clipka wrote:
> but the stimulating photon is *not* absorbed.

OK. But what I was saying is that your statement ""If you deal with 
fluorescence you'll see that *all* re-emitted light is *undirected*"" isn't 
true in general of all re-emitted light, since non-spontaneous emission can 
be caused to be directed.

>> Maxwell's equations are a statistical summarization of the actual behavior.
> 
> Nay. They are an *exact* description of the *waveforms* which *determine*
> statistical behavior (the "probability wave" of a particle between actual
> interactions).

I'm pretty sure we're agreeing here. "description of the probability wave 
which determines statistical behavior" is pretty much a "statistical 
summarization of actual behavior (of individual particles)", in my book.

>> Sort of. What would keep interference from working between an absorbed
>> photon and a re-emitted photon?
> 
> The fact that the photon has at last stopped being a wave (having just a certain
> *probability* to be somewhere) and started being a particle (actually
> interacting *somewhere* particular).

But if you don't actually "measure" that interaction, it doesn't turn into a 
particle. You can get interference between particles that have already been 
measured, so I'm not sure what your point is?

I suspect we're both, at this point, arguing nonsense, as it's impossible to 
tell whether a photon has "reflected" off an electron or been "absorbed and 
reemitted" as another photon. You're arguing you can tell the difference. 
Everything I've read says photons "interact" with electrons in exactly one 
way, characterized by electron charge, electron mass, and polarization of 
the respective particles.

> It is also described of the "probability wave" of the photon having "collapsed".
> 
> That's the moment where Maxwell can go home, and have a break until another
> photon is emitted.

How do you measure the difference between a photon being absorbed and an 
identical one being reemitted, or the same photon taking a different path, 
or a photon "reflecting" off an electron?

> What on earth should a "change of direction kind of absorption" be?

Like what happens when light goes through a lens. It interacts with the 
electrons in the glass and winds up moving at a slower speed therefrom. Why 
would a lens change the average speed of light if not because it's spending 
time being absorbed and reemitted?

> Strictly speaking, there is no such thing as a change of direction in a photon
> anyway 

In QED terms, there's no such thing as the direction of a photon at all. :-) 
That's why I said above we're both kind of arguing nonsense now.

>>> so the re-emitted light's probability wave has no way of interferencing with it,
>> Also incorrect. You can get interference between two photons that aren't
>> even in the same light cone any more.
> 
> I'm not sure about this one - but if this is actually the case, then the effect
> is obviously limited to the time when *both* photons "travel", i.e. exhibit
> probability wave nature. As soon as one of the photons is absorbed, the other
> can't interfere with it anymore.

This is counter to my understanding.
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
You can wait until after the photon has hit the detector, then determine 
whether you'll see interference or not.

> Individual photons can't interact with individual electrons unless they collapse
> their probability wave and choose a particular electron to interact with.

I don't believe that's correct. I'm certainly not well-schooled in this, but 
I don't believe an "unobserved" interaction with an electron by a photon 
will collapse the probability wave, or one would not have "virtual photons" 
and "virtual electrons" interacting with real photons and electrons.

You may be right, tho.

> But the question *does* make sense from a quantum physics point of view: There's
> a difference between a photon's *probability wave* "bouncing off" a whole bunch
> of electrons all at once (by interferencing with itself due to the disturbance
> in the EM field caused by the charged particles), or a photon actually
> *interacting* with an individual electron in an "absorb and re-emit" kind of
> fashion.

OK.

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

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