Talk:Afshar experiment

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Contents

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

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)
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)
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)
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 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)

[edit] 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)

[edit] 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)

[edit] 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 ψ = 0 then you will get probability ψψ * = | ψ | 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)