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

Revision as of 01:21, 29 September 2023

Revision as of 22:33, 6 October 2023

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The single/double slit image is simply wave interference, no duality shown. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 16:59, 29 June 2023 (UTC)

== [[Ehrenfest's theorem]] ==

Copying conversation from my talk page, as it seems best to continue here:

"Hi [[User:MichaelMaggs|MichaelMaggs]] I am a little confused by your comments concerning Ehrenfest's theorem and quantum mechanics, could you elaborate on why you believe it doesn't cure apparent quantum-classical paradoxes?

:--Best [[User:Bosonichadron2|Bosonichadron2]] <!--Template:Undated--><small class="autosigned">—&nbsp;Preceding [[Wikipedia:Signatures|undated]] comment added 20:58, 3 August 2022 (UTC)</small> <!--Autosigned by SineBot-->

::It's not correct to say that "Many of these paradoxes can be cured", as that implies that QM is wrong in some way. Most of the so-called 'paradoxes' are in truth things that appear from a day-to-day perspective simply weird. We should be explaining to beginner readers that such weirdnesses are unavoidable and are real, no matter how counterintuitive they may at first appear. They are not things that can be explained away by Ehrenfest or any amount of classical analysis. If there are particular and specific examples of beginner missapprehensions that [[Ehrenfest's theorem]] can help dispel, by all means let's include them. But we do need a specific reliable source for that, not just a statement to that effect. [[User:MichaelMaggs|MichaelMaggs]] ([[User talk:MichaelMaggs#top|talk]]) 10:02, 4 August 2022 (UTC)

:::I respectfully disagree with your first sentence, because if we take the definition of paradox as Webster defines it (using 2a) and replace it in the sentence that I wrote originally:

:::"Many of these paradoxes can be cured using Ehrenfest's theorem, which shows that the average values obtained from quantum mechanics (e.g. position and momentum) obey classical laws."

:::with the definition paradox:

:::Many of these '''statements that seem contradictory''' can be cured using Ehrenfest's theorem, which shows that the average values obtained from quantum mechanics (e.g. position and momentum) obey classical laws.

:::The above sentence certainly does not make a value judgement on the correctness either of the two classical or quantum "statements" it simply says that there are '''apparent''' contradictions. But then goes on to say that many of them are not contradictions at all, because of Ehrenfest's theorem.

:::With paradoxes like

:::"How is it that Newton's laws are wrong at the atomic scale, but then perfectly correct when dealing with systems which are simply large collections of atoms?"

:::easily being cured by Ehrenfest's theorem. These questions being the most natural, obvious and fundamental a student might bring up, mention of Ehrenfest's Thm is extremely helpful if not absolutely necessary. As to the point of citations, the entire purpose of Ehrenfest's Thm is to answer questions/paradoxes like the above and therefore satisfy the correspondence principle. I could add a citation, but it would just be a copy of the citations which are already present in the main article on Ehrenfest's Theorem, which I linked to and is well-written, so I believe a citation would be inappropriate for that reason.

:::What are your thoughts? [[User:Bosonichadron2|Bosonichadron2]] ([[User talk:Bosonichadron2|talk]]) 16:41, 4 August 2022 (UTC)

[[User:MichaelMaggs|MichaelMaggs]] ([[User talk:MichaelMaggs|talk]]) 12:02, 5 August 2022 (UTC)

:::: The third paragraph, with Feynman's quote, is all that needs to be said in the lead. [[Ehrenfest's theorem]] is far too subtle and sophisticated to be included in the lead of this beginner's article. No beginner following that link would be able to glean anything useful from even the first sentence of the Ehrenfest's theorem lead. More useful to a beginner would be a non-technical explanation of the [[Correspondence principle]], which is referred to lower down, but is not developed.

:::: The assertion that Ehrenfest's theorem (which is technically quite specific) "cures statements that seem contradictory" seems far too broad, and a reliable source for the exact wording to be used really is essential if it is to be mentioned. The E th article discusses nothing about apparent or real contradictions, let alone that the theorem can be considered a 'cure'. Few if any physicists would maintain that contradictions can be cured without (at the very least) a solution to the measurement problem. [[User:MichaelMaggs|MichaelMaggs]] ([[User talk:MichaelMaggs|talk]]) 12:02, 5 August 2022 (UTC)

:::::@[[User:MichaelMaggs|MichaelMaggs]]

:::::" The assertion that Ehrenfest's theorem (which is technically quite specific) "cures statements that seem contradictory" seems far too broad, and a reliable source for the exact wording to be used really is essential if it is to be mentioned. The E th article discusses nothing about apparent or real contradictions, let alone that the theorem can be considered a 'cure'. "

:::::After reading the article again, I think this is a good point, I'll find a citation.

:::::Is the word "beginner" defined anywhere? [[User:Bosonichadron2|Bosonichadron2]] ([[User talk:Bosonichadron2|talk]]) 12:21, 5 August 2022 (UTC)

::::::These "Introduction to..." articles are supposed to provide a non-technical overview of a subject for non-specialists, but with repeated edits there is a tendency for them to become more and more complex. Rather than "beginner" it would perhaps have been better to refer to the "non-specialist" or "non-physicist" reader. [[User:MichaelMaggs|MichaelMaggs]] ([[User talk:MichaelMaggs|talk]]) 12:39, 5 August 2022 (UTC)

:::::::Yes, "beginner" should not be used of someone with roughly a high school education who is curious about quantum mechanics and some of its specific topics. "Newcomer" also seems a bit judgmental. The legal definition "reasonable person" doesn't feel right. Is there such a thing as an "average person"? That would be my choice. Otherwise, I am fine with "non-physicist", except that many non-physicists may be fine with mathematics. In QM, as I've said, the truth can '''only''' be expressed fully in mathematics--that is the way that Nature actually works at the atomic scale; but WP articles ought not to include any mathematics in their lead or first few paragraphs, so as not to be off-putting. [[User:David spector|David Spector]] ([[User Talk:David spector|talk]]) 15:40, 8 July 2023 (UTC)

:::::::Both mathematics and "Ehrenfest's theorem" are forms of jargon: specialized vocabulary expressing complex ideas quickly to those trained in the subject. To be successful an "introduction" needs to focus on those un-trained in the subject but nevertheless interested. For a complex fundamental topic like QM, I would expect 'interest' to grow out of a curiosity and thus exposure to scientific and technical ideas. We shouldn't have to explain "atoms" or "electrons" as general concepts for example, but neither should we expect such a reader to be excited about the constants in Planck's blackbody radiation formula. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 15:55, 8 July 2023 (UTC)