Talk:Quantum mechanics

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I am changing this statement around because of its inaccuracy:

"The first study of quantum mechanics goes back to the 17th and 18th centuries when scientists such as Robert Hooke, Christian Huygens and Leonhard Euler proposed a wave theory of light based on experimental observations."

This is not accurate Young et all were not studying quantum mechanics, neither was that their intention, but merely studying the properties of light. This would be like claiming ancient attempts to understand light were studies of electromagnetism, it confuses the issue. Just because Young et all studied light does not mean he knew, wanted, or was studying quantum systems. Second the source listed for this sentence does not even make that claim, and is not a work on the history of quantum mechanics, but an advanced science text book on optics. Belief action


To avoid clutter I have undone my disambiguation effort.

I think that the literature should be a guide. The term 'quantum mechanics' is mostly well delineated there. So are the terms 'old quantum theory' and 'quantum field theory'. It is true that quantum field theory gives quantum mechanical values to its fields. But that leaves them conceptually distinct. I think the literature takes the distinctions to be obvious in ordinary language, not calling for much talk about them. I think Wikipedia has gone wrong in seeming to or trying conflate or confound them in places such as the present article.Chjoaygame (talk) 00:43, 28 December 2014 (UTC)

It is true that quantum field theory gives quantum mechanical values to its fields.
It's fields usually take values in the set of linear operators on Hilbert space. Hilbert space valued fields (wave functions in a basis) are still present. They just don't occupy the center of the stage. Dynamics and physically extractable interpretations lie mostly in the operators (Heisenberg picture.)
But that leaves them conceptually distinct.
Just no! The difference is that particles can be crated and destroyed (you have more operators on a bigger Hilbert space than in QM 101). YohanN7 (talk) 12:28, 28 December 2014 (UTC)
I don't feel confident in reading this. ? One or two typos?Chjoaygame (talk) 17:38, 28 December 2014 (UTC)

Another approach to QFT[edit]

You don't seem to appreciate Weinberg's approach to QFT. There are other approaches, namely (for instance) canonical quantization. In passing from classical mechanics for a fixed number of point particles to QM 101, one employs canonical quantization. Observables are turned into (not necessarily commuting) operators on a suitable Hilbert space. Exactly the same procedure can produce (a specific) QFT. Take a classical field (like the EM field or a quantum field of the QM 101 version), and apply canonical quantization to it. This amounts to replacing field theoretical poisson brackets (linked article incomplete here) and turn them into commutators, and promoting the involved quantities to operators on the space of classical fields. For a good reference, see Field Quantization by Greiner and Reinhardt. (You don't need to add in special relativity. It is just that special relativity makes QFT unavoidable.)

It is quantum mechanics all the way. YohanN7 (talk) 13:02, 28 December 2014 (UTC)

As I read you here, you are saying that quantum field theory is a specialized part of quantum mechanics? You are taking quantum mechanics as having expanded, from the version discussed at the the 1927 Solvay Conference, that has a fixed number of particles in the system, with domain the configuration space, to the current version with indefinitely many particles, with domain ordinary physical space-time? In other words, you are saying that 'quantum mechanics' includes quantum field theory? And string theory?
I wrote the just-preceding paragraph some hours ago, but didn't post it. Now, after reading your post of 23:09 on 28 December 2014 I think I can answer my questions it that paragraph with a 'yes'.Chjoaygame (talk) 00:00, 29 December 2014 (UTC)
If you skip that "domain"-talk, which is of no consequence (as explained to you elsewhere by not only me), and if you skip "specialized version of" and replace it with "application of", then yes and yes, respectively. This is my taking, but this is not important. What is important is that it is the only taking I have ever seen in the literature. Nowhere have I found an exposition of QFT that says "guys, now we are going to define a fundamentally different type of quantum mechanics, which you may not have seen before, in order to be able to apply it to classical fields. The new version of quantum mechanics, ...". It is, in the most basic texts rather something like "guys, now we are going to apply quantum mechanics to classical fields. It is done as follows...". See the difference?
It is the application of the one and only quantum mechanics to new (I should really use the word "domains" here, but it is at present busy, for this, see the next paragraph) areas.
Here we go once again with the "domain": In QFT the "domain" is exactly the same as in your 1927 Solvay Conference version. Elements of QFT Hilbert space are functions of configuration space (a big one, I admit that), see e.g Fock space. If you want to, they are just multi-particle wave functions. For a perfect reference to see this connection, see section 3.2 in Greiner, Reinhardt Field Quantization, the relevant passage being
\Phi^{(n)}_{[n_1 n_2 \ldots]}(x_1, x_2, \ldots, x_n, t) = \langle x_1, x_2, \ldots, x_n, t|n_1, n_2, \ldots\rangle
The quantity
\Phi^{(n)}_{[n_1 n_2 \ldots]}(x_1, x_2, \ldots, x_n, t)
therefore can be identified with the wave function of an n-particle system in coordinate space known from ordinary quantum mechanics. (They go on to show that Φ satisfies the ordinary (multi-particle) Shrödinger equation.
If this is not good enough for you, nothing is. (If so, I'd rather see that you don't edit or try to influence this article from this talk page. Readers of the article read talk pages too.) It is a completely different story that some operators on QFT Hilbert space are functions of spacetime. Are you perhaps confusing things because of the Heisenberg picture employed?
The reason I wanted to get rid of the easy two points of below (you know which) is that I do not have time for these endless debates about what should be obvious if you intend to contribute to the article. I also too easily become irritated, something I cannot, unfortunately, blame on my young age. For this, I apologize, but I'll not respond anymore to any counterarguments you may have. I have other articles to prioritize. YohanN7 (talk) 09:40, 29 December 2014 (UTC)

1920s quantum mechanics not obsolete[edit]

There is an endless thread above, Lede is missing an important point that begins very well. However, the first paragraph end with the disastrous

Indeed, 1920s quantum mechanics was obsolete by the mid-to-late 1930s.

But why is this disastrous? Ain't it true?
The original poster unintentionally misunderstood his source. This has cost an enormous amount of confusion on this talk page, and has put an end to any improvements of the article. The reason is that what was referred to as as "1920s quantum mechanics" was never defined on the talk page, and people have taken the statement at face value since it was a referenced statement. There are two separate interpretations of what constitutes "1920s quantum mechanics":

  • It can refer to the initial course in quantum mechanics which I call QM 101 in this thread. This interpretation refers to the description of quantum phenomena by the non-relativistic Schrödinger equation, or its relativistic analogues, the Klein-Gordon equation and the Dirac equation.
  • It can refer to the mathematical framework and postulates of the "1920s quantum mechanics" (as more rigorously put by Neumann et alles later on).

The reference of the original poster obviously uses the first interpretation.
The problem is this:
The terminological use of the reference in question is not the same as the terminological use in this article. This article (in the relevant places) implicitly uses the second interpretation. Indeed, I dare say that the use in this article is the most common one in the literature treating modern theories. The resulting confusion is precisely what happens when inexperienced and/or not at the moment attentive readers take punchlines and quotes out of their context. I am sorry if I am stepping on anyone's toes here, but this needs to be said.

I advice inexperienced readers to not read the lengthy discussions above. It will only serve to confuse. It will seem that we are all in violent disagreement. We aren't, we just not fully agree yet because there still some explaining to do to each other. What is obvious to the attentive reader has not been obvious to all.

In light of this, the article is not at all in a disastrous shape.
I'll conclude with this bold statement:

Indeed, 1920s quantum mechanics is as alive and kicking as ever. It lives on unaltered in virtually every modern widely accepted theory or proposed theory. Indeed, General relativity and quantum mechanics in various applications is what we are sure that we have that are close to CORRECT theories (but not entirely correct). All others are speculative.

Nota bene, this uses the second interpretation of above. Note too, it shouldn't be taken too literally. Quantum mechanics is, for instance, not axiomatized in a way accepted by everybody. There are also other kinds of interpretations that people have argued about for close to 100 years. (Wave function collapse anyone?) Quantum mechanics is in other words not precisely and conclusively defined. But the essence of what is claimed can be referenced to practically all world class authorities in QED and beyond, provided care is taken when quoting and interpreting quotes.
What to do with the mess (that is admittedly there) in the article?.
For my suggestion, see the thread preceding this one. I do not want to reiterate once again what I said there, though the reader might find it hard to extract the essence due to all quarreling. But we desperately need more people to chip in, either to support or pick apart into atoms what I have written in this post. YohanN7 (talk) 11:36, 29 December 2014 (UTC) Addendum:
I managed to find the relevant part deep into the reference in question. Here it is:

The term “quantum mechanics” has two uses. One is as the general category of quantum techniques, of which quantum field theory is one application. String theory would be another application. The second use is in its specific application to discrete objects that we think of as point-particles; this is what we learn first in school, for example for describing electrons in atomic physics. Let’s call that “1920s quantum mechanics” to avoid confusion. In other words, 1920s-quantum-mechanics and quantum-field-theory are both examples of the general class of things that operate according to the general principles of quantum mechanics

YohanN7 (talk) 12:21, 29 December 2014 (UTC)

requested in-line citations[edit]

quantum phenomenon

In-line citations have been requested for the following: "The physically existing entities of quantum mechanics are strictly demanded to be completely described experiments, that is to say, the source, the potential or possible intermediate adventures, and the destination of a quantal entity or system." The reason for the request was given as "reason=This sounds very WP:POV". The sentence is an ordinary language version of the final opinion of Niels Bohr, who is often cited as one of the engineers of the Copenhagen interpretation. Since the term 'Copenhagen interpretation' was not coined until the mid 1950s, by Heisenberg, it is no stretch to include Bohr's 1939 opinion. I think the questioned sentence is pretty much orthodox Copenhagenism, though it is generally conceded that a precise and authoritative definition of that term is hard to find. I regard the cited references as orthodox Copenhagenism. Rosenfeld is perhaps an authority on that.

To save editors the trouble of checking the now supplied citations, I have copied some quotes here.

  • <Wheeler. J.A., Zurek, W.H. editors (1983). Quantum Theory and Measurement, Princeton University Press, Princeton NJ, p. viii.>

"... every atomic phenomenon is closed in the sense that its observation is based on registrations obtained by means of suitable amplification devices with irreversible functioning such as, for example, permanent marks on the photographic plate, caused by the penetration of electrons into the emulsion ... the quantum-mechanical formalism permits well-defined applications referring only to such closed phenomena and must be considered a rational generalization of classical physics." cited from Bohr (1958), pp. 73, 90, which is a reference to Bohr, N. (1958), Atomic Physics and Human Knowledge, Wiley, New York; I have verified these references against the original publication; the quotes are not exact but are close modulo a few words.

  • <Wheeler & Zurek 1983 p. xvi>

"Had quantum mechanics stopped here, its deepest lesson would have escaped attention: "No elementary quantum phenomenon is a phenomenon until it is a registered (observed) phenomenon"." The enclosed quotation marks are in Wheeler & Zurek, in their preface, but I don't know exactly why. I am guessing that perhaps they are loosely citing the following, that was read about the same time as the publication of the 1983 book by W&Z.

  • <Miller, W.A, Wheeler. J.A. (1983/1996). Delayed-Choice Experiments and Bohr's Elementary quantum phenomenon, pp. 72–84, Foundations of Quantum Mechanics in the Light of New Technology: Selected papers from the Proceedings of the First through Fourth International Symposia on Foundations of Quantum Mechanics, (1996) ed. S. Nakajima, Y. Murayama, A. Tonomura, World Scientific, Singapore, ISBN 9810228449 [reprinted from Proc. Int. Symp. Foundations of Quantum Mechanics, Tokyo, 1983, pp. 140–152], p. 72.>

"What one word does most to capture the central new lesson of the quantum? "Uncertainty", so it seemed at one time; then "complementarity"; but Bohr's final word "phenomenon"—or, more specifically, "elementary quantum phenomenon"—comes closest to hitting the point. ... It is the fruit of his 28 year (1927–1955) dialog with Einstein, especially as the discussion came to a head in the idealized experiment of Einstein, Podolsky, and Rosen. In today's words, no elementary quantum phenomenon is a phenomenon until it is registered ("observed" or "indelibly recorded" phenomenon), "brought to a close" by an "irreversible act of amplification"."

  • <Petersen, A. (1968). Quantum Physics and the Philosophical Tradition, Belfer Graduate School of Science, Yeshiva University, New York and M.I.T. Press Cambridge MA, LCN 68-17359, pp. 120–121. Petersen worked with Bohr.>

"Terminologically, the principal result of Bohr's analysis of Einstein's imaginary experiments was the concept of a quantum phenomenon. [footnote: The phenomenon-terminology first appeared in Bohr's paper, "The Causality Problem in Atomic Physics", in New Theories in Physics, Paris, 1939] Bohr came to regard it as the basic element of the quantal description. It contains the specification for how to apply the formalism in a well defined way. The formalism yields unambiguous physical statements only when applied to a quantum phenomenon."

  • <Bohr, N. (1939). The Causality Problem in Atomic Physics, in New Theories in Physics, Conference organized in collaboration with the International Union of Physics and the Polish Intellectual Co-operation Committee, Warsaw, May 30th – June 3rd 1938, International Institute of Intellectual Co-operation, Paris, 1939, pp. 11–30, reprinted in Neils Bohr, Collected Works, volume 7 (1933 – 1958) edited by J. Kalckar, Elsevier, Amsterdam, ISBN 0-444-89892-1, pp. 303–322.>

"The essential lesson of the analysis of measurements in quantum theory is thus the emphasis on the necessity, in the account of the phenomena, of taking the whole experimental arrangement into consideration, in complete conformity with the fact that all unambiguous interpretation of the quantum mechanical formalism involves the fixation of the external conditions, defining the initial state of the atomic system and the character of the possible predictions as regards subsequent observable properties of that system. Any measurement in quantum theory can in fact only refer either to a fixation of the initial state or to the test of such predictions, and it is first the combination of both kinds which constitutes a well-defined phenomenon."

  • <Rosenfeld, L. (1957). Misunderstandings about the foundations of quantum theory, pp. 41–45 in Observation and Interpretation: A Symposium of Philosophers and Physicists, edited by S Körner, Butterworths, London, p. 42. Rosenfeld worked with Bohr. In effect, Rosenfeld is known partly because he was an accepted transmitter of Bohr's thinking.>

"A phenomenon is therefore a process (endowed with the characteristic quantum wholeness) involving a definite type of interaction between the system and the apparatus."Chjoaygame (talk) 13:10, 7 February 2015 (UTC)


I would like a little time to produce good citations for the following, for which also they are requested.

  • "Obviously by definition, if only the initial condition is given, the process is not determined." If one reads the definition of a quantum phenomenon proposed by Bohr, then this sentence is merely logical exposition of that definition. I think a citation is hardly needed, since it is just a re-statement, in ordinary language, of the definition of a quantum phenomenon.
  • "Its final condition is predictable causally but only probabilistically." This is stated for example by Born and many others, but I will need a little time to find exact citations. It is strictly orthodox Copenhagenism.Chjoaygame (talk) 13:23, 7 February 2015 (UTC)
I can help you with this last one. It is the time evolution of the wave function (which is given once the Schrödinger equation is solved), or equivalently and abstractly, the time evolution operator of the theory applied to a state, in combination with the Born rule. It is in every book. The first one is incomprehensible. YohanN7 (talk) 13:47, 7 February 2015 (UTC)
Yes the last one is in every book. So I wondered why you asked for a citation for it. I thought you must have been looking for something very authoritative and elegant, that's why I wanted a little time.
As for the first one, I will briefly explain. An experiment gets some particles from a source, in their initial condition, and lets them suffer some adventures, and then detects the survivors when they reach the destination, their final condition. For a quantum phenomenon, source and destination must be defined. With only the source specified, the phenomenon is undetermined because determination requires also the destination to be specified. To me this looks like obvious elementary logic.Chjoaygame (talk) 13:55, 7 February 2015 (UTC)
I wanted a citation because Weinberg needs to go from there - as explained in the cn. This mess cannot be traced to Winberg, perhaps a poplular science magazine from the 1920's. You also need to cut out all but one citation for the first sentence because you give it (a today fringe opinion) seriously undue weight. (Leave Bohr in, its apparently his POV (and terminology?) All references are really references to Bohr anyway per your list above). YohanN7 (talk) 14:45, 7 February 2015 (UTC)
It appears as if you really believe people will understand what you are talking about when you go on in your "ordinary language" descriptions. This is not the case. A student of QM will get totally lost. The terminology seems deliberately chosen to depart from every standard there is. The result is a bunch of undefined terms (phenomenen, source, destination,quantal analyzer (your own invention you have admitted),...) that have a meaning only in your head. It is much better if you straightforwardly describe a scattering experiment in ordinary terminology that I think you might mean (but I'm not sure about this). YohanN7 (talk) 15:01, 7 February 2015 (UTC)
I have removed the other citations as you requested. I see you don't want me to cite Weinberg for it, but just now you told me it is in every text. Except Weinberg? I will spend some time finding a good citation from Heisenberg or Born; I seem to recall they both say it.Chjoaygame (talk) 16:14, 7 February 2015 (UTC)


The article states (with one million citations from few and a couple of philosophers plus Bohr),

The physically existing entities of quantum mechanics are strictly demanded to be completely described experiments, that is to say, the source, the potential or possible intermediate adventures, and the destination of a quantal entity or system.

This is not the only view. For example, Dirac postulated the physical existence of Dirac sea, i.e. that the negative energy states allowed by his equation are occupied. He didn't specify experiments in terms of sources, potentials, adventures or any destination. On the contrary, he postulated that it cannot be experimentally detected. It is unobservable. Less dramatic are virtual particles. They too are, by definition, unobservable, yet they are believed to exist (at least they are ingredients in every QFT there is). Quarks are believed to exist. The theory is that they will never be observed (Color confinement), no matter how you try with sources, potentials, adventures and destinations.

Having the attitude that "I don't see it, therefore it cannot exist" is scientifically..., well, dangerous. It is not a very common attitude nowadays.

The whole section is highly problematic and needs to be toned down and trimmed off of obscurities like "quantal entity" and various "adventures" whatever these things are. It is fringe. It is pseudo-science. YohanN7 (talk) 13:30, 7 February 2015 (UTC)

I see in Choaygame's last post that it is Bohr all the way here. He is not the only figure in QM. YohanN7 (talk) 13:37, 7 February 2015 (UTC)

As for quarks, so far as I understand, the evidence for them is in "completely described experiments", in my words, copying Bohr. I didn't say anything about "observing" or "not observing" them; those are your construals not mine.Chjoaygame (talk) 16:43, 7 February 2015 (UTC)
Can you please make a precise definition of "completely described experiments" then? I mean not gibberish that refers too other undefined terms existing only in your head? Your sentence now logically reads (yes, it does, read it)
physically existing entities = completely described experiments
You are equating two undefined things, with no meaning and extract from it (you think) the deepest of messages of quantum mechanics.
YohanN7 (talk) 00:38, 8 February 2015 (UTC)
Precise definition of "completely described experiments": experiments described by full specification of devices that produce and that register quantum mechanical systems. This is Bohr's definition. It is the sources, especially the well respected authority, Wheeler, who extract the deep message. I am reporting Wheeler and others. In quantum mechanics, this is what Bohr says. Perhaps he is talking gibberish, but that is Copenhagenism for you; the section is reporting on Copenhagenism. There are many physicists who reject Copenhagenism, and many who accept it. I am just reporting it, neither accepting nor rejecting it. I gave detailed sources because I knew what they said was controversial, but you asked me to remove them. Which I did.Chjoaygame (talk) 02:06, 8 February 2015 (UTC)
However much one might agree or disagree with it, the Copenhagen view is worthy of being spelled out, for the following reason given in the article:
"According to Steven Weinberg, "There is now in my opinion no entirely satisfactory interpretation of quantum mechanics."[1]
The Copenhagen interpretation - due largely to the Danish theoretical physicist Niels Bohr - remains the quantum mechanical formalism that is currently most widely accepted amongst physicists, some 75 years after its enunciation."
That is why I wrote this section.Chjoaygame (talk) 05:07, 8 February 2015 (UTC)
  1. ^ Weinberg, S. "Collapse of the State Vector", Phys. Rev. A 85, 062116 (2012).
On "completely described experiments", the job of an experimentalist is to log everything they use and do throughout the experiment, analogously for theorists their job is to define and describe everything necessary clearly and correctly, these things must be done anyway. Just saying you are using superfluous terminology, that experiments must be "completely described", if not then whoever has done the experiment (real or thought) is a shoddy physicist (or team of physicists). M∧Ŝc2ħεИτlk 20:10, 8 February 2015 (UTC)

For reference, the hopeless section is Quantum mechanics#Copenhagen interpretation of quantum versus classical kinematics, and it's a disaster. Once again Chjoaygame, you have used the unhelpful terms like "strictly" and "adventures", in a totally unreadable sentence as the quote shows... The rest of the section is not better either. You seem to keep insisting that physics must be wordy descriptions of events and experiments, and maths is just fancy notation and machinery to perform calculations which have nothing to do with "physical existence". I will get back to this thread later. M∧Ŝc2ħεИτlk 18:13, 7 February 2015 (UTC)

Yes, the section will have to go if it doesn't improve much and quickly. YohanN7 (talk) 00:38, 8 February 2015 (UTC)
We cannot have an article saying
physically existing entities = completely described experiments
Niels Bohr is turning in his grave. YohanN7 (talk) 00:45, 8 February 2015 (UTC)
With respect, I think you are not an adherent of Copenhagenism, and you have perhaps not read much of what Bohr had to say. I have surveyed some of his work and secondary sources about it. The sentence to which you object starts "In the Copenhagen view of quantum mechanics, the physically existing entities of quantum mechanics", advertising clearly that it is reporting the Copenhagen view. I don't think the report would make Bohr turn in his grave.Chjoaygame (talk) 02:15, 8 February 2015 (UTC)
Since you have changed it, it starts with something else than before, yes, it begins with what you say. May I ask you to quote your sources? That is, do not put it into your own words, just take four five sentences of Bohr and place it in the article? That way, the risk of something getting lost in translation is reduced. I am not the only one to find your writings unintelligible. YohanN7 (talk) 15:17, 8 February 2015 (UTC)
Perhaps at this point I may be permitted a slight diversion. Kalckar was an associate of Bohr. Kalckar's introduction to his reprint of Bohr 1939 includes the following.
""Causality and complementarity", thus being the penultimate article in this volume, is a distillate, so concentrated that it may remind us of one of Bohr's favourite stories; he told it not without a touch of playful self-irony: It happened that a small Jewish community in Poland learned that a famous rabbi was going to lecture in a little town in the vicinity. The members of the community were all rather poor and it was impossible for them all to go and listen to the teachings of the rabbi. Instead they sent the brightest young member as an observer, in order that he would come back to report on the new insights he had imbibed. In due time the young man came back and recounted his experience: "The rabbi gave three lectures. The first was simple and lucid and I understood every word of it. The second talk was even better: deep and subtle: I did hardly understand a single sentence, but to the rabbi it was all transparent and obvious to grasp. The third, however, was by far the greatest and most unforgettable experience: neither the rabbi nor the audience understood a single word of it!""
Bohr was notorious for changing his papers right up to the last moment of the proof stage.Chjoaygame (talk) 01:54, 9 February 2015 (UTC)
To User:Maschen. I don't think what you allege, that mathematics has nothing to do with "physical existence". I think that quantum mechanical mathematics should match or reflect physical existence, and that it is part of the job of the physicist and Wikipedia editor to expound that match in ordinary language. Léon Rosenfeld is a respected source who says so. Broadly speaking, I think that some articles tend to neglect that part of the job.Chjoaygame (talk) 02:32, 8 February 2015 (UTC)

Chjoaygame, now you have supplied quotes. That is good. It remains only that you display the quotes and remove your interpretation of them. The quotes are difficult to understand as they come. One more layer (your interpretation) between quantum mechanics and the reader renders everything completely impossible to understand. For example, you are inventing language, and apparently think this is a poetry session. YohanN7 (talk) 08:11, 9 February 2015 (UTC)

Bohr is not the sole author of the Copenhagen interpretation. Heisenberg and Born are part of the story. Bohr is widely recognized as being difficult to read. You do not like how I have rendered the material. It is not a bad thing to use a word such as 'registratory'. Its meaning is perfectly obvious in context. It has now been replaced by another nearby word, so is no longer grounds for objection. That I like to emphasize by use of rhyme does not mean that I think this is a poetry session. I don't accept that what have written is impossible to understand. I accept that it requires careful reading. I think you demand too much when you ask for pure Bohr quotes in the body of the article.Chjoaygame (talk) 10:39, 9 February 2015 (UTC)
It is your insistence on using words only (your words and terminology) instead of established terminology for which the words have a well-defined mathematical and physical meaning. You claim quite rightly that a mathematical expression has no (physical) meaning without an interpretation in words. It goes the other way too. An equation with physical interpretation says more than a thousand words. (Compare a picture says more than a thousand words.) I do not require a full mathematical description, but it would help if you included measurement and scattering and/or particle decay. These are the terms that an inexperienced junior undergraduate will at least recognize from the initial lectures in QM. Without this ground to stand on, this reader will be totally lost in Bohr's quotes or your translation of them. That is to say, you need to exemplify "experiment" with scattering to make it concrete. For a scattering experiment, you need to prepare the system in a predetermined in state. It is completely irrelevant how this is made. It does not affect the result of an experiment in any interpretation. You need to measure the out state. How this is done is likewise immaterial. (It affects the quality of measurement if you have a shitty detector. It is not the same thing.) It is a completely separate issue what happens in the measuring process. (For this you need probably the wave function for the measurement apparatuses as well as for the experimentalists in the vicinity and by extension the whole universe. Nobody knows. The CI asserts that the wave function of the system collapses, and this should of course be mentioned.) You might object that this doesn't qualify as a "phenomenon" according to your interpretation. This is acceptable since very few works seriously with that phenomenon of your.
Again you are filling up with more references. Again I say WP:UNDUE. The Dirac quote is applicable to my version of this (a concrete experiment), not involving complete descriptions (wave functions) of preparatory or "registratory" devices. The Bohr quotes deal mostly with the separate issue of measurement, now you do need to take the whole system (particle system + apparatuses) into account. This is a subject of its own with its own article. You do not need the "phenomenon" of yours to adequately describe quantum kinematics in the Copenhagen interpretation (or any interpretation).
To clarify if you find this unclear. We nee only the in state and the out state for the discussion about quantum kinematics. (This is standard terminology with a firm mathematical description and physical interpretation.) The "complete description" (you have left it undefined what that means, but it is clear that saying, for instance, "Stern-Gerlach apparatus" is insufficient, it adds absolutely nothing to only specifying the in state) of apparatuses enter only in deeper issue of what might happen in a measurement. YohanN7 (talk) 15:44, 9 February 2015 (UTC)
Thank you for this helpful advice.Chjoaygame (talk) 20:41, 9 February 2015 (UTC)


Editor Dirac66 is right that "registratory" does not appear in the Oxford English Dictionary. I am glad to see him here. I would say, however, that experienced or native speakers of English are entitled to make up their own words according to the general rules of word formation.

I wrote 'registratory' to rhyme with 'preparatory', to emphasize the complementarity between preparation and registration that characterizes quantum mechanics and is key to the present discussion.

Editor Dirac66, would you accept 'preparative' and 'registrative' for the same purpose?

Again for emphasis I wrote "demanded" where Editor Dirac66 prefers "required". Perhaps he is right.Chjoaygame (talk) 02:29, 9 February 2015 (UTC)

Quantum mechanics is a difficult subject, so it seems preferable not to invent new English words when existing words are adequate. If you want a rhyme, I suggest rewording the sentence to use the nouns 'preparation' and 'registration'. Perhaps 'In the Copenhagen view of quantum mechanics, phenomena must be described as experiments, with complete descriptions of the devices used for the initial preparation of the system, and of the final registration of the result, as well as of the potential or possible intermediate processes.' We could also replace 'registration' by the more usual 'observation' (or 'measurement' although that doesn't rhyme). Dirac66 (talk) 17:43, 9 February 2015 (UTC)
This is better, but far from enough. What is a "phenomenon"? A thunderstorm? What is "complete description"? A drawing? A wave function? The what potential? (Scattering potential maybe.) We have huge problems here with just one sentence. That's just one sentence in the hopeless section. I propose its deletion. YohanN7 (talk) 17:55, 9 February 2015 (UTC)
  • To Editor Dirac66. Thank you for your comment. I did check the OED for registrative; it's there. I used that word registratory because the literature about this specific subject routinely uses the word register for this purpose. Like you, I find it a little off-beat. My observation is that 'register' is widely used by Continental speakers of English in contexts like the present one. They use it more or less routinely when I would expect to hear 'record'. I suppose that the relevant literature, such as by Günter Ludwig, is largely by Continental authors. Considering the circumstances, I now think it better to leave it more nearly as you put it. I have changed some forms of expression.Chjoaygame (talk) 20:03, 9 February 2015 (UTC)
  • To Editor YohanN7. Thank you for your comment. I drew attention to the difference in kinematics, because Born and Heisenberg in particular wrote about that. It fits naturally with Bohr's eventual shift from 'complementarity' to 'phenomenon' as his key concept for quantum theory. It seems you find this very objectionable. (I used the word potential in its ordinary language sense because Heisenberg used it in that sense in this context. But, as you say, it also has a sense as a term of art. Accordingly, I have deleted the word.) I recognize that you would like to delete the whole section. I have now moved the section to be a sub-section lower down the page.Chjoaygame (talk) 20:03, 9 February 2015 (UTC)Chjoaygame (talk) 20:35, 9 February 2015 (UTC)