Photon Size: Direction & Probability

[marlon]

Repetitive like always, But,

But, again you chose NOT to answer them. You are looking less credible by every post you make. Anyways, ...

1- A photon can not be a point particle.

This is a blunt violation against the basic principles of the standard model (read the webpage and check the references at the end of the article). You use laser physics later on to make your point but doesn't it strike you as being strange that you violate the very theoretical model that explains all this laser phenomenae correctly ?

Because when light of a lamp glints to a sheet of iron, we won't see any affect of photons and lighting under it. While we know that there are free spaces among moleculs of iron that can be sufficent for crossing the infinity number of these points (photons) that it is a paradox.

Newsflash, maybe that's because photons INTERACT with matter (atoms, phonons, etc) ?

If we assume that a photon is a point particle then the propagator (for example a laser) must propagates infinity number of photons in an arbitrary time interval that it is an unreal imagination.

Huh ? What do you mean by propagator ? Photons are the constituent particles of the laser. As a matter of fact "a laser" is just a bunch of photons with specific properties. I challenge you to show me ANY publication that explains the laser (from population inversion on...) using the photon size concept. In return, i will give you plenty of references where they DON'T :

Applied Physics B: Lasers and Optics (ISSN 0946-2171)
IEEE Journal of Lightwave Technology (ISSN 0733-8724)
IEEE Journal of Quantum Electronics (ISSN 0018-9197)
IEEE Journal of Selected Topics in Quantum Electronics (ISSN 1077-260X)
IEEE Photonics Technology Letters
Journal of the Optical Society of America B: Optical Physics (ISSN 0740-3224)
Laser Focus World (ISSN 0740-2511)
Optics Letters (ISSN 0146-9592)
Photonics Spectra (ISSN 0731-1230)

The Nobel Prize in Physics 1966 Presentation Speech by Professor Ivar Waller. Retrieved 1 January 2007.

Gould, R. Gordon (June 1959). "The LASER, Light Amplification by Stimulated Emission of Radiation". The Ann Arbor Conference on Optical Pumping.
Gould's conference presentation and the public introduction of the term laser are mentioned in:

Chu, Steven; and Townes, Charles (2003). "Arthur Schawlow", in ed. Edward P. Lazear,: Biographical Memoirs, vol. 83, National Academy of Sciences, p. 202. ISBN 0-309-08699-X.

G.P. Karman, G.S. McDonald, G.H.C. New, J.P. Woerdman, "Fractal modes in unstable resonators", Nature Vol. 402, 138 (11 November 1999).


marlon

ps : i am still waiting for that photon-size equation, though.

 

[Anonym]

I think its the ability to correlate the ideas/information given/known and there's not a lot, it seems, on the 'size of photons'--(of which can be taken not 'too far'/'in new directions' here on the forum before it becomes 'speculative' and is not accepted on the forum--which is fine).

The coherence length seems to me the adequate wave mechanical parameter or close to it. It is well defined mathematically measurable quantity that may be applied universally to CED, QED and at HEP (limit when Lt and Ls go to zero). Whether it is close to zero or exactly =0 for the structureless objects is now matter of the standard experimental and theoretical analysis.

Whether it is accepted on the forum or not interest me as the last year snow. I use the standard notion accepted in CED and QED during last 40 years.

Regards, Dany.

 

[Anonym]

But this is ridiculous. You made it sound as if the PDG isn't updated to reflect the BEST knowledge that we know of today. I did not make a reference to the PDG book from 10 years ago!

It sounds to you exactly opposite to what I wrote. What is “ridiculous”? My understanding of your intensions or the technical details? If I missed your point, I quit. If you do not agree with the specific technical realization, we may find eigenschaften.

Any way, my impression is that the quantity of home made philosophical considerations going up last time and the quality of the technical discussions going down. If I identify your intensions correctly, you want to stop that. I want let you know that I am ready to cooperate and help where I can. However, we are macroscopic bodies and therefore not identical (surely we have different longitudinal and transversal coherence lengths).

Regards, Dany.

 

[Anonym]

As these quantities are always characteristics of the emitting system, it is not sensible to extract a characteristic of a single photon from it.

How you define a single photon?

Regards, Dany.

 

[jal]

The coherence length seems to me the adequate wave mechanical parameter or close to it. It is well defined mathematically measurable quantity that may be applied universally to CED, QED and at HEP (limit when Lt and Ls go to zero). Whether it is close to zero or exactly =0 for the structureless objects is now matter of the standard experimental and theoretical analysis.

You might want to add

As far as I can figure out, everyone assumes that an emitter of a photon cannot emit a photon bigger than what it is. Also, an absorber of a photon has got to be bigger than the photon.

The size range of a photon seems to disturb this forum. Yet you all accept without argument the size range of an other dimensions.

Constraints on the radius of extra dimensions for the case of two flat dimensions of equal radius
r < 90-660 nm (astrophysics; limits depend on technique and assumptions)
r < 0:22 mm, CL = 95% (direct tests of Newton's law; cited in Extra Dimensions
review)

Maybe it's because you all want the size of a photon to be able to fill the size of our 3d universe.
I'm not doing the speculation... I'm just learning from the data presented by others

 

[rewebster]

Repetitive like always, But,

1- A photon can not be a point particle. Because when light of a lamp glints to a sheet of iron, we won't see any affect of photons and lighting under it. While we know that there are free spaces among moleculs of iron that can be sufficent for crossing the infinity number of these points (photons) that it is a paradox.

2- If read my fore posts, you see that I answered this question in other way. If we assume that a photon is a point particle then the propagator (for example a laser) must propagates infinity number of photons in an arbitrary time interval that it is an unreal imagination.

Thanks.
Mr Beh

so, which theory are you working from?


(and, please, mentors, don't lock this thread if he gives the answer that I think he may)

-----------------------------------------------------

The coherence length seems to me the adequate wave mechanical parameter or close to it. It is well defined mathematically measurable quantity that may be applied universally to CED, QED and at HEP (limit when Lt and Ls go to zero). Whether it is close to zero or exactly =0 for the structureless objects is now matter of the standard experimental and theoretical analysis.

Whether it is accepted on the forum or not interest me as the last year snow. I use the standard notion accepted in CED and QED during last 40 years.

Regards, Dany.

that's most of what is being discussed, I believe, whether it's zero or not.

(and, maybe, whose standard is correct/accurate)

 

[rewebster]

Included



As I mention in my post #136 above, people here use Greek’s notion of size. Apparently it is related to the question whether size is a matter. Indeed it is relevant parameter when we talking not QT but sex.

Regards, Dany.

Well, well, well---I have NEVER thought about PHOTONS being possibly male or female EVER before in my life--my, my, my...until now

maybe that's what FRA was talking about in another thread--evolutionary particles


so, Anonym, which of those theories carries the most weight in you mind for photons? (your post #153)

------------------------------------------------

Maybe it's because you all want the size of a photon to be able to fill the size of our 3d universe.

no comment

 

[Anonym]

which of those theories carries the most weight in you mind for photons? (your post #153)

I am not sure I understand the question. Each one is defined within its own range of validity and naturally connected with each other. The photon waveform is defined as usual by the boundary and the initial conditions.

Regards, Dany.

 

[Cthugha]

How you define a single photon?

What do you want to hear?

The basic quantity of the quantized em field?
Something represented by a n=1 fock-state?
A click on the detector?
A bright pixel on a CCD?
The "result" of a streak camera doing single photon counting?
The emission of a single photon source?
Light with g_2(\tau=0)=0?

Tell me, how you would like to combine photon size and coherence length and where the definition of a single photon comes into play. Just guessing what you are aiming at, makes it somehow hard to answer, especially as a single photon has different meanings concerning different experiments.
The meaning of "single photon" in single photon creation is different from the meaning of "single photon" in single photon detection for example.

 

[rewebster]

I am not sure I understand the question. Each one is defined within its own range of validity and naturally connected with each other. The photon waveform is defined as usual by the boundary and the initial conditions.

Regards, Dany.

it just seems that you like QED and I was thinking if you knew Feynman's stuff really well if he ever mentioned photon size (or, really, did he 'theorize' about anything close (real photons)--and not 'virtual photons' --I think I read something about smaller (?) than Compton's on the virtual(?)----QED -it is something else.
--------------------------------------------------

I like this one:

If a photon had no size in some way or another then it wouldn't exist. And as far as I'm concerned until someone proves that light has no mass or otherwise I'll reserve my judgement on the validity of any of the counter arguments

#90 post on about the same subject

https://www.physicsforums.com/showthread.php?t=104657&page=6

It's got to be of interest (to many) and frustrating (to many who have to try to re-explain it over and over again) as often as this subject comes up (everywhere) and if it was DEFINTE one way or the other--there wouldn't be any discussions like this SO often.

---------------------------------------
reilly has a good 'summation' post (#120) on same thread:

(just part below:)

" physics is all about challenging theories; that's what professional physicists do. But, do note that sometimes challenges are met with hostile reations, and the challenge become very contentious. So, at time, physics is a contact sport. And, surprise, many professional physicists are arrogant -- I know more than you do kind of stuff -- so they tend to ignore beginners, with whom they are not kindly disposed to discuss basis. "

 

[Anonym]

What do you want to hear?

The emission of a single photon source

The meaning of "single photon" in single photon creation is different from the meaning of "single photon" in single photon detection for example.

The philosophy leaves to you, please.

Anyway the section you mention is not about photon size, but spatial coherence (coherence length, coherence area, coherence volume,...). As these quantities are always characteristics of the emitting system, it is not sensible to extract a characteristic of a single photon from it.

Your statement is nonsense (philosophy) if you are not able to define a single photon.

Regards, Dany.

 

[Cthugha]

The emission of a single photon source

In the case of an ideal single photon source, the coherence volume is at least a volume, in which there is just one photon.
In that case it might make sense to at least take it as an upper bound for size, but the usual layman coming in here and asking for the size of a photon is certainly not interested in the very special case of subpoissonian statistics.

The philosophy leaves to you, please.

Your statement is nonsense (philosophy) if you are not able to define a single photon.

It is neither philosophy nor nonsense to mention, that there are different meanings of the term "single photon" in physics.
As the initial question of this topic was not specified, I was of course talking about what is experimentally measured by single photon counting, which is the more general case.

So in the case of poissonian or superpoissonian statistics the meaning of coherence volume reduces to the volume, in which individual photons are indistinguishable. And that is certainly not a quantity, which tells us something about the size of just one of them.

Anyway even in the case of single photon sources coherence times depend strongly on the system, but not much on the characteristics of the photon. In such devices antibunching is a signature of the system being unable to emit several photons at once (single molecules or single QDs for example). This is not comparable to antibunching of fermions, free electrons for example, where the effect of antibunching is a result of the characteristics of the particle itself.

 

[marlon]

How you define a single photon?

Regards, Dany.

As a chunck of energy

http://hyperphysics.phy-astr.gsu.edu/hbase/mod2.html#c3

marlon

 

[Schrodinger's Dog]

If a photon had no size in some way or another then it wouldn't exist. And as far as I'm concerned until someone proves that light has no mass or otherwise I'll reserve my judgement on the validity of any of the counter arguments

Well I'm not quite as controversial as I was a year and a half ago so shoot me Bit out of context anyway. I seem to vaguely remember I said that because I don't like people saying absolutely light has no mass beyond doubt, as much as I don't like people trying to prove it does, we're not in a position to claim absolute certainty of either, so it's a bit of a waste of time.

I'm not a big fan of absolute answers in science, I don't think scientists are, as they are not scientific. So you can probably find me on both sides of the argument in the forums history, depending on how it the answer is phrased, if it's phrased as an absolute condition that a photon has no mass then I say no that is not true explicitly.

If it says it is useless to discuss it, or we have an upper bound limit on the size of a photon of 6.6 nm or whatever etc, and we know from our equations that light cannot have mass, then I'm fine with that.

Leave the absolutes to religion is my philosophy.

That said I think it's best to say light has no mass, because it is useful, where as claiming it does have mass is impossible to prove and an exercise in philosophy, thus my current stance on the good side of the force .

 

[rewebster]

If it says it is useless to discuss it, or we have an upper bound limit on the size of a photon of 6.6 nm or whatever etc, and we know from our equations that light cannot have mass, then I'm fine with that.

Leave the absolutes to religion is my philosophy.

That said I think it's best to say light has no mass, because it is useful, where as claiming it does have mass is impossible to prove and an exercise in philosophy, thus my current stance on the good side of the force .

so, the well trodden path is the best way?

 

[DaTario]

I would like to share some reflections of mine.

First, coherence volume seems to be a good start point to this discussion (the size of a photon). Sources that shoot one photon at a time seems to be a well defined concept-apparatus. With this in hand, interferometric analysis seems to point to coherence volume as the FAPP volume of one photon.

Second. Objection to what is written above may comes from the following. Assuming photon as a wave train, it seems reasonable to consider it, most of time, a multi-frequency structure, presenting frequency variations along the line joining the source and the detector. I am considering here an atom in fluorescence process (point source) and the Weisskopf-Wigner theory for the spontaneous decay. If the wave train presents frequency variation in the logitudinal direction, of course the interference will diminish even if the photon is still going through the interferometer. Experiments with twin photons (photons generated by second order process k -> k' + k") allow us to detect one of these two photons and be aware that the other photon is entering (with certainty) the interferometer. I don't want to go far into this, but I would like to emphasize that non-monochromatic nature may lead to underestimation of photon's length via interferometric precudure.

Finally I would like to put in the same post my insatisfaction with these points:

1) If
E = h \nu
and
E = m c^2
how does one solve the question of not ascribing a mass to the photon.


2)
If one measures the photon length and area (photon volume). How does one correct it relativiscally to obtain proper length? Infinites will appear.

Thank all for the attention

Best wishes,

DaTario

 

[marlon]

I would like to share some reflections of mine.

First, coherence volume seems to be a good start point to this discussion (the size of a photon). Sources that shoot one photon at a time seems to be a well defined concept-apparatus. With this in hand, interferometric analysis seems to point to coherence volume as the FAPP volume of one photon.

Allow me to respond with my opinion on this. I have been reading quite some posts in which the idea of "coherence length is the photon length" is proposed. I think this is confusing because we are referring to a particle-like concept (length, volume) by using a wavelike concept (coherence length). This is another consequence of misinterpretation of the dual nature inherent to quantummechanics. I mean, why must we always mix the particle and wavelike notions ? To what purpose ? Both visions are dual and are not supposed to be used simultaneously. What purpose does that serve ? Looking at the QM formalism, one can only conclude that this is completely incorrect and therefore, this discussion is limited to a sequence of speculations for exactly THAT reason !

marlon

 

[rewebster]

Allow me to respond with my opinion on this. I have been reading quite some posts in which the idea of "coherence length is the photon length" is proposed. I think this is confusing because we are referring to a particle-like concept (length, volume) by using a wavelike concept (coherence length). This is another consequence of misinterpretation of the dual nature inherent to quantummechanics. I mean, why must we always mix the particle and wavelike notions ? To what purpose ? Both visions are dual and are not supposed to be used simultaneously. What purpose does that serve ? Looking at the QM formalism, one can only conclude that this is completely incorrect and therefore, this discussion is limited to a sequence of speculations for exactly THAT reason !

marlon

do you mean that you would like the thread moved to the Classical Physics area?

 

[DaTario]

Allow me to respond with my opinion on this. I have been reading quite some posts in which the idea of "coherence length is the photon length" is proposed. I think this is confusing because we are referring to a particle-like concept (length, volume) by using a wavelike concept (coherence length). This is another consequence of misinterpretation of the dual nature inherent to quantummechanics. I mean, why must we always mix the particle and wavelike notions ? To what purpose ? Both visions are dual and are not supposed to be used simultaneously. What purpose does that serve ? Looking at the QM formalism, one can only conclude that this is completely incorrect and therefore, this discussion is limited to a sequence of speculations for exactly THAT reason !

marlon

I think your point is quite good. Note however that we are searchig for spatial characterization of an phisically existent object. Or less, we want the photon to be an existing object, so we must offer such spatial characterization. At the background of this structure we call photon there is vacuum in the simplest case. Vaccum as we know, must be a configuration of EM with some noise, implying no interference and no coherence at all. For this reason, the experimental perception of coherence must have something to do with the spatial characterization of the photon.

But I still agree with you in that there seems to be a strange fusion of concepts related to the dual nature. Perhaps, understanding how one can mix this notions in a logical and sound manner, we can achieve a better analysis.

best wishes

DaTario

 

[pervect]

I would like to share some reflections of mine.

First, coherence volume seems to be a good start point to this discussion (the size of a photon). Sources that shoot one photon at a time seems to be a well defined concept-apparatus. With this in hand, interferometric analysis seems to point to coherence volume as the FAPP volume of one photon.

Second. ... I don't want to go far into this, but I would like to emphasize that non-monochromatic nature may lead to underestimation of photon's length via interferometric precudure.

Finally I would like to put in the same post my insatisfaction with these points:

1) If
E = h \nu
and
E = m c^2
how does one solve the question of not ascribing a mass to the photon.2)
If one measures the photon length and area (photon volume). How does one correct it relativiscally to obtain proper length? Infinites will appear.

Thank all for the attention

Best wishes,

DaTario

For starters, there might be some purposes for which "coherence volume" is not the practical thing one is interested in, but it's certainly a quantity that is of interest.

Note that the coherence length (and coherence volume) of a photon is not a property of the photon itself, it is a property of how the photon is prepared, i.e. what state the photon is.

For instance, using a stellar interferometer, the transverse coherence length of a photon from a distant star can be kilometers long - and its longer the further away the star is. A close star would have a much shorter coherence length than a further away star. So the coherence length of a photon depends on how it is prepared (and also on where it is being observed), it's not a property of just the photon. There are some related points I'll get into later.

The coherence length question is not at all related to the question of the mass of a photon. Even without defining a coherence volume, it is clear that photons can have a well-defined value of energy. The point is that E^2 - |p|^2 c^2 is an invariant for any isolated system, and that this invariant is the so-called invariant mass of the system. This mass is a property of the system itself, and for an isolated photon, this mass is zero. See any of the numerous threads on mass in relativity, or the sci.physics.faq http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

In contrast, the energy of a photon depends on the observer - an observer at rest will see the photon with one frequency, someone moving with respect to that observer will see the photon with a different frequency.

So the energy (aka relativistic mass) of a photon is NOT a property of the photon, but a property of the photon and a specific observer. The invariant mass of a photon is a property only of the photon, it does not depend on the observer (that's what makes it invariant under the Lorentz transform).

Also - a photon has no "proper volume", nor does it have a "proper frame". There isn't any way around the infinites that you point out. Nor should you expect there to be one.

To get back to something I promised to talk about earlier, in the case of a single photon, one can get away with thinking that the wavefunction of the photon occupies standard 3 dimensional space (ignoring the time dimension). If you start to study the quantum mechanics of more than one particle, you'll quickly come up against the fact that the wavefunction does NOT occupy physical space, but rather occupies a form of phase space.

For instance, the wavefunction of two photons requires a 6-d space, it cannot be described in a 3-d space.

 

[marlon]

do you mean that you would like the thread moved to the Classical Physics area?

Not at all, this thread is where it belongs.

I think your point is quite good. Note however that we are searchig for spatial characterization of an phisically existent object. Or less, we want the photon to be an existing object, so we must offer such spatial characterization.

Well, i understand your intentions but as i have mentioned before, this search starts off from "shaky foundations". I mean, the first question in this case is : "what is a photon" , Well, if we all would look at how a photon is defined in QM, we we would find out that a photon is defined as a piece of energy. QFT teaches us how photons arise if we quantise the EM field. In other words, if we adopt the QM definition of a photon, we are basically talking about a discrete amount of energy. That is all ! I don't understand where the "position" comes in. If we adopt the QFT photon definition, we know that a photon arises as a vibration of the EM field to which we can attribute particle like concepts like momentum. NOWHERE in QFT is there every anything mentioned on the spatial location of that EM-field vibration. Again i ask, why bringing in the notion of photon position ?

The closest thing you will get for a connection between photon and position will be this : the spatial coordinates in the EM waves equation. So, using the wavelike concepts of QM, one can indeed use cogerence length etc etc and connect it to spatial coordinates through its equation. But, once you start talking about photons, you are no longer in the wavelike world !

marlon

 

[rewebster]

-----------------------------------

"Well, i understand your intentions but as i have mentioned before, this search starts off from "shaky foundations". "

I've only been around (here) for about a year, and what I have seen is that there (almost definitely) will be a thread on:

how big is a photon?

What is a photon?

wave/particle whatever dilemma problem

are we having photons for dinner?


If you go by one 'definition', someone else brings in some 'old' definition, or some recently published blankety-blank; so, what's a father to do? beat the child, scold the child, teach the child, assume the child knows nothing, bless the child, or the one about you never know what will come out of the mouths of a child---and, then, on what level on what scale of from 1-100,---I don't know what is the age of the youngest PF member or the oldest (HA-ha)---


Personally---I like Photons---whatever they are and whatever we find them to be.

 

[marlon]

If you go by one 'definition', someone else brings in some 'old' definition

Well, that's a bit easy to justify all the speculations going on. What other photon definition is there except that quantummechanical one ? I mean, QM describes the photon and QED describes it's behaviour. Both definitions are more or less equivalent with respect to the theoretical background in which they are defined. So, that's that !

marlon

 

[DaTario]

First, Thank you Pervect, I agree to most of what you've said.

Not at all, this thread is where it belongs.


Well, i understand your intentions but as i have mentioned before, this search starts off from "shaky foundations". I mean, the first question in this case is : "what is a photon" , Well, if we all would look at how a photon is defined in QM, we we would find out that a photon is defined as a piece of energy. QFT teaches us how photons arise if we quantise the EM field. In other words, if we adopt the QM definition of a photon, we are basically talking about a discrete amount of energy. That is all ! I don't understand where the "position" comes in. If we adopt the QFT photon definition, we know that a photon arises as a vibration of the EM field to which we can attribute particle like concepts like momentum. NOWHERE in QFT is there every anything mentioned on the spatial location of that EM-field vibration. Again i ask, why bringing in the notion of photon position ?

The closest thing you will get for a connection between photon and position will be this : the spatial coordinates in the EM waves equation. So, using the wavelike concepts of QM, one can indeed use cogerence length etc etc and connect it to spatial coordinates through its equation. But, once you start talking about photons, you are no longer in the wavelike world !

marlon

Marlon,

Let me see if I understand well your picture with a somewhat simple example.

Consider two pendula coupled in a usual "graduation in physics" scheme. If just one of these pendula start moving, soon this one will be at rest and the other, at this time, will be moving with maximum amplitude. You will like to say that both pendula are exchanging quanta of energy (photons in a metaphorical sense) but you will be pleased to say that these quanta of energy has no well defined position.

Let me know if this example and the presented explanation are well suited to your understanding of this photon issue.

best wishes

DaTario

 

[marlon]

Consider two pendula coupled in a usual "graduation in physics" scheme. If just one of these pendula start moving, soon this one will be at rest and the other, at this time, will be moving with maximum amplitude. You will like to say that both pendula are exchanging quanta of energy (photons in a metaphorical sense) but you will be pleased to say that these quanta of energy has no well defined position.

That's exactly what i meant when i referred to the QFT picture, yes.

Additionally, one can certainly not make any claims on photon position based upon the photon definition which has NOTHING to do with spatial coordinates but with "bits of energy".

marlon

 

[rewebster]

Well, that's a bit easy to justify all the speculations going on. What other photon definition is there except that quantum mechanical one ? I mean, QM describes the photon and QED describes it's behaviour. Both definitions are more or less equivalent with respect to the theoretical background in which they are defined. So, that's that !

marlon

In your mind, then, all the questions are answered and there shouldn't even have be a discussion?---this is all a waste of time (in a way, except for, maybe, 'teaching' purposes)?


or do you have any questions?

 

[DaTario]

That's exactly what i meant when i referred to the QFT picture, yes.

Additionally, one can certainly not make any claims on photon position based upon the photon definition which has NOTHING to do with spatial coordinates but with "bits of energy".

marlon

I myself like to go back to the particle to particle picture and see photon as just a quantum of exchange in interactions.

 

[marlon]

In your mind, then, all the questions are answered and there shouldn't even have be a discussion?---this is all a waste of time (in a way, except for, maybe, 'teaching' purposes)?


or do you have any questions?

I have many questions, some of them i would like to solve during my PhD. But one must not ask any question, one must ask the right question. In other words, one can ask questions but if the content of those questions violates some basic theoretical principles, then one should be honest enough to admit that the question itself does not solve any problem, it only confuses.

I myself like to go back to the particle to particle picture and see photon as just a quantum of exchange in interactions.

Me too, photon position or photon size has been proven NOT to exist in that theoretical framework.

marlon

 

[lightarrow]

1. I agree a photon is a quantum of electromagnetic field.
2. I agree it has not a definite position.
3. As Pervect notices: "the energy (aka relativistic mass) of a photon is NOT a property of the photon, but a property of the photon and a specific observer."
4. Many people seems to agree on the fact photon has no size.

Conclusion: a photon IS NOT AN OBJECT TRAVELLING FROM SOURCE TO DETECTOR.

If someone thinks this conclusion is wrong, please explain.

 

[LorentzR]

1.
Conclusion: a photon IS NOT AN OBJECT TRAVELLING FROM SOURCE TO DETECTOR.

If someone thinks this conclusion is wrong, please explain.

I'm convinced that lightarrows conclusion is correct.

I believe there is a growing body of evidence to suggest that light does not require a carrier particle.

The most notable being that if the constituents parts of matter cannot have exact locality relative to our inertial reference frames then the "photon's raison detre vanishes. The justification for such an object cannot be sustained.

Something can only have size if it physically exists in the first place.

It is inherent uncertainty of position and time of the charged "particles" of matter that allows them to interact directly?

 

[ZapperZ]

I'm convinced that lightarrows conclusion is correct.

I believe there is a growing body of evidence to suggest that light does not require a carrier particle.

Are you saying there are no photons? And what "growing body of evidence"? Can you give some references (and no Wikipedia, please)?

The most notable being that if the constituents parts of matter cannot have exact locality relative to our inertial reference frames then the "photon's raison detre vanishes. The justification for such an object cannot be sustained.

But one can say that to every single quantum particles. A Cooper Pair has no exact position in the superfluid - that's the whole reason why it has long-range coherence. At the same token, photons and other quantum particles have definite position upon measurement, or else, what exactly are those photomultipliers and CCD detectors measuring? So what exactly do you mean by "cannot have exact locality" here?

Zz.

 

[rewebster]

But one must not ask any question, one must ask the right question. In other words, one can ask questions but if the content of those questions violates some basic theoretical principles, then one should be honest enough to admit that the question itself does not solve any problem, it only confuses.
marlon

When I read this part of your statement, I thought it sounded like part of some politician's speech.

(like 'what does "is" mean?')

I have many questions, some of them i would like to solve during my PhD.

so---do you have a theory?----or is it an 'interpretation'?

 

[rewebster]

At the same token, photons and other quantum particles have definite position upon measurement, or else, what exactly are those photomultipliers and CCD detectors measuring? So what exactly do you mean by "cannot have exact locality" here?

Zz.

Are you saying that photons have size?

(I haven't read all of your Posts: 8,981)

 

[ZapperZ]

Are you saying that photons have size?

(I haven't read all of your Posts: 8,981)

Nope.

However, there seems to be a misconception here in this thread. Saying that one can measure a position doesn't mean that one knows the size of the object. There are no "size" operator in QM, at least, not that I know of. There is, however, a position operator. When photons hit a photographic plate, you can tell where that is and its position. However, that has nothing to do with its size because of the nature of the interaction and the nature of the detection. The \Delta(x) is the spread in a repeated measurement of the position of the object, not the width of the object.

Zz.

 

[rewebster]

Nope.

However, there seems to be a misconception here in this thread. Saying that one can measure a position doesn't mean that one knows the size of the object. There are no "size" operator in QM, at least, not that I know of. There is, however, a position operator. When photons hit a photographic plate, you can tell where that is and its position. However, that has nothing to do with its size because of the nature of the interaction and the nature of the detection. The \Delta(x) is the spread in a repeated measurement of the position of the object, not the width of the object.

Zz.

doesn't that make it a good question then? could it be addressed in some way? ('some way' that hasn't been addressed so far) ---is HUP complete?--or is it just an 'unknown' factor/parameter/?? at the present time?

----------------------
(this was one of the areas I was beating around the bush in the HUP/accelerator thread)

 

[ZapperZ]

doesn't that make it a good question then? could it be addressed in some way? ('some way' that hasn't been addressed so far) ---is HUP complete?--or is it just an 'unknown' factor/parameter/?? at the present time?

What doesn't make a good question? What is the size of a photon? I think I've said this a few times already. That's like asking how sharp is green.

And I don't know what you mean when you ask if HUP is complete.

Zz.

 

[rewebster]

What doesn't make a good question? What is the size of a photon? I think I've said this a few times already. That's like asking how sharp is green.
And I don't know what you mean when you ask if HUP is complete.

Zz.

'How sharp is green?'---that's the direction I was heading--

-that statement 'How sharp is green?' is incomplete. Green is a descriptive term for an object/something. Just because you made an incomplete statement ''How sharp is green?'' doesn't mean that it means 'nothing'--it's just an incomplete statement/thought.

(I could have a pile of 20 knives for sale, of which 'one' is green--and someone looking at them could ask that question)



are you (z) completely satisfied/happy/content/'no problem-be happy' with the 'photon' as far as QM (theory)/classical (dealing with accelerators) as it stands now? What are you (z) looking for (as far as photons are concerned)?

----------------

'cooling lasers' are part of this too, I believe.

 

[Anonym]

doesn't that make it a good question then? could it be addressed in some way? ('some way' that hasn't been addressed so far) ---is HUP complete?--or is it just an 'unknown' factor/parameter/?? at the present time?(this was one of the areas I was beating around the bush in the HUP/accelerator thread)

Zz is right. Instead disputing you should reformulate your question using the standard terminology. For example, that is how your question looks like when you use the standard references:

How BUNCH length is related to the (longitudinal/transversal) coherence length?(my post #12)

How do you know the difference between the classical electrons bunches and the coherent wave packets?(my post #18)

Regards, Dany.

 

[rewebster]

Zz is right. Instead disputing you should reformulate your question using the standard terminology. For example, that is how your question looks like when you use the standard references:

How BUNCH length is related to the (longitudinal/transversal) coherence length?

How do you know the difference between the classical electrons bunches and the coherent wave packets?

Regards, Dany.

good questions and maybe he can answer those

but that's limiting; and limited as far as to answering specific situations(usually accelerators, I'm thinking--I can guess not always though);

and using terminology (bunches) that is specific to an area limits the overall idea, to me at least.

 

[ZapperZ]

'How sharp is green?'---that's the direction I was heading--

-that statement 'How sharp is green?' is incomplete. Green is a descriptive term for an object/something. Just because you made an incomplete statement ''How sharp is green?'' doesn't mean that it means 'nothing'--it's just an incomplete statement/thought.

(I could have a pile of 20 knives for sale, of which 'one' is green--and someone looking at them could ask that question)

But your "knives" CAN have a property of being green. A photon was never defined as a particle with a size in real space. It is, however, defined in energy (and momentum) space. Thus, when you ask for the size of a photon, you are asking for something it was never defined with. That is why that question is similar to asking "How sharp is green?". Those are two things never associated with each other.

are you (z) completely satisfied/happy/content/'no problem-be happy' with the 'photon' as far as QM (theory)/classical (dealing with accelerators) as it stands now? What are you (z) looking for (as far as photons are concerned)?

I am pretty happy with photons and what we can know using it. There are many things that can't be explained using anything else (I've listed several already a few times on PF).

Zz.

 

[lightarrow]

But one can say that to every single quantum particles. A Cooper Pair has no exact position in the superfluid - that's the whole reason why it has long-range coherence.

So coherence length is related to a particle's position, so the same for a photon's position?

 

[rewebster]

But your "knives" CAN have a property of being green. A photon was never defined as a particle with a size in real space. It is, however, defined in energy (and momentum) space. Thus, when you ask for the size of a photon, you are asking for something it was never defined with. That is why that question is similar to asking "How sharp is green?". Those are two things never associated with each other.

Zz.

never defined?---maybe not, but it has been theorized a lot about (and for a long time):

http://en.wikipedia.org/wiki/Light

down to the 'Theories about light' section. (ol' wiki is good for some things)

--and "defined in energy (and momentum) space" may be only the first steps in the process.

Thus, when you ask for the size of a photon, you are asking for something it was never defined with. Zz.

I don't think I have asked 'what is the size?' yet here--but I do find the question interesting to think about as far as its possibility; and, as it (the question) has a long history, with no definitive answer---and that may be why the thread is a long one (even though variations of it have come up probably (x^n)-1 times on the PF.)

I am pretty happy with photons and what we can know using it. There are many things that can't be explained using anything else (I've listed several already a few times on PF).

Zz.

that's good---and that being in an area where the defined knowledge that there is on the photon has to be used to do what you do, that makes sense---but you also would use any 'new' knowledge that was found, too, wouldn't you?
----------------
isn't this one a 'fun' one

from wiki:

Ptolemy (c. 2nd century) wrote about the refraction of light, and developed a theory of vision that objects are seen by rays of light emanating from the eyes

 

[ZapperZ]

never defined?---maybe not, but it has been theorized a lot about (and for a long time):

http://en.wikipedia.org/wiki/Light

down to the 'Theories about light' section. (ol' wiki is good for some things)

--and "defined in energy (and momentum) space" may be only the first steps in the process.

Hey, you should know by now to never use a wikipedia reference with me.

If you have an exact citation where the size of a photon has been defined, I'd like to know about it.

I don't think I have asked 'what is the size?' yet here--but I do find the question interesting to think about as far as its possibility; and, as it (the question) has a long history, with no definitive answer---and that may be why the thread is a long one (even though variations of it have come up probably (x^n)-1 times on the PF.)

Is a question that has no clear-cut definition interesting? I suppose philosophically, it is. But in physics? Just think. In all those particle detectors that not only detect the various particles but also "EM showers" (i.e. photons), never once is there any kind of discussion whatsoever about the size of the photons they detected. Why do you think that is? I mean, these ARE the people who study elementary particles, after all. They either don't seem to care, or they think this is not a meaningful question. Again, when I asked this to an experimentalist who works at the ATLAS detector at CERN, his reply was "what in the world is a photon size and why do we care?" Yet, on here, we seem to be tripping over each other to discuss this. Do we know more than they do, or something that they don't? You answer that, because I can't.

that's good---and that being in an area where the defined knowledge that there is on the photon has to be used to do what you do, that makes sense---but you also would use any 'new' knowledge that was found, too, wouldn't you?

Sure, but is this really the issue here?

I don't work in studying fundamental particles. I do, however, USE the knowledge to accomplish something else. I used photons to study spectroscopy of strongly correlated system, and I use photons to generate electrons for a particle accelerators. As far as I can tell, the issues that I deal with are fully described by what we know now.

Zz.

 

[ZapperZ]

So coherence length is related to a particle's position, so the same for a photon's position?

Er.. why are you asking me this? I'm not the one who holds that opinion.

Zz.

 

[Anonym]

isn't this one a 'fun' one

from wiki:

Ptolemy (c. 2nd century) wrote about the refraction of light, and developed a theory of vision that objects are seen by rays of light emanating from the eyes

Compare (post #21):

you would indeed observe that there is a photon present through its interaction with the detector (emitted EM radiation for example: the light signal from the detector).

I guess that this is an important idea developed in his Ph.D. thesis.

Regards, Dany.

 

[Anonym]

but that's limiting; and limited as far as to answering specific situations(usually accelerators, I'm thinking--I can guess not always though).

I do not agree with you. I guess that Zz is doing the most general case (in ED). And in contrast with the possible fantasies he is doing real life.

Regards, Dany.

 

[lightarrow]

Er.. why are you asking me this? I'm not the one who holds that opinion.

I'm asking you because you were the one who wrote: "But one can say that to every single quantum particles. A Cooper Pair has no exact position in the superfluid - that's the whole reason why it has long-range coherence".
From this I deduce you put in relation position and coherence lenght.

 

[ZapperZ]

I'm asking you because you were the one who wrote: "But one can say that to every single quantum particles. A Cooper Pair has no exact position in the superfluid - that's the whole reason why it has long-range coherence".
From this I deduce you put in relation position and coherence lenght.

.. and I wrote that in reply to this:

The most notable being that if the constituents parts of matter cannot have exact locality relative to our inertial reference frames then the "photon's raison detre vanishes. The justification for such an object cannot be sustained.

.. which means that if we apply that logic, even Cooper Pair "cannot be sustained". This is obviously absurd. However, it is you who made the connection with "size", since that is what you asked me. I made no such connection, and thus, that question shouldn't be associated with me.

Zz.

 

[lightarrow]

.. which means that if we apply that logic, even Cooper Pair "cannot be sustained". This is obviously absurd. However, it is you who made the connection with "size", since that is what you asked me. I made no such connection, and thus, that question shouldn't be associated with me.
Zz.

I haven't talked about size, I'm simply trying to understand the meaning of your statement: "A Cooper Pair has no exact position in the superfluid - that's the whole reason why it has long-range coherence".
If the meaning it's not what I have deduced from your statement, then explain which is it.

 

[ZapperZ]

I haven't talked about size, I'm simply trying to understand the meaning of your statement: "A Cooper Pair has no exact position in the superfluid - that's the whole reason why it has long-range coherence".
If the meaning it's not what I have deduced from your statement, then explain which is it.

A BE condensate, by definition, has long-range coherence. You can naively think of a cosine or sine function, or even something of the form exp(ikx) that extends for a very long distance when compared to the lattice spacing of the solid. This is how you describe such a system in the simplest form. The particle you are describing is spread out all over that range. If you don't believe me, try to find <x> for something having that kind of a wavefunction.

... and it is this description that is the cause of the existence of a supercurrent.

Zz.