Posted: Sep 15, 2011 7:56 pm
zaybu wrote:
This paper talks about "first quantization" to describe photons. Just elemerntary stuff.
If you think that applying first quantization to photons is "elementary", then you have a different definition of elementary to the one I have !
zaybu wrote:
To be honest, twistor, if you want to study QFT, Weinberg is THE book. All that stuff you linked to is passé.
That's a rather off-hand dismissal of some interesting and controversial discussions, whereas in fact the quantum field theory you are presenting as the shizzle forms the basis of first year postgraduate theoretical physics courses.
zaybu wrote:twistor59 wrote:zaybu wrote:All particles are subject to the Heisenberg Uncertainty Principle. It's just that fermions obey different statistics than bosons. The only time you will need to consider waves is when you are dealing with a large number of photons. In that case, the wave picture gives you adequate results. But when you deal with one on one: one photon with one electron, or two electrons exchanging a photon, then the particle picture is the only one that makes sense. Either that or you might as well throw Feynman's diagrams under the bus.
Imagine I have an ideal experimental setup - an optical cavity, and I put a single quantum of monochromatic light in there. Would you really want to call that a "particle" ?
Yes, if it's a "single" quantum, it will behave like a particle. The hard trick is to produce a "single" quantum one at a time. The youtube video I linked you to did just that. And the presence of tiny grains appearing one by one on the screen testifies to the particle nature of the photon.
Did you read what I wrote above in the first post of this thread ? You get exactly the same discrete behaviour (flashes building up the interference pattern) if you treat the incident field as purely classical ! The flashes do not provide a proof of the quantum nature of the electromagnetic field - however other things do provide such proof.
QED says nothing of the sort. It merely says that one way (perturbation theory) of computing the effects of the interaction is to treat the system as if virtual quanta are exchanged. However this is merely a calculational device. If you could solve the nonlinear interaction exactly, there would be no need to invoke virtual particles. The electromagnetic field, however, does allow real excitations, namely the photons that we can measure.