Talk:Double-slit experiment

Add AB double slit in text?

A nice addition by Jähmefyysikko of an AB effect double-slit. I would consider including it here in more detail, carefully. I could ask the authors for images if needed as I know them. It is tricky, but it does include some deep QM results for non-contact interference etc. Ldm1954 (talk) 17:49, 5 September 2023 (UTC)

I also think a two-paragraph summary would naturally fit into the main text under Variations of the experiment. Having experimental figures (if that's what you had in mind) might be too much for this page. For main AB article they would be great. Jähmefyysikko (talk) 06:18, 8 September 2023 (UTC)

Copenhagen non-interpretation

The section "Copenhagen interpretation" contains a bunch of blather about the plurality of Copenhagens, but nothing about the interpretation of the double slit.

I propose to remove this section completely as redundant with the full page on the topic and to replace it with a section "Conventional interpretation" which simply gives an interpretation of the double slit experiments discussed here. Johnjbarton (talk) 17:41, 7 September 2023 (UTC)

I disagree. That would be your interpretation of things, and not encyclopedic. Ldm1954 (talk) 20:37, 7 September 2023 (UTC)

I'm confused by your reply. Any replacement would of course have to be reliably referenced.

My claim is that the current section is off topic. It says nothing about double slit experiments. Controversy about Copenhagen belongs elsewhere. Johnjbarton (talk) 21:54, 7 September 2023 (UTC)

I think it could be shortened and brought more in line with how the intro of the Copenhagen interpretation article currently goes, and then we could add more about what Copenhagen-type interpretations have said about the double-slit experiment specifically. XOR'easter (talk) 21:52, 7 September 2023 (UTC)

OK, I've taken a stab at doing that. XOR'easter (talk) 22:12, 7 September 2023 (UTC)

Awesome, thanks. Johnjbarton (talk) 22:25, 7 September 2023 (UTC)

Sorry, but I have the same objection to what you have written as to the edit of the many-worlds interpretation. You have changed that section from general to one specific interpretation in terms of complimentarity. Where has probability gone? Why are you limiting it? Why have you only given one connection?

What was impressive about this article a week or so ago when I made a redirect suggestion was that it tried to fairly represent all interpretations. Now it seems to be losing this, going downhill. Sorry for being blunt. Ldm1954 (talk) 05:24, 8 September 2023 (UTC)

Previously, the article said nothing about how any version/variant of Copenhagen applied to the double-slit experiment specifically. It just had a lengthy passage about how "the Copenhagen interpretation" is hard to pin down. Now there's at least a little about how to make the connection. I stuck to the Copenhagen-oriented books that I had close at hand and what they had to say specifically about the double-slit experiment. XOR'easter (talk) 06:31, 8 September 2023 (UTC)

I have rewritten it so, IMHO, it is balanced. It now includes the 1) complementarity interpretation, 2) the detection-collapse interpretation, and 3) the statistical probability interpretation. Both 2) and 3) are of course "Mermin-type", i.e. they follow directly from the math, they are not philosophical. Feel free to add a 4) and 5) if you feel they are relevant. Inclusivity please. Ldm1954 (talk) 07:29, 8 September 2023 (UTC)

I just didn't want to go beyond what the sources I had in front of me actually said. XOR'easter (talk) 15:25, 8 September 2023 (UTC)

2 and 3 are not referenced.

2 mixes up decoherence and collapse.

These 3 are not different things. #1 Complementarity refers to one aspect: the disappearance of the interference with path distinction. #2 decoherence provides a microscopic explanation for the disappearance within conventional QM. #3 The Born rule is very much a part of every Copenhagen interpretation surely.

I want to change this section to a fully referenced, clear conventional explanation, including a paragraph on decoherence. But I don't want to be in an edit war for this. So I think the better solution is to delete 2 and 3 until they are referenced. The references should include evidence that they differ from 1. Johnjbarton (talk) 15:50, 8 September 2023 (UTC)

Sorry, not true. They are all in the previous section. 2. is an undergraduate QM problem -- when you detect you change the state. It does not mix up decoherence and collapse, it is standard inelastic scattering that you can find in any QM book. Unless the detector is entangled with the incoming wave, there is a statistically random phase shift.

3. Is the Born rule.

Do you insist that complimentarity is the only explanation of life, liberty and the pursuit of happiness? I consider that inappropriate. Ldm1954 (talk) 16:01, 8 September 2023 (UTC)

Please do not misquote me.

Complementarity is simply one of several aspects of the conventional interpretation. These are not 3 different things, but three aspects of the same thing.

If the idea that these three things differ is so elementary, adding a reference should be easy. Johnjbarton (talk) 16:29, 8 September 2023 (UTC)

I'd be happy with what I wrote being expanded. I just think that in this area, it's very easy to wander into synthesis and also very easy to use words in a way that is misinterpreted. XOR'easter (talk) 16:29, 8 September 2023 (UTC)

I do not understand this revert rationale. The old version says A particular experiment can demonstrate particle behavior (passing through a definite slit) or wave behavior (interference), but not both at the same time. So does the new version. The old version invokes the Born rule; so does the new. What "one interpretation" is being insisted upon? XOR'easter (talk) 19:42, 8 September 2023 (UTC)

The edit removed everything except a complimentarity interpretation. That is not WP:NPOV. The Born & collapse/incoherence approaches are not the same. The Born probability is "Shut up and calculate" -- i.e. it is math and philosophy is not needed. The incoherence is standard Fermi golden rule for non-stimulated inelastic scattering. (Contrast with stimulated in a laser where coherence is preserved. Technically you have an incoherent zero-point term.) To detect you change,so long as you are not entangled. Ldm1954 (talk) 19:53, 8 September 2023 (UTC)

I undid that revert. The content removed was referenced and on topic: directly about double slit.

Point of view is not at issue. These references are about double slit. If you have other references about double slit, add them. No reason to remove the reliable existing content. Johnjbarton (talk) 19:58, 8 September 2023 (UTC)

That is exactly what I am saying. You are continually removing all reliable, standard content except a single, narrow view. I accept complimentarity as a philosophical concepts, but it is not the math. What I included is. Math rules, not philosophy. Please be inclusive -- that is one of the central principles of Wikipedia, and also science (done right). Ldm1954 (talk) 20:12, 8 September 2023 (UTC)

Please see Wikipedia:Balance Your Perspectives Ldm1954 (talk) 20:18, 8 September 2023 (UTC)

You are welcome to add balance. However it must be referenced. Please see Wikipedia:Verifiability.

I have no idea what "narrow view" you are complaining about. I am simply reporting what sources say as clearly as I can. The sources we have describe double slit experiments in terms of complementarity. If you think we have too much content about complementarity, find some source that gives a different perspective. I would welcome that. Johnjbarton (talk) 20:35, 8 September 2023 (UTC)

As would I. XOR'easter (talk) 20:43, 8 September 2023 (UTC)

As I already said, please see the reference on the Born rule, and also what you deleted.

For incoherence of inelastic scattering, please read any text book. If you deny this, you deny all spectroscopies and lasing versus spontaneous. Ldm1954 (talk) 09:09, 9 September 2023 (UTC)

As one simple source, see https://doi.org/10.1016/j.ultramic.2015.03.006 and references therein. You will see that Giulio does not cite complimentarity, nobody who really does research with electrons ever does. I may see him tomorrow, and will ask him. Ldm1954 (talk) 09:18, 9 September 2023 (UTC)

The article you link, "Elastic and inelastic electrons in the double-slit experiment: A variant of Feynman's which-way set-up" is a cool electron-which way experiment. They don't choose to cite complementarity for what ever reason, but their conclusions are the same: "Therefore, from this point of view, these experiments may be considered a very close experimental demonstration of the third part of the Feynman thought experiment, which states that interference phenomena disappear when the experimental conditions are set in a way to determine the slit through which the electron passes."

The role of inelastic scattering in the experiment is technological: it is their mechanism to determine 'which way': "Whereas the images taken by selecting the elastic electrons showed the presence of interference fringes, these phenomena were absent with inelastic electrons." "...we may conclude that the loss of coherence is related to the localization of the inelastic electrons within the slits."

Complementarity is just a name for an almost trivial observation: if you change the experiment to detect paths, interference goes away. It does not explain anything, which is why it is never proven "wrong" or excluded in any example. I do not think anyone can build an "alternative" case to complementarity; it is logically equivalent the lack of observation of particle superposition. You could absolutely say the paper does not mention complementarity, but it does not mention many other things as well. The paper does not make the case against complementarity or "for" and alternative. (Which in my opinion is a strength).

The paper would be a great addition to a section on decoherence in double slit experiments in the main body of this article. (All of this interpretation stuff including complementarity is really pointless in my opinion.) Johnjbarton (talk) 15:24, 9 September 2023 (UTC)

I give up, as you persist in misunderstanding, ignoring math. As you state it above complementarity is philosophy not phyiscs. The uncertainty principle is operator commutation; incoherence is density matrix/statistics; loss of coherence is perturbation theory. When you detect a photon/electron/elephant you add an incoherent phase shift. Giulio does not mention complementarit as he is a strong physicist, and knows elastic/inelastic scattering theory.

You continue to ignore everything else but one view, turning this article from somewhat inclusive to restricted. I will remove this page from my watch list. Ldm1954 (talk) 15:35, 9 September 2023 (UTC)

We're talking about the "Copenhagen" subsection of the "Interpretations" section. It is expressly about philosophy. People who espouse Copenhagen-type views say that the double-slit experiment illustrates complementarity. We attain NPOV not by saying all the things that you or I think are part of explaining the double-slit experiment, but by summarizing what the books written by Copenhagen proponents say about it. If what they emphasize is complementarity, then that's what the subsection should emphasize too. XOR'easter (talk) 19:52, 9 September 2023 (UTC)

I came upon this section again. I have added two small sections, one on "Standard quantum physics" with top-quality sources and "Bohr's complementarity" to reflect that rather more general and abstract concept but directly attributed to Bohr.

These two sections avoid insisting that complementarity is "standard". There are sources which would claim it is, but I also know that most textbooks don't teach complementarity.

I hope these changes will allow us to reconsider the "Copenhagen interpretation" section. I want to change this section to simply be a sourced Copenhagen interpretation of the double-slit experiment. Specifically I want to delete to first paragraph, which is not about double slit. It's a long distracting paragraph about historical issues in naming "Copenhagen". I would also delete the main wikilink as the section would not longer be a summary (which does not belong here IMO).

Unfortunately the second paragraph is not a sourced Copenhagen interpretation. It is a sourced interpretation which we have asserted is Copenhagen. Is there a quality source that describes the "Copenhagen interpretation" of double slit? Johnjbarton (talk) 16:04, 1 October 2024 (UTC)

The fundamental problem I have with this article is that I feel that too much is old, and does not reflect current thinking particularly in the electron microscopy/diffraction community. A more modern interpretation is nicely described in a recent article by Peter Schattschneider and Stefan Loffler at https://doi.org/10.1016/j.ultramic.2018.04.007; there are other papers as the idea goes back decades. The most common approach is density matrices, or the equivalent as mutual coherence as discussed in Born and Wolf. (I am not a big fan of the WP page mutual coherence (physics).)

Up until perhaps 2000 only a few people in the ED/EM community worried about these issues, mainly on the question of coherence (or incoherence) of inelastic scattering. With the advent of ACTEM they have become much more relevant. For instance, the only proper way to model the probe in a modern STEM is as a density matrix propagating through a sample.

I would like to see a 21st century interpretation along these lines included. Ldm1954 (talk) 16:52, 1 October 2024 (UTC)

I agree that there are many new interesting variations on the double slit experiment. We might be better off tackling these in a separate article first.

But the specific question I am addressing is two paragraphs in the section "Copenhagen interpretation". The long first paragraph muddies the waters and the second paragraph has three refs to Feynman (who I do not believe ever claimed to represent Copenhagen) and two refs to complementarity, at topic you previously objected to. This is the section I want to fix. Johnjbarton (talk) 22:45, 1 October 2024 (UTC)

I think that section does need to spell out the difficulties with the term "Copenhagen interpretation", since it is both common and confusing. The second paragraph, the one with the Feynman references, basically recapitulated the subsection above, so I removed it and made some other modifications. XOR'easter (talk) 22:56, 1 October 2024 (UTC)

Thank you. However the remaining paragraph has no sources related to the double-slit topic.

Peres is about double Stern-Gerlach. Omnes echos "experts disagree on what is meant by Copenhagen", but never discusses double slit. Faye, Camilleri & Schlosshauer, Scheibe, Rosenfeld, and Mermin are great on difficulties with Copenhagen but never talk about double slit.

So the first part is off topic and the last two sentences are synthesis. I'm not trying to be difficult, but I believe that either one of us would revert this type of content if it were about another topic. The article on double slit should reflect the sources on double slit.

I wonder if there is a suitable source: Copenhagen belongs to no one, so authority on the double slit would be unlikely to speak for "Copenhagen". Johnjbarton (talk) 23:38, 1 October 2024 (UTC)

Omnès discusses the double-slit experiment in The Interpretation of Quantum Mechanics under the names "two-slit device" and "Young interference device". XOR'easter (talk) 23:43, 1 October 2024 (UTC)

Thank you for correcting me. I've made the last two sentences more specific. I think we could just use Omnes refs, but the section is much improved, thanks. Johnjbarton (talk) 00:22, 2 October 2024 (UTC)

Sorry John, but you appear to have misunderstood my comments. I am not discussing variants, I am talking about the 21st century interpretation in the ED/EM community. Once you move from a single wavefunction approach to statistical with mutual coherence/density matrices there is no interpretation issue. However, you objected to including this way back which is when I stopped contributing to this article. Ldm1954 (talk) 10:43, 2 October 2024 (UTC)

N.B., just for this discussion, remember that all current ab-initio whether dft or other are statistical; single wavefunctions are for teaching. Ldm1954 (talk) 10:46, 2 October 2024 (UTC)

Many-worlds interpretation

The "Many-worlds interpretation" section has a single sentence. Ok I deleted the second one, an unsourced claim about many scientists.

This sentence provides no value in my opinion. It does not give enough information to inform.

I don't see anyway that many-worlds can differ from conventional interpretations for double slit. The differences in many-worlds does not show up until after the measurement, so all of the bit about probability distributions and which way analysis is identical.

Does anyone have a copy of the book cited in the sentence to clarify? Johnjbarton (talk) 01:34, 8 September 2023 (UTC)

I think the sentence is wrong, Deutsch is not claiming that double-slit is evidence for MWI, but is just using it as a device to introduce his interpretation. Here's the book: [1]. On p.45 he starts discussing parallel worlds. Jähmefyysikko (talk) 02:05, 8 September 2023 (UTC)

If you remove the section, you are forcing your interpretation onto the article. While I don't believe in the many worlds model, some do. It should be in for completeness and encyclopedic form. Ldm1954 (talk) 05:16, 8 September 2023 (UTC)

I agree. Instead of simple removal, this misleading sentence should be replaced by many worlds description of the experiment. And we can use Deutsch for that. Jähmefyysikko (talk) 05:40, 8 September 2023 (UTC)

I made an attempt at this, but as a source, I found Deutsch's book quite vague. A better source would be useful to make justice for this interpretation. Jähmefyysikko (talk) 07:37, 8 September 2023 (UTC)

https://plato.stanford.edu/entries/qm-manyworlds/ may be useful. Unfortunately it is all squeezing QM into words and philosophy, which is never going to be great. Ldm1954 (talk) 07:59, 8 September 2023 (UTC)

Something feels wrong with basing what we say on a pop-science book, like we're sifting through debris at the bottom of a cliff. XOR'easter (talk) 15:29, 8 September 2023 (UTC)

The Stanford work seemed strong to me, both unbiased and quoting numerous sources. Ldm1954 (talk) 15:43, 8 September 2023 (UTC)

The Stanford Encyclopedia article is good, as they typically are, but it doesn't address the double-slit experiment specifically. It covers some speculations about interference experiments on macroscopic bodies, which is probably too esoteric for our purposes here. We ought to explain what an MWI says about electrons and photons before we go haring off to Wigner's Friend. XOR'easter (talk) 15:49, 8 September 2023 (UTC)

In terms of WP:NPOV we need to include these interpretations unless it is unconditional that they are fake science. We state them, then if relevant point out their problems. For instance, for the Pilot wave I added, with citations, the issue that it does not work right when relativity is included. The Stanford article does mention some issues for many worlds; I am stuck waiting for a delayed international flight so I can't do more at the moment. Ldm1954 (talk) 15:52, 8 September 2023 (UTC)

+1 the book is fluff. Johnjbarton (talk) 16:20, 8 September 2023 (UTC)

David Wallace devotes multiple pages to discussing Deutsch's book in The Emergent Multiverse. Here's what he has to say about the double-slit part: Deutsch (1997) used the two-slit experiment—erroneously, I think—to argue for the existence of parallel worlds; however, in subsequent lectures he has shifted to something more like the Michelson setup I give here, and has noted (in conversation) that his point is better made in that context. And here's pretty much all Wallace has to say about double-slit experiment: [In] the two-slit experiment, there is no parallel-Universe description to offer of the interference process: there is just a quantum system in a very nonclassical state. I can't understand this: is there no measurement problem in the double-slit experiment? Then again, I do lack the background knowledge of the Everettian theory. Jähmefyysikko (talk) 19:14, 8 September 2023 (UTC)

Maybe useful, Google search on "many worlds double slit". There is at least one criticism. Use that to explain the rationale, then point out the problem. Inclusiveness. Ldm1954 (talk) 19:54, 8 September 2023 (UTC)

Regarding background for Everett's theory, Wheeler's two page summary of Everett's thesis paper is silliness free, light on math, and very clear.

Wheeler, John A. "Assessment of Everett's" relative state" formulation of quantum theory." Reviews of modern physics 29.3 (1957): 463. Johnjbarton (talk) 00:25, 9 September 2023 (UTC)

Everett's PhD thesis (available here) clearly says on pg 115 that his theory is wave-only. So the sentence "In each universe the particle travels through a specific slit, but its motion is affected by the interference with particles in other universes." is completely inconsistent with Everett's theory because it has no particles. Therefore the paragraph we have represents Deutsch's view as presented in a pop-sci book. Johnjbarton (talk) 15:35, 9 September 2023 (UTC)

I tried to wrangle the subsection a bit so that it is no longer reliant upon a single source. XOR'easter (talk) 20:56, 9 September 2023 (UTC)

New articles about interpretations

Here is a new Nature article about interpretations, Can the double-slit experiment distinguish between quantum interpretations? I didn't have time to read it yet, but looks interesting. Artem.G (talk) 06:04, 14 September 2023 (UTC)

This paper proposes turning the double slit detector 90 degrees such that the axis now measures intensity parallel to the main axis between the source and the slits. With atomic matter waves they claim measurements when compared to quantitative calculations could distinguish between some interpretations. Its not a long paper but it has 115 references!

I think the work is interesting but too early for use in Wikipedia. On interesting tidbit: they say photons do not act the same due to the "relativistic localization-causality problem" and cite several papers related to the Hegerfeldt theorem. It might be worth reading those refs for addition here. Johnjbarton (talk) 13:40, 14 September 2023 (UTC)

Same.--Chetvorno^TALK 03:49, 15 October 2024 (UTC)

Disagreement over lead sentence

There has been a recent disagreement over the lead sentence. I wanted to get in on the discussion so I thought I'd bring it here to the talk page, if that's okay.
Zanahary prefers:

In modern physics, the double-slit experiment demonstrates that light and matter can satisfy the seemingly incongruous classical definitions for both waves and particles.

Johnjbarton prefers:

In modern physics, the double-slit experiment demonstrates that light and matter can exhibit behavior of either classical particles or classical waves.

In the top version I think the phrase "...light and matter can satisfy the seemingly incongruous definitions of..." is needlessly convoluted. I'm not sure particles and waves actually have "definitions".

In the bottom version, I understand the reason for using "or" rather than "and" - matter and light don't exhibit these properties at the same time or the same part of the experiment. But I think "or" will be confusing for nontechnical readers, they will think: "Okay, this means some matter and light exhibits particle properties and others exhibit wave properties."

I'd suggest In modern physics, the double-slit experiment demonstrates that light and matter can exhibit behavior of both classical particles and classical waves. and clarify the circumstances later, or add the phrase but not at the same time.

--Chetvorno^TALK 03:42, 15 October 2024 (UTC)

Particles and waves do have classical definitions, and “classical particles/waves” doesn’t follow any verbiage I’m familiar with. ꧁Zanahary꧂ 03:46, 15 October 2024 (UTC)

I didn't quite understand. You are objecting to the terms "classical particles" and "classical waves" in John's wording? --Chetvorno^TALK 04:50, 15 October 2024 (UTC)

Yes. ꧁Zanahary꧂ 05:51, 15 October 2024 (UTC)

Maybe instead of trying to go straight to interpretation we should start with the facts. Maybe something along this line:

• In physics, the iconic double-slit experiment, with either light or matter, displays an interference pattern built up one event at a time. The individual event are consistent with quanta or 'particles'; the pattern is characteristic of waves. Quantum mechanics predicts these results while classical theories of particles or of waves do not.

Johnjbarton (talk) 15:34, 15 October 2024 (UTC)

Certainly not. That opening sentence could hardly be more opaque. -Jordgette [talk] 15:40, 15 October 2024 (UTC)

Perhaps you would care to propose a clearer alternative? Johnjbarton (talk) 15:56, 15 October 2024 (UTC)

@Johnjbarton: Agree with Jordgette. The introduction should be understandable by general readers. I mostly like your original lead, I can live with it. But what is your objection to:...can exhibit behavior of both particles and waves? I believe a lot of sources use this wording. The same photon that is absorbed at the screen as a particle becomes part of the collective interference pattern.--Chetvorno^TALK 17:33, 15 October 2024 (UTC)

The problem with the "exhibit behavior of both particles and waves" is that the word "particle" has two meanings, a BB-like object or a quanta. Readers assume BBs but most physics articles assume quanta. That is why I want to use "classical particle".

The "exhibit behavior" is the important bit for me, not 'or' vs 'and'. We just need to avoid making claims about what light and matter "are" vs our observations. I'm ok with your full original proposed version. Johnjbarton (talk) 17:49, 15 October 2024 (UTC)

I agree with all that, and using "classical particles" and "classical waves". Just so I understand, what is your preferred wording? --Chetvorno^TALK 01:04, 16 October 2024 (UTC)

My preferred version is the one in place. But your

• In modern physics, the double-slit experiment demonstrates that light and matter can exhibit behavior of both classical particles and classical waves.

is also fine. Johnjbarton (talk) 02:40, 16 October 2024 (UTC)

I agree with the above version. --Chetvorno^TALK 03:27, 16 October 2024 (UTC)

I still don't like "classical particles" etc. Can we do In modern physics, the double-slit experiment demonstrates that light and matter can exhibit behavior of both particles and waves, classically defined.? ꧁Zanahary꧂ 18:55, 16 October 2024 (UTC)

There is a little ambiguity in whether "classically defined" refers to the particles and waves, or "behavior". But I can live with it. --Chetvorno^TALK 19:31, 16 October 2024 (UTC)

You said above that "particles and waves do have classical definitions..." so what's wrong with "classical particles" and "classical waves"? We can link the adjectives to Classical physics to give readers more info. --Chetvorno^TALK 19:45, 16 October 2024 (UTC)