Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

EPR paradox-failure?

  1. Sep 9, 2010 #1
    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 im still a high-schooler and dunno much about higher math.
     
  2. jcsd
  3. Sep 9, 2010 #2

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  4. Sep 10, 2010 #3
    Re: EPR paradox-failure?!!

    You might find this paper interesting:
    http://arxiv.org/PS_cache/arxiv/pdf/0706/0706.2097v2.pdf
     
  5. Sep 10, 2010 #4

    zonde

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  6. Sep 10, 2010 #5
    Re: EPR paradox-failure?!!

    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.
     
  7. Sep 11, 2010 #6
    Re: EPR paradox-failure?!!

    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?
     
  8. Sep 11, 2010 #7
    Re: EPR paradox-failure?!!

    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?
     
  9. Sep 11, 2010 #8
    Re: EPR paradox-failure?!!

    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.
     
  10. Sep 12, 2010 #9

    DevilsAvocado

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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/" [Broken] (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 [Broken] Theorem[/URL]:
    No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.

    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! :smile:)

    That’s the Million Dollar Question! :biggrin:

    The solution to http://en.wikipedia.org/wiki/Bell_test_experiments" [Broken] 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" [Broken].

    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... :rolleyes:


    P.S. nismaratwork’s sidenote is worth reading... :wink:
     
    Last edited by a moderator: May 4, 2017
  11. Sep 13, 2010 #10

    zonde

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  12. Sep 13, 2010 #11

    zonde

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  13. Sep 13, 2010 #12
    Re: EPR paradox-failure?!!

    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.
     
  14. Sep 13, 2010 #13

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    Re: EPR paradox-failure?!!

    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.
     
  15. Sep 13, 2010 #14

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  16. Sep 13, 2010 #15

    DevilsAvocado

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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?
     
    Last edited by a moderator: May 4, 2017
  17. Sep 13, 2010 #16
    Re: EPR paradox-failure?!!

    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.
     
  18. Sep 14, 2010 #17

    zonde

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  19. Sep 14, 2010 #18

    zonde

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
    Last edited by a moderator: Apr 25, 2017
  20. Sep 14, 2010 #19

    zonde

    User Avatar
    Gold Member

    Re: EPR paradox-failure?!!

    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.
     
  21. Sep 14, 2010 #20
    Re: EPR paradox-failure?!!

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: EPR paradox-failure?
  1. EPR paradox (Replies: 2)

  2. EPR paradox (Replies: 4)

  3. On The EPR Paradox (Replies: 68)

  4. EPR paradox (Replies: 36)

  5. EPR paradox (Replies: 6)

Loading...