Talk:Measurement problem/Archive 1

Orphan comment
I edited it a bit and I hope it's better now...

- — Preceding unsigned comment added by 86.134.195.177 (talk) 09:06, 19 October 2013 (UTC)

Early comments
This article is biased as hell. Less cynicism, more objectivity.

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Yes, this article is disgustingly POV. I happen to agree with its POV, but still. I will work on it tonight if I get some time. Glenn Willen (Talk)   21:43, 4 Aug 2004 (UTC)

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The reference I added some time ago should give a better overview, even if not only focussing on the measurement problem. By the way, whould this article receive an NPOV-tag?

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This stinks of NPOV. Please see Talk:Measurement in quantum mechanics for a suggestion to solve both the many problems of that article, and the POViness of this one. Bth 18:58, 14 Oct 2004 (UTC)

Revolution for the article
Dear ladies and Gentlemen,

I revised the article and the reference at the end is the only thing that was not changed because I believe that it looks OK. My guess is that you will agree that this is a much better starting point for a serious article than the previous one.

Sincerely, Lubos Motl, Harvard University --Lumidek 01:16, 23 Dec 2004 (UTC)

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Waaaay better. The general problem of this entry is, though, IMHO, that the measurement problem is often the reason and ultimately the test for every interpretation of quantum theory, so that any discussion of the measurement problem quickly becomes a discussion of interpretations of quantum theory. Maybe the discussion of any interpretation should be relocated to the interpretation page and instead the measurement problem should be spelled out in detail?

Measurement problem?
I disagree that this is a title appropriate to the 2000s.

I have done a lot of quantum mechanical measurements and have never been aware of any general problem. Wouldn't "process" be a more interesting title? I don't see any article with that name.

The concept of "interpretation of quantum mechanics" is also out of date. I have tried to balance with "philosophical interpretation of classical physics" and had much help doing so, but we should work toward understanding physics before interpreting it.

As a step in that direction, maybe we could have one article explaining the interpolation between quantum and classical descriptions necessary in an experiment from the classical point of view and another from the quantum point of view. The problem with the former is that it is mainly historical, while the problem with the latter is that it so far exceeds possible detailed calculation. David R. Ingham 04:29, 21 October 2005 (UTC)

The short section on philosophy in the Feynman Lectures quantum mechanics volume does not appear to indicate that any change from the conventional scientific method is indicated or that there are consequences for other fields of study.David R. Ingham 05:09, 21 October 2005 (UTC)


 * I think this whole thing should be merged into quantum measurements. Karol 16:26, 22 October 2005 (UTC)


 * My impression of the measurement problem was explaining why the waveform collapses when it is measured, and what conditions are required for it to be considered a measurement at all. Is this accurate? Remy B 15:40, 18 May 2006 (UTC)

A source of ambiguity
The current text has:


 * quantum probabilities (that are able to interfere) to the ordinary classical probabilities.

This formulation involves creating a trap for the non-expert by calling two very different things by the same name, "probabilities." I believe some texts speak of "probability densities" when discussing ψ functions to indicate that what is present is not probably one thing in one case and probably something else in another case, i.e., that there is no randomness or indeterminancy about the ψ function. Instead, in a very absolute way it determines the likelihood with which a macro scale phenomenon will be observed. That the probability that any photon will arrive at point x on the detection screen is the same is better expressed by saying that each photon carries the same probability density of showing up at point x. I don't recall any other term being used to distinguish these two related by very different kinds of things. P0M 17:57, 29 October 2005 (UTC)

Every interpretation must answer?
"The measurement problem is the key set of questions that every interpretation of quantum mechanics must answer."

This so called "problem" is only a problem for *some* interpretations of quantum mechanics. So it is only in need of an answer within the context of those interpretations. I suggest the following:

"The measurement problem is a key set of questions that *some* interpretations of quantum mechanics *try* to answer."

Otherwise, those interpretations which do not see a problem will be prejudged as failing in some respect.

The real problem are those very questions which propose the measurement "problem" as a problem. By way of analogy consider the following question:

"Where is London to be found, outside the UK?"

Notwithstanding the possible presence of towns called "London" that do exist outside of the UK, the answer to this question is "nowhere". That doesn't mean London is nowhere. Nor does it mean that the answer is a failure to solve the problem.

Now consider a question closer to the question at hand:

"Where is a particle to be found, *before* it is found?"

Similar question. Similar answer. Similar conclusions. Simply put, the particle's discovery (in spacetime), like that of London, is not within the boundarys that the question has imposed on the answer. It's discovery belongs to a future that hasn't yet happened. Prior to discovering a particle one can, however, model it's discovery - but one can't actually discover it. Likewise, outside of the UK, one can, if not discover London, at least model it's location.

Carl Looper.

I don't mean to single out this comment, but it's typical of the widespread (if not ubiquitous) failure to understand that the measurement problem is a second-order problem. It refers to a disagreement among interpretations, because the bare quantum theory doesn't provide a clear and unambiguous answer to the first-order problems. In fact, all the interpretations of QM that go beyond Copenhagen have no first-order measurement problem, because they have attempted to solve it. And you can't assert that Copenhagen has no problem, since so few have bought their solution (which is, essentially, to assert that the lack of any evident solution is an irreducible aspect of reality, so suck it up.) Emvan (talk) 11:03, 4 January 2014 (UTC) Eric M. Van.

No positivism in Copenhagen
The statement that Bohr's Copenhagen Interpretation is a positivist theory is frequently made but probably not correct. See: http://plato.stanford.edu/entries/qm-copenhagen/ Furthermore, the statement that Copenhagen Quantum Mechanics does not explain a wave function collapse is rather misleading. In Copenhagen Quantum Mechanics there is no such thing as a wave functon collapse. The wave function is not part of the ontology. The change of the wave function after a measurement can be calculated using the QM formalism but this change of the wavefunction just has nothing to do with what happens in reality.

What is the article's subject?
The article is entitled "Measurement problem" as it stands, however, it is a brief (half-baked) description of various interpretations of QM. The actual problem of measurement is only briefly stated. The statement of the problem differs depending on one's approach. E.g. a physicist may wish to know exactly what makes a "measurement" different from the interactions described by the unitary time evolution, a philosopher may wish to examine what is wrong with the question "where is the particle before the measurement?" etc. A basic physics background could greatly enchance the article.


 * Isn't it true that "the measurement problem" is a kind of shorthand description for some difficulties in settling on an appropriate way to discuss certain things that was actually used by the original group of physicists who tried to come to terms with the new physics they were discovering? If that is true, then it would be worth tracking the locus classicus and citing it in the article. P0M 05:41, 2 May 2007 (UTC)

A word of caution to Carl Looper - the question analogy given above is somewhat along the lines of "if a tree falls and no one hears..." - it is just as valid to ponder this in the case of classical mechanics as it is in the case of QM. As far as I can tell the measurement problem arises in one of its guises in all of the mainstream interpretations of QM - sometimes as endlessly entangled systems, sometimes as inability to interpret "probabilities of the outcomes", most often as vagueness of the term "measurement" (if you know a well-developed, consistent treatement that avoids the difficulty please provide a reference). In Classical mechanics a particle does not need to "have" a position (for example) at all times, however (1) there is no problem with assuming that it does and (2) measurement of the particle's state does not in general alter its time evolution. Classically you can model a an "undetermined" state by a statistical probability distribution, which "can" (but does not have to) be interpreted as a particle being "somewhere - we just don't know quite where". However placing a collection of particles in a "box" and not wondering "where exactly" poduces very different statistical predictions in the Quantum case than in the classical case (e.g. bandgap structure of semiconductors, Bose-Einstein condensation).


 * How does a theory, developed on the basis of actual measurements, subsequently fail to accomodate the very measurements upon which it is based? Because the measurements get edited out. The sound of a tree falling gets excluded, and is replaced by the concept of a tree falling. The wave function which otherwise characterises the distribution of particle detections is re-assigned to characterising the particles which otherwise Platonically "cause" such detections. The only mystery here is how a theory which excludes particle detections can plead ignorance with respect to how to recuperate such detections. - Carl Looper —The preceding unsigned comment was added by 210.9.52.115 (talk) 03:14, 27 February 2007 (UTC).

Change the word mixed state
"the cat seems to be in a "mixed" state": I think the word mixed here should be changed to something else because it can be easily confused with the idea of a mixed state as opposed to a pure state.

Why is an observer needed?
I have read many books on this subject and understood some. Yet no-one has ever explained why an observer is different from any other object in his/her ability to collapse wave-functions. It seems as soon as a wave-function interacts with something else, it will collapse. The "something-else" may be an atom attached to an observer but it could be anything else. Thus the smell coming from the box will tell the observer that the cat died long before he/she observed the outcome. JMcC 10:47, 24 August 2007 (UTC)

I agree; the article does not address this issue. The word "observer" should be omitted alltogether from the article, and change sentences such as "when an observer measures" with "when the (isolated) system interacts with this and that". An "observer" makes everything sound ill-defined and pseeudoscientific.--190.188.0.22 (talk) 23:01, 11 April 2010 (UTC)

The measurement problem
Why do the particles act the way they do when the are observed? They must think they can do whatever the hell they want. Well not when im watchin. Its obvious that these guys will just mess around unless you force them to behave accordingly. I did a double split experiment today, i used an A4 sheet of paper, taped to the window with two slits cut in it. When observed they acted like expected, but sure enough when i looked away they started acting erratical again. Basically i would like to hear some methods on how to control the particles, i propose building a quantum scarecrow that would trick them into behaving how i want. Would this work? If not why not? Any other ideas? —Preceding unsigned comment added by 193.120.116.147 (talk) 12:46, 23 May 2009 (UTC)

An observer is not needed.
Quantum decoherence or quantum interactions are naturalistic phenomena that do not require an observer and measurement is an example of a quantum interaction but has no special status. It is to the shame of physics that the anthropomorphic nature of 'observer' was ever credible within the discipline. Perhaps this state of affairs evolved because the only physical process mentioned in the axioms of quantum theory that everyone learns is 'measurement'. It would be much better if this were replaced everywhere with 'quantum interaction'.Jockocampbell (talk) 22:45, 18 June 2012 (UTC)


 * See: Quantum_eraser_experiment. It is the ability to know something about a quantum state, even if you don't actually use that information.  If you lose the ability to know the state, as in the quantum eraser, interference is restored. The easiest way to know that you know the quantum state is to observe it, but there are other ways. Gah4 (talk) 19:16, 27 March 2019 (UTC)

Merger with Quantum mind–body problem
I've removed the merger tag. It was added in Nov 2010, but there was no corresponding tag on the Quantum mind–body problem article, and there was no section here to discuss any merger. If someone wants to consider a merge then feel free to tag it. but make a case for it here and tag both articles. Aarghdvaark (talk) 14:34, 19 June 2012 (UTC)

Understanding the Meaning of the Concept
I reverted the colossally, mind-numbingly wrongheaded "improvement" made by the anonymous user at 86.134.195.177 on 10/19/13 (their only contribution to Wikipedia). The "measurement problem" does not refer to the impossibility of resolving the apparent incompleteness of QM by explaining what constitutes a measurement, and/or how or whether a wave function collapse happens. It refers to the fact that people do not agree on the correct way to do so. You can't assert that physicists increasingly agree that there is in fact no such problem, until there is universal agreement upon a solution. (It would be like asserting that there is in fact no philosophical problem of free will because you buy the arguments of Daniel Dennett or Robert Kane.) To insert long chunks of text arguing for one specific solution is absurd. I myself am in fact 100% certain that David Bohm essentially solved the first-order measurement problem in 19-freaking-52, but until I publish the work that makes that case and everyone agrees it's correct, the second-order measurement problem remains.

If that user wants to add to Wikipedia, they should add those arguments (assuming they are not original research) to the appropriate pages, where those interpretations of QM are discussed.Emvan (talk) 10:51, 4 January 2014 (UTC) Eric M. Van.

Suggest to protect this file agains vandalism
I am trying for some time to explain why one cannot formulate a realist theory of quantum mechanics giving various citations from recognized experimental and theoretical work. The sources are Physical Review Letters, Nature, Review of modern Physics, etc. As it should be clear by now, there is no such thing as a measurement problem, be it local or non-local. Because of this I do not understand why my changes are always restored and deleted. http://www.nature.com/nature/journal/v446/n7138/pdf/nature05677.pdf E. Schrödinger, Die gegenwärtige Situation in der Quantenmechanik, Naturwissenschaften 23, 807 (1935); English translation by J. D. Trimmer, The Present Situation in Quantum Mechanics: A Translation of Schrödinger's ``Cat Paradox'' Paper, Proceedings of the American Philosophical Society 124, 323 (1980), and other citations have been introduced to underline what now should be common knowledge. I may also add references to textbooks, etc. I consider that the deletion of my comments are acts of vandalism and ask Wikipedia to take some measures against them. — Preceding unsigned comment added by Atreus57 (talk • contribs) 04:24, 11 July 2014 (UTC)
 * The measurement problem is the question of why (or when) a quantum system in a quantum superposition of states appears to collapse to a single eigenstate on interaction with more complicated systems (the "world"). Your addition to the article seems to address the unrelated issue that you need to specify an axis before you can measure spin.  I think you were trying (incoherently) to refer to the nonlocality found in the EPR experiment.  That is a different issue; it refers only to the entanglement of two particles.  The measurement problem refers to why we only observe one or the other direction of spin, and not a "mixture".  The answer relates to the coupling of the quantum state with the measuring apparatus, a complicated system with many particles. -- Chetvorno TALK 05:48, 11 July 2014 (UTC)


 * You claim there is no such thing as a "measurement problem". Where in your sources does it say that?  The only online source you gave, the Nature article, does not mention the measurement problem.  And again, you seem to have confused the measurement problem with the local realism problem of the EPR experiment. -- Chetvorno TALK 05:48, 11 July 2014 (UTC)


 * OR is not suitable for Wikipedia. Xxanthippe (talk) 06:35, 11 July 2014 (UTC).


 * I agree with Chetvorno. I am watching this article for a while now. There have only been a few changes since then and the only vandalism so far was yours. Protection is not necessary. The measurement problem is definitely not a "false" problem, since a whole bunch of quite famous people has been thinking and is thinking about solutions to it. There definitely are some people who claim that there is no problem to be fixed. That is exactly the many-worlds view as it is presented in the interpretations section. However, even if this interpretation was right (and I don't believe it is), changing the article the way you did would be as if you started an article about Creationism with "Creationism is stupid bullshit nobody should care about." That might be your opinion but it is certainly not a neutral view that belongs on Wikipedia. Xaggi (talk) 06:41, 11 July 2014 (UTC)


 * I also undid your changes again. They are definitely wrong placed in the introduction and also in the description of Schrödinger's cat. You could perhaps add them to the Interpretations section in some way or another. They would probably belong to the many world interpreation (althoug the people who answer the measurement problem with denial often also deny this connection). Xaggi (talk) 07:06, 11 July 2014 (UTC)


 * To make it a bit clearer to you, why many people still see a "measurement problem" despite your arguments: Saying that a "measurement" only shows outcomes with certain probabilities doesn't help, because "measurement" is not a defined notion. In principle, every measurement apparatus also must be described by quantum mechanics. So, in your picture, "measuring" a quantum state does not give you two outcomes with 50:50 probability. It rather gives you a measuring device that is now itself in a superposition state of cat being dead and alive (in the example of Schrödinger's cat). This is exactly the point of the many worlds interpreation. But then it is really hard to explain the Born rule: why are measurement outcomes statistically distributed like the absolute-value squared of the wave-function? Xaggi (talk) 07:12, 11 July 2014 (UTC)


 * And the main issue of the measurement problem is not what the probabilities are but why we need a probabilistic description at all. That is, why a quantum superposition as it becomes entangled with more and more of the external world, evolves so the eigenstates are mutually unobservable.  That has been resolved by decoherence. -- Chetvorno TALK 07:47, 11 July 2014 (UTC)
 * Atreus57 reverted again. Atreus57, let's talk about this here and come to a consensus, rather than just revert each other.  -- Chetvorno TALK 08:17, 11 July 2014 (UTC)

The measurement problem has nothing to do with Bell inequalities
I want to comment on the edits by Atreus57 which I will, again, revert (okay, already done by Waleswatcher, thanks) after I tried to explain why they are misplaced in this article (or at least in the main part of this article).

First of all, one should notice, as it already has been pointed out by Emvan above, that it is a bit misleading to talk about "the" measurement problem. The question, in its most naive way, is simply "what happens when a measurement on a quantum state is performed", and there are different proposals how to answer this question. Some of these proposals are mere interpretations, that do not change the laws of quantum mechanics (many worlds, Bohmian mechanics), while others are modifications of the theory (objective collapse models).

To state the problem: Suppose we have a quantum system in a superposition of two eigenstates, psi_1 and psi_2. Now we make a measurement with a (macroscopic) measuring aparatus that can be in two states A_1 and A_2 (e.g. pointer up, pointer down) corresponding to the eigenstates psi_1 and psi_2. According to standard quantum mechanics, the whole system is in a state
 * $$\psi = c_1 \psi_1 A_1 + c_2 \psi_2 A_2$$

with complex coefficients c_1 and c_2. This state will just evolve linearly according to the Schrödinger equation. But this is of course not what our brain sees (it cannot be, since it is a state in 6-dimensional Hilbert space and not in 3-dimensional space). Instead, what our brain sees is either the state psi_1 A_1 (or seeing A_1 on the measuring device in 3-dimensional space) or the state psi_2 A_2 (or A_2 on the measuring device).

Now, physics is about understanding nature. So physics should somehow give an explanation of how this measuring outcomes happen, given the original superposition state.

The answer of the standard Copenhagen interpretation is the "collapse postulate": When a "measurement" is performed, we will get outcomes A_1 or A_2 with probabilities in the ratio |c_1|^2 : |c_2|^2 and the state after the "measurement" will instantaneously jump to either of the states psi_1 A_1 or psi_2 A_2. There is nothing wrong with this (it may seem ugly, but noone says that the laws of nature cannot be ugly) except that the notion of "measurement" is completely undefined. Usually, the point of view that is taken by most people working with quantum mechanics is that this does not matter "for all practical purposes". But of course, if there is such a fundamental difference between "measurements" and other processes, a full theory of nature must provide a unique criterion to distinguish between both. Copenhagen interpretation does not do that, this is the measurement problem in Copenhagen physics.

Now there are several resolutions, described briefly in the interpretations section of the article. The one that is closest to your ideas is probably many worlds. There the point of view taken is basically the following: Asking why your brain sees either A_1 or A_2 is the wrong question. In fact, you have to consider the state
 * $$\psi = c_1 \psi_1 A_1 \times (\text{brain sees} A_1) + c_2 \psi_2 A_2 \times (\text{brain sees} A_2)$$

since your brain is also a quantum system. So basically there are two "worlds", one in which you see A_1 and one in which you see A_2. The appearance of a classical word is then explained by decoherence caused by the environment, but this interpretation cannot give a satisfying explanation of why measurement outcomes always appear with probabilities given by the wave function. In this view there also is a universe in which, at this moment, you are riding pink elephants on the moon.

Bohmian mechanics is a third way to describe the same measuring outcomes with yet another interpretation. So the measuring problem obviously exists in the way that the question what really happens in nature is not resolved. Since all these theories, to the point they are currently understood, make no predictions that differ from standarad Copenhagen quantum mechanics, there is also no way the problem could already be resolved experimentally. The experiments you cite are simply tests of Bell's inequalities. A completely different story.

For those arguing that this is not an issue for physics but rather philosophy, one might also note that collapse models indeed make experimental predictions different from standard quantum mechanics. So, at least as far as this proposal to resolve the measuring problem is concerned, the question what happens during the mesurement is indeed something that can be answered by experiment. So there is definitely physics here. Both models are still compatible with the current state of experiments, so there are indeed two different models that can be experimentally falsified against each other.

Cosidering this, what is your reasoning that makes you think that the measurement problem is "false" and that you "considering all the experimental evidence [...] cannot agree with the content of this page as it is without my completion"? Please refer to the problem I described and explain how you think this problem is resolved. Xaggi (talk) 09:13, 11 July 2014 (UTC)


 * As a "peace offering", and because I am aware of the fact that the point of view taken by Atreus57 is shared by quite a lot of physicists, maybe the conflict could be resolved by adding a section "Controversy" or, maybe nicer, "Is there a measurement problem?", in which a both sides of the argument are explained. To prove my point that a WP:NPOV is necessary, see also this opinion poll (in particular question 5). Although this poll amongst several well-known physicists working on quantum mechanics and related fields is certainly not representative, it clearly shows that there is no agreement on if the measurement problem is an actual problem or not. Xaggi (talk) 09:36, 11 July 2014 (UTC)

There is no need for a "peace offering". I am not at "war". The problem is, there are many mistakes in the article and they should be changed accordingly. Especially considering experimental evidence. The quotations I put in were pertinent and to the subject but completely misunderstood by the editors. A good reference would be Anton Zellinger's papers and books. He is actually in touch with experiments and understands the situation relatively well. There is no evidence for "many worlds" nor for "guiding waves", "hidden variables" etc. While all experimental evidence agrees with a non-realistic, local description of quantum mechanics, as described by Schrodinger with wavefunctions as maximal catalogues of expectations. Surely, there is much dispute but the dispute generally refers to interpretations that have no verification whatsoever. If the controversy is correctly explained (namely that the interpretations proposed for some experiments do not fit to the obtained experimental data) then I am of course agreeing. If however the controversy is about the validity of quantum mechanics itself then I have to protest.


 * I agree that there are several flaws in the article. This is probably why it has only quality rating "C-Class". But you are not making it any better with your edits. Instead you are basically going back to the highly opiniated version this article has been at the beginning. The measurement problem is not about questioning the validity of quantum mechanics. The problem is that the theory requires an interpretation. You give one interpretation. There are others. There is no disagreement on the outcomes of current experiment. This is why your "experimental evidence" does not have anything to do with the measurement problem. All the interpretations and solutions named here would agree on these experimental predictions. But physics is not only about outcomes of experiments, it is about understanding nature. So you need an ontology in addition to your mathematical formulation of the theory. What is the wave-function? What is a measurement? Yours is one possible answert. There are others. The fact that there is no agreement, which one is the best view, or that a lot of physicists think that the current situation is unsatisfying and an alternative interpretation or modified theory is needed, is the main point of what is usually referred to as measurement problem. Xaggi (talk) 10:30, 11 July 2014 (UTC)

So, for the beginning the problem is already when you say you have a system that is in a state psiA+psiB. This cannot be correct because the wavefunction psi=psiA+psiB is not a "state" of the system but a state of maximal knowledge about the system. As Schrodinger used to put it the actual meaning of the wavefunction is that of a catalogue of expectations. So saying that the system has a wavefunction psiA+psiB means that what can be known about the system is that it is not in any of the states psiA or psiB although upon measurement you can detect only state A or state B. My "interpretation" (actually, Schrodinger's... I try to avoid claiming property for things discovered by others) is completely unrelated to the many world interpretation which is wrong for other reasons. Physics is indeed about nature but questions like how comes that a state "happens" when initially the maximal knowledge about the system is a superposition are not questions about nature but about the state of mind of the observer picking a specific experimental design to answer some questions. The questions one can ask are not independent of the apparatus. My example about the spin shows precisely this: there exist no such "state" with spin up or down when there is no axis (an apparatus) to define that axis. So, in the context in which there is no apparatus there is no Sz state whatsoever. That has nothing to do with the EPR experiment which again has nothing to do with non-locality. If I have to explain that then that is simply the fact that the expectation catalogues propagate each and every "entry" in that catalogue in a deterministic way (perfectly local) while the outcome of the measurement remains inside that set. The interference of possible states appears only when you perform a statistics and in that case nothing "non-local" ever happened. This is NOT Copenhagen interpretation. There is no such thing as a "physical collapse". It just is an update of your expectation catalogue. That is not physical. You can of course describe you apparatus quantum mechanically and again this will result in a set of "if-statements": if the atom is like this the apparatus is like this, etc. In this way you will have to consider the interference of different expectations. But all this was known since Schrodinger's paper on the "situation of quantum mechanics"... I find it really disturbing that people still consider this as a problem or misinterpret it in so many ways. One should impose stricter standards for what is written on Wikipedia. The notion of measurement is *perfectly* defined in all cases. Your expectation catalogue will have to be updated according to all the "if-statements" inside the apparatus: if atom A decays then a photon is with that probability. If the photon is emitted then another atom will be excited with that probability, etc. The catalogue will be huge and the problem is not interesting per se... one is not interested to really bring in all microscopic details because all these details may have no independent meaning for the macroscopic state of the system. The simple reason why nature is intrinsically probabilistic is that the laws of nature are very general. There is no special law for every choice one experimenter makes. One has to define the experimental setup and according to it do design a specific question that can be answered by that design. Questions that are not uniquely defined with respect to that design will be answered considering all the possible things that have been ignored when asking an overly non-unique question. It is really as simple as that and no further additions have to be made... Quantum mechanics is perfect...


 * Personally I don't agree that this interpretation is a satisfying solution to the problem. But this is not about personal opinions. It is also not about quality standards on Wikipedia. You say that there is no problem. But you have to acknowledge the fact that a huge number of physicists still sees a problem there. So, since Wikipedia is supposed to give a neutral view on controversial topics, there is certainly something that should be explained on Wikipedia. As some examples take the opinion poll I linked above, the references in the Article (Weinberg, Bassi et al.), Penrose's article from 2014 (Gravitization of Quantum Mechanics I), or pretty much anything ever written by people working on collapse models or Bohmian mechanics. There is a measurement problem. I stated above what the problem is. What you describe is one possible interpretation providing one possible solution. But there are other proposals for other solutions and there is no agreement on which one is right or wrong. As Emvan wrote above: "the measurement problem is a second-order problem. It refers to a disagreement among interpretations, because the bare quantum theory doesn't provide a clear and unambiguous answer to the first-order problems." Xaggi (talk) 10:30, 11 July 2014 (UTC)

Although you do not say why you don't agree with this "interpretation" the solution is certainly in a good textbook. This is indeed not the problem. The actual problem is that this article is describing all the misconceptions about the subject while purposefully ignoring the correct description as it is in all standard textbooks and in the way quantum mechanics was formulated originally. I find this very disturbing and I think this should change. — Preceding unsigned comment added by Atreus57 (talk • contribs) 10:40, 11 July 2014 (UTC)


 * If your solution is in a textbook, Atreus57, what textbook?   Your English is bad enough that I can't understand your argument, so I don't know where it fits in with other approaches to the measurement problem. If your argument is not just your own WP:ORIGINAL RESEARCH, but is an accepted approach that is WP:VERIFIABLE and you can give some WP:RELIABLE SOURCES (I don't see that your existing ones are relevant), as  Xaggi said it is still only one interpretation among many. It does not belong in the introduction as the one and only solution, that is WP:UNDUE emphasis. Then the question becomes, is it WP:NOTABLE enough to be in the article at all?  Even if it is, unless you can get someone to write it more understandably, I don't think it belongs in the article because it just isn't clear. -- Chetvorno TALK 12:43, 11 July 2014 (UTC)
 * My only "original research" related to this was (fortunately) only to search for Schrodinger's paper: see for example here http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Schrodinger_1935_cat.pdf

I don't intend to improve much on what I wrote because I really have only very little time but I think the article should focus on what real science is and take the other unsuccessful essays as they are: essays. I also think the article deserves some curation from an expert. I have no time for that, again, but the article is very misleading in the form it is written now. It suggests that there is a problem with quantum mechanics (false, proved by experiments), it suggests the community of serious physicists has a problem with the measurement in quantum mechanics (false, despite the fact that some might have misunderstood some second year course and still got into higher academic positions) etc. — Preceding unsigned comment added by Atreus57 (talk • contribs) 17:05, 11 July 2014 (UTC) Apart of that, my english is suitable enough to be understood by any reader. It doesn't require any correction but it appears that some editors on this post have no interest in understanding the issues raised. — Preceding unsigned comment added by Atreus57 (talk • contribs) 17:07, 11 July 2014 (UTC)


 * Actually, I had a look at Schrödinger's paper (again) and I really cannot understand how you can take it as an argument for your point. Schrödinger actually mentions the problem: "The expectation catalogue (= psi-function) is therefore changed by the measurement in respect to the variable being measured. If the measurement procedure is known from beforehand to be reliable, then the first measurement at once reduces the theoretical expectation within error limits on to the value found, regardless of whatever the prior expectation may have been." This is exactly the collapse postulate, and this is the basis of the problem: Quantum mechanics is not just linear Schrödinger dynamics, it is Schrödinger equation plus collapse postulate. And the collapse postulate is poorly defined. As Bell puts it: "It would seem that the theory [quantum mechanics] is exclusively concerned about "results of measurement", and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of "measurer"? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system ... with a Ph.D.? If the theory is to apply to anything but highly idealized laboratory operations, are we not obliged to admit that more or less 'measurement-like' processes are going on more or less all the time, more or less everywhere. Do we not have jumping then all the time?".


 * Reviewing the article in a good way is necessary, I agree on that. Unfortunately it is not an easy topic at all. There are a lot of different views on it, and rarely anybody knows enough about all of them. The best thing that could happen would probably be that an expert in philosophy of physics would take a look at the article. The article in the Stanford Encyclopedia of Philosophy about the measurement problem is very nicely written, for example. Xaggi (talk) 18:18, 11 July 2014 (UTC)
 * I agree with Xaggi on Schrodinger. When he was writing, the measurement problem was in a much more primitive state;  the measuring apparatus (world) was treated classically, creating an artificial divide between system and measuring apparatus.  Ideas like Everett's world function were unknown.  I don't know how much Schodinger understood about decoherence; does anyone else?  Perhaps if he had known about decoherence's role in creating the appearance of wavefunction collapse, he wouldn't have been so insistent on an actual collapse?   Atreus57 you seem to base your ideas on Schrodinger. You should realize that a lot has been done on the problem since his time. -- Chetvorno TALK 22:43, 11 July 2014 (UTC)


 * It is really very good to look at Schrodinger's paper. What is not so good is not to understand it completely. Indeed, the "psi-function" is an expectation catalogue. It encodes the maximum available knowledge about the system and not a state of the system, universe, or whatever. There is no "physical collapse" implied because there is nothing to collapse...

"The Psi-function as Expectation-catalog

Continuing to expound the official teaching, let us turn to the already (Sect. 5) mentioned psi-function. It is now the means for predicting probability of measurement results. In it is embodied the momentarily-attained sum of theoretically based future expectation, somewhat as laid down in a catalog. It is the relation- and determinacy-bridge between measurements and measurements, as in the classical theory the model and its state were. With this latter the psi-function moreover has much in common. It is, in principle, determined by a finite number of suitably chosen measurements on the object, half as many as were required in the classical theory. Thus the catalog of expectations is initially compiled. From then on it changes with time, just as the state of the model of classical theory, in constrained and unique fashion ("causally") - the evolution of the psi-function is governed by a partial differential equation (of first order in time and solved for delta(psi)/delta(t)). This corresponds to the undisturbed motion of the model in classical theory. But this goes on only until one again carries out any measurement. For each measurement one is required to ascribe to the psi-function (= the prediction-catalog) a characteristic, quite sudden change, which depends on the measurement result obtained, and so cannot be foreseen; from which alone it is already quite clear that this second kind of change of the psi-function has nothing whatever in common with its orderly development between two measurements. The abrupt change by measurement ties in closely with matters discussedin Sect. 5 and will occupy us further at some length; it is the most interesting point of the entire theory. It is precisely the point that demands the break with naive realism. For this reason one can not put the psi-function directly in place of the model or of the physical thing. And indeed because one might never dare impute abrupt unforeseen changes to a physical thing or to a model, but because in the realism point of view observation is a natural process like any other and cannot per se bring about an interruption of the orderly flow of natural events." and "The rejection of realism has logical consequences. In general, a variable has no definite value before I measure it; then measuring it does not mean ascertaining the value that it has. But then what does it mean? There must still be some criterion as to whether a measurement is true or false, a method is good or bad, accurate, or inaccurate - whether it deserves the name of measurement process at all. Any old playing around with an indicating instrument in the vicinity of another body, whereby at any old time one then takes a reading, can hardly be called a measurement on this body. Now it is fairly clear; if reality does not determine the measured value, then at least the measured value must determine reality - it must actually be present after the measurement in that sense which alone will be recognised again. That is, the desired criterion can be merely this: repetition of the measurement must give the same result. By many repetitions I can prove the accuracy of the procedure and show that I am not just playing. It is agreeable that this program matches exactly the method of the experimenter, to whom likewise the "true value" is not known beforehand. We formulate the essential point as follows: The systematically arranged interaction of two systems (measured object and measuring instrument) is called a measurement on the first system, if a directly-sensible variable feature of the second (pointer position) is always reproduced within certain error limits when the process is immediately repeated (on the same object, which in the meantime must not be exposed to any additional influences)." etc. etc.

So, as Schrodinger observed, there is no such thing as a "state" of the system described by the wavefunction. It is simply a state of maximal available knowledge about the system in a given context. That state can always change abruptly once something else is added (like an apparatus) but it is not the physics that changes abruptly. It is just the knowledge...

also look here: http://web.ihep.su/dbserv/compas/src/feynman48c/eng.pdf "If (5) is correct, ordinarily (4) is incorrect. The logical error made in deducing (4) consisted, of course, in assuming that to get from a to c the system had to go through a condition such that B had to have some definite value, b. If an attempt is made to verify this, i.e., if B is measured between the experiments A and C, then formula (4) is, in fact, correct. More precisely, if the apparatus to measure B is set up and used, but no attempt is made to utilize the results of the B measurement in the sense that only the A to C correlation is recorded and studied, then (4) is correct. This is because the B measuring machine has done its job; if we wish, we could read the meters at any time without disturbing the situation any further. The experiments which gave a and c can, therefore, be separated into groups depending on the value of b. Looking at probability from a frequency point of view (4) simply results from the statement that in each experiment giving a and c, B had some value. The only way (4) could be wrong is the statement, “B had some value,” must sometimes be meaningless. Noting that (5) replaces (4) only under the circumstance that we make no attempt to measure B, we are led to say that the statement, “B had some value,” may be meaningless whenever we make no attempt to measure B6."

It is the combination between the wavefunction interpreted as an expectation catalogue (state of knowledge) and the fact that there is no state that can be assigned to the system unless is measured. Surely, in some cases a state can be assigned even before measurement, namely when such a state is well defined... I can say for example that an electron is a spin 1/2 particle but I cannot say how its spin is oriented because I need a reference for that (an axis) and this happens precisely because it cannot take any direction imaginable (the "classical imagination" simply fails in this case)... This and many other aspects of standard, conservative, simple and well defined quantum mechanics are simply ignored in the main article, referring only to some of the more bizarre and even proved to be wrong so called "interpretations"... — Preceding unsigned comment added by Atreus57 (talk • contribs) 06:23, 12 July 2014 (UTC)

There is no such thing as "classical" physics per se. That is simply an approximation or a limit. Quantum mechanics deals with predictions of correlated (entangled) statistical results. There is nothing *physical* that jumps. Bell puts the problem in a very naive way. He probably is one that did not understand the fundaments properly. There is nothing special about "the measurer" nor is it necessary to be one. It is simply (really simply) that some questions are immaterial for the system considered in the context considered. It is like the question "what is the color of night?" or "what is the color of music?" they may look "philosophically interesting" but are *ill defined* unless you specify something else which is brought by the apparatus. If that "something" is never defined you cannot assign color to music nor color to night etc. Many worlds interpretation is a PERFECT analogy to the medieval question "how many angels can dance on the top of a needle?" I find it a waste of time and I won't deal with this form of "research" because it is meaningless. I maintain my point however, that the article is misleading and HAS to be formulated according to scientific evidence. — Preceding unsigned comment added by Atreus57 (talk • contribs) 06:33, 12 July 2014 (UTC)

Addition to article "measurement problem" at the end of "Interpretations"
Is the following suitable to insert at the end of "Interpretations"?

The measurement problem arises because Quantum Mechanics deals with quantum superpositions that collapse when someone looks. Quantum Field Theory, in its “only fields” sense , provides a picture of reality at every moment, even when no one is looking. This picture consists of fields that are present at every point, but with intensities specified by vectors in Hilbert space, not by simple numbers. These fields evolve deterministically according to the QFT equations. In addition there is a process not described by the equations in which a field quantum deposits its energy into another quantum and disappears. This is a physical collapse, not a collapse of probabilities. Thus the QFT picture of measurement comprises two phases: First an incident quantum interacts with all quanta that it encounters as per the field equations. This interaction is reversible and may be called the “entanglement” phase. Then, at some point that cannot be determined by the theory, the incident quantum collapses into another object and transfers its energy to it, initiating a chain of events that can lead to macroscopic changes. For example, in Schrödinger’s cat experiment, when the radiated quantum collapses into an atom in the Geiger counter, an electric current is created that trips a relay that releases the poison gas that kills the cat. Until that time the cat is alive; after that it is dead. Authorfieldsofcolor (talk) 02:08, 27 November 2016 (UTC)
 * It looks like unsourced OR. Xxanthippe (talk) 02:55, 27 November 2016 (UTC).


 * There's no need to use the help me template on this talk page. I already commented on this proposal at your talk page; the paragraphs above cite Julian Schwinger's 1950s papers, so they're not entirely unsourced, but more recent references cannot hurt. I also can't quite understand why "provides a picture of reality at every moment, even when no one is looking" doesn't contradict "at some point that cannot be determined by the theory". If I put Schrödinger's cat in its box and start the mechanism, what does QFT say has happened to the cat one hour later? The theory should apparently "provide a picture of reality"; I'd read that as "the theory tells me whether the cat is alive or not". That, however, cannot be true; the theory cannot say with certainty whether I will find the cat alive or dead when I look into the box. The latter is acknowledged by the "cannot be determined by the theory" part. Now if the theory provides a picture of reality at every moment, even when no one is looking, what does that picture contain? By looking at the cat and finding it alive or dead I can determine whether the field quantum has deposited its energy into another quantum; the picture provided by the theory cannot contain that information. How does QFT deal with that issue? Doesn't looking at the cat refine my picture of reality in ways that QFT cannot supply? That seems to be highly relevant here. Huon (talk) 03:07, 27 November 2016 (UTC)
 * The Schwinger papers are notoriously difficult; they develop the techniques of non-diagrammatic QFT but do not discuss the measurement problem in any significant depth. Again, unsourced OR not suitable for the article. The talk page is being used to discuss the topic, not to improve the article. Wrong forum. Xxanthippe (talk) 03:25, 27 November 2016 (UTC).
 * I agree, Authorfieldsofcolor's wording does not belong in the article. The wording is sloppy and self-contradictory.  Also, even if the wording is supported by the Schwinger source (which I doubt), a single WP:primary source paper in a physics journal is not enough for inclusion in Wikipedia.  The content would have to be supported by secondary sources, like survey papers or textbooks by other authors, see WP:PSTS. -- Chetvorno TALK 07:39, 1 December 2016 (UTC)

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Recent revert: the stated "problem of definite (or well-defined) outcomes" resolved
I'd like to discuss a recently made (and reverted) [//en.wikipedia.org/w/index.php?title=Measurement_problem&type=revision&diff=824999203&oldid=822421025 addition to the article]: I do not think that Bell's work and the cited quantum optical experiments are resolving the problem posed here, namely "How are the probabilities converted into an actual, sharply well-defined outcome?" This is, i.e., the measurement problem in quantum physics is still considered unresolved by the majority of practitioners as far as I can tell (see, e.g., Steven Weinberg, Zurek, Fuchs etc. all long after the cited experiments): according to many-worlds there is never such a conversion since even the experimentalist looking into the box just gets entangled with the cat-nucleus superposition. According to Copenhagen, there is a "collapse" when the classical measurement device interacts with the quantum system, though it's not clear whether that is the Geiger counter, the toxic-gas bottle or the experimentalist looking in the box - or his friend talking to him later. The picture of "superposed correlations" advocated in the edit is what one gets from assuming that all systems can be treated quantumly (and it's essentially a "many-worlds" or "church-of-the-larger-Hilbert-space" view). However, unless one can do Bell experiments with the cat-nucleus entangled system I don't see that Bell's reasoning (and even a Bell test applied to an entangled cat) helps us to resolve the riddle. Maybe we should discuss the matter here before amending the article?--Qcomp (talk) 15:29, 12 February 2018 (UTC)
 * The talk page is a place for improving the article with reference to well-established sources, not for discussing the topic itself. Xxanthippe (talk) 21:42, 12 February 2018 (UTC).
 * agreed; I meant "discuss the matter of adding such a sweeping statement"; but given that the author seems not interested in discussing (and since even his main source just says "suggested resolution" in the title) I think this is moot and we can close this thread here.--Qcomp (talk) 23:15, 12 February 2018 (UTC)

QIT based approach
Another possible explanation to the measurement problem has been proposed motivated by considerations from QIT. It seems reasonable to me that this article may contain a brief passage reflecting those ideas. However, my edit, after providing more citations, was reverted again for reasons that a consensus should be sought first. Since no further arguments were given I am not sure what to argue at this point, aside from noting that the addition is quite obviously relevant to the topic of this article. So let me know what you think. — Preceding unsigned comment added by Robsedropse (talk • contribs) 13:59, 22 February 2018 (UTC)
 * how does that approach differ from the many worlds or decoherence approaches? In all three cases the system to be measured becomes entangled with the measurement apparatus and then this apparatus with the rest of the world (= "the system A'" in your approach, "the environment" in the decoherence approach). To me the approach you describe appears to be of the "church-of-the-larger-Hilbert-space"-type (i.e.: "everything, even the measurement apparatus and the observer evolve unitarily in a sufficiently large Hilbert space"). Instead of adding a 4th interpretation, I'd rather think we should merge MWI and decoherence, since they only differ in whether they talk about or discard the environment (whereas Copenhagen, De Broglie-Bohm, and spontaneous-collapse are truly distinct). --Qcomp (talk) 16:52, 22 February 2018 (UTC)
 * I agree with Qcomp about Robsedropse proposed addition; I don't see that this "explanation" is notable enough to include.  Whether it is or not, a single research paper, as a WP:primary source, is insufficient to support including it; Wikipedia requires secondary sources (WP:PSTS).  When this subject appears in textbooks or survey articles, we can revisit whether it should be mentioned here. ChetvornoTALK</i> 19:32, 22 February 2018 (UTC)
 * firstly, it's decidedly not my approach or idea; I came across it when researching something else. It's correct that the entanglement with the measurement device is shared with other interpretations. Despite describing a measurement also as a unitary process, the point is made that exactly no auxiliary measure such as MWI or decoherence interpretations would be required. I agree though that this is approach shows similarity with decoherence and I'd have no problem with adding it to that paragraph. I would say that decoherence alone is not enough to explain the measurement problem. At least the authors of the document I cited make a strict distinction in that they do not require a macroscopic absorbing system to come to a classical measurement outcome. I think their insight and fundamental difference is that entropy is conserved by balancing randomness with the negative entropy of the entanglement, which is a QIT consideration. Another difference to decoherence is that in their interpretation a measurement is, in principle, reversible.
 * Regarding the comment of Chetvorno, the paper I cited is not the only one (see for instance my second edit); however I am aware that this is a fairly recent idea, so indeed, we may have to wait for secondary sources as I am not aware of any at this point. Let's not forget however that we are talking about possible or potential interpretations in this section, and while I understand that the article should not be cluttered, this explanation caught my eye as an elegant and noteworthy one, again, as it does not seem to rely on a mind, a subject, a macroscopic system or many universes.Robsedropse (talk) 20:41, 22 February 2018 (UTC)

Copenhagen interpretation
I am reverting change eliminating statement that the C.I. is still probably the most popular interpretation of quantum theory. To help resolve issue, I am adding another more recent citation (a Nature news article) showing that as the date of this poll the C.I. was still the most widely held opinion about quantum theory. This does not mean that the C.I. is the consensus view. Opinions are widely split, but the C.I. is sort of the default view for those working in the field who don't what to get involved in what they probably consider a fruitless exercise in semantics.Polambda (talk) 21:35, 22 March 2019 (UTC)


 * A "probably" statement like appears to violate WP:WIKIVOICE. I would suggest restating it in a way that makes it clear that any information on the topic is extremely sketchy; the major variations between polls mean that no consistent conclusion can be drawn.  —Quondum 22:33, 22 March 2019 (UTC)


 * I wonder what you would get asking how many believed in Newtonian mechanics, special relativity, and general relativity? CI works well enough, often enough, as does Newtonian mechanics, and we mostly know when to use each one. Even more, the statement in question says probably.  How probable?  With probable the statement is pretty much always true, since there is some probability of it. I am for removing the statement, as it doesn't add much to the discussion. It may be the popular interpretation among college students, but not among working physicists, for example. Gah4 (talk) 23:17, 22 March 2019 (UTC)

Did anyone read the poll described in the footnote I added to this statement. The poll was not of college students but working physicists. It indicated that 42% of the physicists supported the C.I. This was the largest percentage of any group and consistent with a previous poll reported in Nature. This is obviously not a majority but a substantial plurality that has stayed quite stable over time. The truth is that with all the recent developments in quantum physics we are not much closer to understanding it. This hopefully will change in the future, but right now C.I. is still the paramount theory. I believe this statement is relevant and helpful in the article. The evidence that we have, although incomplete, clearly and consistently supports the fact that the C.I. is still the most popular theory. This tells the reader something important and I see no reason to remove it.Polambda (talk) 01:13, 23 March 2019 (UTC)


 * I did scan the polls (did you?), and had difficulty attaching the interpretation that you do. Do you understand WP:SYNTH and WP:WIKIVOICE?  Even if the statement were true, this is not reason to ignore these principles: as I suggested, a rephrasing is needed to change it to a voice of reporting what is published, not just making a statement, unless this is a consensus in the stated interpretation in secondary sources.  Can you point to where it says that "C.I. is probably still the most widely held interpretation of quantum mechanics"?  Do I have to point out that it is not "still" 2013, the year of all four of the references listed with the statement?  And do three polls with 42%, 11% and 4% support for CI "clearly and consistently supports the fact that the C.I. is still the most popular theory"?  Note that the fourth reference is based on the first of these polls, and also says "The tongue-in-cheek poll of 33 key thinkers on the fundamentals of quantum theory shows that opinions on some of the most profound questions in the field are fairly evenly split over several quite different answers."  This all seems to be at odds with your statement.  —Quondum 01:45, 23 March 2019 (UTC)

My we get heated about what should be a matter of dispassionate discussion. I quote directly from the Nature article: "Bohr, along with Werner Heisenberg, offered the first comprehensive interpretation of quantum theory in the 1920s: the so-called Copenhagen interpretation. This proposed that the physical world is unknowable and in some sense indeterminate, and the only meaningful reality is what we can access experimentally. As at the earlier Baltimore meeting, the Austrian poll found the Copenhagen interpretation to be favoured over others, but even so it was only held by 42% of the voters." Polambda (talk) 01:55, 23 March 2019 (UTC)

I did a quick scan online on this topic. A paper was published by Aarhus University about another poll in December 2016. "Even though quantum mechanics has existed for almost 100 years, questions concerning the foundation and interpretation of the theory still remain. These issues have gathered more attention in recent years, but does this mean that physicists are more aware of foundational issues concerning quantum mechanics? A survey was sent out to 1234 physicists affiliated to 8 different universities. 149 responded to the questions, which both concerned foundational issues related to quantum mechanics, specifically, as well as questions concerning interpretations of physical theories in general." The result 39% of the respondents supported the C.I. This is statistically the same result as the Nature reported poll.Polambda (talk) 02:10, 23 March 2019 (UTC)


 * Hoo-boy. I'm not interested in the results: they are not relevant to the content of the article other than perhaps as a bit of light humour; I guess I was hoping you'd see the ridiculousness of your logic. The principles of Wikipedia remain, which you seem to insist on ignoring.  —Quondum 02:40, 23 March 2019 (UTC)


 * A poll of 1234 physicists with only 149 responses is pretty suspect. There are ways to correct for response bias, but will likely remove any statistical significance. Note, for example, that 149 responses supporting CI, out of 1234, doesn't show a majority. In many physical science cases, WP:SYNTH doesn't apply, but I believe it does in cases like this. This is not WP:CALC. Gah4 (talk) 14:08, 26 March 2019 (UTC)


 * If I understand you, you are saying that there are times where WP:SYNTH does not apply because the conclusions are so widely accepted by the science community (e.g. the Moon orbits the Earth) that they can be stated in WP without a source, and I agree that this is not such a case. WP:SYNTH says: "Do not combine material from multiple sources to reach or imply a conclusion not explicitly stated by any of the sources."  I do see a conclusion "Yet, nearly 90 years after the theory’s development, there is still no consensus in the scientific community regarding the interpretation of the theory’s foundational building blocks."  —Quondum 16:15, 26 March 2019 (UTC)


 * WP:CALC works where it is only math. WP:SYNTH mostly applies for some social sciences where conclusions are less firm, but I suppose also for some less well understood physical sciences. I believe that there is a different one for widely accepted facts. Gah4 (talk) 01:39, 27 March 2019 (UTC)

I would remove all references to polls. Talking about polls misleads the reader into thinking the question can or should be resolved by taking a poll. The measurement problem is simply an open question and the subject of active research at the moment. What's wrong with that? Sometimes these things take a long time. The existence of atoms was controversial as recently as Einstein's Miracle Year. The atomic hypothesis wasn't resolved by taking a poll. Talk to <b style="color:#69793E">SageGreenRider</b> 22:37, 26 March 2019 (UTC)


 * The statement has to do with how many people believe something. I agreed with the removal of the statement previously. I don't see a good way to find out what people believe, other than asking. I suppose for the atomic hypothesis, it could be done by published writings. In the atomic case, you either do or do not believe it. CI is fuzzier. There is, at least, more than one alternative. Also, you might be able to agree with some parts of CI, and not others. (I don't know that you can do that, but I suspect so.) That makes it harder to make firm statements about what people think about CI. Gah4 (talk) 01:39, 27 March 2019 (UTC)
 * It comes down to WP:UNDUE weight. The article as it stands give undue weight to polls and how many people think what. I don't think such stuff is worthy of a place in a article about a open question in physics. Talk to <b style="color:#69793E">SageGreenRider</b> 16:27, 27 March 2019 (UTC)

The Copenhagen Interpretation is still called the "orthodox" interpretation of quantum physics by most practitioners. You can google Copenhagen interpretation and orthodox to substantiate this fact. It is called the orthodox interpretation because it was the explanation given by Niels Bohr and Werner Heisenberg, the founders of the discipline. That is the reality of the situation and the reason most physicists give it primacy of place. Does it satisfy everybody, no. The polls I cited show about 40% support. That is still far higher than any other interpretation. To deny the reality of these facts does a disservice to the readers of this article. Polambda (talk) 01:08, 29 March 2019 (UTC)
 * Maybe the article could just state the reservations mentioned above. We could say that in a poll of physicists no single interpretation was supported by a majority of physicists. The Copenhagen interpretation received the largest number of votes, 43%, but it should be kept in mind that this was the earliest interpretation, advanced by Bohr and Heisenberg, and for many years the "orthodox" interpretation, and widely mentioned in textbooks. --Chetvorno<i style="color: Purple;">TALK</i> 05:18, 29 March 2019 (UTC)

That sounds reasonable. Let me work on a modification that captures this in a readable way.Polambda (talk) 17:13, 29 March 2019 (UTC) How about something like: The Copenhagen interpretation is the interpretation of quantum mechanics originally put forth by Niels Bohr and Werner Heisenberg. Although at present no single interpretation is supported by a majority of physicists, it continues to receives the largest number of votes among rival theories in recent polls of physicists. For many years it was regarded as the "orthodox" interpretation and has been widely mentioned in textbooks.Polambda (talk) 19:22, 29 March 2019 (UTC)

Writing Confusion
GRW theory and objective-collapse theory are described separately in the article, but GRW theory is an example of objective-collapse theories along with the Penrose interpretation. This is written in a confusing way in the article. — Preceding unsigned comment added by 2601:500:4100:2FC0:F5E4:35BC:8941:3ED7 (talk) 05:07, 15 October 2019 (UTC)

Thank you!
I just wanted to say a big Thank You! to all of you who wrote this article. I think the Interpretations section is a well written, lucid summary of the current state of this confusing topic. This engineer learned some things reading it. It describes the main interpretation families in a neutral way while acknowledging the points of disagreement, and doesn't get bogged down including a bunch of fringe theories. It is really hard to get consensus on articles about this stuff; we all have our favorite interpretations, and since the differences are often not mathematical as much as philosophical, the wording becomes crucial, and edit wars can break out over parsing sentences. This represents a lot of work. Kudos! --Chetvorno<i style="color: Purple;">TALK</i> 18:42, 4 March 2024 (UTC)

Superdeterminism
I'm not an expert but I saw a convincing posting by Sabine Hossenfelder https://www.youtube.com/watch?v=hpkgPJo_z6Y that a potential solution to the measurement problem was to assume that Nature violates measurement independence (aka Superdeterminism ). So I was surprised that it isn't mentioned here. Should it be? Talk to <b style="color:#69793E">SageGreenRider</b> 21:08, 13 March 2024 (UTC)
 * I saw that too. It did sound convincing, but I'm not a physicist either.  I understand the idea goes back to John Bell in 1964; he acknowledged a "superdeterministic" correlation between the sources and detectors in Bell experiments could account for the violation of the Bell theorem, but he didn't think it likely.  I think the idea was revived by Hossenfelder and her collaborator Palmer, her paper is Hossenfelder, Palmer (May 2020) Rethinking Superdeterminism, Frontiers of Physics.  Recently there have been articles about it in scientific mags, Quanta, Feb 2017, New Scientist, May 2021, Sci. Am., March 2022  but I'm not sure how much support it has (yet).  This paper says it "has little support in the physics or philosophy communities".  We have an article on it: Superdeterminism.


 * My feeling is superdeterminism should not be mentioned in this article, unless it gets more popular. The "Interpretations" section only covers the major interpretations of quantum mechanics, the most well known proposed solutions to the measurement problem.  If we mentioned superdeterminism, for WP:due weight we'd also have to mention a lot of similarly speculative interpretations: the ensemble interpretation,  consistent histories,  quantum logic, Von Neumann–Wigner interpretation, transactional interpretation, QBism, modal interpretations, etc. and the section would be a mess --Chetvorno<i style="color: Purple;">TALK</i> 01:51, 14 March 2024 (UTC)
 * I am a physicist. Superdeterminism is about as popular among physicists as flat Earth theory. It's hardly ever mentioned in the literature, and when it is, it is dismissed as a non-starter, as the quotes in Superdeterminism show. So no, we shouldn't mention it here before it becomes popular among physicists. Which will never happen. Tercer (talk) Tercer (talk) 12:10, 14 March 2024 (UTC)
 * Thanks. Yes, it seems like one of those theories that catches attention in the popular science press, giving it the appearance of more support than it actually has. --Chetvorno<i style="color: Purple;">TALK</i> 17:21, 14 March 2024 (UTC)
 * OK. BTW Sean Carroll (who favors many worlds interpretation) doesn't completely dismiss it in his book Something deeply Hidden Quote: "This [prearrangment] seems unpalatable... but some smart people are pursuing the idea." Carroll and Hossenfelder seem to have mutual respect; she wrote a nice blurb for Carroll's book The Big Picture. The Big Picture has a lot about the Laplace's Demon idea and it seems to me that Laplace's Demon idea is quite similar to superdeterminism, but what do I know. Let's see. If it does become popular, you owe me a beer, @tercer ;-) Talk to <b style="color:#69793E">SageGreenRider</b> 18:47, 15 March 2024 (UTC)
 * Laplace's demon is just regular determinism, it has nothing to do with superdeterminism. Usually people who think superdeterminism is even slightly appealing haven't understood how insane it is. Forget a beer, I'll buy you a whole brewery if superdeterminism ever becomes anything other than a fringe idea. Tercer (talk) 20:29, 15 March 2024 (UTC)