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Third Loophole Against Entanglement Eliminated

  1. Apr 24, 2013 #1
    "Third Loophole" Against Entanglement Eliminated

    http://physicsworld.com/cws/article/news/2013/apr/23/third-bell-loophole-closed-for-photons

    CW
     
    Last edited by a moderator: Apr 25, 2013
  2. jcsd
  3. Apr 24, 2013 #2

    ZapperZ

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  4. Apr 25, 2013 #3

    Demystifier

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    I don't think this result is extremely important, given that they say (my bolding):
    "There is one catch, however. To ensure that more than 67% of the pairs were detected, the experiment was done in the lab with Alice, Bob and the source near to each other. As a result, this particular experiment did not simultaneously rule out the other two loopholes. According to Giustina, closing all three in a Canary Islands experiment would be extremely difficult."
     
  5. Apr 25, 2013 #4

    ZapperZ

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    But I think you are missing the point of the experiment. The fair-sampling loophole (which is the target of the experiment) is the only one left that hasn't been closed in ANY experiment till now. The detection loophole, and the locality loophole, all have been closed in different experiments (but not simultaneously). So this was the last one.

    Of course, now, the target is to have an experiment that closes all 3 loopholes simultaneously.

    Zz.
     
  6. Apr 25, 2013 #5

    DrChinese

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    I always thought the fair sampling loophole and the detection loophole were essentially the same. Per Wineland et al (2001):

    "Early experiments to test Bell's inequalities were subject to two primary, although seemingly implausible, loopholes. The first might be termed the locality or ‘lightcone’ loophole, in which the correlations of apparently separate events could result from unknown subluminal signals propagating between different regions of the apparatus. Aspect has given a brief history of this issue, starting with the experiments of ref. 8 and highlighting the strict relativistic separation between measurements reported by the Innsbruck group. Similar results have also been reported for the Geneva experiment. The second loophole is usually referred to as the detection loophole. All experiments up to now have had detection efficiencies low enough to allow the possibility that the subensemble of detected events agrees with quantum mechanics even though the entire ensemble satisfies Bell's inequalities. Therefore it must be assumed that the detected events represent the entire ensemble; a fair-sampling hypothesis. Several proposals for closing this loophole have been made; we believe the experiment that we report here is the first to do so."

    So I understood the Zeilinger et al experiment to be the first to close this loophole using photons. The significance of this (in my puny mind) is that one can envision extending this in a future experiment such that the locality loophole is closed simultaneously. That could not be accomplished with the massive particles used in the Wineland et al study.
     
  7. Apr 25, 2013 #6

    DrChinese

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    In the referenced paper, they say:

    "The two other main assumptions include 'locality' and 'freedom of choice'."

    I don't consider freedom of choice to be a loophole in this type of experiment. Freedom of choice could be equally invoked for ANY scientific experiment as a loophole. So I don't consider it "scientific" at all. But that is just my opinion.
     
  8. Apr 25, 2013 #7

    Demystifier

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    You mean any experiment with PHOTONS, right? Because, I think, it has been closed with charged particles.
     
  9. Apr 25, 2013 #8

    ZapperZ

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    Sorry, yes, with photons. Obviously the fair-sampling issue with charged particles makes no sense since we are not faced with the detection issue there as we do with photons.

    Zz.
     
  10. Apr 25, 2013 #9

    Cthugha

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    No, but at least now all of the loopholes have been closed in a single system, not in different systems. Importance is always somewhat in the eye of the beholder, but I can see why some people will consider that an important result.
     
  11. Apr 25, 2013 #10
  12. Apr 25, 2013 #11
    I think the article's comments about those other "two" loopholes must be garbled. They refer to a 2010 experiment of Zeilinger, apparently the one described in this article:

    phys.org/news/2010-11-physicists-loopholes-violating-local-realism.html

    After explaining how they closed the "locality" loophole, this article goes on to address what they call the "freedom of choice" loophole. It says "To close the freedom-of-choice loophole, the scientists spatially separated the setting choice and the photon emission, which ensured that the setting choice and photon emission occurred at distant locations and nearly simultaneously... The scientists also added a delay to Bob's random setting choice. These combined measures eliminated the possibility of the setting choice or photon emission events influencing each other."

    Maybe I'm mis-reading it, but this seems like just more closure of the "locality" loophole. It doesn't really seem to address the freedom-of-choice loophole at all, which most people (including Bell) have always considered to be uncloseable, since (among other reasons) the setting choices will always share a common causal past. They must define the freedom-of-choice loophole differently than it has traditionally been defined, i.e., different than the "free choice" loophole that Bell described.
     
  13. Apr 25, 2013 #12
    Dr. Chinese:

    "Not to criticize but merely to understand..." (I HATE quoting Bohr but it's funny.)

    I'm gonna try to walk a fine line here and not violate Forum Rules. In the Clauser interview ( http://www.aip.org/history/ohilist/25096.html ):

    "Clauser:

    Well, I'm throwing out locality. Keeping realism and objectivity. The cornerstones are locality and realism. So chuck one, take your pick. So I'm still a realist, and what do I have to give up if I chuck locality. Well, I have to somehow propagate signals faster than the speed of light. As soon as I do that, I automatically create the possibility of causal loops. Now, in a causal loop, A sends a signal to B— And it's all in the back of Bohm's textbook on special relativity. He has a very nice appendix in there where he describes all of this. But A sends a signal to B, B to C, C to D, D sends a signal back to A. And all of the observers are moving relative to each other, and I think that at least two of the four transmissions have to be super-luminal. And then just applying standard special relativity, A gets the answer from D before he sends the signal to B. So he's reversed the time order of these events. So he doesn't like the answer he gets from D, so he doesn't send a signal to A. So it doesn't arrive at B, so it doesn't arrive at D. So he didn't get it, so therefore he can't dislike it, so he does send it. So what does this say. Well, it says, the naive question is, "Well, does he or doesn't he send the signal." He can make the decision, "I will send the signal if I don't receive a signal from D," since that occurs in the other order. So, yes, he does, and no, he doesn't. And naively, I want to say, "Well, this is clearly absurd and impossible. It cannot happen, therefore one of our assumptions must be wrong. The only new assumption was that we could propagate super-luminal signals, therefore that must be wrong." That's the standard logic. Now, let's look at this for a second. What do we have. We have yes, he did, and no, he didn't simultaneously true. History is multi-valued! Where else did we encounter a very similar dilemma. The particle could go through the first slit, or the particle could go through the second slit, but the two are mutually exclusive, but both do occur. Well, let's wake up and smell the physics for a second. Where did we get these. We got one from quantum mechanics. That was the fact that history could have gone both ways, and in fact, must have gone both ways. The other we got from special relativity, which we got without knowing a lick about quantum mechanics. These are very different sources of exactly the same dilemma..."

    I caught Hell for quoting a position I did not believe (to prove a point) but here we are again. What is it about "Choice"? the Tension here is that GenRel rules in a manifestly local manner. What counts for evidence that there is more than Locality and Realism? Clauser shows that "History is Multivalued". Doesn't he?

    The Loophole discussions show that there are arguments that will support Locality Stubbornly! As I said in an earlier post, all an "Einstein" needs is, "Suppose we have an electron...". As soon as this is asserted, the EPR gang has an entrance to claim QM is "Incomplete". This is so because if it is an "Object" in Positive Space, it MUST be there when it is not observed. "And Positive Space is all we have, right?"

    My position is, "Well, no. We have more than that. That's where QM comes in." ('N before you go off on me here, this is what is asserted in Born's Probabilistic Normalization (At least in ONE Physics Textbook I have...): "But the electron has to be SOMEWHERE..." and all of these possibilities sum to "1".)


    I think Clauser's Multi-Valued Histories argument may not be "air-tight" but his thoughts and the Loophole article cited above are pointing to the solution: "How many ways do Super-Luminal signals map onto Positive Spacetime?"

    The Loophole Closures, as well as articles such as, " http://physicsworld.com/cws/article/news/2013/apr/22/spin-waves-carry-energy-from-cold-to-hot " are important! They are pointing us to consider a "something", a Symmetry Break perhaps, that will show that the Unity of the Early Universe was perhaps Super-Luminal and after the Symmetry Break, the handshake between two points to exchange information still occurs Super-Luminally, but the information exchanges occur, not Super-Luminally, but at the Speed of Light.

    But I'm now into Kook Land, math notwithstanding, and for that I apologize - "Not to criticize, but merely to understand".

    CW

    PS: To ZapperZ and Dr. Chinese: If I have stepped way over the line here, I'll edit out the offending passages as before.
     
  14. Apr 25, 2013 #13

    DrChinese

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    If the wave function has physical reality, then they are not mutually exclusive. And there are other viable interpretations too.
     
  15. Apr 25, 2013 #14

    DevilsAvocado

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    This was unexpected. DM you are highly skilled and very smart (=opposite to me) and yet you come to this conclusion? What’s the premise? Thousands of advanced experiments have verified the predictions of QM and NOT ONE has shown the contrary, and all loopholes have been closed individually.

    What’s the hypothesis?? Photons are (without our knowledge) “intelligent science terrorist”?? Gathering before every experiment and collectively agrees on “Today’s Plot”??

    - Hey guys! Today it’s that dude Zeilinger running the silly light cone stuff! RUN LOOPHOLE #3!! :devil:

    Isn’t that more mind-boggling than Entanglement, FTL, Tachyons or whatever??

    (Even the Pilot Wave sounds like Sunday-school compared to the “Photon Terrorist Hypothesis”! :wink:)
     
  16. Apr 25, 2013 #15

    DevilsAvocado

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    I think he showed that history and science is complicated, and that not everybody understands what he’s talking about.

    AFAIK, when DrC talks about 'locality' and 'freedom of choice', it’s in the concept of so called loopholes. When Clauser talks about 'locality' vs. 'realism' it’s in the concept of EPR-Bell and the options that are left to hang on to, and the potential problems with non-locality/causality.

    I agree with DrC; 'freedom of choice' is a ridicules loophole and is basically the end of science (and life as we know it) if it were to be true. Every experiment about to be performed is determined in every microscopic detail. This means we could end all discussions right here – they would be pointless.

    With all due respect, IMHO it only shows that stubbornness is far more common than complete and rigorous knowledge.
     
  17. Apr 26, 2013 #16
    An obvious hypothesis would be that we don't understand what is going on. From that follows that all common hypotheses could be completely off track, leading to false dilemmas of the kind that DrChinese poinnted out in post 13.
     
  18. Apr 26, 2013 #17

    Demystifier

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    I am not saying that all the existing evidence for quantum non-locality is not convincing. It certainly is. What I am saying is that, given all the already existing evidence (including a closed fair sampling loophole with charged particles), this single particular paper does not increase the quality of the overall evidence dramatically. When (and I am not saying "if", but "when") one day experimentalists do find a way to close all 3 loopholes simultaneously, then it will be a much more dramatic increase of the evidence quality.
     
  19. Apr 26, 2013 #18

    DevilsAvocado

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    Thanks DM, apologies for my misinterpretation. :redface:
     
  20. Apr 26, 2013 #19

    DevilsAvocado

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    Could be, however there’s a ‘small’ problem within that logic. Mathematically we do understand exactly what’s going on, and not only that – it’s 100% compatible with the predictions of QM. And as we all know; QM is a “neat little theory” with precision equal to measuring the distance between L.A. and NYC with the accuracy of a human hair.

    So, if someone is claiming that Entanglement/EPR-Bell is wrong because “we don't understand what is going on” – this person is also claiming that QM is wrong, which naturally would be a quite ‘meaty claim’.

    I have no scientific backing – but my gut feeling is that the “Photon Terrorist Hypothesis” won’t be enough here, you’d have to rewrite the entire map between L.A. and NYC! :wink:
     
  21. Apr 29, 2013 #20
    No, not at all. Very different interpretations are possible (and already many abound) concerning the exact same predictions of what will be observed.
     
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