Talk:Introduction to quantum mechanics/Archive 5: Difference between revisions

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What is the proper relationship (as regards conveying useful information) between what people can see in the real world (in a lab if necessary) and what they can gain from abstract laws and equations? [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 18:24, 28 March 2014 (UTC)

{{Talk archive}}

== Spin ==

[[User:Patrick0Moran]] asked in a html comment "Is there anything more about spin that should be said here?"

Yes! The fact that it's something we can actually measure, i.e. the [[Stern–Gerlach experiment]].

Which then leads nicely on to what the consequences of the Stern–Gerlach experiment are. And they're vital: that QM is probabilistic, that measurement affects the thing being measured (wave function collapse), etc. Right now we don't explain any of this, though the section on entanglement relies on all of these concepts. [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 22:23, 1 April 2014 (UTC)

:I think the article on the Stern-Gerlach experiment is already about as suitable to an introduction as it needs to be. The thing that we may need to concentrate more on is the idea of something being quantized. If we can clearly explain that idea then we can fan out to cover polarization, spin, etc. as instances of phenomena involving quantization. We could then refer to the main experimental observations with their quantum characteristics, and give links to the main articles.[[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 21:31, 2 April 2014 (UTC)

::OK, so maybe we could add a "Spin" section between "Wave–particle duality" and "Development of modern quantum mechanics"? As you say, we could take some material from the [[Stern–Gerlach experiment]] article, though I think the focus here needs to be on the fundamental QM concepts that it illustrates, rather than on the experimental details. [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 14:03, 5 April 2014 (UTC)

I've just wikilinked [[quantum state]] and [[Pauli exclusion principle|exclusion principle]] in the Spin section, but these terms are just thrown in without explanation, so it talks over the target reader's head. Could somebody in the know make that part of the intro go a bit slower, please? Thanks everyone for a very helpful article. --[[User:Stfg|Stfg]] ([[User talk:Stfg|talk]]) 11:27, 16 April 2015 (UTC)

== Quantisation ==

Before we do anything special on spin, which is pretty hard to understand because it is a kind of analogy to macro-world spin, I think we need to set things up by discussing quantisation.

Quantisation is something that is so pervasive that it fades out of the discussion and into the background in most writing on quantum mechanics. When it is discussed by people who do not come with a clear understanding of fundamentals, they may believe that frequencies can't have fractional values or that a wavelength that is some fraction, e.g., 1/3, of some known wavelength is impossible in nature. It is important to introduce the idea that the physical process determines how much energy is absorbed or freed in one event, e.g., the fall of an electron in a hydrogen atom from a higher orbital to a lower orbital, that sets both the frequency of the photon involved, its wavelength, and its energy. The early researchers were dealing with hydrogen lamps in a single intertial frame, and they may have unintentionally implied that anybody measuring the energies of the visible hydrogen spectrum would get the same results (even if they happen to be in a spaceship approaching earth at some substantial fraction of c).

To go from that kind of quantisation to the kind that is involved in spin or polarization is going to be difficult. I am not sure yet of how (or whether) to say anything more about it than that it happens — it's either spinning this way or that way, with nothing in between.

When I read one of Einstein's books intended for the general public while in high school I was quite impressed with the way he would set the reader up with all the information needed to anticipate the conclusion he was going to announce. He was like a writer of a detective novel who wrote so that the readers would always figure out who did it before the detective announced why he was arresting somebody. If we can supply beginning readers (i.e., readers who do not already know what the answer is) with an adequate understanding, then we can forestall their going off in some wild direction and getting themselves thoroughly confused. Einstein seemed never to throw out false leads. (Maybe he just had a good editor, but I doubt it.)

I must attend to grass mowing to forestall problems with city government, so I'll have to come back to the problem a little later. [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 17:51, 6 April 2014 (UTC)

:Don't we already discuss quantisation? Quantisation of energy emitted in thermal radiation, light being quantised as an explanation for the photoelectric effect, quantised energy levels in the atomic models... I can think of a really nice demonstration of something else that's quantised, it's called the [[Stern–Gerlach experiment]]... (Thinking about it further, I don't really want to talk about spin at this stage, more about the things I mentioned above, i.e. QM being probabilisitic, the effect of measurement, etc. Exactly what it is that is quantised is difficult to explain, and I agree with you that probably best to just state that it happens.) [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 21:58, 6 April 2014 (UTC)

I think there must be an energy quantum connected to angular momentum. Spin and counter-spin would then be numerically positive and negative (in the same sense that if motion toward the east is calculated on the x axis from an arbitrary 0 point to or toward a positive value, then motion to the west is "negative"). [[User:Patrick0Moran|P0M]] ([[User talk:Patrick0Moran|talk]]) 20:35, 6 April 2014 (UTC)

:There is a quantum number connected to angular momentum, and also one connected to spin. As you say, the different quantised values can be labelled as +ve and -ve, for example see the Pauling quote in the article. It is not "an energy quantum". [[User:Djr32|Djr32]] ([[User talk:Djr32|talk]]) 21:58, 6 April 2014 (UTC)

== Overview Too Long ==

For brevity and quick reference by the average reader, maybe condense the opening overview.--[[User:Lucas559|Lucas559]] ([[User talk:Lucas559|talk]]) 17:32, 20 June 2015 (UTC)

== copyright issue. copy and pasted from the web ==

[[user: 183.83.151.17]] https://en.wikipedia.org/w/index.php?title=Introduction_to_quantum_mechanics&diff=667204247&oldid=666392559 Please paraphrase this edit.--[[User:Lucas559|Lucas559]] ([[User talk:Lucas559|talk]]) 17:36, 20 June 2015 (UTC)

:This content was removed. <span style="font-family:Comic Sans MS; color:grey;">[[User:RockMagnetist|RockMagnetist]]([[User talk:RockMagnetist|talk]])</span> 23:36, 25 October 2015 (UTC)

==Postulates of Quantum Mechanics?==

This article doesn't seem to go into the postulates of quantum mechanics (aside from a brief discussion about eigenstates without really explaining what eigenstates are). I don't think it would be too difficult to explain the postulates of QM in a beginner-friendly way, and not explaining the postulates would mean that readers don't get to learn about the heart of the theory. Plus, the point where students grasp the postulates of QM is usually the point where QM finally "clicks" with them and they realize how simple it is, so if the postulates could be explained, then this article might be a lot less confusing to beginners.

So are the postulates of QM beyond the scope of this article, or is it okay if I (or others) include an explanation of the postulates? --[[User:J00cy|J00cy]] ([[User talk:J00cy|talk]]) 09:41, 25 October 2015 (UTC)

== Intent to add and the immediately remove an image of horses. ==

Horses are gone, but preserved in the history page. FYI, some of us are trying to start a wiki Journal that selects quality articles and preserves them so that teachers may confidentally use the approved version. See [[Wikiversity:First Journal of Science]].--[[User:Guy vandegrift|Guy vandegrift]] ([[User talk:Guy vandegrift|talk]]) 03:47, 11 January 2016 (UTC)

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