from the earth will be slowed down by gravity and will eventually stop and fall back; a photon, however, must continue upward at a constant speed...."

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."

http://www.speed-light.info/speed_of_light_variable.htm
"You can find a more sophisticated derivation later by Einstein (1955) from the full theory of general relativity in the weak field approximation: (....) Namely the 1955 approximation shows a variation in km/sec twice as much as first predicted in 1911."

Pentcho Valev