Talk:Popper's experiment

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Wikipedia Policy Should be Applied[edit]

This article's authorship is very disturbing. I refer not to the accuracy or not of content. However, as noted, an entry titled "Popper's Experiment" is written by someone who's own career work rests on disputing this experiment. In Qureshi's paper "Analysis of Popper’s Experiment and Its Realization" he states "We have shown that Strekalov et al.’s ghost interference experiment, actually implements Popper’s test in a conclusive way." Thus this is purely Qureshi's interpretation of these results. Qureshi continues that the ghost experiment's "result is in contradiction with Popper’s prediction." Again, this is his conclusion, not Strekalov's. Qureshi adds "It could not have been otherwise, because our theoretical analysis shows that the results are a consequence of the formalism of quantum mechanics, and not of any particular interpretation." This is quite damning. If one analyses an interpretation, that's particular. The quantum formalisms Qureshi applies, such as normalization, are interpretations (see Dirac's view.) Further, his results are weighted by prior expectations ("it could not have been otherwise.")

It's to be expected that specialists in a field with particular views may want to shape a Wikipedia entry. Wikipedia undoubtedly objects. But what happens when a Wiki article overlaps a specialist's own article. For this is what happens here. The entry has drawn verbatim content from Qureshi's article; it's structured like Qureshi's article, it includes Qureshi's article images. So this doesn't require much subjectivity. Wikipedia could have a metric that prevents authors from using some percent of personal content in an entry.

This should be reduced to a stub, or little more than one, with a link to Qureshi's article. Wikipedia needs standards applied consistently. Brian Coyle


Dear Tabish, the entry you opened is marvelous! Thanks for doing all this work, it will help all those who are interested in science and QM. Of course, there are also pseudo-scientists editing in Wikipedia, that "edit" without understanding what they edit. Yet, you have my support in case someone incom?petently tries to revert your edits. Nice work! Danko Georgiev MD 03:27, 13 April 2007 (UTC)


I have a comment to make about the FTL section of the article.

You have the Popper experiment. To do it, you use a coincidence circuit. If you try to apply it to FTL signaling, you get rid of the coincidence circuit. That is the only difference between these two types of experiments. Standard, non-FTL experiment, coincidence circuit; FTL-application experiment, NO coincidence circuit.

Only difference: coincidence circuit or no.

I hope I am making my point absolutely clear.

What pray tell then does removing the coincidence circuit have to do with the introduction of cloning? How are you cloning by removing the coincidence circuit? You are not cloning in the Shih experiment, right? Then how is it that all of a sudden you are now cloning when you are applying the apparatus to FTL? (Again, by removing the coincidence circuit.)

Whether or not you believe FTL signaling is possible, the explanation in this section is bogus and should be removed. Otherwise it is an interesting article.

Rjensen88 (talk) 02:13, 21 March 2008 (UTC)RJENSEN88


Dear Tabish, I don't know who has written the text that the Popper's experiment will allow for FTL, but I repaired it, as it was clearly wrong. I am writing paper on No cloning theorem, QM, and MIND, so I am well acquainted with the detailed proof of the No Cloning theorem. Indeed you cannot use entanglements for FTL because you cannot copy unknown QM states. So I have allowed to edit the topic, as I am well acquainted with the FTL issue. Danko Georgiev MD 05:20, 13 April 2007 (UTC)

Popper had stated what he thought the Copenhagen interpretation implied for his experiment. One reading of the result he erroneously attributed to the Copenhagen interpretation, is that it leads to faster-than-light signalling. However, I think that Popper was not even comfortable with the usual non-locality of quantum mechanics, and he may be only talking about quantum correlations between the two particles. His words

...if the Copenhagen interpretation is correct, then any increase in the precision in the measurement of our mere knowledge of the particles going through slit B should increase their scatter

I would like to intrepret as talking about measurement of particle 2 conditioned on the measurement of particle 1, and not implying any FTL. Maybe the language of that para needs to be corrected. --Tabish q 06:56, 13 April 2007 (UTC)
Did the meaning of the original sentence suggest Popper's experiment actually allowed FTL? I read it as saying that "according to Popper", CI allowed FTL. I don't know if this is what Popper thought but that was how the sentence in question came across to me. So I don't know if "repaired" is the right word to use in relation to the rewrite. --Carl A Looper 07:17, 13 April 2007 (UTC)
Hmmm, Tabish beat me to the edit. I should say my response above was to Danko - not Tabish. It was coined prior to Tabish's contribution but appeared after (in case there is any confusion about this) --Carl A Looper 07:27, 13 April 2007 (UTC)
Carl, your expression is clearer than mine - "according to Popper", CI allowed FTL is exactly what I wanted to say. You are right that we are not sure if this is what Popper thought, but some people have definitely understood it that way. --Tabish q 07:38, 13 April 2007 (UTC)
CAUTION! We are not sure what means "faster-than-light communication" at the time of Popper in the mid 20th century. In 1935 Einstein-Podolsky-Rosen also thought of quantum entanglement as "violating relativity". BUT later it was proved that because of no cloning theorem FTL communication is impossible by entanglements only. So John Cramer in 1986 in his famous Transactional interpretation paper used two terms - [i] faster-than-light enforcement of quantum correlations a.k.a quantum entanglement, and [ii] faster-than-light communication [transfer of classical bits] a.k.a superluminal communication. I am afraid that that at the Popper's time the correct distinction between these has not been well-known, so it is quite possible that Popper has not clear idea of what "true" FTL communication is. I believe he meant just the EPR entanglement and q-nonlocality as counterintuitive, thinking as Einstein that relativity and QM are incompatible. However after the no cloning theorem has been proved [I think in the 1980's] it was proved that this is illusory contradiction, and EPR correlations cannot be used for FTL communication. I hope this clarifies the issue. I agree with Tabish on what he says above. Danko Georgiev MD 06:05, 14 April 2007 (UTC)

p.s. It appears to me that neither Popper nor the people who criticized him had clear knowledge on FTL communication. The story is the same as with Afshar, and his opponents like Motl, Unruh, Drezet, etc. Both sides start from wrong understanding, so as a whole, both sides are wrong. :-) Danko Georgiev MD 06:10, 14 April 2007 (UTC)

Yes, need to research Popper some more. But regarding historical perspective, Bohr's response to EPR was relatively clear - indeed Bohr was the one who actually discovered that - irregardless of anything else - EPR could not demonstrate FTL communication (classical information transfer). And while "entanglement" was not as formalised as it is now, it was embryonically there in Bohr's response - it was the reciprical of the non-FTL-communication insight. --Carl A Looper 23:05, 15 April 2007 (UTC)
Carl, I agree with you that although entanglement was not as formalised as it is now, the fathers of QM understood it very well. Now that it is being used in quantum computing, people are making a big deal out of it. I had once asked Daniel Greenberger (of the G-H-Z state fame) about the origin of the word entanglement. He said that Schrödinger coined the term entanglement by using the German Verschränkung. Also, entanglement is at the heart of the Schrodinger's cat problem.--Tabish q 20:24, 16 April 2007 (UTC)

Insight on what happens?![edit]

Dear Tabish, after reading the article I came to the conclusion that narrowing the slit at A or not, will affect the spread of particles at slit 2. However my conclusion is that narrow slit at A will decrease the spread at B, not increase it. I use standard QM thinking. Basicly I think that way - you collapse the state by Renninger type of negative measurement at narrow slit A, say in region . This means that you have negatively measured that the particle does NOT hit the screen of the slit! So now the wavepacket is partially reduced to the region , yet the particle is not detected destructively and it continues to spread from the partially collapsed state, and because the second particle at the wider slit is also EPR correlated it will partially collapse at the region . Now this partially collapsed wavepacket B starts to spread again (exactly as packet A) until it reaches a second screen detecting the scatter. However this secondary spread should be in general smaller than the case when the Renninger partial collapse was not performed. So the spread of particle B I think with narrow slit at A, should be generally smaller that the alternative case when particle A does not pass through narrow slit. Do you agree with my conclusion? The whole article is very tricky, but is my summary what QM says? I have reached it just by Renninger partial collapse idea. Danko Georgiev MD 01:04, 16 April 2007 (UTC) p.s. I think that the spreads of the two particles are equal, and this is the EPR correlation. Whatever the spread of A paprticle is, this will be the spread of B particle. In case when one performs coincidence count, he will discover that all B particles outside the spread of A narrow slit particles, will be correlated with particle A "hits" on the slit screen. For that purpose the screen with the narrow slit A should be some photodetector! I think all this is correct. My analysis lead me to conclude what the experimental data show - narrowing of particle B spread. Danko Georgiev MD 01:55, 16 April 2007 (UTC)

If my analysis is correct, then the text in the article seems to say the same thing, but the caption of fig.4 says exactly the opposite? Is there error in the caption? I thought that putting narrow slit on A, will make the spread of coincidence detected particles B, narrower. Danko Georgiev MD 06:33, 16 April 2007 (UTC)
The caption is all right. The results of the experiment show that if there is a real slit B (as narrow as slit A), then the spread behind it is large. On the other hand, if there is no real slit, but only a virtual slit created by particle 1 passing through slit A, the spread behind slit B is smaller.
I am not sure I follow your argument. From what I understand, it seems to imply that narrower slit A will lead to a narrower spread behind slit B. This is not correct. Narrower slit A leads to a wider spread behind slit B, if one is only talking about coincident counting (meaning, you are only counting those photons behind slit B, whose other partner has been detected behind slit A).--Tabish q 20:07, 16 April 2007 (UTC)
Dear Tabish, I am not sure whether I disagree with you, or we just don't understand each other. Please check the following image and my math sketch. I see no error.

Popper spread.PNG

  • The spread of the wavepacket is function of z (or time, t). I denote this direction a x-direction. So the spread as I measure it is along x direction.
  • Once you detect by the screen the wavefunction everywhere EXCEPT the narrow slit, you perform partial collapse of the wavefunction by negative Renninger measurement. The uncollapsed particle wave is localized only in region of the slit, I called it . It is clear that . Otherwise if then the whole wavefunction will pass through the slit, as if the slit does not exist (of course the ratio says how good this approximation is).
  • The rate of secondary spread after the second slit in my view is exactly the same as the rate of the original spread if the two slits are equal. In this case NEVER the secondary spread is greater than the original spread to be obtained if there is no second slit.
  • If the second slit is narrower than the first slit, then the rate of the secondary spread will be faster, so there will be distance z, for which the original spread if there is no second slit will be greater than the secondary spread, then since the second function describing the secondary spreading is more rapidly growing, there will be z* for which the two spreads are equal, and for distances >z* I agree with you that the spread is greater compared to case when there is no second slit. Do you agree with my explanation? Danko Georgiev MD 02:11, 17 April 2007 (UTC)

p.s. I now realize that my argument is actually filling a "GAP" in the original exposition. Nowhere in the main article text one says what is the original spread of the source, in my case I use to represent it with a slit. So then it depends the "narrow slit" how narrow is it? Is it narrower than the original uncertainty of localization ? If so, then I believe there are discussed three regimes behind the second(narrow) slit and critical distance z* as said above. Danko Georgiev MD 02:35, 17 April 2007 (UTC)

Danko, In the article represent the original "spread" in position and momentum of both particles.--Tabish q 04:19, 17 April 2007 (UTC)
This is fine, so the requested by me information is there. However still the "spread" as I understand it as superposed localization i.e. is function of distance z behind the second slit, and you say the secondary spread is greater for narrow slit compared to original spread without slit. This in my view is not correct, as for the limiting case , for z denoting distance behind the narrow slit, you will obtain slit spread being just which is clearly less than . Did you calculate the distance z* which if exceeded the secondary spread will be greater? Note: this distance z* will be function of the "narrow" slit width. Danko Georgiev MD 04:33, 17 April 2007 (UTC)
Dear Tabish, I was developping my argument thinking of such kind of correlation - if the particle 1 is collapsed to the described state then the particle 2 is collapsed immediately to , where it is essentially the same as with the only substitution -x, instead of x, i.e. suppose the origin of the coordinate system is at the emmision point of the two particles. Why you use the inner product of the global function with the state ? This describes only the probability for the particle 1 to pass the narrow slit. As we speak about the correlated measurement of particle 2 with the case when the particle 1 already passed the slit - then we have the case when this inner product is 1. So I think this inner product is not necessary at first place, to determine the state of the particle 2. And if the original was greater than the narrow slit width i.e. , then additional momentum scatter should be observed. Please see the figure above for sketch. Danko Georgiev MD 09:06, 17 April 2007 (UTC)
Clarification - dear Tabish, I just have read in more detail your formulas, so the spread in position denoted by me as is in your case written as . However if, the particle 1 is collapsed to the state , I think this will be also essentially the collapsed state of the particle 2 too. So taking limit , where is is my sketch above, and looking the expression for I think the position spread goes to zero, while the momentum spread goes to infinity . I don't understand why I obtain different result from you. p.s. I use the Heseinberg inequality applied to the entangled biphoton state, yet I remember that I have read before several years that such usage might not be applied to entangled biphoton state, as it is not single photon. I will try to find this paper in my database. Danko Georgiev MD 00:28, 18 April 2007 (UTC)

License of Fig.1[edit]

Dear Tabish, please put license label on fig.1, otherwise it may be deleted. You forgot to do this. Danko Georgiev MD 06:37, 16 April 2007 (UTC)

Thanks, done.--Tabish q 20:07, 16 April 2007 (UTC)

FTL - unclear[edit]

"The expected additional momentum scatter which Popper wrongly attributed to the Copenhagen interpretation can be interpreted as allowing faster-than-light communication, which is known to be impossible, even in quantum mechanics."

  • [1] In what sense Popper wrongly contributes this claim to CI? Does the sentence mean - the additional momentum scatter is derivable from QM formalism, therefore the additional momentum scatter is valid for all interpretations?
  • [2] Even, if the clarification in [1] is ok, then still I find troublesome this claim "can be interpreted as allowing FTL ..". This is incorrent, and this was the target of my notes. The exact should be "can be erroneously interpreted ..". Basicly, if the interpretation of the mathematics, says the opposite of what the mathematics implies, then such "interpretation" is just "wrong claim" or "misunderstanding" and not true interpretation. Interpretations by definition should all obey the QM formalism, and no interpretation must allow for FTL. Danko Georgiev MD 04:57, 17 April 2007 (UTC)

Interpretations of QM need not be consistent with QM. Interpretation can involve both a "transformation" (ie. which can maintain consistency) or a "translation" - which needn't. When I submit a text to Bablefish (a language translator) it can and invariably does introduce inconsistencys - which are a function of the assumptions encoded in the translator. The upside is that I'm able to express myself in another language. The downside is that some things invariably just don't translate. A transform, on the other hand, doesn't introduce inconsistency unless it is deliberately designed to do so. I can transform a signal from the amplitude domain into the frequency domain and back again - without introducing any inconsistency at all. But I can also use the same transformation to compress a signal, (remove information) and the result will introduce inconsistencys, the upside being that only the information I didn't want preserved is removed.

And apparent interpretations "of QM" may not actually be so. It depends on what is meant by "QM". If by QM we mean the mathematical model then there is no interpretation necessary. There is only one language available for mathematical models and that is the language of mathematics (notwithstanding some variations in the symbols used). But more often than not we're talking about "something" other than the mathematical model. About concepts (such as "reality") that may or may not be addressed by the model. And we are introducing the model into the context of this other discussion - which involves some finesse since we have to either translate the model into terms suitable for the other discussion, or translate the other discussion into terms suitable to the model, or find some common ground, or just stuff up the entire effort. Which is what happens most of the time.

But just because we can and do stuff it up when we venture beyond the mathematical model is no reason to avoid doing so. Because many things (ideas) "outside" of math (not yet formalised) actually can and do translate back into math. Just as many things don't. Heisenberg and Bohr went outside of the box to find ideas that could be translated back into mathematical terms. They ventured into the world of "interpretation" (not of QM because it didn't exist) but interpretation of other "things" (the world etc.) and re-encoded such within the domain of mathematical models - inventing/discovering QM. Interpretation "of QM" can precede the model as much as it echoes the model.

--Carl A Looper 00:42, 25 June 2007 (UTC)

Article is too technical[edit]

The "What is wrong with Popper's proposal?" section of this article seems too technical. The "Popper's experiment and faster-than-light signalling" section is also overly technical. Remember that Wikipedia is an encyclopedia for the general public. There's no need to hit people with wavefunctions. 13:29, 7 June 2007 (UTC)


The article was largely written by Tabish Qureshi himself, who defends a position on the issue, and it is accordingly biased severely towards his views, up to proclaiming them to be "the consensus" (perhaps it is the consensus in physics in general, but certainly not the consensus within the context of people working on this very issue). The article is actually quite good, it's well sourced and the technical presentation leaves nothing to be desired, but it definitely lacks neutrality at some central places. --rtc 05:47, 22 June 2007 (UTC)

  • RTC, I tried to write the article in a neutral manner, but from what you say, it appears that it did not come out neutral. However, at present I am unable to see where the changes should be made. Please, if possible, do point out the places where opposing view (with demonstrated correct physics) has not been given due weight. I will be happy to have other editors volunteering. --Tabish q 08:44, 22 June 2007 (UTC)
    • In my opinion, neutrality is not something that can be achieved by "demonstrated correct physics" alone. What I think contributes to the bias of the article is that it does not sufficiently explain Popper's own views, their context which made him propose the experiment, and the historical development around the whole. (That is, section 'Background' is really insufficient. Such aspects are perhaps not of much interest to a physicist, but for a comprehensive encyclopedia article, they are badly needed.) For example, an experiment related to quantum mechanics is described already in Logic of Scientific Discovery, section 77, and it now carries a note that it was incorrect − what's the relation to the experiment described here? The article does not say what the philosophical problems were that Popper tried to solve and says about his motivation only that it was "to test the Copenhagen interpretation of quantum mechanics". Similarly, it has a strong inclination to reduce Popper's position to purely formal and empirical questions and especially doesn't describe the philosophical part of this position clearly and sufficiently complete. Which interpretation of Quantum mechanics did Popper actually try to defend and which characteristics did it have? For example, did Popper refuse non-locality outright? (From vague information on the web, it seems so, see the "Bell's Theorem" book chapter I refer to farther down.) The article doesn't even mention the word "propensity" and doesn't describe Popper's propensity interpretation of quantum mechanics (which is based on his propensity interpretation of probability) and his notion of "propensity fields". What did he think about Bell's inequations and the EPR paradox? Several Bell test experiments were done before Popper's death. Did he publish comments on them and what was his opinion about them? Popper constantly developed his views and often proposed several alternatives at the same time; did you investigate whether he changed them on this matter after the cited 1985 paper? (Popper worked until two weeks before his death in 1994!) For example, I can find at least one larger publication on the interpretation of quantum physics from 1988, A World of Propensities, and one book chapter, Bell's Theorem: A Note on Locality, in Alwyn van der Merwe, et al, (eds.): Microphysical Reality and Quantum Formulation (1988). Apart from that, I would like to see Unnikrishnan's position described more in detail; even if it seems to be quite non-standard, it can certainly give some interesting insights into alternatives. Further, "Indeed some authors have criticized Popper's experiment based on this impossibility of superluminal communication in quantum mechanics" seems to be misunderstandable. If I understood it correctly, they criticized that Popper didn't notice that the formalism on its own already implied that no such violation can happen, but the quoted text can also be understood to say that he was criticized for even trying to talk of something involving superluminality. Then, to claim that "'...if the Copenhagen interpretation is correct, then any increase in the precision in the measurement of our mere knowledge of the particles going through slit B should increase their scatter' [..] clearly follows from quantum mechanics, without invoking the Copenhagen interpretation" seems wrong to me. Understanding narrowing the slit as an increase in knowledge is already invoking the Copenhagen interpretation, isn't it? Generally, I think think an article shouldn't use weasel words like "some people" and "consensus" (better write something like "the most recent analysis, done by Tabish Qureshi, concludes that ..."). Please attribute all views on the issue to actual people and call them by name. I hope that this gives you some hints on how the article can be improved and made more neutral. --rtc 02:45, 23 June 2007 (UTC)

Yes, rtc has gone directly to the heart of the situation. What is of interest here is not just the physics taking place in the experiment but Popper's take on the experiment. But I wouldn't read Tabish's cursory coverage of Popper's take as biased. It is a good starting point and perhaps rtc could make some useful elaborations here. I certainly disagree with ignoring what Popper thought (ie. as irrelevant). One can't tell from the physics alone what Popper thought. All one can derive (or could have derived) from the physics - is that Popper was wrong - but only if one knew what Popper said (or meant to say) in the first place. However the design of the experiment does provide clues. Why this experiment and not some other? What is the purpose of this experiment? Tentatively answering such questions leads to an indication of Popper's take. But only an indication. The physics doesn't indicate anything at all. All it does is provide the means by which one could have critiqued Popper's take - if one knew what it was in the first place. However the article has made a cursory attempt to do just this. As it should.

--Carl A Looper 23:35, 24 June 2007 (UTC)

For me, I questioned the criticising of Popper on the basis of superluminality, because one should provide exact quotation that Popper said "there is superluminal communication". From general consideration, if one author *sees* a QM "nonlocal effect" as FTL, this is SEVERE MISUNDERSTANDING, and then based on his *own* misunderstanding the author can argue on general relativistic principle that *FTL* is wrong -- but understand here *author's own misunderstanding is wrong*. So my concrete point is "IS THERE DIRECT QUOTATION BY POPER TO SUGGEST FTL?", if NOT, then this is the misunderstanding of the criticizing authors, who criticized not Popper but their own misunderstanding. And thus the whole section should be either re-written or deleted. Tabish did not reply to my queries, so I am not sure why this lack of cooperation. Also I had concrete question on the initial spread of x - Δx, and spread of momentum - Δp. If one has large initial Δx0, there might be theoretically small Δp0, so the second narrow slit minimizing the spread of x to Δx1, should lead to extra spread of p so that - Δp1>Δp0. I even have drawn a diagram to ask whether my terminology is correct or not, but Tabish remained silent. Ah, and also I asked why Tabish uses inner product - if one speaks only about correlated counts then one might consider that the desired collapse has happened with certainty 1, and I see no need of inner product at first place. Danko Georgiev MD 03:28, 29 June 2007 (UTC)
If Popper has ever been talking about FTL, then he did so by showing that FTL was a consequence of a QM interpretation he criticized, and that this interpretation must hence be false if special rlativity is true. You can find a sample page from a German Critical Rationalist encyclopedia online that just happens to contain the entry about FTL. It suggests that Popper of course strongly opposed the existence of FTL, and that this opposition is his reason for rejecting non-locality. If you understand some German, perhaps you can read it yourself at [1], see entry "Überlichtgeschwindigkeit". (It concludes references.) According to this entry, Popper went as far as claiming that a QM interpretation with instantaneous non-local elements violates special relativity even if the predicted effect cannot be used to transmit signals. --rtc 04:17, 29 June 2007 (UTC)
Dear Rtc, you said "Popper of course strongly opposed the existence of FTL, and that this opposition is his reason for rejecting non-locality" - however nonlocality FTL! I don't know what is your education in physics but "superluminal correlation" is not equivalent to "superluminal communication". "Superluminal correlation" = "quantum entanglement" but by no-cloning theorem it follows that superluminal signalling is impossible. In 1935 Einstein believed that nonlocality contradicts relativity, but it is WRONG BELIEF -- nonlocality is NOT contradicting relativity. FTL is contradicting relativity, but FTL is not equivalent to nonlocality. I guess there is some confusion on this topic by Tabish, who himself created the original entry. I don't understand the meaning of what Tabish has written, that is why I have asked Tabish to reply. Possibly Tabish misunderstood the difference between "nonlocality" and "FTL" or possibly he understands them correctly but made typesetting confusion. In any case one should be very careful on the usage of these two words, many layman in QM don't understand the subtle difference. regards, Danko Georgiev MD 05:41, 2 July 2007 (UTC)
Danko, if you read what I wrote carefully, you will notice that I am fully aware that it is commonly held that superluminal correlation is not superlimunal communication. But if I read the CR encyclopedia above correctly, Popper held such a position, just as Einstein did. I hope it is understood that I am not describing what I think about the matter, but what I think Popper thought on the matter. So Popper seems to actually have held this kind of a nonlocality = FTL, and that nonlocality violates special relativity. The CR encyclopedia cites on that matter Quantum Theory and the Schism in Physics, 1982 preface and section VI, footnote 27 at fifth paragraph from the end of the section. --rtc 03:57, 3 July 2007 (UTC)
Dear rtc, even if Popper held the wrong view that entanglement=nonlocality is equivalent to FTL, this simply means that Popper does not understand QM essentials, but this does not clarify my main concern. The main article still says that *Popper was criticized on the basis that Popper's experiment predicts FTL, which is impossible*. This means that the author who criticizes Popper is similarly bad-educated in QM, as Popper, because this putative critique does not notice that Popper does not make difference between nonlocality and FTL. So I haven't read exact sources by Popper, but if you can please post direct quotations in English by Popper. Quotations of what others think Popper has said are false quotations, because are the story from third party. I hope my comments were useful as guidelines, I really don't have the relevant sources to solve this issue. I just say that the current text in wikipedia is completely wrong, and misleading, so Tabish better clarify the issues himself. Otherwise, the whole section better be deleted, or moved to the talk page for repairing. Danko Georgiev MD 09:24, 3 July 2007 (UTC)
Popper seemed to believe that non-locality, even without the possibility of faster-than-light signaling, violated Einstein's interpretation of the formulation of special relativity, and would force a return to Lorentz' interpretation. The following quote is from a footnote on page 20 of Popper's "Quantum theory and the Schism of Physics: Preface 1982: On a Realistic and Commonsense Interpretation of Quantum Theory"
It is often implied by physicists that only the possibility of sending signals whose velocity exceeds that of light would refute special relativity. This, however, is not correct. The moment we say that two distant effects are simultaneous in an absolute sense, we have abandoned Einstein's relativistic interpretation of the Lorentz-Einstein formalism. For within special relativity, two events on the x axis which are simultaneous relative to the inertial system S_1 are never simultaneous relative to the inertial system S_2 unless S_1 and S_2 are not moving relative to each other along the x axis, even if there should be no interaction (and therefore no signaling) between these two events."

Eric Hawk January 23, 2008 —Preceding unsigned comment added by (talk) 05:33, 23 January 2008 (UTC)

I'm a Popper fan, and I like Tabish's article. Everyone here appears to agree that Popper's thoughts should be better included, so here's my take on that.
Popper was not a physicist and his ideas about physics may not necessarily be that important. Yes, he apparently equated "spooky action at a distance" (let's call it SAAAD) with FTL, and didn't Einstein also? -- and I don't think they distinguished between FTL information ("signaling") and communication.
Popper's attempt at a real test of a classical violation is a creditable contribution in itself, but I believe this was in the service of a more fundamental goal springing from his overall program for science: to credibly satisfy the falsifiability criterion for aspects of quantum theory. The strange predictions/conjectures/interpretations of quantum theory beg for this. And it would be equally interesting whether or not falsifiability could be applied to these!
I would say Popper has done very well if people are still running this experiment and discussing it -- thank you very much for writing this article.Vendrov (talk) 11:01, 3 October 2011 (UTC)

Counting particles in coincidence[edit]

Popper suggests that we count the particles in coincidence, i.e., we count only those particles behind slit B, whose other member of the pair registers on a counter behind slit A. This would make sure that we count only those particles behind slit B, whose partner has gone through slit A. Particles which are not able to pass through slit A are ignored.

Do I understand correctly that this implies generating one pair of particles, looking whether an A counter triggers, then using that information to include or not to include data from the B counters in the statistics? That would be an explicit influence of A on B. (talk) 21:48, 19 December 2010 (UTC)

Poorly written Article[edit]

I found this article to be rather useless for doing any research. The information I wanted was unavailable because of the bias of the writers and the confusion. The article mixes up the debates and the experimental facts. I just want the experimental facts. These are not available. I cant determine what the experiment was about. this is typical of wikipedia. I don't want to be told what the conclusion is, or ought to be. The writer is biased and wants to defend Copenhagen. I don't want that I just want the experimental facts and there are not any here that I can use. This article needs a lot of work to be useful to anyone. — Preceding unsigned comment added by (talk) 20:31, 16 January 2012 (UTC)

I also corrected some obvious mistakes where the writer had apparently misunderstood Poppers arguments. These were reverted by some malicious editor. Apparently the writers have not read Popper's book and don't have any understanding of what his argument was. In order to understand the point of the experiment, the reader has to be told what Popper was saying in his book. This article doesn't do that. (talk) 23:59, 16 January 2012 (UTC)

I've had a go at some of this. It's a pity you are not signed in properly. Myrvin (talk) 09:53, 17 January 2012 (UTC)

Let me make this perfectly clear. I am a user and not an editor. I found this article so annoying and frustrating to read that I was compelled to make changes. There seemed to be so many errors. The jargon is obscure and not explained. To make matters worse there are other resources that do a much better job than wikipedia. All you have to do is model after them.

In the end there is no conclusion as to exactly what the results are. Did the experiment validate Popper or not? As I see it , the result refutes the Copenhagen interpretation of QM. — Preceding unsigned comment added by (talk) 21:11, 17 January 2012 (UTC)

I authored a paper [2] which might help answer some of the questions and problems resulting from this wikipedia article. I do attempt to answer whether the Kim and Shih experiment combined with Strekalov et al's. ghost imaging experiment validate Popper and if they refute the Copenhagen interpretation. I hope it can be of some help as Popper's experiment is well worth understanding in depth.Cricha5 (talk) 14:15, 16 September 2013 (UTC)


The date of 1934 in the lead surely refers to P's Logic of S Discovery. There was an experiment in there (p240), but the experiment described here seems to come first from the cited 1982, Qu Theory and the Schism .... If there are no better or earlier references, I shall change the date. Myrvin (talk) 09:53, 17 January 2012 (UTC) Did it. Myrvin (talk) 16:53, 17 January 2012 (UTC)

No, 1934 is the date of Popper's first paper on the subject -- K.R.Popper, Quantum Theory and the Schism in Physics, Die Naturwissenshaften, 22, 807 (1934) Roger (talk) 19:31, 17 January 2012 (UTC)

Thank you Roger. However, the only reference in Popper's work that I can see to a 1934 paper in Naturwissenshaften is a footnote in the 1982 book (of the same name) which says that paper contained "a gross mistake". P (1982) writes "My own experiment, which I published in ... Naturwissenshaften and also in [LSD] (1934), was invalid." This, nevertheless, may have kicked off the EPR paper. At the moment, it seems to me that the paper you mention had the same mistaken experiment as was in the LSD of the same date. The LSD experiment is not the same as the "Popper's experiment" discussed here. I don't think P reckoned this experiment is invalid. I cannot access the paper you mention, and couldn't read the German if I did. Nevertheless, 1982 now seems too late, P was working on the 1982 content round about 1950. But it may not have been published in any form until much later. I have seen it mentioned in other much later papers by others (Short etc.), but they may not have actually seen that paper - perhaps you have.Myrvin (talk) 09:40, 19 January 2012 (UTC)

Ah - I see that the only P work that Short [3] quotes is the 1982 book. Yet he still talks about it being "created in the early 1930's." Myrvin (talk) 10:06, 19 January 2012 (UTC)

However, he does cite the 1934 paper in a later work. Myrvin (talk) 09:46, 20 January 2012 (UTC)

In P's book on Parmenedes, in a section on indeterminism, he refers to LSD, and the 1982 work, and also a piece in Bunge's Quantum theory and reality, Volume 1966. I can't access this properly, but this may be an earlier attempt at describing this experiment. He does not mention the 1934 paper. Myrvin (talk) 09:46, 20 January 2012 (UTC)

This [4] mentions the failed 1934 experiment and says P only returned to quantum theory in 1950, particularly in the Schism postscript written in "the mid 1950's". Myrvin (talk) 10:34, 20 January 2012 (UTC)

This [5] talks about P's 1934 test idea being "reformulated and improved" in 1982 and onwards. Myrvin (talk) 10:48, 20 January 2012 (UTC)

It is strange to remove the 1934 date just because the experiment was "reformulated and improved" decades later. All important experiments are reformulated and improved later. If you read the page on the EPR paradox, it says that EPR proposed an experiment and it describes an experiment involving spin. But the EPR paper does not mention spin. Popper's paper played a role in the early understanding of quantum mechanics, and that should be made clear with a date at the beginning of the article. Roger (talk) 17:27, 22 January 2012 (UTC)
Regardless of the orinal date itself, the lead is self-contradictory in plain-language: it seems to say that others from well before the stated 1982 publication year are "subsequent" to it. OStating just the publication year there makes it seem like the whole theory is fairly recent, rather than just being the ultimate publication of many decades of work. DMacks (talk) 17:34, 22 January 2012 (UTC)

Roger: The EPR papaer doesn't start off with a date, and - if it did - it wouldn't say the date of the spin experiment but the later one. I thought my addition to the Popper's proposed experiment section would be enough to show his early involvement. Interestingly, I had a long discussion (in another article) with a physicist who thought there was no point in paying any attention to Popper in QM, because Popper was only a philosopher. I agree he was important. See later.

DMacks: Yes it is odd. I'll try some different words. If you read the LSD experiment (p240)[6], I would be interested if you think it is anything like this experiment. Maybe we don't need a date in the lead - EPR doesn't. Myrvin (talk) 21:34, 22 January 2012 (UTC)

Well-written articles on Popper's experiment[edit]

Hello to everyone. I wanted to share a whole journal issue devoted to the topic of Popper's experiment HERE. The first article in the issue by Shields explains nicely that Popper's experiment is created in 1982. What Popper proposed earlier in 1934 in German was refuted by Einstein in 1935. Popper was frustrated initially, but in time he decided he can improve his proposal for experiment using entangled particles. In regard to the outcome of the experiment, it depends whether you perform "coincidence" counts or not. Without "coincidence" counts there is no whatsoever evidence for nonlocal effects. Only, if you use a central detector and perform coincidence counts, you will be able to see the "spread" of momentum. This is illustrated very nicely by a spin-1 particle experiment proposed by Tabish Qureshi. I highly recommend reading the articles published in the above issue, and hope that someone can use them to improve this Wikipedia article, which looks complete mess as it is. I cannot do the editing myself in Wikipedia, because I have already editted the journal issue that I am recommending, and many will consider that this is a conflict of interest. So, I will stay away from editing, but if someone wants to ask me a question, I may answer on this talk page. Danko Georgiev (talk) 14:46, 30 November 2012 (UTC)

Aug. 2015

Prof. Tabish Hello!

Thank you for this very useful article on Popper's experiment.

Your last paragraph:

"A more nuanced view recognizes that each individual particle is correlated with its distant partner, not with any given particle that may already be at the distant detector. And these correlated or entangled distant particles must, necessarily, have moved to that distant location with a speed less than or equal to that of light. Thus, even the "ghost slit" effect cannot evidence itself until the distant correlated particle reaches the far distant detector. The effect on the particles the distant detector is measuring is not instantaneously impacted by actions on the local slit, since the affected (entangled) particles cannot reach that most distant detector until a duration has elapsed equal or less than the duration of a light signal sent from the particle source to the distant detector."

Is a bit unclear: why does "The effect on the particles the distant detector is measuring is not instantaneously impacted by actions on the local slit, since the affected (entangled) particles cannot reach that most distant detector until a duration has elapsed equal or less than the duration of a light signal sent from the particle source to the distant detector."

mean that no ftl signal is present?

One can always narrow the slit just before the right photon had passed through the slit,

causing an increase in momentum spread in the left slit FTL.

Did you mean to say that since all photons are connected to a coincidence counter

one must wait until the coincident results are measured?

Thank you very much,

Zvi Dickstein — Preceding unsigned comment added by (talk) 08:02, 23 August 2015 (UTC)