Photon Size: Direction & Probability

  • Thread starter Thread starter alvaros
  • Start date Start date
  • Tags Tags
    Photon
Click For Summary
When a photon is emitted, it propagates isotropically, meaning it can be found in any direction with a probability distribution rather than a fixed path. The concept of photon size is debated, as photons are massless and do not have a defined spatial size; they are better described as energy packets. The discussion highlights the importance of measurement context in quantum mechanics, where the detection of photons depends on the setup of the measuring devices. The interference experiments illustrate that photons exhibit wave-like behavior, complicating the notion of them being point-like particles. Ultimately, the question of photon size remains largely unanswerable within the framework of current quantum theory.
  • #121
Schrodinger's Dog said:
No but then you know that, all I can say is that we have no idea and that current science has no need for a size. To be frank if a photon had an unimaginably small mass, it would make virtually no difference anyway, it's not like the whole of relativity would collapse because a photons size was 1x10-47m

since we have no way of determining it's size or even if it has one due to our methods of detection not being that precise, the question as I said is a matter of semantics and mathematical postulation, ie of no real practical use to science as it stands atm.

If you want me to prove that something does not exist, then you want the philosophy side of the forum, because science can't do that.

While your at it ask what is a photons size, since that's pretty much a philosophical question atm anyway :smile:
Do you know those experments about "freezing light"? If (I'm confident of it) they will be able to store "pieces" of "frozen light" as it seems, how would you negate the problem of having a finite dimensions wave packet of light inside a given matrix? That wave packet will have to be made of some photons!
 
Physics news on Phys.org
  • #122
lightarrow said:
Do you know those experments about "freezing light"? If (I'm confident of it) they will be able to store "pieces" of "frozen light" as it seems, how would you negate the problem of having a finite dimensions wave packet of light inside a given matrix? That wave packet will have to be made of some photons!

Light never propogates at less than c, all "frozen light" is, is when the emission and reabsorption of light in a materials matrix, is sufficient to cause the light's speed in terms of distance over time to slow to a virtual stand still, the photons are not motionless or frozen. The photons themselves are never traveling at less than light speed in this medium or any other medium for that matter.

I'm not sure how this indicates size at all, if I'm understanding the experiments, the light has merely been stopped by absorption in the atoms, thus it is not some photons but merely a more energetic structure that has yet emit those photons or the energy ie the light has been impeded from it's usual free movement in a vacuum to some extent by some sort of sodium atom condensates structure at extremely low temperatures.
 
Last edited:
  • #123
Schrodinger's Dog said:
Light never propogates at less than c,all "frozen light" is, is when the emission and reabsorption of light in a materials matrix, is sufficient to cause the light's speed in terms of distance over time to slow to a virtual stand still, the photons are not motionless or frozen. The photons themselves are never traveling at less than light speed in this medium or any other medium for that matter.

No, you are wrong. Please reffer to this article that see the speed of light by using Bose-Einstein Condensation will reduce.

http://cua.mit.edu/ketterle_group/Popular_papers/Physics%20Today%20v2.pdf

Abstract of that:
Condensates can be a highly nonlinear media not only for matter waves, but also for light. This was dramatically demonstrated recently by Lene Hau and collaborators at the Rowland institute in Cambridge, when they slowed the speed of light to 17 m/s using thecondensate as a dense cold medium. Ultimately, atom lasers may replace conventional atomic beams in applications like precision measurements of fundamental constants, tests of fundamental symmetries, atom optics (in particular, atom interferometry and atom holography) and precise deposition of atoms.

Thanks.
Mr Beh
 
  • #124
https://www.physicsforums.com/showpost.php?p=899393&postcount=4

You could of course read the FAQ, section of this forum to find out why that notion is wrong.

I said photons never propagate at less than c, I am correct in this assertion. Note I specifically said it can be slowed in terms of distance/time but when a photon is propagating it's speed is always c.

Light is slowed by absorption, rapid emission and reabsorption and emission through the lattice structure of a solid, but it is not slowed in the sense that the photons are propagating more slowly than c, they never do this.

Notice they only say it is slowed to 17m/s, this is distance over time, it is not indicating the actual speed of a photon at any given time (t), just it's speed through a solid in terms of the overall speed, this is where the confusion lies.
 
Last edited by a moderator:
  • #125
Schrodinger's Dog said:
https://www.physicsforums.com/showpost.php?p=899393&postcount=4

You could of course read the FAQ, section of this forum to find out why that notion is wrong.

I said photons never propagate at less than c, I am correct in this assertion. Note I specifically said it can be slowed in terms of distance/time but when a photon is propagating it's speed is always c.

Light is slowed by an emission and reabsorption but it is not slowed in the sense that the photons are moving more slowly than c, they never do this.

Just a question: if speed of light slows, then why speed of photons don't slow? If a light ray is created by accumulation of photons that they are propagating, how it occurs that speed of light can slow, but the photons no?
What is your meaning of "terms of distance/time"?
Of course, perhaps I'm wrong.

Thanks.
Mr Beh
 
Last edited by a moderator:
  • #126
Proof.Beh said:
Just a question: if speed of light slows, then why speed of photons don't slow? If a light ray is created by accumulation of photons that they are propagating, how it occurs that speed of light can slow, but the photons no?
What is your meaning of "terms of distance/time"?
Of course, perhaps I'm wrong.

Thanks.
Mr Beh

I know it sounds very odd, but you have to consider that the photon is being absorbed by the lattice structure of a solid and then quickly re-emitted but not without delay, this is where the actual delay occurs, when it is not propagating. When a photon leaves the lattice structure it propagates at c until it meets another part of the structure then it is delayed again by absorption and re-emission until it finally leaves the medium.

At no point in a solid has a photon ever propagated at less than c, it has merely been impeded by the constant absorption and re-emission in the lattice. In a vacuum it has no real impedance and so it's simply propagates at c. this why we say the speed of light in a vacuum is c, but we don't mean the speed of propagation of a photon is ever less than c.
 
  • #127
Good post for Schrodinger's Dog, In other words For scattering processes, the photon takes a path that is a longer distance than the metric displacement along its trajectory. As the photon is scattered, it follows a circuitous path which is constantly changing direction but on average is propagating in a straight-line direction. We derive by using it your conclusion.

Thank you
Mr Beh
 
  • #128
Proof.Beh said:
The photon takes a path that is a longer distance than the metric displacement along its trajectory.

When did you EVER read anything about the trajectory in Schrödinger Dog's (CORRECT) explanations as to why photons "seem to solw down when passing through a medium" ?

Could you pinpoint that out to me, please. Btw, if you still have the time, i am still waiting for some answers to my questions. But i guess you will chose the easy way out and just ignore my posts :smile:

marlon
 
  • #129
Proof.Beh said:
We derive by using it your conclusion.

What exactly are you "deriving" here? All you're doing is taking a simple statement and making it more complicated than it needs to be.
 
  • #130
Schrodinger's Dog said:
I know it sounds very odd, but you have to consider that the photon is being absorbed by the lattice structure of a solid and then quickly re-emitted but not without delay
But in the very FAQ section, ZapperZ explained very well that this is not the case, actually: there isn't any "photon absorption and subsequent photon re-emission", at least in a solide lattice. Or you intended something different?

From the FAQ: "Do Photons Move Slower in a Solid Medium?"
https://www.physicsforums.com/showthread.php?t=104715
A common explanation that has been provided is that a photon moving through the material still moves at the speed of c, but when it encounters the atom of the material, it is absorbed by the atom via an atomic transition. After a very slight delay, a photon is then re-emitted. This explanation is incorrect and inconsistent with empirical observations...
...On the other hand, if a photon has an energy beyond the phonon spectrum, then while it can still cause a disturbance of the lattice ions, the solid cannot sustain this vibration, because the phonon mode isn't available. This is similar to trying to oscillate something at a different frequency than the resonance frequency. So the lattice does not absorb this photon and it is re-emitted but with a very slight delay. This, naively, is the origin of the apparent slowdown of the light speed in the material. The emitted photon may encounter other lattice ions as it makes its way through the material and this accumulate the delay.
So, you mean to say that, from the instant the photon hits side A of the solid lattice to the instant it comes out of side B, the photon has disappeared? And where the energy has gone between the two?
 
Last edited:
  • #131
Gza said:
What exactly are you "deriving" here? All you're doing is taking a simple statement and making it more complicated than it needs to be.

When Schrödinger Dog introduced the discussion of "a photon never propagates at less than c", I did understand its reason that he had explained. Because of that I studied the rejection of reason of this phenomenon in other references that they had explained. There is no any difference both of the our describtions.

marlon said:
Could you pinpoint that out to me, please. Btw, if you still have the time, i am still waiting for some answers to my questions. But i guess you will chose the easy way out and just ignore my posts

I'm sorry. You laten. But,

1- Your questions aren't standard, amenable and irrelevant to discussion, But NONETHELESS we answered them in fore posts frequently.

2- The concepts such as "energy packet" can have spatial coordinates and thus for answering that, I introduced my question in post #30. But you could answer it because of logical reason and depended to valid sources absence.
Besides, you could answer my another question in post #70 that also Anonym had asked you question similar to this.

3- It is obvious that you did read the fore posts none. firstly read them carefully and then ask your PLATITUDINOUS questions.

If you going to repeat your repetitive questions, I won't answer them.

Thanks.
Mr Beh
 
Last edited:
  • #132
Schrodinger's Dog said:
Light never propogates at less than c, all "frozen light" is, is when the emission and reabsorption of light in a materials matrix, is sufficient to cause the light's speed in terms of distance over time to slow to a virtual stand still, the photons are not motionless or frozen. The photons themselves are never traveling at less than light speed in this medium or any other medium for that matter.

I'm not sure how this indicates size at all, if I'm understanding the experiments, the light has merely been stopped by absorption in the atoms, thus it is not some photons but merely a more energetic structure that has yet emit those photons or the energy ie the light has been impeded from it's usual free movement in a vacuum to some extent by some sort of sodium atom condensates structure at extremely low temperatures.
Ok. Now let's consider void. Light doesn't interact with anything in there? There are virtual particles.
 
  • #133
Proof.Beh said:
1- Your questions aren't standard, amenable and irrelevant to discussion, But NONETHELESS we answered them in fore posts frequently.
My questions aren't standard ? :smile:

Again here is what i asked you : "I URGE you to reread the double slit experiment and try figuring out why it is USELESS to be talking about a photon's trajectory in terms of x,y and z. Again, please refer me to a textbook that gives me an equation of this path in terms of x,y, and z. Besides, all of this deals with the trajectory, not the actual photon size. You argue that the energy packet "depends" on x,y and z (whatever that means). Well, it's spatial position DOES because it propagates through space. BUT THAT IS ALL YOU CAN SAY !

Based upon this, what POSSIBLE claims can you make on the photons structure ? What equations describe that size/structure."

You say "a photon has size", i ask you "how can we measure that size" and now you say that's irrelevant ?
C'mon, you are going to have to do better than THAT !

You did NOT answer to my questions, you just decided to bail out of the discussion ! Just check what you did after post nr. 71 !

2- The concepts such as "energy packet" can have spatial coordinates and thus for answering that, I introduced my question in post #30. But you could answer it because of logical reason and depended to valid sources absence.
I refer you to https://www.amazon.com/dp/0582356911/?tag=pfamazon01-20. If you want, check any other intro QM text for that matter.

Besides, you could answer my another question in post #70 that also Anonym had asked you question similar to this.
Actually, if you reread my post (post nr. 71) following your question, you will notice that i asked for a clarification in your question. It was YOU who refused to continue our discussion. Just try to find any posts you wrote with respect to THAT after i asked you for more clarifications :rolleyes:.

3- It is obvious that you did read the fore posts none. firstly read them carefully and then ask your PLATITUDINOUS questions.
As a matter of fact i DID and i ask you again "when did Schrödinger's Dog ever started talking about the particle's trajectory in his explanation". Just reread the posts and you will see that it is YOU who always brings in this concept.

marlon
 
Last edited by a moderator:
  • #134
Cthugha said:
I am quite sure, there is nothing about the size of photons in that book, but I do just have the 1973 version here at the moment. Could you please give me the page, chapter or an exact quotation of the passage you mean, so I can check, what you mean?

Par. 4.2 “Some elementary concepts and definitions” p.148; specifically, p.149 and p. 151.

But only definitions are not enough. You should read the whole book.

Regards, Dany.
 
  • #135
Shahin said:
Ok, i have just said an idea for the size of the photon, i have never said enything about the electron. But i am glad that you can respond propely, and not telling me silly things, and stupid things, like anonym.

I guess you miss a point. First of all, this session is not about “How big is a photon” but about how we handle a problem, since it was discussed in QP of PF several times and start to be boring even before the problem is formulated.

It is common point that one should use the references (the previous discussions in PF included). But kids are not used to do that. That is all point Zz made and suggested to use the “Standard References”. No doubt that he is right and everybody agree. Only we did not agree with the details of the technical realization.

Several decades ago PDG did not included quarks for example. Obviously, it does not mean that the quarks did not exist. Moreover, during about 10 years physicists denied the experimental and theoretical evidence of them. Alternatively, in PDG was always written that the proton life time is infinite (stable). That did not prevent the very important experimental and theoretical investigations in HEP: QCD, experimental verification of the proton decay, GUT’s, etc. Since we did not agree with him, Zz even thought that we do not understand him: <ZapperZ bangs his head into the wall and cries>. But he is simply deadly wrong; he is not familiar with the “Bible” of ED, he does not know the modern electrodynamics.

However, I think that the problem is deeper. It should be clear to everybody that we are talking about field theory and fields (photon, electron, etc.) and the notions used by Greeks are not adequate. Even I. Newton already knew that.

From the pedagogical side, I do not agree with jtbell and agree with R.P.Feynman: it is meaningless to demonstrate more than once the same thing. If one did not understand it, the repetition will not help. In your post # 23 you randomly emitted the gold signal. Lack of understanding allowed you equally well to emit garbage (noise) in your post #35. jtbell explained it to you twice. I doubt that you understood. All that stuff in my POV one should do in his/her own. There is no other way to study physics. It is not picnic, it is spit blood.

Regards, Dany.

P.S. I guess that you do not read my posts and even if you do, the German word “eigenschaften” (alternative) tells you nothing. To those who are interesting, I used reference(that should be standard) to the “elementary particle” of information originally introduced by D.Hilbert and discussed by J. von Neumann in “Mathematische Grundlagen der Quantenmechanik”, Berlin, (1931), ch. III, par 5.

By the way, since after years of study I understand close to nothing, no doubt that you are right. But what wrong with jokes?
 
  • #136
Light arrow I take your first point, that is indeed what I meant to say, thanks for clarifying. Your second point is a tad picky though, ok I should of said that it is extremely unlikely that light will interact with anything in a vacuum thus its speed is c, instead of that it will not, but that would just cloud a fairly straightforward posit that light travels at c in a vacuum. Let's just say that a vacuum that contains particles with which light can interact is not really a vacuum and leave it at that. Assume that vacuum means emptyness even if this isn't entirely possible.

I'm just glad someone actual read a link provided, positively a rarity in the interweb :smile:
 
Last edited:
  • #137
WHAT IS THE SIZE OF A PHOTON?
If you believe in extra dimensions then the size would be limited by the size of the extra dimension.
http://pdg.lbl.gov/2007/tables/sxxx.pdf
p.5
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)
-----------
Therefore, a maximum size of a photon would be either .22mm or 660nm. If you want to assume a way of making a bigger photon squeeze into a small hole (dimension) then you do not have any constraints on the size of a photon.
--------------
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. So, from
http://pdg.lbl.gov/2007/tables/bxxx.pdf
PROTON
Charge radius = 0.875 ± 0.007 fm
NEUTRON
Mean-square charge radius R^2n_ = 0.1161 ± 0.0022 fm2 (S = 1.3)
-----------------
Therefore, we have another kind of constraint on the size of a photon. The size of a proton/neutron.

How small can a photon get? If quarks are proven to emit photons then this would be determined by the sizes of quarks.
----------------
http://arxiv.org/PS_cache/hep-ph/pdf/0611/0611005v1.pdf
QCD, New Physics and Experiment
Giuseppe Nardulli
01 Nov 2006
Abstract. I give a summary of Section E of the seventh edition of the Conference Quark confinement
and the hadron spectrum. Papers were presented on different subjects, from spectroscopy,
including pentaquarks and hadron structure, to the quest for physics beyond the standard model

For EM interactions one gets limit on the mass of a heavy electron: m∗ = 308±56 GeV and = 1253.2±226 GeV, correspondingfor the finite size of the electron a limit of to a
size r ≈ 16×10−18cm . For EW interaction the most stringent limits for the quarks are
rq < 2.2×10−18cm, for the leptons rl < 0.9×10−18 cm, and the form factor puts a limit
on the electron size of re < 28×10−18cm. Finally a scheme to describe all fundamental particles as extended objects of a finite geometrical size was presented by , J¨urgen Ulbricht.
--------------
QUARKS
http://pdg.lbl.gov/2007/reviews/quarks_q000.pdf

See my blog for more references.
 
  • #138
Schrodinger's Dog said:
Light arrow I take your first point, that is indeed what I meant to say, thanks for clarifying. Your second point is a tad picky though, ok I should of said that it is extremely unlikely that light will interact with anything in a vacuum thus its speed is c, instead of that it will not, but that would just cloud a fairly straightforward posit that light travels at c in a vacuum. Let's just say that a vacuum that contains particles with which light can interact is not really a vacuum and leave it at that. Assume that vacuum means emptyness even if this isn't entirely possible.

I'm just glad someone actual read a link provided, positively a rarity in the interweb :smile:
Ok, however I am wondering if the effect of virtual particles is really so small: it would seem that no one has provided yet a generally accepted way of computing the exact value of void's energy density, and not even how void's properties would change, electric and magnetic permittivity, for example (and, so, light's speed).

If it resulted that, at a reasonable level of precision, light propagation wouldn't change much in a void "devoid" of virtual particles, then I would agree with you.
(Thank you for your smile, BTW:smile:).
 
Last edited:
  • #139
jal said:
WHAT IS THE SIZE OF A PHOTON?
If you believe in extra dimensions then the size would be limited by the size of the extra dimension.
http://pdg.lbl.gov/2007/tables/sxxx.pdf
p.5
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)
-----------
Therefore, a maximum size of a photon would be either .22mm or 660nm. If you want to assume a way of making a bigger photon squeeze into a small hole (dimension) then you do not have any constraints on the size of a photon.
--------------
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. So, from
http://pdg.lbl.gov/2007/tables/bxxx.pdf
PROTON
Charge radius = 0.875 ± 0.007 fm
NEUTRON
Mean-square charge radius R^2n_ = 0.1161 ± 0.0022 fm2 (S = 1.3)
-----------------
Therefore, we have another kind of constraint on the size of a photon. The size of a proton/neutron.

How small can a photon get? If quarks are proven to emit photons then this would be determined by the sizes of quarks.
----------------
http://arxiv.org/PS_cache/hep-ph/pdf/0611/0611005v1.pdf
QCD, New Physics and Experiment
Giuseppe Nardulli
01 Nov 2006
Abstract. I give a summary of Section E of the seventh edition of the Conference Quark confinement
and the hadron spectrum. Papers were presented on different subjects, from spectroscopy,
including pentaquarks and hadron structure, to the quest for physics beyond the standard model

For EM interactions one gets limit on the mass of a heavy electron: m∗ = 308±56 GeV and = 1253.2±226 GeV, correspondingfor the finite size of the electron a limit of to a
size r ≈ 16×10−18cm . For EW interaction the most stringent limits for the quarks are
rq < 2.2×10−18cm, for the leptons rl < 0.9×10−18 cm, and the form factor puts a limit
on the electron size of re < 28×10−18cm. Finally a scheme to describe all fundamental particles as extended objects of a finite geometrical size was presented by , J¨urgen Ulbricht.
--------------
QUARKS
http://pdg.lbl.gov/2007/reviews/quarks_q000.pdf

See my blog for more references.

Very good. but, do you know what is the essential problem? Problem is that persons such as marlon and ZapperZ ,though we introduced the sources for proof our claim (a photon has size), they don't agree with existence of size for photon! :smile:

Anyway, they must see your VALID and STANDARD sources to understand there is no sense for their claim.

Thanks.
Mr Beh
 
Last edited:
  • #140
Proof.Beh said:
Very good. but, do you know what is the essential problem? Problem is that persons such as marlon and ZapperZ ,though we introduced the sources for proof our claim (a photon has size), they don't agree with existence of size for photon! :smile:

Anyway, they must see your VALID and STANDARD sources to understand there is no sense for their claim.

Thanks.
Mr Beh

I wouldn't over-extend a statement to be a proof. I think you can say that 'you've introduced the sources your claim', but there is no (I believe) proof for the existence of size for photon.----and either marlon or ZapperZ probably have more knowledge in the area than (you + me) ^2.-- (and probably ^4)--(ok, even maybe even^6)
 
Last edited:
  • #141
rewebster said:
I wouldn't over-extend a statement to be a proof. I think you can say that 'you've introduced the sources your claim', but there is no (I believe) proof for the existence of size for photon.----and either marlon or ZapperZ probably have more knowledge in the area than (you + me) ^2.-- (and probably ^4)--(ok, even maybe even^6)

1- Perhaps they have more knowledge in the area than you (you can explain your personal opinion about your knowledge but it differs for me), but actually they did not prove your claim.

2- Now that I think more, see that their knowledge equal to (your [not my] knowledge)^n, n>>6. Note: everybody can explain his personal opinion about himself only.

3- Again, if you have any claim about this discussion, can introduce it. Of course your last post did not relate to "How big is a photon?" NONE.

Thanks.
Mr Beh
 
  • #142
Anonym said:
I guess you miss a point. First of all, this session is not about “How big is a photon” but about how we handle a problem, since it was discussed in QP of PF several times and start to be boring even before the problem is formulated.

It is common point that one should use the references (the previous discussions in PF included). But kids are not used to do that. That is all point Zz made and suggested to use the “Standard References”. No doubt that he is right and everybody agree. Only we did not agree with the details of the technical realization.

Yeah,--- and I think 'how one thinks about a problem' is what sets people in different categories, too. People can "quote" this and "quote" that all day long--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).

What information one believes one takes to be the basis of his belief system; and that's even here on the forum as there are different categories and sub-categories. Can you 'convert' a relativity person back into a Newtonian classic person? (it's hard to get them back on the farm, etc...). One person's 'standard' isn't another's. --and if you get deeper, which one is 'THE TRUTH' anyway?

Some sub-categories in physics, I don't think, will ever assign (the idea) of 'size' to a photon---so, which ones do? ---so, that logic of that area(s) will be more present in the (this) discussions.


Anonym said:
However, I think that the problem is deeper. It should be clear to everybody that we are talking about field theory and fields (photon, electron, etc.) and the notions used by Greeks are not adequate. Even I. Newton already knew that.

From the pedagogical side, I do not agree with jtbell and agree with R.P.Feynman: it is meaningless to demonstrate more than once the same thing. If one did not understand it, the repetition will not help. In your post # 23 you randomly emitted the gold signal. Lack of understanding allowed you equally well to emit garbage (noise) in your post #35. jtbell explained it to you twice. I doubt that you understood. All that stuff in my POV one should do in his/her own. There is no other way to study physics. It is not picnic, it is spit blood.

Regards, Dany.

P.S. I guess that you do not read my posts and even if you do, the German word “eigenschaften” (alternative) tells you nothing. To those who are interesting, I used reference(that should be standard) to the “elementary particle” of information originally introduced by D.Hilbert and discussed by J. von Neumann in “Mathematische Grundlagen der Quantenmechanik”, Berlin, (1931), ch. III, par 5.

By the way, since after years of study I understand close to nothing, no doubt that you are right. But what wrong with jokes?

Is Newton wrong? Is Newton right?---

Part of the problem, I see, is that people look at peoples ideas sometimes that way--black/white, categorized, etc. ---but a lot do interpret, which I find too, to work best. ---but still, its interpreting with whatever knowledge base/category/'your theory of choice'.


so, maybe, the 'idea' that a 'photon has size' will ONLY be associated WITH certain theories, and that, those theories (your choice) should be referenced, if a 'reference' is made as to make the logic of the discussion more reasonable as some have done.

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

mr. (dr.?) beh---I was wondering, do like the area of Logic more as in philosophy or as in math?
 
  • #143
Would someone care to refute the following
"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."
 
  • #144
jal said:
WHAT IS THE SIZE OF A PHOTON?
If you believe in extra dimensions then the size would be limited by the size of the extra dimension.
http://pdg.lbl.gov/2007/tables/sxxx.pdf
p.5
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)
-----------
Therefore, a maximum size of a photon would be either .22mm or 660nm. If you want to assume a way of making a bigger photon squeeze into a small hole (dimension) then you do not have any constraints on the size of a photon.
--------------
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. So, from
http://pdg.lbl.gov/2007/tables/bxxx.pdf
PROTON
Charge radius = 0.875 ± 0.007 fm
NEUTRON
Mean-square charge radius R^2n_ = 0.1161 ± 0.0022 fm2 (S = 1.3)
-----------------
Therefore, we have another kind of constraint on the size of a photon. The size of a proton/neutron.

How small can a photon get? If quarks are proven to emit photons then this would be determined by the sizes of quarks.
----------------
http://arxiv.org/PS_cache/hep-ph/pdf/0611/0611005v1.pdf
QCD, New Physics and Experiment
Giuseppe Nardulli
01 Nov 2006
Abstract. I give a summary of Section E of the seventh edition of the Conference Quark confinement
and the hadron spectrum. Papers were presented on different subjects, from spectroscopy,
including pentaquarks and hadron structure, to the quest for physics beyond the standard model

For EM interactions one gets limit on the mass of a heavy electron: m∗ = 308±56 GeV and = 1253.2±226 GeV, correspondingfor the finite size of the electron a limit of to a
size r ≈ 16×10−18cm . For EW interaction the most stringent limits for the quarks are
rq < 2.2×10−18cm, for the leptons rl < 0.9×10−18 cm, and the form factor puts a limit
on the electron size of re < 28×10−18cm. Finally a scheme to describe all fundamental particles as extended objects of a finite geometrical size was presented by , J¨urgen Ulbricht.
--------------
QUARKS
http://pdg.lbl.gov/2007/reviews/quarks_q000.pdf

See my blog for more references.

There's a whole lot of errors and really far-our extrapolation in here. For example, you associated all of these based on the values of fundamental particles. Yet, in the PDG book that you cited, if what you said is true, why aren't the size of the photon defined this way? This is what I asked in the very beginning. If this is obvious, why aren't they in the standard references, especially the PDG handbook?

Secondly, you restricted the photon emission process only to the size of proton/neutron by assuming those are the photon emitter. That requires a whole lot of explanation because (i) atomic transition can emit a range of photons with different energies, so they are all of the same "size"? (ii) atomic transition involves electrons changing energy level, so why are proton/neutrons involved here? (iii) One can also get light when electrons combine with holes (that's how you get LED's) between the conduction and the valence bands in a semiconductor junction. So now what? The size of that photon is the size of an electron? (iv) I used to work at a synchrotron light source where I use photons coming from electrons passing through an insertion device such as an undulator. In fact, I can "dial in" the photon energy that I want simply by changing the periodicity of the undulator. So what's the size of the photon there?

Zz.
 
  • #145
Anonym said:
It is common point that one should use the references (the previous discussions in PF included). But kids are not used to do that. That is all point Zz made and suggested to use the “Standard References”. No doubt that he is right and everybody agree. Only we did not agree with the details of the technical realization.

Several decades ago PDG did not included quarks for example. Obviously, it does not mean that the quarks did not exist. Moreover, during about 10 years physicists denied the experimental and theoretical evidence of them. Alternatively, in PDG was always written that the proton life time is infinite (stable). That did not prevent the very important experimental and theoretical investigations in HEP: QCD, experimental verification of the proton decay, GUT’s, etc. Since we did not agree with him, Zz even thought that we do not understand him: <ZapperZ bangs his head into the wall and cries>. But he is simply deadly wrong; he is not familiar with the “Bible” of ED, he does not know the modern electrodynamics.

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!

The PDG, CRC, and CODATA are update regularly to reflect the best known information. I can also say that many years ago, the value of "e" and "h" were determined via extremely primitive and experiments. It is only after we understand superconductivity and SQUIDs are those values now determined even more accurately.

I cited the latest edition of PDG handbook. This is THE best known and accepted values for all the elementary particles today. Will they change as our knowledge evolve. I hope so! But until then, these are the best we can determine. So from the best that we know of, the standard reference cannot produce neither a definition, nor a value, for the size of a photon.

Zz.
 
  • #146
"The Review includes a compilation and evaluation of measurements of the properties of the elementary particles. In the 2006 Review, the listings include 2,633 new measurements from 689 papers, as well as 21,926 measurements from 6,415 papers that appeared in earlier editions. Evaluations of these properties are abstracted in summary tables."

http://pdg.lbl.gov/2007/html/what_is_pdg.html


Pretty impressive, --really

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

I noticed what may be a mistake on their 'authors' page, though:


CERNY, V.


http://wwwppds.ihep.su:8001/doc_index.pp?a0:1

---is listed first, which is often caused when a 'space' is accidentally put in before the first letter, causing it to 'appear' first --which I think is the case here (just as a '!' or a '1'---numeric, or keyboard based layout does)

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

http://wwwppds.ihep.su:8001/a.html

this seems the best page to start from, maybe

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

http://wwwppds.ihep.su:8001/doc_index.pp?p0:1


'dead particles'---funny
 
Last edited by a moderator:
  • #147
Anonym said:
Par. 4.2 ?Some elementary concepts and definitions? p.148; specifically, p.149 and p. 151.

But only definitions are not enough. You should read the whole book.

Oh, thanks, but I am quite familiar with the book of Mandel and Wolf. It has been a faithful friend during my diploma thesis.

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.
 
  • #148
rewebster said:
"The Review includes a compilation and evaluation of measurements of the properties of the elementary particles. In the 2006 Review, the listings include 2,633 new measurements from 689 papers, as well as 21,926 measurements from 6,415 papers that appeared in earlier editions. Evaluations of these properties are abstracted in summary tables."
http://pdg.lbl.gov/2007/html/what_is_pdg.html
Pretty impressive, --really ...

Since Einstein introduced the relativity, if his name was in each author(s) part of a book, it was STANDARD book surely?

Since Bohr was one of the founders of atomic physics, if his name was in each author(s) part of a book, it was STANDARD book surely?

Since Witten introduced the ST, if his name was in each author(s) part of a book, it was STANDARD book surely?

No, there is no special reason for acceptation a book according to name of its aouthor(s). When we see a famous name on cover of a GR book such as P. A. Dirac, General theory of the Relativity, first point that reffer to our mind is that it will be a STANDARD book. But when read the whole of it, we understand that the books such as GENERAL RELATIVITY AND GRAVITATION VOLs (1vs2) by A. Held or GRAVITATION by J.A.Wheeler & C.H.Misner & K.S.Thorne must not be standard and valid because the aouthers of them are not as famous as Dirac!

You must assume that our references, writed by persons that they are your criterion of choosing of a STANDARD book. You must read whole of a book and when you confront a problem, answer it that is it correct or not. Work that we performed it, but did not see a safe solution.

Thanks.
Mr Beh
 
  • #149
jal said:
WHAT IS THE SIZE OF A PHOTON?
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)
-----------
Therefore, a maximum size of a photon would be either .22mm or 660nm. If you want to assume a way of making a bigger photon squeeze into a small hole (dimension) then you do not have any constraints on the size of a photon.
--------------
Hey, i would like to comment on your post.

How do those radii imply that a photon has to be "smaller" as their specific value? Also, a photon is considered to be a point particle in QM, so in QFT the photon STILL is a point particle, otherwise the Lorentz contraction gives strange particle behaviour. Just check the beginning chapters of Anthony Zee's "QFT in a Nutshel" for that matter ! Claiming that a photon is NOT a point particle violates the very foundations of QFT !

Besides, why is such a size value never mentioned in QM or the PDG data ? I have asked Proof Beh this but he refuses to answer ; How would we measure that size and what theoru describes the photon size (equation ?) ?

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.
Err, i have NEVER heard of this and this is not mentioned in your references. What we DO know is that energy conservation needs to be respected. This implies constraints on the mass values of the emittor and absorber. I think you are referring to THAT.

How small can a photon get? If quarks are proven to emit photons then this would be determined by the sizes of quarks.

Why ?

For EM interactions one gets limit on the mass of a heavy electron: m∗ = 308±56 GeV and = 1253.2±226 GeV, correspondingfor the finite size of the electron a limit of to a
size r ≈ 16×10−18cm .
I agree with the stuff you say on mass but could you elaborate on how you acquire the radius ? Aren't these radii referring to the action radius of the interaction ? I mean, just like a form factor in effective field theories ? But such theories use non elementary particles as their degrees of freedom. This does not say ANYTHING about size but about strength of interaction (ie coupling constants expressed in terms of inter-particle distance).

In basic QCD, quarks are represented as point particles for the reason i stated above (basic QFT demand). The dual abelian higgs model gives a first guess for the proton and neutron structure by adding a linear potential (dominant at long range interaction or low energy scales) to the Coulombic exponential decaying potential (dominant at short range interactions). Never EVER is the notion of size used !

If you want a reference for this model, check the Elementary Particle's Presented Thread where i have posted a link to the PDF file.

greets
marlon
 
  • #150
marlon said:
How do those radii imply that a photon has to be "smaller" as their specific value? Also, a photon is considered to be a point particle in QM, so in QFT the photon STILL is a point particle, otherwise the Lorentz contraction gives strange particle behaviour. Just check the beginning chapters of Anthony Zee's "QFT in a Nutshel" for that matter ! Claiming that a photon is NOT a point particle violates the very foundations of QFT !

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
 

Similar threads

I Shape of wave function (probability distribution) of a single photon
  • · Replies 16 ·
Replies
16
Views
728
I Is a photon emitted in a particular direction?
  • · Replies 9 ·
Replies
9
Views
2K
I Do Two Photons in a Radiative Cascade Exhibit Directional Correlation?
  • · Replies 14 ·
Replies
14
Views
2K
I The electron is not point-like?
  • · Replies 21 ·
Replies
21
Views
3K
I 3 photon transfer probability
  • · Replies 2 ·
Replies
2
Views
1K
I Could Quantum Dots Between Optic Fibers Create Photon Interference?
  • · Replies 6 ·
Replies
6
Views
2K
I Do atoms recoil when emitting a photon?
  • · Replies 38 ·
2
Replies
38
Views
6K
A CHSH Bell inequality derivation
  • · Replies 4 ·
Replies
4
Views
2K
I Question about Photons causing Electron Transitions in Atoms
  • · Replies 20 ·
Replies
20
Views
2K
I 2-Slit: How do we know photon guns only produce single photons?
  • · Replies 33 ·
2
Replies
33
Views
2K