Talk:Popper's experiment

message: 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)
thread_title: Untitled

message: 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)
replies: text: 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)

text: 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)

text: 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)
replies: text:  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)

text: 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)
replies: text: 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)
replies: text: 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)
thread_title: FTL

message: 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 x_0. 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 x_0, 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 -x_0. 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)
replies: text: 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)
replies: text: 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)

text: 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.
Image: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 x_0. It is clear that x_0 < x_{full}. Otherwise if  x_0 >> x_{full} then the whole wavefunction will pass through the slit, as if the slit does not exist (of course the ratio \frac{x_{0}}{x_{full}} 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)
replies: text: Danko, In the article \Delta p _{2} = \Delta p _{1} = \sqrt{\sigma^2 + {\hbar^2\over 16\Omega^2}},~~~~ \Delta y_1 = \Delta y_2 = \sqrt{\Omega^2+\hbar^2/16\sigma^2} represent the original "spread" in position and momentum of both particles.--Tabish q 04:19, 17 April 2007 (UTC)

text: This is fine, so the requested by me information is there. However still the "spread" as I understand it as superposed localization i.e. \Delta x 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 z \rightarrow 0, for z denoting distance behind the narrow slit, you will obtain slit spread being just x_0 which is clearly less than x_{full}. 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)
replies: text:  Dear Tabish, I was developping my argument thinking of such kind of correlation - if the particle 1 is collapsed to the described state \phi_1  then the particle 2 is collapsed immediately to  \phi_2 , where it is essentially the same as \phi_1  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 \Psi (p1, p2) with the state \phi_1(p1)? 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 \Delta x was greater than the narrow slit width i.e. \Delta x > x_0, then additional momentum scatter should be observed. Please see the figure above for sketch. Danko Georgiev MD 09:06, 17 April 2007 (UTC)

text:  Clarification - dear Tabish, I just have read in more detail your formulas, so the spread in position denoted by me as \Delta x is in your case written as \Omega. However if, the particle 1 is collapsed to the state \phi_1 (y_1), I think this will be also essentially the collapsed state of the particle 2 too. So taking limit \epsilon \rightarrow 0, where \epsilon is x_0 is my sketch above, and looking the expression for \phi_1 (y_1) I think the position spread goes to zero, while the momentum spread goes to infinity \infty. 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)
thread_title:  Insight on what happens?!

message: 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)
replies: text: Thanks, done.--Tabish q 20:07, 16 April 2007 (UTC)
thread_title: License of Fig.1

message: "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)
thread_title: FTL - unclear

message: 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. 220.233.12.173 13:29, 7 June 2007 (UTC)
thread_title: Article is too technical

message: :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. 77.239.189.223 (talk) 21:48, 19 December 2010 (UTC)
thread_title:  Counting particles in coincidence 

message: 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 71.251.177.33 (talk) 20:31, 16 January 2012 (UTC)
replies: text: 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)

text: I authored a paper  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)
thread_title: Poorly written Article

message: 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)
replies: text: 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)

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

text: 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)
replies: text: 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)
thread_title:  Date 

message: 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)
thread_title:  Well-written articles on Popper's experiment