Hi, I was watching http://video.google.com/videoplay?docid=-2622437302869951111" [Broken] the other day and he described photons by an 'amplitude' which actually means a complex number, which rotates over time. This rotation speed gives the photon's colour/energy/frequency. Then later in the lecture he says that the amplitude (complex number) doesn't actually rotate with time, he says that it is simply that the amplitude at emission rotates with time, and once that photon has been emitted with a certain amplitude, that amplitude doesn't change other than to decrease with the inverse square of distance. Am I right so far? The lecture is also old, from 1979! However, due to the uncertainty over when exactly the photon is emitted, the probability cloud of possible such photons could perhaps be considered as a small packet containing an oscillation of the amplitude, over perhaps a few oscillations, due to the probablistic time period over which it was emitted. But this actual little wave packet wouldn't be rotating those amplitudes over time. Does this make sense? But, whether you wish to call photons the individual point, or the probability cloud, either way, at the receiving end you only get a single amplitude on detecting a photon right? You don't 'see' the whole probability cloud, just a single result. But this would mean that the receiving electron or whatever would not know the frequency of the photon, which it needs to know in order to jump to certain energy states. Did I interpret Richard Feynman incorrectly? Is the frequency a property of a single photon, or a property of how it is emitted? If it is the latter, then what is making the emitter (e.g. an electron) rotate the amplitude over time? It is based on the drop in electron energy levels right? So is it to do with the frequency at which the electron orbits? Thanks, and sorry for the long question (BTW I'm a newby to QM if that wasn't obvious).