Posted: Sep 14, 2011 7:14 pm
by twistor59
Continued off topic discussion from this thread.

The topic in question revolves around whether it is appropriate that we should say that light is composed of particles. My position is this:

1 I fully accept that modern quantum field theory provides the best means for modelling interactions involving the electromagnetic field at a fundamental level.

2 Mode excitations can be induced in the electromagnetic field and these are discrete and countable, and referred to as "photons".

3 Photons do not have the same localizability properties as, say, electrons, and for this reason, I hesitate to call them particles, but prefer the term "field quanta".

Incidentally, it is not correct to say that the two slit experiment such as illustrated in the youtube video proves the particulate nature of light. Exactly the same "discrete flash" behaviour is obtained by treating the incident wave as a classical field, but the valence electrons in the detector according to quantum rules. (Note this does not mean that I don't think light is a quantum field, I most certainly do !). So Einstein was right, but for the wrong reason.

Real evidence for the discrete behaviour in light comes from photon antibunching experiments and scattering processes such as the Compton effect.

I believe Einstein thought that light was composed of "light atoms" which had point sources a bit like the Coulomb field, but summed up to produce the classical wave. That picture certainly wasn't right.