Photon Size: Direction & Probability

[rewebster]

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

whoops--let's see--now, ---do I remember that?



I can maybe see a line in your signature:

"Don't EVER use a Wiki reference with me--I have an accelerator--and I WILL use it.

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

nope, I don't of one---its not in the standard references from what I read here.---you can try jal 's blog

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.

Zz.

They may have thought about it when they were younger (and ignorant).

I think one of the reasons is that you DO know more (have specific knowledge to do what you do). I don't know how to turn an accelerator on--good chance I never will --(in that area--I'm ignorant). --but, that's not saying that someone else asking the question, or reading it here may not develop an interest, even indirectly, enough to take over your job when you retire. Do you think most of us will ever run an accelerator (or even have the interest, or the years of schooling and training to do so?)

Z, are you telling me that you've never (ever) wondered what light is?--what magnetism is? and so on.

I remember some physicist at some school saying when I asked him about 'what causes magnetism' -- He said (paraphrased for the forum here), "don't think about that stuff, it will drive you crazy". I think he was paraphrasing someone else even. Most of the "professionals" have been around long enough, and have thought about it long enough, and knew that if, even Einstein couldn't figure it out--they better quit while they're ahead and not jeopardize their job by going off the deep end.

I don't have to worry about that (yeah, I got it--you think I'm there already and along with most of these 'other' lunies who 'argue' with you). It's not because we're ignorant---it's because we're (me, anyway) enthusiastic STILL. ---we (including me) aren't jaded yet, and talk with the possibility that the answer is out there still---(and, here's the part that you probably find sad for us (me) being us (me and some others, maybe)--'if we only thought about it in a different way'.---and, hopefully, the forum will be a forum and not just a 'cut and paste' from the 'standard references'.

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.

different people have different philosophies about physics for what they want to do

 

[ZapperZ]

I wonder about A LOT OF STUFF! That is irrelevant to what we are discussing here. Just because I tow the "party line" and refuses to speculate about things on here should not be associated with the notion that I do not wonder about such things. I too follow the PF guidelines, and it is inappropriate if I start spewing off all the stuff that I "think" is neat and wonderful, yet I have nothing to back them with.

Zz.

 

[rewebster]

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.

yeah--I know--that is the difference---but at the same time, not all who aren't in the profession are nut cases either.

(so, does that mean that some who are in the profession could be nut cases?)

 

[rewebster]

z--I appreciate the guidelines (especially after being on here about a year)---I've gone to some (most) other sights for a visit to 'see' and have never went back.

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

I agree some may step out of line (spew)--but most of us (who are not in the profession, yet, ever,etc.)--appreciate what is being done here.

--------------------------------
most of post 202 was in response to your question:

"Do we know more than they do, or something that they don't? You answer that, because I can't."

 

[DaTario]

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.

It seems quite to provoke us that light quanta has no position but travels with c and moreover obeys kinematics rules dictated by correlation experiments with twin photon's (spontaneous down conversion for instance).

Of course we may learn this lesson and start building the ontology of photon with such subtleties. Photon is not a typical kind of being and etc...

Weisskopf Wigner theory for spontaneous emission produces the notion of a particle like object, which is corroborated by ecrans. If we are to abandomn this particle view, we should provide explanation for ecrans and the punctual appearance of light on it.

best wishes

DaTario

 

[Anonym]

yeah--I know--that is the difference---but at the same time, not all who aren't in the profession are nut cases either.

That is not what I have in mind. Zz is the experimentalist.

the forum will be a forum and not just a 'cut and paste' from the 'standard references'.

You need the standard references and standard terminology if you want that the other people will understand what you want to say.

I don't know how to turn an accelerator on--good chance I never will.

What is the problem? Just apply to Zz at ANL to be his student/assistant. They need youngers with one leg in the experiment and the other in the theory.

Regards, Dany.

 

[lightarrow]

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.

What does "The particle you are describing is spread out all over that range" mean? Does it mean that a particle with very short-range coherence has a quite well defined position in space? And the same for a photon? It's just a question.

 

[ZapperZ]

What does "The particle you are describing is spread out all over that range" mean? Does it mean that a particle with very short-range coherence has a quite well defined position in space? And the same for a photon? It's just a question.

Er.. I did ask you to find <x>, didn't I? Try it. When you find <x>, that is exactly what I meant when I said it is spread out.

We are trying to put "words" to something that is essentially and foremost, has a mathematical description. So unless you understand what it looks like mathematically, word description will never be able to convey the exact scenario.

Zz.

 

[lightarrow]

Er.. I did ask you to find <x>, didn't I? Try it. When you find <x>, that is exactly what I meant when I said it is spread out.

We are trying to put "words" to something that is essentially and foremost, has a mathematical description. So unless you understand what it looks like mathematically, word description will never be able to convey the exact scenario.

Zz.

Since it seems difficult for you to give direct answers, I will give them for you (so, you can criticize them, it's your preferite task).

1. A photon's wavefunction with coherence length L represents an object traveling in space with a position indefiniteness = L, that is, the photon can be detected in a any instant of time from when the initial end of the train wave reach the detector to when the last end reach it.

1.B The photon is pointlike. But in this case, why differently prepared photons (of the same energy) can have different L?

2. A photon's wavefunction with coherence length L represents an object traveling in space which is spread out in the length L, that is, the entire photon is actually located in all that lenght.

3. ...


Which do you prefer?

 

[ZapperZ]

It is difficult because the term "coherence length" has different physical meaning in different scenario, very much like "phase space". In superconductivity, it is of the scale of the extent of the Cooper Pairs wavefunction.

Since I wasn't the one who introduced the coherence length concept for a photon, I shouldn't be the one who has to answer this for you as far as photons are concerned. All I have given you is some generic concept on how something with long-range coherence can be considered to be spread out all over that range. That's all. If you wish to look beyond this but not care about the mathematical formalism, then I am the wrong person to ask.

Zz.

 

[rewebster]

That is not what I have in mind. Zz is the experimentalist.

that is he that--and probably more

You need the standard references and standard terminology if you want that the other people will understand what you want to say.

hopefully you know that was not what I was saying

What is the problem? Just apply to Zz at ANL to be his student/assistant. They need youngers with one leg in the experiment and the other in the theory.

Regards, Dany.

and from post 51:

I have no professional knowledge in details of the Particle Accelerators.

we could BOTH apply and be ROOM MATES


--but the problem would be, if we did apply and be the junior peon preons in the accelerator world, from what I'm reading that we STILL wouldn't find out 'how big a photon is'

 

[rewebster]

I wonder about A LOT OF STUFF! That is irrelevant to what we are discussing here. Just because I tow the "party line" and refuses to speculate about things on here should not be associated with the notion that I do not wonder about such things. I too follow the PF guidelines, and it is inappropriate if I start spewing off all the stuff that I "think" is neat and wonderful, yet I have nothing to back them with.

Zz.

I don't have problem with the part about you toeing the party line--I think I got that part. --and there is, also to me, a fine line between being subjective in an opinion (from knowledge) and speculative; in that you (and the other mentors) have to define from time to time.


anyway, post 202 was answering to your question, not me just spewing (and I wasn't arguing either)

 

[Anonym]

is HUP complete? hopefully you know that was not what I was saying

Honestly, I have no any idea what you have in mind and what does it mean.

we could BOTH apply and be ROOM MATES

--but the problem would be, if we did apply and be the junior peon preons in the accelerator world, from what I'm reading that we STILL wouldn't find out 'how big a photon is'

Go ahead. I promise it will be great fun not only for Zz but for whole ANL!

However, you missed something. I know 'how big a photon is' in QED but don’t know that in CED yet. I do not need help from them. This is my job.

Regards, Dany.

 

[rewebster]

I know 'how big a photon is'

Regards, Dany.

(shhhhhh-----don't say that aloud around here-----shhhhh)

 

[Schrodinger's Dog]

so, the well trodden path is the best way?

I think it was Zz who lead me from the dark side. He made a rather good post that answered this question in terms I felt made the most sense. If people really want to find out good answers to this they've all been given numerous times before and will suit most people.

To be frank though I was never really that convinced it had mass, I just had questions like a a lot of people do.

In this particular case and with our current level of technology, the well trodden path is best . Words of wisdom do not cover everything, at some point you have to accept that to proceed further along the unbeaten trail you need better machinery

 

[rewebster]

I think it was Zz who lead me from the dark side. He made a rather good post that answered this question in terms I felt made the most sense. If people really want to find out good answers to this they've all been given numerous times before and will suit most people.

To be frank though I was never really that convinced it had mass, I just had questions like a a lot of people do.

In this particular case and with our current level of technology, the well trodden path is best . Words of wisdom do not cover everything, at some point you have to accept that to proceed further along the unbeaten trail you need better machinery

-----LHC ?

 

[Schrodinger's Dog]

I don't think it's going to suffice, it's not so much smashing them apart but how you detect and measure such tiny portions of energy amongst the mass of energetic particles created in a collision; besides establishing the mass or ever more precise upper limits of a photon is not as important as establishing the existence or non existence of say the Higgs Boson, so since detection methods aren't precise enough scientists probably have better things to do with it. I'm not an expert not even close, but I don't think we are anywhere near being refined enough with the machinery atm. I'd ask Zz...

 

[rewebster]

I wasn't too serious when I suggested it---just the idea of 'bigger and better' came up.

I wonder how many betting 'pools' have come up as to how many new particles will be 'discovered'/'created' with the first year there.


well, that's good for you though that's one less worry/thing to think about if it is 'at rest' now.

 

[LorentzR]

But one can say that to every single quantum particles.

Zz.

No! I don’t agree with this statement. The idea of the photon was at least partly introduced as a solution to the old problem of what causes “action” at distance. But the question presupposes the notion of locality. This in the context of modern physics would be the assumption that the “particles” composing matter can be assigned, for any given time, a unique position in space. However, correlation experiment results showing the violation of Bell’s inequality suggest that our world has a non local flavour; casting doubts on the idea that particles of matter can be assigned exact locality relative to our inertial reference frames. This in turn puts into doubt the need for carrier particles to mediate action at a distance. If the locations of “particles” are not fixed exactly relative to our inertial reference frames then neither are the gulfs that separate them and direct interaction between pairs of particles becomes possible when the gulf between them has zero magnitude.

The “particles”/ “fields” of matter must remain in our philosophy it is only the photon (the suggested mediator of force) that is surplus to the explanation of electromagnetism.

 

[LorentzR]

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.

No one has ever observed the position of a photon or any other quantum particle. What you observe is a macroscopic response in a particular experimental set up. The timing and position of the response may be measured with exquisite accuracy but the observable response exists at the end of a sequential causal chain that is necessary to amplify a quantum event to an observable event.

You are observing the location of a macroscopic event that is initiated by a quantum event. There is no clear logical path that links what is observable to where and when the quantum event took place. To give a photon or other quantum particle a definite position on this evidence is unsustainable. All we can say is that somewhere in the four dimensional manifold an event has occurred that has affected our detection device in a particular way. There is no justification based on experimental evidence for assigning a definite position to a quantum object.

 

[ZapperZ]

No one has ever observed the position of a photon or any other quantum particle. What you observe is a macroscopic response in a particular experimental set up. The timing and position of the response may be measured with exquisite accuracy but the observable response exists at the end of a sequential causal chain that is necessary to amplify a quantum event to an observable event.

You are observing the location of a macroscopic event that is initiated by a quantum event. There is no clear logical path that links what is observable to where and when the quantum event took place. To give a photon or other quantum particle a definite position on this evidence is unsustainable. All we can say is that somewhere in the four dimensional manifold an event has occurred that has affected our detection device in a particular way. There is no justification based on experimental evidence for assigning a definite position to a quantum object.

Then you need to write a rebuttal to all the experimental high energy physics papers, and even to condensed matter papers using anything that measures electron and neutron spectroscopy such as what I've shown in my avatar. Look under ANY papers in any physics journal that actually detects these particles and tell them that they're not really detecting that 'quantum event'. Remember, in angle-resolved photoemission experiment, the location where the electron hits the detector just doesn't signify that this electron was there at that time, but also carries information about its energy and "in-plane" momentum while it was in the solid!

Did I see electrons? Of course not! But did I detect that at the instant the detector made its detection, that quantum particle was there? Sure I did! Is this macroscopic? Of course it is! All our measurements are not only macroscopic, they are also classical! That is why I can talk about "position" and "momentum" and "energy", because these are all classical concepts. It is also the CAUSE of the weirdness at the quantum level, because we are asking for properties that are not that well-defined at the quantum world.

Note that in the HUP, there's nothing here that says that you cannot measure, as accurately as technologically possible, the position and momentum of just ONE measurement. The accuracy of these measurements do not depend on the HUP, but depends on the accuracy of the instrumentation and technique. The HUP says nothing about a single measurement. The HUP, however, tells you (i) the accuracy that you can predict the NEXT measurement, given the accuracy that you have imposed on one of the non-commutating observable, and (ii) the spread in the value of that observable after repeated identical measurement.

Zz.

 

[ZapperZ]

No! I don’t agree with this statement. The idea of the photon was at least partly introduced as a solution to the old problem of what causes “action” at distance. But the question presupposes the notion of locality. This in the context of modern physics would be the assumption that the “particles” composing matter can be assigned, for any given time, a unique position in space. However, correlation experiment results showing the violation of Bell’s inequality suggest that our world has a non local flavour; casting doubts on the idea that particles of matter can be assigned exact locality relative to our inertial reference frames. This in turn puts into doubt the need for carrier particles to mediate action at a distance. If the locations of “particles” are not fixed exactly relative to our inertial reference frames then neither are the gulfs that separate them and direct interaction between pairs of particles becomes possible when the gulf between them has zero magnitude.

The “particles”/ “fields” of matter must remain in our philosophy it is only the photon (the suggested mediator of force) that is surplus to the explanation of electromagnetism.

Huh?

What's with the Bell inequality all of the sudden?

Here's what you can do. Write down the wave function for a free particle. Now find <x>. Tell me what is "local" here.

Zz.

 

[LorentzR]

Then you need to write a rebuttal to all the experimental high energy physics papers, and even to condensed matter papers using anything that measures electron and neutron spectroscopy such as what I've shown in my avatar. Look under ANY papers in any physics journal that actually detects these particles and tell them that they're not really detecting that 'quantum event'. Remember, in angle-resolved photoemission experiment, the location where the electron hits the detector just doesn't signify that this electron was there at that time, but also carries information about its energy and "in-plane" momentum while it was in the solid!



Zz.

Sorry for this late response I only rarely get chance to look at your forum

Far be it from me to issue a rebuttal; a lead balloon comes to mind. Within the context of the ARPES experimental setup and other scattering experiments the electron and the “photon” seem to behave as if the were particles. This has been known for many years and the advance in the energy resolution and angular resolution (momentum) does not alter this perspective. But because in this particular experimental set up we can explain the observed “classical” outcome by regarding the electron and “photon” as particles does not mean that is what they actually are. We can not pick and choose our experiments to fit our favourite theories we also have to take into account other experimental circumstances where the idea of a particle fails to explain the observed outcomes.

I cannot agree that particles are actually detected, an observer detects a classical event a change in the observable state of the detector and we only infer it is a response to a quantum event. I have no doubt that the observed change in the state of the detector is consequential on a quantum event occurring. Whether or not the quantum event has a specific location relative to our reference frame and the location of the detector I would suggest is unknowable.

 

[LorentzR]

Did I see electrons? Of course not! But did I detect that at the instant the detector made its detection, that quantum particle was there? Sure I did!

Zz.

This is your inference not what you actually detected or what’s likely to have happened at quantum level?

 

[LorentzR]

Is this macroscopic? Of course it is! All our measurements are not only macroscopic, they are also classical! That is why I can talk about "position" and "momentum" and "energy", because these are all classical concepts. It is also the CAUSE of the weirdness at the quantum level, because we are asking for properties that are not that well-defined at the quantum world.



Zz.

Then perhaps you will agree that the measured values for "position" and "momentum" and "energy" are properties of the changes in the detector(s) and do not necessarily represent the state of a quantum entity immediately before the detection?

Note that in the HUP, there's nothing here that says that you cannot measure, as accurately as technologically possible, the position and momentum of just ONE measurement. The accuracy of these measurements do not depend on the HUP, but depends on the accuracy of the instrumentation and technique.

Zz.

This depends on the group behaviour of the quantum systems forming the measuring apparatus and their interaction within themselves and with the quantum system to be measured as well as the group behaviour of the quantum systems forming the brain and creating the mind of the observer ( Locality for instance may be a property of the observer and not the quantum object). The resulting measurements may be extremely accurate at macroscopic level(classical outcome) but this does not necessarily mean it is providing precise information, say, about the position of something that may be inherently fuzzy.

We must have a better understanding of the group behaviour of quantum systems that form the experimental set up since it is their collective behaviour that allows us to obtain accuracy of measurement relative to our inertial reference frames. Our observations are limited to the macroscopic outcome of experimental situations. We may be capable of fixing the position of these outcomes with extreme accuracy, but this accuracy is created by the group behaviour of the quantum systems forming the detector and the “clocks” and “rulers” needed to fix the response’s location. The place and time of a quantum interaction initiating a detection event cannot be specified from the information we have available to us.

 

[LorentzR]

The HUP says nothing about a single measurement. The HUP, however, tells you (i) the accuracy that you can predict the NEXT measurement, given the accuracy that you have imposed on one of the non-commutating observable, and (ii) the spread in the value of that observable after repeated identical measurement.

Zz.

This reinforces the belief that the quantum objects do not possesses specific locations; their interactions do not possesses specific locations and their particle like behaviour is an illusion created by the integrated behaviour of all the quantum systems participating in the experimental set up. It also reinforces the idea that the wave-function controls of how the distribution of the intensity of a “particle’s” likelihood to interact is projected onto our reference frames.

 

[LorentzR]

[

Huh?

What's with the Bell inequality all of the sudden?
Zz.

My principle reason for doubting the existence of the photon was that its raison deter was to mediate the electromagnetism; to bridge the gulf between charged quantum entities. But if quantum entities don’t have uniquely defined positions in the world then the gulfs separating them are also undefined; opening up the possibility of direct interaction between the charged systems. I therefore brought the evidence of the violation of Bell’s inequality to reinforce the idea that charged quantum systems do not have unique positions in space, since here was further evidence of a non local flavour to our world.



As I wrote earlier you can’t pick and choose your experimental results to reinforce your favourite theory. Our underlying understanding of how things happen must explain all known experimental results if it is to be valid.

Locality is fundamental to classical physics, but the conventional definition seems incapable of explaining in a consistent way all the experimental results obtained by physics. At the heart of the problem is the Born rule that allows one classical description of a quantum entity; where the entity is spatially distributed; to be transformed into possible classical outcomes where the entity becomes point like.

Explaining how this happens in a relativistically friendly manner is one of the great problems of natural philosophy.

Here's what you can do. Write down the wave function for a free particle. Now find <x>. Tell me what is "local" here.

Zz.

Further evidence that you cannot pin point a quantum entity!
Measures of location are facilitated by the collective behaviour of quantum systems and their group “position” in the manifold.

I stand by my assertion that the weight of this evidence suggests that charged systems interact directly, so there is no requirement in nature for man’s photon. So the answer to Alveros’s question seems to be; something that does not exist does not have a size!

 

[ZapperZ]

Then perhaps you will agree that the measured values for "position" and "momentum" and "energy" are properties of the changes in the detector(s) and do not necessarily represent the state of a quantum entity immediately before the detection?

Come again?

Other than the fact that this issue is getting pretty old and I've lost interest in it already, I have no idea what you just said here. If the detector is more of a property of itself, then you have to seriously explain why it just didn't make a detection trigger all by itself. Why does it need a photon (or anything else) to cause a measurement?

You are also forgetting that everything that you detect (including all of your sense) is an interaction of something with something. As an experimentalist, I have to be keenly aware of what I'm measuring and how I'm measuring it. Still, this doesn't address the "size of a photon", because you still have to "detect" the size. While I can point to you a position operator in QM, can you define for me a "size" operator?

This depends on the group behaviour of the quantum systems forming the measuring apparatus and their interaction within themselves and with the quantum system to be measured as well as the group behaviour of the quantum systems forming the brain and creating the mind of the observer ( Locality for instance may be a property of the observer and not the quantum object). The resulting measurements may be extremely accurate at macroscopic level(classical outcome) but this does not necessarily mean it is providing precise information, say, about the position of something that may be inherently fuzzy.

We must have a better understanding of the group behaviour of quantum systems that form the experimental set up since it is their collective behaviour that allows us to obtain accuracy of measurement relative to our inertial reference frames. Our observations are limited to the macroscopic outcome of experimental situations. We may be capable of fixing the position of these outcomes with extreme accuracy, but this accuracy is created by the group behaviour of the quantum systems forming the detector and the “clocks” and “rulers” needed to fix the response’s location. The place and time of a quantum interaction initiating a detection event cannot be specified from the information we have available to us.

I have no clue on what you just said here. You somehow made it sound as if this is something we know nothing about. How do you think they detect those exotic particles in high-energy collisions at CERN and Fermilab? Do you think they are not keenly aware of how exactly the detection works and how they interact with what they're trying to detect? I mean, give these hard-working (and very intelligent) people SOME credit!

Zz.

 

[ZapperZ]

I stand by my assertion that the weight of this evidence suggests that charged systems interact directly, so there is no requirement in nature for man’s photon.

Then I want you to submit a paper to PRL to explain the results of the anti-bunching experiments without invoking the photon picture. Till you do that, I strongly suggest you cease making such statements on here that clearly violates the PF Guidelines. This is the only warning that you will get on this matter.

Zz.

 

[reilly]

[
My principle reason for doubting the existence of the photon was that its raison deter was to mediate the electromagnetism; to bridge the gulf between charged quantum entities. But if quantum entities don’t have uniquely defined positions in the world then the gulfs separating them are also undefined; opening up the possibility of direct interaction between the charged systems. I therefore brought the evidence of the violation of Bell’s inequality to reinforce the idea that charged quantum systems do not have unique positions in space, since here was further evidence of a non local flavour to our world.
As I wrote earlier you can’t pick and choose your experimental results to reinforce your favourite theory. Our underlying understanding of how things happen must explain all known experimental results if it is to be valid.

Locality is fundamental to classical physics, but the conventional definition seems incapable of explaining in a consistent way all the experimental results obtained by physics. At the heart of the problem is the Born rule that allows one classical description of a quantum entity; where the entity is spatially distributed; to be transformed into possible classical outcomes where the entity becomes point like.

Explaining how this happens in a relativistically friendly manner is one of the great problems of natural philosophy.
Further evidence that you cannot pin point a quantum entity!
Measures of location are facilitated by the collective behaviour of quantum systems and their group “position” in the manifold.

I stand by my assertion that the weight of this evidence suggests that charged systems interact directly, so there is no requirement in nature for man’s photon. So the answer to Alveros’s question seems to be; something that does not exist does not have a size!

Wow. A few things: photons were invented by Planck and Einstein to explain black body radiation and the photoelectric effect. The invention of QED - Heisenberg, Pauli and Dirac, and Fermi -- brought Gauge invariance into play. so, in the Coulomb gauge, with divA=0, the particle-particle Coulomb interaction is a direct interaction; in the Lorentz Gauge, for practical purposes, the Coulomb interaction is mediated by photons -- Dirac gives an elegant discussion of the Coulomb gauge in his Quantum theory text.

Gauge Invariance is a big deal, an important deal; photons are tricky, no doubt, but no one has come close to presenting a better idea.Best to check it out.

Re positions: read about the basics of probability theory, then you will see the fallacy in your arguments about positions and interactions and the like.Note also that if positions and "gulfs' are uncertain then the probabilty of direct interactions will be very low. Why?

Regards,
Reilly Atkinson

 

[lightarrow]

Come again?

Other than the fact that this issue is getting pretty old and I've lost interest in it already, I have no idea what you just said here. If the detector is more of a property of itself, then you have to seriously explain why it just didn't make a detection trigger all by itself. Why does it need a photon (or anything else) to cause a measurement?

The particle-like behaviour is manifest in the interaction, not in flight. All we know is that light behaves as wave from source to detector and as particle at the detector. Period.

 

[ZapperZ]

The particle-like behaviour is manifest in the interaction, not in flight. All we know is that light behaves as wave from source to detector and as particle at the detector. Period.

We do? How do you know? Because it can "interfere" with itself? Even single photons? How do you explain the which-way experiments and the anti-bunching experiments, all of which have to occur "during flight" and then detected?

This is getting silly. We are now turning this thread into a "photon" thread. I guess this is probably because the issue of the "size of a photon" is dead and buried but people just can't leave that photon well-enough alone? Again, talk is cheap. Please show a citation where an alternative explanation and description has been done for those two experiments that I cited, plus the multi-photon photoemission.

Zz.

 

[LorentzR]

Come again?

Other than the fact that this issue is getting pretty old and I've lost interest in it already, I have no idea what you just said here. If the detector is more of a property of itself, then you have to seriously explain why it just didn't make a detection trigger all by itself. Why does it need a photon (or anything else) to cause a measurement?

Zz.

I mean that your interaction as the observer is with the detector and not the particle. Locality (of the detection) is a property of the group behaviour of the quantum systems forming the detector and the accuracy of the detector depends on their group behaviour.. Of course the detector needs to interact with something but the position of the actual interaction is not definable, only the response of the detector can have known position. Quantum mechanics only predicts the probable observable and measurable outcomes of experiments

You are also forgetting that everything that you detect (including all of your sense) is an interaction of something with something.
Zz.

Sorry I thought that was exactly what we were talking about; that is the locality of the quantum interaction the initiates a response at an observable position at the detector.

As an experimentalist, I have to be keenly aware of what I'm measuring and how I'm measuring it.
Zz.

I’m sure you are an excellent experimentalist; even so, nature will only permit you to observe the response of the detector to a quantum event and not the event itself.

Still, this doesn't address the "size of a photon", because you still have to "detect" the size. While I can point to you a position operator in QM, can you define for me a "size" operator?
Zz.

If my reasoning is correct such an operator is unnecessary.

I have no clue on what you just said here. You somehow made it sound as if this is something we know nothing about. How do you think they detect those exotic particles in high-energy collisions at CERN and Fermilab? Do you think they are not keenly aware of how exactly the detection works and how they interact with what they're trying to detect? I mean, give these hard-working (and very intelligent) people SOME credit!

Zz.

I do, I think you should conduct a survey and ask them how exactly the detection works and how they interact with what they detect. I suspect you might be in for a surprise.

 

[LorentzR]

Then I want you to submit a paper to PRL to explain the results of the anti-bunching experiments without invoking the photon picture.
Zz.

Sounds like reasonable challenge.

Till you do that, I strongly suggest you cease making such statements on here that clearly violates the PF Guidelines. This is the only warning that you will get on this matter.

Zz.

Sorry! just got carried away

 

[LorentzR]

Wow. A few things: photons were invented by Planck and Einstein to explain black body radiation and the photoelectric effect. The invention of QED - Heisenberg, Pauli and Dirac, and Fermi -- brought Gauge invariance into play. so, in the Coulomb gauge, with divA=0, the particle-particle Coulomb interaction is a direct interaction; in the Lorentz Gauge, for practical purposes, the Coulomb interaction is mediated by photons -- Dirac gives an elegant discussion of the Coulomb gauge in his Quantum theory text.

Gauge Invariance is a big deal, an important deal; photons are tricky, no doubt, but no one has come close to presenting a better idea.Best to check it out.

Incidentally it was Ludvig’s Gauge not Hendrik’s but Lorentz invariant all the same.

Re positions: read about the basics of probability theory, then you will see the fallacy in your arguments about positions and interactions and the like.Note also that if positions and "gulfs' are uncertain then the probabilty of direct interactions will be very low.



Regards,
Reilly Atkinson

That all depends on the descriptions of the interacting entities and their event arena?

 

[ZapperZ]

I mean that your interaction as the observer is with the detector and not the particle. Locality (of the detection) is a property of the group behaviour of the quantum systems forming the detector and the accuracy of the detector depends on their group behaviour.. Of course the detector needs to interact with something but the position of the actual interaction is not definable, only the response of the detector can have known position. Quantum mechanics only predicts the probable observable and measurable outcomes of experiments

Then by your conclusion, all types of measurement is suspect, including those made on electrons, protons, neutrons, neutrinos, etc.. Would you also like to write a paper to PRL and challenge all those experimental papers? For example, look at any photoemission papers such as those using ARPES that actually detect electrons on CCDs. Tell me that the position that I measured on the detector is not the exact position where the electron actually hits the screen, and that my deduction of the momentum based on that position has MORE to do with my interaction with the detector.

You seem to be talking full of hot air. Please make exact citations that actually support what you are saying.

I do, I think you should conduct a survey and ask them how exactly the detection works and how they interact with what they detect. I suspect you might be in for a surprise.

I did! I work in the High Energy Physics division! I talk to these experimentalists all the time. Maybe it is YOU who should be doing that survey.

Zz.

 

[LorentzR]

Then by your conclusion, all types of measurement is suspect, including those made on electrons, protons, neutrons, neutrinos, etc.. Would you also like to write a paper to PRL and challenge all those experimental papers? For example, look at any photoemission papers such as those using ARPES that actually detect electrons on CCDs. Tell me that the position that I measured on the detector is not the exact position where the electron actually hits the screen, and that my deduction of the momentum based on that position has MORE to do with my interaction with the detector.



Zz.

Ok I can measure the position of an electron by passing it through a hole in a barrier and I know exactly where the electron was when it passed through the barrier. I then calculate the probability density for where it might interact with a screen beyond. If the barrier has two holes then I have two measures for the position of the electron as it goes through the screen and the distribution for where it is likely to hit the screen must be modified accordingly. In fact I can have as many measures of the position of where the electron goes through the barrier as a like and each will contribute to where I’m likely to find my interaction on the screen.

So did the electron have an exact position as it went through the barrier?

Does the experimental set-up influence the distribution of the likely measurable momentum along the plane of the screen?

 

[ZapperZ]

Ok I can measure the position of an electron by passing it through a hole in a barrier and I know exactly where the electron was when it passed through the barrier. I then calculate the probability density for where it might interact with a screen beyond. If the barrier has two holes then I have two measures for the position of the electron as it goes through the screen and the distribution for where it is likely to hit the screen must be modified accordingly. In fact I can have as many measures of the position of where the electron goes through the barrier as a like and each will contribute to where I’m likely to find my interaction on the screen.

So did the electron have an exact position as it went through the barrier?

Does the experimental set-up influence the distribution of the likely measurable momentum along the plane of the screen?

You seem to have a very strange way of making a position measurement, and then telling me something else about it. And why are we now talking about a "momentum" along the plane of the screen? This isn't a discussion about the HUP!

The "momentum" that I referred to is the momentum measurement in ARPES where the POSITION of the electron hitting the detector is equivalent to the in-plane momentum of the electron. In fact, it is the in-plane momentum of the electron while it was in the crystal material that emitted the electron in the first place. The resolution of the position corresponds directly to the resolution of the momentum. Refer to any of the latest ARPES papers on high-Tc superconductors, for example, since T. Valla's paper in Science in 1999. You'll see something that looks like my avatar!

Thus, you DO measure a position of electrons, etc. and upon measurement, make a direct connection to the trajectory of that electron back to where it came from. In fact, this is what experimentalists in high energy physics do all the time - making a vertex reconstruction of the event that they detected. They do this for practically everything to distinguish and identify the original particle that made the signal, be it EM showers (photons), muons, etc... We do the same thing for neutrino detectors at SuperK, MINOS, etc, which essentially are photon detectors! So to claim that the position being measured by these experiments have nothing really to do with an actual position of the particle but rather more to do with the detectors themselves is contrary to what is being practiced all over.

Have you noticed that not once have you made any direct reference to anything published or actual experimental work to support what you are saying? Why is that? In addition, when was the last time you actually had to make a photon or electron position detection?

I also notice that you could not tell me how many high energy experimentalists you have surveyed regarding their detection methods. Does that mean that many of the criteria you impose on me does not apply to you?

Zz.

 

[lightarrow]

We do? How do you know? Because it can "interfere" with itself? Even single photons?

Because when you localize a photon, you loose the interference pattern, which is described by wave behaviour. To localize the photon means to detect it. Conclusion: when you don't detect it, the photon is described by a wave, when you detect it, by a particle.

How do you explain the which-way experiments and the anti-bunching experiments, all of which have to occur "during flight" and then detected?

Exactly which of the "which-way experiments" and of the "anti-bunching experiments" are you referring to?

Again, talk is cheap. Please show a citation where an alternative explanation and description has been done for those two experiments that I cited, plus the multi-photon photoemission.
Zz.

What is "multi-photon photoemission"?
Thank you.

 

[ZapperZ]

Because when you localize a photon, you loose the interference pattern, which is described by wave behaviour. To localize the photon means to detect it. Conclusion: when you don't detect it, the photon is described by a wave, when you detect it, by a particle.

I'm sure by now that it would have gotten through you that I am not going to accept something just because you said so. Show me an exact citation of such formulation, please.

Again, check how the dynamics of all the detected particles are done in various experiments and tell me that their ability to reconstruct the particle's path leading to the detected spot is consistent with that you are saying. You may start by analyzing all those ARPES experiments.

Exactly which of the "which-way experiments" and of the "anti-bunching experiments" are you referring to?

ALL of them.

What is "multi-photon photoemission"?
Thank you.

Bingo!

This thread should not be turned into a "photon doesn't exist", especially when you have not offered (or are even aware of) any of those experiments that explicitly invoke the photon picture in the physics.

Zz.

 

[LorentzR]

You seem to have a very strange way of making a position measurement, and then telling me something else about it. And why are we now talking about a "momentum" along the plane of the screen? This isn't a discussion about the HUP!Zz.

I don’t think you can consider quantum interactions without considering the effects of uncertainty.

I used the above illustration to show that the electron can be in more than one place at anyone time.In the ARPES experiment, apart from the measured value, all other values of momentum are canceled out through the electron’s self interference. Because of the free path between the target and the detector! This does not mean the electron does not possesses other values of momentum and position it is just the experimental set up ensures they do not affect the outcome by allowing for their destructive interference. If any object were to be placed near to the apparent path of the electron then the symmetry of the wave pattern would be disturbed and the results compromised.

The "momentum" that I referred to is the momentum measurement in ARPES where the POSITION of the electron hitting the detector is equivalent to the in-plane momentum of the electron. In fact, it is the in-plane momentum of the electron while it was in the crystal material that emitted the electron in the first place. The resolution of the position corresponds directly to the resolution of the momentum. Refer to any of the latest ARPES papers on high-Tc superconductors, for example, since T. Valla's paper in Science in 1999. You'll see something that looks like my avatar!Zz.

I think here you should be referring to the angular distribution of the detector’s responses

Have you noticed that not once have you made any direct reference to anything published or actual experimental work to support what you are saying? Why is that? In addition, when was the last time you actually had to make a photon or electron position detection?

I also notice that you could not tell me how many high energy experimentalists you have surveyed regarding their detection methods. Does that mean that many of the criteria you impose on me does not apply to you?

Zz.

That because it’s all basic Physics! My only deviation is to have asserted that the weight evidence suggests that pairs of spatially extended quantum entities become “super-positioned” and interact directly and the result of their interaction produces a macroscopically measurable event at a specific position relative to our reference grids.

Sorry but this has no citation it just jumped out of my head; so where’s the best place for all the info on bunching and anti bunching?

 

[ZapperZ]

I don’t think you can consider quantum interactions without considering the effects of uncertainty.

I used the above illustration to show that the electron can be in more than one place at anyone time.

Not when it is detected! When I detect it, it has a well-defined position for that one single measurement!

In the ARPES experiment, apart from the measured value, all other values of momentum are canceled out through the electron’s self interference. Because of the free path between the target and the detector! This does not mean the electron does not possesses other values of momentum and position it is just the experimental set up ensures they do not affect the outcome by allowing for their destructive interference. If any object were to be placed near to the apparent path of the electron then the symmetry of the wave pattern would be disturbed and the results compromised.

Er.. say what? Where did you get this? What canceled out?

I think here you should be referring to the angular distribution of the detector’s responses

This is very strange. Have you looked at an electron analyzer and figure out what exactly it is that you're talking about?

That because it’s all basic Physics! My only deviation is to have asserted that the weight evidence suggests that pairs of spatially extended quantum entities become “super-positioned” and interact directly and the result of their interaction produces a macroscopically measurable event at a specific position relative to our reference grids.

I have no idea what you are talking about here. I suppose if you muddle it enough, I'd lose contact with what the issue is all about. You're succeeding.

Sorry but this has no citation it just jumped out of my head;

Ah, now things have some explanation on why they are not making any sense.

so where’s the best place for all the info on bunching and anti bunching?

H. Paul, Rev. Mod. Phys. 54, 1061 (1982)

Zz.

 

[lightarrow]

I'm sure by now that it would have gotten through you that I am not going to accept something just because you said so. Show me an exact citation of such formulation, please.

I believed it was already established.

Again, check how the dynamics of all the detected particles are done in various experiments and tell me that their ability to reconstruct the particle's path leading to the detected spot is consistent with that you are saying. You may start by analyzing all those ARPES experiments.

Which particle's path? In the thread " Why doesn't QM make particles zig-zag as they travel?" Marlon explained that the line we see in, e.g., a bubble chamber, it's not the particle's trajectory.

This thread should not be turned into a "photon doesn't exist", especially when you have not offered (or are even aware of) any of those experiments that explicitly invoke the photon picture in the physics.

Zz.

If you explained what you mean with "multiphoton emission" I could express my opinion on the impossibility to explain it without the notion of photon. A related question: how the experiment of "quantum beats" is interpreted in the photon's paradigm?

 

[ZapperZ]

I believed it was already established.Which particle's path? In the thread " Why doesn't QM make particles zig-zag as they travel?" Marlon explained that the line we see in, e.g., a bubble chamber, it's not the particle's trajectory.

But we are not talking about a "bubble chamber" (that is a whole different matter here and I can easily point to you an even clearly tracking of single-electron motion, which I had already cited and commented on). So don't change the subject AGAIN!

I have no idea what this argument is all about. For some odd reason, you somehow dispute that a detection of a photon, electron, neutron, etc... on some detector somehow cannot be extrapolated back onto a path of where it came from? I'm not talking about BEFORE detection. I'm talking about from the moment of detection.

If this is exactly what you are claiming, then as I've said before, please write a rebuttal to all those astrophysics and high energy physics papers and tell them that their vertex reconstruction is outright false. Other than that, I have no patience left in arguing about the validity of photons because you have made no attempt at doing what I asked you to do, which is to find alternative explanations for all the experiments that I have mentioned.

And I am utterly puzzled why you can't find these experiments yourself. Google Scholar doesn't work for you? I gave you already a review paper on the anti-bunching experiments. Here are the multiphoton papers:

U. Hofer et al. Science v.277, p.1480 (1997).
A. Damascelli et al., Phys. Rev. B v.54, p.6031 (1996).
M. Aeschlimann et al., J. Chem. Phys. v.102, p.8606 (1995).
K. Giesen et al., Phys. Rev. Lett. v55, p.300 (1985).

Until you can come up with a non-photon formulation to describe all this, I suggest you devote your energy it rather than wasting it on here, because as you already know, I'm not going to buy it. And oh, just in case you think I'm just blowing off stuff I barely know, I too have made measurements involving such multiphoton effects, on magnesium photocathodes.

P.S. I noticed that you didn't answer my question about when the last time you looked at an electron analyzer used in ARPES experiments. Why is that?

Zz.

 

[pervect]

This thread is both very long, and seems to be going in about a zillion different directions. Having received complaints about it, I'm going to take the liberty of locking it, because it just doesn't seem to be getting anywhere, and because some of the directions the thread is going in seem to be violating our PF guidelines.

Specifically, we aren't here to defend mainstream science, we are here to explain it.

I will therefore ask people who think that photons are unnecessary to please refrain from posting statements of their opinions unless they can quote a peer reviewed published paper, textbook, or other source which supports this as a current subject of scientific debate in accordance with our guidelines.

It is against our Posting Guidelines to discuss, in most of the PF forums, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion.

I'd also like to encourage people to track down some of the references that have already been quoted if at all possible.

Some other people seem to perhaps have questions which fall within our guidelines, which unfortunately don't seem to be very clear. I'd like to encourage these people to post their questions in some other thread, as long as they are questions that fall within our guidelines.

Meanwhile because this thread is just so long and so incoherent, I'm going to put it out of its misery.