Talk:Afshar experiment/Archive 13

Removed text

I removed the following text from the critiques section:

A more specific criticism is that when fringes are not visible, due to there only being a single photon in a pure state in the apparatus, V and D are defined directly in terms of the photon's quantum amplitudes for passing through pin-hole 1 or pin-hole 2, $\psi _{1}$ and $\psi _{2}$, respectively:

$D={\frac {||\psi _{1}|^{2}-|\psi _{2}|^{2}|}{|\psi _{1}|^{2}+|\psi _{2}|^{2}}}$

$V={\frac {2|\psi _{1}||\psi _{2}|}{|\psi _{1}|^{2}+|\psi _{2}|^{2}}}.$

and hence the Englert-Greenberger duality relation is algebraically satisfied as an equality:

${\begin{matrix}V^{2}+D^{2}=1\end{matrix}}$

so it is unclear how the inequality:

${\begin{matrix}V^{2}+D^{2}\leq 1\end{matrix}}$

can be violated by multiple photons passing through the apparatus as fringes build up.

The following is a partial list of other specific critiques of Afshar's experimental design and analysis. Afshar's rebuttals are available on his Q&A archive [1] and FAQ [2].

I removed it mostly because it seems to espouse a rather naive take on coherence theory, the study of partially coherent light sources. Since WP does not have an article, much less a category of articles on coherence theory, I can recommend only "Optics" by Hecht and Zajac, wherein the later chapters provide an introductory overview accessible at the advanced undergrad level. I don't believe they treat Englert-Grenberger, but they do give an overview of the general context in which such coherence arguments are set. linas 15:43, 16 November 2006 (UTC)

Linas, two things: (1) Why did you remove the sentence regarding my rebuttals and the links for it? If my critics are allowed to have their views reflected in the article, at the very least you should mention that I have responded to them and provide the link. (2) The decoherence, and the Schrodinger equation issue has not been addressed by Michael Price. He needs to explain why they are criticisms of the experiment and its interpretation, and the best way to do that is by writing a paper or two on the topic. Until then these "critiques" should be removed. Even AFTER Michael writes the paper(s), my response should be mentioned. As way of doing this, I am willing to start a new talk page on the issue of addressing Michael's views on decoherence and the Schrodinger equation, given an admin. like you monitors the discussion and makes sure it does not descend to the type of insults dished out by Michael. Best regards. -- Prof. Afshar 16:26, 16 November 2006 (UTC)

Sorry, you are right. I should have also removed the below. Its not clear to me if your rebuttals are addressing specific issues raised by Motl, Drezet, etc. or if they are general, or where they would fit, so I removed them along with the paragraph they were attached to. If they need to be added back in, please ad to the appropriate places. linas 18:07, 16 November 2006 (UTC)

• Bohr's philosophical views on the Complementarity Principle are generally seen as in accordance with the Schrodinger wave equation. Since the latter is obeyed in Afshar's experiment it is not obvious how complementarity can be violated.

• Complementarity is often viewed as being enforced by the uncertainty principle, which is nowhere violated within the experiment.

• The modern understanding of the role of quantum decoherence in the destruction of quantum interference provides a mechanism for understanding the appearance of wavefunction collapse and the transition from the quantum to classical. As such there is no need, in the decoherence view, for an a priori introduction of the classical-quantum divide as enshrined by complementarity, and (again, in the decoherence view) any experiment claiming to violate complementarity needs to address the issue by carefully defining complementarity from a decoherence perspective.

I've removed the above because the criticisms seem very casual and handwaving. linas 18:07, 16 November 2006 (UTC)

Linas, we've heard this claim of handwaving from you before, and the issue was settled then: you ended up admitting it was trivially obvious or boring or something -- I'll get the exact quote if you like. Why are you raising it again? I have restored it: please discuss here first, thank you. --Michael C. Price ^talk 21:29, 16 November 2006 (UTC)

Complementarity does not necessarily, a priori, introduce a classical/quantum dividing line. Decoherence provides a limit on the extent to which the wave function can evolve indefinitely but there is nothing in complementarity to suggest anything might be different there. The classical/quantum divide is arguably an interpretational dividing line which can be constructed a priori or after the fact. Generally, it is the physical production of an observable, as distinct from it's theoretical construction, that otherwise introduces the dividing line. Or not as the case maybe. Both are interpretable. Insofar as complementarity (from an empericist point of view) concerns factual observables it does not follow that complementarity necessarily enforces or requires a dividing line before the production of such observables. Whether this can be read a problem (as in the "measurement problem") depends on the philosophical framework adopted. Carl Looper

Correct, "complementarity does not necessarily, a priori, introduce a classical/quantum dividing line." In fact complementarity goes further than that and actually abolishes the quantum/classical divide altogether. It provides a totally quantum model for handling the loss of interference terms/ wavefunction collapse/complementarity, whatever you want to call the interpretational quantum mystery. Your 2nd sentence means (?) that any w'f' evolution eventually encounters irreversible processes and appears to collapse and I totally agree with the rest of your paragraph. --Michael C. Price ^talk 01:23, 17 November 2006 (UTC)

The decoherence version of complementarity abolishes the dividing line. I agree. But other versions do not. Regarding the second sentence - your reading is reasonable and I might have phrased it better. Decoherence provides for the appearance of a limit in which wave functions appear to collapse. That decoherence provides a useful way of interpreting the wave function collapse is certainly true. It is, however, a big jump, to say that complementarity must therefore be defined in terms of decoherency. In relation to the Afshar experiment (which is, after all, why we are here) that experiment is designed to test "Bohr's" principle of complementarity - which, for historical reasons, can not (or need not) be the same thing as the decoherence version of such. CL.

Your initial qualification is correct and it appeared in the critique as "in the decoherence view". Your point about "Bohr's" complementarity may be correct, but that it hardly a reason for saying that it shouldn't be carefully defined against modern standards.--Michael C. Price ^talk 09:12, 17 November 2006 (UTC)

Decoherence theory is a contribution to modern standards. As is Afshar's experiment. That does not mean we should therefore define one in terms of the other. CL.

With respect to your sentence "As such there is no need, in the decoherence view, for an a priori introduction of the classical-quantum divide as enshrined by Complementarity" - it's hard to follow (given your clarification) what is meant by Complementarity enshrining the quantum/classical divide. Or am I reading it incorrectly? If so, how should I (and/or others) be reading it? CL.

Perhaps if I removed the "a priori" it would be clearer? Or replaced it with "ad hoc"? Bohr maintained that measurements / observations were always understood, by us, in classical terms, whilst the microworld was not subject to the constraints set by our intuition. This is a pretty standard view of what Bohr meant. --Michael C. Price ^talk 09:12, 17 November 2006 (UTC)

Both "a priori" and "ad hoc" are incorrect. The collapse of the wave function, in the "Hesienberg/Bohr" version of such , is the contribution that physical observables make to the otherwise theoretcial construction of such observables. It is just what happens so to speak. The theoretical wave function collapses. It no longer holds. It becomes "wrong". But then the waves were never framed as "right" in the first place. In the Heisenberg/Bohr model they are theoretical waves that represent or predict what is otherwise physically realised. As Bohr once said - there is no "quantum world". There is only what we can say about the observables. But this is just Bohr. Obviuosly we are free to say anything we like - but then we're saying something else. And this distinction is important. We organise what people have said - if only for the historical record. Encyclopedias are an example of this. They constitute a history of what people have said and thought. And we organise all this information. Or try to. It is not about whether Heisenberg or Bohr are right or wrong. That is a question for science. I mean, if decoherence makes the Heisenberg/Bohr model invalid does that mean we should delete all references to the H/B model? This is what fuels historical revisionism - that history is there to be deleted and replaced with (ad hoc) "corrections". This revisionist model fuels much in science - we want what is "correct". And that's okay. But it's not necessarily self-evident what that is or should be. Scientists have to argue their case. But some people think they don't have to do that. CARL LOOPER.

I agree that both "a priori" and "ad hoc" were incorrect, or at least redundant, and I've amended the article accordingly. --Michael C. Price ^talk 23:39, 17 November 2006 (UTC)

I assumed it connects into something like this:

Bohr’s solution was to draw a border between the quantum and the classical and to keep certain objects—especially measuring devices and observers—on the classical side (Bohr, 1928, 1949). The principle of superposition was suspended ‘‘by decree’’ in the classical domain. The exact location of this border was difficult to pinpoint, but measurements ‘‘brought to a close’’ quantum events. Indeed, in Bohr’s view the classical domain was more fundamental. Its laws were self-contained(they could be confirmed from within) and established the framework necessary to define the quantum. - Wojciech Zurek - Decoherence, einselection, and the quantum origins of the classical

Exactly -- I see you have the same understanding that I and the rest of the physics community has of Bohr's approach. That's helpful! --Michael C. Price ^talk 09:12, 17 November 2006 (UTC)

But your clarification appears to change that. CL.

Please explain -- as far as I can see they mesh perfectly. --Michael C. Price ^talk 09:12, 17 November 2006 (UTC)

"the classical-quantum divide as enshrined by complementarity" (original statement)

"complementarity abolishes the quantum/classical divide altogether" (clarification)

Which is fine of course. You are attempting to apply your own idea (that complementarity must be defined in terms of decoherence) to your own statements. And it shows the difficultys involved. What seemed like a perfectly valid idea starts to become a little unstable. What version of complementarity am I talking about? Surely there can only be one version - the correct one eg. the decoherence version of such. The very consistency you seek starts to become undone by the very insistence on consistency. One is using the same word to mean at least two different things. At this juncture you realise that a few sentences just does not provide enough bandwidth for what you might really want to say. That's all. And on that note I'm going to abbreviate my use of Wikipedia's bandwidth and make an apology for the flippant remarks I also made at Afshar's expense when first I ventured here. CARL LOOPER

As I tried to explain, these are not my ideas. And you contradict yourself. Now you say there must be only one version of complementarity, earlier you complained that I needed to address specifically "Bohr's" version..... Finally, I shall be sorry to see you leave, especially since you've starting behaving so civilly. --Michael C. Price ^talk 09:12, 17 November 2006 (UTC)

The "I" of the quoted passage is that hypothetical person who might think they "mesh perfectly". This idea - that they "mesh perfectly" - is an original idea, whether originated by the "I" of the passage, or someone else (as in "someone else's idea"). It is clearly this idea that seeks to establish itself as criticism. This idea is that "Complementarity must be carefully(sic) defined in terms of decoherency", something which our hypothetrical person had not previously done but is now trying to do. And we should congragulate him on actually trying. 'My' argument (and presumably of others), is that this requires at least a short essay rather than a few sentences posing as self-evident truth in the main article. Also, I'm not leaving. I am just keeping my use of talk page bandwidth brief, and in more conformance with Wiki guidlines/policy - which I have not done in the past. CARL.

Your use of "sic" leaves me puzzled. It is not OR if you have sources for both A=>B and B=>C and then to state A=>C. Let's examine the clause that seems to trouble you:

and (again, in the decoherence view) any experiment claiming to violate complementarity needs to address the issue by carefully defining complementarity from a decoherence perspective.

since the statement is conditioned upon "in the decoherence view", what is the problem? Someone who is not convinced by decoherence can ignore it. Finally, yes a short essay might be required to fully explain all this, but that's what the hyperlinks are for.--Michael C. Price ^talk 20:59, 17 November 2006 (UTC)

Yes, I have been following the clarifications you've been making and that's a good start. And indeed, I have no problem with the links to decoherence - although I'd put them after your main argument rather than prior to such. The way you have written it seems to suggest that decoherence theory is arguing that "complementarity must be carefully defined in terms of decoherence.". I mean, I understand why it has been written this way - because if it wasn't written this way it might look as if it was you making the case rather than decoherence theory. CL.

You may think that, I couldn't possibly comment :-) Seriously though, what is relevant is whether the sources are good the the logic sound. --Michael C. Price ^talk 22:59, 17 November 2006 (UTC)

Yes, what is very important is whether the argument is good. The sources provide a context for such an argument. But they do not necessarily provide the argument itself. That is something you have to do. The first step is to be honest and change the semantic structure of your argument to reflect it's correct authorship. This is not a joke. CL.

In relation to your earlier A=>B, B=>C argument. That's actually a nice bit of logic you've got going there. Or at least the basis for one. If A points to B and B points to C then A points to C. Yes. But if A (Afshar) points to C (complementarity) and D (decoherence) points to C (complementarity). Does it follow that A must point to D? CL.

No, of course not, that would be illogical; the question is, is that a good analogy? Since decoherence claims to be able to clarify all QM interpretational issues then the original inference is sound, in the decoherence view. If I said "we've evolved from fish", then a whole load of ***** could contest the statement, but if I said "we've evolved from fish, in the Darwinian view", then we have an uncontestable statement that even Pastor Ted Haggard would agree with. Just an analogy, you understand. --Michael C. Price ^talk 22:59, 17 November 2006 (UTC)

Darwinian theory says we evolved from fish. But decoherence theory does not (yet) say we must (re)define complementarity, carefully or otherwsie, in terms of decoherency theory. CL.

Micheal, the above conversation makes it clear that there are a lot of people with original ideas doing original research on this topic. This wikipedia article is not the place wherein to write up all of these intersting ideas. Which is why I deleted the section I deleted. I'm not too happy that this talk page has become a philosophy coffee clatch.

Perhaps I may have once suggested critiquing the experiment from the decoherence point of view. While this would be an interesting research starting point, "publishing" that research at this article would be a bad idea.

I am sorry that I once said that the Afshar experiment was "boring" or "trivially obvious" or whatever. Like much of the rest of the audience, I was scandalized by the New Scientist article. And, like everyone else, I was compelled to make snide, rude remarks about the stupidity of this experiment. Which I did. I'm now over it, and I think its time the rest of the world got over it as well. If this problem tickles you, then do the research, write it up, publish it. This article should mostly try to stay as close as we can to facts, or at least to points which are not in dispute. (The stuff I moved to this page seems quite disputable). linas 04:26, 17 November 2006 (UTC)

Linas, once again I see you have deleted first and mentioned it at the talk page second.

First you misunderstood, it was not the Afshar experiment that you described as "boring" or "trivially obvious" but the critique I had offered, which case it can hardly be described as original research (another claim that you made and was settled a long time ago).

Second, the deleted text was referenced -- much more heavily than the rest of the article. Did you, for instance, check the statement:

• Complementarity is often viewed as being enforced by the uncertainty principle, which is nowhere violated within the experiment.

against the embedded reference? It's not original research and I hardly see how it can be disputed by anyone with a basic grounding in quantum theory and who has read the reference (the Scientific American article should available to you, if not shall I quote chapter and verse from it?). I hardly think I should have to point this out, but the statement preceeding the reference comes from the SciAm/Nature article and the statement following is accepted as true by everyone (which includes Afshar).

I can appreciate that you have a heavy workload and that you deleted without checking, but please do not repeat this error.

--Michael C. Price ^talk 08:36, 17 November 2006 (UTC)

Come on Michael, even you can't be that illogical! The cited paper, later verified by Rempe et al. in experiments showed that Complementarity is not always enforced by HUP, essentially making them different epistemological phenomena. That means that you can violate Complementarity in certain cases without violating HUP, which is what I have done. It was a major misconception in the physics community that equated both Complementarity and HUP, and I used the ref. in my paper to point out clearly that I was not claiming violation of HUP, only that of Complementarity. The papers predating my paper have no bearing on my work as they do not directly address my experiment. The use of these sources in your contribution to the article does not make it any less of an OR. Why don't you write a paper on the subject and post it on a webpage like others? Instead of spending so much time on Wiki deleting and editing (which shows your not intellectually lazy as some suggested), put your thoughts in a coherent whole, that shows the experiment fails to accomplish what I claim. Surely, you will learn in the course of the research (and you can start by reading ref.s in my paper) that your current statements are at best irrelevant.-- Prof. Afshar 14:19, 17 November 2006 (UTC)

Perhaps you failed to see the significance of the words "often viewed as being"? Of course I realise that "Complementarity is not always enforced by HUP" - look the text of the summary of the paper: "Demonstrates that complementarity is enforced, and quantum interference effects destroyed, by decoherence (irreversible object-apparatus correlations induced by the detector), not by Heisenberg's uncertainty principle itself." Nevertheless this is common, albeit mistaken, view (that HUP = complementarity), and this is what is being reported. The more modern understanding, which the paper discusses, regards complementarity as being enforced by decoherence......... --Michael C. Price ^talk 14:36, 17 November 2006 (UTC)

Prof Afshar is right, here. The deleted text makes logical fallacies:

Bohr's philosophical views on the Complementarity Principle are generally seen as in accordance with the Schrodinger wave equation.

which I paraphrase as no man is an island.

Since the latter is obeyed in Afshar's experiment

so time waits for no man

it is not obvious how complementarity can be violated.[5][6][7]

ergo, time waits for no island. Adding three references to such an absurd claim does not make it right. Its rather flagarent mis-use of references. linas 14:39, 17 November 2006 (UTC)

Perhaps more concretely: "Cars are generally seen as powered by gasoline engines. Since Afshar's experiment uses a gasoline engine, it is not obvious how it cannot be a car.".

Complementarity is often viewed as being enforced by the uncertainty principle[8], which is nowhere violated within the experiment.

"Cars are often viewed as being stopped by brakes, which are never applied within the experiment." OK. So? This is not even an argument. linas 14:45, 17 November 2006 (UTC)

Okay, well the first example seems clear enough, and easy to fix with a subject-object switch. It is easy to complete the 2nd example -- I erred in assuming a modicum of intelligence and technical competence by the reader. There was still no justification for deleting either if the errors were this elementary. --Michael C. Price ^talk 14:57, 17 November 2006 (UTC)

Surely you don't mean what you wrote. Personally, I think elementary errors are a great justification for deleting text. linas 15:05, 17 November 2006 (UTC)

A moot issue since I have corrected them, and thanks for that. --Michael C. Price ^talk 15:11, 17 November 2006 (UTC)

In the interests of fairness and balance I propose that we restore Afshar's blog link and put it in the external links section (along with his critics' blogs/links). Anyone object? --Michael C. Price ^talk 17:42, 17 November 2006 (UTC)

My last changes

If an article were added to wikipedia describing all the reasons why Afhsar might be wrong, this article would not adhere to wiki policies, because it would be original research, conducted not a non-neutral point of view. As such I made the changes to history. Additionally, there is a critisism section, so it is redudant to also litter the rest of the article with critique. Dndn1011 17:34, 17 November 2006 (UTC)

Whether it is OR or not depends on the presence and reliability of the sources, not the content. You are arguing back to front: you don't like the balance, so you argue that it is OR. Better to argue that it is not NPOV and add extra sourced balance. --Michael C. Price ^talk 17:41, 17 November 2006 (UTC)

Can't you give it a break, man! If someone collects too many sources on a subject together at a certain point it becomes OR. The more you scrabble around trying to throw in every concievable argument the more I tend to think it is driven by a fear that Afshar might be right. Just back off a little would be my advice. The world is not full of gullible people with no sense of reason. There is more than enough information to get interested people into the debate, and search engines also provide further information. Science is about a search for the truth via experimentation, debate and reasoning. Afhsar's experiment has caused so much controversy perhaps due to it not being trivially rebutted. Many people have put in effort to add their interpretation to the experiement. Thus whether or not Afshar is correct, he has certainly contributed to the debate in an interesting and constructive way. And since there are still many questions to be resolved in explaining the universe in general, and QM in particular, controversy has to be a good sign of progress being made. Relax man. Dndn1011 18:01, 17 November 2006 (UTC)

You are wrong about collecting sources => OR. That you think I am afraid of Afshar being right I find quite amusing, but no matter. As for the experiment being interesting and constructive, you will find that I have already said the same thing a couple of times. --Michael C. Price ^talk 18:17, 17 November 2006 (UTC)

I did not say collecting sources => OR. I said do that too much and it becomes OR. I am glad I amused you. Sorry I missed those positive statements. Dndn1011 18:32, 17 November 2006 (UTC)

You're still wrong about OR and sources, but I'll guess you find that out the hard way... eventually. --Michael C. Price ^talk 19:47, 17 November 2006 (UTC)

Sigh. Many research papers (as I understand it) are merely collections of references with some inference drawn from an analysis of that collection. I submit this is what you were doing. This is how too many sources grouped together to present a particular view or state a case or present an idea (in this case that Afhsar is wrong) can become OR. As for your "find out the hard way", it is a cheap shot and I can throw it back at you. Dndn1011 12:06, 18 November 2006 (UTC)

You're still wrong: if the inference drawn from the sources is correctly implied then it's not OR; if the inference drawn from the sources is not implied then it's OR. OR simply has nothing to do with the number of sources. Let's take a concrete example. I could find huge number of sources for the Earth being flat: citing them all would NOT be OR. Okay? Nor would mentioning that the pro sources outnumber the cons be OR: that would be an issue of balance.--Michael C. Price ^talk 12:24, 18 November 2006 (UTC)

No, I disagree. As an example, if I can prove X but to do so requires a complex argument that does nothing more than manipulate existing sources, this is OR Even if this proof appear correct and unarguable. For instance, if Pythargoras' theorem had not yet been discovered, and he himself presented his theorem in wikipedia, with all supporting references, it would still be OR. This is because readers would have to conduct their own research in order to verify the validity of the proof. This is one of the definitions of OR for the purposes of wikipedia. In reality perhaps the OR rule represents an ideal than can not always be met without make wikipedia less useful. Of course this creates much in the way of grey areas, admittedly. Dndn1011 13:55, 18 November 2006 (UTC)

Right, so OR can a measure of the complexity of the inference from the sources -- still not the number of sources BTW. Well I'll grant you that is a grey area, since complexity is a subjective matter. However the two resourced critiques I've reinserted into the article really are as simple as A=>B & B=>C implying A=>C, so this is not an issue anymore. --Michael C. Price ^talk 15:46, 18 November 2006 (UTC)

In your opinion Dndn1011 16:47, 18 November 2006 (UTC)

You misunderstand (and I could have been clearer): the subject (QM) and sources are complex, but the grammar and logic is simple. We can debate the veracity of the sources but, if we accept them then, the logic really as simple as A=>B & B=>C implying A=>C. --Michael C. Price ^talk 18:17, 18 November 2006 (UTC)

18:03, 17 November 2006 version

I like this version. I would call for it remaining essentially as it is now. No doubt Mr. Price will want to add more to the critique section. If at the very least I could ask him to place critism of the experiement only in that section. In my opinion there there is quite enough as it stands. But certainly there is no need for critique to be anywhere other than in the critque section. Dndn1011 18:07, 17 November 2006 (UTC)

Boy, you sure make a lot of assumptions. Perhaps you didn't notice that I proposed making exectly the same changes to the critique section three minutes before you actually made them?  :-) --Michael C. Price ^talk 18:13, 17 November 2006 (UTC)

Heh, no. Nice coincidence. I got an edit conflict with you on the talk we obviously were doing stuff at teh same time. Anyway, thank you, I am glad we are reaching a solution. Dndn1011 18:29, 17 November 2006 (UTC)

Well, if you're happy and I'm happy we must be getting somewhere. I do have one extra problem which needs addressing, and that is that the experiment does not reveal interference and which-way information for any individual photon. All photons that are focussed by the lens, to reveal which-way info, must, by definition, have failed to leave a record of interference earlier. Trying to build a statistical argument seems flawed because otherwise we could simply go to the conventional double slit experiment and simply stop every other photon at the double slits to reveal which-way info (i.e. see which slit they each get blocked at) and build up interference fringes from the remaining photons that we don't block. I think this is the problem that troubles Drezet. --Michael C. Price ^talk 20:04, 17 November 2006 (UTC)