On Tue, 16 Sep 2003 20:03:03 -0400, John Anderson
wrote:

A photon moving through matter is not the same entity as a free space
photon. It is a collective effect of the EM field and the charges in the
atoms
of the medium. A free space photon is pure EM field.

When a photon emerges from the medium, it isn't accelerated, it's
converted into a free space photon.

Isn't it great to read the words of an expert - someone who really knows what
he is talking about!

Just explain to me John.... what is the velocity of these 'pure EM fields' in
free space?
What determines that velocity?


John Anderson

G=EMC^2 Glazier wrote:

Tom If a photon is slowed going through glass,water,and air where does
it get the energy to accelerate back to "C" ? Until that question can
be answered I'll stay with my theory. Bert




Henri Wilson.

See my animations at:
http://www.users.bigpond.com/HeWn/index.htm
My latest: http://www.users.bigpond.com/HeWn/movingrod.exe

John A Where did you ever get that crap from? Different photons
that goes at different speeds. What next???? Bert

"G=EMC^2 Glazier" wrote in message
...
John A Where did you ever get that crap from? Different photons
that goes at different speeds. What next???? Bert

Google "Refraction"

Dear G=EMC^2 Glazier:

"John Zinni" wrote in message
.. .
"G=EMC^2 Glazier" wrote in message
...
John A Where did you ever get that crap from? Different photons
that goes at different speeds. What next???? Bert

Google "Refraction"

and/or

permeability and permittivity

Which together define c_medium.

David A. Smith

greywolf42 wrote:

[...]
The reason we're talking at all is about your claim that "the slower
propagation speed is due to PHOTON ABSORPTION AND RE-EMISSION, " and that
this theory is "classical."

I made no such claim. I said that the complete quantum description
in terms of photon absorption and reemission was complicated, but
that the basic features could be understood classically. I even
prefaced my description with

What happens (classically, but the QED picture is roughly the
same, with coherent states of photons replacing electromagnetic
waves) is this:

I wasn't commenting on Born and Wolf's derivation.

And yet you wrote

It isn't 'classical E&M' if it includes the absorption and emission of
photons with atoms. Atoms are not classical E&M structures.

Hence, the derivation of Born and Wolf is not purely classical.
Regardless of how often you repeat this unsubstantiated claim.

Steve Carlip

G=EMC^2 Glazier wrote:

Tom If a photon is slowed going through glass,water,and air where does
it get the energy to accelerate back to "C" ? Until that question can
be answered I'll stay with my theory. Bert

What makes you think it requires energy to accelerate to c? Remember a
photon has no mass.

When it is in a medium such as glass atomic effects in the class cause it to
travel at a speed less than c. Also it us useless to think in terms of if
it is the same photon as the one that went in. There is no way to
distinguish one photon from another so you have no way of telling. It is
simply the wrong way to think about the problem.

Thanks
Bill

Steve Carlip wrote in message
...
greywolf42 wrote:


{much of Steve's snip replaced}
================================
You've really dropped your standards, Steve. A complete snip of the
relevant parts of your post. This is your quote:

"To amplify a little -- while it's true that the slower propagation
speed is due to PHOTON ABSORPTION AND RE-EMISSION,
it's not just that this process ``takes extra time.''
The problem is one of classical electromagnetism,
..." {emphasis added}

*Your* statement was that this was the result of photon absorption
and re-emission. Hence, your current claim that "it doesn't include
photons" is a complete contradiction of your position.

This is just plain silly. I said that the full explanation involves
photon absorption and re-emission, which is certainly true -- after
all, QED is more correct than classical electrodynamics -- but also
that the key features could be understood classically.

Not if those "key features" are photons and quantized atoms.

And again, you felt the need to snip the evidence of Maxwell's
derivation and Ewald's derivation. One would think that you
were embarrased. (As you should be.) Why not just admit to
an 'oops', and retract the (incorrect ) claim that Born and Wolf
is "purely classical?"

Born and Wolf's derivation is purely classical. It involves no
photons, no quantized energy levels, no quantum interactions of
radiation and matter. Planck's constant appears nowhere.
There is nothing quantum mechanical in the derivation, period.

Why don't *you* go read Born and Wolf, and cite any place in their
derivation that uses anything nonclassical. Then we might have
something to talk about.
================================

The reason we're talking at all is about your claim that "the slower
propagation speed is due to PHOTON ABSORPTION AND RE-EMISSION, " and
that this theory is "classical."

I made no such claim.

Here is your direct quote ... again. Since you keep snipping it.

"To amplify a little -- while it's true that the slower propagation speed is
due to PHOTON ABSORPTION AND RE-EMISSION, it's not just that this process
``takes extra time.'' The problem is one of classical electromagnetism,
...." {emphasis added}

So, we see that you made precisely the claim you are now denying. Why not
just address what you meant to say in the above paragraph? Why do you
insist on snipping and denying?

I said that the complete quantum description
in terms of photon absorption and reemission was complicated,
but that the basic features could be understood classically. I
even prefaced my description with

You never mentioned 'complete quantum description' or 'complicated' or
'basic features' or any phrasing remotely resembling your current claim. In
your post (to which I replied on 9/2), the discussion was exactly as
follows:

Tom:
"Also, what is the nature of the interaction? For example, were the above
answer (1), then is the photon being absorbed and re-emitted repeatedly as
it passes through the medium or is the interaction more subtle?"

Bilge:
"Yes, but the process of absorption and emission is more subtle because for
a medium to act as a medium, the interactions of photons with the charges
has to be a collective process in the medium."

Steve Carlip:
"To amplify a little -- while it's true that the slower propagation speed is
due to photon absorption and re-emission, it's not just that this process
'takes extra time.' The problem is one of classical electromagnetism,
though it's not dealt with in much detail in most textbooks; the best
reference I know (there may well be better ones) is section 2.4.2 of Born
and Wolf's classic, _Principles of Optics_."

THEN you started the next paragraph with:

What happens (classically, but the QED picture is roughly the
same, with coherent states of photons replacing electromagnetic
waves) is this:

And finished with this:

"When light enters a medium, it excites atoms, which in turn emit light."

Which is neither the classical EM description, nor that of Born and Wolf (if
I believe your current representations instead of your original
representations).


I wasn't commenting on Born and Wolf's derivation. Now, if Born
and Wolf's derivation has neither photons nor quantized atoms, then
your representation was incorrect -- at best. And your current claim
that the 'full explanation' requires QM is contrary to your evidence.

Which is why I chastised you for snipping the evidence.

And yet you wrote

It isn't 'classical E&M' if it includes the absorption and emission of
photons with atoms. Atoms are not classical E&M structures.

Hence, the derivation of Born and Wolf is not purely classical.
Regardless of how often you repeat this unsubstantiated claim.

Yep. Sorry if I believed that your description was taken from Born and
Wolf. Since that is the implication in your original paragraph.

So -- will you now admit that your original statement was incorrect?
("slower propagation speed is due to PHOTON ABSORPTION AND RE-EMISSION, ...
The problem is one of classical electromagnetism") We all make mistakes, and
this may simply be poor paragraph construction.

greywolf42
ubi dubium ibi libertas