Talk:Quantum mechanics

We need a section shortly after the lead titled something like "Quantum Systems" that defines what a quantum system is and goes into detail about the different types of quantum systems. I'm an IP editor so I can't edit the article.

The impetus for this is: There are many articles in Wikipedia which mention the term "quantum system" or "quantum mechanical system"; Like for example: https://en.wikipedia.org/wiki/Spontaneous_emission . I was reading that article and I wanted to know what a quantum mechanical system is. It is even linked in the article. So I followed the link and I get to the page for quantum mechanics, which explains the field of physics but does not readily define what a quantum system or quantum mechanical system is.

So in short, this article needs a section that goes over what a quantum mechanical system is, including the different types of common systems like molecule, atom, subatomic particle, and potentially many particle systems.

Something like the following:

== Quantum Systems == A quantum system is a physical system that can be analyzed using quantum mechanics. Quantum systems are fundamentally irreducible, in that to analyze the system one needs to know the total state of the system to make any useful observation on it. In contrast, an [[open quantum system]] is one where not all the information about the system need to be known to be able to make a useful analysis. Examples of quantum systems include: * [[atom]]s * molecules * subatomic particles * other many particle systems Mathematically, a quantum system is the [[tensor product]] of its component systems.<ref>https://www.sciencedirect.com/topics/engineering/quantum-system</ref> — Preceding unsigned comment added by 96.227.223.203 (talk • contribs)

I want to open a discussion about whether its reasonable to call Quantum Field Theories like QED (Quantum Electrodynamics) as categories of quantum mechanics.

To my understanding, quantum field theory is a part of quantum physics that developed from quantum mechanics to include special relativity (as well as other properties like creation and annihilation of particles).

The article begins with "Quantum mechanics is the fundamental physical theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms." However, whilst clear and informative for an audience unaware of the subject, I am not sure that this is accurate as quantum mechanics is not the fundamental physical theory that describes the behavior of matter and light -- that would be the standard model (or QED or some future model that humans have not come up with). If we include quantum field theory as a sub-category of quantum mechanics, then it would make sense, but again I am not sure that this is an appropriate categorisation.

An initial part of the article says: > Predictions of quantum mechanics have been verified experimentally to an extremely high degree of accuracy. For example, the refinement of quantum mechanics for the interaction of light and matter, known as quantum electrodynamics (QED), has been shown to agree with experiment to within 1 part in 1012 when predicting the magnetic properties of an electron. I do not think quantum electrodynamics is of quantum mechanics, so another test should be likely used. Oblibion123 (talk) 05:10, 12 December 2025 (UTC)

There was a discussion in WT:PHYSICS some time ago about whether we should try to distinguish quantum physics and quantum mechanics (you might want to search through the archives). The consensus was that this would be too confusing, as many sources treat them as synonyms. That makes QFTs (and QED in particular) part of quantum mechanics, and that's why the article is written the way it is.

You seem to have in mind that quantum mechanics means specifically non-relativistic quantum mechanics. But I think it's better to use the longer expression "non-relativistic quantum mechanics" when we mean that to avoid confusing the readers. Tercer (talk) 11:34, 12 December 2025 (UTC)

If this as been the past consensus, then I will not argue with it. It might still be a good idea to just emphasize that QED is the "extension of quantum mechanics" rather than "the refinement of quantum mechanics". Oblibion123 (talk) 20:46, 12 December 2025 (UTC)

I don't think we can solve this without a very convincing source as a basis for discussions. Here is one of the leading books on QFT:

• Quantum field theory is the application of quantum mechanics to dynamical systems of fields, in the same sense that the basic course in quantum mechanics is concerned mainly with the quantization of dynamical systems of particles.
• Peskin, M. E., Schroeder, D. V. (1995). An Introduction To Quantum Field Theory. United Kingdom: Avalon Publishing.

This makes QFT part of "quantum mechanics". Unfortunately I do not know of any term commonly used for the "quantization of dynamical systems of particles" other than "quantum mechanics".

Peskin/Schroeder indirectly explain the additional complication: the Klein-Gordon equation and Dirac equation are examples of relativistic quantum mechanics from the "quantization of dynamical systems of particles" branch of the topic. So, as they point out, the divide is between single-particle relativistic theory and multiple-particle relativistic theory. A multi-particle relativistic problem treated with single-particle theory will result in causality violations. But that won't stop popular discussions under the banner of "quantum mechanics". Johnjbarton (talk) 18:00, 12 December 2025 (UTC)

In the text where it talks about quantum tunneling the "Classic Route" looks a lot like energy states like where it it has the potential energy to tunnel but not to convert potential to kenetic because: 1. not enough potential energy anyway 2. you will always lose energy to friction. It reminds me of a model of polymorph 1 "Ritonavir" (unstable) to polymorph 2 "Ritonavir" (a lot more stable). I did reasearch and found that the dexmethylphenidate ("Focalin") I take is already in a stable form and it is unlikly there is a more stable form. If you want to talk to me, on the pages I will go more into chemistry then physics. MooMooMoo27 (talk) 13:28, 19 May 2026 (UTC)

The first sentence here is pointlessly pretentious:

• Quantum mechanics is the fundamental physical theory that describes the behavior of matter and of light.

This claim is contrary to how we generally describe theories: we don't proclaim any single explanation to be singularly true. QM is "a" theory that describes behavior of matter. The claim is contrary to the source, which does not say "fundamental". The claim is contrary to the rest of the paragraph which describes QM as a foundation of a bunch of other thing that describe the behavior of matter and light. If we delete a couple of words its a couple of words better:

• Quantum mechanics is a physical theory that describes the behavior of matter and of light.

Johnjbarton (talk) 16:51, 5 June 2026 (UTC)

I think fundamental here just distinguishes it from effective or phenomenological theories like electromagnetism or thermal/statistical physics (which also describe light and matter, but as effective theories). Just my two cents. Sławomir Biały (talk) 17:09, 5 June 2026 (UTC)

But these are all just conjectures that predict or agree with observations to varying degrees and circumstances. "Fundamental" expresses a belief rather than a fact; it is unprovable. "Foundational" makes more sense to me as that expresses the breadth of science built on QM; "the foundational" would express the unique character of this theory in modern physics. Johnjbarton (talk) 18:19, 5 June 2026 (UTC)

The difference between "the fundamental" and "the foundational" seems like splitting hairs to me, to be honest. I do not see how one conveys a fact and the other an opinion; to me, either could be read in either way if you really wanted to. Stepwise Continuous Dysfunction (talk) 18:26, 5 June 2026 (UTC)

If "fundamental" means the same as "foundational" then the word is redundant with the end of the paragraph so we can omit it. The end of the paragraph accurate lays out the pervasive role of QM among the sciences. Johnjbarton (talk) 21:13, 5 June 2026 (UTC)

But it doesn't explain that QM has no underlying theory. Stepwise Continuous Dysfunction (talk) 21:17, 5 June 2026 (UTC)

I would guess that almost every physicist would disagree, which is what the whole "interpretation of QM" bit is about. There are aspects which fit that description. Johnjbarton (talk) 21:38, 5 June 2026 (UTC)

Most interpretations of QM do not say that there is an underlying theory of which QM is an approximation or coarse-graining. Everettians accept QM as just true. QBists accept QM as just true. Consistent-historians don't believe in hidden variables. Interpretations that regard QM as a genuinely incomplete theory are all marginal. Stepwise Continuous Dysfunction (talk) 22:16, 5 June 2026 (UTC)

• Comment adding "the fundamental" is not necessary, given the next sentence describes it as the foundation of modern physics. I also mentioned in my edit summary string theory, which may be considered to operate on a more "fundamental" level. I support Johnjbarton's proposed sentence. Polyamorph (talk) 17:45, 5 June 2026 (UTC)

I'm not committed to the specific word fundamental, but I think we need some adjective there, and fundamental is better than any of the alternatives I've thought up so far. As Sławomir Biały pointed out, it's not an effective theory. The fact that it's not known to be an approximation to a deeper truth needs to be said somehow. The remainder of the paragraph doesn't do this; just saying that QM is the foundation of other topics doesn't go sufficiently far. Newtonian mechanics is the foundation of lots of topics, but it's not fundamental in the sense that QM is. I don't think it matters that the word is "contrary to the source", since that line is supposed to summarize the whole shebang and not be based on a single source anyway. Lose the footnote before losing the adjective, IMO. I also don't see the contradiction between saying that QM is fundamental and that it is the foundation of more specialized theories "that describe the behavior of matter and light". The fundamental thing is the fundamental part of the foundations of the more specialized things.

String theory is beside the point. It's not an established theory in the way that QM is, since it remains stubbornly beyond the reach of experiment, and it's not even more "fundamental" than QM, because it incorporates QM by construction. Stepwise Continuous Dysfunction (talk) 18:14, 5 June 2026 (UTC)

As an alternative, we could add a sentence that says, "It is a fundamental theory, in that it is not known to be an approximation to any more basic theory" (or words roughly like that). Stepwise Continuous Dysfunction (talk) 18:27, 5 June 2026 (UTC)

That's too verbose and unsourced. This isn't an uncontroversial thing to say given that it remains an active area of research and many researchers will argue the theory IS an approximation given it is incomplete. Polyamorph (talk) 21:29, 5 June 2026 (UTC)

But there is no established, well-defined, demonstrably successful theory of which it is known to be an approximation. It's not like Newtonian mechanics, which is an approximation to relativistic mechanics in one direction and to quantum physics in another. It's not like thermodynamics, which is a phenomenological theory where we deliberately gloss over the details and work with coarse-grained pictures of the world. Stepwise Continuous Dysfunction (talk) 22:12, 5 June 2026 (UTC)

The addition is not an improvement for two reasons. 1) it replaces a problematic (for some) word with a more verbose problematic sentence. 2) The lead is supposed to be a summary of the article. So it would be better to get this right in the main text, and then update the lead accordingly. Polyamorph (talk) 09:38, 6 June 2026 (UTC)

It's more verbose, but that's the cost of being more clear, rather than trying to pack too much meaning into a single, rather vague adjective.

And the article does discuss the import of Bell's theorem and the relation of QM to other established physical theories. The line in the intro seems a decent summary of all that. It could be improved, as could many places in the article, no doubt.

(This is SCD, editing from a friend's phone.) ~2026-33597-12 (talk) 17:00, 6 June 2026 (UTC)

I'm worried that our opening paragraph may be propagating a Wikipedia-ism. Is there actually an established division in meaning between the terms quantum mechanics and quantum physics? I have occasionally seen authors try to draw a line between them, but overall, my experience is that they're used pretty synonymously. For example, here's Zeilinger:

The quantum system cannot be assigned properties independent of the context of the complete experimental arrangement. This is just in the spirit of Bohr's interpretation. This so-called contextuality of quantum physics is another central and subtle feature of quantum mechanics.

And here's Jauch:

This is of course a classical experiment in optics and has, in this form, nothing to do with quantum mechanics. It becomes an experiment in quantum physics if one does this experiment with individual photons.

The preface to Hall's Quantum Theory for Mathematicians begins, "Ideas from quantum physics play important roles in many parts of modern mathematics. Many parts of representation theory, for example, are motivated by quantum mechanics...". If there's a distinction there, I can't see it. Here is a book that just says "quantum physics (or mechanics)" straight up. Julian Schwinger's Quantum Mechanics (Springer, 2001) says "quantum physics or quantum mechanics" (p. 1). Likewise, Jaeger uses "fundamental quantum physics" and "fundamental quantum mechanics" synonymously in a paper that our article already cites. Jochen Rau's Quantum Theory (Oxford UP, 2021) includes this passage:

Much of conventional quantum mechanics is dominated (and, arguably, obscured) by rather complicated mathematics, such as functional analysis or the theory of partial differential equations. This makes it sometimes difficult to disentangle the physical concepts from the mathematical methods. Introducing quantum theory under the aspect of information processing, on the other hand, would require only minimal mathematics: essentially, just finite-dimensional complex vector spaces. It would thus offer a much simpler, more direct route to quantum physics, all the way to some of the most fascinating conceptual issues.

Here, "quantum theory", "quantum mechanics" and "quantum physics" all appear effectively interchangeable. Stepwise Continuous Dysfunction (talk) 22:09, 5 June 2026 (UTC)

I do agree that "quantum theory", "quantum mechanics" and "quantum physics" are all synonymous, but I don't see where our leading paragraph is suggesting that there exists a distinction. Tercer (talk) 08:36, 8 June 2026 (UTC)

The second line is "It [quantum mechanics] is the foundation of all quantum physics". This implies that the two are related but different. (No one would say "quantum mechanics is the foundation of all quantum mechanics".) "Quantum mechanics" is treated like the part that all these other theories have in common. If the paragraph actually treated the terms as synonyms, it would be more like, "Quantum mechanics, also known as quantum physics, is ... It is the foundation of many disciplines, including quantum chemistry...". Stepwise Continuous Dysfunction (talk) 18:24, 9 June 2026 (UTC)

Fair enough, that sentence is gibberish. I think your proposal is fine. Tercer (talk) 21:31, 9 June 2026 (UTC)

Sources about QFT will explain why it is not QM, but another quantum thing. For example, the preface and prologue of A. Zee's Quantum Field Theory, As Simple As Possible, distinguishes QFT and QM. Thus equating QM with "quantum physics" is logically inconsistent. Nevertheless Zee says "quantum mechanics (or quantum physics as it is often called)". I think this a side effect of the elephant effect. "QM" means lots of different things depending upon the context/writer/reader. On one end it means Schrodinger equation, on the other of physics involving "quantum".

Our intro seems to have some specific definition in mind, but the entire article is about single particle, non-relativistic Schrodinger equation. So rather than the grandiose "foundational", the article actually sensible. Its definition of QM is the simplest model that include key ideas common to quantum theories.

To address your concern:

1. Put quantum physics as a synonym in the first sentence, per Zee.
2. Change the second sentence, eg: "The concepts of quantum mechanics have been extended and applied across many fields like quantum chemistry, quantum biology, quantum field theory, quantum technology, and quantum information science."

Johnjbarton (talk) 19:20, 9 June 2026 (UTC)

The redirect Quantum systems has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at Wikipedia:Redirects for discussion/Log/2026 July 21 § Quantum systems until a consensus is reached. Tercer (talk) 22:43, 21 July 2026 (UTC)

I removed the phrase and have been described as peculiar and mysterious from the introduction. First, the given source uses exactly the same words, "peculiar and mysterious", so as written this was illegitimate copying. Second, throwing a remark like that into the opening lines runs the risk of being obfuscatory. Third, exactly how "mysterious" we are supposed to find quantum mechanics, and what behaviors are the "peculiar" ones, is a subject of no little debate. As N. David Mermin once wrote:

The second generation, those who were students of the founding fathers in the early postrevolutionary period, seem firmly—at times even ferociously—committed to the position that there is really nothing peculiar about the quantum world at all. Far from making bons mots about dizziness, or the opposite of deep truths being deep truths, they appear to go out of their way to make quantum mechanics sound as boringly ordinary as possible.

The third generation—mine—were born a decade or so after the revolution and learned about the quantum as kids from popular books like George Gamow's. We seem to be much more relaxed about it than the other two. Few of us brood about what it all means, any more than we worry about how to define mass or time when we use classical mechanics. In contemplative moments some of us think the theory is wonderfully strange and others think it isn't; but we don't hold these views with great passion. Most of us, in fact, feel irritated, bored or downright uncomfortable when asked to articulate what we really think about quantum mechanics.

Italics his, bold mine.

I'm not completely opposed to a phrase along the lines of the removed text, in principle, but I think if we're to have it, we need to do it better. Stepwise Continuous Dysfunction (talk) 06:31, 18 August 2026 (UTC)

Come on, that's not plagiarism, we can definitely quote adjectives that have been used by the sources.

I do think calling it "mysterious" is stupid, though, that's a classic map-versus-territory confusion, so I agree with removing the sentence. Tercer (talk) 07:38, 18 August 2026 (UTC)

We can quote, but we can't lift the exact words without quotation marks. Stepwise Continuous Dysfunction (talk) 15:41, 18 August 2026 (UTC)

I disagree. That QM does not match "common sense" (whatever that means) and that its concepts are puzzling to anyone who believes that infinitesimal points whizzing around is intuitive are certainly among the most notable aspects of quantum mechanics as judged by many sources. The Mermin quote is further evidence of this, not a counter argument. Feynman, Mermin, dozens of other sources support a claim like the one removed. Johnjbarton (talk) 14:56, 18 August 2026 (UTC)

A source that says experts have asserted there is "nothing peculiar" about the subject is evidence that we should call it "peculiar" in the opening paragraph? Yes, Mermin himself doesn't hold that position, but the point is that it's more complicated, and the line we had didn't do justice to the situation. Stepwise Continuous Dysfunction (talk) 15:44, 18 August 2026 (UTC)

Mermin describes three positions taken by three different sets of experts. So he clearly thinks this is a notable aspect of the topic. The "nothing peculiar" phase was included by Mermin with words like "firmly", "ferociously", "commited" because it is obviously an artificial position. By the end of the passage he effectively circles back to the first phase:

• Most of us, in fact, feel irritated, bored or downright uncomfortable when asked to articulate what we really think about quantum mechanics.

I don't think this is complicated. QM is not consistent with mental models based on observation of daily life. That much is a salient aspect the topic, probably the only aspect widely discussed in almost every source. I think "peculiar" and "mysterious" sums it up, but other similar words could be used. The aspect, however, must not be omitted. Johnjbarton (talk) 17:01, 18 August 2026 (UTC)

"Peculiar and mysterious" means everything and nothing. Paraphrase instead your "inconsistent with mental models based on observation of daily life", it'll be much more helpful. ~2026-45353-99 (talk) 18:29, 18 August 2026 (UTC)

I don't see how Mermin can be read that way. He's saying that there was an entire generation of physicists who wouldn't have agreed with the claim that QM is "peculiar and mysterious". There's nothing "artificial" about it. And the third generation he describes (his own) is not like the first generation (Bohr, Heisenberg, etc.). Stepwise Continuous Dysfunction (talk) 03:59, 19 August 2026 (UTC)

I restored the phrase before realizing there was a discussion about it here. Contrary to the edit summary the use of the three-word phrase is not plagiarism; it is a direct quote. It needed quotation marks, which I have provided. I'm open to discussion about whether it is the best phrase or whether we should say something different, but leading off by calling it "plagiarism" isn't a good start for that discussion.--Srleffler (talk) 04:18, 19 August 2026 (UTC)

I know I'm being surly here, and part of my motivation for starting this thread was to explain myself more fully than in the edit summary, but it's plagiarism according to academic handbooks and Wikipedia's own guideline (see the second example, "No in-text attribution, no quotation marks, no change in text, inline citation only"). But fine. That aside, it's a phrase that lacks a clear meaning and, to the extent that a meaning can be given it, is disputable.

I'd be more content with phrasing like "often described as counterintuitive". We could probably even omit the footnote, since that would be backed up by the text about interpretations below. Stepwise Continuous Dysfunction (talk) 06:23, 19 August 2026 (UTC)

Length matters. Something as short as "peculiar and mysterious" never counts as plagiarism. Tercer (talk) 06:50, 19 August 2026 (UTC)

Even very short phrases can be distinctive (e.g., "Reader, I married him"; "The game's afoot"). Close copying is fine when there is no real variety in how one could make the statement, which can well be true for a short phrase, but brevity isn't the fundamental criterion. I think in this case that there are enough different ways that one could rewrite the phrase that copying it verbatim without quotation marks is illegitimate.

Anyway, in the hopes of shunting this thread into a more productive path, I have tried my hand at an encyclopedic paraphrase. Stepwise Continuous Dysfunction (talk) 07:13, 19 August 2026 (UTC)

I see you couldn't find an example that used only three words. "The game's afoot" is a terrible example; who exactly are you plagiarising by using it? Shakespeare? Conan Doyle? Mark Twain? It's just a common idiom. Tercer (talk) 07:36, 19 August 2026 (UTC)

That was just an example of a three-word phrase being distinctive, as a point of principle. I thought about picking one from the Mermin column linked earlier, like "ironfistedly soothing attitude" (three words, distinctive, would definitely require quotation marks if used in an article here), or "benignly humdrum" (even shorter, same concerns). I think it'd be fair to accuse me of plagiarism if I just dropped either of those phrases into a Wikipedia article without quotation marks, even if a footnote pointed to Mermin's essay. I didn't include those examples, because I didn't see the value in stressing that issue—not when the phrase was restored with quotation marks, making it technically OK, and we can focus on the more fundamental concern, i.e., what to say in that spot which isn't hopelessly vague or up for dispute. Stepwise Continuous Dysfunction (talk) 08:13, 19 August 2026 (UTC)

Being distinctive is not enough to make it plagiarism, it's still fair game to reuse such short expressions. In any case, "ironfistedly soothing attitude" and "benignly humdrum" are indeed distinctive: searching for these sentences with quotation marks returns very few hits, and all of them are very close to Mermin. "peculiar and mysterious", on the other hand, returns a huge amount of hits, most of which have nothing to do with quantum mechanics. Tercer (talk) 08:36, 19 August 2026 (UTC)

Best case, then, it's still ripping off Feynman's choice to use that wording to describe quantum mechanics specifically. It's still unmarked unoriginality, improper copying. The remedy would be exactly the same: add quotation marks at the bare minimum, or paraphrase. Honest, I've tried to see it your way, but it ultimately seems like a distinction without a difference, at most. I'm done trying to make my case about that, though. Deciding whether the counterintuitiveness of quantum mechanics should be mentioned at that spot, and if so, how exactly, is the important thing. Nobody here so far has been warmer than neutral about those particular adjectives, as far as I can tell; what's the best replacement? Should we keep the solitary citation to Feynman, supplement it with others, remove it and rely on the citations in the main text, or what? Stepwise Continuous Dysfunction (talk) 09:59, 19 August 2026 (UTC)

guys, can we please not crash out, i understand this but this could have been alot more simple if someone hadn't of said "that's (not) plagarism" please dont point fingers and please Always assume good faith in other users.

JG qwerty (talk) 02:13, 2 September 2026 (UTC)