Posted: Sep 13, 2011 8:20 pm
zaybu wrote:twistor59 wrote:zaybu wrote:
It's the many courses in QFT I've taken which convinces me that this is the case !
I would prefer to refer to photons as "field quanta", and reserve the term "particle" for entities that had position operators. Photons do not have position operators (regardless of what Margaret Hawton may say). In fact I am not alone in having this view. Lamb states:Photons cannot be localized in any meaningful manner, and they do not behave at all like particles, whether described by a wave function or not.
I wouldn't put it as strongly as Lamb did - they do sometimes behave like particles (Compton scattering), but I don't like attaching the term "particle" to something without a well defined position operator, since it gives a misleading mental picture.
You have to remember that in QFT, position is no longer an operator. To satisfy Relativity, in which time is on an equal footing with space: x → parameter, and is replaced by the field Φ(x) → operator.
I'm quite aware that spacetime position in QFT is not an operator, but rather a parameter. What I'm talking about is a position operator, not x, which can be defined for electrons (for example), but not for photons.