Steve Carlip wrote in message
...
Bilge wrote:
tom:
Is it due to
(1) electromagnetic interaction between the photon(s) and the medium,

Yes.
[...]

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?

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.

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_.

I believe that the reason that it's not dealt with in most texts of E&M is
that it is a fundamentally QM version of things. It apparently is not
unusual to Born. But other authors (i.e. Lorraine and Corson) seem to feel
that Ewald's approach strays outside E&M theory.

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

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

This is pure quantum description. Classical E&M does not 'excite atoms'
when it enters a medium. See Maxwell, "On Physical Lines of Force."
'Exciting atoms' and reemitting photons is a pure QM idea.

Specifically,

"Paul Ewald's 1916-1917 masterpiece `On the Foundations of Crystal Optics'
describes the selfconsistent interaction of electromagnetic waves with
crystals on a molecular level. While astonishing in its detailed predictions
for X-ray diffraction, full appreciation of the theory and its utility had
to await much later advances in measurement techniques and crystal growth.
Concepts introduced in the theory, now known as the Ewald sphere, Ewald
summation, and Ewald-Oseen extinction, have become mainstays in diverse
areas of modern physics."

The newly emitted light has two components. One is
exactly out of phase with the incoming beam, and destructively
interferes with it. The second looks like the incoming wave, but
has a slightly different phase. The overall effect of this phase shift
is to ``delay'' the propagation, reducing the phase velocity. The
same process continues as the new wave propagates through the
medium, giving a larger and larger phase shift/propagation delay.
The existence of this effect is called the Ewald-Oseen extinction
theorem, and can be used to quantitatively compute propagation
speed, at least in a somewhat idealized medium.

(I should add that this is not a field in which I'm an expert; I
welcome corrections/clarifications.)

This is quite a useful conceptual device (some of which was apparently
borrowed for QED). However, it is over 50 years too late to be the
'classical' version.

greywolf42
ubi dubium ibi libertas

Steve Carlip wrote in message
...
greywolf42 wrote:

Steve Carlip wrote in message
...

[...]

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_.

I believe that the reason that it's not dealt with in most texts of E&M
is
that it is a fundamentally QM version of things. It apparently is not
unusual to Born. But other authors (i.e. Lorraine and Corson) seem to
feel
that Ewald's approach strays outside E&M theory.

I haven't read Ewald or Oseen's original papers, but the description
of them in Born and Wolf is certainly *not* quantum mechanical,
and the derivation in Born and Wolf is purely classical.

It isn't 'classical' if it includes 'photons'. Photons are a purely QM
invention.

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.

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

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

This is pure quantum description. Classical E&M does not
'excite atoms' when it enters a medium.

Of course it does.

Certainly it doesn't! Steve, why did you feel the need to snip the evidence
of Maxwell's derivation and Ewald's derivation? Here is the complete
paragraph -- of which you snipped the reference to classical derivation
(Maxwell) -- which performed this without modern quantised atoms (which
hadn't been 'invented,' yet) at all:
====================================
This is pure quantum description. Classical E&M does not 'excite atoms'
when it enters a medium. See Maxwell, "On Physical Lines of Force."
'Exciting atoms' and reemitting photons is a pure QM idea.

Specifically,

"Paul Ewald's 1916-1917 masterpiece `On the Foundations of Crystal Optics'
describes the selfconsistent interaction of electromagnetic waves with
crystals on a molecular level. While astonishing in its detailed predictions
for X-ray diffraction, full appreciation of the theory and its utility had
to await much later advances in measurement techniques and crystal growth.
Concepts introduced in the theory, now known as the Ewald sphere, Ewald
summation, and Ewald-Oseen extinction, have become mainstays in diverse
areas of modern physics."
====================================

Consider the simplest case, a gas of atomic
hydrogen. A hydrogen atom is an electric dipole, and when
it is placed in the oscillating field of a light wave, its dipole
moment oscillates. That means there's a time-dependent
current -- to a good approximation, the current due to the
oscillation of the electron. That current, in turn, acts as a
source of electromagnetic radiation. What Ewald and Oseen
did was to calculate this radiation, from Maxwell's equations.

A hydrogen atom is more than simply an electric dipole! Dipoles don't have
spherical symmetry.

But this was already addressed in my prior post -- that you "invisibly"
snipped:
=====================================
The newly emitted light has two components. One is
exactly out of phase with the incoming beam, and destructively
interferes with it. The second looks like the incoming wave, but
has a slightly different phase. The overall effect of this phase shift
is to ``delay'' the propagation, reducing the phase velocity. The
same process continues as the new wave propagates through the
medium, giving a larger and larger phase shift/propagation delay.
The existence of this effect is called the Ewald-Oseen extinction
theorem, and can be used to quantitatively compute propagation
speed, at least in a somewhat idealized medium.

(I should add that this is not a field in which I'm an expert; I
welcome corrections/clarifications.)

This is quite a useful conceptual device (some of which was apparently
borrowed for QED). However, it is over 50 years too late to be the
'classical' version.
=====================================

Steve, your posting style is degenerating again.

greywolf42
ubi dubium ibi libertas

G=EMC^2 Glazier wrote:
A photon can not be a photon if it changes speed

Hmmm. Say, rather, that photons don't really "have" a speed.

A photon is really just a factor in an integral of QED, and in the
position representation it connects two events A and B; one then
integrates over all possible positions and times of A, and over all
possible positions and times of B (and the integrand includes
delta-functions that ensure conservation of 4-momentum). How can one
interpret any sort of speed in that??? (one can loosely say it
propagates with all possible speeds in all possible directions, but that
is an over-simplification, too).

That describes just one "diagram". One must sum over all
possible diagrams, and antisymmetrize appropriately....

For on-mass-shell photons, the only contributions to the integral are
from events separated by a null interval, so for them we can say "they
travel at c". But inside a material there are interactions with all the
charged particles of the material, and the result of the sum over
diagrams and antisymmetrization is different from an on-mass-shell
photon....


An electron can't be an
electron if it does not spin at "C"

I don't know what that means. But certainly every electron always has an
intrinsic spin of 1/2.


If you are truly interested in this, I suggest you read:

Feynman, _QED_.
It is a nonmathematical introduction to Quantum ElectroDynamics,
the quantum theory of electrodynamics.


Tom Roberts

greywolf42 wrote:

Steve Carlip wrote in message
...

I haven't read Ewald or Oseen's original papers, but the description
of them in Born and Wolf is certainly *not* quantum mechanical,
and the derivation in Born and Wolf is purely classical.

It isn't 'classical' if it includes 'photons'. Photons are a purely QM
invention.

It doesn't include photons. As I said, it's purely classical. I suggest
that you read Born and Wolf before you make any more claims.

Steve Carlip

Steve Carlip wrote in message
...
greywolf42 wrote:

Steve Carlip wrote in message
...

I haven't read Ewald or Oseen's original papers, but the description
of them in Born and Wolf is certainly *not* quantum mechanical,
and the derivation in Born and Wolf is purely classical.

It isn't 'classical' if it includes 'photons'. Photons are a purely QM
invention.

It doesn't include photons. As I said, it's purely classical. I suggest
that you read Born and Wolf before you make any more claims.

Steve Carlip

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.

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?"


And your invisible snipping of the primary part of the discussion is
replaced:
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
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.

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

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

This is pure quantum description. Classical E&M does not
'excite atoms' when it enters a medium.

Of course it does.

Certainly it doesn't! Steve, why did you feel the need to snip the evidence
of Maxwell's derivation and Ewald's derivation? Here is the complete
paragraph -- of which you snipped the reference to classical derivation
(Maxwell) -- which performed this without modern quantised atoms (which
hadn't been 'invented,' yet) at all:
====================================
This is pure quantum description. Classical E&M does not 'excite atoms'
when it enters a medium. See Maxwell, "On Physical Lines of Force."
'Exciting atoms' and reemitting photons is a pure QM idea.

Specifically,

"Paul Ewald's 1916-1917 masterpiece `On the Foundations of Crystal Optics'
describes the selfconsistent interaction of electromagnetic waves with
crystals on a molecular level. While astonishing in its detailed predictions
for X-ray diffraction, full appreciation of the theory and its utility had
to await much later advances in measurement techniques and crystal growth.
Concepts introduced in the theory, now known as the Ewald sphere, Ewald
summation, and Ewald-Oseen extinction, have become mainstays in diverse
areas of modern physics."
====================================

Consider the simplest case, a gas of atomic
hydrogen. A hydrogen atom is an electric dipole, and when
it is placed in the oscillating field of a light wave, its dipole
moment oscillates. That means there's a time-dependent
current -- to a good approximation, the current due to the
oscillation of the electron. That current, in turn, acts as a
source of electromagnetic radiation. What Ewald and Oseen
did was to calculate this radiation, from Maxwell's equations.

A hydrogen atom is more than simply an electric dipole! Dipoles don't have
spherical symmetry.

But this was already addressed in my prior post -- that you "invisibly"
snipped:
=====================================
The newly emitted light has two components. One is
exactly out of phase with the incoming beam, and destructively
interferes with it. The second looks like the incoming wave, but
has a slightly different phase. The overall effect of this phase shift
is to ``delay'' the propagation, reducing the phase velocity. The
same process continues as the new wave propagates through the
medium, giving a larger and larger phase shift/propagation delay.
The existence of this effect is called the Ewald-Oseen extinction
theorem, and can be used to quantitatively compute propagation
speed, at least in a somewhat idealized medium.

(I should add that this is not a field in which I'm an expert; I
welcome corrections/clarifications.)

This is quite a useful conceptual device (some of which was apparently
borrowed for QED). However, it is over 50 years too late to be the
'classical' version.
=====================================

Steve, your posting style is degenerating again.
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = =


greywolf42
ubi dubium ibi libertas

guys: Imho the photon that comes out is not the photon that entrers the
medium. It is obviously interacting with the medium, hence the
refractive index. So the photon is absorbed and re-emitted as it
interacts with the electrons in the medium. I takes some time for the
absorption re-emission to occur, however between times the photon is
still moving with velocity "c". The "final" photon (the one emitted
into the vacuum) now moves at velocity "c" until it can interact with
matter..

(formerly) wrote:

Dear G=EMC^2 Glazier:

"G=EMC^2 Glazier" wrote in message
...


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 increase in energy?

You don't think the photon's energy is in any way changed because it is in
a medium do you? Maxwell would say not...

David A. Smith

Dear Robert Ehrlich:

"Robert Ehrlich" wrote in message
news:8C%8b.340433$Oz4.124857@rwcrnsc54...
guys: Imho the photon that comes out is not the photon that
entrers the medium. It is obviously interacting with the medium,
hence the refractive index. So the photon is absorbed and
re-emitted as it interacts with the electrons in the medium.
I takes some time for the absorption re-emission to occur,
however between times the photon is still moving with velocity
"c". The "final" photon (the one emitted into the vacuum) now
moves at velocity "c" until it can interact with matter..

Please post in Plain Text.

Using static and dynamic electric fields, we can determine how much
resistance a material provides to an impressed field. We can do the same
for an impressed magnetic field. If you combine the two effects for
frequencies of light you would pass, you get an "amazing" correlation to
the speed of light in the medium.

photon-electron interactions through absoprtion and emission are much too
long to have the low k values we observe.

David A. Smith

greywolf42 wrote:

Steve Carlip wrote in message
...
greywolf42 wrote:

Steve Carlip wrote in message
...

I haven't read Ewald or Oseen's original papers, but the description
of them in Born and Wolf is certainly *not* quantum mechanical,
and the derivation in Born and Wolf is purely classical.

It isn't 'classical' if it includes 'photons'. Photons are a purely QM
invention.

It doesn't include photons. As I said, it's purely classical. I suggest
that you read Born and Wolf before you make any more claims.

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.

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.

Steve Carlip

Steve Carlip wrote in message
...
greywolf42 wrote:

Steve Carlip wrote in message
...
greywolf42 wrote:

Steve Carlip wrote in message
...

I haven't read Ewald or Oseen's original papers, but the description
of them in Born and Wolf is certainly *not* quantum mechanical,
and the derivation in Born and Wolf is purely classical.

It isn't 'classical' if it includes 'photons'. Photons are a purely
QM invention.

It doesn't include photons. As I said, it's purely classical. I
suggest
that you read Born and Wolf before you make any more claims.

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 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.

greywolf42
ubi dubium ibi libertas

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.

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