EPR Paradox Failure Explained for High Schoolers

[jobsism]

EPR paradox-failure?!

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.

 

[DrChinese]

The short answer is that the Heisenberg Uncertainty Principle is a fundamental consequence of quantum physics, while the assumptions of EPR are not. And quantum physics is experimentally supported in all respects to the best of my knowledge.

 

[ThomasT]

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.

You might find this paper interesting:
http://arxiv.org/PS_cache/arxiv/pdf/0706/0706.2097v2.pdf

 

[zonde]

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.

EPR paradox was not intended to bypass uncertainty principle.
EPR paradox was intended to demonstrate incompleteness of quantum mechanics.
It is more concerned with cases where you can predict something with certainty rather than cases where you can't do that.

 

[nismaratwork]

The short answer is that the Heisenberg Uncertainty Principle is a fundamental consequence of quantum physics, while the assumptions of EPR are not. And quantum physics is experimentally supported in all respects to the best of my knowledge.

To the best that any modern measurements can be made, I think you've made an accurate statement.

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

 

[jobsism]

EPR paradox was not intended to bypass uncertainty principle.
EPR paradox was intended to demonstrate incompleteness of quantum mechanics.
It is more concerned with cases where you can predict something with certainty rather than cases where you can't do that.

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

Thanks, Thomas T for the pdf, but it used rather technical terms and i could understand little of it...

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

 

[nismaratwork]

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

Thanks, Thomas T for the pdf, but it used rather technical terms and i could understand little of it...

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

Quick sidenote: I may be wrong here, but I believe that Zonde is one of those who in other threads, has rejected non-locality and Bell tests. Maybe you don't want to take his word on... anything?

 

[nonequilibrium]

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

No, I think a popular misconception is that QM ensures everything is uncertain (if that were true, this sentence would be contradictory). Like for example, QM may say you don't exactly know where the particle is, but it ensures you, for example, of the fact that the particle is somewhere. It doesn't forbid more than it forbids, which is FAR from everything.

 

[DevilsAvocado]

Can anyone please explain to me why the EPR paradox failed to bypass the uncertainty principle?

As you may already have noticed, there are several opinions around this. Some even claims that Einstein did not completely indorsed the http://plato.stanford.edu/entries/qt-epr/" (Einstein & Podolsky had a dispute after the publication). What we can say is that Einstein was not happy about the evolution of QM, and when Heisenberg and Born declared at the Solvay Conference in 1927 that the revolution was over and nothing further was needed – Einstein's skepticism turned to dismay. Einstein could not accept that space and time was removed from any underlying reality, and that QM was to be understood as a probability without any causal explanation.

From this I think we can say that Einstein with the EPR paradox aimed to show that QM was incomplete and fundamentally inadequate. According to Einstein there was a need for something else, as QM was not the appropriate starting point for constructing the new theory he thought was needed.

To grasp the "problem" with proving the uncertainty principle wrong, you can think of this macroscopic example:

Assume you have a time-variant signal, a sound wave, and you want to know the exact frequency of the signal at a given moment. This is impossible. To determine the exact frequency it’s necessary to resample the signal over time and thus lose a degree of precision in the position. In other words a sound cannot be both, the exact time (as in a short pulse) and a precise frequency, as in a continuous tone. Phase and frequency of a (sound) wave in time is analogous to the position and momentum of a (QM) wave in space.​

Einstein was of course intelligent enough to realize this, and he was not especially interested in the question of simultaneous values for incompatible quantities like position and momentum, and Einstein told Schrödinger "ist mir wurst" – literally, it's sausage to me; i.e., he couldn't care less.

Einstein was concerned with an underlying reality that had a causal explanation.

But in 1964 John Bell showed that Local Hidden Variables (LHV) is incompatible with the predictions of QM in "[URL Theorem[/URL]:

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

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

No. If you where a QM particle designed to come to work every day at eight o'clock, and this was repeated for 10 years, we could say that we have a pretty good prediction of your arrival at work, right? But this doesn’t tell us anything about what time you got out of bed, or which way you took to work. Okay? (Einstein wanted to know when you got out of bed! )

Maybe I should rephrase my doubt: As far as i understand, in the EPR paradox, the motion of one particle "somehow" affects the other. I would like to know the theory behind this "somehow" effect in detail(only the theory, not the math).

That’s the Million Dollar Question!

The solution to http://en.wikipedia.org/wiki/Bell_test_experiments" is not settled. We only know that either Locality and/or Reality have to go. That’s all.

If non-locality is proven, then my guess is that it has to have some relation to the QM http://en.wikipedia.org/wiki/Wave_function" .

My personal guess is that we need to merge QM + GR and maybe also find the solution for Quantum Gravity (QG), before we find the final solution to EPR-Bell... I guess... sort of...


P.S. nismaratwork’s sidenote is worth reading...

 

[zonde]

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

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.

Quick sidenote: I may be wrong here, but I believe that Zonde is one of those who in other threads, has rejected non-locality and Bell tests. Maybe you don't want to take his word on... anything?

I do not reject Bell tests. I reject fair sampling assumption used in photon Bell tests. And without it they are not conclusive.

 

[zonde]

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

Not necessarily.
Look you have one particle and you describe it with two non-commuting variables (A1 and B1) i.e. you have uncertainty between them. Now you have entangled particle with variables A2 and B2. There is no uncertainty between A1 and A2 and likewise between B1 and B2.
So your conclusion seems quite natural that this situation violates uncertainty principle. But there is another possibility that both A and B are not descriptions of individual particle. Say A describes individual particle but in this case B doesn't and it is description of slightly different thing.
As an example, photon polarization is property of individual particle but photon phase is not because we don't have reference for measurement of photon phase and it can be measured only relative to another photon.

If you look at technical details of photon Bell experiments you can find there that necessary condition for observation of entanglement is coherence between H and V photons. If this condition isn't met you observe correlation only between H/V polarization measurements but correlation between +45/-45 measurements (it is this other non-commuting variable for photon polarization entanglement experiments) disappears.

 

[nismaratwork]

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.


I do not reject Bell tests. I reject fair sampling assumption used in photon Bell tests. And without it they are not conclusive.

Nothing personal Zonde, but the point is that you're hardly the mainstream view, and someone who isn't familiar with your views should be made aware of that... especially once they express a failure to get your point. The bottom line is that you reject the results of the BSMs, which is the same thing as rejecting the test themselves. Most believe they're conclusive, you don't... that's your choice but you're one of two people I've met (ThomasT being the other) who believes this with any conviction once challenged with a wealth of evidence to the contrary.

Bottom line: someone who is new here deserves to know where you stand; it's not as though I called your knowledge or intelligence into question, I just pointed out that you hold a minority opinion in an arena that is related to his question. Note that I'm not going after your second post after the one I'm currently responding to, but when you hold a relatively unique opinion on a mainstream educational site, it's probably a good idea to lead with that caveat.

 

[ZapperZ]

I do not reject Bell tests. I reject fair sampling assumption used in photon Bell tests. And without it they are not conclusive.

So does that mean that you have written a rebuttal to D. W. Berry, et al., "Fair-sampling assumption is not necessary for testing local realism" Phys. Rev. A 81, 012109 (2010)?

Zz.

 

[DrChinese]

So does that mean that you have written a rebuttal to D. W. Berry, et al., "Fair-sampling assumption is not necessary for testing local realism" Phys. Rev. A 81, 012109 (2010)?

Zz.

Here is a link to the above:

http://arxiv.org/abs/0712.2490

By the way, I think there has been ample evidence that fair sampling has nothing to do with experimental results. I realize that a so-called "loophole free" test is desirable. But it will certainly be an anti-climax after the wonderful work that has been performed in recent years.

 

[DevilsAvocado]

I do not reject Bell tests. I reject fair sampling assumption used in photon Bell tests. And without it they are not conclusive.

Would you say that this test, using trapped ⁴⁰Ca⁺ ions (20 protons and 20 neutrons) and a qubit state fidelity of 99.5%, demonstrating conflict with non-contextuality according to the Kochen-Specker theorem, is conclusive?

http://arxiv.org/abs/0904.1655"[/URL]

[SIZE="3"][B]State-independent experimental test of quantum contextuality[/B]
G. Kirchmair, F. Zähringer, R. Gerritsma, M. Kleinmann, O. Gühne, A. Cabello, R. Blatt, C. F. Roos

[SIZE="1"](Submitted on 10 Apr 2009 (v1), last revised 5 May 2009 (this version, v2))
Journal reference: Nature 460, 494 (2009)
DOI: http://www.nature.com/nature/journal/v460/n7254/full/nature08172.html"

The question of whether quantum phenomena can be explained by classical models with hidden variables is the subject of a long lasting debate. In 1964, Bell showed that certain types of classical models cannot explain the quantum mechanical predictions for specific states of distant particles. Along this line, some types of hidden variable models have been experimentally ruled out. [B]An intuitive feature for classical models is non-contextuality: the property that any measurement has a value which is independent of other compatible measurements being carried out at the same time. However, the results of Kochen, Specker, and Bell show that non-contextuality is in conflict with quantum mechanics.[/B] The conflict resides in the structure of the theory and is independent of the properties of special states. It has been debated whether the Kochen-Specker theorem could be experimentally tested at all. Only recently, first tests of quantum contextuality have been proposed and undertaken with photons and neutrons. Yet these tests required the generation of special quantum states and left various loopholes open. Here, using trapped ions, we experimentally demonstrate a state-independent conflict with non-contextuality. [B]The experiment is not subject to the detection loophole and we show that, despite imperfections and possible measurement disturbances, our results cannot be explained in non-contextual terms.[/B][/QUOTE]

 

[nismaratwork]

So does that mean that you have written a rebuttal to D. W. Berry, et al., "Fair-sampling assumption is not necessary for testing local realism" Phys. Rev. A 81, 012109 (2010)?

Zz.

In the long and ongoing non-locality thread it's pretty clear that, no, Zonde has done no such thing, but that does not sway him. To be fair, I don't think he's ever claimed to have refuted it.

 

[zonde]

Nothing personal Zonde, but the point is that you're hardly the mainstream view, and someone who isn't familiar with your views should be made aware of that... especially once they express a failure to get your point. The bottom line is that you reject the results of the BSMs, which is the same thing as rejecting the test themselves. Most believe they're conclusive, you don't... that's your choice but you're one of two people I've met (ThomasT being the other) who believes this with any conviction once challenged with a wealth of evidence to the contrary.

You are not very careful with your statements.
It is quite a stretch to say that most believe photon Bell tests are conclusive. It might be reasonable to say that most believe results are convincing but it is not the same as conclusive.

Another thing is that the way you put it one might get impression that I reject raw data of Bell experiments and that is of course wrong. I am just questioning interpretation of results and nothing more.

 

[zonde]

So does that mean that you have written a rebuttal to D. W. Berry, et al., "Fair-sampling assumption is not necessary for testing local realism" Phys. Rev. A 81, 012109 (2010)?

Zz.

No, but I have counter example that satisfies their additional assumptions and still produces QM prediction for ~10% coincidence rate.
Do you want to look at it? I have posted it couple of times but I believe attachments are deleted after some time period so I will have to post it one more time.

EDIT: It turned out that second attachment is still there. Here is the https://www.physicsforums.com/showpost.php?p=2617303&postcount=439" with attachment.

 

[zonde]

Would you say that this test, using trapped ⁴⁰Ca⁺ ions (20 protons and 20 neutrons) and a qubit state fidelity of 99.5%, demonstrating conflict with non-contextuality according to the Kochen-Specker theorem, is conclusive?

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.

And it is funny that they define non-locality as contextuality:
"An intuitive feature for classical models is non-contextuality: the property that any measurement has a value which is independent of other compatible measurements being carried out at the same time."
When usual meaning of "context" is surroundings and environment. So I would say that context would be appropriate word for description of detector's state that is involved in measurement of photon under question. And non-contextuality would mean that detector's state doesn't play any role in photon measurement.

But of course formally I can define red as blue and blue as red and within some text it should be taken as valid method.

 

[ThePhysicsGuy]

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.

They deal with two completely different issues (as far as anyone at the moment knows). EPR deals with non-local transmission of quantum state, while the uncertainty principle deals with the limits of obtainable information. So, you've got two distinct issues, obtaining information vs. transmitting quantum state.

 

[nismaratwork]

You are not very careful with your statements.
It is quite a stretch to say that most believe photon Bell tests are conclusive. It might be reasonable to say that most believe results are convincing but it is not the same as conclusive.

Another thing is that the way you put it one might get impression that I reject raw data of Bell experiments and that is of course wrong. I am just questioning interpretation of results and nothing more.

Yeah, but your post in response to Zapperz is most telling, and encapsulates the problem. You don't have a sufficient rebuttal, just your opinion bolstered with what I personally (careful enough) feeble 'logic'.

 

[ZapperZ]

No, but I have counter example that satisfies their additional assumptions and still produces QM prediction for ~10% coincidence rate.
Do you want to look at it? I have posted it couple of times but I believe attachments are deleted after some time period so I will have to post it one more time.

EDIT: It turned out that second attachment is still there. Here is the https://www.physicsforums.com/showpost.php?p=2617303&postcount=439" with attachment.

How do you know your "counter example" is valid? If you think it is, then you should submit it as a rebuttal, rather than argue it here on some public forum. Or do you think it won't pass careful scrutiny by those who are experts in such a field?

Zz.

 

[nismaratwork]

How do you know your "counter example" is valid? If you think it is, then you should submit it as a rebuttal, rather than argue it here on some public forum. Or do you think it won't pass careful scrutiny by those who are experts in such a field?

Zz.

Well he posted it, if not for peer review in a journal then at least for your review. What do you think of it?

 

[DrChinese]

Well he posted it, if not for peer review in a journal then at least for your review. What do you think of it?

This forum (Quantum Physics) is not really intended for posters to present their original ideas. There is a section here for that called "Independent Research" which is moderated & reviewed.

 

[nismaratwork]

This forum (Quantum Physics) is not really intended for posters to present their original ideas. There is a section here for that called "Independent Research" which is moderated & reviewed.

Yeah, I know... I'd call my last post "entrapment" in the strictest legal sense. I'm REALLY tired of the endless lack of traction in a particular thread due to what amounts to that inappropriate use of personal theories (hint... you're not the problem.)

 

[ThomasT]

Most believe they're conclusive, you don't... that's your choice but you're one of two people I've met (ThomasT being the other) who believes this with any conviction once challenged with a wealth of evidence to the contrary.

nismaratwork, you'd better get your facts straight. Zonde (whose presentations I've found interesting and worthy of respect, even if I might not entirely agree with all his conclusions, but then I might not entirely understand them) and I have been exploring somewhat different considerations regarding Bell. He's concerned with the validity of the science. I'm concerned with the validity of the logic. I'm not sure what you're saying, or what you think, that I believe. Regarding what you think, I don't care. Regarding what you're saying, state it clearly and then back it up with some quotes or else retract it.

Regarding jobsism's questions, there have been a few answers to the point. However, nobody has explained it satisfactorily yet. If the heavyweights looking at this thread don't explain it to the OP in sufficient detail, then I will. And, yeah that's right, you don't really want that. So, let's go people -- chop chop, explain, elaborate!

 

[zonde]

How do you know your "counter example" is valid?

I tried to make it maximally lucid. There are not much where an error can hide. The model is split in four worksheets - source, Alice, Bob and result (coincidence counting). It's easy to check that locality condition is satisfied.

If you think it is, then you should submit it as a rebuttal, rather than argue it here on some public forum. Or do you think it won't pass careful scrutiny by those who are experts in such a field?

Counterexamples usually are rather very specific to argument. So my example has limited to no use outside the context of specific argument.
As I see the major problem with different arguments against local realism (including the paper mentioned) is that they are aimed at LHV models that do not justify uncertainty principle or rather simply contradict it.
My example is of the same kind of LHV models so among other considerations I see no point in promoting such approach.

If we talk about that paper you mentioned it just replaces fair sampling assumption with other assumption: "the detection efficiency factorises as a function of the measurement settings and any hidden variable"
If you look in more details it turns out that this "any hidden variable" of single particle can affect only the measurement of that single particle. That clearly ignores all the possible LHV models where collective behavior of ensemble is considered.
That way it doesn't give any arguments against direction that I consider perspective.

 

[ZapperZ]

I tried to make it maximally lucid. There are not much where an error can hide. The model is split in four worksheets - source, Alice, Bob and result (coincidence counting). It's easy to check that locality condition is satisfied.


Counterexamples usually are rather very specific to argument. So my example has limited to no use outside the context of specific argument.
As I see the major problem with different arguments against local realism (including the paper mentioned) is that they are aimed at LHV models that do not justify uncertainty principle or rather simply contradict it.
My example is of the same kind of LHV models so among other considerations I see no point in promoting such approach.

If we talk about that paper you mentioned it just replaces fair sampling assumption with other assumption: "the detection efficiency factorises as a function of the measurement settings and any hidden variable"
If you look in more details it turns out that this "any hidden variable" of single particle can affect only the measurement of that single particle. That clearly ignores all the possible LHV models where collective behavior of ensemble is considered.
That way it doesn't give any arguments against direction that I consider perspective.

Really!

If I have something that either falsifies, or shows a slight flaw in something that was published, I would submit a rebuttal because:

(1) the community needs to know since this is the way science works;
(2) I get an extra publication.

For something that has "... limited to no use.. ", you are certainly milking it pretty often. If you wish to keep using it, you must have it published. If not, I would strongly suggest that this should be the last time you refer to it, per our PF Rules.

Zz.

 

[zonde]

Really!

If I have something that either falsifies, or shows a slight flaw in something that was published, I would submit a rebuttal because:

(1) the community needs to know since this is the way science works;
(2) I get an extra publication.

For something that has "... limited to no use.. ", you are certainly milking it pretty often. If you wish to keep using it, you must have it published. If not, I would strongly suggest that this should be the last time you refer to it, per our PF Rules.

Zz.

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."

 

[nismaratwork]

nismaratwork, you'd better get your facts straight. Zonde (whose presentations I've found interesting and worthy of respect, even if I might not entirely agree with all his conclusions, but then I might not entirely understand them) and I have been exploring somewhat different considerations regarding Bell. He's concerned with the validity of the science. I'm concerned with the validity of the logic. I'm not sure what you're saying, or what you think, that I believe. Regarding what you think, I don't care. Regarding what you're saying, state it clearly and then back it up with some quotes or else retract it.

Regarding jobsism's questions, there have been a few answers to the point. However, nobody has explained it satisfactorily yet. If the heavyweights looking at this thread don't explain it to the OP in sufficient detail, then I will. And, yeah that's right, you don't really want that. So, let's go people -- chop chop, explain, elaborate!

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.

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