Talk:Stern–Gerlach experiment

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Pattern image needed

The article seems to refer to the visible image formed by a free electron on a screen in the S-G apparatus, but fails to include a photograph of such an actual image. I see this lack elsewhere as well. I think the article deserves a real photo of the S-G output, along with an explanation of why it is not a pair of separated dots or short lines as expected from theory. If this is not possible, an explanation of why no such image or explanation can be included would be appreciated. Perhaps I have missed something basic about the S-G experiment. David Spector (talk) 13:03, 25 August 2021 (UTC)[reply]

There is an excellent image of the result from a paper already cited on the page (available here https://plato.stanford.edu/entries/physics-experiment/app5.html). I see no reason not to include it, but what do you mean by "not a pair of separated dots or short lines as expected from theory"? As I see it there are two lines as predicted by the theory, they simply taper out as you go further from center due to the nature of the magnetic field. G1butler615 (talk) 16:33, 29 November 2021 (UTC)[reply]

Just to be clear, the article makes no claims about free electrons. The experiment involves Silver atoms, not free electrons. Johnjbarton (talk) 18:28, 21 February 2024 (UTC)[reply]

Potential future addition to the article

@D bar x recently added this interesting section. However the primary reference appeared this month, is uncited, and the work proposes rather than reports an experimental result. Based on other discussions on WikiProject Physics I have reverted the addition.

Very recently, it has become feasible to experimentally test whether a quantum superposition of two spin-direction wavepackets continue through the Stern-Gerlach magnet, as physics textbooks describe ^[1], or, rather, if transfer of a momentum quantum from the magnet reduces the wavefunction to a single spin-direction eigenfunction ^[2]. A very narrow two-slit screen can now be micro-fabricated. Placed at the exit of the magnet, it would display interference if there is no reduction; otherwise, no interference would be visible.

References

^ Merzbacher, Eugen (1961). Quantum Mechanics (1st ed.). New York: John Wiley & Sons. pp. 249–253.{{cite book}}: CS1 maint: date and year (link)
^ Devereux, Michael (2024). "A simple, practical experiment to investigate atomic wavefunction reduction within a Stern-Gerlach magnet". Journal of Physics B. 57: 152501 – via I.O.P.

Johnjbarton (talk) 22:11, 6 August 2024 (UTC)[reply]

TooSoon

I reverted an addition of content related to this new primary publication:

Devereux, Michael (2024). "A simple, practical experiment to investigate atomic wavefunction reduction within a Stern-Gerlach magnet". J. Phys. B: At. Mol. Opt. Phys.

Generally we use secondary references but there are exceptions for well-cited papers, multiple author papers, or papers from authors with long established publication records. @D bar x you could ask for consensus to include this paper on for example Wikipedia_talk:WikiProject_Physics but I believe the chances are other editors will agree with me that we should wait until this work has more backing. See ef WP:notnews or wp:toosoon. Johnjbarton (talk) 01:57, 28 August 2024 (UTC)[reply]

Someone, not me, inserted the last paragraph of the section on Importance. That physicist has also come to recognize that what we read in all our textbooks about the S-G experiment, namely that a coherent superposition of two spin wave packets continuously develops through the magnet, is mistaken. Obviously, the Wikipedia editors accepted that revision. This is not a trivial understanding about quantum measurement and the foundations of Q. M., but instead, is seminal. Just one example: Zurek's decoherence theory (Physics Today, October 1991) is founded on the assumption that there is a continuous wavefunction evolution through the S-G magnet which can be reversed (see his Figure 2). Because absorption of a momentum quantum reduces the superposition to one spin eigenfunction, reversible measurement is not real. So, of course, there is much resistance from those researchers who have uncritically accepted the received explanation. Please ask the editor of the very last paragraph in "Importance" to evaluate the significance of my suggested experiment, which could refute this persistent misunderstanding. As the famous philosopher of science, Karl Popper, explained, it is the refutation of mistaken hypotheses which produces progress in scientific understanding. And a scientific observation is the way that is done (see Stern and Gerlach).

I'll ask others at the Project_physics talk what they think. D bar x (talk) 18:29, 28 August 2024 (UTC)[reply]

It doesn't belong. Wikipedia's mission is to follow the mainstream scientific consensus, rather than attempting to lead it by the nose. XOR'easter (talk) 19:22, 31 August 2024 (UTC)[reply]

Also, you did add the last paragraph of the "Importance" section. XOR'easter (talk) 00:39, 3 September 2024 (UTC)[reply]

I'm about to pull my hair out (what little is left). I've tried, for over an hour to just join the list of participants on Project_Physics talk. Never mind adding a comment there. Why is Wikipedia so absurdly obtuse in this respect?D bar x (talk) 21:06, 28 August 2024 (UTC)[reply]

I would think Wikipedia would want to carefully explain whatever subject may be considered, not just tell readers the most popular, consensus opinion. The methods of science have shown, over five hundred years, that clear reasoning and controlled observation provide correct explanations to physical phenomena. (A very restricted subject area.) Proof is in the continued progress made in describing the material world. Consider the contrast between what Galileo discovered by observation of the planets with his telescope, and the demanding restrictions of that time's popular consensus. Was Boltzmann correct that atoms exist, or were his unanimous scientific detractors?

I believe the reason for so very little progress over the last hundred years in understanding the foundation of quantum mechanics is due to reliance on consensus, not objective critical reasoning. Even today, the consensus decrees that the wavefunction spin superposition in a Stern-Gerlach is real. It is, in fact, obvious from just a careful examination of the Schrodinger equation for the S-G magnet that the superposition collapses within the magnet, as detailed in the last "Importance" paragraph of this page. A very simple, practical experiment (the scientific method) very carefully examined by peer review in the Journal of Physics B, not consensus vetting, would show Wikipedia readers that the consensus is mistaken about this. D bar x (talk) 21:24, 1 September 2024 (UTC)[reply]

Sorry, but I disagree with your entire line of reasoning. For every Galileo/Boltzmann there are a hundred other theories which looked very promising to adherents but which we no longer consider valid. At the time there was no way to know which was which. Eventually science sorted it out. So it will be for the peer-reviewed paper you mention.

I guess that you mean that 100 years of QM did not turn out the way you wanted, because the idea that there is no progress in QM is absurd.

As for the last paragraph of the Importance section, you can challenge the content as not reflecting the sources or you can challenge the sources as not providing a neutral point of view, but such challenges depend upon a consensus of editors. Johnjbarton (talk) 19:27, 2 September 2024 (UTC)[reply]

True. Moreover, many papers make it through peer review and then sink into obscurity. XOR'easter (talk) 00:18, 3 September 2024 (UTC)[reply]

Silver atoms or silver ions?

The article keeps referring to the silver as atoms, even through they are being deflected by a magnetic field and must, therefore, be charged.

The reader is left to infer that the atoms must be ionized if they react to a magnetic field.

I think just a shot mention of the fact that they're ionized would be good. Rather than just outright replacing every instance of the word atom in the context of this description.

What do you guys think? VoidHalo (talk) 00:00, 1 March 2025 (UTC)[reply]

I suggest you read some of the references. The Friedrich/Herschbach, D. magazine article is a good start. There you will learn about atomic beams and atomic magnetic moments. Or you can just read the Wikipedia article where is says "The experiment is normally conducted using electrically neutral particles such as silver atoms. This avoids the large deflection in the path of a charged particle moving through a magnetic field and allows spin-dependent effects to dominate." Johnjbarton (talk) 02:07, 1 March 2025 (UTC)[reply]

[1] Merzbacher, Eugen (1961). Quantum Mechanics (1st ed.). New York: John Wiley & Sons. pp. 249–253.{{cite book}}: CS1 maint: date and year (link)

[2] Devereux, Michael (2024). "A simple, practical experiment to investigate atomic wavefunction reduction within a Stern-Gerlach magnet". Journal of Physics B. 57: 152501 – via I.O.P.

[1]

[2]