Talk:Afshar experiment/Archive 23

I have voted myself chairman

Yes, the article is a mess and this debate is a mess too. Someone needs to step in. I have done so. I have attempted a clean up and clarifcation of the aritcle up to the ongoing debate section. Please, discuss changes here. The aim is to make a good wikipedia article. Leaving asside details and minor corrections (feel free of course to make minor changes, corrections , etc) I feel that we should sign off on the article up to the ongoing debate section. When we have concensus there, we can get to the difficut bit :)Dndn1011 14:54, 29 January 2007 (UTC)

need big changes

If you want really to change something here first correct the introduction : complementarity has nothing to do with the impossibility for observing wave and particle behavior at the same time as written : in reality any interference shows both at the same time. Second you must change all the part concerning the debate which is i think useless confusing and senseless (a list of reference is more than enough and we dont need quotation of texts: we are not speaking about the bible here ). we must cool down danko (at 4 kelvin) in order to stop his coming back every half day or less (it will be better if he would decide him self not to act against progress ). May be the other protagonists could follow this advice too: this page looks often like a forum about politics every one is speaking but nobody listen... what for . The research of afshar are published this is a fact all the other works (mine included) are in this context only proposals and should not become the center of the present discussion. Let only describe the experiment and its aim on the wikipedia page this is the only fact ... Drezet 15:24, 29 January 2007 (UTC)

By the way : the strange claim that which path information is not available even without grid result from a confusion. From the point of view of linear optics if we suppose the two sources coherent (as it is here whatever said DG) we have always the right to consider the (pure) case with two holes as a sum of two (pure) cases with a single hole. However this is only valid for the field of the wave not for the intensity or a hypothetical photon trajectory which is not defined in QM. So indeed when two beams A or B are crossing it is a non sens to claim that the photon detected after the intersection is coming from A or B. This kind of question is a non question we can not answer it in QM. I found also a bit confusing when somebody try do justify this fact by using the formalism of linear quantum optics and doing some obviously wrong manipulation of symbols. Drezet

First of all, publishing in a peer-reviewed journal should not be taken as a certificate of correctness of a work, although it does impart a degree of respectability to the work. Foundations of Physics has published papers in the past which have clearly wrong conclusions - examples are:
"Experimental realization of Popper's experiment: violation of the uncertainty principle?", Y.-H. Kim and Y. Shih, Found. Phys. 29, 1849--1861 (1999).
"Is the quantum mechanical description of physical reality compl ete? Proposed resolution of the EPR puzzle", C. S. Unnikrishnan, Found. Phys. Lett. 15, 1-25 (2002).
These two specific references are ONLY cited here to caution against giving any certificate of correctness to a published work, and to keep an open mind. This is not to cast any doubt on the work under discussion. To do that, we need valid scientific arguments.
Secondly, I do not understand Drezet's argument. If he is saying that " when two beams A or B are crossing it is a non sens to claim that the photon detected after the intersection is coming from A or B", then he agrees with my point of view that there is no which-way information to start with, and hence no paradox.
I have gone through Afshar's Foundations of Physics paper. The only argument mentioned for saying that there is which-way information, is that of momentum conservation, which is clearly not valid when both the slits are open. On the other hand, the back-of-the-envelop calculation done by me on this page indicates that there cannot be a which-way information. So, there is no paradox and there is no violation of complementarity. The calculation may be small enough to fit on the back of an envelope, but it is fully rigorous. It tells clearly where the catch is in Afshar's experiment.
--Tabish q 17:37, 29 January 2007 (UTC)

Ok i will try to summarize : I agree on the conclusion that there is no which path but not on your reasoning. There is no which path because path is a dangerous word in QM . A path is a classical definition. However QM precludes the complete observation of a path existing independently of any experiment. In classical physics this is possible but not here because you have always an unavoidable and finite interaction between your detector and your photon. This is a problem because you can not test rigourously your definition of a path . I will give you an example: if you a have the two beam previously defined then a possible definition of a path could be the flow lines of the Poynting vector. This was the choice of De broglie for example. This definition looks nice because you can explain every single particle experiments with it. However this choice gives some problems because it can be proved that for symmetry reasons such path are not crossing in the intersection region ( read the last article of Hiley in foundation of physics of December ). Ok so now you will say : well I have a way to test if this is true or not ... I must jut watch the path. Watch the path ? how would you watch this path? If you close one hole the case is completely different and if you use entanglement with a detector ( the so called non destructive which path detector) then the correlation modify non locally the trajectories so that now indeed the path are following the normal intuitive way in straight line. Clearly nature here seems to resist. This is just an example of path definition but all other cases are problematic too. What is observed in afshar experiment in only a click in a particular detector the concept of path is unfortunately very problematic and ambiguous here .

This was for the philosophical back ground not lets consider your maths: In your reasoning you consider a superposition of wave in the interference plane and you wrote: $\psi (x)=a\exp(ikx)+b\exp(-ikx)=(a+b)\cos(kx)+i(a-b)\sin(kx)$ This is only true in one plane (I call it z=0). In fact you must in general write $\psi (x)=a*f_{1}*\exp(ikx)+b*f_{2}*\exp(-ikx)=(a*f_{1}+b*f_{)}\cos(kx)+i(a*f1-b*f_{2})\sin(kx)$ where f1(x,z) and f2(x,z) are two envelops such that f1(x,0)=f2(x,0). Now if you suppose that for z going to + an - infinity f1 and f2 are disjoint (i.e, like before and after the lens of Afshar) you can see easily that the field in such separated regions depends only on a or b separately. For example in the region where f1 is different of zero ( but f2 =0) you have $\psi (x)={a*f_{1}}\cos(kx)+i(a*f1)\sin(kx)=a*f_{1}*\exp(ikx)$ as obviously expected.... your manipulation is just a trick but experiment will not agree with you

There is another problem: it is wrong to tell that the effect of the wires-grid is to remove the sinus part. The sinus contributes on all the plane z=0 and not only at the wires locations. In fact if a=b the sin is not present in such plane z=0 and there is no interaction so that all my reasoning is still OK.... (on that point i think I agree completely with Afshar) Is it enough for you? Drezet 18:44, 29 January 2007 (UTC)

• Dear Everybosy,(i) the expierment "claims to have violated the" PC. It is important to point out exactly what is claimed in the Found. Phys. paper and correctly reflect it in the introduction, and then go on to discuss the controversy or the consensus in the community. (ii) The experimental results indeed VIOLATE the Greenberger-Yasin inequality (See section 5 of the Found. Phys. paper.) Again the claim is that there is a violation, and the experiment is not supportive of the inequality. (iii) Please kindly repost the warning tags on the page header. This article is so terribly messed up that even I cannot follow it. It may be better to revert back to earlier version, which has a proper intro, and warning tags. Tabish, please wait till you hear from the referees of the Journal to which you have submitted your paper as to the value of your ideas. Furthermore, discussing your OR here is against the Wiki policy. BTW/ Found. Phys. is a highly respected journal, and it would serve your aspirations better not to bash a journal with Nobel Laureate editors and authors. Best regards.-- Prof. Afshar 18:34, 29 January 2007 (UTC)

I agree FPL is a good journal. The proof: I even published something in it :)) Drezet 18:54, 29 January 2007 (UTC)

Drezet, thanks a lot indeed for bothering to give a focussed and detailed reply. From the geometry of the experiment you have in mind, I believe all the action is happening in the z=0 place, in the sense that the detectors are also in the z=0 plane. In that case, one would look at $\psi (x,0)$, which should be $\psi (x,0)=(a*f_{1}(x,0)+b*f_{2}(x,0))\cos(kx)+i(a*f_{1}(x,0)-b*f_{2}(x,0))\sin(kx)$ Since $f1(x,0)=f2(x,0)$, you get equal contribution to the detectors from a and b parts. Infact, if the wires are put along the z-axis, f1(x,z) probably has to be equal to f2(x,z) for the whole envelop, to get the dark fringes. --Tabish q 20:25, 29 January 2007 (UTC)

All rigth but in z=0 there is fringes and noway to distinguish the contributions from a or b . However it does not mean that this is true every where since in z= +infinity it is possible to measure contribution depending only on a or b. This demonstrates that in the afshar set up the so called which way information ( I prefer to speak about measure of D)and the measure of interference fringes ( measure of V ) depend on z and that when one can measure V a and b become mixed ( which is logical we speak about fringes). The two kinds of measurement exclude each other and Bohr can sleep in peace (like i will do my self now) . Do you agree? If there is no point of desagreement may be i did not really understand your point.Drezet 21:03, 29 January 2007 (UTC)

Dear Drezet, seems like we are agreeing. However, I would like to add that if one is claiming true violation of complementarity by detecting particle anywhere on z-axis, he/she has to show existence of fringes everywhere on the z-axis too.
To Afshar: Afshar, I think there is no harm in having a healthy physics discussion here. If I am convinced here itself that my thesis is mistaken, I will withdraw the paper myself, without waiting for referee's comments. --Tabish q 04:52, 30 January 2007 (UTC)

• Dear Tabish, I'd prefer the proper channels of peer-review. I cannot spend time here refuting every time OR claims are made. To do justice to your submission, one needs the graphics, equations and correct process of edited communication, for which peer-review system has been devised. This talk page is about the article's accuracy and ensuring OR is removed from it. It is not a bulletin board, weblog, or a forum, and I will not participate in lengthy technical discussion here with anyone. The past experiences with others have always led to more confusion and unfortunately in some cases to unjustified animosity. I'm tired of this farce called Wikipedia. Regards.-- Prof. Afshar 05:19, 30 January 2007 (UTC)

You are being unfair. Wikiepedia is not a farce, it is educating people in a most wonderful way, not only to facts but to the process of establishing them. It can be very frustrating, but ultimately the purpose for a science article such as this is to help people like me, who are not scientists, understand where science is at right now. This article could be very clear and simple. Detailed debate as you say belongs elsewhere. Some people here are doing their best to battle with human nature and get the focus back where it belongs. In the process of doing this many lessons are being learned by manny people including myself. It is a shame if you do not realise the value of this and do not wish to participate, however you participation, although valued and helpful in communicating your own experiment, is not necessary. Dndn1011 11:54, 30 January 2007 (UTC)

Granted Wikipedia is by and large a useful tool, however, it certainly lacks mechanisms to ensure protection of controversial topics from poison-pens etc. as the Seigenthaler affair demonstrated. I cannot count the number of insults I have suffered here, which are numerous and well-recorded in the archives. Wouldn't you feel upset after more than 2 years of "educating" you end up with none of your points acted upon and an article in a perpetual nose dive? -- Prof. Afshar 12:34, 30 January 2007 (UTC)

Yes I would, and I feel your pain. I think there have been some very unwise postings here, and I think you have suffered a lot of abuse for basically just "doing you job". It is an unfortunate aspect of human nature. At least here it is all out in the open and recorded down. I am making a new attempt to get the article on track because it appears that the various arguments have settled down... it seems many people are beginning to realise that this experiment is not so easy to dismiss. We have witnessed the article become more and more inconsistent and messy and we have watched the various attempts to wriggle out of its conclusions and as a neutral party my conclusion is that the article should simply present the facts, the conlusions of the creator of the experiment (i.e. you) and the most clear and important counter arguments that stand up to scrutiny, that are actually countering any claims you make. There is no room for bias, to weasle words, or OR. Once the article has been published in a peer reviewed journal, the quality and notability of counter arguments will need to be improved to match. Right now there are a lot of statements in the article which I consider OR applications of notable viewpoints or simply there because of initial "shoot from the hip" reactions to earlier publications. A great example of this is Bill Unruh's experiment which I consider to be completely irrelevant to this article because it is very clearly not the same experiment at all. I knew this right at the start and wanted to remove it (perhaps I even did at one point) however certain people here kept insisting that it should stay and I have been trying to avoid an rv war. I have been pragmatic, in short, putting my own opinions to one side a little out of respect to others. It is a question of attempting to be a neutral editor. It's hard. But it is a great exercise in self discipline. Dndn1011 13:30, 30 January 2007 (UTC)

Thank you for your understanding and efforts to improve the article. OK, I'll give this another shot. I will spend ONLY 30 Min.s every day to address the questions you have raised below, and try to avoid technical details as much as I can. I would appreciate if other editors could kindly refrain from posting comments (in the section you have designated) until I post my response first. Then we can debate other editor's points of view. Hopefully, this will remedy the problem. Best regards. -- Prof. Afshar 13:51, 30 January 2007 (UTC)

Great, I look forwrad to it. Dndn1011 15:16, 30 January 2007 (UTC)

Organisation

OK Good, thanks for not just reverting my changes. Now we need a systematic approach to fix this article. I ask that we keep one heading per point to address. Please, lets avoid long winded interwoven discussions, we will get nowhere. If you see something you don't like about the article, please create a section with a heading specifying the issue. One section per issue. In each section we can discuss and attempt to reach concensus. In the absence of concensus I will attempt to reflect the majority view, but only as a means to achieving (hopefully) concensus. I think it is clear that this topic is not clear cut and that there are many viewpoints. Let's respect them all and attempt to create a concise article that usefully reflects current thinking. To some extent this has been happening already so lets work together to achieve it fully. Dndn1011 23:06, 29 January 2007 (UTC)

• So, please take note of my posting of 18:34, 29 January 2007 (UTC) above, and correct the errors in the intro. These errors are misrepresentations of the experiment, its intent and its scope; and need to be corrected.-- Prof. Afshar 03:10, 30 January 2007 (UTC)

• OK, I will do but this requires its own heading. Sorry to be pedantic and all that... I will add one once I have read the posting and figured out what to call it. Or alternatively just create your own new heading. Ceratinly your claim that These errors are misrepresentations of the experiment are serious and should be taken seriously. Dndn1011 11:57, 30 January 2007 (UTC)

The validity of the concept of a path of a photon in Quantum Mechanics

This question has been troubling me for sometime and I thank Drezet for affirming my concerns (such affirmations have been a long time coming here). So I believe that this is an important point to mention in the article. Which way information is the same thing as path information. If path information is a concept without validty to a photon, this would seem to render the whole of the debate concerning complementarity moot. Is this not one possible valid interpretation of the experiment? Dndn1011 23:16, 29 January 2007 (UTC)

As was perviously pointed out by myself and Prof. Unruh, the which-way information (WWI) in welcher-weg experiments is not "Which-path" information. It is rather "which-slit" or "which-pinhole" information. Everybody agrees that assigning a path or trajectory for a photon is not in accord with QM. So, when we say we know which hole the photon passes through, we do not mean we assume a precise trajectory for the photon to have chosen, rather we can "trace" it back to the hole it must have passed through in order to satisfy the conservation laws. The one-to-one relationship between the holes and the corresponding images is the key component of the WWI. Regards.-- Prof. Afshar 03:05, 30 January 2007 (UTC)

Dear Afshar, as I have supported you many times when you made correct statements, I will support you now too: YES, one-to-one relationship between the holes and the corresponding images is the key component of the WWI. I will not support however that WWI is there at first place even without the grid. I have convinced myself that Wikipedia is a farce, but I don't complain when the article is edited by someone in a way I consider inappropriate. Danko Georgiev MD 10:16, 30 January 2007 (UTC)

Thank you genetlemen. Now remember I approach you as a reader of the article. I will have as such a reader a very strong urge to ask the following questions. Answers to these will be helpful to creating an article that makes sense.

• If we can say which pinhole, is this not still making an inference about an aspect of the path of the photon that cannot be proven because we can not watch the photon pass through the hole, or measure it as such?
• I don't understand how it can be said that the path of a photon makes no sesne in QM, yet we can still say with certainty that the photon went a certain way. These seem logically exclusive. Paradoxical. Is this the core of the paradox that is demonstrated by the experiement?
• If Danko's view is correct, is this not the same thing as saying that photons never have WWI or Paths under any cirumstances? How can an arrangement of an experiement change the fundemental nature of light?

Dndn1011 12:10, 30 January 2007 (UTC)

Current Status: Awaiting Responses

Afhar's Contibutions to Article

Thank you Prof. Afhsar for the comments you made above I am placing them in their own section here. I would like to correct any difficiencies in the article through the process of concensus that is the method of wikipedia. Please be patient, this will take a bit of time.

Dear Everybosy,(i) the expierment "claims to have violated the" PC. It is important to point out exactly what is claimed in the Found. Phys. paper and correctly reflect it in the introduction, and then go on to discuss the controversy or the consensus in the community. (ii) The experimental results indeed VIOLATE the Greenberger-Yasin inequality (See section 5 of the Found. Phys. paper.) Again the claim is that there is a violation, and the experiment is not supportive of the inequality. (iii) Please kindly repost the warning tags on the page header. This article is so terribly messed up that even I cannot follow it. It may be better to revert back to earlier version, which has a proper intro, and warning tags. Tabish, please wait till you hear from the referees of the Journal to which you have submitted your paper as to the value of your ideas. Furthermore, discussing your OR here is against the Wiki policy. BTW/ Found. Phys. is a highly respected journal, and it would serve your aspirations better not to bash a journal with Nobel Laureate editors and authors. Best regards.-- Prof. Afshar 18:34, 29 January 2007 (UTC)

• Please could you desribe the fundemental claim of the paper here, so the introduction may be corrected.
• Could you please describe in layman's terms what the "Greenberger-Yasin" is. A reference can be supplied for those who wish to investigate further, but it is helpful for the purpose of the article to have a short paragrph describing it.
• The warning tags were removed because they serve no purpose while the article is being actively revised as is happening now. There may be a more appropriate tags to use. However please everyone make your suggests on tags if you feel this is important.
• Discussing OR here is not against wiki policy. It is against wiki policy to have OR in articles. In talk pages, OR is acceptable othersie we could not have productive discussions, especially on whether some piece of an article it OR.

Thanks, Dndn1011 12:25, 30 January 2007 (UTC)

Reply: I don't think this is a good idea. Afshar is free to chime in here as he pleases, but asking him for advice on how to write this article sets a very bad precedent for WP. As a matter of fact, I don't think that very much needs to said about this experiment:

1. Afshar claims (asserts, says) that it challenges the principle of complementarity. Exactly how, we can glean from what Afshar has written in his SPIE paper.
2. Describe the experiment as is currently done in the article.
3. Note (in the intro, certainly, perhaps elsewhere) that there has been considerable controversy, with links to published papers or letters. In some exceptional cases, we can link to blogs (I'm thinking of Motl and Unruh.) Since Afshar is the person in question here, it is also acceptable in my view to have a link to his blog.

I would note that the opening sentence currently is highly misleading. I think it should be made clear that the claim is controversial (although my impression is that Afshar is currently much more circumspect about what the experiment actually proves) --CSTAR 16:54, 30 January 2007 (UTC)

You are out of order, I am not asking for advice on writing the article but for clarification. I am also trying to set a process for resolving the problems with the article, I have specifically asked for issues to be raised seperately in their own sections and not all mixed together. I think it is quite clear from the opening sentence that this is controversial, as it states there is no concensus in physics on the subject. How the word controversial helps create a balanced fair article in teh face of all teh hostility flying around is not clear to me. I think we should use as neutral wording as possible. This is fair enough in my opinion. However if you wish to open debate on this please do so in a seperate paragraph, thank you. Dndn1011 20:57, 30 January 2007 (UTC)

Excuse me? Out of order? This is a public forum, subject only to general rules of civility and guidelines established by WP policy. If you want to bark, go ahead, but not here.--CSTAR 21:05, 30 January 2007 (UTC)

Yes out of order, because you are not respecting the considerable work that has been going on here to attempt to create a good article by concensus, nor my intentions which are honest. That is my opinion. You have your own, opinion and your own agenda. What are you afraid of exactly? That the the article might actually reflect correctly the assertions that Afshar is making? This is the purpose of asking Afhsar for clarification, becuase he claims the article is currently misleading. We will see what he has to say and make changes as needed. You speak of rules of civility, and yet you have immediately turned on a attempt to be civil to Afshar by allowing him a voice in editing the article. And if you think I am coming down hard on you it is because there is no way we will ever sort out the mess of this article unless we stop all this stupid paranoia and bickering and actually work with the facts. My appologies if you feel I am being unfair. Dndn1011 21:19, 30 January 2007 (UTC)

Reply: Though there is no hard and fast rule on WP preventing individuals writing about themselves or their work, it is generally not a good idea. There is a lot of precedent on WP for this claim. I have nothing against Afshar personally --- I think he can attest to this fact. I am only arguing for transparency and consistency with other articles involving living persons. As far as "considerable work" please note that I have been a participant in discussions on this and related articles for nearly two years. --CSTAR 21:36, 30 January 2007 (UTC)

Nothing I have done is challenging any WP policy, I am merely in the absence of anyone else doign it, trying to mediate, after being heavily involved in this article for some time. Mediation just means trying to get everyone to agree, it does not mean dictating the contents of the article. And in offering to act as a mediator, it provides a way for Afhsar to contribute to the discussion. Dndn1011 21:59, 30 January 2007 (UTC)

Current Status: Waiting for Afshar to clarify the position he takes in his own papers.

References to Unruh experiment should be removed because it is not a valid comparison

As an editor of this article, I have considerable problem with Unruh's experiment being included as I see his experiment as being very different to the Afshar experiment. The main problem with Unruh's experiment is that which way information is hidden behind half silvered mirrors, whereas in Afhsar's experiement the debate on the validty of Afhsar's argument seems to hinge upon the use of a lens which apparently shows whichway information directly. I see no reason for Unruh's experiment to be included in this article. Please discuss. Dndn1011 21:06, 30 January 2007 (UTC)

Unruh's experiment was offered by Unruh (a respected expert in the field) as a critique of Afshar's experiment. Your lack of understanding of its relevance is irrelevant and your original research. It should be retained. --Michael C. Price ^talk 21:38, 30 January 2007 (UTC)

Absolutely agree with User:MichaelCPrice.--CSTAR 21:41, 30 January 2007 (UTC)

This is all well and good, but a reader of the article would seek to understand why the two experiments can me claimed to be equivalent. Otherwise the result is confusion. So please go ahead and explain how the two experiements can be claimed to be equivalent, when the Afhsar experiment appears to clearly and unambiguously show which way each photon has gone, and Unruh's does not. For a fair and balanced article, this should be explained in a manner that does not result in confusion in the mind of the reader. Dndn1011 21:55, 30 January 2007 (UTC)

See below. --Michael C. Price ^talk 01:08, 31 January 2007 (UTC)

Reply Unruh claims it is related. He is an established expert and WP simply reports what established experts say on the matter. I don't think there is any more to say on the matter.--CSTAR 22:00, 30 January 2007 (UTC)

I can go with this as long as it is included as a simple reference without going into detail. If we quote parts of the objections in the article, then we should also quote Afhsar's rebuttles to keep the article balanced. Thus I accept your point that it should remain at this time. However I will make a new suggestion regarding the Specific Cirtiques section. Dndn1011 22:09, 30 January 2007 (UTC)

Incidentally, I just reviewed Unruh's blog entry again (http://axion.physics.ubc.ca/rebel.html) and he states the following:

Finally, the lens which focuses the light from the pinholes onto the detectors acts just like the final third mirror in my experment, in separating out the light once again (undoing the interference pattern).

The problem here is that Afshar's experiment could be argued to behave like Unruh's, except for the fact that the lens provides a 1-1 mapping of hole to target according to the normal understanding of optics. This is a crucial difference, and Unruh has not clarified this. What Unruh is effectively saying is that there is no 1-1 mapping of hole to target via the lens because before photons hit the lens they are in a state of interference and do not contain which-way information. Presumably the lens must in some way manufacture an appearance of which way information. There are interesting consequences to this, and I would be interested to know if Unruh or anyone else has attempted to address them. Dndn1011 00:49, 31 January 2007 (UTC)

I think you miss the entire point of Unruh's critique. His experimental setups are to demonstrate that how we interpret complementarity is a function of the *entire* experimental apparatus, even parts and paths which the photons do not explore. Thus the introduction of wires into Afshar's experiment (even for the photons that are not absorbed) alters how we should interpret complementarity, compared to the no-wires setup. You can't just look at how complementarity operates in the no-wires setup and just apply this to the wired setup.--Michael C. Price ^talk 01:08, 31 January 2007 (UTC)

Yes, I understand that is what is claimed. The problem is we are still left in this case with a big question of how it can be that a photon might appear to come from a hole when it actually did not come from that hole. If you hide behind complementarity you are left with that unanswered question. Once again my question is not being answered, but merely being covered up, so that I am expected to ignore this minor detail. I consider this important, however it appears many people do not consider thisimportant. So fair enough for now. Dndn1011 13:03, 31 January 2007 (UTC)

Dear Dino, I have explained in a very elegant way why Unruh's setup is equivalent to Afshar's setup, and I have provided all the necessary math calculations that Unruh did not provide. So your incompetence does not mean that Unruh's experiment is irrelevant. The changes that you did in the article are mainly to destroy useful information that otherwise can be utilized by readers that want to read more, and know more. The argument by CSTAR, that Unruh is well-known is just logical fallacy called appealing to authority, but the truth is that his proposal is good for newcomers in the field. Once one understands the logic in Unruh's setup, he/she can understand Afshar's setup. Once you learn how to add numbers, you can study how to multiply them Danko Georgiev MD 01:48, 31 January 2007 (UTC)

Dear Danko, you have not actually answered my question. But no matter. Oh, and please do not call me incompetant. I am just asking questions.Dndn1011 13:03, 31 January 2007 (UTC)

Danko, judging the relability of sources is Wikipolicy.--Michael C. Price ^talk 07:28, 31 January 2007 (UTC)

Reply to Danko: Re The argument by CSTAR, that Unruh is well-known is just logical fallacy called appealing to authority

As per policy, stated in WP:RS and WP:NOR wikipedia articles should not present new arguments, theories, interpretations. I was not adducing Unruh's established expertise in support of some fact about Afshar's experiment. I used it instead as justification for inclusion of his opinion in the article, following the policy of WP:RS as Michael Price observes. Therefore it is incorrect for you to say that this was an appeal to authority.

Moreover, I urge you to stop trying present your WP:OR here. This is not intended as a comment on the quality of your work, but is rather an attempt to stick to established policy.

Thanks. --CSTAR 17:45, 31 January 2007 (UTC)

I have to agree with CSTAR on this. Unruh's argument is very often mentioned as a critique of Afshar's Experiement, and has existed for some time. It forms part of the debate and is from a notable source. Danko's argument is not often mentioned by anyone except Danko. The enforcement of Wikipedia Policy is not always clear cut for many reasons, but Danko has clearly overstepped the mark by placing his own work into the article, without any validation from a third party. Afhsar's experiment has appeared in print on a number of occasions, Danko's has not.

On a different note, I am not sure of the status of Unruh's argument. Was Unruh's argument ever published outside of the internet? I am not sure the only reference is on Unruh's blog. This does in itself raise an interesting point. We could argue all day about it. However Unruh's argument has been avialable for years, and Unruh is more notable than Danko as I understand it. So a choice has to be made. Like I said though, it can be difficult to decide what is or and what isn't OR. Technically, Danko's work is not OR if it is presented before hand at some other source which is referenced to. If we rule out Danko's reference, we would have to rule out Unruh's to, because this is a link to a private blog and nothing more. I only mention this to highlight the difficulties in interpreting WIkipedia policy. The ultimate solution is to use common sense and concensus in these matters.

Things will get a lot easier once the experiment appears in a peer reviewed journal. At that point, non peer reviewed critiques will probably have to be replaced by peer reviewed critiques as and when they arrive. Unruh's critique might no longer have a place in this article once Afhsar's peer reviewed paper is published, because his critique has not been published in a peer reviewed publication. Well perhaps we should just worry about that when it happens. Dndn1011 21:11, 31 January 2007 (UTC)

WP:OR can't be judged in isolation (I haven't made that up -- that what the policy says); we have to consider other things, such as the relabliity of the source. Bill Unruh is a reliable source, whether he has published this critique or not. Look up Unruh effect and Unruh radiation. --Michael C. Price ^talk 22:30, 31 January 2007 (UTC)

Well, Unruh might not be an expert on this particular experiment. Although what you are saying is true to some extent, one has to be careful. For instance it could be that Unruh's argument is flawed. The possibility is there, and it would be interesting to see what a peer review would say. For now it is a notable critique because it is from a notable person that is all, and yes it is because of his notability that we sway WP:OR in his favor. Time will show whether he is right or not. But it is also true that his argument has never been published and this should be remembered too in the interests of fairness. Dndn1011 00:04, 1 February 2007 (UTC)

Unruh only has to be an expert on quantum mechanics, since Afshar's experiment is quite straightforward to anyone with a solid grounding in quantum physics (which Unruh definitely has). Believe it or not, it's not rocket science, it's just an interesting refinement of the double slit experiment, one of the most studied and analysed experiments of all time. Every undergraduate course and textbook in QM will discuss the double slit experiment. --Michael C. Price ^talk 01:05, 1 February 2007 (UTC)

You make it all sound so simple. According to you there is nothing to discuss because it is all so obvious. My point is that Afshar spent a great deal of time considering the experiment, whereas Unruh appeared to chime in along with a whole load of other people *perhaps* without full consideration of it. In fact far from being trivial, we have seen all kinds of proofs and explanations, and they are not all consistent with each other. This is reflected in the current article. If you care to read Luboš Motl's blog (which is used as a reference) you will see that in efforts to disvalidate Afshar's argument he tends to move around quite a lot. With regard to Unruh, he is inconsistent. To quote from his blog:

• Unruh uses a more transparent experimental setup where some issues can be explained very easily, without various technical complications of Afshar's setup. The only respect in which Unruh's setup seems to be oversimplified is that his framework only contains "completely dark" and "completely bright" area, and therefore the subtlety "thickness of the wires is small" does not arise in Unruh's specific approach. (Thanks to William Unruh for his patient explanation of the isomorphism.)
• Because of the differences between Afshar's and Unruh's setups, it is perhaps useful to talk directly about Afshar's experiment.
• In my opinion both Unruh as well as Kastner replace Afshar's experiment by a completely different experiment that does not capture the main flaw of Afshar's reasoning.

He then goes on to state his reason for saying Afshar is wrong...

• The main flaw is that Afshar does not realize that for a tiny grid, only a very tiny percentage of photons is used to observe the wave-like properties of light; these are essentially the photons for which the which-way information is completely lost. Because most photons go through the lens without any interactions and interference, Afshar is not allowed to say that he observes the wave-like phenomena with visibility close to one. In fact, it is close to zero if a consistent set of photons is used to define both V and K.

What this is saying is that you can't trust a lens. The reason for this (as Afshar has covered) is that all photons are acocunted for and thus there is the *appearance* of which way information even for those photons that couold only have avoided the wires due to interference.

Most of the current arguments run up against the same problem. If all photons deomstrate the appearance of which way information and yet this is impossible, it can only mean that the lens can lie. Tell me where is states that lenses can lie in undergraduate science material.... Dndn1011 01:50, 1 February 2007 (UTC)

Sorry Mr Chairman, your summary of Motl's argument as What this is saying is that you can't trust a lens. shows that we really do need someone with a physics grounding in your role. It also shows why we should just report what the sources says, not interpret them. --Michael C. Price ^talk 02:34, 1 February 2007 (UTC)

Sorry Mr. Sarchastic, the issue is alreday settled on this topic here... we are keeping the reference. However, the question I am asking is one anyone would ask. So, would you care to give the answer? Or are you going to just continue being sarchastic and unhelpful? How can the lens not show the origin of a photon? No one has answered this very simple question yet. Please enlighten me. I keep asking the question because I have not been pointed to the answer, yet. Dndn1011 02:44, 1 February 2007 (UTC)

I'm not being "Sarchastic". If you don't understand quantum physics you will not understand Afshar's experiment. That's just a fact. If people are stimulated by the experiment to tackle QM then that's good and they can go to quantum mechanics. Quit trying to learn or explain QM here.--Michael C. Price ^talk 08:46, 1 February 2007 (UTC)

I am not trying to learn or explain QM. My god, it's become like a religion hasn't it? I am asking blatently reasonable questions in efforts to end up with an article that actually makes sense. What will shut me up is an answer the the apparently basic questions I am asking that actually fits the verifiable facts. I have yet to get an answer to a basic question and this seems to highlight a misunderstanding of the experiment by those who contirbute to the article. For example, your comment below that the wires absorb some photons and these photons lose their WWI. Yes, theoretically this is understood. This has to be the case to agree with the principle of complementarity. However these photons still retain the appearance of WWI. That is the experimental evidence. Note I say "appearance" because I have a far more subtle understanding that you give me credit for. We can not prove the 1-1 mapping of hole to target via the lense, so I qualify this. I can only conclude through your answers you have not grasped that photons that should have hit the wires retain the appearance of WWI. Is it not important that those of us editing the article should properly understand the experiment? My own level of understanding of the experiment appears to be enough to notice inconsistencies in the article between the facts and editor's interpretation of the facts. I am trying to identify the key argument that Afshar uses and interpret it in plain English, because that would be good for the article. Dndn1011 12:31, 1 February 2007 (UTC)

Clarification: There is an error in the above, which I just noticed. I was making a mental jump in my mind and misinterpreted what you were saying. I took your statement "the wires absorb some photons and these photons lose their WWI" to mean "the photons that interacted with the wires but avoided them due to wave like behavior lose their WWI". My fault and my appologies to you for misunderstanding what you are saying. However I was only considering those photons which are actually detected, not those which are not detected because they are scattered/abosrobed by the wires. The scattered photons, as I have said just now elsewhere, may or may not be significant in the interpretation but that is a different issue to the one of what Afhsar's interpretation actually is. Dndn1011 14:22, 1 February 2007 (UTC)

Like an idiot I will once again try to explain why Afshar's experiment does not violate complementarity, despite all the past evidence that it will do no good at all. Complementarity applies to single particles (see Bohr's quote about "the particle"). Each particle is either absorbed by the wires demonstrating wave properties OR passes through the lens demonstrating particle properties (which slit it passed through) BUT NOT BOTH. No photon passes through the lens AND is absorbed by the wires. Therefore no photon demonstrates both particle and wave properties. Ergo complementarity is not violated. -Michael C. Price ^talk 13:22, 1 February 2007 (UTC)

Thank you. However this does not match my understanding of the experiment from what I have read. With the wires in place some photons avoid them in a manner than can only be explained by wave properties. That is, if the photons were behaving as particles, we would expect a far greater number of photons to be absorbed or scattered by the wires than is experimentally observed. In fact it is these 'extra' photons that avoid the wires that are demonstrating wave properties, not those photons with are absorbed or scattered. This is shown by how when both slits are open, fewer photons are absorbed than would be the case if the photons behaved solely as particles. So your interpretation is not that which Afshar presents as I understand it. It does not matter who is right, we are trying to present Afhsar's argument, not yours here. You state "Each particle is either absorbed by the wires demonstrating wave properties OR passes through the lens demonstrating particle properties (which slit it passed through) BUT NOT BOTH.", yet this does not appear to be what Afhsar claims. Instead Afshar is claiming that there are photons that avoid the wires because of wave like behavior, yet are also detected as having come from a particular hole. It is true that no photon passes through the lens and is absorbed by the wires, that is trivially obvious. However the experiment apparently shows that some number of photons must have avoided the wires due to interference and yet must have also been detected via the lens as having come from a particular hole. Ergo some photons have demonstrated both wave and particle behavior in the course of their existence. Granted we don't know which photons, and this may or may not be significant to the interpretation. It is a statistical analsysis. This may also be significant to the interpretation. But we should at least be presenting the argument presented by Afhsar in the article, not one by you or me or anyone else. Notable critiques should be present too, but I feel it is kind of important to state correctly what Afhsar is trying to assert before we add critique, don't you think? Dndn1011 14:04, 1 February 2007 (UTC)

Clarification: When saying all photons are detected, I should say to be accurate, all photons that avoid the wires and are detected. I believe some small nummber of photons do get scattered, because a few photons contribute to the interefence pattern close to the minima, even if the probability of doing so for an individual photon is small. Again this may or may not be significant. Afshar might clarify what consideration his paper has given to this, if any. Dndn1011 14:11, 1 February 2007 (UTC)

Clarification: Motl states "these are essentially the photons for which the which-way information is completely lost". This is counter to the observations that all photons apparently show which way information via the lens. If the lens 'manufactures' which-way information in cases where it is supposedly lost, this can only mean that thw which-way information provided by the lens cannot be relied on. This is what I meant by the lens lying. Dndn1011 02:54, 1 February 2007 (UTC)

Those photons don't provide WWI because they do not go through the lens because they are absorbed by the wires!!!! --Michael C. Price ^talk 08:50, 1 February 2007 (UTC)

How can they be absorbed by the wires and yet still be detected at the target? All the photons are detected. This is the point. You say these photons are absorbed when the experiment apparently shows this is not so. So once again, clarity is what I am seeking and you are not providing any. Dndn1011 12:10, 1 February 2007 (UTC)

How can they be absorbed by the wires and yet still be detected at the target? They aren't. --Michael C. Price ^talk 13:03, 1 February 2007 (UTC)

How can it be that all the photons are accounted for and detected? And yet at the same time some are absorbed? You are still not making sense. Dndn1011 13:21, 1 February 2007 (UTC)

The experiment, according to my understanding, claims all the photons are detected. Do you dispute this? It's fine if you do, like I said what I am seeking is clarity. Whether you dispute this or not is not the point, it is what is claimed by Afhsar as I understand it (Afhsar will clarify I am, sure), and thus would bring clarity to Afshar's argument, and should be mentioned in the article. The dispute over the experimental evidence, if there is any, could then also be added to the article. If you find any references that dispute the experimental findings, we can include them. It is all about being clear about who is saying what, isn't it? Dndn1011 13:28, 1 February 2007 (UTC)

Who says "all the photons are accounted for and detected"? --Michael C. Price ^talk 11:38, 2 February 2007 (UTC)

If I am correct about the various bits of reading I have done, I believe Afshar has clarified in his responses that all photons not scattered by the wires are detected. No doubt Afshar will clarify this point. Dndn1011 11:49, 2 February 2007 (UTC)

Please read other reponses above. There was a misinterpretation of your comments by me. I interpreted your 'absorbed' incorrectly as "interacted with", in the sense of the photon in its wave state passing through the wires. Then I started saying "Asborbed photons are detected". Which is nonsense, if you mean that photons which have their path blocked by the wires = absorbed. I appologise for my inaccurate use of language. This came about in my mind because I was not considering scattered photons as I have covered in my comments above. To summerise: 1. All photons that do not get blocked by the wires are detected. 2. These photons must include some which avoided the wires due to interference. 3. Thus it is proven that some photons must have interfered with themselves (acting as a wave through both slits) and yet also have been detected as coming from one or other hole. This is my understanding of the conclusions of the experiment. The interpretation of this is another matter, as I have said. Dndn1011 12:04, 2 February 2007 (UTC)

Under point 3, do you, or more to the point Afshar, take into account the photons that came through one pinhole and were diffracted by the wire grid so they look like they came through the other pinhole? --Art Carlson 14:20, 2 February 2007 (UTC)

That is as you say a question for Afshar, but for the article we need to focus on what Afshar's claims are. I am hoping that the brief summary I have given is a correct summary of the argument and that Afhsar will confirm it. But this does seem to me to be the central argument. Dndn1011 15:11, 2 February 2007 (UTC)

Dndn1011: 1) & 2) & 3) are all correct, but 3) is not as signficant as you suggest. We already know (from the clasical double slit experiment and a host of other empirical data) that the photons propagate as waves, so the wires are only demonstrating what we already know, that they obey a wave-equation; i.e. the wires do not perform a measurement on the photons they do not absorb. See the previous discussion of null-measurements, information-free "measurements" etc. --Michael C. Price ^talk 14:46, 2 February 2007 (UTC)

This is your opinion and analysis on the experiment, which I have no interest in discussing as that is not the point of the present discussion, which is aiming to correctly convey Afhsar's claims in the article. Dndn1011 15:11, 2 February 2007 (UTC)

Odd: just now you were asking for clarification. When you don't get answer you like/understand suddenly the rudeness returns. Don't bother to ask for any help from me again. --Michael C. Price ^talk 17:21, 2 February 2007 (UTC)

I am Sorry, I really did not think I was being rude, certainly that was not my intention. I have no problwm with your answer, indeed I am happy that finally we seem to understand eachother. I was merely saying that I did not want to argue with you over it because it was not relevant to the task of sorting out the article. I happen not to be convinced by your argument, but we should agree to disagree and leave our interpretations of the experiment out of the discussion otherwise before long we will be at eachother's throats again. So please accept my appology for any unintended offence. Dndn1011 17:36, 2 February 2007 (UTC)

Accepted: just bear in mind it is easy to be unintentionally rude (I know I often am). People who are quick to accuse others of rudeness are usually unbelievably rude themselves. BTW I did not think I was making any controversial claims in my clarification. --Michael C. Price ^talk 18:18, 2 February 2007 (UTC)

Art Carlson: painting the wires black can eliminate photons scattered off the wires. Also making the wires thinner will reduce any general wire-induced diffraction effect to as low a level as we wish. (The wires are placed at the slit-diffraction minima to minimise such effects.) --Michael C. Price ^talk 14:46, 2 February 2007 (UTC)

Painting the wires black will not eliminate diffraction. Making the wires as thin as we wish will not only eliminate diffraction, but also any degradation of the image when only one slit is open, which I thought was an essential part of Afshar's argument. --Art Carlson 15:09, 2 February 2007 (UTC)

I never said painting the wires black would eliminate diffraction; they will eliminate scattered photons though, by absorbing them. I agree with the rest of your statement. --Michael C. Price ^talk 17:21, 2 February 2007 (UTC)

• I agree with Dndn1011's depiction of my arguments in this thread. Also, Art is correct above. -- Prof. Afshar 18:25, 2 February 2007 (UTC)

Comment. Dndn1011 you are free to ask this privately, but knowing the answer to this question will not advance the writing of this article, unless you can cite a reliable source that make the claim. Even if Ed Witten showed up here and resolved the issue, unless he published it (in a paper or in a blog which was reliably known to be his), we couldn't use his wisdom. That's the way it is, for better or worse.

Also note that the talk page is for discussion about the article, not for our general edification. --CSTAR 02:58, 1 February 2007 (UTC)

The reason for asking the question is to help make the article clear. This issue appears central to Afshar's claim and I if no one has an answer it would strike me as an important thing to highlight in the article. It is not a question of adding research here but underscoring an important part of Afshar's claim, at least as I understand it. Thus I am talking about the article, because I am talking about the experiment and what has been published on it. There has existed a bias towards OR critique of the experiment in this article. I am trying to focus on the pertinent facts, of which this appears to be one. Dndn1011 12:10, 1 February 2007 (UTC)

• Dear all, here's my two cents on this issue: Frankly, it is an honor to have Prof. Unruh interested enough in my experiment to have commented on it, regardless of the validity of his arguments. Perhaps he would be inclined to rebut me in the Foundations after he reads my paper there. His views are important enough to quote, even if they were uttered in a seminar to a colleague. Dndn1011, I will address your questions above soon.-- Prof. Afshar 04:07, 1 February 2007 (UTC)

Current status: Keep the reference