Talk:Quantum mechanics/Archive 9

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What is this article about?

That is, what is quantum mechanics, or rather, what should it be in this article?
Quantum mechanics is one of

• The core mathematical formalism = Hilbert space of states, observables, etc (but as little "interpretation" (POV) as possible),

1. My vote goes here YohanN7 (talk) 09:01, 28 December 2014 (UTC)

• Everything that uses the core mathematical formalism = Quantum physics like QED, the Dirac equation, etc, excluding old quantum theory.
• Everything that uses the core mathematical formalism = Quantum physics like QED, the Dirac equation, etc, or old quantum theory from Planck and on.

1. Yes, all of the above - I think this article should be the top-level article for all of quantum physics from Planck onwards, including interpretations, QFT, etc. Djr32 (talk) 17:10, 28 December 2014 (UTC)

• It is the subject taught in the course called Quantum Mechanics 101 = The non-relativistic Schrödinger equation and the one-dimensional harmonic oscillator, etc.

I can understand every viewpoint here, it is just terminology that is set in stone from ones personal experience. With that in mind, I can understand that some may have seen my posts here as very strange. Please cast your vote, but please don't appeal to your personal experience, think about what this article should be about. YohanN7 (talk) 09:01, 28 December 2014 (UTC)

First off, sorry about the overuse of emphasizing below. I feel that it is needed to convey my message most easily and quickly with the least possible misunderstanding. When reading the article a little more carefully, it is clear that every POV is used at some point. The lead focuses on QM 101, with a sprinkle of the "everything goes" versions (application after application) and core QM (since string theory etc is here). The history section can not and should not follow any "rule". The mathematical formulation sections sticks mainly to core QM, but also mixes in QM 101, particularly its interpretations (POV). The interactions with other scientific theories section stick to core QM, but focuses too much on relativistic QM 101. The subsection relativity and quantum mechanics should really be on special relativity, not general. It focuses mostly on the EPR story and has RQM as its main article. This is off topic! It should be QFT leaving the EPR to better suited articles. Core QM and special relativity works perfectly. This is, together with GR, THE achievement of the 1900's. Then the subsection attempts at a unified field theory (here GR should come in). It should be clear to anyone that it is core QM that is meant here, you can't make the QM 101 equations work describing TOE.

This is a mess, but can probably be repaired—beginning with a description of what the term QM can be interpreted as as the very first paragraph in the lead, warning the reader that each interpretation is used subsequently. YohanN7 (talk) 10:41, 28 December 2014 (UTC)

What should be in this article? Another question has also been asked: what should be the title of this article?

It seems there is a degree of support for the proposition that the article is messy. As I read it, Abitslow and YohanN7, and I support that proposition. Perhaps there are others?

How to fix it may not be easy to work out. I think the literature should be a major guide for us.Chjoaygame (talk) 13:27, 28 December 2014 (UTC)

Fair enough, but let us get two major points done with without further ado. I apologize in advance if I come across as an ***-****, trying to pretend to be more knowledgeable than I really am. I am an amateur, but likely more knowledgeable than your next door neighbor unless he or she is a physicist of profession. I often go wrong, but I don't think I go wrong on these two points.

The articles title is and should remain Quantum mechanics. Quantum theory is (rightly) a disambiguation page. Quantum physics is a wider concept. It is presently a redirect here. This is wrong, it should be a disambiguation page, containing stuff like nuclear physics, particle physics, old quantum theory and the gods only know what more. Ref Eisberg and Resnick. Moreover, the articles content (for better or worse) is quantum mechanics in all generality as most perceive it.

The idea that the "quantum mechanics" that enters into QFT and string theory, etc, is in some way fundamentally different from the "quantum mechanics" of Heisenberg, etc, is something that you have to give up. You have been arguing this at length in the former article (now link again) and at the talk pages there and here. If this is discussed further, I'll not participate because I would feel like a parrot talking to a deaf owner.

I find these points too obvious to mangle any further, and the references and quotes from one, max two, sources suffice because nobody disagrees in the reliable literature. There are slips and abuse of language in the literature that you might think support your ideas, especially when taking quotes out of context to "prove" your point. Please don't push this further.YohanN7 (talk) 18:06, 28 December 2014 (UTC)

I am glad you have expressed yourself at some length here. I think it may lead to some clarity.

As I have said above at 17:32 on 28 December 2014 on this talk page just a few minutes ago (while you were writing the immediately above), the idea did not ever occur to me that there might be some other type of quantum mechanics. I have not even thought of arguing for that.

What I have been saying has intended to mean that the 1927 version of quantum mechanics takes the domain of its basic objects to be configuration space, while quantum field theory takes the domain of its basic objects to be ordinary physical space-time. I count that as a fundamental difference. I have regarded 1927 quantum mechanics as an ingredient of quantum field theory. (I regard the conservation of translational momentum as an ingredient of quantum mechanics. That doesn't make me think that quantum mechanics is a version of classical mechanics.) The difference is fundamental because causality has no meaning in configuration space but it does have a meaning in ordinary physical space-time. I regard causality as one of the fundamentals of physics. Chjoaygame (talk) 21:06, 28 December 2014 (UTC)

I'll respond to this one item. You should really argue with the literature instead of doing original research. The basic objects of the 1927 version of quantum mechanics and of QFT are the same. Hilbert space is still there. The states live in there. The "domain", as you call it, of these states is configuration space (if you opt such a basis).

I don't know what you mean by "causality has no meaning in configuration space". Causality in QFT is expressed as that the field operators are commuting at space-like distances. This follows from the cluster decomposition principle that more or less forces that creation/annihilation operators exist and behave like they do (Weinberg Vol 1 Ch 4.) This is a consequence of special relativity being an ingredient alongside QM in QFT. Weinberg derives this fairly rigorously. The same result obtains with canonical quantization (see e.g. Greiner, Reinhardt Field Quantization), but there the result (micro-causality) appears "magically" with little explanation - and has to be verified theory by theory.

The bottom line is this: Sure, QM 101 and QFT are different, but the quantum mechanics that enters into QFT is the same old QM 101. The fact that operators (e.g field operators and Hamiltonian densities) are spacetime dependent is not some new addition to QM 101 - it is something that drops out due to the fact that "classical fields" are quantized, not point particles (here using the second quantization recipe for simplicity). Take QM 101 and special relativity and you can obtain the complete framework for "theoretical QFT". QM 101 and QFT are fundamentally different in one respect (I'll give you that): Namely, they have different fundamental ingredients. QM 101 has only itself. QFT has QM 101 and special relativity. And yes, the idea about quantizing fields as well as particles was around very early on, sufficiently early to say that it belongs to original QM 101 (if that is what bothers you). It is highly misleading (false) to give the readers the idea that QFT is different to QM 101 with respect to quantum mechanics. This Weinberg quote is enough to put an end to this discussion:

First some good news: quantum field theory is based on the same quantum mechanics that were invented by Schrödinger, Heisenberg, Pauli, Born and others...

YohanN7 (talk) 22:43, 28 December 2014 (UTC)

I regard the quantum mechanical entities as lying in the range of the fields of quantum field theory. For me, that makes quantum field theory and quantum mechanics distinct from one another. Whether it makes one a specialized version of the other is a linguistic question, not really a physical one.

As I read you, you have not noticed how important to my comments is my distinction between domains. Perhaps you think that distinction is not important, so it would escape your notice that I think it is? Perhaps you think the distinction is important but not fundamental? Then it would come down to how we read the word fundamental. I think it a dangerous word. Perhaps, therefore, I should not have used it. Of course there are those very clever persons who hold the very clever doctrine that "quantum mechanics has eradicated the foolish and obsolete notion of causality". I think that causality stands in quantum field theory, and that such standing overrules that doctrine. This is another way of saying that I think the distinction between domains is important, without actually using the dangerous word 'fundamental'.Chjoaygame (talk) 21:06, 28 December 2014 (UTC)

I don't think the point about configuration space is particularly important. A configuration space is just the complete set of variables needed to describe a system. For a single particle the configuration space is just ordinary physical space (x,y,z;t). (It could also be expressed, for example, in spherical polar coordinates (r, theta, phi; t) or in momentum space as (px, py, pz; t).) For a two-particle system it's (x1,y1,z1,x2,y2,z2;t). That approach is fine for systems with fixed numbers of particles, but not in the case of particle creation and annihilation in a QFT. Hence I don't think that it makes sense to consider configuration space vs real space to be what determines whether something is QM or not-QM. Djr32 (talk) 22:18, 28 December 2014 (UTC)

I volunteer to write a proposal for a replacement of the first sentence that disambiguate the terms we use and make the reader aware that the terms (especially "quantum mechanics") can mean different things depending on who use it and it what context, but there is no real inconsistency. I'll also point out that different interpretations of QM aren't the main subject of matter, except when indicated. YohanN7 (talk) 18:06, 28 December 2014 (UTC)

Following from my above remarks, if, as I think is the case, you intend to make the article explicitly regard quantum mechanics as a catch-all that includes everything after 1926, I think it would be a good idea to say so in so many words. Perhaps mistakenly, I think it would make many other articles more or less obsolete or in need of re-wording in this respect. Perhaps mistakenly, I think that many articles assume the now obsolete idea that quantum field theory is a radical advance on what we might now call 'classical quantum mechanics'. I think it would place too heavy a burden on the reader to say that the term quantum mechanics in this article has meanings that depend on who uses it and in what context. Till now I have obsoletely thought of 'quantum physics' as the person-and-context dependent catch-all word. I think Steven Weinberg uses the obsolete terminology. But looking at the 2001 Springer version of Julian Schwinger's lectures edited by Berthold-Georg Englert, I find in the prologue (a transcript of an early 1960s public lecture) the following, on page 1, that would support you: "This is particularly significant in connection with the philosophical implications of quantum physics, because quantum physics or quantum mechanics — by which I think we mean finally the rational mode of understanding microscopic or atomic phenomena — has perhaps had the greatest impact of any of the developments of physics upon the mode of thinking or the world picture of the physicist and thereby, indirectly, of the general citizen."Chjoaygame (talk) 21:06, 28 December 2014 (UTC)

No. It is simple and perfectly understandable and presentable. A lecturer in QM 101 holding a lecture on QM 101 primarily means the non-relativistic Schrödinger equation. The same lecturer, now submitting a paper for review to Physics Review on the topic of string theory is by QM not referring to the non-relativistic Schrödinger equation. He is referring to the mathematical framework of quantum mechanics and its postulates. In non of these two cases, he needs to explain to his audience what quantum mechanics is. Then people have a default meaning of what quantum mechanics is. Some would mean QM 101 by default. Such a person would prefer to have the mathematical framework of quantum mechanics and its postulates having a distinguished name. But the same person would understand perfectly well that a quantum gravity expert isn't referring to the non-relativistic Schrödinger equation in a paper on loop quantum gravity. Only you see problems here.

You win. I give up. YohanN7 (talk) 23:09, 28 December 2014 (UTC)

undone

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)

Quote:

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.)

Quote:

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

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

...

$\Phi _{[n_{1}n_{2}\ldots ]}^{(n)}(x_{1},x_{2},\ldots ,x_{n},t)=\langle x_{1},x_{2},\ldots ,x_{n},t|n_{1},n_{2},\ldots \rangle$

...

The quantity

$\Phi _{[n_{1}n_{2}\ldots ]}^{(n)}(x_{1},x_{2},\ldots ,x_{n},t)$

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

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

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)

determination

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)

language

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)

POV

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."

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)

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∧Ŝc²ħεИ_τlk 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∧Ŝc²ħεИ_τlk 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)

Introduction is self-contradictory

The introduction is self-contradictory. It says:" Quantum mechanics is a fundamental branch of physics concerned with physical phenomena at scales typical of the quantum realm of atomic and subatomic length scales" but then goes on to say the "even in the everyday world, many phenomena can be observed with the naked eye, which cannot be explained classically but require a quantum mechanical explanation."

So, macroscopic phenomena require an explanation in terms of a science concerned with microscopic phenomena? The definition of quantum mechanics here is deeply flawed. It is the branch of physics concerned with the quantum realm, but that realm is the entire universe- not just objects on atomic or subatomic length scales. — Preceding unsigned comment added by 153.203.118.142 (talk) 22:36, 20 August 2015 (UTC)

I don't think that's a contradiction. The explanations of those macroscopic phenomena require a study of what's happening at the microscopic level, which is what the definition says quantum mechanics is. Tayste (edits) 22:54, 20 August 2015 (UTC)

The lead (let's call it the lead, not the "introduction"), does indeed have it wrong. It is not about length scale. It is about action scale. To say it is about length scale may be an appealingly clever, sly, and persuasive way of popularizing a subtle concept. But it's still wrong. The thing that is quantal is transfer as measured by action.Chjoaygame (talk) 01:59, 21 August 2015 (UTC)

hasty undoing

Editor ChamithN has made some apparently hasty edits here and here. The main effects of them seem to be the removal of the sentence "It is said to be quantized", and the shift of the sentence "Other physical quantities change in corresponding discrete amounts."

As I read his edit summary, it seems that his reason for removing the sentence "It is said to be quantized" is that he reads it as avoiding a direct statement by use of evasive wording, signaling this by his "WP:WEASEL" and "WP:SPECULATION". The intention of the sentence is to introduce the standard terminology around the word 'quantum'. Without the sentence, the reader is not informed of the terminology at the most appropriate time. The wording is of course not indirect or evasive. It is just a statement of routine language usage.

The shift of the sentence "Other physical quantities change in corresponding discrete amounts" is a predictable but regrettable consequence of the unjustified "improvement" of punctuation that ran two logically distinct and conceptually separate ideas into one sentence, linked by a semicolon. The linking into one sentence gives the questionable and perhaps misleading idea that quantization belongs primarily to all physical quantities, when the more natural and simple idea is that quantization belongs primarily to action, and secondarily to the others.

I wish to avoid edit warring, so for the present I will not try to remedy these problems, but I think they should be remedied in due course.Chjoaygame (talk) 14:53, 2 September 2015 (UTC)

Firstly I must say that I was being bold when I was reverting Chjoaygame, not hasty. I came across this edit while I was patrolling my watchlist. It was apparent to me that this specific content addition contradicts with WP:WEASEL which is a Wikipedia guideline. So I decided that it's best to revert the article to its previous state. I quite agree that the statement "It is said to be..." is commonly used. However, my question is that, does Manual of style guides differently for scientific articles? -- Chamith (talk) 16:26, 2 September 2015 (UTC)

I don't think the addition "contradicts WP:WEASEL" at all. In this particular case, "it is said to be..." just means that a particular terminology is standardly used, not that certain unspecified people have made a certain assertion, which is where weasel wording might arise. W. P. Uzer (talk) 16:37, 2 September 2015 (UTC)

You both are right it seems. I think this is just enough to negate my reversion. This was a huge mistake after all. My bad. I'll revert it back to previous state. Thanks for bringing this up to discussion Chjoaygame. I thought I was being bold but this might as well be considered hasty. Best, -- Chamith (talk) 17:20, 2 September 2015 (UTC)

Thank you, Editor ChamithN, for your magnanimity.Chjoaygame (talk) 17:40, 2 September 2015 (UTC)

wave-function collapse

I think that, in the phrase 'wave-function collapse', the hyphenated form 'wave-function' is a compound adjective that should be written so. This is in spite of the title of the Wikipedia article Wave function collapse, which I think is wrongly written. It is, however, in agreement with Editor PAR's writing 'wave function', when 'wave' is an adjective and 'function' a noun, which I think is right.Chjoaygame (talk) 17:24, 4 November 2015 (UTC)

made an edit to the history section

I have made an edit here. The purpose of the sentence is to point to macroscopic phenomena. The organic molecules that were included in the list are not macroscopic. They are not even large as biomolecules go. This leaves the sentence without a reference. Though of course I don't question its current truth, I think a reference would be a good thing.Chjoaygame (talk) 20:16, 24 November 2015 (UTC)

"Seems perhaps mysterious" needs re-writing

This page needs attention from a trained physicist who is also a skilled writer/editor.

I don't have the technical training to do it right, but I know bad writing when I see it, and this page has some.

"Seems perhaps mysterious" has got to go. This is desperately un-encyclopedic:

• "Seems" has no place here: encyclopedias state facts, or degrees of certainty/uncertainty (that is: facts about limits to our knowledge)
• "Perhaps" has no place here, ditto
• Ditto "mysterious"

This is Wikipedia, not cable television. Let us explain technical subjects with technical language, stripped of all emotional appeal.

Without the condescending implication that You, Dear Reader (or more charitably We, Dear Readers, collectively), may not Get It (because, alas, it "seems perhaps mysterious").

Granted, somebody was trying to say "layman find this difficult to understand".

I am that layman, and I am making this complaint because I came here to out of personal curiosity to learn more about this notoriously difficult-to-understand topic.

There's a link at the top of the page -- "see Introduction to quantum mechanics" -- to cover this case. ("Seems perhaps mysterious" is no more appropriate to that page; I will look into that.)

As I said, I'm not trained, so I'm holding off. But I love this subject matter, and hate bad writing, so please, somebody with all the skills -- fix it, please.

General style tip: shorter (almost) everything. Shorter sentences. Shorter paragraphs. Not short words; always use the right words, of course. But shorter collections of words. Avoid the Semicolon like you would avoid the Jabberwock: it breeds run-on sentences. Be more like Hemingway: telegraphic. This would benefit a great many tech- and math-related articles, which tend to want to explain everything at once, rather than brutally condense the top section to essentials.

Karl gregory jones (talk) 01:17, 12 September 2015 (UTC)

A couple of sentences from the article:

Richard Feynman once said, "I think I can safely say that nobody understands quantum mechanics." According to Steven Weinberg, "There is now in my opinion no entirely satisfactory interpretation of quantum mechanics."

Both authors are very much respected.Chjoaygame (talk) 10:52, 12 September 2015 (UTC)

Feynman used the word 'mystery' in full deliberation:

In this chapter we shall tackle immediately the basic element of the mysterious behavior in its most strange form. We choose to examine a phenomenon which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of quantum mechanics. In reality it contains the only mystery. We cannot make the mystery go away by "explaining" how it works.

Likewise Weinberg:

My own conclusion (not universally shared) is that today there is no interpretation of quantum mechanics that does not have serious flaws, ...

Weinberg allows "perhaps".Chjoaygame (talk) 11:45, 12 September 2015 (UTC)

Another respected text reads:

With the wisdom of hindsight, today one can say that certain qualitative features of nature, apparent well before Planck and Einstein invented quantization, posed profound enigmas for the conceptual structure of classical physics.

Not much difference between mystery and profound enigma, I think.Chjoaygame (talk) 03:47, 13 September 2015 (UTC)

For the article to pretend that QM is not mysterious to its students as well as to its its practitioners is fraud. But I agree that Hemingway wrote better prose than most, in particular better than us. Feel free to edit the prose, even if you aren't an expert in the field at hand. YohanN7 (talk) 12:01, 16 November 2015 (UTC)

The problem is our intuition, which we enrich by our experience. We construe mental models, which are getting blown up by the experiments. A small list, which needs augmenting:

• local realism
• causality
• entanglement
• the yellow submarine (film) is a fair encapsulation of the subversive nature of the conflicts with the construed models. Clearly it is our intuitions which are in for some evolution. I am including a plug for the Heisenberg picture here. --Ancheta Wis   (talk | contribs) 14:03, 16 November 2015 (UTC)

Editor Karl gregory jones started this section indignant that he felt he was being condescended to by the words "seems perhaps mysterious". He said he read them as implying

that You, Dear Reader (or more charitably We, Dear Readers, collectively), may not Get It (because, alas, it "seems perhaps mysterious").

He added "Granted, somebody was trying to say "layman find this difficult to understand"."

No, that wasn't what was meant. There was in the writer's mind no thought that the reader was an incomprehending layman. What was meant was that in the body of the article it is indicated that to some of the brightest minds in the field there seems to be some element of mystery, that they feel cannot be understood, but not all share that view. Perhaps too much to summarize in three words.

I would not favour letting that indignation lead, in this article, to too much chatter about metaphysics, such as causality and spukhafte Fernwirkung, and reconstruction of our intuition. Particularly, I wouldn't favour the use of Bellspeak such as "local realism".Chjoaygame (talk) 10:28, 17 November 2015 (UTC)

@YohanN7, Heisenberg picture is the lead-in for Interpretations of quantum mechanics, as well as the interaction picture. Heisenberg_picture#Mathematical_details is the lead-in for Ehrenfest theorem, which is the basis for the averages upon which the correspondence principle rests. In other words, the averages are for a critical mass or better 'critical number' of instances after which our macroscopic notion of 'time increment' stabilizes. For a small enough number of instances, the averages corresponding to our macroscopic intuition have not yet formed. But the physical instances undeniably exist, even for that small number. The physical instances are still real and can be experimented for, currently at great expense.

But Heisenberg picture is abstract, and is based on concepts which become real to us, at a scale which lies beyond the table-top physics by which we came upon the science, 400-1000 years ago. But the 'ocean of truth' which lies around us (as Newton put it) still awaits us. These truths are not necessarily compatible with our comfortable current table-top intuition. --Ancheta Wis   (talk | contribs) 13:41, 19 November 2015 (UTC)

Hmm... I had a firm grasp of the Heisenberg picture. Or so I thought. Now, I have to reconsider. You made me dizzy YohanN7 (talk) 14:41, 3 December 2015 (UTC)

I apologize for its effect on our intuition.ツ --Ancheta Wis   (talk | contribs) 19:50, 3 December 2015 (UTC)

History

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

This section was added by this edit, dated 25 January 2013, by Editor Belief action. It seems that sections, such as this one, on this page that do not have their dates written into their front appearance are not scheduled for archiving.Chjoaygame (talk) 04:41, 19 December 2015 (UTC)

quantum physics/string theory

This is probably not new but at one time or another we have all been given the thought experiment of a three-dimensional ball moving through a two-dimensional world. For argument's sake let's say what the scientists are observing of the three-dimensional ball they call an “atom”. They mark its position and move on (two- dimensionally) in a measurable way to the next “atom”. At this point they shift the relative position of the “atom” (two- dimensionally) and then returned to their original starting point finding the first “atom” has shifted its relative position the same way as the second “atom”. Would this be a reasonable simplistic description of quantum physics: a change in one atom can have an affect on a seemingly unconnected atom? James Brian MacDonald 12/20/2015 ```` — Preceding unsigned comment added by James B MacDonald (talk • contribs) 08:19, 20 December 2015 (UTC)

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The latest cn tags

@N2e, It should be possible to use named refs in the article to address the multiple cn tags that have just appeared. For example, refs from the Davisson-Germer experiment, or the Solvay conferences ought to address at least a few of the tags. Several of the Abraham Pais histories cover them as well, because he knew the principal people. Let's work on this together.

I have to admit I am not aware of any biological phenomena that require a QM explanation (just guessing, perhaps the rhodopsins in the retina?). If no examples are forthcoming, that claim needs to be fixed. --Ancheta Wis   (talk | contribs) 13:20, 5 April 2016 (UTC)

Yeah, that's what I was thinking. The bio stuff seems very much in need of sourcing, but realistically, I think even the other stuff should be, which is why I challenged a few of the statements in the article. For example, the article asserts that semiconductors are an application of quantum mechanics; seems a bit intuitive, but not exactly "sky is blue" true. So methinks it appropriate to ask for citations that make the point, and to which wikipedia readers can turn to learn just how quantum mechanics play out in semiconductors, since that has not been explained in the article. N2e (talk) 15:52, 5 April 2016 (UTC)

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First one was behind a robots.txt prohibition, so was not archived. Second one I could find on the new website for Acta Physica Polonica B, so I replaced it in the article.  —jmcgnh^{(talk) (contribs)} 09:42, 13 June 2016 (UTC)

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First one was behind a robots.txt prohibition, so was not archived. Second one I could find on the new website for Acta Physica Polonica B, so I replaced it in the article.  —jmcgnh^{(talk) (contribs)} 09:42, 13 June 2016 (UTC)

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First one was behind a robots.txt prohibition, so was not archived. Second one I could find on the new website for Acta Physica Polonica B, so I replaced it in the article.  —jmcgnh^{(talk) (contribs)} 09:42, 13 June 2016 (UTC)

Foreign text in topic box?

Every page related to quantum mechanics that links to the topic box for Quantum Mechanics (I'm not sure what the box is actually called - sorry) appears in another language & script. Is it just my computer? I checked other pages and they all show the same thing to me. PhySusie (talk) 17:04, 8 July 2016 (UTC)

Never mind - it's not doing it now - thanks. PhySusie (talk) 17:28, 8 July 2016 (UTC)

External links modified

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Links to Wikibooks

I think all completed wikibooks shall be referenced on appropriate Wikipedia articles, at least the good ones. On this page, there is a link, on the left, to an unfinished wikibook on quantum mechanics. According to me, it shall be removed, because the book is unfinished. There are two completed wikibooks on quantum mechanics. I will add a reference to one of them, not to the other, because there would be a conflict of interest, since I am its author. --Thierry Dugnolle (talk) 07:17, 28 April 2017 (UTC)

Lead image caption

The lead image caption ends with the statement: The brighter areas represent a higher probability of finding an electron. But doesn't it have to read of finding the electron, since there is only one in a hydrogen atom? Sorry, if you should find this question silly – I'm not a physicist... Greetings--Hubon (talk) 00:53, 4 May 2017 (UTC)

PS: By the way, it might be useful to briefly explain what exactly we see in this picture – a computer simulation?--Hubon (talk) 00:59, 4 May 2017 (UTC)

There are only a few exact solutions to Schrödinger's equation; the hydrogen atom's electron orbitals is one of them (source: R.P. Feynman, my lecture notes). It's an exact picture of the electron's shape, at various excitations. A spherical shape would be the most common shape for an electron at the lowest energy state. The mathematical form of Schrödinger's equation is called a functional equation, a function of a function. I'm afraid you are going to have to give up the the electron part of your request. It helps to be relaxed about what you are seeing, when you are dealing with the uncertainty principle: (Briefly, if you zero in on a quantum-scale phenomenon, it will elude you, as your overt action will affect it). --Ancheta Wis   (talk | contribs) 10:29, 4 May 2017 (UTC)

You can trap electrons, see Penning trap. --Ancheta Wis   (talk | contribs) 10:34, 4 May 2017 (UTC)

You're right, Hubon, the caption should probably tell readers what they are looking at. "Wavefunction of the electron" would probably be better than "solution to Schrodinger's equation", although the term wavefunction is already in the picture. --Chetvorno^TALK 15:06, 4 May 2017 (UTC)

@Chetvorno: Thanks for commenting. So, if I understand you correctly, we basically see the graph of a mathematical function here, right? By the way, how come I didn't receive an alert after you mentioned me here? @Ancheta Wis: Thanks to you, too, tough I have to admit that I can't quite follow, and I'm also not sure whether your post really answers my question whether, and if so, why the caption in question should still give the impression as if there were more than one electrons in a hydrogen atom. Please excuse me if I seem to be dense on this issue. Best--Hubon (talk) 17:16, 4 May 2017 (UTC)

There would be one electron because a hydrogen atom, being electrically neutral, has one proton. --Ancheta Wis   (talk | contribs) 04:41, 5 May 2017 (UTC)

@Hubon: I changed "a electron" to "the electron" in the caption; thanks for catching that. The picture is a computer-generated simulation, calculated from mathematical solutions to the Schrodinger equation, showing the electron's wavefunction, the probability of finding the electron at different locations around the atom's nucleus, for different amounts of energy. The electron in the hydrogen atom can absorb different discrete amounts of energy, called its energy levels. I think the top left image is the ground state, the lowest energy state which is the state a hydrogen atom is usually in. The other drawings show the atom at higher energy levels; the electron could be excited to these levels by absorbing a photon of light, for example. For each energy level the electron's wavefunction, also called an orbital, has a different shape, meaning the probability of finding the electron has a different distribution in space. In quantum mechanics, an alternate way of viewing these wavefunctions is that an electron is a wave circling the nucleus, and the different orbitals are standing waves, the way a guitar string or jumprope can vibrate in different standing wave patterns. --Chetvorno^TALK 18:06, 4 May 2017 (UTC)

@Chetvorno: Thanks a lot for fixing that and clarifying the issue! I'm glad that finally my point is understood. Kind regards--Hubon (talk) 20:54, 5 May 2017 (UTC)

External links modified

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The introduction

The introduction says/said that 'Quantum mechanics differs from classical physics in that energy, momentum, angular momentum and other quantities of a system are restricted to discrete values (quantization)'. However, many properties are only restricted to discrete values when the system is 'bounded' -- e.g. a free electron can have any energy and any momentum (on a continuous scale), while an electron bounded in an atom only can have discrete energy values.

I made a slight change in the introduction, changing 'system' to 'bounded system'. It makes the sentence a bit more difficult to read and understand, but since there's a separate article Introduction to quantum mechanics I judged for correctness in favour of readability in this article. Happy to discuss, though.

--Itangalo (talk) 09:28, 16 October 2018 (UTC)

The initial condition needs to be stated; your latest contribution appears to assume a distribution of masses, as in a neutron star merger. I agree it could happen quickly, in that case. --Ancheta Wis   (talk | contribs) 09:46, 16 October 2018 (UTC)

@Itangalo: Thanks, but the literature seems to disagree:

Google	Scholar	Books
"quantum mechanics" "bound system"	3420	1410
"quantum mechanics" "bounded system"	539	116

I have undone your edit. I agree with the other edits. Cheers. - DVdm (talk) 09:50, 16 October 2018 (UTC)

Awesome. Thanks. --Itangalo (talk) 10:00, 16 October 2018 (UTC)

Status of photon theory

@Jip Orlando: The additions by the anonymous IP which you questioned here are basically correct, but they might possibly have been better phrased. See Einstein and the quantum, an article/section of which I am a 96% contributor. I do not know what percentage of acceptance there was in 1915. I do know that Bohr was an outstanding holdout until discovery of Compton scattering.

It would be OK for you or for somebody else to restore the verbiage, but maybe the some of the dates, etc. could be validated more closely. Prokaryotic Caspase Homolog (talk) 20:59, 25 October 2019 (UTC)

@Prokaryotic Caspase Homolog: cool, thanks! I will clean up a little of the writing style. Fun name, by the way. Jip Orlando (talk) 21:05, 25 October 2019 (UTC)

About the use of mathematics and the assumption of understanding in the Quantum Mechanics articles

In my opinion, all the articles related to the QM topic need to start with some general easy-to-understand statements that cover their topic, before they launch into an opaque sea of mathematics and technical minutiae. WP articles on QM should try, in my opinion, to teach the whole topic in a way understandable by any generally educated adult at the beginning of every article.

This is particularly relevant to the QM articles because much of QM runs counter to what we believe as obvious or commonsense physical ideas (the way nature works), due to our longtime and exclusive familiarity with the everyday world (macroscopic scale, relatively high temperatures, etc.). Our natural but limited intuition needs to be supplemented with an entirely new, different, and sometimes contradictory intuition that is correct for how nature works on a very tiny scale. It is a different world, one where tiny random particles with minute lifespans appear everywhere and everything is fuzzy, yet perfectly structured. It is a world best described by strange new kinds of mathematics, rather than commonsense laws of motion.

I never learned QM as an undergraduate, although I did major in physics (graduated back in 1968). I've learned something about QM in recent years from many sources, including published papers (such as from the wonderful arxiv.org), YouTube videos, articles in WP, and an online course at MIT. But I am currently having more success understanding the many concepts of QM from watching a video course in all of QM that is deliberately "watered down" (simplified) for the general intelligent public, through the Great Courses Plus streaming video channel. It is presented by one of the pioneering physicists in the fields of quantum computing and encryption who manages to make all the ideas easy to understand. This includes simplifying the mathematics. I find this useful so I can understand all the more general topics first, before I start learning the mathematics in detail. If the presenter of this course can accomplish this, which he does, then this serves as proof that the WP articles can be improved such that all the detailed QM ideas (example: the proof that quantum entanglement cannot provide faster-than-light communication) can be presented in a way that an intelligent adult can understand without confusion and without much mathematics. Two suggestions are to repeat some of the same ideas in different articles, and to focus on confusing concepts and add more words until the concepts have been clearly (even if not completely) described.

In my opinion, WP should start each technical article, and especially each QM article, with an "intuitive" or "descriptive" overview of the topic. The present article does this fairly well, starting with the fundamental idea that QM deals with what happens in nature on the scale of Planck's constant, which is unimaginatively tiny. But many of the other articles about specific QM topics do not do this well at all.

A random example is Quantum noise, which starts with an obscure, almost circular definition ("quantum noise refers to the uncertainty of a physical quantity that is due to its quantum origin"). This definition is only true with certain definitions of terms. After all, a quantum state, even a mixed or entangled state, has absolutely no noise: it is a quantized property. After this definition it launches into descriptions of various kinds of noise observed in the everyday regime, not the quantum regime, confusing the reader further. The rest of the article does avoid getting mired in mathematics, but the article is unmotivated and difficult to understand.

I can appreciate that QM can be understood on two levels: first, a simplified (and slightly incorrect) level that almost anyone can understand, and second, the full information, based on experiment and theory, as employed in the latest published papers on the subject. Some people want to learn at the first level, and some (such as professional physicists) want information on the second level, such as for quick reference. WP articles do make an attempt to address both levels, but it has a long way to go, in my opinion, to get the first level right. Comments and corrections are welcome. David Spector (talk) 20:34, 23 November 2019 (UTC)

In general, I agree with your criticism that the QM articles need to be better explained for general readers. However there is a Introduction to quantum mechanics article which is written for nontechnical readers, so I think it's ok that this article is written on a more advanced level. --Chetvorno^TALK 22:37, 23 November 2019 (UTC)

I would even venture to say that Introduction to quantum mechanics is the article that serves to solve the very problem brought up, if only for specifically the quantum mechanics article. For other articles such as the mentioned quantum noise, it may be beneficiary to attempt to start introduction sections. This could probably be brought up at a wikiproject somewhere, but I don't know how specific or general the problem may be. _{Integral Python} ^{click here to argue with me} 14:02, 25 November 2019 (UTC)

make page: quantum caustics

• https://www.google.com/search?q=quantum+caustics — Preceding unsigned comment added by 2A02:587:410E:CA26:4457:E00:4701:E3FC (talk) 14:47, 10 July 2020 (UTC)

Caustic (optics) — Preceding unsigned comment added by 2A02:587:410E:CA26:4457:E00:4701:E3FC (talk) 14:51, 10 July 2020 (UTC)