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The Pound-Rebka experiment confirmed the Newtonian tenet that, as light falls in a gravitational well, its speed increases exactly as the speed of any falling particle does:
http://www.einstein-online.info/spotlights/redshift_white_dwarfs
Albert Einstein Institute: "One of the three classical tests for general relativity is the gravitational redshift of light or other forms of electromagnetic radiation. However, in contrast to the other two tests - the gravitational deflection of light and the relativistic perihelion shift -, you do not need general relativity to derive the correct prediction for the gravitational redshift. A combination of Newtonian gravity, a particle theory of light, and the weak equivalence principle (gravitating mass equals inertial mass) suffices. (...) The gravitational redshift was first measured on earth in 1960-65 by Pound, Rebka, and Snider at Harvard University..."
Is this compatibility between the Pound-Rebka experiment and Newton's emission theory of light dangerous for Einstein's theory? Many Einsteinians don't know the answer to that question and teach, just in case, that the speed of light does not increase at all:
http://www.amazon.com/Why-Does-mc2-Should-Care/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."
Pentcho Valev pvalev@yahoo.com