How does quantum electrodynamics actually explain HOW reflection occurs on a microscopic scale?
Note that Feynman's QED lecture series/book is not sufficient, as he only assumes that light DOES reflect ('turn around and go back') in order to expound his path integral theory. My question is why does light have the propensity to turn around in the first place.
Is it just the absorption and re-emission of photons, and if so, why does it happen so uniformly (i.e. on a shiny thing, entire scenes are reflected near-perfectly). In essence, why are flat things shiny? Are all the molecules arranged at exactly the same angle?
Answer
the process is coherent--- the same photon is bouncing off all the atoms at once, and you only get constructive interference when the angle of reflection is equal to the angle of incidence. The condition is that the surface is smooth on the scale of the wavelength of light, so that the light can excite each atom independently, and coherently add up all their contributions. This is Feynman's explanation in QED, I think you just misunderstood it as saying that reflection is assumed--- he just assumed rescattering, and then shows you that it happens in the reflected direction preferentially.
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