Say it has xnm wavelenght. It hits an atom that reflects it, then another different atom absorbs it, why? Also what determines if particles like free neutrons or some hadrons will absorb a particular wavelenght? Why does gold absorb all wavelength except yellow and why does it also seem to reflect a small portion of the light(shine). Is the interactiom of photons with atoms and elemental particles well understood and explaind... with some laws. Ive tried reading some electrodynamics but havent gotten as far to see if a photon copulates with a particle or not or why it would.