How do objects really reflect light?

We all know that if light comes to an object some of it's wavelength would get absorbed by the object as the form of thermal energy, and some would be reflected and that's how we see different colours from objects around us.

But i'd like to know how they reflect them in the first place, does it has to do with the photoelectric effect but in a much lower energy level? Photons hitting the object's surface causing the electrons to enter a higher quantum state thus emitting the excess energy back in the form of EMR when it enters a lower quantum state or it's original state? Seems like it may be wrong and i haven't found enough literature to find an explanation for this problem.

Anyway I've watched a video about how mirrors work and it adds to the problem. Mirrors would reflect light by creating a wave that exactly cancels the incoming wave from an EM wave source like light. Because they are sprayed with some metal substances (usually silver or aluminium) which are basically protons and neutrons in a sea of electrons that are in an equilibrium state (no net force), they would try to stay in that state (like most objects in nature do) by creating an EM wave that cancels the incoming EM wave, which would appear to be a wave that has the exact same wavelength, amplitude, etc. but different period, hence mirrors reflect light. But in this case we all know that not every object is made of some metal substances, I'd love to know how things really reflect light.


1 Answer 1


White substances reflect light by multiple reflections at surfaces. (Well maybe not "really", one could talk about scattering by Lorentz oscillators, where Lorentz oscillators are a classical model for a quantum mechanical phenomenon, so time-dependent Schrödinger, and then on to QED.)

So in first approximation, transparent materials reflect at surfaces because of the difference in refraction index. For example glass reflects 4 % at normal incidence. Water and ice a bit less. But snow has lots of surfaces, and multiple scattering gives diffuse reflection of the incoming light. A white substance.

Also other white substances are finely grained transparent materials: salt, sugar, paper, sand, etc.

  • $\begingroup$ So is this index of refraction, if I'm not mistaken, somehow related with the resonance absorption and dissipation absorption of a quantum system (say, an atom in an object)? And if so, then do objects reflect light because their atoms "absorbs" the energy from a photon and dissipate it in some specific wavelength? $\endgroup$
    – Felix
    Commented Dec 4, 2019 at 12:49
  • $\begingroup$ That is the next level in what "really" happens, the reason for a larger index of refraction. Easiest is the non-quantum picture of Lorentz oscillators with resonance frequencies in the UV. They do not absorb, they radiate at the driving frequency. This changes the phase velocity of light in materials. $\endgroup$
    – user137289
    Commented Dec 4, 2019 at 12:54
  • $\begingroup$ Ah i get it now... thank you so much for helping $\endgroup$
    – Felix
    Commented Dec 4, 2019 at 14:02

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