Talk:Afshar experiment/Archive 20

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Archive This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Contents

Enough already!

This is getting ridiculous! This talk page already has more entries than Einstein's talk page. Please refrain from posting general discussions here. This page is not a forum or a weblog. Any discussion not directly related to the article and its content/structure should be conducted elsewhere. For now, I will move any such discussion to the user page of the individuals involved, no exception.-- Prof. Afshar 07:45, 7 December 2006 (UTC)

Thanks, it is better! Danko Georgiev MD 07:50, 7 December 2006 (UTC)
Thanks from me too :) --Carl A Looper 08:06, 7 December 2006 (UTC)

Einstein will be jealous. --Carl A Looper 08:08, 7 December 2006 (UTC)

  • Finished archiving November discussions. It was a lot of work. From now on, let's stick to the guidelines on the top of this page, and keep the discussions to a minimum necessary. Thanks for your anticipated cooperation. P.S. If you think the archives can be improved please do not hesitate to do so.-- Prof. Afshar 02:50, 8 December 2006 (UTC)

2007 Conference on "What is a Photon"

For those of you who are interested, here's a link to a major conference on the nature of light where most of the giants of the field including Scully (A&M), Schleich (Ulm), Boyd (Rochester), Khrennikov (Vaxjo), Eggleton (Sydney U.), Myers (Harvard), Walmsley (Oxford), and others are attending (the papers are screened by the members of the Program Committee): THE NATURE OF LIGHT: WHAT ARE PHOTONS? (OP201) -- Prof. Afshar 03:16, 8 December 2006 (UTC)

Thanks Prof Afshar. --Carl A Looper 05:29, 8 December 2006 (UTC)

Ongoing debate

I've rearranged the ongoing debate so that all points are under the rubric of ongoing debate.

I've also clarified the principle in terms of it's origin within an epistomological framework - which was quite a revolutionary thing for the time.

I found this quote by Arthur Eddington in "The Philosophy of Physical Science". Cambridge University Press. Reprint in 1958. He is speaking about quantum theory in a chapter called "The Scope of Epistomological Method". It is but a short quote and serves only as a starting point:

"In physics everything depends on the insight with which the ideas are handled before they reach the mathematical stage"

--Carl A Looper 03:32, 9 December 2006 (UTC)

I remind you that an arXiv preprint is not a reliable source. Furthermore, the structure of the "ongoing debate" paragraph is such that it is not clear what is actually a direct quote, what is a paraphrase or what are the editor's (yours I suppose) own words. Please correct this or I will slap again an POV banner on this.--CSTAR 04:01, 9 December 2006 (UTC)
Re Ongoing Debate section.
The first point is by myself and dndn1011, with further elaboration by myself in response to the "philosophical system" characterisation - which is what I initially had there but which you questioned and for which I agree. So I've sought to make it clearer. But insofar as I have not provided additional sources I've recontextualised it as part of the "Ongoing Debate" rather than an introduction to such - which was it's original purpose - ie. I've done this to be fair, even though I don't actually think it should be recontextualised this way.
The second point is by me - and is perhaps gratutious.
In the exchange section, of the ongoing debate section, the first point is by Michael Price and the second counterpoint by me. Originally Michaels's points were framed as general critiques. But attempts to remove Michael's points (by myself and others), on the basis that it constitutes Original Research by Michael Price, were continually counter-edited (ie. put back in) by Michael Price. Rather than continuing this "getting nowhere" edit/counter edit process, I put the counterpoints in instead, and reframed the entire thing as ongoing debate. --Carl A Looper 04:47, 9 December 2006 (UTC)
Re: "arXiv preprint is not a reliable source"
I'm not sure what you mean by this. I myself haven't used any sources other than my own library of books published by various institutions. The link to "Epistomological Problems" is provided by Michael, and I have read it before in other books as well. Indeed I've probably got it buried in my library somewhere. It is the same text from which Afshar has quoted Bohr and is not in dispute as far as I understand.
My Eddington quote is just for inspiration - for anyone who might like to think beyond the idea that quantum theory was delivered by the Stork. --Carl A Looper 06:40, 9 December 2006 (UTC)
Re: I'm not sure what you mean by this. In the paragraph
Bohr's principle of complementarity is an epistimological principle. ... The historical record consists of texts from which the principle of complementarity can be reconstructed, such as "Discussion with Einstein on Epistemological Problems in Atomic Physics", in Albert Einstein: Philosopher-Scientist, P Schilpp ed (Open Court, La Salle, IL, 1949).[15][16]
Supporting ref [15] is to an arXiv paper.
I must say that that paragraph is very confusing. I think what you are trying to say is this
(although I don't necessarily agree with it)
  1. The complementarity principle as formulated by Bohr is vague.
  2. Given that it's vague, some formalizations of it could shown to fail by experiment and not contradict anything about QM.
Surprisingly I do agree with Danko on one point: The consistent histories formulation of the complemntarity principle is widely accepted as being rigorous and is (most likely) not shown to fail by Afshar's experiment.--CSTAR 15:58, 9 December 2006 (UTC)
I agree, the paragraph is very confusing and its relevance to Afshar's experiment is opaque to say the least. I moved the link to the further reading section and deleted the rest of the paragraph. Irrelevant philosophical musing about the complementarity principle are better explored at talk:complementarity (physics). We need to stay focussed on Afshar's experiment here. --Michael C. Price talk 09:55, 11 December 2006 (UTC)
Michael. Please restore the link to Epistomological Problems. This is an important historical document that defines the context in which the Afshar experiment operates. Your link to an Analog Science Fiction and Fact article is a laughable subsitute. It's own reference is precisely the very document you have removed! Please stop vandalising history to suit your own personal belief systems --Carl A Looper 02:02, 12 December 2006 (UTC)
I've now put new links to the supposed "unreliable" document and removed the laugable substitute. Please have a read. It is not there for plundering quotes. --Carl A Looper 02:40, 12 December 2006 (UTC)
Ok. I'll find a better link to the Bohr reference. But no - Im not saying Bohr's definition of the principle is "vague". Others might find it that way. Just mentioning the word "philosophy" or "epistomology" is enough to give many that impression - but this is absolutely not the case. Otherwise it would be impossible to formulate any mathematical model in the first place. But Bohr's philosophical method (fortunately) means the principle is testable. Bohr does not rule out, in advance, that a violation can't be demonstrated. Otherwise he would have just said to Einstein's experiments - no Einstein - you are wrong. End of story. --Carl A Looper 21:49, 9 December 2006 (UTC)
And I too totally agree with Dankos analysis - on a very wide front - irregardless of whether it is institutionally "original". My position is that this story is not over. Consistent historys is one solution. It is, however, not the only solution. And other solutions need not be automatically assumed to be "Inconsistent Historys". --Carl A Looper 22:17, 9 December 2006 (UTC)
But none of this necessarily matters with respect to Afshar's experiment. Afhsar's experiment has clear boundarys and addresses Bohr's principle of complementarity. The experiment does not address my formulation, or Griffith's formulation, or Danko's formulation. It addresses Bohr's formulation. That Bohr did not write it down in clear mathematical notation is not an obstacle. It just means one must do a bit more reading - such as the one provided (but the more the better). To put it in simplistic terms - if Griffith's formulation of complimentarity is found unviolated by the Afshar experiment then so what? Does that make Bohr's principle any more rock solid? Now of course, whether Bohr is right or wrong is not actually that important. But for the moment - getting a picture of precisely that is important. Once one has demonstrated Bohr is incorrect - on his own terms - the principle can be said to be "violated". And it allows a change to how quantum theory can be given more room to develop beyond it's epistomological framework. A move, I might add, that has been going on irregardless of Bohr's principle anyway. --Carl A Looper 23:02, 9 December 2006 (UTC)
If I can put it even simpler terms. Bohr's pronciple of complementarity has been sitting around for eighty years implying that experiments such as Afshar's are physically impossible. Afshar's experiment opens a door which had rusted shut. And when the door is finally opened the institution says - oh no - you can't open that door. Bohr said so. --Carl A Looper 23:34, 9 December 2006 (UTC)
I mean just look at Michael's attempt to restore the principle of complementarity. Michael is a good representation of where many thinkers are already located - where QM is not just - as Feynman might put it - a mathematical construction. QM is real. The wave function is real. It's 100.1 % real. This is already a violation of the epistomological constraints that the principle of complementarity embodys. To work from such a position, and try to put Humpty Dumpty back together again is the most ironic thing I've had the opportunity to witness. --Carl A Looper 00:08, 10 December 2006 (UTC)
Dear Carl, you are hopelessly ignorant of the breadth and depth of the 80-years old debate over interpretations of quantum mechanics. Statements such as "The wave function is real. It's 100.1 % real." show what an utter neophyte you are. You really need to read up on the subject and stop pushing your own blinkered POV. --Michael C. Price talk 09:15, 11 December 2006 (UTC)
Dear Michael, I am characterising your position (and others) - not mine. You begin from the assumption that the wave function is a reality. Neither Bohr nor Heisenberg did this. They began from an empericist position and developed a rationalisation of what they observed. They refused to assert any conclusion that the rationalisation was equivalent to a reality (ie. some invisible world independant of knowledge). That is, however, what subsequent generations of thinkers have done. And you are an example. You think the wires are unnecessary. Because you think the wave function is already there. You think it is a reality. I personally remain on the side of Bohr and Heisenberg. Which is why I require that interference be demonstrated in an emperical manner (if only to the extent that it has). And most interpretations of QM, of which I am very familiar, are invariably a priori violations of this emperical framework. They begin from within a Platonic/Cartesian assumption that images be regarded as illusions and that some God/Demonic reason must be the cause of such. They introduce no new data and just endlessly reformulate the minimal rationalisations which otherwise constitute QM - which don't actually need any reformulation or re-interpretation. Unless there is any new data, no re-interpretation is actually required. However, re-interpretation becomes important in the relatively new field of information science, and that is where I pick up and re-evaluate interpretations of QM as interesting. --Carl A Looper 23:10, 11 December 2006 (UTC)
If you were attempting to characterise my position with the "The wave function is real. It's 100.1 % real." statement then you are an even less worthy debater than I thought. Nowhere here have I used the reality or unreality of the wavefunction. Like Danko amd Afshar you are assuming that anyone that has a different position from yours is an idiot. --Michael C. Price talk 00:51, 12 December 2006 (UTC)
I don't think you are idiot Michael. And I'm sorry for the way in which you or I have managed to depict Michael Price as an idiot. You can redeem this by restoring the link to the Epistomological Problems page and removing your link to the Analog Science Fiction and Fact page. --Carl A Looper 01:03, 12 December 2006 (UTC)
Don't worry, I've now done it myself. --Carl A Looper 02:45, 12 December 2006 (UTC)
Dear Carl, please be more cautious when you formulate a thesis. First, "complementarity" is not Bohr's, Afshar's, Georgiev's, ..., etc. It is clear mathematical principle. Second, "interpretation" that stands for narration of the mathematics itself is something like a "clothing" that should be consistent. You cannot claim "which way" as "interpretational only" unless you have mathematical reason for that in a form of one-to-one correspondence. If you don't have this needed (!) math substrate, then the semantics of "which way" becoms "bla-bla way". And thirds, do not be so merciful for Afshar's huge error, because he not only argues against Bohr, he also makes WRONG V2 + D2 = 2 prediction. Here comes into play my proof and here is the place where you should appreciate the originality of my work. I am the first author to prove that from D=1 and V=0, as argued by Drezet, Unruh and Motl [i.e. all of them argue that which way is there, but Afshar did not show interference, i.e. "mixed density matrix"], one if take "pure density matrix" will obtain exactly the opposite result D=0 and V=1. And please do NOT underestimate the fact that I am also the first author (only in the Afshar's debates) who showed direct link between complementarity and density matrix - I can provide you a multiple quotations that Afshar, Unruh and others "do NOT realize" that pure state density matrix + which way is math inconsistency. So all of these "physicists" (?!) do not have even a slight idea what the ontological status of the density matrix is - yes, this is elementary concept when you start to study QM, that is why I had to study carefully this introduction by lectures of Eisenstein, and other university professors. If to make ridiculuous predictions is one of the criteria for being a physicist, then yes, I am not a physicist, I am MD, and neuroscientist [now doing PhD in molecular pharmacology and neuroscience]. Danko Georgiev MD 09:00, 11 December 2006 (UTC)
Hi Danko, the mathematical principle of "complementarity" is not at issue. Indeed the entire domain of math is unaffected by any experiment in physics. And by entire domain I include not only what already exists within such but everything from here to eternity that will be included within such. That is why we use math. But to read experimental physics as just the a posterio demonstration of math is to read physics as redundant. In relation to math it could very well be redundant. But I remind you that Newton introduces calculus to solve a problem in physics. We can treat calculus as already there, waiting to be discovered by Newton. I certainly treat it this way. But it's discovery is given additional impetus by questions/answers discovered within physics. --Carl A Looper 23:46, 11 December 2006 (UTC)
Dear Carl, if "the entire domain of math is unaffected by any experiment in physics" please focus your attention on Afshar's claim that he has V2 + D2 = 2, where he obviously claims to have violated math theorem by experiment. Please focus on the main issue which has always been Afshar's wrong thesis V2 + D2 = 2, that is why PRL rejected his manuscript. What Bohr have said, wanted to say, or never said, is of no interest for me, or anyone who is interested in QM itself. I am using QM to study brain processes, and this is all I want. Whether Bohr was right or not, will NOT affect in any way Afshar's wrong thesis which I will stress upon V2 + D2 = 2. This is the ONLY issue that should be repaired immediately in the main article, and you can do it with clear statement that at this point Afshar is clearly wrong. Then you can continue your philosophical inquiry on Bohr. p.s. BTW V2 + D2 = 2 has nothing to do with Boh'r name, as clearly confessed in Wikipedia by Afshar. This inequality appeared decades later after Bohr introduced the idea of complementarity Danko Georgiev MD 01:15, 12 December 2006 (UTC)
Hi Danko, there is nothing mathematically wrong with the expression V^2 + D^2 = 2, as you well know. It is only that a result of two is contrary to the duality relation theorem which otherwise defines the result - in advance - to be one or less. This is not a requirement of math. It is only a requirement of the theorem. It does throw into question the wisdom of using the duality theorem to express a violation of BPC. It is somewhat hazardous in this respect but insofar as the theorem constitutes a common definition of BPC it is not necessarily that unwise. However the task of the experiment is not to violate the theorem. It is to violate BPC. It just means the theorem does not signify the said violation of BPC, since the theorem defines, in advance, the answer to be one or less. And why does it do this? Because it is based on BPR being correct. It's limitation is arguably this very assumption. --Carl A Looper 08:37, 12 December 2006 (UTC)
The thesis is in the experiment itself, and the way in which it demonstrates a violation of Bohr's principle. Just have a read of the history between Bohr and Einstein. The experiment is completely understandable in terms of this context. You don't actually need any math at all. If I define the sky as blue then the sky is always blue. Even when the sky is red, because the words "red sky" must be a reference to some other definition of sky. --Carl A Looper 01:45, 12 December 2006 (UTC)
But there is more to be investigated on the mathematical side. The theorem is definitely a good starting point. But so too is the experiment. How each determines the possible evolution of the other is really quite interesting as far as I'm concerned. --Carl A Looper 09:28, 12 December 2006 (UTC)
To be quite honest Danko my original critique of the experiment remains intact and has not changed. However, it was based on a reading of Bohr which was not really what Bohr was saying - but what I understood he was saying. I too saw no which way information in the Afshar experiment. You know that of course. Now my model of complementarity was not violated. But where we fell out is over your quantum-realist model which jarred with my quantum-non-realist model. But I was okay to follow you down that path. No problem. I enjoyed your point of view immensely. In the meantime, I re-read Bohr in terms of what he was saying (rather than what I thought he was saying) and I saw how the Afshar experiment does indeed demonstrate a violation of Bohr. When I read your quantum-realist take on the Unrah/Afshar setups it just confirmed the same results I got using my quantum-non-realist model. My undecideables were called "entangled observables". I see them as equivalent to the inequality you identified. And presumably what others have identified. So nothing original here. But that's why I enjoyed your paper. It independantly reached an idea similar to my own. But neither necessarily represent what Bohr was talking about. They exist as a rationalisation of what Bohr meant. It's as if the implications of what Bohr was saying are right but what he actually said is not. I believe we need to identify how the xor operator is to be correctly used. And I think this requires a double articulation rather than a single one. In Bohr's principle the xor operation is a double articulation. Complementary setups > Complementary results. This happens in EPR as well. It is only during the interval between one articulation of xor and the other that we're in a disconnect. Bohr is happy to hold off this "paradox" in the knowledge that any reconnection of the observables will close the disconnect. In the Afhsar experiment it is as if the double articulation has not been completed. It is like an open wound. I think we need to find the second xor operation. Or at least that's what I'm exploring. But it won't make Bohr any more right. --Carl A Looper 11:01, 12 December 2006 (UTC)

BTW, I also disagree with the characterization of complemetarity given in the overview section

The principle of complementarity states that two complementary physical observables cannot both be measured for any given quantum particle without one measurement disturbing the other.

I particularly object to the use of "disturbance" of the other measurement. --CSTAR 15:28, 11 December 2006 (UTC)

  • You can replace "disturbing" with "affecting" if you wish to distinguish between HUP and PC, nonetheless, PC dictates that partial measurement of one complemenatry observable lead to, at best, a partial measurement of the other, as shown in the relationship between V and K in the Greenberger-Yasin inequality. It must however, be made clear that the HUP inequality which also shows a type of reciprocal relationship between two conjugate observables such as energy-time, or momentum-position is DIRECTLY required by QM formalism due to the Fourier transform process. This is distinctly different from the underlying mechanism for the enforcement of PC, which is still being investigated, and has been shown to be independent from HUP under certain circumstances. --Prof. Afshar 17:36, 11 December 2006 (UTC)
Re: PC dictates that partial measurement of one complemenatry observable lead to, at best, a partial measurement of the other, as shown in the relationship between V and K in the Greenberger-Yasin inequality. . I don't think there's any disagreement about that. However, complementarity seems to me to be a more fundamental restriction (formalized in many ways, very often in operator-theoretic terms). Whether or not that's what the Afshar experiment disproves is irrelevant for this article. The current wording "its proponents claim disproves Niels Bohr's principle of complementarity" seems to be satisfactory to everybody (as well as being factually accurate.) I don't want to get into a discussion whether it's right or wrong, since the WP rules about no OR on this page are fairly explicit.--CSTAR 16:16, 12 December 2006 (UTC)
Agreed. P.S. I think you "cut and pasted" my quote instead of "copy and paste", which I restored. -- Prof. Afshar 02:40, 13 December 2006 (UTC)

Archives

I redistributed the 12 archives of this page (and also some content of the current talk page) into 19 archive pages because the size of some archives was very large (not suitable for slow internet connections). I fixed the links in the archive box as can be seen above. --Meno25 01:48, 13 December 2006 (UTC)

Shokran Meno25. -- Prof. Afshar 02:41, 13 December 2006 (UTC)

Inconsistency of Afshar's interpretation

Dear Afshar, one really good US physicist producing papers on quantum entanglement, delayed choice quantum erasure, etc., has evaluated my paper in the following way (name of the physicist will not be announced yet):

  • "Thank you for sending me your paper. I am reading it with great interest. I would caution you against relying on anything from Wikipedia, but otherwise I am finding your arguments and explanations very appealing. I hope to give you specific comments soon. Best regards, xxx"

I suggest you to restore again the link to the deleted paper of mine, and please do not characterize in the future the work of others, before you read and understand what is the whole point about:

Yet, this is not a big deal, but I think that the process triggered by my paper will be irreversible. Mathematical proof can not be simply busted away, so it's time to re-evaluate your position and behaviour. Regards, Danko Georgiev MD 10:33, 29 December 2006 (UTC)

  • Dear Danko, I'm sure that if that "Physicist" sees your record on the internet, he/she would quickly distance him/herself from you. Some people may be so critical of my work that anything resembling an argument against my position would be good enough for them initially. However, rest assured that I will respond to that "Physicist" with the same rigor I have responded to Bohr's views once he/she makes his support of your "paper" public. As for restoring the link to the "paper" in the article, until you have published it in a peer-reviewed physics journal I will remove it as crackpottery because it contains a clear violation of the conservation laws, pointed out by myself, Drezet and prominent physicists such as Prof. Unruh. Regarding the "math", they are the standard formalism of QM discussed by innumerable physicists for decades, thus not novel. Again your statements such as "the process triggered by my paper will be irreversible" is a standard crank stance. You should let others say that for you.-- Prof. Afshar 16:44, 29 December 2006 (UTC)
Afshar, don't consider yourself the "center of the Universe", the mentioned physicist has nothing to do with your setup, so he is interested mainly in the discussion of complementarity that I have provided. There has been some claims already in the literature that complementarity is result from uncertainty relations, or entanglement. I show that complementarity indeed depends on the very nature of quantum superposition, and thus is tighly connected with the density matrix of the qubit. Thus entanglements that will lead to diagonalization of the reduced density matrix of the qubit are important, but complementarity is much deeper than that. Complementarity is intimately connected to the density matrix of the qubit. If one claims which way information in the case of your setup where the photon has pure state density matrix, then he\she is inconsistent, and this was done by the claimed by you "famous" Unruh, Drezet, etc. Danko Georgiev MD 17:39, 29 December 2006 (UTC)


Original Research (OR) alert

  • To Danko, and any other OR pusher: Please refrain from posting ad.s on your OR in Wikipedia. Publish your papers in a peer-reviewed physics journal, and if relevant, it may be included in the article. All forms of OR will be removed and violators reported to admin.s Best regards. --Prof. Afshar 18:03, 29 December 2006 (UTC)

Afshar's papers available at ArXiv

I have added direct links to Afshar's papers available at ArXiv. Now one can have a better idea what exactly Afshar says. Some of the details were not available in his 2003 paper. Particularly in his SPIE paper he says that detection at the image plane leads to prediction P = | ψ1 | 2 + | ψ2 | 2 with the prediction of no interference pattern at the focal plane. Yes, if you interprete the setup in which way you must accept that claim, plus accepting that the photon's density matrix is of mixed type (Afshar says "decoherent" in his paper). So yes, all of this is true, and is clearly stated in my PhilSci 3048 paper. I call this "Unruh's which way interpretation" which is consistent, but is experimentally disprovable. Then I show that at the image plane the P = | ψ1 + ψ2 | 2 distribution is producing the same picture as the P = | ψ1 | 2 + | ψ2 | 2 distribution. So there is possibility to obtain the same image at the image plane without "which way" information. Basicly if the photons are coherent as in Afshar's setup without grid there is no which way information at first place. If one puts different polarization filters on the pinholes he will receive mixed density matrix and will have really which way information, but then putting the grid before the lens will absorb photons. Finally, if one interprets the results as which way plus pure state density matrix of the photon he will be mathematically inconsistent. How one mathematically arrives at the same intensity distributions for pure state and for mixed state setups? Well, I have shown that for mixed which way setup one has e.g. at image A the amplitudes \psi_{1}=1/\sqrt{2}, \psi_{2}=0, while for pure state setup one has e.g. at image A amplitudes \psi_{1}=1/\sqrt{8}, \psi_{2}=1/\sqrt{8}. I think the link to my paper should be restored again, and better be done by Afshar himself as he vandalized the main article. Danko Georgiev MD 02:57, 13 January 2007 (UTC)

Recent addition

I am not happy about the detailed analysis presented in the recent addition "Fundamental flaw in Afshar's argument". It is not appropriate to have such a claim without this having been vetted by other experts. As a non expert it does not seem to make sense because a photon is detected at either detector on a photon by photon basis, and accouting for all photons. The experiement works one photon at a time. Since each photon is detected on either detector, according to the principles of optics and lenses, this appears to be which way information. It can't just be ignored, unless the truth is that the photons always pass through both, and detection shows something else. The current paragraph is presenting itself as a difinitive proof and I can't just take the word of one person that it is valid. There needs to be debate on this first. So I have reverted again. Especially take note of the claim "Same way, in Afshar's experiments, after interference, each wave packet gives contribution to both the detectors.". This is appears to contradict the experimental evidence that after interference each photon is detected only on one detector, not both. Please do not revert again until other voices have expressed themselves here. I am reverting on the basis of NPOV until others have had a chance to comment. Thank you. Dndn1011 14:39, 17 January 2007 (UTC)

Incidentally I reviewed the paper, and along with many other claimed refutations of violation of complementarity, immediately simplifies the experient in order to develop the argument. It appears (although I am not an expert as I said) to then apply an argument related to Unruh's, using a half silvered mirror. The first thing this papaer does is remove the incovenient lenses. The paper might be making the error of taking the context of Afhsar's experiment operating with a stream of light and then converting that into a single photon equivalent. This probably is in error as Afhsar's experiment on a photon by photon basis cannot be so easily correlated with an experiement in which complementarity cannot be violated. In essence I think it is like saying "This experiement is really just the same as a whole class of experiements that do not violate complementarity". In any case, I believe it possible that Complementarity is not falsifiable because in order to prove it false it is nescessary to know the path of a photon without destroying it. Since this is impossible, it may be impossible to prove Complementarity wrong. If a theory is not falsifiable then it is not scientifically valid, apparently Dndn1011 15:16, 17 January 2007 (UTC)
OK I did it, it was not hard. I believe I have proved that complementarity is not falsifiable. Please feel free to take my argument apart. But it seems pretty water tight to me. Dndn1011 15:47, 17 January 2007 (UTC)

220.224.21.140 is not working to concensus

This poster keeps reverting the article to their own agenda without discussion here. I cannot revert again without risking a three revert infringement. As for you 220.224.21.140, you are disregarding the accepted protocols for dispute reslution and ask you to remove your edits pending a discussion here. Wikipedia is not meant to be a platform for your opinions. I have questioned your addition and you have not responded this is unacceptable behavior. Dndn1011 16:37, 17 January 2007 (UTC)

Sorry about that

Sorry about the additions, without discussion. Was unaware of Wikipedia rules/ethics.

The argument is quite simple. Afshar (and most others) assumes that the two wave-packets coming from two slits just pass through unaffected to the detectors. The basis for this is just the observation that when one slit is closed, only one detector clicks. This doesn't imply that when both slits are open, the same will hold. Because now the two wave-packets meet and interfere. What happens in the interference region is that part of the two wave-packets cancel each other (dark fringes), and part of the wave-packets reinforce each other.

The following simple example will make it clear. Let there be a state which is a superposition of two opposite momentum states. This can signify a superposition of two waves travelling in opposite direction, and crossing at some point. Say the part coming from slit A is \exp(\imath kx) and that coming from B is exp(- \imath kx). Clearly, the two parts are moving in different directions, so that one will reach one detector and the other will reach a different detector. (Ideally we should be dealing with wave-packets, but the arguments easily extends to that) So, when the two parts meet in the interference region, the state at the point of crossing can be written as:

  • \psi(x) = \exp(\imath kx) + \exp(- \imath kx)

Now this state can also be written as

  • \psi(x) = [\cos(kx) + \imath \sin(kx)] + [\cos(kx) - \imath \sin(kx)]

The two square brackets represent parts coming from different slits. The two sin(kx) terms cancel out to give the dark fringes. What is left is:

  • \psi(x) = [exp(\imath kx) + exp(-\imath kx)]/2 + [\exp(\imath kx) + \exp(- \imath kx)]/2

Thus even the part which had momentum k, gives a superposition of momentum k and -k because of interference. So, the part which was moving in one direction with momentum k, now gives a SUPERPOSITION of two parts, one moving in one direction ad the other moving in the other direction. Same holds for the part which was moving with momentum -k. Clearly, if you are in place of any detector, you will see identical parts coming from both the slits towards you. Thus, each detector gets contributions from both the slits. But as the parts reaching the two detectors belong to one single particle, only one detector will register it (randomly) at a time (wave-function collapse or whatever...). So, there is no which-path information in the detector clicks. —The preceding unsigned comment was added by 220.224.21.140 (talk) 18:50, 17 January 2007 (UTC).

Note: dear anonymous, please use the inbuilt laTex function in Wikipedia. I have edited your math equations to make them more clear. Danko Georgiev MD 09:34, 18 January 2007 (UTC)
Comment why the proof by anonymous (220.224.21.140) is invalid. Dear anonymous, it is very easy to speak about the focal plane and explain how the interference occurs, but let me say WHY there is a small problem when you discuss the lens action at the image plane. Please note that when the only pinhole A is open at image B reaches NO intensity. So the overall quantum amplitude is ZERO but not as unstructured mathematical zero (perceived as lack, complete emptiness, etc.), but "structured zero" that is result from destructive self-interference. So if some quantum aplitude comes from A to image B, then squaring this complex number will always give as result summation of the complex and the imaginary components |a + \imath b|^2 = a^2 + b^2 , so by this mathematical argument the zero intensity at image B must be obtained only via squaring of zero real part and zero imaginary part coming from slit A. Yet, here is the deep question of this "self-destructive interference zero". But fortunately the loophole that your argument has can be filled in, by much deeper argument on distinguishability/indistinguishability of quantum states and showing that the principle of complementarity (PC) is superior to the which way claim. Indeed PC is tightly connected with the density matrix of the qubit, and all which way claims must follow from the density matrix. For details, see my PhilSci entry. I recommend that the argument by anonymous in its current form NOT be included in the main text since it is with loophole. Danko Georgiev MD 09:57, 18 January 2007 (UTC)