Talk:Copenhagen interpretation/Archive 2

Lead's "does not yield a description of an objective reality"
The second sentence of the lead tells us that the Copenhagen interpretation "holds that quantum mechanics does not yield a description of an objective reality".

The exercise of the word objective here is misleading and inappropriate for a Wikipedia lead sentence because it is not an ordinary-language usage of the word. It is not made apparent by the sentence that the word objective is being used in a special or peculiar sense preferred by Niels Bohr.

An ordinary-language description of a physical or natural thing implicitly admits or presupposes that that description refers to observable aspects of that thing. In ordinary language, one does not intend to describe unobservable natural things, unless one explicitly announces so. The sentence does not announce so. In ordinary scientific language, an objective description is one that is independent of the subjective variations that different observers might give their respective descriptions. It does not mean that it is independent of any means of observation. That the thing is observable is taken to intend that some means of observation is exercised. That the exercise is said to be objective intends that it does not depend on who does it. If it is inevitable that the means of observation affects the result of observation, the result of the observation is objective if it does not depend on the subjective contribution of the observer, even though the means of observation affects the result.

But Niels Bohr, being an auto-didact and self-appointed metaphysician to overrule all others, does not see it like that. He sees it that if the result depends on the means of observation, then it is not objective. He does not employ the ordinary-language use of the word objective. He intends that the description is not objective merely if it depends on the means of observation, regardless of who is exercising it. He is not making a metaphysical distinction between the means of observation and the observer. Of course he thinks he is very clever to elide this distinction. No, he isn't. Words such as subjective and objective are not freely available as playthings for auto-didacts. The lead sentence is using the word objective in Niels Bohr's peculiar sense, not the ordinary-language sense, without indication of the peculiarity of its language usage. This is not right for a Wikipedia lead sentence.Chjoaygame (talk) 22:50, 1 November 2014 (UTC)

undid good faith edits; need to follow protocol
I undid two good faith edits. They were of doubtful or unstated source. They did not follow the customary protocol. Edits should be sourced and follow protocol.

The edit about 50% was in brackets. It was not clear whether it was reporting details from the cited source, or whether it came from somewhere else. In general, if a thing is worth a place in the article, it is worth an unbracketed place.

The edit about the cat was in the form of a footnote labelled as a "reference". Footnotes are mostly to be avoided. If it is worth saying, it is worth saying in the body of the text. The edit was chatty and no reliable source was cited for it. Editorial chatter without reference to reliable source is contrary to Wikipedia policy. Reliable sourcing is mainly from preferably several established textbooks, perhaps supplemented by articles, from respected journals, that have been cited with approval a number of times by other respected journal articles or established textbooks.

You could try again, following protocol and citing reliable sources.Chjoaygame (talk) 07:55, 16 November 2014 (UTC)


 * The original text with the "Copenhagen solution" ("The wave function reflects our knowledge of the system" ... "means that once the cat is observed") cited no sources just as well. Therefore it should be removed. But OK, the problem is not so significant here. 178.42.112.207 (talk) 21:21, 16 November 2014 (UTC)


 * Yes, the previous text was also sub-standard. That is a reason to delete it, as you suggest, or replace it with good text, reliably sourced, not to add more sub-standard material. There is plenty to do to improve this article.


 * As for your improvement of the 50% thing, it is a step in the right direction. But still tendentious, because it says, unsourced, "as is often the case". Wikipedia should be neutral, not tendentious.


 * Papers in arxiv are very borderline as sources. Strictly they do not have status as reliable sources. If sourcing is only from arxiv, it is on thin ice, or worse. Many editors try to hide from this, but they don't do Wikipedia a service thereby. Reliable verifiability is perhaps the key Wikipedia policy. Wikipedia is not intended to rival Google.


 * I feel uncomfortable talking with you as an IP address. Many regular editors give themselves an account name to make it easier to communicate with them. I think there is no security risk in doing so. Certainly there is an advantage in doing so, to make conversation easier to follow.Chjoaygame (talk) 22:44, 16 November 2014 (UTC)

edit summary for undoing of an edit that linked to Occasionalism
For this undo, the edit summary reads "No, it is not part of the Copenhagen interpretation that all events are taken to be caused directly by the divine."

For obvious reasons I am not simply undoing that undo, but I am here saying that it was not good enough that it was not accompanied by a proper talk page explanation. Moreover, I am saying that it is reasonably defensible or well-arguable that it was a wrong undo.

Albert Einstein is well known to have said and thought that the Copenhagen interpretation was a religion. Moreover, the article to which the undone edit linked, Occasionalism, has as the second sentence of its lead, "(A related theory, which has been called "occasional causation", also denies a link of efficient causation between mundane events, but may differ as to the identity of the true cause that replaces them.)"

There are plenty of reliable sources that more or less agree with Einstein and that parenthesis. The link was a see also. It it reasonable to allege that the Copenhagen interpretation is a religious or philosophical doctrine. It is not proper Wikipedia neutrality to censor out that allegation. It may be appropriate to present argument against the allegation, but simple censorship is contrary to Wikipedia policy. One may agree with a vast number of physicists, in the opinion that Einstein after 1927 was a doddery old fool, but as a Wikipedia editor one must accept that it is no more than a notable opinion or point of view. Rosenfeld says that Einstein's name on the EPR paper made it "a bolt from the blue" to Bohr. Bohr is said to have had a horseshoe by the front door of his country house, and when challenged that he shouldn't believe in such things, to have replied that he didn't believe in them, but that the horseshoe worked even if one didn't believe in it.

I think the undone see also link should be restored.Chjoaygame (talk) 01:23, 21 January 2015 (UTC)
 * An entertaining but nonsensical argument when applied to a hard science page in an encyclopedia. Why not cite Lao Tze or Confucius, both of whom made comments which could conceivably be construed as connected to particle physics? The difficulty, Chjoaygame, is as comedian Steven Wright said: "You can't have everything. Where would you put it?" If every Wikipedia editor's personal philosophical hobbyhorse has to be linked to every Quantum Physics page, it dilutes the value of the factual content in favor of random babbling. JacquesDelaguerre (talk) 06:37, 21 January 2015 (UTC)


 * You have not offered an argument that calls for a reply.Chjoaygame (talk) 07:18, 21 January 2015 (UTC)
 * You have offered a fanciful explanation for why a page about superstition should be linked from a hard science page. No argument is needed. Feel free to edit philosophy and religion pages, but please don't "improve" the science pages with nonsensical material. JacquesDelaguerre (talk) 15:59, 21 January 2015 (UTC)


 * It takes quite a stretch of the imagination to find the relevance in the linked page. I see there is a mention of an author who describes a similarity between occasionalism and the Copenhagen interpretation, though the parallel there is between a god and an observer, so the metaphor seems confused. If one allowed speculative links like this, as JacquesDelaguerre implies, the 'see also' section would be longer than the article. Besides, the main thrust of occasionalism appears to be to ascribe a godlike will behind the course of events, which appears to be directly contrary to the Copenhagen interpretation. The Copenhagen interpretation says absolutely nothing about the causation of any particular observation being selected, only about probabilities. I agree with the removal of the link. —Quondum 17:25, 21 January 2015 (UTC)

physical interpretation
A new edit writes "The Copenhagen interpretation is a loosely-knit informal collection of axioms or doctrines that attempt to express in quotidian language the mathematical formalism of quantum mechanics."

I think that the Copenhagenist interpretations are not so much aimed at producing quotidian language, as they are aimed at matching the mathematical formalism with physical meaning.
 * I don't know two quantum physicists prominent in the field who agree on the physical meaning! :) JacquesDelaguerre (talk) 21:28, 12 February 2015 (UTC)


 * I guess you are right about that.Chjoaygame (talk) 01:58, 13 February 2015 (UTC)

It is true that, for this purpose, Copenhagenism demands the use of ordinary language; for example Bohr writes "Here, it must above all be recognized that, however far quantum effects transcend the scope of classical physical analysis, the account of the experimental arrangement and the record of experimental observations must always be expressed in common language supplemented with the terminology of classical physics."

The language, however, is just the vehicle for the interpretive task, which is to express the physical meaning of the mathematical formalism. For example, non-commutativity of operators is a simple mathematical fact. The interpretative question is what does that mathematical fact mean in physical terms? The call for supplementation by the terminology of classical physics signals a call for physical interpretation, beyond only quotidian language. In ordinary language, non-commutativity means that 'multiplication' depends on the sequential order of the 'factors'. This is not yet a physical meaning. The non-commutativity has the physical meaning that no laboratory apparatus can bring about physical coexistence of the respective physical states represented by the non-commutative operators.Chjoaygame (talk) 13:35, 12 February 2015 (UTC)

Key is that the account of the apparatus not use quantum theoretical ideas or language. It's a specific kind of arcane language that is to be avoided, namely quantum mechanical language. This is well explained by Günter Ludwig. I would like to emphasize the positive duty of interpretation: to tell how to build apparatus that embodies given items of the mathematical formalism, and how to find the mathematical formalism to describe given apparatus. The fellows in the workshop making the apparatus know nothing of quantum mechanics, and should positively avoid learning its concepts, as a matter of principle. They speak ordinary language laced with classical physical ideas.Chjoaygame (talk) 18:08, 12 February 2015 (UTC)
 * I do not disagree with much of what you have said, merely asserting that the revised text is a little better than what stood there before. Along the lines of the CI itself, let's strive to keep the article reasonably intelligible to the layman ... so if you can improve the intro without making it longer, go ahead! JacquesDelaguerre (talk) 21:26, 12 February 2015 (UTC)


 * You are right that we should strive to keep the article reasonably intelligible to the layman. All three, Bohr, Heisenberg, and Born, explicitly said that the quantum postulate has big philosophical implications, perhaps more or less unrecognised by professional philosophers.Chjoaygame (talk) 02:31, 13 February 2015 (UTC)

fact not perception
A new edit writes "The fundamental axiom of the Copenhagen interpretation is the "postulate of the quantum", that subatomic events are only perceptible as indeterministic physically discontinuous transitions between discrete stationary states."

I think that Copenhagenism intends much more than how things are perceived. I think Copenhagenism refers to how things happen. For example, Bohr writes of "the discontinuous exchange of energy between atoms required by the quantum postulate." Born writes "Every process consists of elementary processes, which we are accustomed to call transitions or jumps". Born and Heisenberg report "a (spontaneous) change of state consists, also in the continuous spectrum, in a “jump” of the system from a point W′ to another W′′ ".

I think these people are talking about fact, not perception.Chjoaygame (talk) 15:15, 12 February 2015 (UTC)
 * Interesting point. I was trying specifically in that edit to avoid the mistake of confusing our perception (through our instruments and measurements) of the "quantum universe" with any existential reality, which is it seems, precisely what Bohr was saying when he suggested to Einstein that "we may have reached the limits of the usefulness of visualization". QM doesn't tell us what's happening, what it looks like, what it smells like "down there" in Subatomia :) It gives us a schematic mathematical tool for a limited description, which doesn't begin to meet up with anything tangible to the human organism until about the point of angular bonds in chemistry. So I used the word "perception" which, to judge from your comment, may be too loaded a term for this article. I will not be offended if you improve my prose which, I firmly believe, was an improvement on the previous somewhat tangled introduction which I found yesterday on this page. Thank you for your comment! JacquesDelaguerre (talk) 17:02, 12 February 2015 (UTC)


 * Thinking a little more about this. Copenhagenism recognizes three elements in a report of an atomic phenomenon. (1) the atomic object itself. This is mostly imperceptible to naked sensation, and is even an inference rather than an ordinary macroscopic physical object. That doesn't make it unreal or unfactual or entirely imperceptible or merely a subjective interpretation. It is perfectly real, though perhaps not too easy to describe, or even may be unvisualisable. (2) the apparatus that prepares and detects the atomic object. This is an arrangement of ordinary perceptible, enduring, and real physical objects. (3) the many members of the laboratory team who read and re-read and check and discuss and agree about the instrumental record of the phenomenon. There can be agreement about the results because they are easily perceptible, because of the design of the apparatus. No subjectivity remains here if the laboratory team is working well. I think Wigner missed this point. It is true that there is room for interpretive difference about where there boundary is drawn between (1) and (2), but that is neither mysterious nor essentially subjective: one can report on it in a perfectly objective way.Chjoaygame (talk) 19:45, 20 February 2015 (UTC)


 * Léon Rosenfeld writes


 * "... It is essential to realize that any observation involves a sharp separation of the nondescript flow of events into two parts: the observer and the observed system. It is by performing—or rather imagining—this cut, that the observer takes up a “detached” position which enables him to speak of the observed system “objectively”, i.e. in the same way as any other observer taking his place. Cuts of this kind can be made in many ways—one may look at the same thing from many points of view—but the concepts framed to state the results of the observations are related to the standpoint of the observer in such a way that it is always possible to pass from any one standpoint to any other, full objectivity is thereby ensured. In physics, where we confine ourselves to the aspects of experience from which all manifestation of life is excluded, the only part of the “observer” that enters into the picture is itself a physical system, an apparatus which records signals or permanent marks left in it by the observed system, and which any real observer (or sufficiently complex “brain”) can examine and “read” at leisure whenever he wishes."


 * Rosenfeld, L. (1967). Niels Bohr in the thirties: consolidation and extension of the conception of complementarity, pp. 114–136 of Rosental, S. (1967).
 * Rosental, S. editor (1967). Niels Bohr. His life and work as seen by his friends and colleagues, North-Holland, Amsterdam.Chjoaygame (talk) 08:37, 21 February 2015 (UTC)

language
The lead currently starts with this sentence: "The Copenhagen interpretation is a loosely-knit informal collection of axioms or doctrines that attempt to express in everyday language the mathematical formalism of quantum mechanics."

The problem here is not whether to use the words 'quotidian' or 'everyday'. The problem here is that the sentence is not focused on what needs to be said. The interpretation is an expression of a match between mathematical formalism and physical meaning. The concept of physical meaning is not explicitly mentioned in the sentence. It is nearly trivially true that the expression is to be in ordinary language supplemented with the concepts of classical physics. But the attempt is at expressing a match between mathematical formalism and physical meaning, not at putting mathematics into ordinary language.Chjoaygame (talk) 15:45, 22 February 2015 (UTC)

Heisenberg writes about the early days when the Copenhagen spirit was being developed:

"... But I noticed that mathematical clarity had in itself no virtue for Bohr. He feared that the formal mathematical structure would obscure the physical core of the problem, and in any case, he was convinced that a complete physical explanation should absolutely precede the mathematical formulation."


 * Heisenberg, W. (1967). Quantum theory and its interpretation, pp. 94–108 in Rozental, S. (1967).
 * Rosental, S. editor (1967). Niels Bohr. His life and work as seen by his friends and colleagues, North-Holland, Amsterdam.Chjoaygame (talk) 17:03, 22 February 2015 (UTC)

Typo or unusual language
"10.In the present state of physical knowledge, the intestinal workings of atomic and subatomic processes are not open to visualization in ordinary space-time or causal pictures.". Intestinal is probably an autocorrect, but not being knowledgeable in the field, I just wanted to make sure that word isn't one of those imaginative uses of language that physicists are given to. David Brooks (talk) 17:50, 20 February 2015 (UTC)


 * The word 'intestinal' here is neither a typo nor an autocorrect. It is an echo of the use of the word by Antoine Lavoisier and Pierre-Simon Laplace in their classic Mémoire sur la chaleur (Mémoires de l'Académie des sciences (1780), pp. 355–408) on their caloric theory, used also more recently with the same meaning by Clifford Truesdell. The reason for the use here is rhetorical, to bring the reader to pause and reflect on the essential inaccessibility to direct observation of the mechanisms of atomic and subatomic processes. True, it has a colourful or slightly eccentric or obsolete or as you say imaginative feeling about it, and is not the most routine language. Perhaps there is some reason why Wikipedia should avoid such scientific literary allusion or such oddity. If you feel so, I will not object to replacing it by some less colourful word such as for example 'inner'.Chjoaygame (talk) 19:17, 20 February 2015 (UTC)


 * I like it. See comment below. ~ J. Johnson (JJ) (talk) 20:48, 10 March 2015 (UTC)

"the intestine workings of atomic and subatomic processes"?
I'm curious about the use of the word "intestine" here. My edit was reverted (with the edit comment: reverted to classical physical terminology, this is not purple prose; see Lavoisier and Laplace, Truesdell). Since these names are not mentioned in the article, and my Googling seems to turn up only biology-related books, could I have a pointer to an example of this use in a physics text? —Quondum 00:08, 10 March 2015 (UTC)


 * I have above on this page cited the use of the word by Lavoisier and Laplace in their classic work on their caloric theory. Also I have pointed to its use by a respected recent author, Clifford Truesdell. Right here I don't have hard copies of those sources, which I previously borrowed from the library. But now I Google it at your request. I find as follows.


 * I find I was problably working from the original French. I find also on the internet an English translation that uses the more colourless English word 'internal', so in English I have only the example of Truesdell, who is a fine writer of English and a reliable source on thermodynamics. He uses the word seven times in his The Tragicomical History of Thermodynamics 1822–1854 (1980), Springer, New York, ISBN 0387904034. The word is an ordinary word of the English language (see OED), and Wikipedia uses ordinary language. I don't think Wikipedia has a rule that one must use the most colourless word, as long as one represents the meaning of the source accurately. So I think it reasonable to use the word 'intestine' here for the present purpose.Chjoaygame (talk) 01:34, 10 March 2015 (UTC)Chjoaygame (talk) 07:17, 10 March 2015 (UTC)


 * Remember your audience... you are writing this article in order to inform the general public. As a member of the general public, I can tell you that I found the sentence in question uninformative and confusing.  I have no idea what is meant by the word "intestine" in the sentence.  From the context, I assume it is not referring to a body part, but I don't know what it is supposed to mean.  Please use some other word. Blueboar (talk) 16:22, 10 March 2015 (UTC)
 * I would echo User:blueboar's comment. While WP:COMMONNAME is aimed at article titles, WP:COMMONSENSE might allow that we aim it at article content as well, where appropriate. English is a language that lives and changes: a metaphor which makes sense to an Englishman of the Victorian age may not do so to a modern international speaker of the language. Or, perhaps we should all start using the Old English Thorn character þ or Y in place of "th", as in the much-loved "Ye" spelling of "The". After all, it is more colourful.... &mdash; Cheers, Steelpillow (Talk) 19:01, 10 March 2015 (UTC)
 * I would like to add WP:TONE. Wikipedia should be written in an encyclopedic, businesslike tone.  We should write for our audience and our audience comes here prepared to digest plain, modern English. Darkfrog24 (talk) 19:55, 10 March 2015 (UTC)


 * Why should Wikipedia prose be reduced to uniform grey cardboard suitable for eighth-graders? Good writing should occasionally titillate and even tease with colorful usages many readers might find novel; it should not be boring. After all, the goal of any encyclopedia is not merely to inform, but also to educate, and that often means pulling people out of their ruts of ordinary familiarity.   And if "intestine workings " is the actual word a source uses, then a direct quote absolutely must use the same word (no alteraions of a source!).  For indirect quotes and translations, yes, there could be a queston of proper representation. If the usage is not ordinary enough just insert an explanation: "the intestine [internal] workings ...." ~ J. Johnson (JJ) (talk) 20:49, 10 March 2015 (UTC)
 * Colour can harmonise but colours can also clash. The occurrence in the article was not a direct quote, nor was it even grammatical - the correct form would be "intestinal workings". The phrase "internal workings" would be suitably cardboard paraphrase, but in the modern understanding the term "workings" is not particularly useful since it implies a systemic causal dynamic≠ which we nowadays suspect to be incorrect. Personally I'd go for somthing like "inner reality" which, like listening to the radio, lets the consumer imagine their own picture - and, as has been said, "I prefer listening to the radio rather than watching TV, the pictures are better." But I'd rather have cardbaord I understood than the clash of colours that "intestine" provided. &mdash; Cheers, Steelpillow (Talk) 21:48, 10 March 2015 (UTC)
 * According to the Oxford English Dictionary, since 1664, English usage in this context, as an adjective, is 'intestine'.Chjoaygame (talk) 13:34, 11 March 2015 (UTC)
 * I am not an eighth-grader, J. Johnson. I hold two degrees, and I would have assumed that "intestine" was vandalism or added by someone with limited understanding of English before I supposed it was an instance of the archaic meaning.  As to why Wikipedia should be uniform and plain, the answer is because it is an encyclopedia.  People come to tertiary sources for straightforward text.  They can go to articles, newspapers and books for more colorful styles of writing.
 * If you want to add some color, feel free to look for a direct quote from Lavoisier that would fit well with the rest of the article. "...intestine [internal]..." would be appropriate in that case. Darkfrog24 (talk) 22:45, 10 March 2015 (UTC)
 * Nor have I implied otherwise. What I was referring to was the level of competence of the "average reader" some editors think we should cater to. Which I have been told is at the eight-grade level. (Tenth-grade, apparently, in the U.K.) ~ J. Johnson (JJ) (talk) 00:32, 11 March 2015 (UTC)


 * I agree with Blueboar's comment of 16:22, 10 March 2015. Use a word readers will understand, please, rather than one that looks like vandalism. -sche (talk) 18:36, 11 March 2015 (UTC)

the word 'locality'
With reference to this present article, the word 'locality' is currently under discussion at Talk:Interpretations of quantum mechanics. A few notes about it might be useful here, since the present article is perhaps not quite explicit on that word. I think the word in the present context is largely an invention of later scholars, not part of the original Copenhagen language. Thus it may be problematical to discuss whether Copenhagenism is "localist" or not.Chjoaygame (talk) 00:43, 10 March 2015 (UTC)Chjoaygame (talk) 01:41, 10 March 2015 (UTC)

Bell 1964
The Introduction reads


 * "THE paradox of Einstein, Podolsky and Rosen [1] was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality [2]. In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics. It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty."Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

Wigner 1976
In lectures quoted by , Eugene Wigner says


 * "The preceding argument shows that any theory of hidden variables conforming with the postulate of locality is in conflict with quantum mechanics."Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

Howard 2007
Howard writes


 * "In brief, separability asserts the existence of independent real states of affairs in spatially separated regions, and locality asserts that the real state of affairs in one region of space cannot be affected super-luminally by events in another region. Locality is entailed not only by relativistic locality constraints but also by the requirement that theories be testable, for were locality not to obtain then there would be no principled way to distinguish the falsity of theory’s prediction about the outcome of a measurement from the effects of stray extraneous influences from afar. Separability is defended as a well-nigh necessary, a priori condition for the possibility of the objective individuation of physical systems (more on this below)."Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

Weihs et al. 1998
These authors write in their introduction


 * "The assumption of locality in the derivation of Bell’s theorem requires that the individual measurement processes of the two observers are spacelike separated."Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

De Muynck 1986
De Muynck writes


 * "From the following, however, it should be clear that the mere existence of hidden variables is sufficient to yield the Bell inequalities. Hence not only local but also nonlocal hidden variables theories are incompatible with quantum mechanics. Local and nonlocal theories being on an equal footing it also follows that the Bell inequalities are completely irrelevant to the problem of (non)-locality in hidden variables theories."Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

Tommasini 2002
Tommasini writes


 * "In fact, any kind of “nonlocality” or instantaneous “distant influence” is unacceptable in a relativistic world: due to the relativity of the simultaneity, suitable observers would describe this influence (whatever it is) as an effect of the future on the past [18]. Fortunately for science, there is a way to completely reconcile the quantum theory with locality, causality and special relativity. This solution is quite natural and is based merely on known physics."Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

Bohr and Heisenberg
I did not find convincing evidence that either Bohr or Heisenberg habitually used the term 'locality' in the present sense. This looks to me like an argument that it is not useful to try to say whether Copenhagenism is or is not 'localist'.Chjoaygame (talk) 00:43, 10 March 2015 (UTC)

Comments
It is generally accepted that the quantum mechanical formalism uses a state description of which the domain is configuration space, not ordinary physical space-time. In this sense, one might propose that quantum mechanics is "non-local". On the other hand, 'non-locality' is sometimes interpreted or intended to mean 'in violation of the rule against spooky actions at a distance'. Some people then try to make out that quantum mechanics essentially entails spooky actions at a distance. Indeed there is a vast industry busy at this, with research money flowing. Others argue that the quantum mechanical formalism does not refer to or deny action at a distance, but simply does not explicitly trace space-time linkages, though the term 'locality' is not used. I think Bohr and Heisenberg were of this view. Whether you like to say they believed in locality is up to you, a matter of opinion, I would say. Wikipedia should avoid seeming to commit itself on the semantical question of whether or not Copenhagenism is "localist".Chjoaygame (talk) 00:43, 10 March 2015 (UTC)


 * My tentative opinion is that where Copenhagen is distinguished from the von Neumann interpretation, Copenhagen should be considered local. Bohr et al seemed to be denying that EPR proves nonlocality. Some people do accuse Copenhagen of nonlocality, but it appears that they are really accusing the von Neumann interpretation of that. Roger (talk) 03:00, 10 March 2015 (UTC)


 * Hairsplitting specialist debates over nuances of local realism form the least valuable and most tedious content of an historical article intended for general readership. The article should speak conservatively and sparsely on the subject. JacquesDelaguerre (talk) 05:05, 10 March 2015 (UTC)


 * Yes, but that is also a cop-out. The reader looks up these interpretations in Wikipedia, and wants to know which are local, and which are non-local, as well as which have various other properties. It is bad enough that articles about quantum mechanics give conflicting views of what it is about. We ought to give an answer for a particular interpretation. If the reliable source disagree, then we ought to say that. Roger (talk) 05:16, 10 March 2015 (UTC)


 * So do you propose to pull some answer out of the hat, just so as to avoid a "cop-out"? We have to have a coherent definition of locality. And it seems that claims of the Copenhagen interpretation being local will be hotly debated. From Principle of locality § Copenhagen interpretation:  'This "vanishing" is postulated to be a real physical process, and clearly non-local (i.e., faster than light) if the wavefunction is considered physically real and the probability density has converged to zero at arbitrarily far distances during the finite time required for the measurement process.'  Does this sound like support for locality? —Quondum 06:13, 10 March 2015 (UTC)


 * That sentence refers to some non-Copenhagen interpretations. I would say that section supports Copenhagen being local. Roger (talk) 06:42, 10 March 2015 (UTC)

Locality can (in one particular sense) be expressed as a requirement on the Lagrangian (in that formalism, which allows for encompassing far-reaching applications of QM). The field or its derivatives Lagrangian density at a point in configuration space should not depend on the values of the fields or the derivatives at other points at the same time (edit: or at any time). (This is not the same as saying the solution of field equations may not depend on the fields at other points taken at times in the past.) I think this conforms with the CI and that CI is local in this sense. It still allows for quantum entanglement as far as I know, which is perhaps spooky but not action at a distance. Non-local theories (in this precise sense) have not been found to work. Either they break Lorentz invariance or they break the unitarity of the S-matrix (non-conservation of probability). YohanN7 (talk) 13:42, 10 March 2015 (UTC)

There is a classical 1933 paper (which I haven't had the pleasure of reading yet) by Bohr and Rosenfeld that might be worth looking up. It deals with causality, expressed as commutation relations vanishing for spacelike distances in QFT. It is not exactly the same thing as non-locality of course, but clearly related if you want to know what Bohr actually had in mind regarding locality/non-locality. YohanN7 (talk) 14:16, 10 March 2015 (UTC)
 * The constant danger on Wikipedia is that of the editor informing the reader of more than the editor actually knows. Let's be modest here and not belabor the most obscure aspects that stumped Einstein and Bohr. It's enough to say that the Copenhagen Interp holds that local reality can't be established by the mathematics of quantum mechanics. That's probably more than enough for the reader and more than most of the working physicists on the planet can prove :) JacquesDelaguerre (talk) — Preceding undated comment added 21:07, 10 March 2015 (UTC)
 * It is enough to say what? Please clarify and prove that statement. There is enough whimsical ramblings due to undefined terminology that could mean anything in this article already. YohanN7 (talk) 08:54, 11 March 2015 (UTC)
 * The point of the article is to help the reader grasp the very basics, however tenuously, not to prove our own erudition. Trying to shovel every nuance we collectively have ever heard of into the article is not an exercise in editorship, it's a manifestation of egotism or of obsessive compulsive disorder. The greatest service to the readership that any editor could perform would be to shorten the article by about 2/3. I'm tempted to wade in with a machete but I hate to listen to grown men cry :) JacquesDelaguerre (talk) 05:26, 12 March 2015 (UTC)
 * .... I see I didn't answer one of your questions, YohanN7 .. The meat of the Cop. Interp. is that local realism is not reconcilable by means available to quantum mechanics. That has metastasized in the intervening decades to become a dogma in certain circles that local realism is existentially excluded, "beyond here there be dragons" as it were. But it's pretty much the entire point of Copenhagen that QM doesn't provide any answer of that sort. JacquesDelaguerre (talk) 05:33, 12 March 2015 (UTC)
 * What I am reacting against is that the CI refuses to talk about physics in the language of physics (which is mathematics). I can accept that. But then if, in addition, it is insisted upon that terminology remains mathematically undefined, then the whole thing is useless. It is worth than useless. I do not know what the CI says about things such as locality, but I'd like to know. You make a point of it not being clear. Not impressive. YohanN7 (talk) 10:44, 12 March 2015 (UTC)
 * We're essentially documenting history. Modern physics doesn't lean on the CI, preferring (somewhat rigidly) to avoid the existential issues and focus on the immense accumulated store of mathematical and physical research (jokingly called in the field "Shut up and calculate!"). Our task here is to document what the (long-dead) authors said, to edify and arouse the curiosity of the student, and to relate the CI to modern physics. We should resist the urge to parade our knowledge or debate minutiae, which obscures the conciseness and readability of the article. It's really quite good and needs only some trimming. Anyway, that's how I feel about it, YohanN7, thank you for engaging in discussion. JacquesDelaguerre (talk) 15:48, 12 March 2015 (UTC)
 * The way you put it, the CI wouldn't even pass as a subject in the History of science. I bet that Bohr is turning in his grave. He was a scientist, not an old fool as he is portrayed as in this article. (our task is, ..., to edify and arouse the curiosity of the student ... LOL, your task dude is to report on what the CI is, no more, no less. Not to win first prize in a poetry competition.) YohanN7 (talk) 17:54, 12 March 2015 (UTC)


 * "... an old fool as he is portrayed as in this article". I am not sure where that comes from. I think the article doesn't intend so. It is widely acknowledged that Bohr is very hard to understand. That does not make him an old fool. The most up-to-date and helpful author on this subject is perhaps Mara Beller. See also the books by Folse, and by Murdoch, and articles by Don Howard. Bohr felt that his insights into quantum physics were unduly or inappropriately ignored by the usual philosophical crowd. I think it fair to say that, though he wrote a lot for a long time, he did not quote standard philosophers as much as did Heisenberg. His philosophical status is not easy to specify. It is widely thought that Bohr played a big part in creating "the Copenhagen interpretation" but perhaps not widely agreed as to exactly and uniquely what that is, and how far it goes into philosophy.Chjoaygame (talk) 01:01, 25 March 2015 (UTC)

Principle 5
As stated, principle 5 is just wrong. There is also the possibility that the undefined terms (e.g. pure case, incompatible) have a completely different meaning than I read them to have (i.e. eigenstates, non-commuting).

The story in actuality is that the involved operators have a complete set of eigenfunctions. Any state can be expressed in terms of eigenfunctions of any operator endowed with a complete set of eigenfunctions. Any two states can be added mathematically. Whether this does or does not correspond to a physically realizable state is another issue, see superselection rule. YohanN7 (talk) 12:28, 25 March 2015 (UTC)

It has come into question in modern times whether incompatible conjugate properties can indeed never be defined for the same time and place.
Now, that is quite a statement. (What they ALL believed for close to 100 years is WRONG.) It is not supported by a reliable source. This article has enough bullshit that is going to confuse the beginner. Do you really want to add to the mess statements of this sort? YohanN7 (talk) 12:06, 24 March 2015 (UTC)
 * There's a difference between citing a dissident opinion and believing that opinion. I myself don't agree with the tacit implications of the physicsworld.com piece, but the section of the Copenhagen interpretation article we are discussing is about objections to the Copenhagen interpretation. The physicsworld.com article is representative of an entire class of objections, whether well-founded or not. It's just an example. JacquesDelaguerre (talk) 12:11, 24 March 2015 (UTC)
 * I do understand your point, and even agree with it to some extent. Please then find a good source for the disputed sentence. A dot-com thingie from 2015 simply isn't enough because the disputed sentence does question all of QM, not only the CI. The HUP is a mathematical fact (something far beyond the "ordinary language" bullshit presented in the present article) following from how reality is modeled in QM. If this is wrong, then the whole model for QM is wrong and QM is wrong. YohanN7 (talk) 12:27, 24 March 2015 (UTC)
 * Here's an interesting summary of the controversy, which seems to be resolving in favor of Heisenberg's original thesis. JacquesDelaguerre (talk) 12:42, 24 March 2015 (UTC)
 * I agree, it is interesting. While Nature (magazine) is perfectly acceptable as a reference, I'd still like to know how wide-spread this controversy is. It is also of some importance if Nature (not the magazine, mother Nature) is undecided, and, if so, how much, or whether all uncertainty is about our ability to measure things. As long as we aren't clear on these issues ("can indeed be defined" is ordinary-language-mumbo-jumbo), it is best to say nothing. YohanN7 (talk) 13:48, 24 March 2015 (UTC)
 * I would agree if one's purpose is purely scholarly and instructional but here we are trying to summarize the entire scope of an historical scientific viewpoint, which includes sociological elements, which would necessarily include even unreasonable argumentation provided it was widespread and had assumed sufficiently broad sociological dimensions. An encyclopedic discussion of the Theory of Evolution cannot ignore opposition to the theory, however wrong-headed it may be, because it is significant to the reader if not to the specialist. Here we certainly can't ignore well-documented recent research which purports to cast doubts upon Heisenberg, especially under a header "Among objections some have offered ..." JacquesDelaguerre (talk) 14:26, 24 March 2015 (UTC)
 * Yes, fringe theories can and should be excluded from science-related articles. If included, they need to be presented clearly with unobjectionable citations. The sentence in the lead (painfully incorrect as it stood with its "same time and place" before I fixed that particular point) is not clear enough to warrant inclusion. But relax, I'm not going to cause you any trouble. It is clear that this article is reserved (in your's and Chjoaygame's opinion) for the purpose of being non-scientific. It even makes a point about being murky if you read it carefully. YohanN7 (talk) 14:44, 24 March 2015 (UTC)


 * It is I think accepted by the relevant scholars that the Copenhagen interpretation is nowhere stated uniquely and authoritatively.


 * The label 'Copenhagen interpretation' is a convenient hat rack for opinions. It might be argued that the use of the term is more sociological than exactly physical. Heisenberg said in 1955 that he was sorry he invented the term. It would not worry me to see the term deconstructed and the article removed except as a disambiguation. Some editors think that the Copenhagen interpretation is the standard interpretation, some think it is the orthodox interpretation; some think it is clearly enough stated to be potentially wrong; some think if you don't accept the Copenhagen interpretation you are thereby automatically wrong. Part of the problem is Niels Bohr's renowned verbal prolixity and dare I say it obscurity. There are other parts to the problem.


 * With respect, the statement about non-definability is intended to reflect the very explicit and oft-stated view of Niels Bohr. He did not think non-measurability did justice to the problem. If it is not definable then a fortiori it is not measurable. Bohr is famous for insisting on the non-definability, as opposed to non-measurability, as the primary reason. Whether Bohr's thought about this is right is a matter of debate. I think it is not a matter of debate that he thought it.


 * It seems the former wording of exactly what is not definable is not acceptable. I happily accept that it could be improved. I wouldn't quibble about that if experts have their views. Two compatible variables are not "measured" at the same time and place because only one variable can physically be "measured" at one time and place. Compatible variables are said to be """simultaneously""" measurable because if the beam is "analysed" with respect to $A$ and then passed to an analyser for $B$ and then passed again to a copy of the analyser for $A$, the output is restricted to the copy-same output channel for $A$. If the variables are not compatible, then the output is not so restricted, but is in several output channels. The usual wording for this is """simultaneous""" measurement, but the word 'simultaneous' is more conventional than literally accurate.


 * Part of the problem is that "measurement", as the word is customarily used in quantum mechanics, physically has two importantly different and distinct components: (1) analysis, e.g. a bifringent crystal, and (2) detection, e.g. a Geiger counter. Sometimes people say "measure" when they mean 'analyse' and sometimes they mean 'detect', and sometimes they mean both at once. Failing to consider these two very different physical components I think leads to much confused talk and perhaps misunderstanding. One can pass a beam to analyser after analyser nearly as often as one likes, but a detector is usually a dead end for the beam that enters it.Chjoaygame (talk) 22:13, 24 March 2015 (UTC)

The problem is to figure out what definable means physically and mathematically. It is not clear in the article. One possibility is that he (Bohr) means that there is no such state in Hilbert space (interpreted as the non-existence of such states in nature). There is no such state (e.g. simultaneous eigenstate of position and momentum operator) in Hilbert space under the "usual rules" of canonical quantization where the "standard" replacement of position and momentum is made. If this is what Bohr means by "definable", the the article should say so. If not, it should still present what is meant by the term. The now referenced article is talking about measurements, not about anything being definable. YohanN7 (talk) 11:37, 25 March 2015 (UTC)


 * There is room to improve the article.Chjoaygame (talk) 11:59, 25 March 2015 (UTC)


 * There is. Before spending too much time on it, I'd like to ask User:Jaxdelaguerre what his general standpoint is. On this talk page, he refers to this article as a "historical article intended for general readership". He also refers to this article as "hard science". The POV seems to depend on exactly who he is disagreeing with for the moment. If this disagreement is a point in itself, I am not interested in improving the article.
 * I agree in full that there is ambiguity as to what the CI is, but I strongly disagree that the options we present must be ambiguous (murky/ordinary language using undefined non-standard terminology). I have never believed that an article that is easy to read (because the words are each understandable in isolation) is better than an article that forces me to think and grasp new concepts presented exactly for what they are, not soothed over using meaningless words. YohanN7 (talk) 13:13, 25 March 2015 (UTC)
 * My general standpoint?

''Two monks were watching a flag flapping in the wind. One said to the other, "The flag is moving."'' The other replied, "The wind is moving." ''Huineng overheard this. He said, "Not the flag, not the wind; mind is moving."'' JacquesDelaguerre (talk) 15:48, 25 March 2015 (UTC)


 * Total nut-bag (as partially suspected). No further investment of time and effort is called for on my part. YohanN7 (talk) 16:04, 25 March 2015 (UTC)

What is a "discrete entity" ?
The Copenhagen Interpretation denies that the wave function is anything more than a theoretical concept, or is at least noncommittal about its being a discrete entity or a discernible component of some discrete entity.

Doesn't "discrete" mean "conceptually or physically discontinuous from its surroundings" ? I think it's being misused to mean "physically real" or perhaps "concrete entity". 89.217.0.130 (talk) 20:20, 20 April 2015 (UTC)

Subjective versus objective
In the section Metaphysics of the wave function, whose choice was it to use the terminology "subjective" versus "objective" for these views of the wave function? I would think "formalist" (or "nominalist" or "positivist") versus "realist" would be much more accurate.

You would not normally characterize reliance on a prediction machine that is resistant to interpretation as "subjectivist".

Maybe give some citations where it's used that way? There may well be some; it seems a likely blurring to me, even though I take issue with it. 89.217.0.130 (talk) 20:41, 20 April 2015 (UTC)


 * The terms 'subjective' and 'objective' are very often used in the relevant literature. 'Positivist' and 'realist' are often used. Rightly or wrongly, 'formalist' is not. At least, that is my fallible recall.


 * I think 'subjective' and 'objective' are enemies of clarity in this area, but still the terms are used, and probably we cannot avoid discussing them.Chjoaygame (talk) 21:05, 23 April 2015 (UTC)

What does non-separable mean?
I had trouble understanding this sentence:

It is a key concept of quantum theory, expressed in quantum mechanics by the non-separable characteristic of the wave function, that its domain is configuration space, not ordinary physical space–time.

and similar difficulties at Talk:Wave–particle_duality.

It's not clear to a reader who encounters this what "non-separable" means here. Something about the speed of light? Or about the fact that it is a joint function of all variables and you can't "separate" them? -- I guess both, and you really are pointing to the Bell paradoxes. But the answer is postponed until the section entitled Non-separability of the wave function further down.

I also disagree with the contrast between "configuration space" and "ordinary physical space–time" as the domain of the wave function. "Configuration space" has no time variable. The correct contrast is between "configuration space cross time" and "ordinary physical space–time". I am afraid this detracts from the pithy quality of the axiom, but it can't be avoided. Psi depends on x_1,x_2,... and t.
 * In the Schrödinger picture it's "configuration space cross time". In the Heisenberg picture the cross time goes in the operator.Chjoaygame (talk) 21:31, 23 April 2015 (UTC)

Also "ordinary physical space-time" is ambiguous between Minkowski space-time, or Newtonian space-time, or just R^3 x R. Structurally, these are pretty different from one another, precisely for questions like these. As we know, even Schroedinger of one particle has infinite propagation speed, and this is already a "separability" problem in the sense of not respecting the speed of light. So to my eyes the "nonseparability" comes from two sources, that psi gives joint probability information for separated points, and that psi has infinite propagation speed. If you want "separability" to refer to just the first one of these, it would have to be said.

From Don Howard on separability (I just pulled this up a random):

''This is a fundamental ontological principle governing the individuation of physical systems and their associated states, a principle implicit in many classical physical theories. It asserts that the contents of any two regions of space-time separated by a non-vanishing spatiotemporal interval constitute separable physical systems in the sense that (1) each possesses its own, distinct physical state, and (2) the joint state of the two systems is wholly determined by these separate states. (1989, pp. 226-7)'' --From "Holism, Separability, and the Metaphysical Implications of the Bell Experiments", in James T. Cushing & Ernan McMullin (eds.), Philosophical Consequences of Quantum Theory. University of Notre Dame Press. 224--253 (1989)

I like this better than just "obeying the speed of light" (my previous notion, which I came in with) because it has the ring of a widely-applicable and fertile ontological principle. However, the physics principle has to be stated more precisely than this.

Upshot: Separability (in physics) needs its own article.
 * 89.217.0.130 (talk) 20:14, 20 April 2015 (UTC)


 * As for a separate article on separability: the word is already the source of a gobbledygook industry. I would like avoid feeding more into that industry.Chjoaygame (talk) 21:31, 23 April 2015 (UTC)
 * Looking at the section called Non-separability of the wave function, the second paragraph is not understandable.


 * The evolution of the system, as determined by the Schrödinger equation, does not display particle trajectories through space–time. It is possible to extract trajectory information from such evolution, but not simultaneously to extract energy–momentum information.


 * Why can we extract trajectory information? You just said the equation does not display particle trajectories.


 * Why does uncertainty prohibit trajectory information at the same time as energy-momentum? Are they dual? Is trajectory just "position" and energy-momentum just "momentum"? What does trajectory information even mean, with regard to Heisenberg? I don't see how to apply Heisenberg to it.


 * The two kinds of information have to be extracted on different occasions, because of the non-separability of the wave function representation.


 * I can't understand this assertion because I don't know the example or thought experiment that covers this. It leaves me hungering for a "Main Article" on the topic to explain it to me.


 * In Bohr's thinking, space–time visualizability meant trajectory information. Again, in Bohr's thinking, 'causality' referred to energy–momentum transfer; in his view, lack of energy–momentum knowledge meant lack of 'causality' knowledge. Therefore Bohr thought that knowledge respectively of 'causality' and of space–time visualizability were incompatible but complementary.


 * To my ears, this is approaching scientific gobbledygook. What kind of physics term is "space-time visualizability"? I can't see how this can link to anything substantive that I know about the subject or could use for anything. "Causality" is better, but I can't grasp what Bohr could possibly have been thinking. It reads like a sophmore essay.


 * The sentence tried to summarise Bohr as interpreted by Howard. The term 'space-time visualizability' is one conventional even if wrong translation of 'anschaulicheit'. This is a major concern in the literature, even if unsubstantive. If by reading Bohr and others you can grasp and tell us about what Bohr was thinking, you will have done well.Chjoaygame (talk) 21:31, 23 April 2015 (UTC)


 * So, what was the thing about non-separability that Bohr noticed?
 * 178.38.89.28 (talk) 01:33, 21 April 2015 (UTC)


 * It would add greatly to the comfort of other editors if you would very kindly choose for yourself a suitably non-identificatory User name and routinely use it. I feel uncomfortable chatting with a number. I think a user name does not create a security problem.Chjoaygame (talk) 21:11, 23 April 2015 (UTC)


 * Non-separability means Bohr &al's concept of QM is that the wave function can be calculated but cannot be isolated as a "thing" separate from the particle nature of quantum physical phenomena. They felt that metaphors, visualizations, etc., were useless, that QM only offered mathematical tools for statistical prediction and provided no existential, local-realistic explanation. Debroglie-Bohm took a different approach, they believed in the existential, local reality of the wave function. Their math worked, too, but did not thrive in the QM research community, losing mindshare to the approach used today. JacquesDelaguerre (talk) — Preceding undated comment added 04:14, 24 April 2015 (UTC)


 * I seem to recall that 'separability' has been used differently in two historical epochs. I am not advocating either usage, but a comment may be useful. In a general configuration space, and more especially in a general generalised quantum configuration space, every particle is 'present' at every point; a point does not represent a place. In ordinary physical space-time, a point represents no particular particle, but does represent a place and time. That is all that was meant by 'separable' in the old literature. In the post-Bell literature, separability refers to to question of whether we happens at one point of space-time is 'influenced' by what happens at another point separated from it by a space-like interval. I am not trying to say that there is a vast and deep difference between these meanings, but I do intend to say that I seem to recall that the emphases are different in the two historical settings. I am not trying to advocate any usage. Subject to a check on my recall, I think Bohr and other early writers, most especially Schrödinger, were more focused on the old emphasis.Chjoaygame (talk) 05:01, 24 April 2015 (UTC)

Principle 7 is too long to be a principle
Under the section Principles, Principle #7 (starting with Different wave functions can be linked in a so-called tensor product...) stands out as being very long and discursive.

After introducing the tensor product, Principle #7 turns into a mini-essay on the implications of tensor products for the problem of measurement -- the interesting line of inquiry that arises when you couple the "quantal system" with the "measuring device" as a quantum tensor product, then compare this to the idea of wave function collapse via a classical measuring device. A birefringent crystal is mentioned. The resulting discussion suffers from the usual difficulties of trying to cram a whole new theory into a marginal note or the question session of a talk, namely it's really interesting but there isn't enough space to really develop the line of research.

Shouldn't this "Problematik" have its own paragraph or section somewhere?

Then principle #7 could be boiled down to its essence, which is perhaps the simple idea that particles in interaction are represented by tensor products. Although because no source is mentioned, I'm not sure myself what the essence should be.
 * The simplest fix IMHO to #7 would be to delete everything after "which is the tensor product". JacquesDelaguerre (talk) 15:14, 21 April 2015 (UTC)

My uncertainty on this point does bring to mind another issue concerning this article -- it would be useful to distinguish "Principles of the Copenhagen Interpretation" (in particular) from "Principles of Quantum Mechanics" (in general). The tensor product, by itself, seems like the latter. 89.217.0.130 (talk) 19:59, 20 April 2015 (UTC)


 * Heisenberg would first say that he is sorry to have introduced the term 'Copenhagen interpretation'. He would, I think, say that the Copenhagen way of thinking avoids the many misinterpretations. I listed the tensor product because it is needed to make sense of things, not because misinterpretations don't use it. While academically convenient, it might be perhaps ahistorical or otherwise overwrought to try to separate the principles of quantum mechanics from the Copenhagen way of thinking.Chjoaygame (talk) 05:12, 24 April 2015 (UTC)

Summary of objections to Copenhagen Interpretation in introduction
I replaced a somewhat diffuse sentence in the introduction by the sentences:

''There have been many objections to the Copenhagen Interpretation over the years. Some have objected to the discontinuous jumps when there is an observation, or the probabilistic element that is introduced upon observation. Others have objected to the subjectiveness of requiring an observer, the difficulty of defining a measuring device, or persistence of classical physics to describe the "laboratory" in which the results are measured.''

I hope these 5 kinds of objection are well-supported in the section on "Criticism". I see that most of them are. Note that the objection about "subjectivity" has been more or less met -- already by some of the famous early guys -- by replacing the conscious observer by a "measuring device"; then the weight of the objection shifts to the "difficulty of defining a measuring device". However, the objection about subjectivity is historically important, so I put it in.

There remain two sentences in the introduction about objections to CI. They are:

(1) ''Others have observed that there is little consensus as to the physical meaning of wave–particle duality.

(2) ''Yet others have pointed out that some research has called into question whether incompatible conjugate properties can indeed never be defined for the same time.

Both of these statements seem to be irrelevant to the Copenhagen Interpretation; they sound more like objections to quantum mechanics. But I'll leave them alone till I've studied the article some more. 178.38.171.5 (talk) 17:51, 20 April 2015 (UTC)


 * The idea of wave-particle complementarity was very large in Bohr's mind. Heisenberg saw things perhaps differently. It would misrepresent history to try to leave the wave-particle thing out of an account of 'the Copenhagen interpretation'.


 * The impossibility of definition of certainly and exactly determined coexisting position and momentum was very big in Copenhagen thinking, a major weapon in the war with Einstein. To try to say it is quantum mechanical as distinct from Copenhagenist would, again I think, misrepresent history.


 * It would be more useful to study the literature than to study the article!Chjoaygame (talk) 05:34, 24 April 2015 (UTC)

The whole introduction is confusing. Very little of it says what the CI, to a layman. It needs a rewrite. Roger (talk) 22:59, 7 September 2015 (UTC)


 * I agree. It should be rewritten from scratch.  Unfortunately there are not many people with both the necessary expertise and the time to do so, especially given that whatever good work gets done will be eroded later.  A big part of the problem in the current article is that some of its editors evidently don't understand quantum mechanics, which makes it impossible to write about an interpretation of it.   74.64.38.121 (talk) 11:40, 8 September 2015 (UTC)
 * The biggest problem with this article has always been argumentative grad students who think they understand QM . Waleswatcher seems to be the most skilled at both editing and the subject matter to appear in recent years, I hope s/he does more work on the article. JacquesDelaguerre (talk) 12:31, 8 September 2015 (UTC)

My disagreements start with the very first sentence. The CI is not an expression of mathematical formulas in everyday language. It is a way of interpreting those formulas, but not a substitute for those formulas. I also think that the discussion of axioms, configuration space, and objections is way too confusing and dubious for an introductory paragraph. I suggest cutting all that out, and leaving something simple like this:

The Copenhagen Interpretation is a way of understanding the formulas of quantum mechanics. While everyone agrees that there are experiments confirming those formulas, the meaning has generated some controversy. The interpretation is a set of explanations devised by Niels Bohr and Werner Heisenberg in the 1920s, and widely accepted in textbooks.

Alternatives to the Copenhagen Interpretation include the many-worlds interpretation, the De Broglie-Bohm (pilot-wave) interpretation, and quantum decoherence theories. Roger (talk) 17:17, 9 September 2015 (UTC)
 * Well, there's a lot to what you say, Roger. Maybe the difficulty in smithing this lede is, as Bill Clinton might say, "the meaning of meaning". As Bohr pointed out, visualization may not help in the circumstance of apparently being forced mathematically to deny the possibility of reaching any local realistic explanation. So in your suggested lede, you may want a different word or phrase than meaning. Anyway, I've taken another crack at it, at least it's shorter now! JacquesDelaguerre (talk) 18:27, 9 September 2015 (UTC)


 * Here is a physicist who says that there is no such thing as the Copenhagen interpretation! Actually it is an informed opinion that quotes Bohr and makes some good points. I don't get your objection to the word "meaning". Yes, I am sure people disagree on what ought to be in a meaning. They also disagree over whether quantum mechanics even needs an interpretation. Roger (talk) 18:50, 9 September 2015 (UTC)
 * Ha, interesting link. As for finding meaning in abstracts, Lewis Carroll covered that nicely:

''[S]aid the Mouse. '—I proceed. "Edwin and Morcar, the earls of Mercia and Northumbria, declared for him: and even Stigand, the patriotic archbishop of Canterbury, found it advisable—"'''

'' 'Found what?' said the Duck.   'Found it,' the Mouse replied rather crossly: 'of course you know what "it" means.'   'I know what "it" means well enough, when I find a thing,' said the Duck: 'it's generally a frog or a worm. The question is, what did the archbishop find?' '' JacquesDelaguerre (talk) 19:06, 9 September 2015 (UTC)

incompatibility
I here respond to one of the demands for clarification made by this edit. The relevant item is "Incompatible wave functions cannot be superposed."

Dirac wrote in the first edition: "This, of course, is true only provided the two states that are superposed refer to the same beam of light, i.e. all that is known about the position and momentum of a photon in either of these states must be the same for each."

Compatibility has much the same meaning as commutability. Wave functions from the same generalized quantum configuration space form a vector space, and can be added. Not from different generalized quantum configuration spaces. For a given particle, for example, one generalized quantum configuration space might be specified by a list of three position coordinates. Another might be a list of two position coordinates and one momentum. Another might be a list of three momentum space coordinates. That's three different vector spaces. They all correspond with one and the same abstract state vector space, but that one abstract vector space lacks a specification of configuration space, and therefore lacks a specified method of preparation. The three vectors could not come "from the same beam". A position coordinate cannot be 'added' to a momentum coordinate.


 * Dirac, P.A.M. (1930). The Principles of Quantum Mechanics, 1st edition, Oxford University Press, Oxford UK.Chjoaygame (talk) 08:29, 24 April 2015 (UTC)


 * I do not have the first edition, but a search doesn't find that language anywhere in two more recent editions, and you did not provide enough context to see what was actually being said there. Anyway, the statement I deleted from the article is false - any two wavefunctions can be superposed.  There are no restrictions on that whatsoever.  That is one of the most basic facts about quantum mechanics.  Dirac says so himself, very clearly: "Conversely, any two or more states may be superposed to give a new state." p.12,, 4th edition.   Waleswatcher  ( talk ) 10:04, 6 September 2015 (UTC)


 * In the 4th edition the more or less corresponding text on page 8 is as follows.


 * Corresponding to the description that we had in the case of the polarization, we must now describe the photon as going partly into each of the two components into which the incident beam is split. The photon is then, as we may say, in a translational state given by the superposition of the two translational states associated with the two components. We are thus led to generalization of the term 'translational state' applied to a photon. For a photon to be in a definite translational state it need not be associated with one single beam of light, but may be associated with two or more beams of light which are the components into which one original beam has been split.† In the accurate mathematical theory each translational state is associated with one of the wave functions of ordinary wave optics, which wave functions may describe either a single beam or two or more beams into which one original beam has been split. Translational states are thus superposable in a similar way to wave functions.


 * † The circumstance that the superposition idea requires us to generalize our original meaning of translational states, but that no corresponding generalization was needed for the states of polarization of the preceding section, is an accidental one with no underlying theoretical significance.


 * Perhaps this may clarify. I previously cited the 1st edition because it seemed succinct.Chjoaygame (talk) 20:08, 21 September 2015 (UTC)


 * The meaning of that is perfectly clear: in QM, states where the photon is in different places can be superposed, much like states with different polarization can be superposed in classical optics.  A little later he points out that the fact that states where the photon is in different places can be superposed is a specific example of a general principle, namely that any two (or more) states can be superposed.  Contrary to what you assert above, there is no restriction on that whatsoever, nor is there any such thing as "incompatible wavefunctions", nor is there any problem superposing a state specified in terms of position with one specified in terms of momentum.   Waleswatcher  ( talk ) 23:11, 21 September 2015 (UTC)


 * I wrote above: "Dirac wrote in the first edition: "This, of course, is true only provided the two states that are superposed refer to the same beam of light, i.e. all that is known about the position and momentum of a photon in either of these states must be the same for each." In reply, Editor Waleswatcher above writes: "I do not have the first edition, but a search doesn't find that language anywhere in two more recent editions, and you did not provide enough context to see what was actually being said there." Likewise, Editor Waleswatcher writes here: "there is really no reason to discuss "beams" at all, especially not in a "concept" section that is supposed to gently introduce the idea of quantum superposition."


 * These views proposed by Editor Waleswatcher are contrary to how Dirac saw it. Dirac's deliberately gentle and non-mathematical introduction is wholly predicated on the idea of beams, as one may verify by reading the 4th edition, starting for example here. Careful reading of Dirac's text shows that in the later editions, that Editor Waleswatcher says he searched in vain, Dirac does indeed rely on the superposed states coming from the same beam, contrary to Editor Waleswatcher's claim. For example, Dirac writes on page 13: "What will be the result of the observation when made on the system in the superposed state? The answer is that the result will be sometimes a and sometimes b, according to a probability law depending on the relative weights of A and B in the superposition process. It will never be different from both a and b." The superposition is here considered observable as a splitting of a single beam, as implied in context. The word beam doesn't explicitly appear in the sentence, but the common input beam is needed for the result to be "sometimes a and sometimes b". On page 5, for example, Dirac uses the word beam 8 times. On page 6, once. On page 7, 8 times. On page 9, 15 times. On page 10, Dirac writes "a very strange idea has been introduced—the possibility of a photon being partly in each of two states of polarization, or partly in each of two separate beams". As cited by me, the first edition does make this point about the beam explicit, but this is dismissed by Editor Waleswatcher on the grounds that he didn't read it. How much of the first edition does he expect me to transcribe into this talk page to provide him with the "context" he wants?


 * Dirac is not entirely an easy read, but he is reliable. According to Helge Kragh on his page 77: "When Heisenberg received the fourth edition of Principles in 1958, he gave Dirac the following fine compliment: "I have in the past years repeatedly had the experience that when one has any sort of doubt about difficult fundamental mathematical problems and their formal representation, it is best to consult your book, because these questions are treated most carefully in your book."" Again, Kragh says on his page 78: "Most physicists welcomed Dirac's exposition and praised it for its elegance, directness, and generality. To Einstein it was the most logically perfect presentation of quantum mechanics in existence."


 * To make his own points, it is thus evident that Editor Waleswatcher misreads or misrepresents Dirac's text, which is a reliable source.Chjoaygame (talk) 08:57, 8 January 2016 (UTC)

In any vector space, two vectors can be added. From this, it does not follow that the coordinate representation of two different vectors using two different coordinate systems can be added to yield a new vector; the result is, in general, nonsense. In other words, states may be added (unless there is a superselection rule in which case the states can be added mathematically, but the resultant state is not physically realizable), not two wave functions referring to different bases. YohanN7 (talk) 10:33, 8 January 2016 (UTC)


 * Thank you for this constructive comment. It brings out that a state, unspecified, and a wave function, unspecified, are not necessarily quite the same thing.
 * In talking about states, corresponding with vectors, one makes assumptions or presuppositions about the correspondence. Your preliminary phrase, "In any vector space" is therefore important and valuable. The correspondence relies on proper respect for it. Physically, in Chapter 1, Dirac deals with this by his first edition comment: "This, of course, is true only provided the two states that are superposed refer to the same beam of light, i.e. all that is known about the position and momentum of a photon in either of these states must be the same for each."
 * Chjoaygame (talk) 11:31, 8 January 2016 (UTC)

Pseudoscience
There is a quote, as well as I remember that goes "The worst case of pseudoscience pretending to be science foisted on students today is the Copenhagen interpretation of quantum mechanics." I haven't been able to find any reference to it, though. (I think it was on a radio program.) It isn't easy to find with a web search, as too many unrelated things appear. Maybe someone here knows about it? It does seem that CI is taught as the only interpretation in the usual way QM is taught. Gah4 (talk) 04:57, 16 May 2016 (UTC)


 * Seems like it should matter whose being taught in this assertion. Is CI the way that QM is most commonly taught to serious physics students or students in HS/Physics 101, etc? It seems to me that popular understanding of QM is at least as much Many-worlds as CI (people love the idea of parallel universes). Actual physicists, on the other hand, have to know the difference between the math and it's interpretation, utility and episteme, etc. The surveys referenced on this page (sources 43-45) seem to suggest that the most common views amongst serious physicists are either wholly or partly compatible with CI. This doesn't seem to paint CI as pseudoscience. Pwoodfor (talk) 13:29, 27 August 2016 (UTC)


 * They teach Newtonian mechanics in high school and Physics 101, not because it is correct, but because it is easier to teach, and also works most of the time. Seems to me that is also true of CI. Then again, when teaching Newtonian mechanics, it isn't usual to come right out and state that it is wrong. Students only learn that later. Gah4 (talk) 09:44, 7 September 2016 (UTC)

Uber
I revert out


 * Problematically, the interpretation requires an irreversible collapse of the wave function. It presumes that an "über-"observer exists which is not part of the quantum-mechanical system and is not a quantum mechanical system (which would imply the behavior can theoretically be reversed). There is no evidence such an observer exists: every system which has been brought under sufficient control has strictly followed the tenets of quantum mechanics.

The original source given was a video of a lecture and the new source added is... an article essentially based on the same lecture (What follows is a lecture that I gave at...). For reasons unclear to me it's also asserted that it's an article in Fortschritte der Physik but if so a ref to the journal would be more appropriate; as far as I can tell the arxiv pdf makes no such claim.

So much for the sourcing. What of the substance? The arxiv preprint does use the term "uber-observer" but doesn't obviously make the same claims as the text here makes, and the "There is no evidence" seems to be editorial interpolation William M. Connolley (talk) 21:47, 17 June 2018 (UTC)

As for sourcing: the lecture was given, is was turned into a preprint, and then an article in Fortschritte der Physik. If you follow the doi you get the article. I guess I could also refer to the article directly. It appears youtube videos can be source: https://en.wikipedia.org/wiki/Wikipedia:Videos_as_references

As for the substance. You state that it doesn't obviously state the same claim, but you are not explaining the gap. In the video (around 16:00) it says that "the experiment is not subject to the rules of quantum mechanics" It clearly links reversibility to the rules of quantum mechanics. The assertion after the refs is based simply on their not being a nobel prize or other serious assertion for anybody having found any system violating quantum mechanics.Jmv2009 (talk) 22:12, 17 June 2018 (UTC)


 * The source is the text. The video is fluff, best removed. Also, I'm rather hoping someone more knowledgeable will comment William M. Connolley (talk) 07:09, 18 June 2018 (UTC)

Most taught interpretation?
In the introduction, there is currently a citation needed flag on the claim that the Copenhagen interpretation is one of the most commonly taught interpretations. As someone in the field, this fact seems self evident and not really requiring of a citation - nonetheless, I know that's not how wikipedia works. The citation added explicitly states it is the most commonly taught at the beginning of section 4.8 here (link opens pdf, but article citation leads to the meta page). Other possible support comes from this (link opens pdf) study on page 15, which in my opinion obliquely implies it is the most commonly taught (in that it is the most commonly held, and most people who hold it have not changed their preference in interpretation). Further this article explicitly claims it is often the first and only interpretation taught. I went with the original study as I felt it had more legitimacy. Fireballs619 (talk) 14:31, 26 March 2019 (UTC)


 * I suspect it is more commonly taught, though I am even more sure that Newtonian mechanics is taught more than QM. Newtonian mechanics is taught in high-school physics, and in the earlier years in college, where many will only take one or two years. On the other hand, measurement problem indicates probably still the most widely held interpretation of quantum mechanics (regarding CI) and there is discussion on that one. Like Newtonian mechanics, CI works much of the time, and people who use it (should) know when it works. Newtonian mechanics has been known to be wrong for over 100 years, yet they still teach it. CI has been questioned for a long time, with more and more experiments showing its problems. Gah4 (talk) 18:26, 26 March 2019 (UTC)


 * Most physicists were perfectly happy with the jumble of ideas that purportedly constituted the Copenhagen interpretation itself, since the question about the meaning of quantum physics had little bearing on their work.

Feynman video and recent book.
here is a link to a Richard Feynman lecture at Cornell. He conveniently never mentions interpretations. More recently there is the book Through Two Doors at Once which, among others, explains the results of some more recent experiments. The rules of QM haven't changed much over the years. Experiments comparing interpretations, especially CI, against the known QM rules always seem to show the QM is right, and interpretations wrong. (Probably that should trace back to Schrodinger's cat.) Gah4 (talk) 18:42, 26 March 2019 (UTC)


 * As an interpretation, the CI does not conflict with any known observations of QM. I am not sure what you mean by the claim the "QM is right, and interpretations are wrong". Do you mean that the equations of QM correctly predict observation? Because interpretations concern themselves with what those equations *mean*, and do not propose their own equations as alternatives. Fireballs619 (talk) 19:20, 28 June 2019 (UTC)


 * The What is Real book is pretty much a history and current state of interpretations of QM. Maybe it should be required reading for editors of this page. Otherwise, I am not sure I can say more about it. Gah4 (talk) 19:41, 28 June 2019 (UTC)


 * I have read that book, and maintain by claim that the CI does not conflict with any know experiment. Indeed, I am still not sure even what you mean that "QM is right, and interpretations are wrong". In any case, can you clarify what changes you are proposing by mentioning the Feynman video and book? Fireballs619 (talk) 16:05, 3 July 2019 (UTC)

Copenhagen is still a realist theory
I am by no means a Bohr scholar, but I have serious issues with the structure of this article. I think in many ways it misrepresents Bohr's interpretation by conflating it with a rather uncritical 'textbook' interpretation.

My two main objections are that Bohr is most definitely an 'entity' realist in that he believed quantum systems existed in the world. From the SEP

"It is certain that Bohr regarded atomic objects as real (ATDN, p.93 and p.103). Their existence has been confirmed by countless experiments. Hence, phrased in a modern terminology Bohr might be classified as an entity realist in the sense that experiments reveal their classical properties in relation to an experimental set-up. "

I do not believe this is represented in this current Wikipedia article in its explanation of his epistemic interpretations of the wave function. The article further confuses the subject by positing that Copenhagen is a collapse theory. Again, see the SEP.

"Hence, those physicists who accuse this interpretation of operating with a mysterious collapse of the wave function during measurements haven’t got it right. Bohr accepted the Born statistical interpretation because he believed that the ψ-function has only a symbolic meaning and does not represent anything real. It makes sense to talk about a collapse of the wave function only if, as Bohr put it, the ψ-function can be given a pictorial representation, something he strongly denied."

"But Bohr never talked about the collapse of the wave packet. Nor did it make sense for him to do so because this would mean that one must understand the wave function as referring to something physically real."

"[Dieks] analysis results in a finding that Bohr’s qualitative interpretation is in line with modern non-collapse theories."

Who is currently watching this page? I don't want to step on any toes, but feel several corrections are necessary. — Preceding unsigned comment added by Lessconfusedthanbefore (talk • contribs) 19:42, 26 April 2020 (UTC)

Misinterpretation of the Bohrian view
I believe that this article incorrectly attributes a positivist slant to Bohrs interpretation. Although this is indeed the view taken by his student Heisenberg, and is often taken as being representative of the copenhagen interpretation, it is not true of Bohrs ideas (regardless of whether they make it into the definition of the cophenhagen interpretation). I myself still struggle to come to terms with Bohrs relationist notions of measurement and reality, but I am certain that it is unfortunately not as simple as a positivism.

Also with regards to whether interpretations of QM is a subject for physics or metaphysics, it is as much physics as Einsteins deriving of the lorentz transformations (ie. special relativity). Both attempt to clarify and extend an existing operationally adequete although conceptually incomplete theory by questioning what relation the theory has to reality.

Nic. — Preceding unsigned comment added by Rainbowpants (talk • contribs) 17:19, 26 February 2006 (UTC)

Made a few corrections
Mainly POV things.

I removed the phrase

"Einstein's Relativity demonstrates that "instantaneous" has meaning only for observers sharing a single reference frame. No universal time reference exists so the "instantaneous wave function collapse" of the Copenhagen Interpretation is left undefined."

since it builds on the misunderstanding that the wave function collapse should be understood as a physical process (it should not). The "instantaneous wave function collapse" is not really a problem in quantum field theory or relativistic quantum mechanics, and in the various "delayed choice" experiments as well as in Einstein and Rosens article on the subject from 1931 we see that the shift involved in the observation/reduction of the wave function is so fundamental it actually stretches backwards in time. — Preceding unsigned comment added by Agger~enwiki (talk • contribs) 18:15, 28 March 2006 (UTC)

Decoherence invented by Bohm in 1952?
In the section Nature of collapse, it is said that Bohm invented decoherence, but the article about decoherence credits it to Zeh in 1973... Which is it? Topologicalinsulators (talk) 11:48, 17 January 2020 (UTC)

I've corrected this section, unless anyone has sources to credit Bohm, but I think they are entirely separate discussions. I wonder how much this even needs to be discussed on this page. This section should probably be buffed up to talk specifically about Bohr's interpretation. Lessconfusedthanbefore (talk) 19:52, 26 April 2020 (UTC)