To: atm{at}shore.net
From: MLThiebaux 
Reply-To: MLThiebaux 


The classical theory of light is described by Maxwell's equations which
lead to a classical linear wave description of light.  Classical linear
waves interfere linearly as in diffraction but DO NOT scatter from each
other (i.e. change direction by bumping off each other).

However, when Maxwell's equations are quantized, scattering is predicted --
called photon-photon scattering  -- mainly through the creation of virtual
or real electron-positron pairs.  This is a real computable quantum
mechanical effect but very difficult to observe because of its very low
(yet nonzero) probability.

"It is unlikely that the scattering of light by light and other
non-linear effects will play a physical role, even in the interior of stars
where the density of photons is very high."  W. Heitler (The Quantum
Theory of Radiation, 1954).

I don't know whether it has ever been observed in the laboratory or
elsewhere. Not that it hasn't been looked for.

Martial Thiebaux
Rawdon Hills, Nova Scotia

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