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Afshar's experiment

  1. Nov 27, 2007 #1
    [Mentor's note: these posts were split off from this thread, because IMO they go far beyond the original thrust of that thread.]

    :confused:But we read below from recent 2007 experiment that Einstein was correct--we do "know" what happens to electron between slit and screen, e.g., QM really is incomplete as now confirmed by experiment:
    What am I missing in this discussion ?

    Edit: Here is the 2007 publication I talk about--in peer reviewed journal of physics:
    Last edited by a moderator: Dec 2, 2007
  2. jcsd
  3. Nov 27, 2007 #2
    Ah, the old Afshar experiment (and with single photons, for what it's worth)! Rade, there are two things to note: it's bad form to overemphasize Einstein (despite his historic contribution it is flatly unscientific to look to him for authority in modern physics; in particular he was generally wrong about quantum mechanics, and it would be exceedingly tenuous to say this experiment is any different), and this Afshar's experiment is open to other interpretations than Afshar's (a basic issue is whether he would find the same results without any double slit).
  4. Nov 27, 2007 #3
    Well, I guess the term old is relative, seems like 2007 publication not so old to me. Your second note finds a possible yes answer here if you have interest:http://arxiv.org/ftp/quant-ph/papers/0702/0702210.pdf
    As to your first note..I think Einstein not need me to defend his science nor his authority to modern physics.
  5. Nov 27, 2007 #4
    By old, I mean "the Afshar experiment" is "well-known", and from the physorg description the only difference in the new experiment this year is lower intensity (which I don't find interesting because I couldn't imagine anyone expecting that to change the result, and indeed it apparently did not).

    Regards the arxiv, I'd like to point out that it's preferable to link to abstracts rather than pdf directly. The main/abstract pages not only let the user choose which format in which to download the full article, but more importantly tend to cite which peer review journal published the article (aiding the decision whether to bother at all).
  6. Nov 28, 2007 #5

    I’ll grant you the Afshar experiment created quit a buss a couple years ago, by claiming a successful “argument against Complementarity” and to refute the completeness of QM by answering the “which way” question in a stunning two slit experiment with real results.
    Technical rebuttals obviously has not prevented publication of it. Which is OK – it gives you and me real results to look at and put into proper perspective.
    So the question is: 1) have we shown a flaw in QM or 2)is this just a Magic Trick that has fooled many including Mr Afshar.
    Lets take a look:

    He produced a interference pattern with known number of photons by timing his count of individual photons going though the slits. Putting wires in the dark spots of the pattern and with a lens behind the several wires he focuses all the light back down to with to a single detector with only one of the double slits.
    Using the same time interval as before he should observe half the photons with only one slit open; BUT he sees less than that, obviously the wires are blocking some of them!
    He does the same with the other slit open – exact same results, except he needed to place a second detector near the other to capture the photon from the other slit.
    Now with both slits open both detectors detect a full count of half the photons each! Meaning we know the pattern is there at the wires because the full count means no photons hit any of the wires (kind of like knowing the moon is there without looking). He has collected photons with a known interference pattern and he Knows Which Slit They Came Through!
    ……..All right! Success time to shine Afsher’s shoes for a trip to Stockholm.

    One last question for Afsher before we buy the plane ticket.
    For any one photon he now knows which slit it came from please identify for us between which pair of wires did it go though?

    Rade unless someone can define “Which Way” rather than just “Which Slit” with something other than the HUP I’m not chipping in for the plane ride.
    You see all he did was exchange one uncertainty with a new one, in a very “Complementarity” way per Niels Bohr.
    Just a little magic miss-direction by taking your attention off of “Which Way” and putting it onto “Which Slit” only in this case it seems the magician is the one most fooled by the trick.
  7. Nov 30, 2007 #6
    Fair enough. I shall email Dr. Afshar with your comment and report back if I get an answer.

    One question of something that concerns me about your post--why is such an obvious falsification of his experiment, that is so clear to you, not so clear to the professional physicists that peer reviewed his publication ? Seems to me (if I am to take your argument seriously) that not only the magician Afshar was the fool, but the entire editorial board of the journal must then be fools--that is, if your argument holds. But you see, I find this hard to agree with when I look at who is on the editorial board--as I post below. Also, do you really believe the editor of the journal at the time of the Afshar paper, Dr. Gerard ’t Hooft, Utrecht University, The Netherlands (1999 Nobel in Physics) did not consider your comment above ? If what you claim is so obviously true, I do not see how this paper would have been sent to a group of peer physicists to review, let alone be published.

    Please understand, I am NOT trying to be rude or insulting--I only seek the facts about this experiment, I have no idea for which fools the QM bell tolls. Final question, have you addressed your concerns to Dr. 't Hooft ?


    Foundations of Physics
    An International Journal Devoted to the Conceptual Bases and Fundamental Theories of Modern Physics
    Chief Editor: G. 't Hooft
    ISSN: 0015-9018 (print version)
    ISSN: 1572-9516 (electronic version)
    Journal no. 10701
    Springer US
    Online version available
    Online First articles available

    Editorial|Description|Editorial Board
    Editorial Board
    Chief Editor:
    Gerard ’t Hooft, Utrecht University, The Netherlands

    Associate Editors:
    Paul Busch, University of York, UK;
    Dennis Dieks, Utrecht University, The Netherlands;
    Erik Verlinde, University of Amsterdam, The Netherlands;

    Editorial Board:
    Jeffrey Bub, University of Maryland, MD, U.S.A;;
    Arthur Fine, University of Washington, Seattle, U.S.A;
    Bas van Fraassen, Princeton University, NJ, U.S.A.;
    Robert Geroch, University of Chicago, IL, U.S.A.;
    GianCarlo Ghirardi, University of Trieste, Italy;
    Sheldon Goldstein, Rutgers University, NJ, U.S.A.;
    Daniel Greenberger, The City College of CUNY, NY, U.S.A.;
    Alan Kostelecky, Indiana University, IN, U.S.A
    Tim Maudlin, Rutgers University, Bloomington, U.S.A.;
    D. Carlo Rovelli, Centre de Physique Theorique de Luminy, Marseilles, France;
    Abner Shimony, Boston University, MA, U.S.A.;
    Lee Smolin, Perimeter Institute, Canada;
    C. Anton Zeilinger, University of Vienna, Austria;
    Wojciech H. Zurek, Los Alamos National Laboratory, NM, U.S
  8. Nov 30, 2007 #7
    That's a little rude, Rade. Why not just email him your own comment ("QM really is incomplete as now confirmed by experiment")?

    The journal (or the editorial board) certainly made the right decision publishing the article on Afshar's experiment, simply because its noteworthiness and controversy raise the impact of that journal (and hence increase profits). Whether Afshar's personal interpretation is actually correct is irrelevant to that decision, so it was quite unnecessary for you to recite the editors names to us.

    Since you insist only on appealing to higher authorities, rather than directly considering the actual arguments yourself, you need only check http://en.wikipedia.org/wiki/Afshar_experiment" [Broken] for links to detailed specific responses from reputable other physicists (especially Unruh). So now you need to explain why their claims should carry less weight. :biggrin:
    Last edited by a moderator: May 3, 2017
  9. Dec 1, 2007 #8
    Well, if so, then I offer a public apology to whomever may feel offended. Recall, I was not the first on this thread to imply that someone was a fool--the tone this conversation has taken just did not sit well with me. Obviously, we must wait for peer reviewed dialog and future experiments using Afshar approach to decide status of QM--not the personal opinion of posts on Physics Forum.
  10. Dec 1, 2007 #9
    I did not call Afshar “a Fool”, so please do not represent that I did. I will grant you maybe I should use “In My Opinion” and say that IMO I though he was fooled by his own experiment. Just because we may be tricked by magic, we do not consider ourselves to be fools for it.

    As I said in my post, “rebuttals obviously has not prevented publication” of Afsar and that I like that it was published because it gives “you and me real results to look at and put into proper perspective”. I like seeing real results of real experiments rather than relying on the conclusions of others.
    Peer review does not require the conclusions that Afsar draws be correct, only that they are worth reading, even if others (like R.E. Kastner) disagree. So I expect folks like Dr. Gerard ’t Hooft, Utrecht University to at time publish ideas they do not agree with.

    Yes, I have emailed the Afshar team and others before, but as self taught Local Realist doing individual research with no academic credentials in physics I can hardly expect them to treat me as a “peer” worth reading or replying to.
    But, if you know some one willing to review and recommend material based on content rather than background, even for arxiv by all means PM me.
  11. Dec 1, 2007 #10


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    You have to laff at us (and I do include myself here)... we managed to jump WAY past the original post all the way to Afshar in just a couple of posts...

    I don't take any issue with the experimental results, but his paper is hardly a refutation of QM and is certainly not proof that QM is incomplete. For QM to be incomplete, a more precise state of a system must possible. Where is it?

    You still can't beat the HUP. That is the rigorous version of Bohr's complementarity. I expect that after time, it will be clear that Afshar has created an experiment where Bohr's ideas are only being minimally challenged anyway: He places the wires at places where there are local minima expected. So naturally it doesn't change the outcomes much. I would guess that as the wires are moved into positions in which the probability of a particle being detected increases, you will see that the apparent effect disappears.

    But I will say that the editorial board you mentioned blows me away. I had never bothered to look at that before, and those names are all gods to me. :)
  12. Dec 2, 2007 #11
    OK, I trend very lightly here, and it is NOT my intent to be rude to anyone. But, IMO, this is a very important topic, so I will proceed. If the moderators of the Forum decide to remove this post, that is fine with me.

    In Post #7, a very specific critical comment concerning "which-way" vs "which-slit" was made about the Afshar et al. (2007) paper on the double-slit experimental design. Here are the links to the 2007 paper and other citations by Dr. Afshar:

    ::Afshar SS, Flores E, McDonald KF, Knoesel E. (2007). "Paradox in wave-particle duality". Foundations of Physics 37 (2): 295-305. http://arxiv.org/abs/quant-ph/0702188

    Other reports:

    ::Afshar SS (2003). "Sharp complementary wave and particle behaviours in the same welcher weg experiment". IRIMS:quant-ph/030503: 1-33. http://www.irims.org/quant-ph/030503/

    ::Afshar SS (2005). "Violation of the principle of complementarity, and its implications". Proceedings of SPIE 5866: 229-244. http://arxiv.org/abs/quant-ph/0701027

    ::Afshar SS (2006). "Violation of Bohr's complementarity: one slit or both?". AIP Conference Proceedings 810: 294-299. http://arxiv.org/abs/quant-ph/0701039

    In response to those comments from Post #7, I indicated that I would email Dr. Afshar to see if he had any response. I received permission from Dr. Afshar to post his responses. Here they are.

    At this point, I drop out of any further discussion on this issue--I will let the community of professional physicists proceed.

    Emails received by Rade (12/1/2007) from Dr. Afshar concerning comments in Post #7:

    1. Please feel free to post my words verbatim. I don't think it would resolve anything, as these issues need rigorous analysis and discussion best done through professional conferences and papers, but I see no harm in correcting a misconception even if it is on an internet forum. I just don't have the time to chime in directly myself. Many of these questions (hundreds in fact) have been addressed in my weblog when I had more time to spare couple of years ago http://irims.org/blog/index.php/questions/2004/09/25/questions_welcome#comments Regards--S

    2. R--RandallB argues that "which way" is not the same as "which slit". He is incorrect, and to make sure, he can ask Prof. Unruh, whom he seems to accept as the expert. He is also, more than welcome to write a response paper to Found. Phys., where in due course he will get his response, but rest assured, in the context of welcher-weg experiments, as that discussed between Bohr and Einstein, "which way" is exactly "which slit." I can provide various references for this assertion, some of which can be found in my papers, but let him ask Unruh for now. I hope this helps. Regards to both.--S
  13. Dec 2, 2007 #12
    Hey Rade, would you please post the exact message you sent, so that we can understand the context of that response?

    Just as an example, I don't remember RandallB ever mentioning Unruh. I know I mentioned him myself in the very post, where I warned you that it is rude to forward someone else's comments without permission (even just the lost context is enough to misrepresent the person, which is potentially slander; more could be learnt by them directing their own emails), but I mentioned him in an argument against blindly accepting someone's opinion (obviously I'd be unimpressed if you had mixed that into your email backwards as Afshar's response suggests).
  14. Dec 2, 2007 #13
    The message I sent to Dr. Afshar was to review the post--I sent him the link to the thread and asked him to review it--he read the entire thread--he read your comment about Unruh--he sent to me the response I posted above.
  15. Dec 2, 2007 #14
    Don’t know why he thinks Prof. Unruh is my reference (I assume he misread other posts as mine), don’t know Unruh have not read his stuff. I draw my own conclusions based on my own understanding of the meaning of “Bohr's complementarity” which is what the Afsher experiment claims to Violate.
    I do agree that the context of ‘welcher-weg’, as discussed between Bohr and Einstein on interference patters is correctly defined as which way through "which slit" as compared to individually observed photons forming an interference pattern. Meaning a certainty of pattern locations, in “complementarity” contrast to the uncertainty of "which slit”.

    However IMO Afsher results simple give a new and different observation of certainty vs uncertainty. Knowing "which slit" for each photon down stream of the pattern area, however that also gives a “complementarity” uncertainty of the precise slot between wires “which way” detail for individual photons passing through the interference area. Attempts to observe and regain that detail would remove the possibility of later seeing the "which slit" information in the Afsher experiment.

    Thus in my opinion reported observations by Afsher is supporting “Bohr's complementarity” concept. That is:
    - as we better ‘know’ position the more uncertain momentum.
    - OR converting the idea to a simple experiment where we are certain about the position of individual photons making a pattern on a screen as we are just as uncertain about "which slit" ie. the Bohr and Einstein discussion.
    - AND NOW THE AFSHER discussion in a new result that gains certainty about "which slit" at the cost of losing the detail of where individual photons are in the pattern area. Bohr would surly argue that is a “complementarity” uncertainty; as the wires only confirm the pattern exists but fails to provide complete which way information for individual photons.

    I think the experiment IS Valuable and am glad it has been published, I just disagree on the conclusions and that is how science should work towards a final conclusion –sorting out the disagreements.
    As to having my opinions considered in that debate, I’ll look into how to submit a response to Found. Phys. as Dr Afsher suggests. He has credentialed standing in the scientific community I don’t. Maybe I am being pessimistic but I do think that makes a difference in how submissions are treated.

  16. Dec 3, 2007 #15

    Hans de Vries

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    Some historical context about the complementarity principle and the typical "Bohr was right" and "Einstein was wrong" account of the 1927 Solvay conference might be of interest.

    This is a nice piece of historical research:

    Neils Bohr vehemently denounced Einsteins idea of the "light quantum" for almost 14 years until just shortly before the Solvay conference. That is, he supported only the "wave behavior" Then, when he finally accepted Einstein's photon it was still in the form of what seems to me a compromise with his partner Heisenberg on the Copenhagen interpretation. This is what became the "complementarity principle"

    The most orthodox form of the "complementarity principle" often heard nowadays implies that there are two different types of photons. One is a particle and the other is a wave. One can asks oneself how the "particle type" (which does not interfere) can be correctly refracted by the lens in Afshar's experiment if it has no wave behavior.... (refraction IS interference)

    In any case, Bohr's partner in the Copenhagen interpretation, Heisenberg, never mentions such an orthodox interpretation. For Heisenberg the "complementarity principle" is just a recognition of the fact that wave behavior and particle behavior are both just approximations. For instance in his book "The physical principles of Quantum Mechanics" he just briefly discusses the "complementarity principle" in 4 pages but never makes such statements as "the photon is either a wave or a particle".

    Regards, Hans
    Last edited: Dec 3, 2007
  17. Dec 5, 2007 #16

    Other than to assume it means approximations in the form of statistical uncertainties will always remain somewhere in real observations (as they do for Ashar) I may never really know what the "complementarity principle" is.

    Thanks Hans, good reference.
  18. Feb 1, 2008 #17
    Post-selecting not the same as defining a trajectory through a particular slit.

    The indirectly observed interference pattern (via the grid not diminishing the final intensity) confirms that each photon is in a superposition of slit states at that point. That interference unambiguously means each photon went through both slits. Two Schrodinger waves are in superposition, but (downstream from the grid) the corresponding photon is forced to decide which spot to land in when the beams intercept the final screen. So you can post-select for which spot. That doesn't mean you can infer that the photon in question "really" went through the corresponding slit--it went through both. See my latest paper on arxiv.org.
  19. Feb 1, 2008 #18


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  20. Feb 1, 2008 #19


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    That's indeed the point. All these errors in interpretation come from a post-experiment re-interpretation of a superposition as a statistical mixture. That's what I've been saying on that experiment for a long time now...
  21. Feb 1, 2008 #20
    although, it was peer reviewd and published in Foundations of Physics and bunch of serious phycisist stand behind it.
    You don't think Afshar has thought about all the different criticism over the last 7 years he's been doing this experiment ?
    It seems a lot of people are just arrogant towards Shariar S. Afshar cause he falsified CI & most likely MWI in a single experiment.
    Kinda like how we falsified creation when we found the first fossil record:D
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