I don't really understand that except that it confirms that photons do not exhibit mass. (I'll take "infra red" to include LF radio too.) When I asked what he said about low frequency photons, I was wondering about the situation with interference from two independent synchronous, RF sources. This is such an easily produced phenomenon at RF and not that difficult with two phase locked lasers, apparently.yes,I know what he has said.He said to give photon a mass in low energy limit to avoid infrared divergence and then combining it with cut-off provided by bethe in non-relativistic limit gives a fully divergenceless result i.e. no infrared divergence!and take mass zero in the end.mass is invariant.
If, indeed, it were really necessary for actual photons from each RF source to interfere with each other in order to produce an interference pattern then surely we would expect an awful lot of photons from each source not to interfere ('cancel' in one direction) - producing a very diluted interference pattern. In fact, very deep, stable nulls (0.1% amplitude) can be formed from two independent RF sources. If the sources are actually not phase locked at all but just very stable and slowly drifting past each other, a very clean interference pattern can result. (All that is necessary is that the amplitudes are equal, of course)
So the choice is between saying that, magically, pairs of matched photons are always present in the two 'beams' so that they can combine into a perfect pattern or that the interference is nothing to do with photons at all and the photons only turn up when they're actually detected (which is in line with the Copenhagen interpretation, I think).
I wish someone could comment on this and find the flaw - if there is one.