"Are Photons Matter, and Do They Obey Newton's Law of Gravity?"
by Ted Huntington
Are photons matter, and do they obey Newton's laws of gravity? For more than a century the majority of people in science would answer this question "no".
The view that particles of light are matter is not a new idea, and it seems clear that Newton believed that light was a particle, and by default then, it can be presumed that Newton believed that particles of light obey the inverse distance law of gravitation just like planets do, although to my knowledge Newton never explicitly stated this in writing.
The "corpuscular" theory of light would lose popularity among that tiny crowd of people on planet earth who endeaver in science. This theory of particles of light as being material objects lost favor when Thomas Young found that light passed through two slits causes interference patterns that seemed to imply that light is a wave, and interestingly, the idea of light being beams of particles with wavelength represented by distance between particles (similar to sound) was ruled out. The majority of those who follow science began to accept that light was not "corpuscular" but was instead a wave. Initially, the view was that light was a longitudinal wave as sound is, but the phenomenon of light polarization, seemed to prove to people's satisfaction that light is a transverse wave. And a very exotic and math-rich theory was created by James Maxwell, where light, as a transverse wave, conveys magnetism in one dimension and electrism in another dimension. This view is still the prevailing belief. When Michelson and Morley showed that the speed of light remains constant in a horizontal plane, this seems to have implied to Albert Einstein that the speed of light was a fundamental constant of the universe, a kind of "glue" that holds together the laws of matter, space and time. As an aside, an important truth to note, is that the concept of time and space dilation arose from an effort to save the "aether theory" (the idea that some material, an aether gas of some kind, fills all space in the universe, and is the medium that moves in a beam of light, much as air or water is the medium for sound). George FitzGerald theorized that the Michelson Morley result that the speed of light is the same in all horizontal directions (relative to the center of earth), must mean that space contracts in the direction of the light's movement, just enough, in an exact amount, if you can believe, to compensate for any change in velocity of light due to the earth's movement through the aether. Lorentz developeed this idea further. Einstein dropped the idea of an aether, but kept the idea of space and time dilation. In addition, the "corpuscular" theory of light as a particle was revived by Planck and Einstein, but without the explicit belief that particles of light are material. Einstein created an exotic and mathematically complex theory, the General Theory of Relativity, that views time as being depended on matter and velocity. My own belief is that time is the same value everywhere in the universe. For example, if the time=midnight here in the Milky Way, then the time=midnight in the Andromeda Galaxy too. I reject time and space dilation, but certainly the majority accept this theory and the few claimed experimental proofs. Sorry, for the long diversion, but some of this background is important ot get the context of the history of views about the nature of light.
The prevailing view of the past century has been that of Einstein's "General Theory of Relativity", which views photons, particles of light, as moving at a constant velocity, having no mass, and being viewed as "energy". Any idea of particles of light being pieces of matter and obeying the laws of gravity have not arisen since the time of Newton, over 200 years ago. Why has this view of particles of light as pieces of matter that obey the inverse distance law of gravity been neglected and rejected for more than 200 years? I don't know why for sure, but there are certainly some beliefs that stand in the way of this theory. For one, the experiment of Michelson-Morley seems to imply that the speed of photons never changes. There is evidence that the speed of light may change, from everyday experience. When a person looks in a mirror, light has changed direction 180 degrees from a light source back to your eye. Possibly the particles of light have maintained their velocity in doing this 180 degree turn around, but the possibility of photons coming to a complete stop, and bouncing back in the opposite direction (as would be implied by simple collision physics) cannot be ruled out. If the photon does stop and bounce back, clearly, the velocity of photons is not constant, and maybe they do obey Newton's law of gravity, in which case, we might feel that Newton and his crowd may have seen farther than perhaps modern people would give them credit for. But the case for particles of light maintaining a constant velocity during this 180 degree turn around allows for a constant velocity light particle theory to continue. If the velocity of light does obey the law of gravity, if photons do feel the influence of gravity, just like a ball thrown up in the air on earth does, perhaps the effect can be measured here on earth. Perhaps the large gravity of earth (at least relative to the gravity of a human) might actually slow a the movement of a photon moving away from earth, and likewise, the gravity of earth, might slightly accelerate the velocity of a photon moving towards earth. If not, then it would seem that the velocity of photons really may be constant, and may never accelerate. A simple experiment to measure the speed of light in both vertical directions (a variation of the Fizeau, Foucault, Michelson-Morley experiments) might reveal an actual change in velocity for light. That certainly would be an exciting find. To know that all matter is probably made of particles of light, that photons are probably the basis of all matter, and that like all matter, photons obey Newton's law of gravity, would give a logical cohesive picture and understanding of the universe. But if not true, no such view should be held, because of course, ultimately the truth is most important. In fact this method, of measuring delays in the velocity of particles against the gravity of earth, is one method of determining the mass of high speed particles such as electrons, protons, etc. in order to discern between the influence of gravity and that of electricity on pieces of matter. The Pound-Rebka experiment might be evidence that the velocity of light is affected by the immense gravity of earth.
So where do photons get this incredibly high velocity from, if they are matter? This is another question that any theory of the universe should provide answers for. Very high velocities for matter is very possible. The key to generating high velocities is to lower the distance between two pieces of matter as much as possible. Because the force of gravity, definied by the inverse distance equation increases the smaller the distance separating two pieces of matter, the lower this distance (the denominator in the simple gravity equation F=Gm1m2/d^2) the larger the force of gravity, and therefore the larger the velocity a piece of matter will obtain. This is a principle applied in sending interplanetary ships from earth. The ships are sent as close as possible to massive bodies like the Sun, and planet Jupiter to get a "gravitational assist". The massive gravity of those bodies greatly increases the velocity of the ships in a way that the combustion of the small quantity of hydrogen and oxygen fuel on a ship cannot. So it may be that, photons obtain this very high velocity, when they collide with other photons, where the distance between the two photons might be very small, and so the force of gravity between them might be very high. In fact, that two photons, in practice, can only get some finite distance apart, might be the reason the speed of light appears to be so consistent at 3e8m/s. In addition, there are no other pieces of matter known that are smaller than a photon, and so there is nothing except other photons in the way of any given photon to slow it down. Unlike, larger clusters of matter, such as our ball thrown in the air, or rolled on the ground, photons have no friction, and photon collisions may be perfectly elastic without any loss of velocity. Since we cannot see photon collisions up close, we will probably forever be guessing about the nature of those collisions. Another wonderful experiment is to determine if, in fact, photons do collide with each other. Simply pointing two powerful photon filled beams of light at each other and measuring for reflected photons in other directions might be one method of verifying that photons do bounce off each other and not just other objects such as mirrors, coffee cups, and telephones. Perhaps photons bouncing off each other is what explains the interference patterns of light sent through two slits or reflected by a diffraction grating. We should not stop guessing and trying out new theories when it comes to science. I should add as yet another aside, that I reject the "big bang" "expanding" "background radiation" universe theory, and think a universe of infinite size and age is more likely, simply because there must be galaxies so far away that not even one particle of light from them reaches our tiny telescope detectors.
So it may very well be that Isaac Newton's principle belief that particles of light, like all other matter, obey the inverse distance universal law of gravitation. I am calling for the above experiments to be done, to determine if there is, in fact, any measurable difference in the velocity of light by the gravity of earth. Perhaps in the far future, humans will be able to run this experiment against the mass of Jupiter, the Sun, and even larger bodies of matter. How exciting would that be to find that, yes, the velocity of light is not constant as was believed for more than a century, or no, that the velocity of light does appear to remain constant. Either way, the result is interesting and informative. To measure the speed of light vertically, the mirror method might not be the best method, and very large distances might be needed. All that is needed is to measure if there is a difference in time between the sending and receiveing of a light beam from bottom to top with the time from top to bottom. The distance must be held constant, or be so large that the measured difference would rule out any error. This picture of a universe of infinite size and age, filled with space and matter, the matter composed only of photons, is my current opinion of the most likely physics of the universe. This view seems to be the most simple, logical and consistent with the observed reality.