Do you think photons (quanta of EM radiation) experience any resistive forces whilst propagating?
Photons have energy E = h nu = h c/lambda (nu frequency, c speed of light, lambda wavelength, h Planck’s constant) But E = mc2 So m = h/(lambda c) Photons do have mass and are affected by gravitational fields. Astronomers use this in what is called “gravitational lensing”. For reasons that I don’t understand, the deflection predicted by special relativity is twice as large as that predicted just from the mass. Hence the very famous experiment that confirmed special relativity in 1919. I’m not sure why you think photons tend to speed up. And if they have any mass at all, they will be affected by gravitational fields, like everything else. Experiments with high-energy particles shows that the speed of light is indeed a kind of cosmic speed limit.
