EPR Paradox Failure Explained for High Schoolers

[nismaratwork]

I get your point.

But it seems it wouldn't be necessary to consider anything like that. With some delay I finally understood what this article is about.
It gives necessary condition that justifies fair sampling assumption. And this condition is experimentally verifiable!
So you don't have to blindly assume fair sampling, you can test it.

From conclusions of discussed paper:
"In the case where hidden variables are allowed, then the relevant condition is that the efficiency factorises as in Eq. (7). Any condition that depends on the hidden variables can not be proven to hold, because it is possible that it might be violated for values of the hidden variable that it is not possible to prepare. However, it is possible to falsify it. The great advantage of providing a necessary condition, as we have done, is that if it can be shown not to hold, then the sampling is shown to be of a form that invalidates the CHSH-Bell inequality. In contrast, if the condition that is tested is not necessary, then testing it is not useful. Showing that it does not hold does not show that the sampling is of a form that invalidates the CHSHBell inequality, and it cannot be conclusively shown to hold. Thus our results put testing of the sampling in Bell experiments [43] on a rigorous basis."

Your argument is an Ouroboros of failed logic, old arguments, and personal prejudice eating the tail of ThomasT's own (see above adjectives) arguments. Do you REALLY think this forwards your viewpoint, to simply repeat the same statements in slightly different configurations? After reading dozens and dozens of pages where Dr Chinese, Devils Avocado, RUTA and others tear it apart, I'm just amazed that you continue so blindly.

 

[DevilsAvocado]

No, it is not conclusive. The effect of manipulation crosstalk is not rigorously explored. On the good side they do some manipulations to prevent measurement crosstalk but still they treat photons (their actual measurement equipment) as classical particles and therefore you can not fully relay on their reasoning.

This is interesting. Are you claiming that all measurements of QM phenomena, to be valid, must be non-classical measurements? Only "QM measurements" for QM phenomena??

This is revolutionary... what happened to decoherence...??

I have one question though – If only "QM measurements" are valid measurements, how can we be sure of what we have finally measured??

(I take it you are not rejecting the Heisenberg uncertainty principle, also.)

And it is funny that they define non-locality as contextuality:

Noncontextuality – If a QM system possesses a property (value of an observable), then it does so independently of any measurement context, i.e. independently of how that value is eventually measured.

 

[ZapperZ]

I get your point.

But it seems it wouldn't be necessary to consider anything like that. With some delay I finally understood what this article is about.
It gives necessary condition that justifies fair sampling assumption. And this condition is experimentally verifiable!
So you don't have to blindly assume fair sampling, you can test it.

From conclusions of discussed paper:
"In the case where hidden variables are allowed, then the relevant condition is that the efficiency factorises as in Eq. (7). Any condition that depends on the hidden variables can not be proven to hold, because it is possible that it might be violated for values of the hidden variable that it is not possible to prepare. However, it is possible to falsify it. The great advantage of providing a necessary condition, as we have done, is that if it can be shown not to hold, then the sampling is shown to be of a form that invalidates the CHSH-Bell inequality. In contrast, if the condition that is tested is not necessary, then testing it is not useful. Showing that it does not hold does not show that the sampling is of a form that invalidates the CHSHBell inequality, and it cannot be conclusively shown to hold. Thus our results put testing of the sampling in Bell experiments [43] on a rigorous basis."

Er.. I don't get it. Isn't this the whole point of what I'm trying to convey, that YOUR questioning about fair sampling is actually moot if some conditions are met? And it has nothing to do with requiring 100% detection loop-hole free either. You questioned the inherent fair-sampling criteria in Bell-type measurements. This article has shown that it isn't so.

Zz.

 

[zonde]

Er.. I don't get it. Isn't this the whole point of what I'm trying to convey, that YOUR questioning about fair sampling is actually moot if some conditions are met? And it has nothing to do with requiring 100% detection loop-hole free either. You questioned the inherent fair-sampling criteria in Bell-type measurements. This article has shown that it isn't so.

This article replaces fair sampling with testable condition. Until this condition is tested interpretation of Bell tests have the status of "if". When it will be tested we will get rid of that "if". Situation will be resolved by experiment - exactly the way it should be in physics.

Fine until this condition is tested we can replace fair sampling assumption with weaker assumption that we can call ... (?) "sampling that is equivalent to fair sampling".

Is this ok?

 

[ZapperZ]

This article replaces fair sampling with testable condition. Until this condition is tested interpretation of Bell tests have the status of "if". When it will be tested we will get rid of that "if". Situation will be resolved by experiment - exactly the way it should be in physics.

Fine until this condition is tested we can replace fair sampling assumption with weaker assumption that we can call ... (?) "sampling that is equivalent to fair sampling".

Is this ok?

Yes, and what does this have anything to do with the your "counter example" that you've been trying to sell? Recall that you used it as the centerpiece as an INHERENT problem in all Bell-type experiments, even those testing the CHSH violation.

Zz.

 

[zonde]

Yes, and what does this have anything to do with the your "counter example" that you've been trying to sell?

Nothing. I thought that this paper was a no-go theorem and as a result completely misinterpreted it. And therefore I tried to argument against it using this "counter example".
But as this theorem is not a no-go theorem my "counter example" have nothing to do with it.

Recall that you used it as the centerpiece as an INHERENT problem in all Bell-type experiments, even those testing the CHSH violation.

Sorry, can't recall that.

 

[zonde]

This is interesting. Are you claiming that all measurements of QM phenomena, to be valid, must be non-classical measurements? Only "QM measurements" for QM phenomena??

No. I said classical particles not classical measurements. Please read carefully.
Classical particles don't have inherent phase. Photons have.

Noncontextuality – If a QM system possesses a property (value of an observable), then it does so independently of any measurement context, i.e. independently of how that value is eventually measured.

Then I will avoid "Noncontextuality". It seems that this term is too ambiguous.

 

[nismaratwork]

Nothing. I thought that this paper was a no-go theorem and as a result completely misinterpreted it. And therefore I tried to argument against it using this "counter example".
But as this theorem is not a no-go theorem my "counter example" have nothing to do with it.


Sorry, can't recall that.

Zonde... did you SERIOUSLY just play the "I don't recall senator" card?

 

[ThomasT]

In my view, the notion of you explaining your own views on the subject of EPR and non-locality to Zapperz is also a win, so please I would urge you to do so. This is, in essence, your chance to resolve over 80 pages of cyclical discourse with an impartial arbiter... I for one am confident that your view is not one which is correct, but beyond that it certainly doesn't meet PF requirements, anymore than Zonde's. Fire away ThomasT, I don't expect even the view of staff to change your behavior or arguments, but at least it might spare those who read and participate in related threads from dealing with identical interjections every few pages.

What are you talking about, nismaratwork? I asked you to state clearly what you think it is that I believe, since you seem so bent on associating it with Zonde's consideration(s). But you've responded in a very vague and seemingly inflammatory way. You say you're confident that my view is incorrect and yet you don't seem to know what my view is. You also say that my view "certainly doesn't meet PF requirements". What does that mean? You insult Zonde by telling the OP not to believe anything that he says about anything. Now what kind of talk is that? If you think that Zonde's concern about an aspect of the science in certain experiments is unfounded, then engage him in discussion about it.

Your post ends with the following statement/question:

You're the one who has a love affair with Malus' Law, right?... god, please, explain that.

And I again have to wonder what you're talking about. Yes, Malus Law is an empirical law that's an important component of classical and quantum optics, but what does it have to do with the OP's questions?

Anyway, can we get back on topic?

I provided a link to a paper that dealt, somewhat, with jobsism's question regarding "why the EPR paradox failed to bypass the uncertainty principle". It was a bit technical. So, let's start again with jobsism's original question.

He asked:

Can anyone please explain to me why the EPR paradox failed to bypass the uncertainty principle? I would appreciate it if minimal maths is used, because I am still a high-schooler and don't know much about higher math.

Ok, I'm not exactly sure what jobsism means by "the EPR paradox failed to bypass the uncertainty principle". So, hopefully, jobsism or somebody will clarify that.

I'm not sure what, if anything, the uncertainty principle (hup) has to do with EPR. Hopefully somebody will clarify that also.

Does the following statement by EPR depend on an application of some formulation of the hup: "when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality"? If so, is it a correct application of the hup?

If qm in general and the hup in particular are taken to apply only to experimental preparations and recorded data (the mainstream interpretation) and not to the existence or properties of an underlying reality, then how does the hup facilitate EPR's above-quoted statement?

Anyway, EPR or not, there's just no way to ascertain precisely how formal qm corresponds to an underlying reality. An underlying reality can't be talked about objectively, scientifically. This is the problem that the Copenhagen Interpretation (which includes the hup) addresses. The existence and properties of some proposed underlying reality are a matter of speculative inference and can't be definitively evaluated scientifically. When Bohr or someone else says that qm is a complete description of physical reality, I take them as referring to the physical reality that's amenable to objective, scientific study (ie., the material, instrumental preparations and recorded data). And it does seem that qm gives as complete an accounting as can be given of that physical reality.

But predicting something with certainty in QM, itself violates the uncertainty principle, doesn't it?

I don't think so. The hup expresses a quantitative, proportional relationship, mediated by h (the quantum of action) between certain, associated measurements like position and momentum, time and energy, angular position and angular momentum, etc. It says that the product of the uncertainty (the deviation from the average value of a set of measurements) of, say, a set of position measurements, and a set of momentum measurents (wrt similarly prepared systems) can't be less than h.

Wrt just position or just momentum measurements, or measurements associated with certain filter settings in Bell tests, etc., of entangled particles, then it's possible, via applicable conservation laws, to predict with certainty the outcome at A if the outcome at B is known, and vice versa.

Maybe I should rephrase my doubt: As far as i understand, in the EPR paradox, the motion of one particle "somehow" affects the other.

That was the hypothetical alternative that they dismissed, wasn't it?

I would like to know the theory behind this "somehow" effect in detail (only the theory, not the math). Am i understand that it basically is due to the wave nature of matter?

There's no mainstream theory about this, afaik. There is the de Broglie-Bohm 'theory' which exhibits certain 'nonlocal' formal transformations. But there's no way to know if this corresponds to an underlying reality. The formal nonlocality is, prima facie, a mathematical convenience that accords with knowledge of certain statistical results and ignorance of underlying mechanisms.

 

[nismaratwork]

ThomasT, having seen you play footsie for over 60 pages of the EPR thread started by Deepak Kapur, you may understand why I have no desire to engage with you AT ALL in this subject. Perhaps I have the points you make mixed with Zonde's; I admit that after reading a few dozen pages I found them nearly interchangeable... one of you continually referred to Malus' Law as though it were somehow pertinent to the issue of non-locality, BSMs and EPR being discussed.

The issue here is that now we're outside of that particular thread, and it's no longer a relatively knowledgeable group who can easily dismiss your view, and Zonde's lack of support for his. I felt it was wise to give a friendly 'heads up" as to the source of the information, baseless as it was... your entrance here was not intended or desired... at least you don't cite material you've written, but fail to submit for peer review. Was that clear enough?

You end by mentioning deBB, and refer to formal non-locality as a mathematical convenience... I believe the OP and others deserve better than such a rough and inaccurate treatment of the subject material. If you believe that, then by all means present your alternative, or evidence against non-locality which renders this a mathematical exercise. Certainly there are interpretations of QM and features of it such as non-locality, and that's predicated on a lack of understanding as to the "underlying mechanisms" to quote you. Unfortunately, that's not very informative, and would tend to lead away from the crux of the issue: Either mathematical formalism for the sake of results, or useful interpretations to form a valid ontology. You offer neither here, and without Dr. Chinese, or RUTA or others to offer a more... seasoned... approach, I felt it would be amiss to let such assertions slide.

 

[ThomasT]

ThomasT, having seen you play footsie for over 60 pages of the EPR thread started by Deepak Kapur, you may understand why I have no desire to engage with you AT ALL in this subject. Perhaps I have the points you make mixed with Zonde's; I admit that after reading a few dozen pages I found them nearly interchangeable... one of you continually referred to Malus' Law as though it were somehow pertinent to the issue of non-locality, BSMs and EPR being discussed.

The issue here is that now we're outside of that particular thread, and it's no longer a relatively knowledgeable group who can easily dismiss your view, and Zonde's lack of support for his. I felt it was wise to give a friendly 'heads up" as to the source of the information, baseless as it was... your entrance here was not intended or desired... at least you don't cite material you've written, but fail to submit for peer review. Was that clear enough?

Uh ... no. So far, the only on-topic thing you've offered, in post #5, is:

EPR was concerned with challenging the notion of action-at-a-distance.

Which Zonde countered, in post #10, with this point:

This is incorrect of course.
From EPR paper:
"For this purpose let us suppose that we have two systems, I and II, which we permit to interact from the time t=0 to t=T, after which time we suppose that there is no longer any interaction between the two parts."
So EPR uses locality as condition for their own example.

Which point you, apparently, acquiesced to, and then proceeded to write some more off-topic, off-point, and incorrect (wrt what you say I believe) stuff, and continued, in a somewhat derisive tone, with your comments about Zonde. Zonde and ZapperZ have been having a nice discussion about Zonde's concern.

As for the OP taking anybody's word for anything, I agree that he shouldn't take anybody's word for anything. But in asking questions at PF, he'll get a number of perspectives, and different ways of thinking about his concerns.
And regarding your critique of Zonde, well maybe he's wrong, but he's certainly not wrong for questioning the science involved in certain experiments. We're supposed to do that. He's concerned that certain sampling assumptions might not be well founded. I always just assumed that they were well founded, considered things in the ideal, and wondered what can be definitively inferred about an underlying reality from BI violations, as well as the form in which models of entanglement can be rendered. It does seem that we're going to have to do without realism -- at least a certain sort of explicitly local realism, and at least for the foreseeable future.

As for your contention that the contributors to this thread aren't knowledgeable enough to easily dismiss my views, well, I'd consider ZapperZ, DrChinese, ThePhysicsGuy, Zonde, mr. vodka, and DevilsAvocado to be knowledgeable enough. And while a few in that group have undoubtedly, wrt past threads, dismissed certain of my views, they've also, in the process, helped clarify lots of things.

You end by mentioning deBB, and refer to formal non-locality as a mathematical convenience... I believe the OP and others deserve better than such a rough and inaccurate treatment of the subject material. If you believe that, then by all means present your alternative, or evidence against non-locality which renders this a mathematical exercise.

There isn't, and afaik there can't be, any evidence for or against nonlocality. There are interpretations. If the more or less explicit nonlocality of deBB isn't just a mathematical contrivance, then what, in nature, does it refer to? Gravity used to be considered a nonlocal phenomenon. Now it's local.

Certainly there are interpretations of QM and features of it such as non-locality, and that's predicated on a lack of understanding as to the "underlying mechanisms" to quote you. Unfortunately, that's not very informative ...

The following is a quote from this paper, Experimental Study of A Photon as A Subsystem of An Entangled Two-Photon State, located here: http://arxiv.org/PS_cache/quant-ph/pdf/9811/9811060v1.pdf

Following the creation of the pair, the signal and idler may propagate to different directions and be separated by a considerably large distance. If it is a free propagation, the state will remain unchanged except for the gain of a phase, so that the precise momentum (energy) correlation of the pair still holds. The conservation laws guarantee the precise value of an observable with respect to the pair (not to the individual subsystems). It is in this sense, we say that the entangled two-photon state of SPDC is nonlocal. Quantum theory does allow a complete description of the precise correlation for the spatially separated subsystems, but no complete description for the physical reality of the subsystems defined by EPR. It is in this sense, we say that quantum mechanical description (theory) of the entangled system is nonlocal.

... and would tend to lead away from the crux of the issue: Either mathematical formalism for the sake of results, or useful interpretations to form a valid ontology. You offer neither here, and without Dr. Chinese, or RUTA or others to offer a more... seasoned... approach, I felt it would be amiss to let such assertions slide.

The "crux of the issue" regarding "mathematical formalism for the sake of results, or useful interpretations to form a valid ontology" might be phrased as the following question: How are you going to evaluate a proposed ontology of an underlying reality? Why do you think it is that the mainstream interpretation of qm is the instrumentalist/probabilistic interpretation?

 

[dx]

EPR's criterion of 'physical reality' is the following: "If, without in any way disturbing a system, we can predict with certainty a value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity."

Let two bodies A and B interact. If we know the momentum of A and the momentum of B before the interaction, then the momentum of A after ther interaction can be determined by a measurement of B's momentum after the interaction, without disturbing A. Thus EPR would want to assign a 'physical reality' to the momentum of A. On the other hand, If the body B is sufficiently heavy to serve as a measuring instrument, then we can determine the position of A after the interaction by measuring the position of B. Since again we have not interfered with A, this position also has an element of 'physical reality'. So apparently, the conjugate variables P and Q both have 'an element of physcial reality', even though the quantum mechanical description does not allow such a simultaneous fixation of conjugate quantities.

The solution of the paradox requires the recognition that the above measurements refer to two mutually exclusive experimental arrangements. In the arrangement suited to predict the momentum of A, there must be a latitude in the position of B which is not compatible with its use in the other experiment as a position measuring device, where it must be assumed to be heavy enough that an exchange of momentum with A does not affect its velocity. Thus, the two quantities p and q cannot be simultaneously be given unambiguous meaning, but only as part of two experimental arrangements which are mutually exclusive.

 

[DevilsAvocado]

EPR's criterion of 'physical reality' is the following: "If, without in any way disturbing a system, we can predict with certainty a value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity."

Very true. Einstein tried to show that there is an underlying reality that has a causal explanation. The Heisenberg uncertainty principle states that this is impossible. John Bell showed that Einstein was wrong, and that QM predictions and EPR-Bell experiments without any doubts verifies that Local Realism is false.

We can have non-local realism, or local non-realism, or non-local non-realism, but not local realism. This is a fact that is accepted by scientific community. Anyone giving a different view is just advocating not peer reviewed personal theories and speculations.

The Heisenberg uncertainty principle is correct. Einstein was wrong.

 

[nismaratwork]

Very true. Einstein tried to show that there is an underlying reality that has a causal explanation. The Heisenberg uncertainty principle states that this is impossible. John Bell showed that Einstein was wrong, and that QM predictions and EPR-Bell experiments without any doubts verifies that Local Realism is false.

We can have non-local realism, or local non-realism, or non-local non-realism, but not local realism. This is a fact that is accepted by scientific community. Anyone giving a different view is just advocating not peer reviewed personal theories and speculations.

The Heisenberg uncertainty principle is correct. Einstein was wrong.

Well said, and it makes me really hope that the foundations community can put something together. I can't help but believe that these debates would be less cyclical if there was something concrete to point to as an alternative to having proved what cannot be true. Unless a theory emerges which matches or exceeds QM's predictions with LHVs (impossible), the need for a framework beyond formalism may be necessary if only to calm some fractious elements.

ThomasT: I didn't intend to respond, but this is simply incorrect:

As for your contention that the contributors to this thread aren't knowledgeable enough to easily dismiss my views, well, I'd consider ZapperZ, DrChinese, ThePhysicsGuy, Zonde, mr. vodka, and DevilsAvocado to be knowledgeable enough. And while a few in that group have undoubtedly, wrt past threads, dismissed certain of my views, they've also, in the process, helped clarify lots of things.

I never said any such thing; I am referring to the list of people who ARE knowledgeable enough to easily dismiss your views, as well as Zonde's. I should also be clear that virtually anyone who is familiar with Aspect's, Bell's, and Zellinger's work is also capable of the same feat... the issue is making you or another understand that in less than 40 pages of text with you running in circles all the while. To be fair, I made a shorter list, but the point remains... please don't misrepresent what I said, especially to the point of reversing it entirely. Beyond that, I have no desire (as I said in my previous thread), to engage with you in the slightest.

 

[DrChinese]

EPR's criterion of 'physical reality' is the following: "If, without in any way disturbing a system, we can predict with certainty a value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity."

Let two bodies A and B interact. If we know the momentum of A and the momentum of B before the interaction, then the momentum of A after ther interaction can be determined by a measurement of B's momentum after the interaction, without disturbing A. Thus EPR would want to assign a 'physical reality' to the momentum of A. On the other hand, If the body B is sufficiently heavy to serve as a measuring instrument, then we can determine the position of A after the interaction by measuring the position of B. Since again we have not interfered with A, this position also has an element of 'physical reality'. So apparently, the conjugate variables P and Q both have 'an element of physcial reality', even though the quantum mechanical description does not allow such a simultaneous fixation of conjugate quantities.

The solution of the paradox requires the recognition that the above measurements refer to two mutually exclusive experimental arrangements. In the arrangement suited to predict the momentum of A, there must be a latitude in the position of B which is not compatible with its use in the other experiment as a position measuring device, where it must be assumed to be heavy enough that an exchange of momentum with A does not affect its velocity. Thus, the two quantities p and q cannot be simultaneously be given unambiguous meaning, but only as part of two experimental arrangements which are mutually exclusive.

Very nicely stated! It is the *simultaneous* existence of the non-commuting elements of reality which is at question - and is NOT embedded in quantum theory. EPR thought it was "reasonable" to assume they exist simultaneously. Reasonable, yes, but still incorrect as we now understand (a la Bell, Aspect). If you accept their incorrect assumption, you would conclude QM is incomplete. Otherwise, QM appears to be "complete" in the EPR sense.

 

[ThomasT]

If you accept their incorrect assumption, you would conclude QM is incomplete. Otherwise, QM appears to be "complete" in the EPR sense.

I know what you mean, and agree. However, just to clarify, the "EPR sense" of completeness has to do with an underlying reality, doesn't it? And, the 'qm sense' of completeness has to do with material, instrumental preparations and the resulting data, doesn't it? So, can we say that qm is complete insofar as it refers unambiguously to preparations and data, but that we have no way of knowing if it's actually a complete description of an underlying, measurement independent, reality, or even if such a reality exists?

Bringing this around to jobsism's first question, "Can anyone please explain to me why the EPR paradox failed to bypass the uncertainty principle?". I'm not sure if he's asking why EPR violated the hup, or why it didn't violate the hup, or what. I'm not even sure if the hup is applicable to the EPR scenario (a couple of posters seemed to indicate that it isn't). I'm also not sure if the situation dx described is identical to the EPR scenario. If you, or dx, or somebody, would answer these questions, it would be much appreciated.

In the meantime, although you're probably already familiar with them, the following papers might be interesting to those who aren't:

Measuring Position and Momentum Together
http://arxiv.org/PS_cache/arxiv/pdf/0804/0804.4333v1.pdf

The Standard Model of Quantum Measurement Theory: History and Applications
http://arxiv.org/PS_cache/quant-ph/pdf/9603/9603020v1.pdf

 

[ThomasT]

I never said any such thing; I am referring to the list of people who ARE knowledgeable enough to easily dismiss your views, as well as Zonde's. I should also be clear that virtually anyone who is familiar with Aspect's, Bell's, and Zellinger's work is also capable of the same feat... the issue is making you or another understand that in less than 40 pages of text with you running in circles all the while. To be fair, I made a shorter list, but the point remains... please don't misrepresent what I said, especially to the point of reversing it entirely. Beyond that, I have no desire (as I said in my previous thread), to engage with you in the slightest.

What you said, in post #40 of this thread was:

The issue here is that now we're outside of that particular thread, and it's no longer a relatively knowledgeable group who can easily dismiss your view, and Zonde's lack of support for his.

And I replied that I think that the contributors to this thread are knowledgeable enough to easily dismiss my view.

Anyway you still haven't stated what view you, apparently, think needs to be dismissed. I've asked some questions in this thread. If you can help answer them, it would be appreciated.

 

[ThomasT]

The Heisenberg uncertainty principle states that this (that there is an underlying reality that has a causal explanation) is impossible.

Not that I disagree with you DA, but the deeper meaning (beyond the statistical interpretation) of the hup has been, and still is afaik, a subject of some debate. I'm just curious where you read this, or how you (independently) came to this interpretation.

 

[ThomasT]

EPR's criterion of 'physical reality' is the following: "If, without in any way disturbing a system, we can predict with certainty a value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity."

Let two bodies A and B interact. If we know the momentum of A and the momentum of B before the interaction, then the momentum of A after ther interaction can be determined by a measurement of B's momentum after the interaction, without disturbing A. Thus EPR would want to assign a 'physical reality' to the momentum of A. On the other hand, If the body B is sufficiently heavy to serve as a measuring instrument, then we can determine the position of A after the interaction by measuring the position of B. Since again we have not interfered with A, this position also has an element of 'physical reality'. So apparently, the conjugate variables P and Q both have 'an element of physcial reality', even though the quantum mechanical description does not allow such a simultaneous fixation of conjugate quantities.

The solution of the paradox requires the recognition that the above measurements refer to two mutually exclusive experimental arrangements. In the arrangement suited to predict the momentum of A, there must be a latitude in the position of B which is not compatible with its use in the other experiment as a position measuring device, where it must be assumed to be heavy enough that an exchange of momentum with A does not affect its velocity. Thus, the two quantities p and q cannot be simultaneously be given unambiguous meaning, but only as part of two experimental arrangements which are mutually exclusive.

Thanks for weighing in, dx. My solution to the 'paradox' has been that the hup doesn't apply to the EPR scenario. But then I never really put much stock in EPR and might have been operating under a misapprehension. Anyway, in EPR isn't there a joint unambiguous measurement, p at A and q at B, then the subsequent inclusion of deduced attributes, and then on to their argument? What am I missing?

 

[dx]

I'm also not sure if the situation dx described is identical to the EPR scenario.

A situation identical to EPR can be treated as follows: Take a diaprhram with two narrow slits, and let two particles of known momentum pass through them. If the momentum of the diaphragm is known exactly before and after the particles pass through, then A = p₁ + p₂ and B = q₁ - q₂ are exactly known, which is compatible with quantum mechanics since [A, B] = 0. Therefore, if we measure p₁, then we know that p₂ = B - p₁. Or, if we measure q₁, then we know q₂ = q₁ - A. So even though we are presented with a free choice of determining either p₂ or q₂, of the second system by measuring only the first system, q₁ - A and B - p₁ do not commute.

The point is that the criterion formulated by EPR is revealed to be ambiguous in light of the actual conditions that we are faced with in atomic physics, where concepts such as 'state' and 'behavior' cannot retain their usual meaning due to the existence of the quantum of action. The feature of individuality that underlies the comprehension of atomic phenomena is irrational within the scope of classical visualization and mode of explanation. However, any attempt of extrapolation of our causal spacetime description into the atomic domain must ultimately rest on the heavy scales and clocks, whose behavior is and must be accounted for classically. Thus in judging the form that such an extrapolation can take, we are essentially involved in an analysis of the possibilities of definition and observation, with due attention paid to the quantum of action, whose consideration is inevitable in any such analysis. Such an analysis, performed by Bohr, has shown that any situation which permits a causal account of a quantum process excludes a spacetime account of that process, and vice versa. Thus, the description of physical reality provided by quantum mechanics cannot be a causal-spacetime description, but a 'complementary' description, where the role of the measuring instruments is central. In fact, the quantum mechanical formalism must be viewed simply as a tool for such a complementarity description, whose well-defined application must always refer to the exact conditions of the experiment.

 

[DrChinese]

I know what you mean, and agree. However, just to clarify, the "EPR sense" of completeness has to do with an underlying reality, doesn't it? And, the 'qm sense' of completeness has to do with material, instrumental preparations and the resulting data, doesn't it? So, can we say that qm is complete insofar as it refers unambiguously to preparations and data, but that we have no way of knowing if it's actually a complete description of an underlying, measurement independent, reality, or even if such a reality exists?

The word "complete" in this context has always been a misnomer. The idea was that EPR "proved" (wrongly as it turns out) that QM was incomplete. That never meant that QM was truly "complete" in the sense that you use it. As far as we know, QM is complete. As far as we know, a more complete theory could be forthcoming. Either of those could be correct.

 

[DevilsAvocado]

Einstein tried to show that there is an underlying reality that has a causal explanation. The Heisenberg uncertainty principle states that this is impossible.

Not that I disagree with you DA, but the deeper meaning (beyond the statistical interpretation) of the hup has been, and still is afaik, a subject of some debate. I'm just curious where you read this, or how you (independently) came to this interpretation.

Well, I have to admit that this could be labeled as my own "interpretation", sort of (... and I pray to the "old one" that it’s correct ... and after reading dx last post, I think we can say it is ).

But I was not totally guessing out of a sea of personal speculations. This is the hard-core facts:

• Einstein was involved in the development of QM, and received the 1921 Nobel Prize in Physics for his discovery of the law of the photoelectric effect.
  
  
• The photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality.
  
  
• As the QM revolution progressed, Einstein felt skepticism.
  
  
• In 1925 Werner Heisenberg introduced Matrix mechanics (describing how the quantum jumps occur) that removed space and time from any underlying reality.
  
  
• In 1926 Max Born formulated the Born rule, stating that QM was to be understood as a probability without any causal explanation.
  
  
• Now Einstein's skepticism turned to dismay, he could not accept this as the "final verdict" of QM.
  
  
• Einstein did not reject the statistics or probabilities on their own. It was the lack of any reason for an event that Einstein rejected.
  
  
• Niels Bohr was dismayed by none of the elements that troubled Einstein. He made his own peace with the contradictions by proposing a Principle of Complementarity that emphasized the role of the observer over the observed.
  
  
• The first serious attack by Einstein on the "orthodox" conception took place during the Fifth Conference of Physics at the Solvay Institute in 1927.
  
  
• In 1935 Einstein, Podolsky, and Rosen published the famous paper "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?", which was primarily authored by Podolsky, based on discussions with Einstein and Rosen, known as the EPR paradox.
  
  
• The Heisenberg uncertainty principle states that certain pairs of physical properties, such as position and momentum, cannot be simultaneously known to arbitrarily high precision.

Now, we could dive deep into a "philosophical" discussion on simultaneity, but the core is that the more precisely one property is measured, the less precisely the other can be measured.

Thus, if it is impossible to know the "whole world", not because of lack of precise measurements, but because of the nature of the system itself, we can hardly talk about "an element of a physical reality", right?

The harder we "squeeze" to pinpoint things down, the bigger effect of HUP. A striking example of this:

Walter Lewin (MIT) – The Heisenberg Uncertainty Principle

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Thus, Einstein’s ambition to show that there is an underlying reality is blocked by the Heisenberg uncertainty principle (+ Matrix mechanics). And a causal explanation is blocked by the Born rule.

QM is correct (so far).

 

[DevilsAvocado]

I can't help but believe that these debates would be less cyclical if there was something concrete to point to as an alternative to having proved what cannot be true.

Yeah, the no-go theorem causes some "trouble", as "some" want to give the impression of a "don’t-go theorem"... but behind every no-go there is (must be?) a "yes-go theorem". The problem is we don’t know what it is, yet.

 

[zonde]

The word "complete" in this context has always been a misnomer. The idea was that EPR "proved" (wrongly as it turns out) that QM was incomplete. That never meant that QM was truly "complete" in the sense that you use it. As far as we know, QM is complete. As far as we know, a more complete theory could be forthcoming. Either of those could be correct.

You can' t say this unless you have proven non-locality. If you prove non-locality then you can say that EPR describes non-physical situation when they use idea that two entangled systems stop interacting when they are spatialy separated.

 

[nismaratwork]

You can' t say this unless you have proven non-locality. If you prove non-locality then you can say that EPR describes non-physical situation when they use idea that two entangled systems stop interacting when they are spatialy separated.

I find this more than a little difficult to swallow given your response to post #34, and ZapperZ general line of questioning. I'm curious, given the inability to definitely prove any theory, just what is the standard of proof you require in this situation? I assume it's less than the impossibility of a theory that is utterly proven, and something more than simply making many right and no WRONG predictions...

 

[zonde]

I find this more than a little difficult to swallow given your response to post #34, and ZapperZ general line of questioning. I'm curious, given the inability to definitely prove any theory, just what is the standard of proof you require in this situation? I assume it's less than the impossibility of a theory that is utterly proven, and something more than simply making many right and no WRONG predictions...

First of all to test theory you have to make falsifiable prediction.
CHSH inequalities do not provide such prediction if you assume fair sampling. If CHSH inequalities are not violated it always can be asscribed to decoherence of entangled state.
So if you want to make falsifiable test you have to test fairness of sampling.

And that is what the article was about that ZapperZ mentioned.

 

[DrChinese]

First of all to test theory you have to make falsifiable prediction. CHSH inequalities do not provide such prediction if you assume fair sampling. If CHSH inequalities are not violated it always can be asscribed to decoherence of entangled state.

The CHSH test, like most Bell tests, assumes a type of fair sampling. Since the inequality IS violated, decoherence is not an issue. I am sure there is another technical point in the cited article, but really, is it worth beating to death? Not trying to be mean, but really...

 

[DevilsAvocado]

First of all to test theory you have to make falsifiable prediction.

No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.

 

[ThomasT]

Well, I have to admit that this could be labeled as my own "interpretation", sort of (... and I pray to the "old one" that it’s correct ... and after reading dx last post, I think we can say it is ).

But I was not totally guessing out of a sea of personal speculations. This is the hard-core facts: ...

Thanks DA. Just noticed these latest posts. Must read dx's post carefully, as well as yours. Will get back to you (and dx) if I don't understand or disagree with something. I agree with the way DrChinese puts it, though our phrasings of things can be a bit different and sometimes that can get confusing. Not really sure what Zonde's saying in his post #54. And last but not least I haven't completely read the papers I posted. Must run now. Thanks to all, and if jobsism, the OP, is out there: what do you think, has any of this helped? Later, TT.

 

[DevilsAvocado]

dx & DrC, or anyone else who knows what he’s talking about.

I have been thinking about the Heisenberg uncertainty principle. Could we make this analogy?

Assume we want to know the exact frequency of a sound wave at an exact moment. To determine the exact frequency it’s necessary to resample the signal over time and thus lose a degree of precision in the position. Therefore it’s impossible to get exact values for both, independently of measurement method.

This is not a problem for cars, humans, leopards or billiard balls etc, since they are well defined solid objects.

According to QM, all microscopic particles are to be treated as a wave function, or wave packet (before measurement):

[PLAIN]http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/Wave_packet_%28no_dispersion%29.gif/300px-Wave_packet_%28no_dispersion%29.gif

Thus we will have exactly the same problem as with the sound wave. The position of a microscopic particle is uncertain – it could be anywhere along the wave packet.

The explicit premise of Hidden Variable interpretations is value definiteness:

All observables defined for a QM system have definite values at all times.​

Since we can easily see that the Heisenberg uncertainty principle exclude value definiteness all Hidden Variable interpretations are doomed.

Correct?