# Is quantum mechanics a complete theory of nature?

by nortonian
Tags: mechanics, nature, quantum, theory
P: 1,563
 Quote by nortonian 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.
P: 59
 Quote by zonde 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?

 Quote by Cthugha 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.
PF Gold
P: 1,376
 Quote by nortonian 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.
 P: 390 Is quantum mechanics a complete theory of nature? No.
 PF Gold P: 1,376 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.
P: 1,583
 Quote by 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.
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.
PF Gold
P: 1,376
 Quote by lugita15 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?

 Quote by lugita15 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:
 Quote by Einstein's Reply to Criticisms: 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.
P: 59
 Quote by 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 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.
P: 1,563
 Quote by nortonian 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.

 Quote by nortonian 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.
P: 59
 Quote by Cthugha What? Which local phenomena appear non-local according to qm? I know of none.
Polarization
 Quote by Cthugha 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.

 Quote by Cthugha 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?
P: 1,563
 Quote by nortonian 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).

 Quote by nortonian 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.

 Quote by nortonian 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?
P: 59
 Quote by Cthugha 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.

 Quote by Cthugha 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
P: 1,563
 Quote by nortonian These disputes are caused by differences in language. You are using quantum speak while I use physical speak.
I do not think so.

 Quote by nortonian 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.

 Quote by nortonian 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.

 Quote by nortonian 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.

 Quote by nortonian 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.

 Quote by nortonian 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.
P: 59
 Quote by Cthugha It is not even clear to me about which scenario or experiment you are talking.
Momentum exchange is instantaneous for particle collisions.

 Quote by Cthugha 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

 Quote by Cthugha 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.

 Quote by Cthugha 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.

 Quote by Cthugha 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.
P: 1,563
 Quote by nortonian 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.
P: 59
 Quote by Cthugha 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.
 P: 1,583 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?
P: 1,563
 Quote by nortonian 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.

 Quote by nortonian 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.

 Quote by nortonian 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.

 Quote by nortonian 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.

 Quote by nortonian 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.

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