Talk:Introduction to quantum mechanics

encyclopedic tone

I removed the template:tone after I removed some uses of pronouns. If you have other specific complaints about tone, please add them here. Johnjbarton (talk) 17:29, 16 March 2024 (UTC)

Quantum entanglement

The section on "Quantum entanglement" says

• Nature leaves open the possibility, however, that two electrons can have both states "superimposed" over each of them.

There is no such thing. Quantum states are superimposed. They are not "over" electrons.

• Recall that the wave functions that emerge simultaneously from the double slits arrive at the detection screen in a state of superposition.

Where do I start? "emerge simultaneously" ? "functions...arrive at the screen"? And so on. The section may well be renamed: "Many things to unlearn about quantum mechanics". Johnjbarton (talk) 17:38, 16 March 2024 (UTC)

The fundamental problem with the "Quantum entanglement" section is the doomed attempt to explain these issues using "particle" models. Superposition and entanglement are quantum phenomena, in fact quintessential quantum phenomena.

Unfortunately describing the phenomena correctly with QM with references at an introductory level is not easy. Most introductory texts assume readers want to know about particles and fall in to the trap of giving them what they want. Johnjbarton (talk) 18:19, 16 March 2024 (UTC)

EPR in "Introduction"

The EPR experiment confounds even advanced students of physics. The amount of space it takes in this "introduction" is not warranted IMO.

I think the key facts for introduction to EPR are:

• Einstein challenged QM, expecting to make the case for hidden variables.
• Bell described an experiment which would test for hidden variables.
• Experiments verified QM and not hidden variables.

So nothing about entanglement/locality etc is really introductory. All that needs to be explained are "hidden variables", and very little about that. Our wikilinks can lead the curious to read more.

The discussion of "entanglement" should be part of the egregiously missing section on superposition. Johnjbarton (talk) 15:59, 17 March 2024 (UTC)

I don't think the topic of hidden variables can be covered without the concept of entanglement. Every no-hidden-variable theorem that doesn't use a many-particle state and entanglement is even more frightful to explain (e.g., Gleason's theorem). But entanglement is an important enough idea that an introduction could justifiably approach it from multiple directions, e.g., one section focused on no-hidden-variables results and another that tries to convey something about superpositions of tensor product states not being separable. XOR'easter (talk) 16:37, 17 March 2024 (UTC)

EPR managed to define hidden variables in one sentence: "While we have thus shown that the wave function does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists."

We know there is a lot of nuance in the Bell analysis, but the question I raise is "what single fact about EPR is notable for someone with no QM background"? Theorems and entanglement do not make my candidate list. It's pointless to bring them up because we can't provide enough context for such a reader to get anything valuable from them. (A form of argument I have learned from @XOR'easter ;-) Johnjbarton (talk) 17:11, 17 March 2024 (UTC)

I don't think it's impossible to provide that context.

If the question is "what single fact about EPR is notable for someone with no QM background?", the answer might well be "Einstein was part of it".

I'm certainly not dedicated to the text as it currently stands. My edits were just to replace the long meander that was there before with text adapted from articles that have been more thoroughly vetted. XOR'easter (talk) 17:17, 17 March 2024 (UTC)

Yes I understood that, and its definitely better! Johnjbarton (talk) 17:38, 17 March 2024 (UTC)

Wave function collapse

I propose to delete this section. This is common topic in interpretations but not a matter subject to experimental observation. The current text makes statements that are not correct and which present a way of thinking outside of quantum physics, eg "its quantum wave function has disappeared with it." The presentation of a time-independent wavefunction with language of time-dependence is simply incorrect. Also no references.

The absence of a complete model for measurement is notable but I don't know of any source that we could cite explaining how QM can be both one of the most well verified models and yet not have such a model. Johnjbarton (talk) 17:37, 17 March 2024 (UTC)