Photon Energy Density (was "Re: Microwave Power" on SPR)
FrediFizzx
comments. It might even be too speculative for SPF. ;-) But we will
see.
"Chalky" <chalk...@bleachboys.co.uk> wrote in message
news:33359b7d-3bc1-4a65...@h9g2000yqa.googlegroups.com...
> On Dec 25, 1:55 pm, "FrediFizzx" <fredifi...@hotmail.com> wrote:
>
>> E^2 = (hbar w^4)/(4pi^2 c^3)
>>
>> For the case of a single photon n = 1. w is omega, angular
>> frequency.
>> It is the only variable in the above expression. In units of hbar =
>> c =
>> 1, the "static" E field amplitude of a photon (if we can even talk of
>> such a thing) would be,
>>
>> E_0 = +,- w^2/2pi
> [...]
>> Well, perhaps that is the answer above. :-) I'm wondering why no one
>> has asked how I derived it.
>
> Well, yes, that would be nice too (I had hoped that anyone answering
> this question would also explain why the answer was what it was)
Well, this might be too speculative for SPR; if that is the case I will
move it to SPF. I derived it heuristically using dimensional analysis
primarily. I'll try to make a long story short here; start with the
energy of a photon,
E = hbar*w
Then what might be an expression for its energy density? We need an
expression that is energy/volume. Thinking of the relation w =
2pi*c/lambda, we might guess (actually more than a guess but trying to
make the story short here),
u_ph = 2pi*hbar*w/lambda_w^3 = hbar*w^4/(4pi^2*c^3)
Then the EM field energy density with identical in phase photons could
be,
u_em = hbar*w^4*n/(4pi^2*c^3)
Which can also be expressed as the square of the "static" E field
amplitude. The question here would be; why 2pi/lambda_w^3 for the
volume element? Well, that is the speculative part. Perhaps some might
like (2pi/lambda_w)^3 better. But what I arrived at is a long
derivation with a couple of assumptions about modeling the quantum
"vacuum" as a relativistic medium with microscopic bound charge = +,-
sqrt(hbar*c) in CGS units. I will explain more if anyone is interested.
> I am also curious about how you appear to have managed to sidestep the
> issue of how close to monochromatic the source is. From Fourier
> theory, the more monochromatic the source, the more cycles are needed
> within each photon wavepacket, which will obviously impact on the
> amplitude of the wave.
Yep, that has always been a tough one for modeling photons. :-) I
sidestepped the issue by just claiming it is an ideal case. But I am
not sure that the number of cycles will actually impact the amplitude
since I doubt if we could even say a photon has any cycles. Though,
if we could, I would say two cycles max. It is a strange beast since a
photon is a relativistic "particle".
Best,
Fred Diether
Rich L.
...
> Yep, that has always been a tough one for modeling photons. �:-) �I
> sidestepped the issue by just claiming it is an ideal case. �But I am
> not sure that the number of cycles will actually impact the amplitude
> since I doubt if we could even say a photon has any cycles. �Though,
> if we could, I would say two cycles max. �It is a strange beast since a
> photon is a relativistic "particle".
>
> Best,
>
> Fred Diether
I think you are mis-conceiving what a "photon" is. I realize that QED
talks of photons as particles, like electrons and protons and
baseballs, but it is clear to me from diffraction experiments that
that the photon is more a conceptual/mathematical object than a real
object. All that can really be said about photons is that their
energy is proportional to the frequency, and that they are emitted and
absorbed. Any attempt to derive a size, shape, location, path of
propagation, etc. is misguided and will give different results for
different initial assumptions.
For example, a CW laser has a very narrow line width (small delta f)
and consequently the "size" of the photon would be calculated as many
wavelengths. In the case of light sources used for holography the
size of the photon would calculate out to several inches or even
feet. On the other hand a Ti-Sapphire laser producing fempto second
pulses will be producing photons with a length of just a wavelength or
two, and a very uncertain frequency (large delta f). In the latter
case one could try to argue that the narrow pulse is the superposition
of many photons, but the counter argument is that if the pulse is
attenuated so that, on average, only one photon is passed per pulse,
you would still see the very narrow time correlation and the wide
scatter in measured photon energy, even though only one photon was
present per pulse. So here you have two cases of photons with similar
energy, but very different time and space extent.
It is a misconception to think of a photon as having any particular
physical existence between emission and absorption.
Rich L.
FrediFizzx
news:6457610d-d18b-4e8b...@j14g2000yqm.googlegroups.com...
> On Dec 28, 8:18 pm, "FrediFizzx" <fredifi...@hotmail.com> wrote:
> ...
>> Yep, that has always been a tough one for modeling photons. :-) I
>> sidestepped the issue by just claiming it is an ideal case. But I am
>> not sure that the number of cycles will actually impact the amplitude
>> since I doubt if we could even say a photon has any cycles. Though,
>> if we could, I would say two cycles max. It is a strange beast since
>> a
>> photon is a relativistic "particle".
> I think you are mis-conceiving what a "photon" is. I realize that QED
> talks of photons as particles, like electrons and protons and
> baseballs, but it is clear to me from diffraction experiments that
> that the photon is more a conceptual/mathematical object than a real
> object. All that can really be said about photons is that their
> energy is proportional to the frequency, and that they are emitted and
> absorbed. Any attempt to derive a size, shape, location, path of
> propagation, etc. is misguided and will give different results for
> different initial assumptions.
I can assure you that I am not mis-conceiving what a photon might be or
not. I have been studying photons for several years now. Basically
just goofing around here to see what others might think. :-) Photons
are just like electrons in that nobody knows what they really are. But
it is fun to conjecture about what they might be. In my model of the
quantum "vacuum" as a relativistic medium, all gauge bosons such as
photons have to be "wavicles". Their particle aspects purely come from
the medium.
I came across an interesting article last night; "The Maxwell wave
function of the photon".
http://arxiv.org/abs/quant-ph/0604169
>From the abstract;
"James Clerk Maxwell unknowingly discovered a correct relativistic,
quantum theory for the light quantum, forty-three years before Einstein
postulated the photon's existence. In this theory, the usual Maxwell
field is the quantum wave function for a single photon. When the
non-operator Maxwell field of a single photon is second quantized, the
standard Dirac theory of quantum optics is obtained. Recently,
quantum-state tomography has been applied to experimentally determine
photon wave functions."
The quantum wavefunction of a photon is simply the Maxwell EM field.
> For example, a CW laser has a very narrow line width (small delta f)
> and consequently the "size" of the photon would be calculated as many
> wavelengths.
Do you have a reference for that calculation? I recall a very long
discussion on SPR about how long the wavetrain of a photon might be and
I don't think it was ever resolved.
> In the case of light sources used for holography the
> size of the photon would calculate out to several inches or even
> feet. On the other hand a Ti-Sapphire laser producing fempto second
> pulses will be producing photons with a length of just a wavelength or
> two, and a very uncertain frequency (large delta f). In the latter
> case one could try to argue that the narrow pulse is the superposition
> of many photons, but the counter argument is that if the pulse is
> attenuated so that, on average, only one photon is passed per pulse,
> you would still see the very narrow time correlation and the wide
> scatter in measured photon energy, even though only one photon was
> present per pulse. So here you have two cases of photons with similar
> energy, but very different time and space extent.
Sure. But I believe what you mention above is compatible with the
"wavicle" concept. My ideal case is about what we might call "ordinary"
free space photons.
> It is a misconception to think of a photon as having any particular
> physical existence between emission and absorption.
:-) That is only your opinion. Is the moon there if I am not looking
at it? For me, it surely is.
Best,
Fred Diether
Tom Roberts
> Photons
> are just like electrons in that nobody knows what they really are.
I disagree. Strongly. We know EXACTLY what photons are. To wit: a photon is the
factor in the integral corresponding to a squiggly line in the Feynman diagram
being computed in the perturbation approximation to QED (or the standard model,
which includes QED as a subset).
Note that everything I say here is completely in line with
standard QED. It's just that I am pointing out things that
are usually not pointed out or mentioned, because they
are so basic and obvious. So much so that all too often
they are ignored, just as fish ignore the water.
No other meaning makes sense, once you think about it in sufficient detail. Note
that it is an experimental issue whether or not there are any phenomena or
"things" in the real world that correspond to photons. As is well known, there
are aspects of the world that behave like photons, though it is often difficult
to call them "objects" or "things" or "particles" or "waves"....
Ditto for electrons....
Yes, A LOT of people confuse that mathematical factor in the model (theory) with
real-world objects. We even have detectors we call "photon counters". But when
push comes to shove, the meaning of photon is as I said above, regardless of how
many people make this confusion. The underlying issue is the necessary
distinction between model and world -- photons are ineluctably part of the MODEL.
This is really a verbal shortcut. Experienced and knowledgeable
physicists are aware of the PUN involved. But neophytes might not
be. In most cases the pun is of no major consequence, but
recognizing and avoiding it is essential in discussions like this.
> it is fun to conjecture about what they might be.
That is possible ONLY if one conflates the model with the world. DON'T DO THAT!
> The quantum wavefunction of a photon is simply the Maxwell EM field.
Only for a VERY unusual meaning of "is". The usual meaning implies these two
things are identical or the same; that QUITE CLEARLY is not the case.
For instance, the classical EM field is a field on spacetime.
But a wavefunction is NOT such a field; it is a functional
on Hilbert space. There are other differences....
Exercise for the reader: explain why a photon (aka squiggly line
in a diagram) cannot possibly "have" a wavefunction. Hint: first
describe what a wavefunction actually is.
>> For example, a CW laser has a very narrow line width (small delta f)
>> and consequently the "size" of the photon would be calculated as many
>> wavelengths.
>
> Do you have a reference for that calculation? I recall a very long
> discussion on SPR about how long the wavetrain of a photon might be and
> I don't think it was ever resolved.
Don't confuse the coherence length of a laser with the "length of photons".
It is certainly true that Fourier's theorem implies that waves with narrow
linewidths must have long wavetrains. One can compute the relationship
mathematically, and obtain Heisenberg's famous relation.
But don't confuse this with "photons", because to relate them one must devise an
EXPERIMENT that can MEASURE the length of a photon, and which can be computed in
QED. Good luck....
>> It is a misconception to think of a photon as having any particular
>> physical existence between emission and absorption.
>
> :-) That is only your opinion. Is the moon there if I am not looking
> at it? For me, it surely is.
You confuse two VERY DIFFERENT issues. Specifically, Rich L. said "... any
PARTICULAR physical existence...[emphasis mine]". Once one understands what
photons actually are, it's clear that there is no possible way to make any sort
of a MEASUREMENT on a photon between its emission and absorption (whatever that
means -- I assume the endpoints of its leg in the diagram in which it appears).
That is QUITE DIFFERENT from "non-existence".
That brings up a major difficulty in identifying photons with
specific physical phenomena: one must sum up all relevant
diagrams and (anti-)symmetrize the result over all external
legs. This screws up any possible mapping of a specific
photon in a certain diagram to any real-world phenomenon.
In some cases one can make an APPROXIMATE mapping (i.e. one
can show that one diagram dominates and all others are
negligible); sometimes that approximation is incredibly good
(e.g. when the endpoints of the photon leg are physically
located a macroscopic distance apart). It is only in this
last sense that one can claim to have observed or identified
photons in the real world.
Please remember that physics is the process of creating and testing MODELS of
the world. The model is NOT the world; the map is NOT the territory; the image
is NOT the object. Conflating model with world generates all sorts of confusions
-- DON'T DO THAT.
Don't forget: EVERYTHING we know about the world is really
knowledge about a MODEL of the world. The model we use in
everyday life is so ubiquitous and so good that all too
often people forget that it is a MODEL.
Tom Roberts
FrediFizzx
news:AaudnS4dIZD...@giganews.com...
> FrediFizzx wrote:
>> Photons are just like electrons in that nobody knows what they really
>> are.
>
> I disagree. Strongly. We know EXACTLY what photons are. To wit: a
> photon is the factor in the integral corresponding to a squiggly line
> in the Feynman diagram being computed in the perturbation
> approximation to QED (or the standard model, which includes QED as a
> subset).
Not really what I am talking about, Tom. Photons are quanta of the
electromagnetic field. I will quote what Griffiths says about fields in
"Introduction to Electrodynamics"; "...I can't tell you, then, what a
field is--only how to calculate it and what it can do for you once
you've got it."
[snip}
>> it is fun to conjecture about what they might be.
>
> That is possible ONLY if one conflates the model with the world. DON'T
> DO THAT!
Sorry, but I CAN do whatever I please as far as conjecturing about
models of the world. Think about what you said more carefully and I
think you will find it pretty silly.
>> The quantum wavefunction of a photon is simply the Maxwell EM field.
>
> Only for a VERY unusual meaning of "is". The usual meaning implies
> these two things are identical or the same; that QUITE CLEARLY is not
> the case.
Hmm.. seems like you didn't read the article I posted the link for.
Here is the link again.
http://arxiv.org/abs/quant-ph/0604169
> For instance, the classical EM field is a field on spacetime.
> But a wavefunction is NOT such a field; it is a functional
> on Hilbert space. There are other differences....
>
> Exercise for the reader: explain why a photon (aka squiggly line
> in a diagram) cannot possibly "have" a wavefunction. Hint: first
> describe what a wavefunction actually is.
You should have read the article but here is some more from Milonni's
"The Quantum Vacuum: An Introduction to Quantum Electrodynanics" to
ponder; "...Even in the case of a single photon (n = 1), the classical
wave theory gives the same spatial dependence as quantum theory for the
intensity, but this pattern represents the relative probability
distribution for finding the photon."
Please read the article then when done with that, you can take a look at
"Measurement of the transverse spatial quantum state of light at the
single-photon level".
http://www.uoregon.edu/~oco/Group_Pages/Raymer/publications/100_pub_mgr.pdf
Best,
Fred Diether
GSS
....
> > FrediFizzx wrote:
>>> Photons are just like electrons in that nobody knows what they really
>>> are.
>
>> I disagree. Strongly. We know EXACTLY what photons are. To wit: a
>> photon is the factor in the integral corresponding to a squiggly line
>> in the Feynman diagram being computed in the perturbation
>> approximation to QED (or the standard model, which includes QED as a
>> subset).
>
> Not really what I am talking about, Tom. �Photons are quanta of the
> electromagnetic field. �I will quote what Griffiths says about fields in
> "Introduction to Electrodynamics"; "...I can't tell you, then, what a
> field is--only how to calculate it and what it can do for you once
> you've got it."
>
quanta bounded in space? Can you mentally visualize a finite bounded
region of space that at any given instant, contains the quanta of the
electromagnetic field? If so, how is this boundary computed?
In this regard let me present my view regarding physical existence of
fields in general.
It is important to note that a value assigned to any space point in a
physical field, always represents some physical property associated
with that point (and its neighborhood). Of course, all physical fields
will have their mathematical representations. Let us consider a
continuum of space points representing the vacuum or empty space. We
can always define a mathematical field by assigning certain numbers or
mathematical functions to all points in the space continuum. If such
numbers or mathematical functions do not represent any physical
properties or parameters associated with these points of the empty
space or vacuum, such a field can have no physical significance or
physical 'existence'. A major contradiction prevailing in the current
viewpoint is that the space continuum representing vacuum or empty
space can support physical fields but the corresponding physical
properties associated with all space points, cannot represent any
physical medium.
Do you agree?
Best regards
GSS
http://book.fundamentalphysics.info
mercury
Near the end of his life Einstein wrote: �All 50 years of conscious
brooding have brought me no closer to the answer to the question what
are the light quanta. Of course today every rascal thinks he knows the
answer but he is deluding himself.�
If don�t know there is a biannual conference on the issue of what is a
photon. Just do a google.
Rich wrote:
>I realize that QED talks of photons as particles, like electrons and protons and >baseballs
I think QED regards photons exclusively as quantized waves � the
amplitudes are introduced, quantized and then using pure math physical
quantities are derived. Absolutely no talk about point-like particle.
Do you agree?
Freddie Fizzz wrote
>I came across an interesting article last night; "The Maxwell wave function of >the photon".
I fact the concept was introduced by Byalnicki-Birula (and Sipe
later).
Tom Roberts wrote:
>a photon is the factor in the integral corresponding to a squiggly line in the >Feynman diagram being >computed in the perturbation approximation to QED
I know that Feynman diagrams are just a way of calculating � what here
can be called a photon??? Photon is a digit � not a particle????? Are
not talking about the propagator? Can you cite your source please!
Tom Roberts wrote:
>For instance, the classical EM field is a field on spacetime. But a wavefunction >is NOT such a field; it is a functional on Hilbert space.
The real physics is the double slit experiment (or better Mach -
Zehnder interferometer) � one needs really some wave (or exitation of
a field) there (probabilstic or not) in order to account for the
behaviour. The state vector is just a way to calculate.
As the talk goes about photons I would like to present my current
understanding of the photon. It changed many times and I expect it can
change in the future�
There was time I thought that the photon is just a wave /or group of
waves (capable of making QM collapse in contrast to the ordinary
waves (sound waves etc.)
But regarding Elitzur-Vaidman bomb-testing problem one must be aware
that the photon (and any particle) has two aspects �
1. A wave (a wave function or excitation of the EM field if you ike).
It is representing the amplitudes for the probability /or a real
process in the Bohm � de Broglie sense.
2. A particle � a point-like object � the photon itself.
I don�t support the probabilistic nature of the WF � for it means that
the particle movement is influenced by distant fermionic objects in an
non-casual non-material way. How else would you understand the
influence of a possible trajectory (the amplitude) on the real
trajectory. For in the Mach Zehnder (also in Elitzur-Vaidman bomb-
testing problem) the particle must take one path (unknowingly which)
and the posibility that it can take the other path influences the
direction of the particle after the second beamsplitter.
I think that the WF (or the excitation of the field) is real but it
(WF) can interract only with its own particle. So the need for WF
collapse fails out � by the detection of the particle WF doesn�t
dissapear � it just becomes undetectable because it can not interract
with anything else more. As far as I imagine the WF carries energy,
momentum and polarization but they all have been transferred to the
particle in the process of interraction of the particle with another
particle.
So WF is somewhat unobservable before and even more after the
detection of the particle.
I would like to hear other opinions on what is a particle which would
make understand it better.
Ilian
Tom Roberts
> "Tom Roberts" <tjrobe...@sbcglobal.net> wrote in message
> news:AaudnS4dIZD...@giganews.com...
>> FrediFizzx wrote:
>>> Photons are just like electrons in that nobody knows what they really
>>> are.
>>
>> I disagree. Strongly. We know EXACTLY what photons are. To wit: a
>> photon is the factor in the integral corresponding to a squiggly line
>> in the Feynman diagram being computed in the perturbation
>> approximation to QED (or the standard model, which includes QED as a
>> subset).
>
> Not really what I am talking about, Tom. Photons are quanta of the
> electromagnetic field.
This is PRECISELY what you are talking about. Or rather, what you are trying to
talk about. You say "Photons are quanta of the electromagnetic field", which is
meaningless until you define your terms -- when you do that, ultimately you'll
come down to what I said: "a photon is the factor...". Or you will uses highly
non-standard terms, as in the paper you referenced (in which "photon" has a VERY
non-standard meaning, as do "wavefunction" and other words).
Raymer and Smith are counting on their readers having rather
wishy-washy definitions of such words in mind. In particular,
they expect the word "photon" to be divorced from QED, which
is rather silly and leaves it UNDEFINED rather than loosely
defined as they hope....
> I will quote what Griffiths says about fields in
> "Introduction to Electrodynamics"; "...I can't tell you, then, what a
> field is--only how to calculate it and what it can do for you once
> you've got it."
Right. Physics is about MODELS. We can compute using those models, but we cannot
describe the correspondence between quantities in the model and objects in the
world, because to describe objects in the world requires a MODEL. There is an
unbreachable gulf between world and model, and you keep talking as if it doesn't
matter. Griffiths understands this, and goes on to discuss the MODEL, not the
world (which he says right up there he cannot tell you about).
Exercise for the reader: what aspects of the real world do
you know directly? hint: does your mind process anything
other than thoughts? What is the relationship between thoughts
and objects in the real world? -- in particular how are such
relationships established? And by whom?
Once you recognize that EVERYTHING you know about the world is really about a
MODEL OF THE WORLD that you have constructed for yourself, you will be able to
see my point. Until you realize that, you will think everything I say here is
"Not really what I [FrediFizzx] am talking about".
As I said before, this is so fundamental and pervasive that most authors do not
mention it. Most of the time that's OK, but not in the sort of discussion you
are attempting.
>>> it is fun to conjecture about what they might be.
>>
>> That is possible ONLY if one conflates the model with the world. DON'T
>> DO THAT!
>
> Sorry, but I CAN do whatever I please as far as conjecturing about
> models of the world.
But if you want other people to understand what you say, you must use words with
their standard meanings. Yes, as I said, many people who should know better
confuse world and model, or at least write that way. DON'T DO THAT!
> Think about what you said more carefully and I
> think you will find it pretty silly.
I see nothing silly in anything I wrote. I do see rather silly things in what
you wrote -- clear evidence to me that you confuse model and world so thoroughly
that you are unaware of the distinction.
Model building is not just physics, it is ESSENTIAL to your
everyday life -- it is the quintessentially human mode of
survival. You started building models of the world well
before you learned any words.
>>> The quantum wavefunction of a photon is simply the Maxwell EM field.
>>
>> Only for a VERY unusual meaning of "is". The usual meaning implies
>> these two things are identical or the same; that QUITE CLEARLY is not
>> the case.
>
> Hmm.. seems like you didn't read the article I posted the link for. Here
> is the link again. http://arxiv.org/abs/quant-ph/0604169
That article is revisionist history at its worst -- they ascribe THEIR
interpretations of MODERN physics to Maxwell.
Using TODAY's meanings of words, the "quantum wavefunction of a photon" cannot
possibly be "the Maxwell EM field", as I said.
And you REALLY need to do my exercise:
>> Exercise for the reader: explain why a photon (aka squiggly line
>> in a diagram) cannot possibly "have" a wavefunction. Hint: first
>> describe what a wavefunction actually is.
HINT2: the above-referenced paper touches on this.
Tom Roberts
FrediFizzx
> FrediFizzx wrote:
>> "Tom Roberts" <tjrobe...@sbcglobal.net> wrote in message
>> news:AaudnS4dIZD...@giganews.com...
>>> FrediFizzx wrote:
>>>> Photons are just like electrons in that nobody knows what they
>>>> really are.
>>>
>>> I disagree. Strongly. We know EXACTLY what photons are. To wit: a
>>> photon is the factor in the integral corresponding to a squiggly
>>> line in the Feynman diagram being computed in the perturbation
>>> approximation to QED (or the standard model, which includes QED as a
>>> subset).
>>
>> Not really what I am talking about, Tom. Photons are quanta of the
>> electromagnetic field.
>
> This is PRECISELY what you are talking about. Or rather, what you are
> trying to talk about.
No, not even close. What I was talking about with the statement
"...nobody knows what they really are" is more in the vein of this;
http://spie.org/documents/Newsroom/Imported/480/2006110480.pdf
"The nature of light: what are photons?"
I particularly like what Roychoudhuri says near the beginning,
"Physicist Sir Roger Penrose recently underscored the lack of reality in
our current theories about how the world works." in reference to
Penrose's book "The Road to Reality".
> You say "Photons are quanta of the electromagnetic field", which is
> meaningless until you define your terms -- when you do that,
> ultimately you'll come down to what I said: "a photon is the
> factor...". Or you will uses highly non-standard terms, as in the
> paper you referenced (in which "photon" has a VERY non-standard
> meaning, as do "wavefunction" and other words).
Most members of this group already exactly know the "terms" relating to
photons. I suspect you have been hanging out on the un-moderated groups
a bit too much.
> Raymer and Smith are counting on their readers having rather
> wishy-washy definitions of such words in mind. In particular,
> they expect the word "photon" to be divorced from QED, which
> is rather silly and leaves it UNDEFINED rather than loosely
> defined as they hope....
Hmm....
http://arxiv.org/find/grp_physics/1/ti:+AND+functions+AND+photon+wave/0/1/0/all/0/1
There is actually quite a bit of research going on in this area of
photon wave functions. But I believe what Raymer and Smith say as it
just makes good common sense. But here is a more comprehensive paper by
them that maybe you will actually read.
http://arxiv.org/abs/0708.0831
[snip the rest since it is a bit off-topic for this thread]
Now... back to the topic of this thread; Photon Energy Density. Take my
semi-classical result,
E^2 = (hbar w^4 n)/(4pi^2 c^3)
E is the electric field, w is omega, angular frequency and n is the
number of identical in phase photons, and plug it into the Maxwell wave
equations as,
E_0 = +,- sqrt[(hbar w^4 n)/(4pi^2 c^3)]
I believe you will find that it gives the correct answers. At least it
seems to match what Jackson says on page 4 of "Classical
Electrodynamics, 3rd ed." Now, some have indicated that it might not be
good for n = 1. But perhaps you can crank up the QED machine and check
that out for yourself. Seems to be OK to me AFAICT. Also, AFAICT, this
is new; I have not been able to find this result anywhere else. There
was a cavity QED paper that I ran across several years ago that had
something close to it but lost track of it and can no longer find it.
Best,
Fred Diether
glird
> Zehnder interferometer) � one needs really some wave (or exitation of
> a field) there (probabilstic or not) in order to account for the
> behaviour. The state vector is just a way to calculate.
>
> As the talk goes about photons I would like to present my current
> understanding of the photon. It changed many times and I expect it can
> change in the future�
>
> There was time I thought that the photon is just a wave /or group of
> waves (sound waves etc.)
>
> But regarding Elitzur-Vaidman bomb-testing problem one must be aware
>
> 1. A wave (a wave function or excitation of the EM field if you ike).
> It is representing the amplitudes for the probability /or a real
> process in the Bohm � de Broglie sense.
>
> 2. A particle � a point-like object � the photon itself.
>
> I don�t support the probabilistic nature of the WF � for it means that
> the particle movement is influenced by distant fermionic objects in an
> non-casual non-material way. How else would you understand the
> trajectory. For in the Mach Zehnder (also in Elitzur-Vaidman bomb-
> testing problem) the particle must take one path (unknowingly which)
> and the posibility that it can take the other path influences the
> direction of the particle after the second beamsplitter.
> I think that the WF (or the excitation of the field) is real but it
> (WF) can interract only with its own particle. So the need for WF
> collapse fails out � by the detection of the particle WF doesn�t
> dissapear � it just becomes undetectable because it can not interract
> with anything else more. As far as I imagine the WF carries energy,
> momentum and polarization but they all have been transferred to the
> particle in the process of interraction of the particle with another
> particle.
> So WF is somewhat unobservable before and even more after the
> detection of the particle.
>
> make understand it better.
>
> Ilian
Some experiments have been interpreted as proving that light cannot
be a wave system. Other experiments have been interpreted as proving
that light cannot be a particle.
Instead of concluding that light therefore can't be
a wave OR a particle, physicists concluded that it is BOTH!
mercury
> > brooding have brought me no closer to the answer to the question what
> > are the light quanta. Of course today every rascal thinks he knows the
> > answer but he is deluding himself.
> > photon. Just do a google.
>
> > Rich wrote:
> > >I realize that QED talks of photons as particles, like electrons and protons and >baseballs
>
> > amplitudes are introduced, quantized and then using pure math physical
> > quantities are derived. Absolutely no talk about point-like particle.
> > Do you agree?
>
> > Freddie Fizzz wrote
>
> > >I came across an interesting article last night; "The Maxwell wave function of >the photon".
>
> > I fact the concept was introduced by Byalnicki-Birula (and Sipe
> > later).
>
> > Tom Roberts wrote:
> > >a photon is the factor in the integral corresponding to a squiggly line in the >Feynman diagram being >computed in the perturbation approximation to QED
>
> > can be called a photon??? Photon is a digit not a particle????? Are
> > not talking about the propagator? Can you cite your source please!
>
> > Tom Roberts wrote:
> > >For instance, the classical EM field is a field on spacetime. But a wavefunction >is NOT such a field; it is a functional on Hilbert space.
>
> > Zehnder interferometer) one needs really some wave (or exitation of
> > a field) there (probabilstic or not) in order to account for the
> > behaviour. The state vector is just a way to calculate.
>
> > As the talk goes about photons I would like to present my current
> > understanding of the photon. It changed many times and I expect it can
> > change in the future
>
> > waves (sound waves etc.)
>
> > But regarding Elitzur-Vaidman bomb-testing problem one must be aware
>
> > 1. A wave (a wave function or excitation of the EM field if you ike).
> > It is representing the amplitudes for the probability /or a real
>
> > 2. A particle a point-like object the photon itself.
>
> > I don t support the probabilistic nature of the WF for it means that
> > the particle movement is influenced by distant fermionic objects in an
> > non-casual non-material way. How else would you understand the
> > trajectory. For in the Mach Zehnder (also in Elitzur-Vaidman bomb-
> > testing problem) the particle must take one path (unknowingly which)
> > and the posibility that it can take the other path influences the
> > direction of the particle after the second beamsplitter.
> > I think that the WF (or the excitation of the field) is real but it
> > (WF) can interract only with its own particle. So the need for WF
> > dissapear it just becomes undetectable because it can not interract
> > with anything else more. As far as I imagine the WF carries energy,
> > momentum and polarization but they all have been transferred to the
> > particle in the process of interraction of the particle with another
> > particle.
> > So WF is somewhat unobservable before and even more after the
> > detection of the particle.
>
> > make understand it better.
>
> > Ilian
>
> � Some experiments have been interpreted as proving that light cannot
> be a wave system. �Other experiments have been interpreted as proving
> that light cannot be a particle.
> � Instead of concluding that light therefore can't be
>
> - Show quoted text -
No at all. Some experiments show that is is a particle. Other thta it
is a wave. So it is both.
Ilian
======================================= MODERATOR'S COMMENT:
Please trim (delete) uncommented quoted text. -fd
Tom Roberts
> Some experiments have been interpreted as proving that light cannot
> be a wave system. Other experiments have been interpreted as proving
> that light cannot be a particle.
> Instead of concluding that light therefore can't be
> a wave OR a particle, physicists concluded that it is BOTH!
No. From knowledge of what a photons are, it is clear that they are neither
particles nor waves. They are QUANTUM OBJECTS, for which your everyday
experience provides no clue about their behavior, and your everyday vocabulary
provides no words to discuss them. They can only be understood via a
mathematical analysis of their behavior, which requires an understanding of the
perturbation approximation to QED.
Speaking loosely, photons have both "particle-like" and "wave-like" aspects:
* like waves they cannot be precisely located.
* like particles they are always detected as a positive integer
multiplying some minimal energy, and individual ones are always
detected via a single electron in a single detector.
* there is an amplitude associated with "each" photon; the amplitude
squared gives the probability of detecting "the" photon, and like
waves these amplitudes interfere with each other.
But photons have aspects contrary to anything of your everyday experience:
* one cannot identify any specific photon (they are all identical
and indistinguishable; this has a profound impact on how their
amplitudes interfere).
* one cannot count photons precisely (except in certain rather
contrived situations)
* for any macroscopic phenomena, there are usually an immense number
of photons involved.
* one cannot ascribe a definite trajectory to any photon; one can
ascribe an APPROXIMATE trajectory to the average of a collection of
them.
* virtual photons can generate either a repulsive or attractive force.
* photons carry intrinsic spin, and multiple photons can be created
with "entangled" spins, which is radically outside your everyday
experience.
[I point out I am speaking quite loosely here, because your
statement indicates a rather serious confusion about what
photons are and how they behave. Nothing I say here
contradicts what I said earlier, though the connection can
be rather distant.]
Tom Roberts
FrediFizzx
> * virtual photons can generate either a repulsive or attractive
> force.
I would like to see a specific reference for that. I suspect the word
would be "transmit" rather than "generate".
Best,
Fred Diether
FrediFizzx
> No at all. Some experiments show that is is a particle. Other thta it
> is a wave. So it is both.
In the viewpoint of the quantum "vacuum" as a relativistic medium,
photons (and all gauge bosons) would/could be "wavicles" like phonons.
Particle aspects would/could be due to actual physical contact of the
medium "particles" with matter "particles" and all being quantum
objects. Feynman was probably right in that we will never actually know
what really happens at the interaction "point" of interactions of
quantum objects but it doesn't stop us from imagining what might be
going on. For me, it is all about relativistic and quantum "vacuum"
effects and that space and time are emergent from their interactions.
Best,
Fred Diether
mercury
Have you read my post from 3.01.2010. I think that Elitzur Vaidman
effects needs a particle in the very classical sense (and a wave too).
Ilian
Tom Roberts
Pick up any graduate-level textbook on QED. As for "generate" vs "transmit", the
word choice is not of importance.
Tom Roberts