I can see that you’re not one who is much for agreeing to disagree, huh? Okay.

It depends. Because of my nickname, I like to talk about light and photons [

], so I've studied this subject and discussed it in the forums, for several years.

For an electron, you can have non-zero momentum p even at very low speeds, because of its non-zero mass. Then De-Broglie relationship: [tex]\lambda[/tex] = h/p tells that, in the limit h --> 0, [tex]\lambda[/tex] = 0, that is, frequency should be infinite.

And since the product of wavelength and momentum has to remain the same

? We are making the limit h-->0, so it doesn't remain the same!

In any case you keep forgetting that we’re treating it as a classical particle for which the relationship: [tex]\lambda[/tex] = h/p ignored.

But the point is that *you have to prove* treat it can be treated as a classical particle.

Thus it means nothing in the classical sense to take a classical limit of a photon.

Exactly! Read again what you have written here [

]

JP and myself explained how it works in a classical sense.

JP wrote this:

<<Good point. After reading that and a bit more thinking, I believe that what's going on with these "classical photons" is two limits. If we have a field made of photons, the classical limit does not correspond to taking h->0, but rather to taking many photons. In this limit, you recover Maxwell's equations, but you've lost information about the behavior of individual photons.

Then you take a second limit corresponding to wavelength->0 which gets you ray optics. So essentially, your "classical photon" is an arbitrary packet of energy assigned to propagate along a ray. It's related to real photons only insofar as the sum over many photons gets you the classical field, which you then use to define rays.>> So JP, essentially, says: OR you recover classical electromagnetism, and

you have lost information about the behaviour of individual photons, OR you come up with the geometrical optics approximations and

you can talk about packets of energy assigned to propagate along a ray.

But this is exactly what I've already written to you in previous posts [

]

You certainly can’t change the textbooks

Sincerely I have never read "classical photon" in a book of physics.

or change the usage of the center of mass of a two photon system in the textbooks. As I have asked too many times now with no response – why do people insist in using the scenario I’ve described and never came to a wrong answer.

Please explain, in detail if you please, what it means when you say “You can’ do that!” when so many people do it,

"So many people" are able to localize a photon in flight? Forget it...

and very successfully too I might ad. You imply that you can’t draw a worldline of a photon in a spacetime diagram and yet physicists do it all the time.

How do you draw a photon's worldline between (0,0,0,0) and (1,1,0,0)? Just for curiosity.

E.g. referring to finding the center of mass of two photons you claimed “You can't localize a photon, so you can't do that.” When in fact derivations based on the localizability of property of a photon that plays a crucial role in its use in the derivation, you know, the one you claimed can’t be done. While you’re at it please state in detail what you mean whey you say “You can’t localize a photon”. Again you claimed that just because I was speaking about classical physics you claimed that I was speaking about quantum mechanics, again with no proof provided. I suggest that you take a look at the derivation again http://home.comcast.net/~peter.m.brown/sr/einsteins_box.htm just pas Eq. (. Nothing about a quantum nature about anything is mentioned in there. Easy as cake. Over and over again you keep making the unfounded assertion that you can’t localize a photon but then never state what that means in practice. Then you later claim that you “so you can’t speak of photons”. Then you go on an claim I don’t know a lot about QM just because you didn’t understand what I wrote and you didn’t appear to go back to JPs post to see the context in which I made the statement which makes you think I don’t understand QM. As JP says and I believe him Maybe there's a reason why you can't, but based on my (admittedly limited) understanding of the Standard Model, I don't see why this would be.

I've already explained in simple terms why you can't localize a photon, but you don't accept it because, you say, it works only for photons described in quantistic sense; I tried to show you that this is the only description for the term "photon" and so we are in a loop...

I sincerely don't know what else I could say.