Is quantum mechanics a complete theory of nature?

[zonde]

The trouble with trying to prove quantum mechanics wrong is that they insist that you come up with better predictions. All one has to do is prove that the predictions are based on a superficial understanding of nature or photons or whatever.

Wrong
All one has to do is demonstrate that falsifiable prediction of theory actually fails.

Question for you: is quantum entanglement falsifiable prediction of quantum mechanics?

If Bell was using an incorrect model then he is proving something about quantum mechanics, not reality.

Even if Bell was using incorrect model we can use his theorem as baseline to analyze viability of different local realistic explanations for entanglement.

 

[nortonian]

Important things first:
That is NOT how bunching works.

The important things are not models. They are things like momentum and time that qm uses in an inconsistent manner. Let's get away from models of em interaction and look at the fundamental questions. A qm photon is delocalized and is integrated over an infinite number of frequencies so it does not fit the pattern of other particles. A proper model of the photon must be localized with a diffuse field of a single frequency similar to other particles. The qm model changes depending upon the energy of the photon. Sometimes it is localized sometimes not.

Another fundamental question concerns how qm deals with time. In optical experiments qm uses a single time parameter, the phase, when defining photons. A model that uses superposed photons to define detection is able to include continuous time into the energy absorption/emission process. The fields of superposed photons cause the outer electrons of photosensitive atoms to oscillate. If the superposition is of sufficient intensity the electron is forced into a higher orbital, where after a finite decay time it drops back and emits a photon. The conservation of momentum is exactly obeyed.

In the qm model the superposed fields and detection event are both included in the photon so that observation is an instantaneous event. (The path integral method does use both times but it integrates over all time a questionable practice.) The interaction does not take place in continuous time as would be necessary to include momentum in a description. If we introduce momentum into a description of photon states, how does a single photon cause excitation? It would be necessary for the photon to impact the electron with precisely the amount of energy to raise it into a higher orbital without knocking it out of the atom completely. Visualization is not possible. I have a problem with that because I am thinking, what are they hiding? Where is the momentum? The important stuff, the fundamentals, the details are skipped over.

Quantum mechanics treats time and momentum inconsistently.

Wrong
All one has to do is demonstrate that falsifiable prediction of theory actually fails.

Question for you: is quantum entanglement falsifiable prediction of quantum mechanics?

Even if Bell was using incorrect model we can use his theorem as baseline to analyze viability of different local realistic explanations for entanglement.

Question for you: If they are not actually photons, but rather detection events then what difference does it make? Unless you give me a description that includes momentum they are not photons.

 

[Cthugha]

The important things are not models. They are things like momentum and time that qm uses in an inconsistent manner.

No.

Let's get away from models of em interaction and look at the fundamental questions. A qm photon is delocalized

It can be. It does not have to.

and is integrated over an infinite number of frequencies so it does not fit the pattern of other particles.

If it is non-monochromatic it can be necessary to integrate over some frequencies. This is not always necessary and that is not different from other particles.

A proper model of the photon must be localized

Definitely not!

with a diffuse field of a single frequency similar to other particles. The qm model changes depending upon the energy of the photon. Sometimes it is localized sometimes not.

This is very wrong. You are aware that the photon concept of a single frequency which you can use as a basis for constructing em fields and the single photon state as an eigenstate of the photon number operator are different things, right?

Another fundamental question concerns how qm deals with time. In optical experiments qm uses a single time parameter, the phase, when defining photons.

An eigenstate of the photon number operator does not even have a well defined phase due to uncertainty.

A model that uses superposed photons to define detection is able to include continuous time into the energy absorption/emission process.

I thought the important things are not models?

The fields of superposed photons cause the outer electrons of photosensitive atoms to oscillate. If the superposition is of sufficient intensity the electron is forced into a higher orbital, where after a finite decay time it drops back and emits a photon. The conservation of momentum is exactly obeyed.

I described in my last post why that model is wrong, how it is ruled out and how it can be tested, I will not repeat that as you just ignored it before.

In the qm model the superposed fields and detection event are both included in the photon so that observation is an instantaneous event. (The path integral method does use both times but it integrates over all time a questionable practice.)

This is nonsense. You need to consider photon creation and annihilation operators at DIFFERENT times to describe emission and absorption events.

The interaction does not take place in continuous time as would be necessary to include momentum in a description. If we introduce momentum into a description of photon states, how does a single photon cause excitation? It would be necessary for the photon to impact the electron with precisely the amount of energy to raise it into a higher orbital without knocking it out of the atom completely.

You know that typical detectors do not use some isolated atoms, but some solid state detector material which has a continuum of excitable states, right? Even for single atoms I do not see your problem. Photons with matching energy are absorbed. Others are not. This has nothing to do with momentum. For momentum you need to check the wavevector.

Visualization is not possible.

That is simply wrong.

I have a problem with that because I am thinking, what are they hiding? Where is the momentum? The important stuff, the fundamentals, the details are skipped over.

Quantum mechanics treats time and momentum inconsistently.

Sorry, but I cannot help you much as you are claiming plain nonsense. The proper way is to read and understand what qm says about this and then ask questions to deepen understanding and not to make up something you do not like and then claim that this is what qm says.

 

[zonde]

Question for you: If they are not actually photons, but rather detection events then what difference does it make?

We are speaking about Bell theorem right?

Then the difference is that we can not be sure that detection events will pair up perfectly with assumed perfect detectors. Basically we can not claim that fair sampling assumption holds and therefore Bell theorem does not apply.
However if detection events would pair up perfectly for efficient detection then there is no difference.

 

[nortonian]

Sorry, but I cannot help you much as you are claiming plain nonsense. The proper way is to read and understand what qm says about this and then ask questions to deepen understanding and not to make up something you do not like and then claim that this is what qm says.

The reason for your objections is that I am trying to describe things in ordinary space what is customarily done in Hilbert space. I got sidetracked, ahead of myself and clearly I was generalizing too much. It is pointless to continue in this vein. You came in late to the thread and missed the early discussions and I would like to return to that because this is a discussion of whether qm is complete. For that reason I ask that you look at post 4 and see if you agree keeping in mind the whole of qm, gravitation, particles, renormalization, etc. not just Bell's thm.

We are speaking about Bell theorem right?

Then the difference is that we can not be sure that detection events will pair up perfectly with assumed perfect detectors. Basically we can not claim that fair sampling assumption holds and therefore Bell theorem does not apply.
However if detection events would pair up perfectly for efficient detection then there is no difference.

I do not pretend to a complete understanding of the Bell thm, but if what we are calling a photon is actually classical then it is about classical measurements and/or the properties of detectors. Please look at the Marshall papers, especially "The myth of the photon" which I cited in an earlier post to see the theoretical basis for that conclusion.

 

[zonde]

Please look at the Marshall papers, especially "The myth of the photon" which I cited in an earlier post to see the theoretical basis for that conclusion.

I looked at this paper and my response was (post #14):

Santos [and Marshall] says in abstract of this paper:
"It also requires us to recognize that there is a payoff between detector efficiency and signal-noise discrimination."
This indeed seems to be the case for SPAD detectors. But it turns out this is not a general rule for any detector:
NIST Detector Counts Photons With 99 Percent Efficiency:
“When these detectors indicate they’ve spotted a photon, they’re trustworthy. They don’t give false positives,” says Nam, a physicist with NIST’s Optoelectronics division. “Other types of detectors have really high gain so they can measure a single photon, but their noise levels are such that occasionally a noise glitch is mistakenly identified as a photon. This causes an error in the measurement. Reducing these errors is really important for those who are doing calculations or communications.”

So prediction of this model turns out to be false. I see no point looking further.

 

[Cthugha]

I do not pretend to a complete understanding of the Bell thm, but if what we are calling a photon is actually classical then it is about classical measurements and/or the properties of detectors. Please look at the Marshall papers, especially "The myth of the photon" which I cited in an earlier post to see the theoretical basis for that conclusion.

I have had a look at that paper and there are many good reasons why it actually never gor published somewhere. While their idea to sort classical and non-classical states by means of the Wigner density is odd, but at least consistent from their point of view, they basically have no arguments and sometimes claim wrong stuff. The worst point is their claim that "With respect to the “nonclassical” states of the light field currently widely reported as having been observed, our response is that something approximating the squeezed vacuum, as described by equation (6), has been observed; this, however, according to our new classification, is a classical state, though not Glauber-classical."

At first that means they only talk about SPDC processes and completely ignore single photon sources which have been realized are definitely not amplified squeezed vacuum. Second, the similarity between SPDC and amplification of some vacuum modes of the em field is well known. Pretty much any spontaneous emission process can be understood as amplification of a vacuum mode. All in all the important point is that their claim of "Planck-classicality" being more important than the standard Glauber definition is not tenable. Apart from that the explanation that any SPDC process creates a field with a positive Wigner density is not tenable at all. See e.g. "Amplification of Quantum Entanglement" by De Martini (PRL 81, 2842–2845 (1998)) for a sketch of how the Wigner function of such a state actually looks like.

Add the arguments Zonde presented and it becomes clear that the proposal of Marshall and Santos is just not in accordance with what actually happens.

 

[nortonian]

So prediction of this model turns out to be false. I see no point looking further.

If quantum mechanics is complete on the microscopic level then what we observe is all that exists and a detection is a photon. On the other hand, if it is incomplete then we do not observe all that exists, we don't know how the detection is produced and we don't have a good model. How do you know which of these choices is the correct one? There is no optical experiment that identifies a single photon with the assurances of the photo electric effect so I prefer to say even though there is a good mathematical model there is not a good physical model so I choose not to reject locality. Is there a problem with that?

I have had a look at that paper and there are many good reasons why it actually never gor published somewhere.
Add the arguments Zonde presented and it becomes clear that the proposal of Marshall and Santos is just not in accordance with what actually happens.

OK so there is no competing theory to quantum optics, but that doesn't mean it is the final answer or that it is complete. Qm does not include general relativity and cannot explain life, consciousness, and chaos theory; all of which are local realistic phenomena. Instead of asking how is it possible for non-local phenomena to occur, the question should be rephrased to ask, why do local phenomena appear to be non-local when viewed according to the laws of qm? Only when that question is answered will it be possible to make progress towards answering more fundamental questions.

 

[zonde]

I prefer to say even though there is a good mathematical model there is not a good physical model so I choose not to reject locality. Is there a problem with that?

There is no problem with that part.

About other things - we do not need theory of everything to make testable statements. Strictly speaking all our theories about physics are incomplete. It's that scientific method does not allow conclusive proof of a theory.

 

[Kholdstare]

Is quantum mechanics a complete theory of nature? No.

 

[zonde]

Considering that there is no complete theories of physics in a sense that they give conclusive statements maybe it's more sense to talk about completeness or incompleteness of QM as consistency or inconsistency of theory.
I suppose that was the sense how Einstein was talking about incompleteness of QM - that different representations of the same physical situation within the theory are not in conflict with each other.

 

[lugita15]

Considering that there is no complete theories of physics in a sense that they give conclusive statements maybe it's more sense to talk about completeness or incompleteness of QM as consistency or inconsistency of theory.
I suppose that was the sense how Einstein was talking about incompleteness of QM - that different representations of the same physical situation within the theory are not in conflict with each other.

No, I think what Einstein meant by incompleteness is when a theory points "outside itself" in some sense. In other words, when it gives an indication that there are other theories needed to either supplement it or supplant it. For instance, Maxwell's theory of electromagnetism seems to imply that charged particles are unstable if the only forces acting on them were the electromagnetic forces gotten from Maxwell's equations, so all by themselves they suggest that there is something in nature other than Maxwell's equations.

 

[zonde]

No, I think what Einstein meant by incompleteness is when a theory points "outside itself" in some sense.

There are no self-contained physics theories. So what is the sense to talk about incompleteness this way?

In other words, when it gives an indication that there are other theories needed to either supplement it or supplant it.

How it gives that indication? By not being able to give unequivocal predictions? Shouldn't work. Such theory would be simply dismissed.

There is nice letter where Einstein tries to explain his position - Einstein's Reply to Criticisms
From there:

What does not satisfy me in that theory, from the standpoint of principle, is its attitude towards that which appears to me to be the programmatic aim of all physics: the complete description of any (individual) real situation (as it supposedly exists irrespective of any act of observation or substantiation). Whenever the positivistically inclined modern physicist hears such a formulation his reaction is that of a pitying smile. He says to himself: "there we have the naked formulation of a metaphysical prejudice, empty of content, a prejudice, moreover, the conquest of which constitutes the major epistemological achievement of physicists within the last quarter-century. Has any man ever perceived a 'real physical situation'? How is it possible that a reasonable person could today still believe that he can refute our essential knowledge and understanding by drawing up such a bloodless ghost?" Patience! ...

So he talks about real physical situation as it supposedly exists irrespective of any act of observation or substantiation. And this is supposed to be opposite for positivistic attitude.

This gives quite different picture than the one you are drawing. It's not about lack of another theory but about lack of metaphysical core for the theory that we could call model of reality.

 

[nortonian]

Considering that there is no complete theories of physics in a sense that they give conclusive statements maybe it's more sense to talk about completeness or incompleteness of QM as consistency or inconsistency of theory.

I agree.

The Bell theorem is a mathematical rule describing the behavior of a mathematical model (the photon) in order to define a physical concept (locality). In order for qm to be consistent a physical model is needed to define a physical concept.

 

[Cthugha]

Qm does not include general relativity and cannot explain life, consciousness, and chaos theory; all of which are local realistic phenomena. Instead of asking how is it possible for non-local phenomena to occur, the question should be rephrased to ask, why do local phenomena appear to be non-local when viewed according to the laws of qm?

What? Which local phenomena appear non-local according to qm? I know of none. Your argument is pretty moot. Why should qm explain life or consciousness? That is not even the domain of physics. Regarding nonlinear dynamics (or chaos theory as you call it) there is the field of quantum chaos that studies how to treat chaotic classical systems in terms of quantum mechanics.

The Bell theorem is a mathematical rule describing the behavior of a mathematical model (the photon) in order to define a physical concept (locality). In order for qm to be consistent a physical model is needed to define a physical concept.

The concept of the photon is as physical as the concepts of gravity, atoms or angular momentum are.

 

[nortonian]

What? Which local phenomena appear non-local according to qm? I know of none.

Polarization

Your argument is pretty moot. Why should qm explain life or consciousness? That is not even the domain of physics.

Qm is fundamental to all microscopic phenomena. Life began at the microscopic level and unsuccessful attempts have been made to explain both it and consciousness in terms of quantum mechanics. In any case general relativity alone suffices as an example.

The concept of the photon is as physical as the concepts of gravity, atoms or angular momentum are.

Then why is momentum not conserved locally for photons that produce interference fringes?

 

[Cthugha]

Polarization

That is not really an answer that explains much. Polarization as such is a property of a system and calling it local or non-local is kind of odd. Do you point at Bell tests? They do not "look" non-local, they are (modulo the typical disclaimer that it might be local if realism is dropped).

Qm is fundamental to all microscopic phenomena. Life began at the microscopic level and unsuccessful attempts have been made to explain both it and consciousness in terms of quantum mechanics. In any case general relativity alone suffices as an example.

As Anderson said: "more is different". It would be quite daring to declare complex fields explainable by physics alone. This will not work for biology, social sciences or chemistry. Explaining consciousness is the realm of biology and I really doubt there is an explanation purely in terms of physics. I do not understand the reference to general relativity. Of course it is complicated to marry qm and gr. That is well known, but what does it have to do with the topic and hand? The pure fact that you have locality in some subfield does not mean that teverything is local.

Then why is momentum not conserved locally for photons that produce interference fringes?

Within the coherence volume of some light field momentum is conserved. Do you have any example where it is not conserved?

 

[nortonian]

That is not really an answer that explains much.

The pure fact that you have locality in some subfield does not mean that everything is local.

These disputes are caused by differences in language. You are using quantum speak while I use physical speak.

Within the coherence volume of some light field momentum is conserved. Do you have any example where it is not conserved?

Momentum is not an averaged quantity in physical speak. It is applied instantaneously. However, my purpose in starting this thread was not to change quantum speak but to point out that it is incomplete because it cannot be expressed physically with classical terminology and that there must be another way to interpret what is observed that has a wider scope. Qm was formed over many years by consensus as a statistical description of nature. This is especially true of quantum optics which evolved in a rather erratic manner with much confusion before arriving at a consensus. (See R. Hanbury Brown The Intensity Interferometer) In the end a bunch of physicists got together and decided that a detection event is a photon without a shred of hard physical evidence to confirm it. It seems to me that deciding questions of what is real or true, i.e. physical questions, should not be left to such a tenuous process. Although the statistical interpretation used by qm is internally consistent it is not consistent at all when compared to the evolution in space and time of all physical processes (the correspondence principle is a cheap attempt to make it consistent everywhere). What make me so sure? Because it has happened before.

It is not necessary that these hypotheses be true. They need not even be likely. This one thing suffices, that the calculation to which they lead agree with the result of observation. Preface to “On the Revolutions of the Celestial Spheres” by Nicolaus Copernicus 1543

 

[Cthugha]

These disputes are caused by differences in language. You are using quantum speak while I use physical speak.

I do not think so.

Momentum is not an averaged quantity in physical speak. It is applied instantaneously.

It is not even clear to me about which scenario or experiment you are talking.

However, my purpose in starting this thread was not to change quantum speak but to point out that it is incomplete because it cannot be expressed physically with classical terminology

Sorry, but that does not make sense. QM is more advanced than classical mechanics. Of course one will then also need an adequate terminology that goes beyond that of classical mechanics.

This is especially true of quantum optics which evolved in a rather erratic manner with much confusion before arriving at a consensus. (See R. Hanbury Brown The Intensity Interferometer)

The HBT experiment was performed before the field of quantum optics even existed. Although it is sometimes termed the first experiment in quantum optics, giving it that name is a bad idea because the HBT-effect is entirely classical. Also it did not take too long to arrive at a consensus. The experiment by Hanbury Brown and Twiss, the questions raised by Brannen and Ferguson and the reply by Purcell all happened within one year, 1956. The quantum treatment of the effect has been discussed by Fano already in 1961.

In the end a bunch of physicists got together and decided that a detection event is a photon without a shred of hard physical evidence to confirm it.

It has been pointed out to you three times now that this is simply not true. You can easily check the higher order moments of a light fields and find out whether a detection event corresponds to a single photon Fock state or something entirely different. Having g^{(2)}(0)=g^{(3)}(0)=...=g^{(n)}(0)=0 is a strict and an unambiguous criterion for having a single photon Fock state. If you have some other peer-reviewed publications that state otherwise please present them.

Although the statistical interpretation used by qm is internally consistent it is not consistent at all when compared to the evolution in space and time of all physical processes

Again, please provide an example. I do not have the slightest idea what you mean.

 

[nortonian]

It is not even clear to me about which scenario or experiment you are talking.

Momentum exchange is instantaneous for particle collisions.

QM is more advanced than classical mechanics. Of course one will then also need an adequate terminology that goes beyond that of classical mechanics.

Yes, of course

it did not take too long to arrive at a consensus. The experiment by Hanbury Brown and Twiss, the questions raised by Brannen and Ferguson and the reply by Purcell all happened within one year, 1956. The quantum treatment of the effect has been discussed by Fano already in 1961.

As Hanbury Brown described it there were false starts, misunderstandings, and some initial confusion before arriving at a consensus.

It has been pointed out to you three times now that this is simply not true. If you have some other peer-reviewed publications that state otherwise please present them.

Of course no evidence exists that disproves qm. I am talking about a lack of evidence with respect to particle properties, a deficiency. The term 'photon' is used loosely in qm as has been recognized. There is no optical experiment similar to the photoelectric effect that indicates either by energy or momentum exchange that detections may be identified with single photons. Conservation of energy and momentum are applied statistically in interference experiments. This is not acceptable for a physically consistent theory.

Again, please provide an example. I do not have the slightest idea what you mean.

In a consistent theory it would not be necessary to define an arbitrary transition between quantum and classical by introducing a correspondence principle.

 

[Cthugha]

I am talking about a lack of evidence with respect to particle properties, a deficiency. The term 'photon' is used loosely in qm as has been recognized. There is no optical experiment similar to the photoelectric effect that indicates either by energy or momentum exchange that detections may be identified with single photons.

And I told you four times now that antibunching IS an accepted and unambiguous way to identify single photons. Where is your problem with that? Please provide some arguments why you think it is not enough.

 

[nortonian]

And I told you four times now that antibunching IS an accepted and unambiguous way to identify single photons. Where is your problem with that? Please provide some arguments why you think it is not enough.

Detection devices sample a volume of space-time much greater than the theoretical size of a photon. Because of this there may be errors in the physical interpretation of data from anti-bunching experiments. This has occurred in the past in other areas. For example, Loudon (2000) in the introduction of his book asserts that

“Taylor (1909) failed to find any changes from the classical fringes of a Young interferometer when the light source was so feeble that only one photon at a time was present in the apparatus”.

There are several errors and/or omissions with this statement:
1. Taylor calculated photon number by comparing it with average light intensity, however the fluctuation of photon density in the light beam is and always will be unknown because detectors are not perfect recording devices.
2. Photographic emulsions depend on the developability of silver bromide crystals to record the arrival of photons. This occurs in two stages lasting approximately 10-6 sec, and is characterized by the ejection of an electron and subsequent neutralization of a silver atom. ( C.E.K.Mees & T.H. James, The Theory of the Photographic Process, (MacMillan, NY), 1966.) The chemical properties of the crystals together with quantum efficiency of film have been used to calculate the estimated number of photons required to develop a silver halide crystal and found to be approximately 100 photons. (P. Kowaliski, Applied Photographic Theory (Wiley, NY), 1972.) Taylor did not know this so his experiment is flawed.
3. A more recent study has found no interference fringes even after 336 hours of exposure with a photodetector, a finding which directly contradicts the idea that a photon interferes only with itself. (E. Panarella (1986). "Quantum uncertainties", in W.M. Honig, D.W. Kraft, & E. Panarella (Eds.) Quantum Uncertainties: Recent and Future Experiments and Interpretations, (p. 105) New York: Plenum Press.)

If Loudon is unaware of these properties of film then how do I know that the photodetection process was properly analyzed? I have found no analysis of its physical properties in his book. The correct interpretation of anti-bunching and other quantum optical experiments is based on the physical nature of detections and is therefore suspect unless these questions can be resolved.

 

[lugita15]

nortonian, rather than getting bogged down in the weeds of how we know a photon detection is really a photon detection, let me ask you this. The proof in the Herbert link I gave you just involves correlations of detector clicks, whatever is causing those clicks. The point of the proof is that no local hidden variable theory can explain the correlations of detector clicks predicted by QM. Do you agree with this conclusion?

 

[Cthugha]

Detection devices sample a volume of space-time much greater than the theoretical size of a photon.

This completely depends on the experimental setup. You have detectors with large and small area and (while size is ill defined) the volume on which a photon is localized tends to be on the order of the coherence volume which can vary drastically.

Because of this there may be errors in the physical interpretation of data from anti-bunching experiments. This has occurred in the past in other areas. For example, Loudon (2000) in the introduction of his book asserts that
There are several errors and/or omissions with this statement:
1. Taylor calculated photon number by comparing it with average light intensity, however the fluctuation of photon density in the light beam is and always will be unknown because detectors are not perfect recording devices.

This is plain wrong. It is non-trivial to reconstruct the whole photon number statistics because detectors are almost never ideal. However, the fluctuations can be measured very well as the ratio of the fluctuations to the mean photon number can be measured quite well and is independent of detector efficiency. This is why people always measure g^{(2)}(0) and not the whole photon number distribution.

2. Photographic emulsions depend on the developability of silver bromide crystals to record the arrival of photons. This occurs in two stages lasting approximately 10-6 sec, and is characterized by the ejection of an electron and subsequent neutralization of a silver atom. ( C.E.K.Mees & T.H. James, The Theory of the Photographic Process, (MacMillan, NY), 1966.) The chemical properties of the crystals together with quantum efficiency of film have been used to calculate the estimated number of photons required to develop a silver halide crystal and found to be approximately 100 photons. (P. Kowaliski, Applied Photographic Theory (Wiley, NY), 1972.) Taylor did not know this so his experiment is flawed.

Yes, but who cares? The measurement by Taylor anyway has absolutely nothing to do with showing that photons have a particle nature. Also nobody uses photographic emulsions in measurements of photon number statistics. One uses avalanche photodiodes for that purpose.

3. A more recent study has found no interference fringes even after 336 hours of exposure with a photodetector, a finding which directly contradicts the idea that a photon interferes only with itself. (E. Panarella (1986). "Quantum uncertainties", in W.M. Honig, D.W. Kraft, & E. Panarella (Eds.) Quantum Uncertainties: Recent and Future Experiments and Interpretations, (p. 105) New York: Plenum Press.)

The ideas of photons interfering only with themselves as proposed way back by Dirac was already refuted in the 60s. Roy Glauber formulated a funny punch at Dirac's famous statement in some of his publications, maybe even in his Nobel lecture. I need to check that. The idea that there is also multi-photon interference is well known, but this is something you do not see in a simple double slit experiment. Also whether or not you see an interference pattern in a double slit experiment also depends on the distance between source and slit and the size of the light source. I do not know what your experiment is aiming at. Anyway, it does not really matter. Such experiments are not the ones used to validate the natur e of photons.

If Loudon is unaware of these properties of film then how do I know that the photodetection process was properly analyzed? I have found no analysis of its physical properties in his book. The correct interpretation of anti-bunching and other quantum optical experiments is based on the physical nature of detections and is therefore suspect unless these questions can be resolved.

You are aware that Glauber got a Nobel prize for the theory of optical coherence and the physics of optical detectors? Read his work (or his Nobel lecture for an easy introduction) or a good book (Mandel/Wolf is the bible of quantum optics, for beginners Fox's introduction to quantum optics is also ok and maybe easier to understand). Talking about photographic films in connection with experiments which tell us nothing about photon statistics is throwing red herrings. The key signature of the photon nature is antibunching and the necessary physics about detectors can be found in the books and publications I mentioned. If you find any flaws in these that is a good starting point for discussion. Just wrongly claiming that detectors are not understood is not.

 

[nortonian]

nortonian, rather than getting bogged down in the weeds of how we know a photon detection is really a photon detection, let me ask you this. The proof in the Herbert link I gave you just involves correlations of detector clicks, whatever is causing those clicks. The point of the proof is that no local hidden variable theory can explain the correlations of detector clicks predicted by QM. Do you agree with this conclusion?

Yes, I agree, but I do not think it is significant with respect to locality because it has to do with detections not with the causes of the detections.

I do not know what your experiment is aiming at. Anyway, it does not really matter. Such experiments are not the ones used to validate the natur e of photons.

Talking about photographic films in connection with experiments which tell us nothing about photon statistics is throwing red herrings. The key signature of the photon nature is antibunching and the necessary physics about detectors can be found in the books and publications I mentioned. If you find any flaws in these that is a good starting point for discussion. Just wrongly claiming that detectors are not understood is not.

For you a photon does not exist until it is observed. For me it is impossible to observe a single optical photon because more than one photon is needed to create a detection event. The experiment described in 3 proves this for interference effects. The experiments in 2 were able to prove it for photographic film in general because the development process occurs very slowly. It probably cannot be proven for photodiodes because the reaction time is quicker. You seem to think I am trying to say that qm is wrong. Not at all. I just want it to be made clear that there is a physical difference between what causes a detection and the detection itself. I have not seen any published work that attempts to distinguish between them. Why is that important? Because it deals with physical reality and locality. If qm wants to draw conclusions about what is real it had better analyze all aspects of an experiment, not just what it chooses to.

 

[Cthugha]

For you a photon does not exist until it is observed. For me it is impossible to observe a single optical photon because more than one photon is needed to create a detection event. The experiment described in 3 proves this for interference effects.

This is not correct. The experiment in 3 shows that more than 1 photon is needed to create a detection event for the detector used.

The experiments in 2 were able to prove it for photographic film in general because the development process occurs very slowly.

Indeed photographic film typically does not show single photon sensitivity. That is generally accepted. However, it is trivial that detectors without single-photon sensitivity like film or most CCDs are not able to detect single photons. This is why one uses detectors with single-photon sensitivity or even the ability to resolve photon numbers for experiments where single photons matter.

It probably cannot be proven for photodiodes because the reaction time is quicker. You seem to think I am trying to say that qm is wrong. Not at all. I just want it to be made clear that there is a physical difference between what causes a detection and the detection itself. I have not seen any published work that attempts to distinguish between them.

No, I am just saying that you are arguing from a standpoint which roughly corresponds to the beginning of the seventies. I have given you plenty of references on detector theory, most prominently the Mandel/Wolf and references therein. If you choose to ignore them, I cannot help you much. There are plenty of publications about SPADs and single photon sensitivity.

Why is that important? Because it deals with physical reality and locality. If qm wants to draw conclusions about what is real it had better analyze all aspects of an experiment, not just what it chooses to.

You always fall back to discussing detectors which are not sensitive to single photons and completely ignore like 35 years of publications on detectors like avalanche photodiodes which are sensitive to single photons. I said before that antibunching is THE key signature of single photons. Perfect antibunching is impossible to measure using detectors which are not single photon sensitive.

 

[nortonian]

The experiment in 3 shows that more than 1 photon is needed to create a detection event for the detector used.

No, it shows that more than one photon is needed for interference. The complete experiment was as follows: The initial step in the experiment was to produce a diffraction pattern using coherent light and a 20 second exposure time. A filter was then inserted in the beam so that 2.5 hours were required to obtain an equivalent intensity. No light at all was registered by the film. Exposure time was increased to 17.5 hours and a nearly 10 fold increase in intensity before the film registered the presence of the light beam. A diffraction pattern was still not observed. Even by increasing the exposure to 336.3 hours and a 100 fold increase in intensity the expected diffraction pattern could not be obtained. The same result was also obtained by using a detector of the photoemissive type.

Indeed photographic film typically does not show single photon sensitivity. That is generally accepted.

Then why did Loudon use Taylor's experiment, which uses film, as proof of single photon interference in his textbook?

However, it is trivial that detectors without single-photon sensitivity like film or most CCDs are not able to detect single photons. This is why one uses detectors with single-photon sensitivity or even the ability to resolve photon numbers for experiments where single photons matter.

You seem to be saying that single photon interference does not occur for film but it can occur in experiments with improved detectors like the ones Mandel describes. I don't see why interference should depend on what detector is used. Either you are making a distinction between the terms "photon" and "one-photon state", or you are saying that if SPAD detectors were used in experiment 3 they would detect an interference pattern.

I have given you plenty of references on detector theory, most prominently the Mandel/Wolf and references therein.

Please be patient.

 

[lugita15]

Yes, I agree, but I do not think it is significant with respect to locality because it has to do with detections not with the causes of the detections.

But the whole point of the proof is to show that whatever is causing the detections can NOT be described by local hidden variables.

 

[Cthugha]

No, it shows that more than one photon is needed for interference. The complete experiment was as follows: The initial step in the experiment was to produce a diffraction pattern using coherent light and a 20 second exposure time. A filter was then inserted in the beam so that 2.5 hours were required to obtain an equivalent intensity. No light at all was registered by the film. Exposure time was increased to 17.5 hours and a nearly 10 fold increase in intensity before the film registered the presence of the light beam. A diffraction pattern was still not observed. Even by increasing the exposure to 336.3 hours and a 100 fold increase in intensity the expected diffraction pattern could not be obtained. The same result was also obtained by using a detector of the photoemissive type.

I routinely perform similar experiments and diffraction and interference patterns never change with intensity. The only case where this happens is when you use detectors relying on TPA (two-photon-absorption) or even multiple photon absorption. This is for example the case when you have a detector based on some semiconductor having a bandgap and use photons that have energy less than the bandgap. In that case you need to have two or more photons arriving within the coherence time of the light to create a transition and a detection event. That can basically happen for every detector that has some characteristic "activation energy" like the mentioned semiconductor detectors or photographic film when low-energy photons are used. So it would be necessary to know the wavelength of the light used and the exact kind of detectors used before one can interpret anything.

Then why did Loudon use Taylor's experiment, which uses film, as proof of single photon interference in his textbook?

I do not know. I also do not like Loudon's book, but that is a matter of taste. I just would like to point out that single photon interference does not mean that single photons are present, but that interference between different photons is not present. By the way a state containing several indistinguishable photons within the coherence volume does not qualify as having DIFFERENT photons. This is a tiny point which is often overlooked. Actually single photon interference is not the best name for the phenomenon, but it is the one which has grown historically. Also whether or not one sees interferencealso depends on the detector dimensions and time resolution compared to the spatial and temporal coherence properties of the light used.

You seem to be saying that single photon interference does not occur for film but it can occur in experiments with improved detectors like the ones Mandel describes. I don't see why interference should depend on what detector is used. Either you are making a distinction between the terms "photon" and "one-photon state", or you are saying that if SPAD detectors were used in experiment 3 they would detect an interference pattern.

I do not know experiment 3 and it is hard to tell without knowing details like wavelength and coherence time of the light used, angular size of the light source as seen by the detectors, detector resolution and so on. I can tell you that in any experiment I performed interference patterns do not vanish at reduced intensity - unless of course the signal becomes smaller than the dark count rate of the detector used. Regarding the terminology "photon" and "single-photon state" please see my last comment.

Please be patient.

No problem. One does not read the Mandel/Wolf within a day or even a week. It takes really long.

 

[nortonian]

I do not know experiment 3 and it is hard to tell without knowing details like wavelength and coherence time of the light used, angular size of the light source as seen by the detectors, detector resolution and so on. I can tell you that in any experiment I performed interference patterns do not vanish at reduced intensity - unless of course the signal becomes smaller than the dark count rate of the detector used.

I have a copy of the manuscript and will see what it says.

But the whole point of the proof is to show that whatever is causing the detections can NOT be described by local hidden variables.

I strongly suspect that a detection event is caused by the superposition of fields from many photons. There are several reasons for this.
1. A photographic detection is caused by a superposition of photons, or the fields of photons, so perhaps the same mechanism is what causes detections in other types of detectors.
2. The photon is defined as a wave-packet function whose mean energy is given by hbar times an average over its frequency components. This supports the idea of many superposed fields acting on the detector.
3. The wave packet is delocalized whereas the detection is localized. Either there is a wave function collapse, a conceptual device I prefer to avoid, or there is a local superposition of fields that causes the detection, which is preferred because it avoids non-locality.
4. The argument that a SPAD only detects single photons is a clear objection to these arguments; however, it was defined to be that way and due to uncertainty there is no way to positively distinguish between the two possibilities.
When these points are taken together it means that there is a possibility that the detections are not non-local, but rather due to em fields which always act locally. In that case the Bell theorem is not about non-locality, it is about a characteristic of the light source, or whatever other physical object is being measured.