Richard Feynman: "I want to emphasize that light comes in this form - particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you probably learned something about light behaving like waves. I'm telling you the way it does behave - like particles. You might say that it's just the photomultiplier that detects light as particles, but no, every instrument that has been designed to be sensitive enough to detect weak light has always ended up discovering the same thing: light is made of particles." QED: The Strange Theory of Light and Matter, p. 15 http://www.amazon.com/QED-Strange-Th.../dp/0691024170

Here Feynman is correct. As far as its speed is concerned, light does indeed behave like particles. Its speed varies with the speed of the source, like the speed of ordinary projectiles, and it accelerates in a gravitational field just as falling bodies do (in the gravitational field of the Earth the acceleration of falling photons is g). Consider this:

Paul Fendley: "First consider light shined downward in a freely falling elevator of height h. [...] By the time the light hits the bottom of the elevator, it [the elevator] is accelerated to some velocity v. [...] We thus simply have v=gt=gh/c. [...] Now to the earth frame. When the light beam is emitted, the elevator is at rest, so earth and elevator agree the frequency is f. But when it hits the bottom, the elevator is moving at velocity v=gh/c with respect to the earth, so earth and elevator must measure different frequencies. In the elevator, we know that the frequency is still f, so on the ground the frequency f'=f(1+v/c)=f(1+gh/c^2). On the earth, we interpret this as meaning that not only does gravity bend light, but changes its frequency as well." https://www.yumpu.com/en/document/vi...5-paul-fendley

Substituting f=c/λ (λ is the wavelength) into Fendley's equations gives:

f' = f(1+v/c) = f(1+gh/c^2) = (c+v)/λ = c(1+gh/c^2)/λ = c'/λ

where

c' = c+v = c(1+gh/c^2)

is the speed of light relative to an observer on the ground or, equivalently, relative to an observer in gravitation-free space moving with speed v towards the emitter. Clearly the speed of light varies with both the gravitational potential and the speed of the observer, as predicted by Newton's emission theory of light and in violation of Einstein's relativity. Many scientists know and sometimes even teach that, more or less explicitly:

"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://sethi.lamar.edu/bahrim-cristi...t-lens_PPT.pdf

University of Illinois at Urbana-Champaign: "Consider a falling object. ITS SPEED INCREASES AS IT IS FALLING. Hence, if we were to associate a frequency with that object the frequency should increase accordingly as it falls to earth. Because of the equivalence between gravitational and inertial mass, WE SHOULD OBSERVE THE SAME EFFECT FOR LIGHT. So lets shine a light beam from the top of a very tall building. If we can measure the frequency shift as the light beam descends the building, we should be able to discern how gravity affects a falling light beam. This was done by Pound and Rebka in 1960. They shone a light from the top of the Jefferson tower at Harvard and measured the frequency shift. The frequency shift was tiny but in agreement with the theoretical prediction. Consider a light beam that is travelling away from a gravitational field. Its frequency should shift to lower values. This is known as the gravitational red shift of light." https://courses.physics.illinois.edu...re13/L13r.html

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..." http://www.einstein-online.info/spot...t_white_dwarfs

"Let's say you, the observer, now move toward the source with velocity vo. You encounter more waves per unit time than you did before. Relative to you, the waves travel at a higher speed: v'=v+vo. The frequency of the waves you detect is higher, and is given by: f'=v'/λ=(v+vo)/λ." http://physics.bu.edu/~redner/211-sp...9_doppler.html

"vo is the velocity of an observer moving towards the source. This velocity is independent of the motion of the source. Hence, the velocity of waves relative to the observer is c + vo. [...] The motion of an observer does not alter the wavelength. The increase in frequency is a result of the observer encountering more wavelengths in a given time." http://a-levelphysicstutor.com/wav-doppler.php

Pound, Rebka and Snider knew that their experiments had confirmed the variation of the speed of light predicted by Newton's emission theory of light, not the gravitational time dilation predicted by Einstein's relativity:

R. V. Pound and G. A. Rebka, Jr, APPARENT WEIGHT OF PHOTONS http://journals.aps.org/prl/pdf/10.1...sRevLett.4.337

R. V. Pound and J. L. Snider, Effect of Gravity on Gamma Radiation: "It is not our purpose here to enter into the many-sided discussion of the relationship between the effect under study and general relativity or energy conservation. It is to be noted that no strictly relativistic concepts are involved and the description of the effect as an "apparent weight" of photons is suggestive. The velocity difference predicted is identical to that which a material object would acquire in free fall for a time equal to the time of flight." http://virgo.lal.in2p3.fr/NPAC/relat...iers/pound.pdf

Pentcho Valev