The Equivalent Rest-mass of Photon

The photon (P), one of the elementary particles of the Standard Model, is considered massless. The Universal Gravitation Law states that the gravity force (GF) takes place only between bodies having a mass. Einstein's prediction, based on the Theory of General Relativity, provides that the light is conditioned by the action of the GF. However observations showed that the P feels GF. Lord Eddington, with his famous observation in 1919, confirmed completely what Einstein had said. During a sun eclipse, indeed, it was possible to observe that the light coming from far away stars, when passing next to the sun rather than propagate in straight line, followed a trajectory bended towards the sun. We know that two massless Ps, meeting, materialise in a couple of quark-antiquark, or even in a couple muon-antimuon which, summed up, have a mass of 400 electrons. The energetic value (E) of the P is represented by the Planck's constant (h) - equal to 6.625. 10(-27) [erg . sec] - times its frequency (f): E - hf. The value of f is not defined, but extremely variable, according to the EM spectrum. Thus we should indicate f with 10(n) [1/s], where n can start from 0, that is one cycle per second (we cannot exclude it), to a very high frequency gamma P. Thus it is possible to represent the E of a P in this way: E = h . 10(n) [1/s]. If we apply the Principle of Equivalence Mass-Energy (E - mc(2)) to the P, our calculations show that the P has a minimum equivalent rest-mass (Zero Point Mass) equal to 10(-48) [g].