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This is a quote from Wikipedia:

In classical electrodynamics, light is considered as an electromagnetic wave, which is described by Maxwell's equations. Light waves incident on a material induce small oscillations of polarisation in the individual atoms (or oscillation of electrons, in metals), causing each particle to radiate a small secondary wave in all directions, like a dipole antenna. All these waves add up to give specular reflection and refraction, according to the Huygens–Fresnel principle.

My question is, how do all the waves add up to give the direction of angle-in equal to angle-out if they are going in all directions? Also, in reflection does the photon get absorbed and re-emitted or does it act like a dipole antenna?

Rory Shaughnessy
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2 Answers2

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Classical light is a superposition of photons, each mathematically described by a wavefunction. For a reflection that can transfer images the scattering of the individual photons has to be elastic so that the phases are retained, i.e. there is coherence. Absorption and reemission of individual photons will destroy the images , as you suggest.It has to be elastic for a mirror, because inelastic scatters change the energy of the photons and therefore the colors.

So I do not consider the quote you give to be an accurate representation of what is happening.

It can be shown that the classical electromagnetic field emerges from the quantum, using quantum field theory, but classical electrodynamics is quite accurate in describing the behavior of light.

See also this link.

anna v
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Semi-classical, classical, Huygens are all great principles and proved there worth historically in explaining various phenomena. If you dig a little deeper though, as you are doing, the theories can not explain all observations like scattering. The double slit experiment is another example, new theories were made to explain why even single photons or electrons (sent one after the other) still produced the diffraction pattern. If you want to dig deeper you can read more on Quantum Optics, Quantum Mechanics, Feynman's line integral and other theories. In modern practice the interaction of light with matter is governed by quantum mechanics/optics which adds a probability (or uncertainty) concept to most behaviour.

PhysicsDave
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