What causes photon diffraction through thin air?

[Schrodinger's Dog]

I was thinking about difraction grating experiments and slit experimenets in general when I got to thinking what is it that actually diffracts the photons as they pass through the slit which is to all intents and purposes thin air? I've heard about inteference and looking at water it's obvious with molecules why this happens, but photons don't interact very readily at all so how does this work? is this one of those grey areas or is there something interesting going on?

 

[jtbell]

is there something interesting going on?

Yes. Quantum-mechanical particles do not behave like classical particles. They don't behave like little billiard balls that simply bounce off of obstacles or each other, or interact with each other according to the laws of classical physics. No one (as far as I know) has come up with a "classical" picture of QM that doesn't fail under some circumstances (i.e. doesn't agree with some experiments), or doesn't have some "weird" features anyway.

 

[Schrodinger's Dog]

Ah i see, I asked a colleague of mine and he said, well to be honest when I was studying physics at degree level they never really did answer that question satisfactorily(so I'm thinking obviously at some point most people ask this question and are given the same answer)
Just trying to find out if in the 35 years since he'd studied physics, if there had been any ideas concerning this. It's kind of pleasing in a way to have your question unansered, it makes you feel like your asking the right questions in a strange sort of way. But it's kinda like an itch you can't scratch

 

[Schrodinger's Dog]

here's something interesting if not entirely related I read in a magazine

Surface plasmons affect the way light reflects off agrating, if light is polarised in the same direction as the grooves, the spectrum is continuous, but perpendicularly polarised light can couple to surface plasmons and be absorbed at certain wavelengths.

It doesn't explain difraction but it is being used in gratings to focus light,something that was not possible before.

The applications are endless, metal films that are transparent, imaging living cells probing the vibrations of single molecules. Interesting stuff