Talk:Afshar experiment

I'm back.
Hey, I'm back! Sorry about the absence, I've been busy. Didn't mean to make you all wait so long. Now, as I understand, Afshar made edts which have been reverted. Although he shouldn't of made the edit, I don't entirely blame him. It's frustrating when someone disappears without notice.

This whole process seems to be going nowhere, and the point-by-point system is not working. And yes, Danko is right, I do take offense at your statement. I realize you are frustrated, but excuse me for occasionally changing my mind. If I was to be so stubborn as to never change my mind on this article, then I would hardly be a decent mediator.

Now, as to the OR issue. With the "Specific Critiques" section, we are essentially saying "Some scientists disagree. For example, here is what Professor X has said about this." We are not saying "Some scientists disagree. For example, the arguments made by Professor X are completely true, undeniable, and totally disprove Professor Afshar." We are only stating two things as fact in the "Specific Critiques" section. We are stating that some scientists (specific scientists, not just 'some scientists') disagree, and that they have made the following arguments. We are not stating that those arguments are correct, peer-reviewed, or that they prove Afshar wrong. We are only stating that these people have made these arguments against Professor Afshar's interpretation. It brings to mind the legal disclaimer one hears so often: "The viewpoints contained herein are the views of the individuals that expressed them, and do not necessarily represent the views of FOX Networks or its employees."

In terms of reliability of sources, we do not need to show that the "Specific Critiques" are correct. We only need to show that those statements and ideas really were expressed by the same people we cite. It doesn't matter if the places Bill Unruh or any of the other people made their remarks or published their articles were peer-reviewed. It only matters if we can verify that yes, Bill Unruh really did say/publish that, and not someone using his name.

Note that this only applies to the "Specific Critiques" section.

I will be here as often as I can, however, I may not be online every day. Please, bear with me and play nice while I'm gone. If you feel that I might not see a specific comment on the talk page, please, leave me a message on my talk page.

One last thing: Please, do not post comments on this discussion page saying "Mediator, do this." "Mediator, I'm obviously right. Enact my suggestion now!" It annoys me, and it makes me no more likely to do what you want. This kind of comment assumes that I will automatically side with whoever wrote it, ignore the ongoing debate and any other viewpoints and do whatever you want. It is like standing up in the middle of a trial and telling the jury "This has gone long enough. Please, end the trial and rule in my favor now." I am not naming names, although it seems almost everyone has made some number of these comments. Again, if you want to make sure I get a message, post it on my talk page. Sdirrim 04:55, 7 April 2007 (UTC)

Afshar violations of General Relativity
I will not comment on the results of Afshar's attack on my work, and the journal where it is published - they are obvious, I have deleted personally everything that connects my work and this article. However I want to give the following information to all participants of this discussion, because I think they must always look for the truth without emotions. So Afshar stated:
 * "A journal that publishes papers that violate special relativity is a sure sign of the type of referees it has. Publication in this journal is also a clear indication of the type of author it attracts. No self-respecting physicist would even refer to "Progress in Physics" let alone publish there."

And here I provide quotation from Afshar's 1998 work, where Afshar URGENTLY insists on paradigm shift that will violate general relativity!
 * "A novel method of derivation of Mass/Inertia is advanced and its application to Dark Matter dynamics is discussed. It is proved that gravitational mass of any particle is not constant at all distances and that the Machian approach to inertia as that employed in Einstein's General Relativity is incorrect. ... The MACHO team's failure to find the baryoinc candidates to dark matter enforces the urgency of this paradigm shift."

Well, Afshar so far did the following verifiable statements
 * [i] the Nobel prize of Enstein for the photoelectric effect should be taken back [New Scientist],
 * [ii] the idea of photon is dead [New Scientist],
 * [iii] Bohr's complementarity is wrong [Found. Phys.],
 * [iv] General relativity is wrong and urgently one should take the novel Afshar theory of mass/inertia Afshar, 1998.

Afshar, please tell us What comes next? p.s. As I have seen Afshar has Wiki-entry I think to update the article of Afshar and add section "Research and novel achievements" where I intend to list the points [i]-[iv]. Afshar, will you support my edit? BTW you fully deserve to have Wikientry, where one will have the opportunity to get accustomed to ALL your novel ideas, that the Afshar experiment article presently did not cover. Danko Georgiev MD 06:56, 7 April 2007 (UTC)


 * Violations of existing theorys can differ in important ways. In particular, there are:
 * 1. violations which can occur as a result of reading the original theory "incorrectly" - ie. reading it in a novel way (consciously or otherwise).
 * 2. violations which can occur despite a "correct" reading of the original theory.
 * In the first case a novel theory is substituted for the original theory - it is incorrectly placed under the name of the original theory. This is an a priori violation which may in fact lead to no existant problems at all - due to faults in the original theory - which have been inadvertently solved in the substitution. In the second case a novel theory is not substituted, but required since the original theory has identifiable faults. The first kind of violation is unacceptable since it introduces a novel theory via the back door (even if it solves any problems with the original theory). It violates the existing theory in an historically ignorant manner. The second type of violation is "acceptable" since it is not, a priori, a function of misreading the original theory. Type two violations demand the introduction of a novel theory (through the front door), and these "front door" novel theorys should always be encouraged. --Carl A Looper 23:04, 11 April 2007 (UTC)
 * Dear Carl, when it comes for Afshar to judge the quality of "Progress in Physics" the journal where I have disproved his utter nonsense, it is claimed by Afshar to be "disreputable" because published theories that promote anti-relativistic viewpoints. However when it comes to judge the Afshar's competence in physics, promotion of anti-relativistic viewpoints is something deserving encouragement ??? ??? ??? Danko Georgiev MD 06:17, 12 April 2007 (UTC)


 * Although I'm encouraging novel theorys, I'm not suggesting they may be any good - they would still need to be assessed. But if there are problems with an existing theory then whatever the ongoing candidates for a solution might be, they would have to be novel ie. new, different from, or "anti" the original theory. What else could they be - the same as the original theory? Regarding the right journal's to publish - I wouldn't worry about that - Afshar is pulling your chain. And you are taking the bait. You can publish wherever you like. It would be good to publish in the right journals though - wouldn't it - eh? --Carl A Looper 07:24, 12 April 2007 (UTC)
 * I personally like to submit to mathematically oriented journals. I don't know what means to publish in the "right journals"? I am not Afshar, so I do not want to put my stamp on journals and say which is reputable and which is disreputable. Danko Georgiev MD 08:33, 12 April 2007 (UTC)


 * Hi Danko. Yes, the "right journal" depends on a lot of interacting criteria and one man's "right journal" is another man's "disreputable source". When I was making films in my youth, I always dreamed of having my work screened ("published") in a big cinema on 35mm film, in widescreen format. I eventually achieved this aim - a short computer animated film, released in Australia, and screening with the feature film, "Scanner Darkly". It was a big deal for me. It was the "right journal". But my early Super 8 films, screened in the local pub, remain just as relevant and important (and many remain more so). --Carl A Looper 22:30, 12 April 2007 (UTC)

Popper's experiment
People involved in the discussion here might be interested to know that there now exists a wiki entry on Popper's experiment.


 * Thanks Tabish. Enjoyed the article very much. Will discuss further there. --Carl A Looper 22:50, 12 April 2007 (UTC)

Which-Way problem solved
Hello,

As far as I understand, critics claim this experiment does not give details about which pinhole the photon went through and therefor does not give which-way information, thus the experiment is false.

Couldn't electrons be used instead of photons, this way one separate electron can be fired at a time, hitting only one detector (giving which-way information). When repeated a million time, we could see that the 'grid' has had no effect and thereby proving that the electron has also acted as a wave.

I believe this setup would be superior to Afshar's idea, yet I could not think of a proper replacement for the lens which would need to defract the electron to the detectors.

Could any real physicists comment on my idea.

Thank you,

LAUBO 21:05, 20 April 2007 (UTC)

This argument is exactly equivalent to the one which Unruh gives in his different thought experiment with mirrors in an interferometer. --Tabish q 19:40, 21 April 2007 (UTC)
 * Having no which-way information in this experiment has nothing to do with the particles being photons or electrons. You will ALWAYS get only a single click. However, the question is whether a particular detector clicking, in the case of both the slits being open, gives one information about which slit the particle passed through? Because closing one slit leads to only one particular detector clicking, one tends to erroneously associate each detector with a respective slit, even when both the slits are open. A careful analysis will show you that the answer is no. A simple way to see it is the following. Firstly, in quantum mechanics, particles obey schrodinger eqn, hence there is a wave-function associated with them, which makes even electrons behave like waves. Now if the interference is there, all the particles are coming from the bright fringes (dark fringes transmit no particles, by definition). Experimentally afshar blocks the dark fringes, so even experimentally we are sure that particles do not pass through the dark fringes. Bright fringes are formed by equal contribution from both the slits (what we call constructive interference in classical wave optics). Once the contributions from the two slits are added up, the which-way information is lost for good! However, the wave-function of the particle at the bright fringes is such that the particle has equal probability of going to either of the two detectors. But now the which-way information is not there, and the detector click doesn't tell us which-slit the particle came from.
 * Dear Tabish, PLEASE do not misinterprete Unruh, and do NOT speak about Georgiev's argument applied to Unruh's setup. Indeed in my analysis is where I show there is no which way, Unruh does not show it. Unruh believes there is which way information and interference at the same time! Please read carefully, before you post. P.S. In my recent paper I made 1-to-1 mapping with your waves for Afshar's setup. Simply I have expanded the canceled sinh terms in the form of exponential functions, then simplify the algebra, so I have recovered 8 waves. Then I map the 8 waves (4 cosh waves and 4 sinh waves) from your calculation with the 8 waves in Georgiev's description of Unruh's setup. PLEASE note that the setup decribed by me, is composed of two Mach-Zehnder interferometers, so basicly I even obtain exactly the opposite "clicking" of detectors (compared to Unruh's original description) when one puts obstacles on interferometer paths. So Unruh is completely wrong on everything, except the fact that the so-called by me "Unruh's setup" is equivalent to Afshar's setup. My recent work is the first clear 1-to-1 mapping, and will appear online soon. Best, Danko Georgiev MD 07:12, 22 April 2007 (UTC)

I see this experiment still has a lot of controversy around it. Thank you both for your help anyway. I can't wait to become more educated in physics so that I could understand atleast a small part of this all. LAUBO 09:27, 22 April 2007 (UTC)
 * Dear LAUBO, it is enough if you understand mathematics to understand the correct description of the experiment and why there is no which way information even if there is no grid or obstacles on photon paths. Unfortunately, most of wiki-editors involved here and are "slaves" of authority and are "afraid" to think with their own head. Also, strikingly Art Carlson, possibly tried to understand Unruh's setup, then reached the correct conclusion that I have published, and mis-attributed it to Unruh. (Carlson and Tabish, should be careful when they speak about Unruh's work, and also better be acquainted with my work, because I personally don't like attributing my analysis to Unruh.) A nice introduction and full explanation of what is going on with 8 interfering waves is given in my published work Georgiev (2007) PP vol.2: 97-103. All issues of Progress In Physics here. Unruh's reply Unruh (2007) PP vol.3: 27 unfortunately contains many errors, but at least says clearly that there is both interference and which way information - I hope this is good information for Art and Tabish!!! My reply [comming soon]. Danko Georgiev MD 00:35, 23 April 2007 (UTC)

If you do block the dark fringe (introduce the wire-grid in Afshar's experiment), you are in effect recording interference. But once you have blocked the dark fringe, Unruh argues, you can no longer claim that there is which-way information. Which-way information is lost. So, in this case there IS interference, but there is NO which-way information. So you see, nowhere does Unruh claim that there is which-way information and interference at the same time. Now let me explain where I disagree with Unruh. Unruh asserts that IF you do NOT block the dark fringe, you do not KNOW that it is dark. And hence you cannot assume that photons do not pass through that region. I believe that if you have blocked a path and checked that no photons come that way, and that it is really dark, even after removing the block, you should be able to say that the path is still dark. This is just common logic: if you have checked by putting a block that no photons go a particular way, why should photons suddenly start going that way, just because you have removed the block? This is the ONLY essential difference between Unruh's and my view. --Tabish q 20:35, 26 April 2007 (UTC)
 * Dear Danko, unfortunately, you are reading between the lines that Unruh wrote. Let me first quote Unruh in his comment on your paper, "However, he then implies that I hold certain positions about the interpretation of the experiment, interpretations which I neither hold nor are contained in my description." Unruh does NOT say that there is interference and which-way information at the same time. What he says amounts to the following. Without blocking the dark fringe path (or in Afshar's experiment, without putting the wire grid), you cannot say that there is interference. Interference is not an abstract thing, it is a measured property. If you do not block the dark fringe, you CANNOT  claim that it is dark, and that there are no photons passing through. So, you cannot invoke any argument of which-way information getting lost. So, in this case, there is which-way information, but there is no interference. (remember, this is Unruh's view I am talking about, not mine)
 * Dear Tabish, I have personal correspondantion with Unruh since 2004, and I know word-by-word ALL his published sources. Unruh SAYS there is interference, and which way, but ONLY measuring the interference destroys the which way information. I have explicitly formulated elsewhere in my work - KNOWLEDGE of interference ITSELF erases the which way information. And the knowledge is equivalent with the MATHEMATICAL description of the setup. If you that there is interefence you don't need to measure it. Unruh is wrong, you misattribute words to Unruh that he never said. Please be sure you are well acquainted with Unruh's claims before you speak on his behalf. p.s. LET US TALK ON UNRUH'S INTERFEROMETER TALK PAGE or by e-mail.Danko Georgiev MD 05:18, 27 April 2007 (UTC)

Direct disproof of Tabish's thesis on what Unruh says is this passage:

"The [coherent] system is arranged so that the interference at the second half silvered mirror is such that now all of the photons go on path 3. path 4, like the dark fringes in Afshar's setup, contains no photons. These will fall on detectors 5 and 6. Furthermore, one can still argue that any photon which fell on detector 5 came from path 1 and those on 6 came from 2." Unruh in rebel, 2004

Unruh knows that there are no photons EVEN IF THEY ARE NOT MEASURED, and says there is which way information. Dear Tabish, please be sure that I am very strict in everything, and I never lie or get misleaded in what others say! I am correct what Unruh says, you are misleaded. I do not want to be enemy of yours, simply Unruh is saying wrong things, and he is the one "in the opposite camp". The provided by you quotation of Unruh accusing me of misrepresentation is misleading, and I have rebutted him completely - expect soon the PP article of mine. Danko Georgiev MD 05:26, 27 April 2007 (UTC)


 * Dear Danko, this is too fine a point to get into an argument about. What I have said has also been cross-checked by personal communication with Unruh. Please keep cool, and realize what the difference is between yours and Unruh's point of view. You say, "the knowledge is equivalent with the MATHEMATICAL description of the setup". However, Unruh, like many others, believes that there cannot be any knowledge without measuring. Throughout his article, he has only talked of measuring interference and measuring which-way information. However, I believe that mathematically, existence of which-way information is incompatible with the existence of interference (this is what I have shown in my work). But if I say that Unruh is claiming the opposite, then I am putting words in his mouth. He only talks about measuring, and drawing conclusions from measurements. --Tabish q 07:13, 27 April 2007 (UTC)
 * Dear Tabish, I am cool! All these anti-realist errors are widely commented in my forthcomming PP reply. Yes, mathematically interference and which way are incompatible, this is what YOU say, and what I say. It is NONSENSE = language confusion = pseudoscience to say "there are no photons (mathematically)" and then "but I have to measure my mathematics" to confirm it. This is to say "2+2 = 4 (mathematically)", but "unless I measure that 2+2 = 4 physically for everyindividual case I am not sure in the math theorem"! Do you see that one of camps will be a very confused and ignorant in mathematics? I will confess publicly that I am wrong, once one finds error in my maths. Unruh posted clearly "no photons", I am not putting "words in his mouth". p.s. I decided not to send you my article before publication, please wait 1 week, it will possibly appear online by then. Best, Danko Georgiev MD 08:07, 27 April 2007 (UTC)
 * Dear Tabish, here is my official reply to Unruh.

Georgiev DD. Exact Mapping of Quantum Waves between Unruh's and Afshar's Setup (Reply to W. Unruh). Progress In Physics 2007; 3: 28-33.

Regards, Danko Georgiev MD 12:25, 5 May 2007 (UTC)

Hi Danko, I've been away from the debate for a while but thought I'd pop in. I want to defend measurements. There is no need to measure whether 2+2=4 (as you argue) but the measurements done in quantum theoretical experiments are not this type of measurement. Adding 2 and 2 together on a calculator would be what you are talking about. If the calculator said 5 it would be wrong. Either physically wrong (taking place in a universe other than the "real" one) or just incorrectly programmed, or "broken" (crossed wires etc.). But the measurements that take place in quantum theoretical experiments are not this sort of thing. They don't necessarily represent anything other than what they are. They have no opportunity to be wrong. They are "things" in themselves. For example, a detector click. This is a physical signal, which can be reproduced, eg. by recording the click and playing it back later. "Click". It can be stored on your hard drive, and emailed to a friend. It can propogate all over the world and back again. It's evolution within this domain is the stuff of information theory and media theory etc. One could play the "click" in an art gellery and it would have different meaning from being played at a physics conference. It is within the realm of information but no less physical. It travels via sound, electricity, re-encoded in the switch states of computer RAM and so on ad nauseum.

In quantum theory we're still dealing with actual signals - eg. actual detector clicks - but before they exist as such. We do so using a model of the nature of this click before it became an actual click - before it is an actual signal - when it was still just a "virtual" signal. But it is only by virtue of the fact that we can predict the actual click (statistically speaking) that we can speak of a "virtual" signal at all. But in the end analysis we are still talking about what actually happens - ie. the actual click. We're not talking about what the click represents - ie. the so called "reality" behind the click. We're not talking about our mathematical model. The click does not speak about our mathematical model. It is our model that is doing the speaking and our model is speaking about the click. About measurements.

But we can do it the other way as well. We can use measurements to speak about the model. But this does lead to the strange idea of measuring our model - which is what I think, you are objecting to. And I would too. But in the absence of a model, for example, in a search for another model this is exactly what you would do. And the early quantum theorists did just that. Not because they wanted to confirm or prove their model but because they didn't even have one. They were "reverse engineering" the measurements so to speak.

What's strange is that the discovered model implys the "universe" should be reconsidered, not as the reality behind an image, or behind a detector click, but these very things themselves - the actual signals. The entire "reality/model/signal" thing is sort of shifted around by one beat. Reality is now the signal which once upon a time represented reality. And what was once upon time reality is now the model, and this now represents the signal. It is hardly surprising that this can engender confusion in language as much as anything else. And so we have to explain ourselves. We have no choice. We can't fall back on a few words - we have to elaborate. For example, what is meant by "anti-realist"? This is not a trick question. It is an important one. Are we talking about Platonic reality, Kantian reality, Cartesian reality, Stoic reality, postmodern reality, etc.?

The relationship between relativity and quantum theory really shows this up. Hopes for Everything Theory are based on the assumption that there is some hidden unity (eg. mathematical model) lurking underneath the relationship between these two theorys. But the incompatibility between these two theorys is not anything new. It's an imcompatibility that's been understood by philosophy (if not solved) for thousands of years. Theoretical Physics just reproduces this incompatibility. Whether it can reproduce any solution remains to be seen. Or perhaps it can produce it's own - that would be weird.

Carl (sorry forgot to sign in)

oooooooooooooooooooooooooooo January 4. 2008 -- From Dave

Just my two cents on this thing. First, yes, of course, certainly, without question, we do know which pin hole the photon went through when it registers. The light is focused by the curved lens and the only way it can be focused, to a particular spot, is if it’s going through the lens (anywhere across the curved lens) from a particular angle, thus showing up at one spot or the other [see basic optics for goodness sake]. Second, the 2 waves (split off from 1) were there because we know the double slit phenomena is well established. The 2 intersecting waves make their way through the grid like rays or "spokes" of light (derived from an original single photon). The spokes make it through the grid (except for an occasional, rare photon bouncing off the grid). Third, the experiment is not about “knowing or not knowing the which way path information,” this is not at all necessary, but about the intersecting of the waves (or the so called wave function) [Special Note: Some confusion can arise because of other experiments where the fringe pattern is wiped out. Although often believed, however, this is not at all due to “knowing the which way information” but actually the sandwiching together of a fringe and anti-fringe pattern because of the experimental set up]. Fourth, how can this be? Now it comes down to reason and theory, and you can take your pick. My best guess is something along the lines of the Many Worlds Theory (i.e. there’s actually a zillion photons intersecting, and probabilistically becoming more likely to be perceived at the points of intersections, but only 1 can be eventually observed). In which case the photon percieved at the detector is just 1 of many that are not percieved. However, with the Many Worlds Theory it is thought that the realities split off from a point, while, in my opinion, they were always there to begin with - and we only perceive one of them.

-- Dave —Preceding unsigned comment added by 70.53.123.41 (talk) 23:26, 4 January 2008 (UTC)

Experiment Details
Hello,

I would like to ask some details about this experiment. I need it for my own use, but I also believe it is essential for an encyclopedia to have this data.


 * What are the precise dimension of the experiment? - lens at 4.2 m after the slits, image at 5.58 m after the slits.
 * How big are the pinholes? - 0.25 mm
 * How far appart are they from eachother? - 2 mm
 * How big is the grid, lines and spaces between? - you can calculate the interference pattern by yourself at 4.2 m after the slit, take the photon wavelength of 650 nm.
 * What type of lens? - doesn't matter
 * What type of detector? - doesn't matter

Thank you, LAUBO 09:33, 22 April 2007 (UTC) Answered directly by me, Danko Georgiev MD 00:42, 23 April 2007 (UTC)
 * If you need this information, why don't you read Afshar's article? --Art Carlson 10:27, 22 April 2007 (UTC)

Thank you very much Danko! Art, I was not able to find the article.
 * In the second paragraph of the introduction, "a peer-reviewed article appeared in Foundations of Physics" is footnoted (note 1 of the references). Clicking on that link leads you to arXiv, where you can download a pdf version. Where did you run into trouble? --Art Carlson 18:15, 24 April 2007 (UTC)

I am unfamiliar with ArXiv and did not notice the link to the PDF. Thank you very much, this is a big help for me.
 * this paper is the original one, from where I have taken the details of the lens setup reported in New Scientist. Danko Georgiev MD 23:37, 24 April 2007 (UTC)

Mediation Cabal case status?
What is the status of the MedCab case here? Do you need another mediator or can I close the case? --Medcabemail 22:25, 9 May 2007 (UTC)

dark fringes transmit no particles, by definition
This has been bugging me for some time (and I'm sure it would bug Tabish as well)

"dark fringes transmit no particles, by definition" - Tabish

The quote is from the following (my apologys for quoting in full but I don't want to be misleading in terms of context, in particular where Tabish says "a simple way to see")

"Having no which-way information in this experiment has nothing to do with the particles being photons or electrons. You will ALWAYS get only a single click. However, the question is whether a particular detector clicking, in the case of both the slits being open, gives one information about which slit the particle passed through? Because closing one slit leads to only one particular detector clicking, one tends to erroneously associate each detector with a respective slit, even when both the slits are open. A careful analysis will show you that the answer is no. A simple way to see it is the following. Firstly, in quantum mechanics, particles obey schrodinger eqn, hence there is a wave-function associated with them, which makes even electrons behave like waves. Now if the interference is there, all the particles are coming from the bright fringes (dark fringes transmit no particles, by definition). Experimentally afshar blocks the dark fringes, so even experimentally we are sure that particles do not pass through the dark fringes. Bright fringes are formed by equal contribution from both the slits (what we call constructive interference in classical wave optics). Once the contributions from the two slits are added up, the which-way information is lost for good! However, the wave-function of the particle at the bright fringes is such that the particle has equal probability of going to either of the two detectors. But now the which-way information is not there, and the detector click doesn't tell us which-slit the particle came from. This argument is exactly equivalent to the one which Unruh gives in his different thought experiment with mirrors in an interferometer." --Tabish q 19:40, 21 April 2007 (UTC)

But here is an experiment that puts the idea of "dark fringes not transmitting particles" into question.

Imagine Afshar's experiment but instead of the wires at a set of nodal points (where the wave function cancels out to zero - ie. the "dark fringes") one instead places an aperture at each node, everywhere else (by definition of an aperture) thwarting transmission of any particles.

Downstream from each aperture is arranged a small lens (on each aperture) to focus any particles (light waves) emerging from such apertures, onto a detector (for each aperture).

One will clearly see, from the formalism, and presumably (therefore) experiment, that particles (waves) do emerge from the "dark fringes". It is only at the nodal point itself that particles can't be detected. But the wave function can pass through such points and describe detections that can happen beyond such.

If the wave function (or rather the square of such) is interpreted as where a detection could take place, as distinct from where it does take place, the only relationship between these two ideas is that a detection takes place at one of the locations where it might have taken place - irregardless of where and when it does take place. In other words, there is no need for the concept of a collapsing wave function. If a detection takes place at some specific location, in a particular spacetime frame of reference (as it does), there is no requirement that it instantaneously change where it "could have" taken place. It can still be regarded as having been able to have taken place elsewhere. The fact that it "no longer can" need not have any affect on the idea that it still could have taken place elsewhere. But normally it does, ie. we find ourselves unable to maintain the idea, after a detection has occured, that it still could have taken place elsewhere - but it still could have.

Indeed, to ask which aperture a particle went through can be translated as asking in which aperture we "could have" detected a particle. The answer, which clearly contradicts Bohr (and to some extent Afshar) is both apertures.

Bohr clearly considers it possible for a particle to be retrospectively interpreted in terms of a classical path model, ie. as a path through only one aperture (in a two aperture setup) - but only if the eventual detection can't be traced back to both of the apertures (ie. can only be classically traced back to one aperture) - as is the case in the Afshar experiment.

But it is always the case (for all eternity), irregardless of where a detection does take place, where else it could have taken place - and where else it couldn't!

Carl Looper.


 * Dear Carl, I reply to this post, just to prevent the readers from getting the wrong impression that what you have written makes any sense. The meaning by Tabish is CLEAR -- the dark fringes if they are assumed to be "completely dark" by definition transmit no photons! Yes, if $$\psi=0$$ then you will get probability $$\psi \psi^{*}=|\psi|^2=0$$. So you should put very small appertures which have to capture only the completely dark point at the centre of each fringe, so the aperture diameter $$d \rightarrow 0$$ and again no problem. You require finite $$d \neq 0$$ so in this case you get "not completely dark fringes" and thus you are not allowed to criticize Tabish, since $$\psi \neq 0$$. By the way, I don't understand what is puzzling you. If you want to read correct mathematics, you can use the links provided at http://www.sciuni.com/physics.html Danko Georgiev MD (talk) 07:00, 16 February 2008 (UTC)


 * Dear Danko, just in case readers get the impression that anything you have written makes sense, nothing is transmitted by the dark fringes at all, because the transmission point is the source. In any case, since we can never measure the passage of the photon and only detect it at the end (when it is destroyed) it is impossible to verify any theory on the passge of the photon.  You can argue all you like about "correct mathematics" but not you nor anyone else in the world can prove the mathematics is correct by measuring what happens to the photon during its 'travel'.
 * To me this whole thing is pretty obvious if you stop the obsession with mathematics (which is fine as long as its application is valid) and instead use common sense. Let's start with the question of what the lens does.  Without the lens, you get an interference pattern.  Photons might hit either target, most will miss, and if you have a bigger target behind the two smaller targets you will see an interference pattern.  It is not possible to determine the path of the photon from knowlegde of the source and the point of detection.  All you know is there is a light source and a point of detection.  You know nothing else.  Therefore it can be argued that just as it is impossible to measure what happened, it is impossible in infer anything about what happened from the information provided.  It is a big mystery.  There is no mathametics that can help you understand what happened.
 * Close either slit, and we see only photons hitting the appropriate detector. Aha! We say.  We know which hole the photon went through.  Alas, this is a fallacy.  All we really know is there was a light source and a point of detection, just like before.  And we infer that it took the path through the hole because when we look at the experiment it seems clear to us that it is the only logical way.  In other words, after detection we mentally backtrace to understand what happened.  This is actually not very scientific.  The photon could have gone through the material directly, instead of through the hole.  We just don't know for sure.  We assume it, because looking at the experiment it seems the only possibility.
 * Block both holes and what do we know? Nothing.  If there are no other detectors, we know only that light is emitted but there is no mathematics to tell us what happens to them.  We assume that the holes have something to do with letting light through, clearly there is a relationship, but the actual mechanism is completely unclear.  Photons could, for example, travel only in straight lines in reality, and through some not understood mechanism be delayed in time to make them appear to have taken a longer route.
 * How likely this seems is not the point; the point is what can be proven. You can not prove this idea wrong.  Since it is not possible to detect the direction of incidence of a photon, we infer the path that a photon took by what exactly?  By the time it took to reach the target.  Well, perhaps it went in a straight line, but just moved more "slowly".  As ridiculous as this may sound, I doubt it can be proven wrong, which is my point.
 * So anyway back to the lens... when we use the lens, photons are detected on either target but not both. Well on each detection we do the same thing: we infer the direction of the photon from what we understand about lenses ans how they work.  But yet again, we have no idea if this is true, we infer it.  It is a guess. There is no proof.  It is an assumption.  ::Finally the wires are put in place, and we find that the photons appear not as disturbed by the wires as we would expect if they had only passed through one hole or the other.  Is this really so suprising?  No I think not.  It is to be expected.  This is because before the lens we cannot infer anything about the paths of photons.  This is because there is no measurement possible.  They are not detected at the wires.  All we know again is that a photon was emitted and detected and we infer the entire history of the photon from the arrangement of the experiment.  What can we infer?  That all detected photons went through one or other of the slits, and yet sampling many cases we observe that too few photons are blocked by the wires which is only possible if some photons actually passed through both holes even though all are detected as going through one only.  This conflict is the evidence required to show the limitations of our inferences.  Inferences based on the idea of time and travel in a classical sense.  The only rational thing to do is throw such classical inferences out of the window at this point.  The experiment proves quite clearly that the concept of photons travelling and 'experiencing' time in a classical sense simply do not appply.  When this is accepted there is no longer any conflict.  And as I understand it, neither the Copenhagen interpretation.  This is iron tight arguing here.  Mathematics cannot save you. Irontightarguments (talk) 02:05, 14 May 2008 (UTC)
 * The above comment is unscientific. I give just one example - when closing one slit, and then we infer that the photon should have passed through the other slit (hole), and not directly through the opaque material around the slit (hole) we infer it from another postulate - namely that the material is completely non-transparent. If you make the material made of glass, then it will be transparent, and there is no big deal if you make a slit in the glass. Every knowledge that we have is given by true statement = true proposition, which we take as granted (axiom, basic postulate, or premise) or we prove it (theorem). Without mathematics there is no common sense, and all discussions are meaningless. Without mathematics there is no room for scientific dialogue. Nothing iron tight here. Danko Georgiev MD (talk) 17:19, 16 May 2008 (UTC)
 * No it is not unscientific: it is beyond your capacity to understabnd it, your being so blinded by the light (if you pardon the pun). You have not addressed the fundemental point I raised, which is that the nature of matter and light tells us NOTHING about the path of photons.  Once again, since you can not actually watch a photon travel through glass, it is impossible to prove it passes through it.  Show me the mathematical proof.  You can't prove it.  Try.  Any argument you present will contain an assumtption, just like your attempt at rebuffing my argument does.  Your argument contains the assumption that photons travel in the classical sense of travelling.  Now it is all well and good making that assumption until some evidence appears that contradicts it.  If a whole array of experiments and thought experiments were not enough to cast doubt on the assumption, then Afshar's experiment certainly does.  You can argue all you like about the mathematics, but fundementally all the mathematics you and others who try to deny common sense present is flawed because every one of these mathematical arguments has within it the flawed assumption.  This is why there is no agreement on why Afhsar is wrong.  See.. if there was an iron tight mathematical proof, everyone would be nodding in agreement.  They are not.   There may be a mathematical solution, but only one that does not make the assumption that light can be thought of as travelling in the classical sense of travel (involving space and time).  The conclusion is distrubing to some scientists, but often the response of scientists to ideas that challenge traditional thinking are not treated scientifically.  Much to the shame of the human race.  Irontightarguments (talk) 18:21, 16 May 2008 (UTC)
 * See.. if there was an iron tight mathematical proof, everyone would be nodding in agreement.  you're kidding, right? --Michael C. Price talk 06:42, 7 June 2008 (UTC)
 * Lol, OK I was getting carried away Irontightarguments (talk) 21:50, 24 June 2008 (UTC)
 * I get Danko's argument (I think). If an aperture, centred on a dark point, is reduced in radius to zero - then no wave can pass through such an "aperture". Anything larger than a zero radius aperture accomodates the possibility of an off-centre (ie. non-dark point) through which a wave might have passed. However waves (last time I looked) do not come to an abrupt stop at a dark point. They pass right through such dark points. It's called a "zero crossing". The only point at which no photons can be detected is (of course) the dark point itself. Before and after that point, they are detectable (in non-dark points). My argument was simply that the dark point "admits" photons in the same sense that a cinema admission ticket "admits" one to the cinema.


 * But I also get Ironman's argument - indeed I have argued something similar on most occasions. But the context is different. One is about what happens in theory and the other about what happens in fact. The wave function is theoretical (not factual). One can "see" the wave function using the mind's eye (thought, math, simulation, etc). One can not see it in fact. So when we speak of the wave function behaving this or that way we are speaking in the theoretical sense. We can "see" the wave function travels through apertures, glass, dark points, interferes with itself, etc. in theory. We can test theory using mathematics - ie. testing the theory for self-consistency. If it is already constituted mathematically then it will already be consistent.


 * The two domains (theory and facts) are not unrelated. While the wavefunction is theoretical it signifys, at the very least, where a particle detection (ie. a fact) might occur. It can also signify more than that - it can also signify "reality", ie. not just (f)actuality), but that is a more complicated proposition. We can test for self consistency (mathematics). We can test for it's relationship to facts but not always - the factual context may not (yet|ever) be known. But can we ever test for it's relationship to reality? I don't see how - unless by "reality" we mean the theory itself - in which case no test is necessary - the theory is it's own reality (identity) - by definition.


 * For the purpose of completeness I might take on Danko's specific arguments


 * "the dark fringes if they are assumed to be "completely dark" by definition transmit no photons!"


 * The important word here is "transmit". A dark fringe (or point) doesn't allow detection at that point (ψ = 0). But it does allow transmission through that point.


 * if $$\psi=0$$ then you will get probability $$\psi \psi^{*}=|\psi|^2=0$$. So you should put very small appertures which have to capture only the completely dark point at the centre of each fringe, so the aperture diameter $$d \rightarrow 0$$ and again no problem. You require finite $$d \neq 0$$ so in this case you get "not completely dark fringes" and thus you are not allowed to criticize Tabish, since $$\psi \neq 0$$.


 * Well yes, if you reduce the aperture radius to zero then you will fail to get a transmission, but not because there is a dark point there but because there is no aperture at all! Try a zero radius aperture on top of a "white point". You won't get a transmission there either. And besides which, Tabish was not suggesting a zero radius aperture at the location of a dark fringe (or point). Admittedly though, you can not experimentally demonstrate the transmission of a photon through a dark point. You can only do so theoretically. So sure - my experiment doesn't prove anything. But in my defense, the experiment was a mind experiment, a pointer to the theoretical case - ie. where wave functions do pass through zero.


 * --Carllooper (talk) 04:41, 9 April 2009 (UTC)


 * Hello Carl, I will just point out that your last explanation is false. I don't say $$d=0$$, I say $$d \rightarrow 0$$. And I use the mathematics of Limit of a function like this: $$ \lim_{d \to 0}f(d) = 0 $$. Clearly if your comment was true, it will imply that for all functions $$f(d)$$ you get $$ \lim_{d \to 0}f(d) = 0 $$. Yet, this is obviously false, and your comment is mathematically ungrounded. To let the aperture diameter go to zero is equivalent to get the wavefunction value of a point. I hope you get the point. And yes, I mean that if you go out of this single point at the center of the dark fringe, you will start collecting points that are partially dark, so hence their transmission is not exactly zero Danko Georgiev MD (talk) 08:24, 18 April 2009 (UTC)


 * Very good argument! Since the diameter of the aperture (d) does not reach zero (as it must if it is to be an aperure) then the "point" being tested can never be dark, (can never be a point!) ie. one can not experimentally demonstrate that a dark point transmits particles. While I agree with this, it does not invalidate the theoretical point I'm making (that dark points transmit particles). But that said, lets stay within the experimental domain. Given that an aperture (by defintion of such) approaches zero without reaching zero (d->0) it means the experiment can't have any completely dark points (p == 0) in the first place since the waves are constructed using apertures (d->0). In other words, when talking about "dark points" in any actual experiment we must be talking about near-dark "points" (p!=0 and d!=0). In such a context the discussion of dark points (p==0) transmiting particles (or not) becomes irrelevant. But lets not lock ourselves into the limits of experiment. On what basis can one argue that a dark point does not transmit particles? If we are talking about dark points in the first place (p==0) then we have crossed that line between experiment and theory. By what definition does p==0 not transmit particles (other than that transmission is a wooly concept in the first place) - Carl Looper —Preceding unsigned comment added by 150.101.201.248 (talk) 01:07, 20 April 2009 (UTC)


 * Carl Looper, it's not true that a wave (quantum or classical) can be in some sense transmitted through a point where the displacement is always zero. If the displacement is always zero at a point then you can put a barrier there without making any difference. In the case you're describing—a solid wall with gaps only where the wave vanishes—you can close all of the gaps without making any difference. It might be easier to see this in the sum-over-histories formulation. The source-to-detector amplitude is equal to the sum over all slits of the source-to-slit amplitude times the slit-to-detector amplitude, and by assumption the source-to-slit amplitudes are all zero. Or look at it in terms of Huygens' principle—wave oscillation at the slits can be considered to be the source of all wave activity on the far side of the wall, and there's no oscillation at the slits. -- BenRG (talk) 11:17, 20 April 2009 (UTC)
 * I completely agree with BenRG, and do not understand why Carl fails to see a simple math fact. You have the wavefunction zero somewhere, so you can put obstacles as much as you like, due to the normalization constraints you know that somewhere else the wave amplitude (squared) is summed up to 1 $$ \sum_i |\psi_i|^2=1$$ . Zero is zero, so putting obstacle there is no problem whatsoever. Concerning the interference pattern, there are points where the wavefunction is exactly zero, so it is impossible to block only them, yet blocking some partially bright surrounding dots, within some good approximation can be considered as if you put the obstacle into completely dark region. Of course, as I have also explained in my discussion with Unruh on the pages of Progress in Physics, it matters whether you put obstacles if you want to remain mathematically consistent. Tabish Qureshi misunderstood Unruh and thought that Unruh says "no obstacles in Unruh's setup, which way info, no interference", however unruh himself made it clear that he means "no obstacles in Unruh's setup, which way info, existent interference". Tabish Qureshi misunderstood Unruh because he thought Unruh is consistent mathematically, yet Unruh himself said clearly that his position is not the one Tabish says, so Unruh is mathematically inconsistent. And last, without talking only mathematics, there is no why to have meaningful discussion on the topic, and I see nothing that ordinary wikipedia editor can contribute to the main article. Afshar's experiment produces correct QM results, however Afshar's explanation of the results is wrong. That's all. Danko Georgiev MD (talk) 05:21, 21 April 2009 (UTC)
 * If by transmission we are talking about a variation in amplitude at a single point in space then obviously such a definition of transmission would have zero displacement (ie. change in amplitude) at the dark point. But by such a definition there is no transmission (as I otherwise understand it) "through" any other point as well. Or to put it another way - if we're talking about variations at a single point in space I don't understand (obviously) how that can be given the name "transmission". At issue is obviously how transmission is defined. I wouldn't define it as a change in amplitude at a single point in spcae.


 * By "transmission" what would I mean (and would have thought a typical meaning) is the evaluation of the wave function along all unobscured rays passing through the point in question. There is not anything, other than an obstacle, that disallows the evaluation of a wave function through that zero point. There is obviously some finesse required to define "transmission" - not just spatially but in time - as well. Transmission involves, as i understand it, the transfer of information from one place to another. And I do not see how dark points can be theorised as providing an obstacle to such information transfer. There are various uncertaintys involved that will smear out any signal - eg. the fact that one can not experimentally determine exactly where a particle was emitted means that there is a limit on where one can exactly locate a dark point (ie. for a single particle). The best one can do is nominate a region of space within which a dark point is deemed to be sitauated. Carl Looper.


 * Just as we can not specify a zero radius aperture (if we are to continue talking about apertures) we can not specify a zero radius obstacle (if we're to continue talking about obstacles). All this means is that neither an aperture nor an obstacle can be used to infer whether dark points transmit, or do not transmit particles since we can only ever approximate a dark point (ie. experimentally speaking).


 * But if we define (rather than experimentally specify) a dark point then there is no such problem. For example let us select only those wavelets (necessarily rays) that cross a particular point in space. We can't select these rays in an actual experiment due to the uncertaintys associated between particle and setup, but we don't have to, since we are defining a dark point rather than experiemntally specifying such.


 * By definition of a dark point all of the wavelets intersecting our point must cancel out at the point in question. All we have to do is evaluate the wavelets at some arbitrary moment in time (t0) prior to intersection at the dark point (it will be a circle around the dark point) and at some arbitrary moment in time (t1) after intersection (another circle around the dark point). Between t0 and t1 is what I understand as the "transmision" of the wavelets through the point in question. If I was coding this up in a computer simulation where I was visualising the evolution of such a wavefront over time I would not be asking the program to stop evaluating the wavefront when it converged on zero. I would ask the wavefront to continue right through the zero point and back out again. --Carllooper (talk) 02:35, 29 April 2009 (UTC)


 * You're mistaken in thinking that two wave packets aimed at an aperture from different directions, and timed to cancel at the aperture, will reemerge on the other side. If they cancel perfectly at the aperture then nothing will emerge out the other side; if they cancel approximately then the signal on the other side will be correspondingly weak. If the theory is linear and you consider each wave packet independently, you can understand this as being due to diffraction destroying the directional information. But it's probably easier to just recognize that wave theories are local and there can't be any vibration in the region beyond the aperture unless there's vibration at the aperture. -- BenRG (talk) 16:36, 25 April 2009 (UTC)


 * Ben's objection is - at least - close to the same definition of transmission as I'm using. By "aperture" (however) I do not a mean an experimentally physical one (as previously clarified) but mean the theoretical operation whereby one deselects (or otherwise ignores) any rays that do not cross the point in question, (the point in question becomes the point source of selected Huygen wavelets). I don't know how else one would interpret "transmission through a point". In addition the rays would not be independant wave packets insofar as they are the component wavelets of a single primary "mother" wave - ie. we are talking about one and the same wave (a single particle).


 * But I must admit I do not know where this leads. If one can not experimentally deselect rays that do not pass through the point (or otherwise obscure just those that do).


 * I should add that I did not consider directional information was ever there in the first place. What direction does a wave propogate? It propogates in all directions (in relation to it's point source). So the "loss of directional information" is not an issue for me. But I understand how the comment might have helped someone who was assuming directional information. I am, however, persuaded by the idea of wave theories being "local", ie. that wave theorys are based on what occurs locally rather than globally. I get it. The idea is that there is a loss of all information at the point in question (apart from the zero value at a specific point) so any iteration which begins at such a point has nothing on which to base what happens next (or even prior!) - other than the propogation of zero. I don't quite know how to object to this so I won't. --Carllooper (talk) 02:35, 29 April 2009 (UTC)

Ok. I've convinced myself I was completely wrong. Even using a global interpretation of the wave function the wavelets emanating from a dark point must sum to zero amplitude insofar as 50 percent of the contributing wavelets must have been of opposite phase to the other 50 percent, (if the point is question is defined/specified as dark) ie. the sum of those contributing wavelets, expanding out from the dark point must be zero - the point source ensuring the wavelets remain spatially inseparable (from each other) across their entire wavefronts - and therefore summable (must be summed)at each point across their entire wavefronts - the sum being zero at every point across their entire wavefront. The phase/time invariance of the amplitude at the dark point is not just local (at the point) but quasi-global since no subsequent experimental operation (obstacle/aperture) can ever divorce the point married wavelets, ie. any assumed directional information in the contributing wavelets becomes unrecoverable (one can not decompose the result of an addition). My error was in deferring (not completing) recomposition (addition) of the wavelets. Thanks to all for making the effort to point out my complete stupidity - but more importantly - to help me out of such an unfortunate state. I humbly apologise. --Carllooper (talk) 02:35, 29 April 2009 (UTC)


 * Don't apologize, it's all good. -- BenRG (talk) 13:02, 29 April 2009 (UTC)


 * Thanks Ben. Much appreciated. --Carllooper (talk) 04:16, 2 May 2009 (UTC)

Formatting
The "Specific critiques" section should not use indent, it makes paragraphs look like quotes. GregorB (talk) 15:53, 5 July 2008 (UTC)


 * Not to mention that whereas the critiques section goes into detail quoting all over the place, the section in support only provides links. This would seem unbalanced to me. Irontightarguments (talk) 19:44, 8 July 2008 (UTC)


 * BTW the sources that are claimed to support Afshar do not seem to. O'Hara's for example.  I can't see where it says Afshar's interpretation is correct; it is offering another interpretation. --Michael C. Price talk 16:59, 18 April 2009 (UTC)


 * Upon examination only John Cramer seems to support Afshar, so I've moved the other links. I've also made their abstracts visible. --Michael C. Price talk 17:20, 18 April 2009 (UTC)

Game over, guys.
Peer review has finally caught up: Illustration of quantum complementarity using single photons interfering on a grating, New J. Phys. 10, 123009 (2008) --Michael C. Price talk 14:47, 14 August 2009 (UTC)

Added a couple more refs. I removed the claim that there is no consensus. It seems that there is a consensus within the peer-reviewed literature. 0-3 against the claim. Reworded the intro to better reflect this and maintain NPOV. I also removed the WP:OR anon-IP-inserted claim that these refutations were suspect. --Michael C. Price talk 08:52, 15 August 2009 (UTC)


 * Scientific consensus is a bit more than a head count among half-a-dozen scholars. It may be getting there.. 1Z (talk) 09:10, 15 August 2009 (UTC)

I have removed the non-peer reviewed stuff from the lead (again), inserted by a sockpuppet of Afshar (it is just desperate POV-pushing that we've come to expect here). Debate is always ongoing; this is not in itself noteworthy. Mention it in the main body of the article if you must, Mr A. --Michael C. Price talk 11:32, 15 August 2009 (UTC)
 * Only becuse there are peer reviwed papers gainst Afshar it does not mean the debate is finished or the claims in the papers are correct. The papers disagree with each other on why Afshar is wrong. The paper you mentoned is not using the same experimental technik as Afshar group so it is not clear that their claim even works for his experiment. You are really biased. With your standard Galileo is wrong also because at his time people wrote papers against him. The SPIE conference shows that debate is still going and no concensus is made in the community. Please stp pushing POV —Preceding unsigned comment added by 85.132.47.9 (talk) 21:40, 15 August 2009 (UTC)
 * Your response is WP:OR. Wikipedia doesn't care if in your opinion the refutation is flawed (it isn't BTW); it has been published (along with two others that say the same thing, that complementarity is not violated), and that is the end of the matter.
 * Your self-comparison to Galileo is laughable and puts you quite high on the crackpot index.
 * Mention that the debate is ongoing in the main body (oh, it already does...) but it does not merit mention in the lead -- it is not well sourced enough and is silly WP:SOAP. Many things are debated -- that does not mean there is any merit to the claims.  Of the peer reviewed responses it is 0-3 against Afshar.
 * --Michael C. Price talk 23:12, 15 August 2009 (UTC)

And note the telling comment from the conclusion of the latest study
 * While the results may not appear as a big surprise,

in others words, this is all pretty trivial stuff. There is no debate really. --Michael C. Price talk 02:44, 16 August 2009 (UTC)
 * The statement that the debate is over and Afshar's claims have been "denied" are OR. Says who? you? Experts are still debating it. You remove the link latest Peer-reviewed paper defending Afshar claims, August 6 2009. Evidence is against your argument that "Game is Over" but you decide to remove the evidence. You should be shamed of yourself. What happened to NPOV? Discuss here.85.132.47.9 (talk) 05:59, 16 August 2009 (UTC)
 * You obviously have no idea what peer-review means. A list of conference speakers and topics is not peer-review.  We need articles published in peer-reviewed journals for high quality sources to satisfy WP:REDFLAG.  See WP:RS for basic details.
 * BTW New Scientist is not a peer-reviewed journal either. It's fine for reporting gossip and chit-chat, but not for reporting hard science claims.  Again, see WP:RS. --Michael C. Price talk 09:26, 16 August 2009 (UTC)

NPOV must be followed by all
I am not Afshar. Everytime somone supports afshar you call them Afshar. I have physics PhD and I live in Azerbaijn. People like Micael Price are the one that started false accounts to slander him. I like him necause he stood up for himself and his religion. Here is a quote from a facebook forum: "In the Harvard forum back in 2003, people would sign up for the science forum rapidly. There were many fake accounts that were traced back to several conspiracy skeptics that tried to discredit Afshar. This was back in the fall of 2003, I do believe. He was slandered for his Iranian decent more so than his actual experiment. People were trying to say that these people were paid by another scientist. In 2006, Bush enforced a law that you can't post on fake accounts or something to that effect and Harvard (after 3+ years) deleted these accounts. It was a big deal." I know some people were fired. So Price, be careful not to destroy his or your own reputation here by libelous accusations, you are not anon.85.132.47.9 (talk) 23:09, 15 August 2009 (UTC)
 * I think this response speaks for itself. No further comment required.--Michael C. Price talk 01:44, 16 August 2009 (UTC)
 * I think you learned lesson.Thank you.85.132.47.9 (talk) 06:19, 16 August 2009 (UTC)
 * If believing that makes you happy, that's fine with me.--Michael C. Price talk 09:28, 16 August 2009 (UTC)

Peer-review
Price, if peer review means something is correct, then Afhsar's peer review publication in Foundations of Physics must mean the end of all discussions. That is not ture. Peer-review only means that the paper passes simple rules and is not "obviously" wrong. So why do you have a dual standard for Afshar and others? Explain please before you change the text in the article.85.132.47.9 (talk) 15:35, 17 August 2009 (UTC)


 * There is no dual standard. Since you seem to understand peer-review why can you not understand that excluding non-peer reviewed stuff from the lead is even-handed?


 * Please read the welcome message I've just posted to the top of your talk page.--Michael C. Price talk 15:46, 17 August 2009 (UTC)
 * OK A compromis is you accept addition of 'some' at end of sentence, because peerreview does not mean final decision for all of physicists. It is true unbiased and not OR. I wish you can at least agre to that85.132.47.9 (talk) 19:49, 17 August 2009 (UTC)
 * How about "others"? --Michael C. Price talk 20:01, 17 August 2009 (UTC)
 * Sorry was on vacation. Thank you. But I sill think the debate (with reliable source) should be mnetioned in the introdution. OK?85.132.47.9 (talk) 23:26, 30 August 2009 (UTC)
 * Sorry but the "debate continues" is WP:weasel words. There is no continuing debate in the literature -- and if/when there is, then giving the peer-reviewed citations should be sufficient. --Michael C. Price talk 06:30, 20 October 2009 (UTC)
 * I do not want to support Afshar's propaganda in any way. I just want to point out that Illustration of quantum complementarity using single photons interfering on a grating, New J. Phys. 10, 123009 (2008) cite my Prog. Phys 2007 paper, as evidence against Afshar at the same time with citation to Ole Steuernagel (and this citation is supposed to validate that there is consensus of why Afshar is wrong). However my work leads to exactly opposite conclusions of what the authors claim to have shown in their paper, so I don't know why they cite me at all. The peer-review process is very slow, so one should talk about consensus 20-30 years after a debate, so that all the viewpoints have been clrified and properly understood. At present everyone thinks he is right, and does not try to understand alternative viewpoints, which might be much better Danko Georgiev MD (talk) 03:48, 20 October 2009 (UTC)
 * Eh? If by "At present everyone thinks he is right" you mean Afshar this is not true; all the peer rewiewed sources (including yours) say Afshar is wrong.  I guess you mean that everyone thinks only their own viewpoint is correct?  But then why do V. Jacques et al cite Steuernagel, for example, unless they think Steuernagel is correct? Suggests that they are looking at alternative viewpoints as well as their own. --Michael C. Price talk 06:26, 20 October 2009 (UTC)
 * While the critical authors agree on rejecting Afshar's claim, they explicitly disagree with each other on their reasoning. Some beleive there is full visibility, and no which way, some believe other way around, some belaive both are lacking, and Kastner specifically criticizes the very idea of which way that everbody sles including Afshar uses. This is clear, from the categorization of the papers in the critics section.
 * Mr Unsigned Anon, please logon and sign your posts;
 * This is wp:or unless you can show me a reliably sourced citation that says they disagree with eachother. The papers in the critics' section don't count since some are unpeer-reviewed -- the whole section is a mess that needs pruning (or deleting).
 * As far as I can see the only criticism of one of the critics' sources by another is where one cited peer-reviewed source complains that another un-peer-reviewed source (Drezet) has made the same mistake as Afshar. So that doesn't count.--Michael C. Price talk 09:29, 31 October 2009 (UTC)
 * The OR calim is bogus. Based on the categories of arguments in the section, which provides a short explanation of papers by citing each of them, anybody can easily agree that the arguments presented by some authors are diametrically opposed to each other-with some saying Vis high-WWI low, others saying WWI high-Vis low, etc. On peer-review, there are no requirements for Wikipedia articles to be solely based on those. Unruh's web commentary is notable because he is reputable and reliable enough without a PR paper, while the so-called "peer-reviewed" paper by Georgiev is highly suspect. —Preceding unsigned comment added by 146.115.26.31 (talk) 15:46, 31 October 2009 (UTC)
 * Most of the critiques section can be deleted now that we have an array of peer-reviewed reliable sources (all of which are negative). A short summary of the critical reaction should be possible.  They're all saying the same thing -- it doesn't work for single photons (contrary to Afshar's claims) and, hence, it doesn't work for multiple photons. --Michael C. Price talk 02:25, 9 November 2009 (UTC)
 * I personally would not call "suspect" even Afshar's paper published in Found. Phys. or the subsequent reply by Flores, though these are "peer-reviewed" but wrong. In the case of my paper I do not see anything suspicious, moreover it is cited by V. Jacques et al. who did not found anything suspicious. At best in my paper there is one claim true - that Afshar is completely wrong, while in Afshar's work the truth content is zero. So please clarify what "suspect" means?Danko Georgiev MD (talk) 00:30, 9 November 2009 (UTC)
 * Do you have a ref for Flores' reply? --Michael C. Price talk 02:25, 9 November 2009 (UTC)
 * Price, Why do you keep removing relevant information from the article introduction (article history shows several edit wars during an extended period of time on this very issue.) The critics definitely disagree amongst each other on why Afshar is wrong. That is very relavant to the article and clearly discussed in the article. You wish to remove the entire critics section to hide the fact they disagree? That is truly unethical, and cause for a major OR and POV sanction. I am going to alert admins and arbitration if you keep pushing your personal opnions as facts on this article. Another unethical and false claim you make is that the experiment failed at the single photon regime. Afshar's Found Phys paper actually reported a single photon experiment, and I highly doubt it would have been published if they had lied about it, so why do you say it failed for single photons? Do you have any evidence supporting this assertion, or is this another OR? —Preceding unsigned comment added by 204.9.220.41 (talk) 05:02, 9 November 2009 (UTC)
 * All these points have been discusssed ad-nauseum.
 * And why is it, after all these years, that you can't even create a login account or remember to sign your posts? I shall not be responding to any anon IP contributions any more.  It is just a waste of time.
 * --Michael C. Price talk 08:56, 9 November 2009 (UTC)
 * The fact that you just outright lie about the facts of the article have been discusse ad nauseum? Where is the ref that says the Found Phys paper was not single photon? Provide the ref. and tone down ur POV before you revert again. —Preceding unsigned comment added by 146.115.26.31 (talk) 19:14, 9 November 2009 (UTC)
 * Ditto previous response. --Michael C. Price talk 17:12, 10 November 2009 (UTC)
 * That is no response at all. You are not being reasonable.12.7.82.66 (talk) 17:40, 10 November 2009 (UTC)
 * I'm glad to see that you signed your post. Now please create an account (it only takes a minute).  It makes it easier for all of us to follow the conversation.--Michael C. Price talk 17:48, 10 November 2009 (UTC)

Disagreements among critics
Lets discuss this issue in a calm manner. Price please engage equitibly without namecalling. Do you agree that the critics disagree with each other about why Afshar is wrong? If not, please indicate why not with a reference to the actual publication, otherwise a simple look at the current critics section shows that they have opposing views on the visibility of intereference and availability of which way information. Awaiting a civil discourse.12.7.82.66 (talk) 17:45, 10 November 2009 (UTC)
 * I'm glad to see that you signed your post. Now please create an account (it only takes a minute and you only have to do it once).  It makes it easier for all of us to follow the conversation.--Michael C. Price talk 17:49, 10 November 2009 (UTC)
 * No, I'm good thak you. There are no requirements for anyone to make accounts here. A lot of anons contribute to Wikipedia without an account. If you have a substantive argument to make please go ahead.12.7.82.66 (talk) 18:23, 10 November 2009 (UTC)
 * Yes, lots of anons contribute directly to articles, but far far fewer engage in productive dialogues. You don't have to use you real name.  Anything will do.--Michael C. Price talk 18:27, 10 November 2009 (UTC)
 * While MP likes to project himself as someone willing to engage in productive dialogue he has no qualms about censoring any discussion he doesn't like. He'll happily delete contributions in the discussion page if it doesn't accord with his pov - and disguise his prejudice as innocent conformism to wikipedia rules.    —Preceding unsigned comment added by 202.6.86.1 (talk) 23:10, 21 April 2010 (UTC)
 * It wasn't too difficult as you said :) So please explain your POV.Sfsupro (talk) 18:45, 10 November 2009 (UTC)

Thanks. The statement that the critics disagree with each other is unsourced. If you look at just the peer-reviewed sources they do not contradict each other. As I previously explained. Some of the lower-quality, unpeer-reviewed sources do disagree with each other, but then what do you expect from such sources? The fact remains that the peer-reviewed sources not only don't contradict eachother, but actually cite each other.

The whole critics section is a mess and all the unpeer-reviewed stuff should be deleted. It would not be tolerated in other articles. No reason to make an exception here. --Michael C. Price talk 19:00, 10 November 2009 (UTC)
 * It's not as simple as that Michael. The disagreements are delineated in the body of the article itself. Right now I'm supervising a Master's thesis on this very topic, and cannot discount Unruh's arguments, just because he did not bother to publsih his views in a journal. Unruh is a major physicist whose views cannot be ignored. On the other hannd, not all the peer-reviewed material cited are worth the paper they were written on. Georgiev's paper is so riddled with errors that mentioning it in a thesis is the end of the oral session. So where do you draw the line?Sfsupro (talk) 19:08, 10 November 2009 (UTC)
 * Agree about Unruh (I nearly mentioned him earlier). Which parts of Danko's paper are you disagreeing with? --Michael C. Price talk 19:18, 10 November 2009 (UTC)
 * Glad u like Unruh. On G its more like which part one can agree with :) Have a class will get back afterwards.Sfsupro (talk) —Preceding undated comment added 19:49, 10 November 2009 (UTC).
 * Michael I don't know if you teach or not, but there are strict academic standards that would absolutely prevent us from allowing patently wrong material in our (or our mentee’s) work. Here's a quick reason why Georgiev's paper is poison in this regard:  In his terse response, Unruh says: "...In no conventional quantum formalism do such states exist..." Without going into unnecessary details here, Unruh demonstrates the complete lack of formal understanding of quantum mechanics by G, as well as his careless misrepresentations of Unruh's views. In an e-mail to me, he made even more graphic remarks about his interactions with G. At any rate, in general, Progress in Physics is a crackpot source that would kill any scholarly work that contains a reference to it. As an example of how we deal with this kind of issue here's a 2009 Master's thesis on Afshar's experiment from University of Oslo that does not even mention G's paper, let alone discuss or criticize it. I would do away with it in the body of the article to keep the unnecessary confusion to a minimum. This stuff is confusing enough on its own ;) If you like I can help with the cleanup, after we concur about it here of course. Incidentally, how do you make graphics like the ones in the article, I would like to add one to the page.Sfsupro (talk) 11:22, 11 November 2009 (UTC)
 * Reply to Sfsupro: First, Unruh's claim "...In no conventional quantum formalism do such states exist is non-sense, instead quantum histories discussed in my article are well-defined. See either my work Danko Georgiev (2012). Quantum Histories and Quantum Complementarity. ISRN Mathematical Physics Volume 2012 (2012), Article ID 327278, 37 pages, or read Griffith's texbook on QM. Second, who wrote a master thesis and did not cite my work is of no importance for science as a whole, and QM in particular. If you think my work is "poison", then Feynman sum-over-historties should be "poison" too, because this is what I used in my works. Danko Georgiev (talk) 11:51, 3 February 2012 (UTC)
 * Unfortunately my graphic skills are non-existent.
 * I was putting off a cleanup of the critiques section until I had thoroughly reviewed all the relevant references. Re Unruh/Danko, thanks for the Unruh pdf, I hadn't see that before. I shan't get the chance to digest until tomorrow next week, but I'm happy to accept Unruh's views as correct in the meantime. (I recall that I thought his critique of Afshar's model was sound.) And Unruh is sourced which is great.  And they reference Unruh's critique of Afshar, which is also great since it means we can cite that as well.
 * --Michael C. Price talk 12:27, 11 November 2009 (UTC)
 * Hey no particular rush really. Take your time, just remember to show your proposed changes here first so we can discuss it. This is a hot topic in my circles, so bear in mind that there are many more sources that you may not be aware of. Would be happy to share in due course.Sfsupro (talk) 15:40, 12 November 2009 (UTC)


 * Dear wiki-fighters, it is really fascinating for me to see that after all these years people are still fighting to death concerning the interpretation of the optical experiment by Afshar et al. .   While it is  very clear for me  and for 99% of the scientific community (sadly too busy to discuss with you) that there is no contradiction between the results and the usual interpretation of quantum mechanics given by Bohr and co. I  find very usefull these kind of hot debates because they show the interest of a large public for various interpretation of QM.  It is however sometimes going too far because some  of the comments are very unpleasant or non scientific  (like those of  Georgiev which is an amazing amateur with radical claims  sometimes close to schizophrenia).  It is very courageous of Michael Price to fight so hard for a bit of logic and rationality in this world of brutes.   May be it is a lost cause  but    I can only wish him to find the energy for succeeding in its tasks.


 * Danko is a passionate person - which can cause a lot of problems - but his theoretical arguments are well thought out. He just needs somebody with more diplomacy to explain his work - because Bohr is no longer with us. —Preceding unsigned comment added by 202.6.86.1 (talk) 03:57, 22 April 2010 (UTC)

An old participant: --Drezet —Preceding unsigned comment added by 147.173.67.99 (talk) 17:50, 30 November 2009 (UTC)
 * I hope those who believe themselves are experts in QM and want to discuss my work, read carefully my notes at my user page. It is unserious for all those "Ph.D. physicists" to claim my argument is wrong, provided that they do not understand it at first place. In any natural science, if you claim to be expert, you should have the capacity to understand even wrong work, and then to find from where the error results. On my user page I have tried to write the ABC, so that everyone with minor effort could understand the main idea. Danko Georgiev MD (talk) 15:06, 11 May 2010 (UTC)

New peer-reviewed paper
Arxiv: quant-ph/0504115 "Logical analysis of the Bohr complementarity principle in Afshar's experiment under the NAFL interpretation".

To appear in International Journal of Quantum Information (IJQI), Vol. 8, Issue 3 (April 2010).

See Sec. 2 "Summary of the main argument and conclusions" for the argument refuting Afshar's claims of a violation of the Bohr complementarity principle and the Englert-Greenberger duality relation.

When this paper appears in print (possibly in 2-3 months' time), I plan to edit the article on the Afshar experiment to include the journal reference to my work and a brief summary of my arguments therein. Before editing the main article, I will post here what I plan to include, so that any objections/modifications can be thrashed out.

Rks123 (talk) 00:01, 30 January 2010 (UTC)


 * Best to let others add your paper to the article, to avoid WP:COI. --Michael C. Price talk 07:30, 21 April 2010 (UTC)


 * My paper Arxiv: quant-ph/0504115 has now been published:
 * "Logical analysis of the Bohr complementarity principle in Afshar's experiment under the NAFL interpretation", Int. J. Quantum Information, Vol. 8, Issue 3 (2010) pp. 465-491.
 * Here is the link to the journal article:
 * http://dx.doi.org/10.1142/S021974991000640X
 * I request the Wikipedia Editors to include this reference in the main article, perhaps with the abstract also included (see the above link). Readers may be pointed to Sec. 2 of the paper ("Summary of the main argument and conclusions") for the gist of the argument refuting Afshar's claims of a violation of Bohr's complementarity principle and the Englert-Greenberger duality relation in his experiment. -- Rks123 (talk) 07:25, 21 June 2010 (UTC)
 * I tried to read the full article to make sense of the abstract, but it seems to be a paysite. The abstract is hard to follow (a lot of jargon) and the last sentence seemed to be starting to say something when it unexpectedly terminates (should there not be a verb on the end?). I get the sense that it says that complementarity is not violated by the setup, but can't fathom much beyond that. -- cheers, Michael C. Price talk 12:27, 12 January 2011 (UTC)
 * The paper is available on arXiv . -- Belsazar (talk) 19:19, 14 January 2011 (UTC)

Extended Complementarity
What was otherwise here (but deleted by Michael Price) intersects with ideas in common with Danko's common-sense proposition. But rather than reinstate those words I'll just defer to Danko:

"To accept that there is "which way" information is equivalent to accepting that the setup with both paths unobstructed is a statistical mixture of the two single path setups with obstructions so the complementarity rule for making retrospective predictions is P ==|ψ1|^2 +|ψ2|^2. This alternative formulation of the principle of complementarity is in a form of instruction as to how to make the correct retrospective reconstruction of a mixed state setup — it says that mixed state setups should be retrospectively reconstructed with P =|ψ1|^2 +|ψ2|^2 distribution." - Danko Georgeiv

Danko also provides the instructions for making the correct retrospective reconstruction of pure state setups.

The salient point he makes is that a mixed state distribution differs from a pure state distribution (with the obvious exception of zero nodes and any other aliasing one might like to construct):

|ψ1|^2 + |ψ2|^2 does not equal |ψ1 + ψ2|^2

So one can both experimentally (and mathematically) disprove that a pure state experimen,t such as Afshar's, allows for both a pure state reconstruction and a mixed state reconstruction. Danko goes on to argue that the mixed state reconstruction is untenable anyway - since both apertures are open at the same time. A conventional mixed state distribution occurs only if each aperture is open at different times. Now Bohr doesn't elaborate complementarity to this extent but he probably should have (if he could). But there are times where Bohr almost sounds like he is allowing which way interpretations on double aperture setups (providing a gap for Afshar's critical experiment) - and that's a deabatable problem with Bohrs expression of complementarity (and the Copenhagen Interpretation in general). Consider the following:

"This point is of great logical consequence, since it is only the circumstance that we are presented with a choice of either tracing the path of a particle or observing interference effects, which allows us to escape from the paradoxical necessity of concluding that the behaviour of an electron or a photon should depend on the presence of a slit in the diaphragm through which it could be proved not to pass." - Neils Bohr

Is Bohr suggesting a particle could be proved not to have passed through the slit? It's sort of difficult to say. IHe could be simply framing complementarity in terms that would be classically comprehendable (albeit risking misunderstanding of the very thing he is expressing). Or it could be that he simply had not thought through how the principle might be (mis)comprehended in classical terms. Or he miscomprehended the principle himself (ie. had one foot too firmly planted in the classical camp). There is a lot of useful work that could be done in re-reading Bohr. Afshar's experiment is a good starting point. But while it might throw into question Bohr's expression of the complementarity principle it need not throw into question any mathematical definition of such (since mathematics is founded on consistency).

Irregardless of how one interprets Bohrs position, Danko provides a mathematically consistent way to extend Bohrs principle of complementarity beyond "only the circumstance", or to be more generous to Bohr: to simply restate Bohr's principle in clearer (mathematical) terms.

Afshar (on the other hand) is effectively arguing that we should introduce a 'paradox' (inconsistency) when interpreting (retrospectively reconstructing) the Afshar experiment. Danko argues the opposite - that we should not.

If we choose to avoid a paradox (as surely Bohr would have agreed) then Danko provides (well grounded) instructions for doing so.

But if we choose to accept a paradox (as some of us obviously can - myself not excluded) then what are we doing? Is it science? Its certainly not good mathematics (if one can say there is such a thing as bad mathematics).

I might also add that Unruhs response to Danko's work: "In no conventional quantum formalism do such states exist" does nothing to help Unruh's argument. Once upon a time the Aether was a convention. But what is at stake for Danko is not convention per se, but something very different. I'd suggest "understanding" might be a good word. Danko's follow up paper argues contrary to Unruh's claim, that his (Dankos) previous paper was conventional. But the effectiveness or otherwise of Dankos follow up argument does not change the original argument. It simply clarifys it in even more formal (conventional) terms.

We don't need to take the word of famous physicists or Danko to form an opinion. We can work through, and test these things out, ourselves. That's the beauty of science and mathematics.

A joke for Danko: Does two plus two always equal four? No. Just as often one plus three equals four.

--Carllooper (talk) 01:08, 23 April 2010 (UTC)

Article needs better explanation
I am reading the article and do not understand what is the result of the experiment. There is description of the experimental setup, but it does not say what are the measured parameters, and why is it even considered to violate something. Why even this experiment was conducted, whatever it detects seems to be very trivial - when both holes are open, both detectors detect light. When one hole is closed, still both detectors detect light, though one detector will have much less light, similar as to diffraction grating, or hologram readout. Where is the experiment? Can somebody explain it? MxM (talk) 16:16, 11 January 2011 (UTC)


 * If you can't see the point of the experiment, then you've probably understood it correctly - many of us feel the same way! However I will try and improve the explanations. -- cheers, Michael C. Price talk 12:10, 12 January 2011 (UTC)


 * The idea behind the experiment, as I understand it, is that placing a series of parallel wires at points that would be dark bands in the interference pattern a normal two slit experiment and observing that more light makes it through than would if there were no interference pattern, such as when only one slit is open, allows the experimenter to infer there is interference, a property of waves. The lens and pair of photo-detectors allows the experimenter to infer which slit a photon passed through; that it only passed through one and so would not interfere with itself. If both those inferences are correctly made it means the photon manifest as a wave passing through both slits at the same time and as a particle passing through only one.  That would be very important because it would suggest Bohr's Complementarity principle, which is very widely accepted, is in error.
 * Pema Sung (talk) 10:55, 16 January 2011 (UTC)
 * The statement about the implication for Bohr's Complementarity principle is the controversial part. Everybody agrees that the results are as predicted by the equations of QM - if some people's interpretation of Bohr's Complementarity principle are at variance with the expected and actual results then so much for their interpretation of Bohr's Complementarity principle. -- cheers, Michael C. Price talk 12:06, 16 January 2011 (UTC)
 * I (finally) wrote a paper about that curious story more than 7 years after the beginning of it even though I discussed that already in 2003 and 2004 (lack of time, lack of interest who knows it...). Any way, the complete reference of the paper is  : Aurelien Drezet, Progress in Physics vol 1, page 57-67 (2011);   may be it could be useful for the web page and for the present discussion. Regards.  (Drezet (talk) 17:01, 16 February 2011 (UTC))

PS There is also an older version on axiv at http://arxiv.org/abs/1008.4261 (Drezet (talk) 17:12, 16 February 2011 (UTC))

Article needs better description of the experimental results
Is User:Afshar around? The description of the experimental results is unclear, as presented here. Let turn the laser brightness to high, leave both holes uncovered, and put the wires in place. The lens should image each pinhole reasonably well: one should be able to look at a screen located at the image plane, and clearly see the pinhole, including any burrs, imperfections, dents, etc. in that pinhole. Let's say I am looking at pinhole A imaged in this way. While I am looking at this image, suppose pinhole B is blocked. Does the image of pinhole A change/degrade/get brighter or dimmer as pinhole B is blocked/unblocked? The way that the article is written, it seems to imply that the image of pinhole A will be "degraded" when pinhole B is blocked. I find this very hard to believe.

What I expect to happen is that the image of pinhole A is unaffected, although, when pinhole B is unblocked, I expect some diffuse haze to be added to the image of pinhole A. So, for example, if A is blocked, and B is unblocked, then the image plane of pinhole A should only show haziness, due to light from B diffracting from the wires. Covering and uncovering B makes this haze come and go. Otherwise, the image of A should be unaffected. Right? With A blocked, B unlocked, one should see nothing but this haziness -- or is it possible, that the wires diffract light from B in such a way that some weak, blurry image of pinhole B is formed at the location of image plane of A ??? Enquiring minds want to know...

The point is that if hole A is covered, and B is not, and we still get light at the image plane of A .. surely, this will be covered in the original paper, right? We'll see photos of this, right?

Because of this, I'd like someone who has actually witnessed or performed the experiment to confirm or deny the existence of these effects. The article, as written, remains rather totally ambiguous about this. However, answering this question would seem to have a material affect in how one should interpret the results. linas (talk) 07:15, 26 December 2011 (UTC)


 * OK, the figures in the 2007 Arxiv paper answer my questions. The description of the experimental results in this article are misleading/incorrect, they don't really match up with what the arxiv paper is saying. linas (talk) 07:46, 26 December 2011 (UTC)

Assuming that the reader already knows what you are talking about
In the lead it says, without any preparation whatsoever, "The result of the experiment, that a grid of wires can be ignored when both slits are open, is in accordance with the standard predictions of quantum mechanics;" To somebody who hits this sentence for the first time it seems to say that grids of wires can be ignored. What grids of wires? All that seems to be accomplished is that the reader is going to look for something more about these mysterious wires. So this grid violates complementarity? No, that can't be it. Putting a grid in someplace violates complementarity? That can't be the meaning. An experiment might produce results that violate complementarity, but what experiment? So maybe it is that a Young experiment modified, somehow, by inclusion of a grid will give results that violate complementarity? Is that it? It's not so hard to say, if my guess is correct. Please give a break to the reader who does not already know what the intended meaning is. P0M (talk) 03:52, 29 December 2011 (UTC)

Classical optics vs. Quantum optics


I wanted to note that several important works have been published after the original dispute here ended by intervention of mediators, between Afshar and other parties. For example, Drezet's 2011 Progress in Physics article brings interestingly the predictions of Bohmian mechanics into the discussion, and also my own peer-reviewed work has been published online as an open access article [http://www.isrn.com/journals/mp/2012/327278/ D. Georgiev (2012). Quantum Histories and Quantum Complementarity. ISRN Mathematical Physics Volume 2012 (2012), Article ID 327278, 37 pages]. In this combined theoretical and computational work, I have solved the Fresnel integrals for Afshar's setup, which show clear interference fringes in coherent setup FIGURE 7. The Wikipedia article is written using some high school ray optics, which has nothing to do with quantum mechanics. The light does not go in straight rays, and confuses the ordinary reader by appealing to Afshar's naive understanding of ray refraction. Instead the photon probability distribution changes at different planes behind the slits and the lens as shown in Figs. 7 and 9 in my article. Becuase my article is open access and distributed under Creative Commons license, I have uploaded the two most important images in Wikipedia see Fig. 1 and Fig. 2 on the left. If any editor thinks these images are relevant, he can just transfer them to the main article under appropriate section.

In 2004, Afshar announced a prize of 1000$ at :
 * "Dear Mr. Knapp, Very briefly, if you can write the wavefunction of EACH of the images as a 50%/50% superposition of the wavefunctions originating from the two pinholes, then I would concede that there is no which-way information in the images, and you will be eligible to win my $1000 prize for this feat. However, I am confident that you--or anyone else for that matter--won't be able to do it without breaking the quantum-mechanical rules of calculation!" Posted by: Shahriar S Afshar at August 8, 2004 11:47 PM

In my article I have done just that: written the wavefunction of EACH of the images as a 50%/50% superposition of the wavefunctions originating from the two pinholes and I did not break the quantum-mechanical rules of calculation. Also, I believe that solving the Fresnel integrals and publishing them was necessary, because a single picture is worth a thousand words. Indeed, compared to the images created by Afshar using classical (high-school) ray optics, they show how different quantum optics really is.

My proof, using Feynman sum-over-histories, illustrates nicely what Feynman wrote in 1983 in his book "QED: The Strange Theory of Light and Matter", Princeton University Press. There in footnote 3 on pages 55 & 56, one can read: "This is an example of the "uncertainty principle": there is a kind of "complementarity" between knowledge of where the light goes between the blocks and where it goes afterwards - precise knowledge of both is impossible. I would like to put the uncertainty principle in its historical place: When the revolutionary ideas of quantum physics were first coming out, people still tried to understand them in terms of old-fashioned ideas (such as, light goes in straight lines). But at a certain point the old-fashioned ideas would begin to fail, so a warning was developed that said, in effect, "Your old-fashioned ideas are no damn good when ..." If you get rid of all the old-fashioned ideas and instead use the ideas that I'm explaining in these lectures--adding arrows for all the ways an even can happen--there is no need for an uncertainty principle!"

Why Feynman disliked Bohr's and Heisenberg's anti-realism and puts both "uncertainty principle" and "complementarity" in quotes could be explained both by the superiority of Feynman sum-over-histories approach in resolving QM "paradoxes", and by the rudeness of Bohr, who ridiculed everyone who happened to disagree with him. When the young R. Feynman presented for first time his geometrization of quantum electrodynamics (QED) (so called Feynman diagrams) at The first Shelter Island Conference on the Foundations of QM "Niels Bohr, the father of QM, leapt from his chair in disgust. He hated Feynman's diagrams because they went completely against everything he'd devoted his life to. He believed that atomic particles could not be visualized under any circumstances. Feynman defended his new theory, trying to explain that the diagrams were simply a tool to help visualise his new equations. But the rest of the scientists, including Dirac, wouldn't hear it, calling him an idiot who understood nothing about QM". From: "The Illusion of Reality". Narrated by Jim Al-Khalili. Atom. BBC. BBC Two. 2008-02-04.

I hope my brief historical survey is of interest, because many including W. G. Unruh show the same rude behavior toward Feynman sum-over-histories approach see Unruh's video lecture and provide erroneous explanations why Afshar experiment does not disprove complementarity. Of course, if QM were predicting that in coherent dual-slit setup the lens provides which-way information as Unruh, Motl, Steuernagel, Bohr and other anti-realists think, then I think Afshar deserves congratulations for the good job. However, there are people like me, Reitzner and Qureshi, who have shown that the lens does not provide which-way information in coherent dual-slit setup, therefore Afshar's major premise fails and there is no paradox. Danko Georgiev (talk) 11:40, 3 February 2012 (UTC)


 * Hi Danko, you left a note on my talk page. If you wish to include a short summary of your results, in a format just like all of he others, in this article, then that seems a reasonable thing to do. I strongly discourage any other modifications of the article. linas (talk) 18:22, 21 February 2012 (UTC)


 * Dear Linas, here is a concise 3 sentence summary of my work. You suggested that inclusion of this text is OK, so to avoid possible criticism I prefer if you incorporate the text yourself:




 * I think inclusion of the image is worthy! This is essentially the image that justifies not only my claim, but also the claims by Reitzner and Qureshi! Comment: Also I think these 3 entries should be grouped together. As you know I have been defending my thesis since 2004 in the Wikipedia talk page, and deposited preprint in 2006 at PhilSci, which was published in 2007 in Prog. Phys., so this is a case in which 3 independed researchers come independently to the same conclusions. Reitzner's paper is claiming that the two peak image is "interference pattern" i.e. what I show in the Figure 1, but he showed only the "two peak image" without showing what is going on "in between" and most people cannot really understand why Reitzner claims such a thing. Of course you can modify the caption a bit mentioning that this image is illustrating the thesis by Georgiev, Reitzner and Qureshi, and add refs. I hope my proposal is OK? Danko Georgiev (talk) 07:50, 1 March 2012 (UTC)
 * I'm not sure that we need to get too hung up over the use of straight line light rays in the explanation; they are the conventional way of explaining single and double slit results and they work just fine for me. Mention of Feynman sum-over-histories (graduate or post-graduate level) seems unnecessary, since the ray approach (high school level) already works. Everybody (with the possible exception of Afshar) agrees that the results of Afshar's set-up are entirely in line with conventional quantum mechanical calculations.  The current diagrams explain that quite well, and in an accessible way.  I suspect most readers will not follow the proposed diagrams (they don't immediately make sense to me, for example). Perhaps this explanation can be placed in a separate section, but the current explanation, as Linas says, should stay as it is, IMO. -- cheers, Michael C. Price talk 11:22, 1 March 2012 (UTC)
 * Dear Mike, I do not see how the ray optics helps? According to ray optics photon from slit 1 goes always to detector one along straight line, and it is impossible to end up at detector 2! According to classical ray optics Afshar is correct (!) and I am not sure how you can disprove Afshar's thesis using ray optics (??). According to Feynman sum-over histories, it is possible for a photon to pass either slit 1 or 2 to go to a bright fringe and then end up at detector 1 or 2 by 50/50 chance. This has nothing to do with ray optics and is purely quantum behavior. For the discovery of the sum-over-histories and its application to QED Feynman got the 1965 Nobel Prize in Physics, but more importantly the sum-over-histories applies equally well to weak and strong interactions, and possibly to quantum gravity as well. Anyway, what do you think about inclusion of 3 sentence summary of my work? Danko Georgiev (talk) 13:15, 1 March 2012 (UTC)
 * Look at the diagram in the article; the rays split at slits by diffraction. This is conventional. Feynman merely explains how/why we can adopt this picture. If this needs explaining somewhere it might be in a more general article about optics or interference or such like. -- cheers, Michael C. Price talk 13:49, 1 March 2012 (UTC)
 * Dear Mike, I see very well the diagram but it uses different colors for rays passing through slit 1 and slit 2. [[Image:Afshar-experiment.png|thumb|right|250px|Fig.1 Experiment without obstructing wire grid]] Therefore there is no ray that goes through slit 1 and ends at detector 2! If the rays are denoted with the same color then it will look like rays through either slit can go to either detector, but again this is purely quantum effect, and cannot be justified by classical ray optics. I don't want to get into confrontation with you, so I just propose inclusion of my text summary similarly to Qureshi and Reitzner summaries, without any figure! I hope this is OK with Linas too, because he proposed "If you wish to include a short summary of your results, in a format just like all of he others, in this article, then that seems a reasonable thing to do". I do not insist on inclusion the image, people who are interested to read my open access article can find it easily. Regards, Danko Georgiev (talk) 11:46, 2 March 2012 (UTC)
 * I don't care whether we call it classical ray optics or quantum ray optics, it is still ray optics, and the diagram seems to do a good job of explaining it. Talking about Feynman-sum-over-histories just seems to obscure the issue.  As Linas said, it is just Huygens-sum-over-histories. -- cheers, Michael C. Price talk 12:04, 2 March 2012 (UTC)
 * OK, Mike agreed. The summary as it is written, with the image removed, implies only my own position as it has been published. I propose inclusion of my summary as a part of the critique section, as there are other researchers, whose summaries are concisely present. Is such proposal OK with you? p.s. Sorry, for proposing inclusion of image, I am now convinced it was not good proposal. Danko Georgiev (talk) 12:16, 2 March 2012 (UTC)
 * Mostly agree w/Mike here. The caption on the wave optics picture is wrong: interference does not remove which-way info. So, for example, ocean waves interfere with one-another, one still knows "which way" they are going. Besides, the Feymnann path integral is for quantum interference; and has an h-bar factor in it. Here, we are getting just classical wave optics, with no h-bar dependence.  So I think mentioning Feynmann just completely misses/confuses the issue; this has nothing at all to do with quantum sum over histories, but is instead just plain old classical wave mechanics (classical, Huygens style sum-over-histories aka Huygens–Fresnel principle).  Here's one way to explain this: you can do the Afshar experiment in a plain old water ripple tank, and you would get exactly the same results as Afshar gets for light.  This proves that the Feynmann integrals have nothing at all to do with this problem; there is no factor of i-hbar anywhere in the calculation. (Besides, Feynmann may have gotten the prize, but Mott (and others??) certainly did the quantum variant of sum-over-histories first, decades(?) before Feynmann. Now Feynmann deserved the prize, but he's not the inventor of sum-over-histories.) Anyway, for the Afshar expt, these are just plain old classical Huygens sum-over-histories, not Feynmann sum-over-histories.linas (talk) 22:05, 1 March 2012 (UTC)
 * Dear Linas, I would like to have your support for modifying the article, within your proposal to "include a short summary of your [my] results, in a format just like all of the others". I do not insist on inserting my figure, because modifications are to be based on consensus, and I did not have neither your nor Mike's support. In regard to Feynman's approach, I share the viewpoint posted below by 98.154.13.159 that the hbar enters into the picture by the fact that there is only one click at the detectors, not two half-clicks. If a single photon "click" is detected at the detectors, and one knows that there is interference pattern along the way, then this photon must have passed through both slits to make the interference pattern, and then make a single click at one of the detectors. If the detector "click" implies that the photon has passed through one and only one slit, but not both slits at the same time, then you have Afshar's paradox, etc. I agreed that there is no need for the image, so my summary above correctly states only my viewpoint - if it is wrong, so be it! After all, the purpose of the critique section is NOT to say who wins the debate, but to state who said what. I state here that the following 2 sentence summary correctly represents my viewpoint. I have discarded the image from it, so if you think it is ok, you might transfer it to the critique section as it is. i moved the proposed text just below this post. Regards, Danko Georgiev (talk) 12:13, 2 March 2012 (UTC)

**** "D. D. Georgiev (Kanazawa University, Japan). Georgiev analyzed Afshar's setup within the framework of Feynman's sum-over-histories formulation and concluded that with or without the grid if the both slits are open there is no which way information once the branch vectors from each slit overlap . He solved the Fresnel diffraction integrals and argued that each peak at the image plane is created by constructive interference of branch vectors coming from both slits ."


 * I agree that the Feynman stuff is irrelevant and will only add to the confusion, but Linas, there is a big difference between Afshar's exp and the waves on a ripple tank. The electromagneitc field is quantized, that is where the hbar sneaks into Afshar's set up. In the ripple tank, both "images" of the slits ripple simultaenously. In Afhar's only one image clicks "a photon" at a time. That is really the significance of the experiment, otherwise as you said, in the wave mechanics, there is no problem between which way information and interence. It is only in quantized field version of QM that you can't have both, and his experiment shows we do.98.154.13.159 (talk) 01:27, 2 March 2012 (UTC)
 * Dear 98.154.13.159, I wanted to contact S. Afshar by e-mail, but his rowan.edu e-mail account was inactive. I would be glad if you can provide help. Please use my e-mail found here. Danko Georgiev (talk) 13:09, 2 March 2012 (UTC)


 * I suppose its OK to add that short summary, but I will say it again: you mis-represent your own calculation: it is not a Feynmann sum-over-histories, but a classical, wave-mechanics summation, using a quantum notation.  Since it is a classical calculation, there is no surprise (to me) that there is no which-way information.  I'm certain that a true, full, second-quantized calculation (a true Feynmann sum-over-histories) would show the same thing, and so personally, I find none of this surprising.  Now, to me, I will say that "wave function collapse" in quantum mechanics still remains a true, bizarre mystery, but I think that looking at the Afshar experiment is the wrong place to look. Well, I should be careful: its not a bad place to look, but I don't see anything hiding in these bushes.  There are many other strange places to visit in quantum mechanics, and, perhaps after visiting more of them, the true nature of the problem and solution becomes more clear. linas (talk) 15:48, 19 March 2012 (UTC)
 * Dear Linas, thanks for your reply. I do not misrepresent my own calculation, there are several sections of my article devoted to the issue of "quantum history", and what is the difference between Feynman sum-over-histories and Griffiths "consistent/decoherent" histories. I am busy with other projects, so I do not really think it will be productive for me to repeat here arguments that are nicely summarized/explained in my article. Just a couple of specific comments on what you wrote: (1) nowhere in my arguments I have mentioned wavefunction collapse, it is irrelevant; (2) the main problem to be solved is this one - if you open slit 1, then waves at D1 have say amplitude of 1, whereas at D2 the wave amplitude is ZERO; if you open slit 2, then waves at D2 have say amplitude 1, whereas at D1 the wave amplitude is ZERO. Unruh, Afshar and others argue that when you open both slits you SUM the two results, and because ZERO waves from one slit go to the opposite slit, the which way information is intact. What I proved is that this logic is not correct, and the proof requires usage of Feynman quantum histories (a fact that you seem to overlook). The "ZEROES" in the single slit experiments at the opposite detectors are produced by destructive interference, which CANNOT OCCUR in the coherent double slit because there is ANOTHER destructive interference at an earlier time at the bright fringes shown in the figure above. regards, Danko Georgiev (talk) 03:18, 22 March 2012 (UTC)

Disagreement Amongst Critics
I think it is notable to explain that there is disagreement amonst Afshar critics. Here is direct quote from article: "They are united in their rejection of the claims of a violation of complementarity, while disagreeing amongst themselves as to precisely why Afshar is wrong." Some accetp interference only some accept which way only and some neither. Actually even conversation above shows this disagreement also. The other problem is Flores-Knoesel paper responding to Kastner is incorrectly listed as critics. Does anybody know why? 98.154.13.159 (talk) 07:40, 2 March 2012 (UTC)
 * That quote from the article is not proof. It isn't sourced.  In fact I think we should remove it. -- cheers, Michael C. Price talk 11:56, 2 March 2012 (UTC)
 * Dear Mike, the above post is correct for the fact that Flores-Knoesel paper is not critique of Afshar, but critique of Kastner and therefore specific support for Afshar. I propose moving this support paper to the section Support for Afshar's thesis. Regards, Danko Georgiev (talk) 13:12, 2 March 2012 (UTC)
 * I can't see the support for Afshar in the abstract. Note: a critque of Kastner does NOT imply support for Afshar. -- cheers, Michael C. Price talk 16:37, 2 March 2012 (UTC)

Specific critiques section
Reading through the article, this section seems to be a big mess to me. The back and forth doesn't give the reader much background to what the critiques are. Why is which way information important? What does Afshar say the implications of his results are? Why are these important? What is the importance of the critiques? Could the article be better served by a more general section detailing the impact of the experiment, what is the major views of the scientific community on the experiment. This shouldn't include the counters by Afshar, without more explaination behind the Specific Critiques section, it reads like a mess to me, and it takes up over half the article in a back and forth arguement.Savage1987 (talk) 18:03, 11 December 2012 (UTC)

Experiment illustration
I found it obscure by this statment: "which is why we see the pinholes separately in the image plane close to the mirrors before the photon-detectors." Would it be possible to add illustrations for that image plane position in the pictures?

101.99.18.130 (talk) 07:32, 31 October 2014 (UTC)PQdzung

External links modified
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Tabish q paper
David Eppstein had removed one of the entries from Specific critiques section, apparently with the argument that the cited work was published by a publisher who is now believed to be "predatory". I don't think that is a justifiable reason since the article cites arxiv papers and also articles on personal websites. I have this undone that edit. — Preceding unsigned comment added by Tabish q (talk • contribs) 06:04, 7 April 2016 (UTC)

The above paper is also on the arxiv (http://arxiv.org/abs/quant-ph/0701109). This directed at David Eppstein who thinks that this paper is not reliably published. Tabish q (talk) 06:18, 7 April 2016 (UTC)


 * To be clear, the content that Tabish wishes to add, is as follows, inserted just under the discussion of W. G. Unruh's reaction:


 * Tabish Qureshi (Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi),


 * Qureshi, in his paper published in a peer-reviewed journal, does a wave-packet analysis of the Afshar experiment, and argues that even though Afshar's experiment has genuine interference, individual detectors clicking do not give which-path information. Through a mathematical analysis he shows that in the region of overlap of the wave-packets, if the state is such that the modulus square of the wave-function gives an interference pattern, the which-path information is necessarily lost.


 * As this is a WP:SELFCITE, would editors here please discuss whether this source is reliable, and the proposed content is supported by the source, and if this is appropriate WP:WEIGHT for this content? Thx Jytdog (talk) 18:14, 7 April 2016 (UTC)

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Contest deletion
I'm relatively new to Wikipedia, but not new to quantum measurement, having published four peer-reviewed articles on the subject. I don't know if I'm using the proper forum for my concern. Hope this is the right place to make my case.

I added three paragraphs to the Afshar experiment, which were quickly deleted, because it says they were 'fringe' physics. I'm sure my addition is not fringe physics since it's based on the emphatic assertion of our new Nobel laureate, Roger Penrose, subsequently reiterated in great mathematical detail by Mohr at the NIST and Smith and Raymer at Oxford U. I want to contest the deletion of my addition, and tried to do that yesterday, but don't presently see that critique anywhere on the Afshar page.

Please tell me what's become of my protest from yesterday, and how I ought to continue to contest deletion of my addition to the page.D bar x (talk) 05:17, 9 December 2020 (UTC)