(February 1, 2022 at 3:54 pm)Jehanne Wrote: Does light accelerate?
That's not a dumb question. It highlights how different massless particles are.
The answer is "no". Light always travels at its natural speed, given the medium it is traveling in. It always wants to travel at the speed of light in vacuum, but interactions with dielectric materials affects its phase and therefore its actual velocity (slowing it down).
Particles that have no mass cannot slow down or speed up - they can only be delayed by inference in a dielectric (though one can argue that is really a continuous destruction and recreation, and it is this effect that is "apparently" causing the photon to slow - but they are really new photons all the time).
If I were a photon, I would figuratively "see" my creation and destruction simultaneously, and have no concept of time.
