Is quantum mechanics a complete theory of nature?

In summary, the conversation discussed the concept of quantum entanglement and its implications on the completeness of quantum theory. The inability to specify momentum in quantum theory raises the question of whether it is incomplete. The EPR experiment and Bell's theorem were mentioned as examples of this debate. The conversation also touched on the difficulties of defining and detecting photons, and the limitations of our current understanding of quantum mechanics.
  • #1
nortonian
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The wave function represents all that can be known about a quantum system, but that usually means that we only know the energy. In the case of entanglement we know the energy but not the momentum (e.g. angular momentum) of its components. When one component of an entangled system (one spin up and one down) is measured the wave function collapses and we immediately know the spin of the other particle with a speed exceeding that of light. However, if we knew how the momentum of the quantum system was distributed to begin with we could describe the system without a need for measurement and entanglement would not be an issue. So based on the inability of quantum theory to specify momentum it seems to me that quantum theory is incomplete. And due to the uncertainty principle a complete theory is impossible.
 
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  • #2
nortonian said:
... So based on the inability of quantum theory to specify momentum it seems to me that quantum theory is incomplete.

This question has been considered. Have you already read this?

A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Physical Review 41, 777 (15 May 1935)

http://www.drchinese.com/David/EPR.pdf
 
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  • #3
You might find this information of use - http://www.perimeterinstitute.ca/News/In_The_Media/Fair_Dice:_new_research_shows_quantum_theory_complete/
 
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  • #4
Thanks for that link. I had of course read about the EPR experiment but never seen the original.

I also followed the link to the philosophical discussion of the same question which I think is a reasonable way to formulate an answer.
1. quantum mechanics is the most complete theory/description of nature that we have.
2. nature itself is the only complete description

IOW our descriptions of nature will always be inadequate, and understandably so
 
  • #5
nortonian, you may already know this but EPR is by no means the end of the story. Long after the EPR paper, J.S. Bell proved a theorem in quantum mehanics that poses some challenges to Einstein's view. "quantumtantra.com/bell2.html" is a good explanation of Bell's proof which is relatively easy to understand. Once you understand Bell's theorem, you can try to puzzle out the philosophical implications concerning quantum mechanics.
 
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  • #6
N. Herbert's description is excellent. The best I've seen. Thanks.

He concludes: After almost a century of contact with nature's peculiar quantum way of doing business we are still lacking a quantum world view that does justice to our new knowledge of the way the world really works.
 
  • #7
I always wonder if physicists aren't repeating Lord Kelvin's "predictions" that never materialized:
There is nothing new to be discovered in physics now, All that remains is more and more precise measurement.
 
  • #8
bohm2 said:
I always wonder if physicists aren't repeating Lord Kelvin's "predictions" that never materialized:
Kelvin gave a caveat to this statement, however:
The beauty and clearness of the dynamical theory, which asserts heat and light to be modes of motion, is at present obscured by two clouds. I. The first came into existence with the undulatory theory of light, and was dealt with by Fresnel and Dr Thomas Young; it involved the question, How could the Earth move through an elastic solid, such as essentially is the luminiferous ether? II. The second is the Maxwell-Boltzmann doctrine regarding the partition of energy.
The first one was the difficulties of the aether, which led to Einstein's theory of relativity. The second was the ultraviolet catastrophe, which led to quantum mechanics. We can only hope to be that prescient!
 
  • #9
funny how those two clouds obscured a vast mountain range.
 
  • #10
Lugita, I have had time to ponder on Nick Herbert's description of Bell's Theorem in your link and I have some ideas I would like to share with anyone out there whose interested to see if they make sense. In the example he uses a calcite crystal to separate a beam of light into two beams of oppositely polarized light. Photodetectors are then used for two purposes: to “count” the photons in each beam and to detect the polarization of the beam. Since you are already familiar with it I won't go into detail. I don't think the thought experiment he uses is a good one. Photons are bosons meaning that more than one can occupy the same state. One of the consequences is that photon bunching occurs in light beams and they are detected as coincidences when separated by beam splitters (Brown-Twiss effect). According to the Brown-Twiss effect when Herbert uses a calcite crystal to divide a light beam into two beams polarized at 90 degrees and measures photon coincidences he is actually dividing bunches into smaller bunches and is detecting and comparing bunches not photons. When you change the polarization of the detector (its angle) whether you detect a photon bunch may depend partially upon the size of the bunch. I also question his interpretation of detection properties. How can you define a photon to be a detection event without looking at the properties of a detector? The time required to register a single detection event by a photodetector is on the order of 10-9 seconds, and single photons have periods on the order of 10-12 seconds. By that measure there could be thousands even hundreds of thousands of "photons" in a single event.
 
  • #11
nortonian said:
According to the Brown-Twiss effect when Herbert uses a calcite crystal to divide a light beam into two beams polarized at 90 degrees and measures photon coincidences he is actually dividing bunches into smaller bunches and is detecting and comparing bunches not photons. When you change the polarization of the detector (its angle) whether you detect a photon bunch may depend partially upon the size of the bunch. I also question his interpretation of detection properties. How can you define a photon to be a detection event without looking at the properties of a detector? The time required to register a single detection event by a photodetector is on the order of 10-9 seconds, and single photons have periods on the order of 10-12 seconds. By that measure there could be thousands even hundreds of thousands of "photons" in a single event.
There are reasons to believe that there are just so many photons as we think.

I will try to explain. Let's say you place two detectors right after PDC source in two outputs. Now you measure how many single detections you have and how much of them are paired with detections in other detector. For detector you have parameter called quantum efficiency (QE) that says (in %) how many photons you can detect with this detector. If you calculate rate between single detections and paired detections using this QE parameter it agrees very well with observed rate. And second thing is that if you increase detector's QE than rate of paired detections increases as well so that for QE=100% you would have ~100% paired detections and practically no unpaired single detections.

You might want to look at this as well:
Single-photon detector characterization using correlated photons: the march from feasibility to metrology
 
  • #12
you measure how many single detections you have

Zonde you refer to "measure and detection" as though they can be equated with "photon" even though you don't say that. How do you know that a detection is a photon? Can anyone verify that without violating the uncertainty principle? The idea has also been disputed before. "arxiv.org/pdf/quant-ph/9711046" where they say that "The down conversion is, more accurately, a correlated amplification of certain modes of the zeropoint field." I am not sufficiently acquainted with the theory to understand all their arguments but I have not seen an answer to their objections. It seems that everyone wants to jump on the quantum band wagon before considering all the evidence.

In the bunching model you can keep on splitting a beam until it can't be detected and you will still have coincidences in the beams because you can never detect all of the bosons in an energy state. A detection event includes all the photons in an energy state, not just one.
 
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  • #13
Going back to my original post I think that quantum theory can include a description of its own incompleteness if we will only recognize that.
 
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  • #14
nortonian said:
Zonde you refer to "measure and detection" as though they can be equated with "photon" even though you don't say that. How do you know that a detection is a photon?
You mean, how do I know that detection is caused by photon and it is only one and undividable?
If so then I guess my answer is something like that: I do not know but any viable alternative makes no difference (at this time).

nortonian said:
The idea has also been disputed before. "arxiv.org/pdf/quant-ph/9711046" where they say that "The down conversion is, more accurately, a correlated amplification of certain modes of the zeropoint field." I am not sufficiently acquainted with the theory to understand all their arguments but I have not seen an answer to their objections.
Santos 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.”

nortonian said:
It seems that everyone wants to jump on the quantum band wagon before considering all the evidence.
I am trying to consider evidence as much as I can. And I do not want to jump anywhere.
Always ready to explain why I think that quantum entanglement has local realistic explanation. :wink:

nortonian said:
In the bunching model you can keep on splitting a beam until it can't be detected and you will still have coincidences in the beams because you can never detect all of the bosons in an energy state. A detection event includes all the photons in an energy state, not just one.
There is something missing. For coherent source there is no correlation between two outputs of beamsplitter. As I see this directly contradicts your bunching model.
 
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  • #15
StevieTNZ said:
You might find this information of use - http://www.perimeterinstitute.ca/News/In_The_Media/Fair_Dice:_new_research_shows_quantum_theory_complete/

The choice of the meaning for the word "complete" seems to be a bit strange sometimes. In that paper you linked it is taken to mean "no theory could have more predictive power than quantum mechanics", but that is hardly the mathematical definition of the word.

Compare for example with the discussions on Gödel's theorem with respect to quantum mechanics. Here, complete means that within the set of axioms used, there are true statements that cannot be proven true. With such a definition, there are strong indications (if not proofs) that any physical theory, and therefore also quantum mechanic, cannot be "complete", because it's not compatible with "consistent", which seems to be a required property.
 
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  • #16
There is another paper on detection event vs. photon by Marshall http://www.mendeley.com/research/myth-down-converted-photon/ which specifically addresses parametric down conversion.

For coherent source there is no correlation between two outputs of beamsplitter.

Right. The bunching model refers to partially coherent light. The purpose of bringing that up was to show that even if there were only one photon in a detection event it would be impossible to know that for sure (this is also true of extremely low intensity light). A detection event is similar to Maxwell's demon, a door is opened for a fraction of a second in hopes of admitting one photon. Except that the door is open one thousand times longer in time and many thousands of times wider than a single photon.

It seems that everyone wants to jump on the quantum band wagon before considering all the evidence.

What we say here is irrelevant because we don't have access to the press. I am talking about N. Herbert and all the other "experts" who choose what evidence to consider when pronouncing on the nature of reality and other questions. Maybe they are thinking about the royalties they can get in science fiction works.
 
  • #17
nortonian said:
Lugita, I have had time to ponder on Nick Herbert's description of Bell's Theorem in your link and I have some ideas I would like to share with anyone out there whose interested to see if they make sense. In the example he uses a calcite crystal to separate a beam of light into two beams of oppositely polarized light. Photodetectors are then used for two purposes: to “count” the photons in each beam and to detect the polarization of the beam. Since you are already familiar with it I won't go into detail. I don't think the thought experiment he uses is a good one. Photons are bosons meaning that more than one can occupy the same state. One of the consequences is that photon bunching occurs in light beams and they are detected as coincidences when separated by beam splitters (Brown-Twiss effect). According to the Brown-Twiss effect when Herbert uses a calcite crystal to divide a light beam into two beams polarized at 90 degrees and measures photon coincidences he is actually dividing bunches into smaller bunches and is detecting and comparing bunches not photons. When you change the polarization of the detector (its angle) whether you detect a photon bunch may depend partially upon the size of the bunch. I also question his interpretation of detection properties. How can you define a photon to be a detection event without looking at the properties of a detector? The time required to register a single detection event by a photodetector is on the order of 10-9 seconds, and single photons have periods on the order of 10-12 seconds. By that measure there could be thousands even hundreds of thousands of "photons" in a single event.

I believe zonde and others have already answered this, but the short answer is that your hypothesis is experimentally refuted. The reason is that the BBo crystals that create the entangled photon pairs produce only thousands per second, which are easily resolved into individual detection events when you are looking at fast detectors. In other words, there are no bunches going into the beamsplitters. Therefore there can be no bunches coming out. Furthermore, these experiments are also done with polarizers sometime rather than splitters, no change in outcomes. Plus, the same entanglement is seen when you are looking at properties other than polarization. The fact is that each photon of the pair (Alice and Bob) heralds the arrival of the other one.

Yes, it is always technically possible that there are 2 photons being detected at EXACTLY the same time at both detectors and masking as 1, but this is far-fetched (and meaningless) in the extreme. There is no evidence of any effect like this at all. So the idea of this occurring at the calcite splitter is not viable. Unless, of course, you want to make up some new ad hoc physics.

See for example:

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

Observing the quantum behavior of light in an undergraduate laboratory
J. J. Thorn, M. S. Neel, V. W. Donato, G. S. Bergreen, R. E. Davies, and M. Beck

While the classical, wavelike behavior of light ~interference and diffraction! has been easily
observed in undergraduate laboratories for many years, explicit observation of the quantum nature of light ~i.e., photons! is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light. Spontaneously downconverted light is incident on a beamsplitter and the outputs are monitored with single-photon counting detectors. We observe a near absence of coincidence counts between the two detectors—a result inconsistent with a classical wave model of light, but consistent with a quantum description in which individual photons are incident on the beamsplitter. More explicitly, we measured the degree of second-order coherence between the outputs to be g(2)(0)50.017760.0026, which violates the classical inequality g(2)(0)>1 by 377 standard deviations.
 
  • #18
nortonian said:
... I am talking about N. Herbert and all the other "experts" who choose what evidence to consider when pronouncing on the nature of reality and other questions. Maybe they are thinking about the royalties they can get in science fiction works.

This is an out of the blue comment, and I don't see any connection to the subject matter. Around here, an expert is an expert. Not an "expert".
 
  • #19
This is an out of the blue comment, and I don't see any connection to the subject matter. Around here, an expert is an expert.

I agree.:smile:

There are 8 pages of historical developments and experimental discussions in the paper you cite but only two sentences are used to define what a “single photon” is. I don't question the accuracy of the experiments or that they are able to make good predictions. I question the assumptions that they begin with and the logic behind them. Can you cite something more basic?

I believe that the Marshall and Santos papers I cited do a better job of looking at fundamentals. Although they do not offer a more accurate theory they have the advantage that they reject non-locality. Will you comment on their argument that when the zero point field is used to describe the photon it is actually a classical model?
 
  • #20
nortonian said:
Right. The bunching model refers to partially coherent light. The purpose of bringing that up was to show that even if there were only one photon in a detection event it would be impossible to know that for sure (this is also true of extremely low intensity light). A detection event is similar to Maxwell's demon, a door is opened for a fraction of a second in hopes of admitting one photon. Except that the door is open one thousand times longer in time and many thousands of times wider than a single photon.
I am trying to understand your objections. Do you think that all the reasoning should start with something that we know for sure? And if we do not know for sure anything than we can do no reasoning, right?

But then I do not understand how this bunching model is better. Or maybe I do:
nortonian said:
I believe that the Marshall and Santos papers I cited do a better job of looking at fundamentals. Although they do not offer a more accurate theory they have the advantage that they reject non-locality. Will you comment on their argument that when the zero point field is used to describe the photon it is actually a classical model?
You believe that single-photon model somehow implies non-locality but bunching model implies locality.

Well, I do not agree. Single-photon model by itself does not conflict with local realism.
On the other hand Bell theorem applies to your bunching model just as well.
 
  • #21
nortonian said:
Going back to my original post I think that quantum theory can include a description of its own incompleteness if we will only recognize that.
It seems that it's reasonable to assume that the quantum theory is an incomplete description of physical reality. And that the incompleteness of the theory, in a certain sense, can be deduced/inferred from the theory itself. But, afaik, when people speak of the completeness of quantum theory they don't mean that it's a complete description of physical reality (After all, how could anyone ascertain that -- what might it refer to?). Rather, what they mean is that the quantum theory incorporates everything that's known about reality via quantum experimental phenomena.

So, how can your OP possibly ever be definitively answered?
 
  • #22
I am trying to understand your objections.

For my part, I am trying to understand what a photon is, but when I look at the literature I am receiving contradictory information. If we don't know for sure what a photon is then it is ridiculous to use that model to reject locality. My objections to quantum mechanics are that the fundamentals are dealt with on a purely phenomenological basis. If you can't see it it doesn't exist. To show what I mean I have checked a well-respected source from the article you cited: R. Loudon, The Quantum Theory of Light, 3rd ed. ~Clarendon, Oxford, 2000.

“The one-photon state has the important and distinctive property that it can produce only a single current pulse in the ionization of a photodetector.”

DrChinese, If we are talking about one-photon states then when you said
Yes, it is always technically possible that there are 2 photons being detected at EXACTLY the same time at both detectors and masking as 1, but this is far-fetched (and meaningless) in the extreme.
then I agree that you are right not because it is physically impossible, but because it was defined to be impossible.

Loudon also states the following:

“A one-photon excitation in such a mode (spatial mode) is distributed over the entire interferometer, including both internal paths.” page 2.

I understand this to mean that the one-photon state is delocalized and because it is in both arms at the same time it is a non-local definition. It should not be surprising that a non-local model would result in non-locality.

When quantum mechanics rejects a physical model such as bunching because it is viewed as incomplete they insist that a better model must give better predictions. IOW better predictions is more important than a local theory? We can have both locality and predictive power if we admit that it is impossible to know for sure what constitutes a detection event.

ThomasT do you equate reality with what we observe? IOW is there more to reality than what we observe?
 
  • #23
nortonian said:
For my part, I am trying to understand what a photon is, but when I look at the literature I am receiving contradictory information. If we don't know for sure what a photon is then it is ridiculous to use that model to reject locality. ...

Now you are mixing metaphors. There are a lot of ideas about what a photon is, but with none of them is there a local realistic way to explain Bell test results. So no, you will be out on your own on this objection.

As to the bunching phenomena you postulate, all you have to do is give me a specific scenario and I believe we can explain why this does not apply. Please recall that there are probably hundreds of different types of Bell tests which violate local realism, many which do not use photons at all. For example, see:

http://www.nature.com/nature/journal/v409/n6822/full/409791a0.html

Local realism is the idea that objects have definite properties whether or not they are measured, and that measurements of these properties are not affected by events taking place sufficiently far away1. Einstein, Podolsky and Rosen2 used these reasonable assumptions to conclude that quantum mechanics is incomplete. Starting in 1965, Bell and others constructed mathematical inequalities whereby experimental tests could distinguish between quantum mechanics and local realistic theories. Many experiments have since been done that are consistent with quantum mechanics and inconsistent with local realism. But these conclusions remain the subject of considerable interest and debate, and experiments are still being refined to overcome ‘loopholes’ that might allow a local realistic interpretation. Here we have measured correlations in the classical properties of massive entangled particles (9Be+ ions): these correlations violate a form of Bell's inequality. Our measured value of the appropriate Bell's ‘signal’ is 2.25 ± 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called ‘detection’ loophole.

So your model needs a little revving up to explain this. 'Cause there ain't no bunching of Beryllium. :smile:
 
  • #24
nortonian said:
If we don't know for sure what a photon is then it is ridiculous to use that model to reject locality.
Yes, it is ridiculous to reject locality. Point. Without any "if ... then ...". Please try to understand that. It has nothing to do with different models of photons.

nortonian said:
My objections to quantum mechanics are that the fundamentals are dealt with on a purely phenomenological basis. If you can't see it it doesn't exist.
Yes, I agree. They are valid objections.
 
  • #25
As to the bunching phenomena you postulate, all you have to do is give me a specific scenario and I believe we can explain why this does not apply.

Quantum mechanics (from Loudon):
The typical quantum-optical experiment produces one- or two-photon excitations described by a spatial wave-packet, with some degree of localization. The wave-packet function is expressed as an integral over contributions from waves with a range of frequencies, or wave vectors. We treat the fields as classical quantities and impose the quantization only on the field energy.

Hypothetical bunching model:
Photons are localized with a diffuse external field and a single frequency. By themselves they do not have sufficient energy to cause a detection event, but the superposition of fields of many photons leads to intensities sufficient to cause a detection event. Detections are caused by the superposed fields of photons.

Starting in 1965, Bell and others constructed mathematical inequalities whereby experimental tests could distinguish between quantum mechanics and local realistic theories. Many experiments have since been done that are consistent with quantum mechanics and inconsistent with local realism. But these conclusions remain the subject of considerable interest and debate, and experiments are still being refined to overcome ‘loopholes’ that might allow a local realistic interpretation.

It is thereby assumed that realism can be defined by a mathematical analysis of experiments. Don't you think that this is presumptuous? It seems more likely that realism is more fundamental than quantum mechanics. The problem with quantum mechanics is that it only accepts challenges to its interpretations that abide by its rules. In the Nature article there are two objections to violations of the Bell inequality: that there is a subliminal communication and that not all detections were recorded. It does not suggest what to me is the real cause, that the detection event is incorrectly interpreted. Bell's inequality is a commentary on the nature of detection events, not locality or photons. Clearly we cannot look behind the phenomena to determine the truth, but as long as that possibility exists local realism has not been disproved.

It seems that it's reasonable to assume that the quantum theory is an incomplete description of physical reality. And that the incompleteness of the theory, in a certain sense, can be deduced/inferred from the theory itself. But, afaik, when people speak of the completeness of quantum theory they don't mean that it's a complete description of physical reality (After all, how could anyone ascertain that -- what might it refer to?). Rather, what they mean is that the quantum theory incorporates everything that's known about reality via quantum experimental phenomena.

Quantum mechanics should be able to say what part of reality cannot be observed, IOW precisely define its own limitations.

You believe that single-photon model somehow implies non-locality but bunching model implies locality.

Well, I do not agree. Single-photon model by itself does not conflict with local realism.
On the other hand Bell theorem applies to your bunching model just as well.

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. If Bell was using an incorrect model then he is proving something about quantum mechanics, not reality.
 
  • #26
nortonian said:
1. Hypothetical bunching model:
Photons are localized with a diffuse external field and a single frequency. By themselves they do not have sufficient energy to cause a detection event, but the superposition of fields of many photons leads to intensities sufficient to cause a detection event. Detections are caused by the superposed fields of photons.

2. Don't you think that this is presumptuous? It seems more likely that realism is more fundamental than quantum mechanics. ... Clearly we cannot look behind the phenomena to determine the truth, but as long as that possibility exists local realism has not been disproved.

1. What you are describing is a classical picture and this model has been experimentally falsified, as I cited above. Also, please note that down converted photons do not qualify for the general excitation modes Loudon describes as they follow a very specific set of rules due to how they are collected. Recall that a single photon of a specific wavelength is split into 2 photons with twice the wavelength (half the frequency). Filters insure that improper frequencies are excluded. So the math doesn't work for there to be 2 on one side and 1 on the other.

2. No, it's not presumptuous in light of Bell. If you accept "elements of reality" as defined by EPR, you must reject local realism. Or not, if you simply reject everything you don't want to believe. (I can't assist on that side.)
 
  • #27
nortonian said:
The trouble with trying to prove quantum mechanics wrong is that they insist that you come up with better predictions.

This is a part of the scientific method in that it is considered a waste of time to come with with theories which are no better than existing theories. A few people are still in a similar denial over relativity, asserting that spacetime is actually flat. And yet no superior model supports that contention.

A better model is a better model. However, we now know that won't be one which is local realistic.
 
  • #28
DrChinese said:
1. What you are describing is a classical picture and this model has been experimentally falsified, as I cited above. Also, please note that down converted photons do not qualify for the general excitation modes Loudon describes as they follow a very specific set of rules due to how they are collected. Recall that a single photon of a specific wavelength is split into 2 photons with twice the wavelength (half the frequency). Filters insure that improper frequencies are excluded. So the math doesn't work for there to be 2 on one side and 1 on the other.

2. No, it's not presumptuous in light of Bell. If you accept "elements of reality" as defined by EPR, you must reject local realism. Or not, if you simply reject everything you don't want to believe. (I can't assist on that side.)

1. It is not a classical model. Quantization is imposed on energy absorption by way of classical field superposition and on energy emission by way of electron transition. As far as down converted photons, it seems we have a misunderstanding. What you call a photon I am calling a detection event caused by classical superposition of fields. Quantum mechanics has defined them to be the same: photon absorption = photon emission. How do you know energy absorption and electron decay are symmetric processes? They are not simultaneous events.
2.From my post #4
1. quantum mechanics is the most complete theory/description of nature that we have.
2.nature itself is the only complete description
From my last post:
It seems more likely that realism is more fundamental than quantum mechanics.

You didn't challenge my earlier post so why now?


DrChinese said:
This is a part of the scientific method in that it is considered a waste of time to come with with theories which are no better than existing theories. A few people are still in a similar denial over relativity, asserting that spacetime is actually flat. And yet no superior model supports that contention.

A better model is a better model. However, we now know that won't be one which is local realistic.

You believe it is not a better theory to preserve local realism. I believe it is a better theory irrespective of whether better predictions are obtained. What is wrong with striving for a theory with local realism so long as experimental predictions are obeyed? I don't think this is similar to disagreements with SR at all since curved space-time can be experimentally observed. Quantum mechanics says it is observing photons but no optical experiment can prove that.

The only reason you know that there will be no local realistic model is because it was defined to be non-local.
“A one-photon excitation in such a mode (spatial mode) is distributed over the entire interferometer, including both internal paths.” Loudon
 
  • #29
Important things first:

nortonian said:
“The one-photon state has the important and distinctive property that it can produce only a single current pulse in the ionization of a photodetector.”

This is the correct trademark of identifying single photons!

nortonian said:
Hypothetical bunching model:
Photons are localized with a diffuse external field and a single frequency. By themselves they do not have sufficient energy to cause a detection event, but the superposition of fields of many photons leads to intensities sufficient to cause a detection event. Detections are caused by the superposed fields of photons.

That is NOT how bunching works. Bunching occurs for thermal or similar light (but not for coherent or non-classical) and a similar process occurs in situations when two photons start out in different states and can end up in the same state. It does not happen on any occasion, especially there is no tendency for these two photons to stay in the same state. Also the timescale over which bunching occurs is roughly the coherence time of the light which is typically in the picosecond to femtosecond range for SPDC and therefore pretty short.

nortonian said:
DrChinese, If we are talking about one-photon states then when you said
DrChinese said:
Yes, it is always technically possible that there are 2 photons being detected at EXACTLY the same time at both detectors and masking as 1, but this is far-fetched (and meaningless) in the extreme.
then I agree that you are right not because it is physically impossible, but because it was defined to be impossible.

You can always easily check whether you have a single photons state or more photons present (for a state that can be prepared repeatedly of course) by placing a beam splitter in the beam and checking whether both can fire simultaneously. For a state containing two photons, you will see them fire as photons do not have the tendency to take the same exit port of a beam splitter if they entered via the same entrance port, but are independent. If you just have 1 photon, they will never fire simultaneously. This experiment has been performed and published at least a few hundred times in the community working on single photon sources. Also you could simply use photon-number resolving detectors or two-photon absorption to show that.

nortonian said:
I understand this to mean that the one-photon state is delocalized and because it is in both arms at the same time it is a non-local definition. It should not be surprising that a non-local model would result in non-locality.

This is true for some single photon states, but not for all. If you have heralded single-photon states or turnstile single photon sources, they are pretty localized.
 
  • #30
Cthugha said:
You can always easily check whether you have a single photons state or more photons present (for a state that can be prepared repeatedly of course) by placing a beam splitter in the beam and checking whether both can fire simultaneously. For a state containing two photons, you will see them fire as photons do not have the tendency to take the same exit port of a beam splitter if they entered via the same entrance port, but are independent. If you just have 1 photon, they will never fire simultaneously. This experiment has been performed and published at least a few hundred times in the community working on single photon sources. Also you could simply use photon-number resolving detectors or two-photon absorption to show that.

Thanks for explaining this better than l could. :smile:

I thought the citation might help nortonian, but he would have to read it first.
 
  • #31
nortonian said:
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?

nortonian said:
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.
 
  • #32
Cthugha said:
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.

zonde said:
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.
 
  • #33
nortonian said:
The important things are not models. They are things like momentum and time that qm uses in an inconsistent manner.

No.

nortonian said:
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.

nortonian said:
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.

nortonian said:
A proper model of the photon must be localized

Definitely not!

nortonian said:
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?

nortonian said:
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.

nortonian said:
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?

nortonian said:
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.

nortonian said:
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.

nortonian said:
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.

nortonian said:
Visualization is not possible.

That is simply wrong.

nortonian said:
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.
 
  • #34
nortonian said:
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.
 
  • #35
Cthugha said:
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.

zonde said:
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.
 

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