Talk:Many-worlds interpretation

Theory not mentioned here

Some scientists claim that when a solution results to many answers, all occur at the quantum level of the same universe, and when the first generation of these parallel solutions of a single wavefunction become involved in a new interaction, all the wavefunction collapses to the new point of least energy, and the secondary wavefunction expands from there, and it repeats the process again and again. So we have one universe with scouting wavefunctions (Feynmanism).

This is an extremely mainstream idea and we must analyze it better.

The word observation is erroneous, silly and romantic.

Matematically only percentages of strength of interactions exist. I compose poetry but it's a result of the memoremotional ( < memory + emotional ) limbic system, not of the analytical frontal lobe, neither a result of the mathematical parietal lobe.

Thanks for showing, in the first paragraph, who coined the term "many worlds." .... However,

... however, it would be helpful if you could include in the first paragraph the name Everett gave to his theory. I read it somewhere and I'm looking for it again 2600:8801:BE31:D300:487F:9A92:9BAB:92D2 (talk) 17:55, 19 July 2022 (UTC)

That is included in the History section. It's not relevant enough for the lead, as hardly anyone uses that name. Tercer (talk) 06:19, 20 July 2022 (UTC)

Unfortunately the term "Many worlds interpretation" has multiple meanings. Everett's thesis is one complete version but it is named "relative states". Deutsch "Fabric of Reality" version is way off this track. Johnjbarton (talk) 17:14, 9 September 2023 (UTC)

Quantum Field Theory

Everett's original article states that the MWI (then known as RSI) covers quantum field theories, but there is no mention of this in the article. cheers, Michael C. Price ^talk 08:10, 8 December 2022 (UTC)

Incorrect citation

The article says under Properties:

"MWI removes the observer-dependent role in the quantum measurement process by replacing wavefunction collapse with quantum decoherence."

Giving the reference Zurek, Wojciech (March 2009). "Quantum Darwinism". Nature Physics. 5 (3): 181–188. arXiv:0903.5082. Bibcode:2009NatPh...5..181Z. doi:10.1038/nphys1202. S2CID 119205282.

But the Zurek article explicitly disavows any connection to Everett theory. In a paragraph citing Everett's PhD thesis Zurek says: "Indeed, “reality” or “existence” of universal state vector seems problematic." "And there is only one copy of the Universe. Treating its state as if it really existed [26, 27, 28] seems unwarranted and “classical”." Johnjbarton (talk) 17:21, 9 September 2023 (UTC)

I also think this sentence has cause and effect backwards. Quantum decoherence theory was developed by Zeh after reading Everett. So this sentence is an invention.

Since interpretations are not theories, their role is to spark new ideas which then become testable theories. Johnjbarton (talk) 17:39, 9 September 2023 (UTC)

Zeh read Everett after developing his ideas but before publishing; he came to the idea of a universal wavefunction independently [1][2].

Perhaps we could tweak the article to say "Modern versions of MWI...". XOR'easter (talk) 21:14, 9 September 2023 (UTC)

Thanks for the refs, very interesting.

I would prefer not to maintain the fiction that there is a MWI. That's how we get into these long-winded discussions about what MWI/Copenhagen/Duality/etc means. Rather I think we should report what the sources say. I guess you would agree that we shouldn't say Zurek's work is about MWI when it clearly is not. Similarly I think it synthetic to group Zeh/Zurek under MWI. MWI should be DeWitt's and I guess Deutsch or whomever avows it. It's fine to say the DeWitt builds on Everett and that's how we come to discuss Everett here, but his work is "Relative state" and Zurek's is "Quantum Darwinism" (or several other possible titles, depending on the decade). Johnjbarton (talk) 21:40, 9 September 2023 (UTC)

The point is that modern Many-Worlds does incorporate decoherence. See e.g. the book by Wallace "The Emergent Multiverse". We do not present the ideas in chronological order here, or pretend that Many-Worlds started and ended with Everett's paper. Tercer (talk) 02:20, 10 September 2023 (UTC)

I'm not saying that the sentence would be removed; I didn't remove it because I think it is correct. However the reference is not correct.

If your claim is correct, then the reference in the sentence should be to Wallace, not Zurek.

(We should also not pretend that Many-Worlds started with Everett's paper because he never said that.) Johnjbarton (talk) 15:10, 10 September 2023 (UTC)

I agree that the reference should probably be replaced. A paper that is skeptical about the existence of a universal wavefunction isn't advancing the kind of interpretation that the text here implies it is. Nor is the Zurek paper a systematic review of what other people have proposed. XOR'easter (talk) 17:32, 10 September 2023 (UTC)

Distortion of Everett's thesis?

The article cites Everett's PhD thesis when it says: "MWI was developed with the explicit goal of allowing quantum mechanics to be applied to the universe as a whole, making quantum cosmology possible."

Here is what Everett actually says about his motivation:

Nevertheless, we have a strong desire to construct a single a11-embracing theory which would be applicable to the entire universe. From what stems this desire? The answer lies in the second type of prediction - the discovery of new phenomena - and involves the consideration of inductive inference and the factors which influence our confidence in a given theory (to be applicable outside of the field of its formulation).

I changed the text to make this clearer. To be sure it's still not correct, as the sources on quantum cosmology point to multiple origins for the MWI-like ideas. Johnjbarton (talk) 22:27, 10 September 2023 (UTC)

The article says:

Everett noted that such entangled systems can be expressed as the sum of products of states, where the two or more subsystems are each in a state relative to each other.

But Everett never uses the word "entanglement".

Am I being pedantic? Shouldn't we report what people said or at least make it clear that we are reinterpreting things they said? Johnjbarton (talk) 22:39, 10 September 2023 (UTC)

Yes, you are being pedantic. Physics is already complicated enough without insisting on "original" terminology. There's no doubt that Everett was talking about entangled states. Tercer (talk) 07:34, 11 September 2023 (UTC)

If there is no doubt then we should easily be able to find a source to back that up. (I agree that is what he means, but IMO it is wrong to say the people said things they did not in fact said). Johnjbarton (talk) 14:30, 11 September 2023 (UTC)

MWI is a realist, deterministic and local theory?

Realist? There is only one state for whole universe, how can the observer's mind not be involved? Deterministic? Only in the same sense that all QM is deterministic. As soon as we exam the results we discover randomness of outcomes. Local? The way we get determinism is by having a whole-universe state.

There is a ref in the next sentence: let's look!

"There is a consistent Lorentz covariant model of quantum phenomena which violates local causality but is local in Bell’s 1964 sense: the Everett picture."

and

"In our discussion of locality in the Everett interpretation we have sought to provide a constructive example illustrating precisely how a theory can be dynamically local, whilst violating local causality; "

So, is it local? Deterministic?

I assert that the given reference provides ample evidence that no simple sentence like the one in the article is sensible. Johnjbarton (talk) 02:26, 11 September 2023 (UTC)

What part exactly do you want to change? The quotes support the interpretation being local. MWI is deterministic in contrast to interpretations that propose one outcome is chosen randomly and the others don't happen. Having only one state for the whole universe makes it a realist interpretation. No minds involved. --mfb (talk) 02:35, 11 September 2023 (UTC)

I want to change the paragraph to fairly reflect the content of the source. That is clearly not the case now.

My preference would be to delete the paragraphs. These "properties" are not physics or science. They are not measurable or falsifiable. They are philosophical categories whose meaning and value have been debated for centuries. That debate continues as the source cited -- in a philosophy/history journal -- makes abundantly clear.

Any claims made beyond this source need references. I have some to contradict the paragraph that I can add as well. Johnjbarton (talk) 14:27, 11 September 2023 (UTC)

Just to give some examples of the challenges of these categories, Leggett describes "macroscopic realism" Leggett, Anthony J., and Anupam Garg. "Quantum mechanics versus macroscopic realism: Is the flux there when nobody looks?." Physical Review Letters 54.9 (1985): 857. And of 'nonlocal realistic' theories: A J Leggett 2008 Rep. Prog. Phys. 71 022001. There are articles in philosophy journals like Lambare, J.P. "On the Meaning of Local Realism". Found Phys 52, 98 (2022). https://doi.org/10.1007/s10701-022-00618-1 and so on. I can fill pages with sources for these kinds of issues.

So rather than attempt to fit MWI into categories that are themselves debatable, we would be better off starting with what MWI says directly or what sources say about MWI in regards to these characteristics. I also think this is more interesting for readers. Johnjbarton (talk) 23:18, 11 September 2023 (UTC)

There's zero controversy about Many-Worlds being realist and deterministic. About locality, one might need to distinguish between dynamical locality (about which there's no controversy) and state locality (about which there is controversy). Tercer (talk) 07:40, 11 September 2023 (UTC)

Great so it won't be difficult to add sources. Johnjbarton (talk) 14:28, 11 September 2023 (UTC)

Observers

(I want to be clear: my criticisms of this article are aimed at making it clearer, more correct, and more verifiable.)

In one part of the article we read "MWI removes the observer-dependent role in the quantum measurement process ..." Later we read a lot of discussion that contradicts this claim, eg "what the observer sees and the state of the object have become correlated by the act of measurement or observation. "

These both can't be true. I believe the first one is not correct. I think the sentence is motivated by some fringe interpretations of QM involving human thought processes. But that is not an orthodox interpretation and thus the meaning of "observer-dependent role" needs referencing. Johnjbarton (talk) 15:18, 11 September 2023 (UTC)

Wheeler's view of MWI in later years.

I remove this line once and plan to do so again:

Everett had already left academia in 1956, never to return, and after his death, Wheeler disavowed the theory. 

The sentence references Osnaghi, Stefano; Freitas, Fabio; Olival Freire, Jr (2009). "The Origin of the Everettian Heresy". Studies in History and Philosophy of Modern Physics. 40 (2): 97–123. Bibcode:2009SHPMP..40...97O. CiteSeerX 10.1.1.397.3933. doi:10.1016/j.shpsb.2008.10.002.

But when you read the reference you see that Wheeler's disavowal was only claimed by Dewitt. And as I quoted in my first removal, the same source in the same paragraph says "As is apparent from this passage, Wheeler’s attitude towards Everett’s work was not as clear-cut as described by DeWitt".

Thus this contentious disavowal is incorrectly reported in the article.

We could go in to all of this, but to me its a silly He said/She said. Wheeler published top physics articles long after Everett's death so he had plenty of time to publish a disavowal.

And Wheeler does some serious disavowing related to MWI. Specifically writes against the universal wavefunction thing as part of his critique of the notion of determinism. I will include that work in the article. In the meantime the incorrect information should be removed. Johnjbarton (talk) 23:32, 11 September 2023 (UTC)

In Search of Schrödinger's Cat John Gribbin, page 246

Perhaps it is only fair, at this point, to mention that Wheeler himself has recently expressed doubts about the whole business. in response to a questioner at a symposium held to mark the centenary of Einstein's birth, [Wheeler] said of the MWI, "I confess that I have reluctantly had to give up my support of that POV in the end, much as I advocated it in the beginning - because I'm afraid it carries too great a load of metaphysical baggage."

cheers, Michael C. Price ^talk 02:38, 12 September 2023 (UTC)

Here's the original source of the statement. It is a discussion with Wheeler, Wigner, Dirac and others in a symposium in Einstein's honor. Jähmefyysikko (talk) 06:06, 12 September 2023 (UTC)

See also this from 1976. There was also something relevant (about Wheeler putting the "relative state interpretation" at arms' length while Everett was still alive) in Byrne's biography of Everett ([3][4] and some other passages). XOR'easter (talk) 14:56, 12 September 2023 (UTC)

Thanks, I will make some edits. (I have to say I'm unsure why Wheeler's "opinion" as opposed to his published work is so notable.) Johnjbarton (talk) 16:00, 12 September 2023 (UTC)

Thanks! Sadly, that one comment at the end of a session of questions for Wheeler, is by far the least interesting thing he said that day.

L. Cooper (Brown U.): I had not meant to bring this up, but I think that if you take the Everett-Wheeler interpretation of the quantum theory seriously, you do not really have to violate causality in your shutter experiment. I admit I have not had a chance to analyze this particular ex- periment completely, but in other experiments of the same type, with your own interpretation, I do not believe you have to violate causality. Do you have any comment on that?

Wheeler: The interpretation of quantum mechanics that Hugh Everett gave us some years ago and that Leon Cooper himself elucidated considerably more is one in which branches, if I can put it that way, in the act of observation are simultaneously present. I confess that I have reluctantly had to give up my support of that point of view in the end- much as I advocated it in the begin- ning because I am afraid it creates too great a load of metaphysical baggage to carry along. But - they say nobody knows sin like a sinner.

So what does Wheeler say? That he gave up support for "branches ... in the act of observation are simultaneously present"? That would be my interpretation based on Wheeler, John Archibald (1977). Lopes, José Leite; Paty, Michel (eds.). "Include the Observer in the Wave Function?". Dordrecht: Springer Netherlands: 1–18. doi:10.1007/978-94-010-1196-9_1. ISBN 978-94-010-1198-3. {{cite journal}}: Cite journal requires |journal= (help). See the quote in Universal wavefunction. Johnjbarton (talk) 15:56, 12 September 2023 (UTC)

Ok I added "Observers and Wheeler's perspective".

I think Wheeler's role in MWI is sufficiently notable to warrant a section. And it also gives a way to discuss the observer aspect that Wheeler focused on.

I don't think my text is awesome however. Please review. Johnjbarton (talk) 17:45, 12 September 2023 (UTC)

It looks like one of the references is broken.

I will try to have further comments later. XOR'easter (talk) 21:56, 12 September 2023 (UTC)

Fixed ref, thanks. Johnjbarton (talk) 22:18, 12 September 2023 (UTC)

This unreferenced, extreme description of Wheeler's viewpoint is back. I have been advised that I should not edit until a consensus on the topic is reached. Johnjbarton (talk) 15:49, 14 September 2023 (UTC)

I don't know why the text is stressing what Wheeler said after Everett's death when Wheeler began distancing in the 1970s. XOR'easter (talk) 17:23, 14 September 2023 (UTC)

Merge Universal wavefunction in to this article?

I just discovered the small page Universal wavefunction. Wouldn't it be better include here? Johnjbarton (talk) 00:08, 12 September 2023 (UTC)

I agree with this. Crossroads ^-talk- 01:02, 12 September 2023 (UTC) struck per below Crossroads ^-talk- 22:53, 12 September 2023 (UTC)

No merge. As the article says it received work from Hartle an Hawking, so is a concept that moved beyond MWI. cheers, Michael C. Price ^talk 02:31, 12 September 2023 (UTC)

The claimed connection between Hartle&Hawking and Everett is not supported by the sources currently in the article. Please comment at Talk:Universal wavefunction. Jähmefyysikko (talk) 04:13, 12 September 2023 (UTC)

Support merge. Universal wavefunction is the central concept of MWI, so it's natural to discuss it here, especially since the current state of that page is not great.

Even if the Hawking-Hartle concept is found to be related, there is still some difference in the emphasis, since we are not necessarily interested in the whole universe in MWI. Hartle-Hawking state can be used to discuss the wavefunction of the universe. See a comment by User:Lumidek on Talk:Hartle–Hawking state#Complicated which indicates the connection. Jähmefyysikko (talk) 06:27, 12 September 2023 (UTC)

Argument at Talk:Universal wavefunction convinced me that it should not be merged, since that wavefunction also features in quantum cosmology. Its not completely unrelated to MWI in that context either, but in many cases it might be too surprizing to click a link wavefunction of the universe and end up in MWI. Jähmefyysikko (talk) 20:32, 12 September 2023 (UTC)

I also disagree with the merge. The "universal wavefunction" was just an aspirational goal of Everett, and the following literature on Many-Worlds seldom deals with it. I think it's more useful to keep Universal wavefunction about actual proposals for a wavefunction of the universe. Tercer (talk) 14:16, 12 September 2023 (UTC)

Ok but that page needs work.

Resolved

Johnjbarton (talk) 21:46, 12 September 2023 (UTC)

Claim of "objectively real"

The lead sentence says: The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is objectively real, ... What is the reference for this claim?

It can't be Everett. In Appendix II of his PhD thesis, "REMARKS ON THE ROLE OF THEORETICAL PHYSICS", he outlines a perfectly reasonable stance that theories are just theories: "a physical theory is a logical construct (model),". He uses the word real as a synonym for valid: "It is therefore improper to attribute any less validity or "reality" to any element of a superposition than any other element...".

Both of the references in the section "Debate whether the other worlds are real" related to Everett are second hand accounts by an investigative journalist and a member of a rock band. Many non-scientists don't understand the difference between a theory that models reality and reality (what ever that even means).

I don't think this claim belongs in the lead. Johnjbarton (talk) 22:16, 12 September 2023 (UTC)

The link under "objectively real" points to Philosophical realism, which is to say philosophy. In every other way a reader would take this article as a physics article. An MWI article or section of this article clearly labeled as philosophy with references would be fine. But we should not mix up physics and philosophy without calling out the differences. Johnjbarton (talk) 22:30, 12 September 2023 (UTC)

The next sentence is:

This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe.Tegmark, Max (1998). "The Interpretation of Quantum Mechanics: Many Worlds or Many Words?". Fortschritte der Physik. 46 (6–8): 855–862. arXiv:quant-ph/9709032. Bibcode:1998ForPh..46..855T. doi:10.1002/(SICI)1521-3978(199811)46:6/8<855::AID-PROP855>3.0.CO;2-Q. S2CID 212466.

Tegmark, as far as I can tell, says no such thing.

I'm noticing a trend. Every reference I have checked is either off the mark or wildly incorrect :-( Johnjbarton (talk) 14:22, 13 September 2023 (UTC)

From the lead: "evolution of reality as a whole in MWI is rigidly deterministic and local."

Everett says the wave function changes deterministically. Reality is observed from inside and this perception is not deterministic.

The field equations of QM are local so MWI being local in any trivial sense of the word is not notable (Tegmark IIIB) Johnjbarton (talk) 14:40, 13 September 2023 (UTC)

John, you are editing with only be superficial knowledge of the subject matter and making howling errors. E.g. Everett does assert the reality of the wavefunction. cheers, Michael C. Price ^talk 18:51, 13 September 2023 (UTC)

Wonderful! Show me. Here is the dissertation I read: https://www.pbs.org/wgbh/nova/manyworlds/pdf/dissertation.pdf Johnjbarton (talk) 18:53, 13 September 2023 (UTC)

That cat again.

Part of the caption of the nice split-film image at the top of the article says:

"in different branches of the multiverse, both of which are equally real, but which do not interact with each other"

In the Tegmark reference also in the top of the article:

What Everett does NOT postulate: At certain magic instances, the the world undergoes some sort of metaphysical “split” into two branches that subsequently never interact.

One of these is not correct or complete.

I removed the last two phrases but @Tercer reverted that with: "obviously they'll interact if you interfere them. the lack of interaction is for the standard version of the thought experiment where there's no interference"

Why does the caption call out the idea that they do not interact? The only important thing for readers to know is the branching. That is what the interpretation requires. The claim "equally real" is dubious, disputable, philosophical add on. Some of us real people believe we live in the real world. I believe most readers will agree and no scientist can disagree since this is not science. "Branches never interact" contradicts Tegmark who calls out this issue prominently. If the caption must call out "never interact" then the details for why Tegmark's claim does not apply should be included. I don't think that is needed: just delete the non-information.

The image should convey the flavor of MWI not delve in to debatable details. Johnjbarton (talk) 15:14, 13 September 2023 (UTC)

"Equally real" is fundamental for Many-Worlds. If only one of the branches is real you have a single-world interpretation. The lack of interaction is also fundamental, otherwise you'd hardly have "worlds" or, as Deutsch puts it, "parallel universes". We should definitely include this information at the top of the article, we convey the essential part of the interpretation with it.

I haven't read Tegmark's paper, I don't know what is he talking about it, but both these issues are so fundamental for the interpretation that they are covered by several of the references the article already has. Don't make me waste my time looking for quotations. Tercer (talk) 15:46, 13 September 2023 (UTC)

"Don't make me waste my time looking for quotations." That's why we are here. I don't believe your claims of "equally real" because "reality" is a philosophical position, not physics.

If you don't have time to read the references, then let someone who does edit the article. Johnjbarton (talk) 15:54, 13 September 2023 (UTC)

From a footnote in the very lead of this article: each with a different result of measurement being recorded and observed, all coexisting equally. Maybe you should familiarize yourself with the subject before wasting everyone's time. Tercer (talk) 16:40, 13 September 2023 (UTC)

Leading with physics not philosophy.

As an article in the physics WikiProject I believe the subject should be introduced as physics, not philosophy.

I don't think we should start with

The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is objectively real, and that there is no wave function collapse.

The first phrase is debated and philosophy and the second phrase is obscure for non-expert readers.

We should start with physics:

The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that "all isolated systems evolve according to the Schrodinger equation". Since the universe as a whole is isolated, this implies that the universal wavefunction also obeys the Schrodinger equation and that all possible outcomes of quantum measurements are physically realized in some "world" or universe so the wave function collapse postulate is not required.

Even non-expert readers will know that the Schrodinger equation is a QM thing and be intrigued to learn more or turn away as choose. But they won't be thinking the article is philosophy.

I made this change but @Tercer did not like it and reverted it. Johnjbarton (talk) 15:49, 13 September 2023 (UTC)

I have no opinion yet about the "obscure for non-expert readers" part, but I am confused by the "physics, not philosophy". The subject of how to interpret quantum mechanics is necessarily a philosophical one. XOR'easter (talk) 16:21, 13 September 2023 (UTC)

Yes, interpretation is not theory, but it is about physics. Everett's dissertation Appendix II discusses this as does Feynman in his QM intro chapter, similarly Schrodinger's "What is an elementary particle?". I'm not objecting to the lack of testability, but to the focus on "reality" and "determinism" with unqualified links to philosophy articles. These words have very interesting consequences in MWI and to sweep that all away with a link is bad for readers. The difference between MWI and other interpretations is in large part bound up in the way we interpret these words. The words and their meaning in MWI should be discussed with references, not summarily asserted. Johnjbarton (talk) 16:46, 13 September 2023 (UTC)

I wouldn't be surprised if terms like "reality" and "determinism" (and "locality", etc.) need more explanation. I'm still confused, though. What is wrong with linking a philosophical term to a philosophy article? XOR'easter (talk) 16:56, 13 September 2023 (UTC)

The implication of the link is that the words linked have the meaning described in the article linked. The universal wavefunction is not required by all proponents of MWI to have "mind-independent existence"; see Wheeler 1977. Since all minds in MWI are within the universal wavefunction, the very meaning of "mind-independent existence" deserves discussion. The simple sentence with a link makes the reader believe that this is a closed and obvious issue, but rather this is a contentious unresolved "interpretation of an interpretation". There are PhD dissertations on this subject: Lehner, Christoph Albert. Quantum mechanics and reality: An interpretation of Everett's theory. Stanford University, 1997. There are books with question marks in the the title: Saunders, Simon, et al., eds. Many worlds?: Everett, quantum theory, & reality. OUP Oxford, 2010.

This is not "the sky is blue", it is an unsourced assertion.

The issue with determinism is similar. Deterministic evolution of a universal wave function does not result in deterministic outcomes in our perception. That is a fascinating concept, not a one line link to a philosophy article.

These are subjects that should be covered in the article with adequate references not asserted and not in the lead. Johnjbarton (talk) 17:27, 13 September 2023 (UTC)

The book "Many Words?" is a collection of papers supporting and attacking the interpretation. As far as I remember none of the detractors, and certainly none of the supporters, takes issue with determinism and realism.

Again, I urge to actually read some references before editing this article. Arguing based on a book's title is frankly ridiculous. Tercer (talk) 18:40, 13 September 2023 (UTC)

Sorry, I'm still catching up. What's the issue with the question mark being in the title? As noted just above, it's a collection of essays pro and con. XOR'easter (talk) 16:35, 14 September 2023 (UTC)

Perhaps a more palatable, less contentious approach is to first develop the content then reconsider the lead as a summary of it. Johnjbarton (talk) 18:25, 13 September 2023 (UTC)

Unhelpful edits

Lots of unhelpful editing from one editor, despite universal opposition on the talk page. Unless anyone else objects I shall revert all the changes in a few days cheers, Michael C. Price ^talk 20:06, 13 September 2023 (UTC)

I'm very puzzled by this reaction and the line of reasoning. I'm doing my best to read the reference cited in this article as well as others I've found. The edits have made are supported by references but the challenges are supported by 'unhelpful' or claims about uncited things happening decades ago. I have opened Talk topics on every issue where there were existing references and even some that were not referenced.

I'm sorry you don't agree with the references. I think you formed an opinion which you hold strongly but which is not based on evidence cited in the article. All you need to do is provide references to back up your claims. I did. Both points of view should remain and be fairly represented. Johnjbarton (talk) 21:10, 13 September 2023 (UTC)

If you are suggesting to revert the edits in this diff, then I do object. Most of the edits are good: there is good copyediting, small but important additions which make the meaning of the text more precise, sources added, and improvement on the structure of the page. Jähmefyysikko (talk) 21:11, 13 September 2023 (UTC)

According to Peter Byrne

Our article says:

According to Peter Byrne, Everett believed in the literal reality of the other quantum worlds.Byrne, Peter (2010). The Many Worlds of Hugh Everett III: Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family. Oxford University Press. ISBN 978-0-19-955227-6.

And yet in Barrett, Jeffrey A. and Byrne, Peter. The Everett Interpretation of Quantum Mechanics: Collected Works 1955-1980 with Commentary, Princeton: Princeton University Press, 2012. https://doi-org.wikipedialibrary.idm.oclc.org/10.1515/9781400842742

Peter Byrne writes in the Biographical Introduction:

In the second appendix of his long thesis, Everett points out that since his theory could not make predictions differentiating it from the standard collapse, hidden variables, or stochastic theories, it was largely a matter of taste how one interprets the quantum mechanical equations.28 For himself, he was convinced of its empirical correctness (as far as explaining the subjective experience of quantum measurement), and he did not believe that any model was capable of fully capturing “reality.”

Just after that sentence Byrne has the same quote from Everett's dissertation as I included in the article.

So either the reference in the article is inconsistent with other things Byrne said or the sentence summarizing Byrne's book is incorrect. Johnjbarton (talk) 23:34, 13 September 2023 (UTC)

In the same volume of collected works edited by Byrne there is a letter from Everett to DeWitt, pg 253, with:

When one is using a theory, one naturally pretends that the constructs of the theory are “real” or “exist.” If the theory is highly successful (i.e. correctly predicts the sense perceptions of the user of the theory) then the confidence in the theory is built up and its constructs tend to be identified with “elements of the real physical world.” This is, however, a purely psychological matter. No mental constructs (and this goes for everyday, prescientific conceptions about the nature of things, objects, etc., as well as elements of formal theories) should ever be regarded as more “real” than any others. We simply have more confidence in some than others.

In my opinion it is beyond doubt that the line "Everett believed in the literal reality of the other quantum worlds" is incorrect based the sources available at this time. Should other sources arrive, the doubt would remain but we could include both views. Johnjbarton (talk) 23:48, 13 September 2023 (UTC)

The passage from Everett no where refers to the reality or non-reality of the wavefunction. Similarly with the "heresy" point. You are pushing your own original research, which is explicitly contradicted by other sources. cheers, Michael C. Price ^talk 08:55, 14 September 2023 (UTC)

Quoting the beginning of section 3 of Everett's Rev. Mod. Phys. paper: This paper...postulates that a wave function that obeys a linear wave equation everywhere and at all times supplies a complete mathematical model for every isolated physical system without exception. It further postulates that every system that is subject to external observation can be regarded as part of a larger isolated system. The wave function is taken as the basic physical entity with no a priori interpretation (emphasis in original). In other words, every isolated system has a wavefunction; the wavefunction is what is (the basic physical entity). And the previous year, he wrote, The physical ‘reality’ is assumed to be the wave function of the whole universe itself. By properly interpreting the internal correlations in this wave function it is possible to explain the appearance of the macroscopic world to us, as well as the apparent probabilistic aspects. (Quoted on p. 140 of the Byrne biography.) On p. 144, Byrne writes, Everett repeatedly wrote that the branches are “equally ‘real.’ ” On the reasonable premise that he considered at least one branch to be “real,” then, for him, all are “real.” On p. 172, Everett is quoted as writing, In theory the universal state function is the realized fact. In superposition after measurement all elements actually realized (comment on a letter from Norbert Wiener). There's more in other places. Any hedging on Everett's own part seems to be more about acknowledging that quantum mechanics might ultimately be wrong. XOR'easter (talk) 16:24, 14 September 2023 (UTC)

Thanks for your efforts. Any thoughts on why Everett wrote his Appendix II? Any thoughts on why S. Osnaghi et al. review would devote a section (5.1) to a discussion of Everett's use of quotes around "real"?

Everett was a physicist and a sophisticated thinker. At the minimum don't you think the strong assertion about his belief should be qualified? Johnjbarton (talk) 17:06, 14 September 2023 (UTC)

It's not really my place to speculate why anyone wrote a particular block of text (not here, anyway). The whole "Debate whether the other worlds are real" section seems a little unclear on what is actually being debated. XOR'easter (talk) 17:30, 14 September 2023 (UTC)

I'm okay with the entire "Debate" section being removed - it reflects a debate from before the release of biographical material cleared up the matter of Everett's beliefs. The debate should probably in the Hugh Everett page, anyway. cheers, Michael C. Price ^talk 18:20, 14 September 2023 (UTC)

Collapse was widely regarded as artificial

The article current says:

Wave function collapse was widely regarded as artificial and ad hoc,Wimmel, Hermann (1992-05-26). Quantum Physics And Observed Reality: A Critical Interpretation Of Quantum Mechanics. World Scientific. p. 45. ISBN 978-981-4505-46-8.

However the Wimmel reference is a fringe QM theory, not in any way representative of any collection of physicists and it makes not claims to be such. It does argue against collapse, but that is not the summary we get in our article. Furthermore the book dismisses MWI as not a serious interpretation. Page 8.

This is in the section "Alternative to wavefunction collapse" which incorrectly describes Everett's approach. He never mentions Occam. Everett's reasoning concerns multiple observers (B observing A observing system) and concerns the consistency of applying a QM to micro and macro systems. His arguments are much better than slamming collapse as "artificial" (duh its a postulate after all). Everett didn't need to take a poll to remove it and neither to we. Johnjbarton (talk) 01:06, 14 September 2023 (UTC)

Two sections for deletion

The "Debate" section on the reality of other worlds, and "Observers and Wheeler's perspective" don't add to the article. I propose excision. cheers, Michael C. Price ^talk 22:39, 14 September 2023 (UTC)

My opinion: Yes on Debate. No on Wheeler.

Wheeler had a large impact on MWI, certainty notable in this context, almost as important as DeWitt.

The relationship between MWI and observation is clearly important. It was Everett's first argument; it dominated Wheeler's Assessment; it is what makes MWI more interesting than decoherence.

Mixing these originally was me being lazy. Wheeler's contributions where directly around observation so coming up with separate content did not come to me. Johnjbarton (talk) 02:54, 15 September 2023 (UTC)

Wheeler, as Everett's thesis supervisor, had an impact (mostly negative, but some positives) on the presentation of MWI in its early days, but his views on collapse evolved into his 'participatory universe' view and the 'delayed eraser' experiment - nothing to do with MWI. cheers, Michael C. Price ^talk 05:38, 15 September 2023 (UTC)

As Everett's thesis advisor Wheeler allow Everett's ideas to be known to the world. Wheeler did not need to take Everett in to his group (Everett didn't have a physics background and his interests did not match Wheeler's work). Wheeler did not need to spend endless hours helping Everett revise his thesis and to prepare it for publication. Wheeler did not need to put his reputation on the line by writing his Assessment article for publication in the same issue of Reviews of Modern Physics as Everett's paper (which might not have even been accepted without Wheeler). Without Wheeler's active involvement we would not be discussing Everett at all. His work would be some notes in a basement.

Wheeler's other work, which was primarily on gravitation and black holes but also included some other areas in QM, does not detract from or matter as far as his role in MWI goes.

However, our personal opinions of Wheeler are not so important. How can we improve the article?

My proposal is to rename the section to say "Wheeler's perspective", add a little more content to flesh it out, and to move it to between the "relative state" and "renamed to many worlds" sections. What do you think? Johnjbarton (talk) 15:00, 15 September 2023 (UTC)

This not an article about Wheeler. It is about Many Worlds. Who cares what Wheeler thought about things. Move it to Wheeler's pages. cheers, Michael C. Price ^talk 15:43, 15 September 2023 (UTC)

Wheeler published on the topic. The Heresy history paper mentions him over 250 times. DeWitt of Many Worlds only rank 80 mentions. Wheeler absolutely belongs here.

I cleaned up the Wheeler section. If we only want to include Wheeler's published scientific contributions I'm ok with that. I included the change-of-heart reference only to clarify a previous version. Johnjbarton (talk) 16:11, 15 September 2023 (UTC)

Yes to both. The "debate" section is a ridiculous he-said-she-said, devoid of any scientific content. The section on Wheeler is rather personalist. Who cares what Wheeler thought? The article is not about him, it's about Many-Worlds, and the relevance of his work for Many-Worlds is essentially zero. Tercer (talk) 17:14, 15 September 2023 (UTC)

Agreed. Wheeler's only relevance is as Everett's thesis advisor, and that is covered elsewhere. cheers, Michael C. Price ^talk 18:14, 15 September 2023 (UTC)

Wouldn't you say then that Everett's work is also irrelevant? Wheeler published more on the topic than Wheeler did. He talked to more people about the idea than Everett did. In some cases the theory was called Everett-Wheeler.

Based on actual sources rather than personal opinion I can't understand where this idea about Wheeler comes from. You claim of his only relevance is completely opposite of the comprehensive history cited in the article, Osnaghi, Stefano; Freitas, Fabio; Olival Freire, Jr (2009). "The Origin of the Everettian Heresy". Studies in History and Philosophy of Modern Physics. 40 (2): 97–123.

If the article is about DeWitt's work, then let's split out a new article on Relative States and start here with DeWitt. Johnjbarton (talk) 18:21, 15 September 2023 (UTC)

The "heresy" talks about Wheeler's (mostly destructive) role as Everett thesis advisor, and that is already covered in the article.

There is no substantive difference between Everett's Relative state formulation and DeWitt's many worlds popularisation. cheers, Michael C. Price ^talk 18:33, 15 September 2023 (UTC)

This article presents Many-Worlds as it is understood today, more than 6 decades after Everett published his work. And the current sources almost never cite Wheeler's work or mention Wheeler's ideas. He is historically relevant as Everett's supervisor, and that's it.

Of course the Osnaghi et al. paper mentions Wheeler all the time, that paper is about the history of the interpretation. This implies we should mention Wheeler in the history section, as we indeed do. Tercer (talk) 19:10, 15 September 2023 (UTC)

Thanks, this argument makes sense to me.

What throws me off is the Overview that has Formulation (Everett), Relative state (Wheeler's name and which Wheeler was heavily involved in) and Renamed many-worlds (Dewitt). So a major portion of the Overview is history that simply omits one of the three key players. Johnjbarton (talk) 19:37, 15 September 2023 (UTC)

Yeah, that's a dumpster fire. It belongs in the history section, not in an overview section. "Relative states" is of only historical interest, nobody uses this terminology anymore. It's also hardly relevant who came up with the name "many worlds" and when, the only relevant thing is what the sources call the interpretation nowadays: either "Many-Worlds interpretation" or "Everett interpretation". Tercer (talk) 19:47, 15 September 2023 (UTC)

Yes, I'm pretty sure I've only seen "relative state interpretation" used in a historical sense to refer to Everett's original proposal. XOR'easter (talk) 17:04, 16 September 2023 (UTC)

So do you think we could consolidate the historical content from Overview into History and refocus the overview on what MWI is? Johnjbarton (talk) 18:21, 16 September 2023 (UTC)

Indeed, and I wish I had done that myself. When I worked on this article a couple of years ago it had more serious problems and eventually I ran out of energy. Tercer (talk) 21:07, 16 September 2023 (UTC)

I have removed the two sections, saving just a paragraph which I added to the history section. The article still meanders a bit, back and forth, but at least it is a bit less cluttered now. cheers, Michael C. Price ^talk 18:39, 15 September 2023 (UTC)

Key sources defining "Many-worlds interpretation"?

The current article uses lots historical references outside of the history section. It seems like, outside of the history, one sentence on Everett and one on DeWitt should be enough (even one for both). That would shift the focus of the overview to the MWI. But what would be an agreed core definition?

Tegmark summarizes MWI in a few paragraphs. Is that an adequate definition? Is there another key source better or in addition? (I'm saying to exclude any other refs or points of view, just to have a sourced definition of MWI as a base). Johnjbarton (talk) 22:24, 16 September 2023 (UTC)

Kent's 1990 criticism encompassed the variations as follows: Many-worlds interpretations share two essential characteristics. First, they suppose that there exists a definite physical reality, which can be put into correspondence with parts of a mathematical formalism. This assumption is necessary if an MWI is to have any useful content. [...] There seems to be no dispute in the literature on this point: if a theory is not mathematically realist then it is not an MWI. Second, they base the mathematical formalism on a state-vector $|\psi \rangle$ which belongs to a Hilbert space $V$ and has a purely hamiltonian evolution. Vaidman's pro-MWI entry in the Stanford Encyclopedia of Philosophy says that his MWI has two conceptual parts. Part (i) states that the ontology of the universe is a quantum state, which evolves according to the Schrödinger equation or its relativistic generalization. The other half is A prescription which sets up a correspondence between the quantum state of the Universe and our experiences. XOR'easter (talk) 00:06, 17 September 2023 (UTC)

Tegmark is seriously outdated. A better reference is Wallace's book (currently ref 14). Tercer (talk) 08:49, 18 September 2023 (UTC)

Just to avoid future confusion,currently 14 is Wallace, David (2012). The Emergent Multiverse: Quantum Theory According to the Everett Interpretation. Oxford University Press. ISBN 978-0-19-954696-1 Johnjbarton (talk) 17:28, 18 September 2023 (UTC)

Article already opens with coincise definition: MWI = real wavefunction and no collapse. So why are we discussing this??? cheers, Michael C. Price ^talk 18:51, 18 September 2023 (UTC)

The definition in the lead references a historical source, which we've agreed is not our goal in the article. The source which contains several articles not all of which are agreed to define MWI according to previous discussions (Wheeler, and the Cooper/van Vechten article). The source includes DeWitt's 1970 article which calls the theory EWG, for Everett-Wheeler-Graham. So this source seems like a poor choice for defining MWI.

In addition two sources challenge the idea that MWI is one consistent thing:

• Marchildon, Louis. "Multiplicity in Everett׳ s interpretation of quantum mechanics." Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 52 (2015): 274-284.
• Kent, Adrian. "One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation." Many worlds (2010): 307-354. Quote from the abstract: "Many different and incompatible attempts to define a coherent Everettian quantum theory have been made over the past 50 years."

I think your short definition is pretty good, but mixes up "real" and "wavefunction". To me the only thing that really unites all of the variants is insisting that the implications of Schrodinger's postulated wave equation be completely explored without additions. That naturally eliminates the collapse postulate. The variants take different tracks to explore the consequences of "without additions". Personally I think summarizing some of the different tracks would make a more interesting article than insisting that MWI is only one thing (reality as real multiple worlds which we can't ever check or see). But in any case agreeing on a defining reference or two would help set up the core of the article. Johnjbarton (talk) 23:07, 18 September 2023 (UTC)

Worked out example

From article:

In particular, it [MWI] models a measurement as a unitary transformation, a correlation-inducing interaction, between observer and object, without using a collapse postulate, and models observers as ordinary quantum-mechanical systems.

Is that a metaphysical description or does it describe a mathematical theory? And if it is mathematical, is there a worked out example? I.e. one describing an actual unitary transformation M corresponding to a measurement. It could be something simple like a superposition |0>+|1> being observed yielding 0 or 1, like in the Schroedinger's Cat experiment. How does M make sure that two later observers see the same state of the cat? It would be nice if there was an explanation that the article could include or point to. Thanks. 2601:644:8501:AAF0:0:0:0:4838 (talk) 00:08, 17 September 2023 (UTC)

The first part of you sentence, "models a measurement as a unitary transformation, a correlation-inducing interaction, between observer and object, without using a collapse postulate" is not unique to MWI. The whole body of work called quantum decoherence is just like that. Your worked example was done in 1929 by Nevill Mott, see Mott problem.

The second part "models observers as ordinary quantum-mechanical systems." is meta-physics if you want "observers" as humans or redundant with the first part of the sentence if "observers" can be excitations of atomic systems that subsequently are amplified. So No or Yes, depending on your choice ;-)

I gather from recent posts on the form of this article that MWI insists on humans in the loop so to speak, so then No example can be created. See Testability in the article. Johnjbarton (talk) 00:18, 17 September 2023 (UTC)

local splitting

DeWitt later rowed back on his extreme splitting view, in line with the modern view that splitting can be viewed as a softer more local process. cheers, Michael C. Price ^talk 03:25, 20 September 2023 (UTC)

Please don't put such a weird back-and-forth in the footnote. The Wikipedia way is to present the consensus position, not the details of the position of one particular person.

Moreover, that's quite overkill for the cat example. Tercer (talk) 06:57, 20 September 2023 (UTC)

I have moved it from the cat example. At the moment it sits as a footnote, but can change this later. cheers, Michael C. Price ^talk 09:30, 20 September 2023 (UTC)

@Tercer Could you explain which "details of the position of one particular person" you are referring to? Johnjbarton (talk) 14:44, 20 September 2023 (UTC)

The going back-and-forth about what exactly DeWitt thought about splitting. Tercer (talk) 16:03, 20 September 2023 (UTC)

I agree with you and I have exactly the same opinion about Wheeler's almost identical "change". Both changed their points of view regarding branching based on new ideas. Neither one "disavowed" the core MWI focus on pure wave equation. Physicist change their point of view based on models all of the time. It's not a religion where people take vows then disavow.

I tried several times to remove ", and in 1980, Wheeler disavowed the theory." from the article. Each time @Michael C Price reverted it. Would you agree to remove this phrase? If not, how can we not include almost the same comment about DeWitt at the same point in the article?

IMO the article does not present Wheeler with a Wikipedia:Neutral point of view. Wheeler went way beyond his role as PhD advisor to advocate for Everett's thesis. It has been argued that this historical information is not needed in an article on MWI. Fine, then surely a negative comment about Wheeler is also not needed.

I'm asking for consensus to remove the Wheeler phrase. Johnjbarton (talk) 16:45, 20 September 2023 (UTC)

As several others already told you, Wheeler did disavow the theory. DeWitt didn't. Moreover, the sentence about DeWitt was in the lead. It does not belong there. In the lead we should describe what the interpretation is, not what specific people think about it. The sentence about Wheeler is in the reception section, it does make sense there. Tercer (talk) 17:35, 20 September 2023 (UTC)

Literature and alternate histories

I am minded to restore a trimmed down version of the literature section. It was culled with the comment that worlds split with quantum events, not human decisions - which is false since human decisions are quantum events, along with all other events. I have seen, on other platforms, people question whether alternate histories are actualized in MWI, even after reading this article. Clearly the point needs to be emphasized for the lay reader. cheers, Michael C. Price ^talk 10:41, 30 November 2023 (UTC)

I am not convinced that mainstream references actually support the following statement: All of the historical speculations entertained within the alternate history genre are realized in parallel universes[6], which seems very speculative. With quick reading, I did not find this in Refs.[6] either. The figure about a fictional history of the US also undermines the credibility of the article (and the theory). Jähmefyysikko (talk) 15:19, 30 November 2023 (UTC)

True, ref 97 is a better source for the claim. I'll move the ref. See also Tegmark quote in the preceding section, which supports this.

The point about the "fictional" history of the US, is that it is not fictional in some Everett worlds, if we take the MWI seriously . cheers, Michael C. Price ^talk 16:34, 30 November 2023 (UTC)

I don't understand the phrase "genre are realized in parallel universes" in this sentence. I assume that what is meant is "genre occur in at least one of the infinite number of parallel universes."

The sentence, as it currently reads, is inappropriate. It states a fantasy as a fact, exactly the same as claims about religious miracles. Compare these sentences:

• "The miracles of Jesus are miraculous deeds attributed to Jesus in Christian and Islamic texts."
• "All of the historical speculations entertained within the alternate history genre are realized in parallel universes."

In the first sentence the encyclopedia carefully connects the extraordinary claim to the sources which make the claim. In the second sentence the miracles are stated a fact.

Similarly "Fictional histories which break the laws of physics (e.g. have magic) are not realised." makes an unverifiable claim as a fact.

The fact that such fictions exist and the nature of their content are notable. Statements claiming that such fictions are "realized" is WP:EXTRAORDINARY. Johnjbarton (talk) 17:08, 30 November 2023 (UTC)

Some "fantasy " as fact is exactly what Deutsch (and Tegmark) are claiming. Check out the Beginning of Infinity ref. cheers, Michael C. Price ^talk 17:11, 30 November 2023 (UTC)

I agree with WP:EXTRAORDINARY. Tegmark quote is under 'speculative implications'. This should be placed there also, and attributed to Deutsch and Tegmark, not presented as an absolute truth.

The image caption includes too much WP:SYNTHESIS, and should be removed. The image is very rasterized and gaudy anyway. Jähmefyysikko (talk) 17:33, 30 November 2023 (UTC)

The whole point of the MWI is that a seemingly extraordinary fact (existence of parallel worlds or timelines) is true. This is why many people find the MWI absurd or incredible - but that can't be helped, it comes with the theory. Which is precisely why the article needs to be explicit on this point. cheers, Michael C. Price ^talk 17:37, 30 November 2023 (UTC)

It does not follow from the existence of parallel universes that for each fictional universe there would exists some microscopic realization, even if there are no imnediately apparent violations of physical laws. There might be more constraints on the realized universes than there are on the imagination of the writers. But it is all speculation, and if you claim otherwise, there should be stronger refs than Deutsch's semi-pop science book. Jähmefyysikko (talk) 18:00, 30 November 2023 (UTC)

In have given three strong references, all from professors of physics (Deutsch, Tegmark, DeWitt), so dismissing the idea as "semi-pop science" is not justified. cheers, Michael C. Price ^talk 19:28, 30 November 2023 (UTC)

The Beginning of Infinity is undeniably popular science. And as far as I can tell (the references aren't very specific), Tegmark and DeWitt do not talk about fictional universes, so using them as references is misleading. Jähmefyysikko (talk) 20:07, 30 November 2023 (UTC)

I changed the paragraph to attribute this point of view to Deutsch. Johnjbarton (talk) 22:32, 30 November 2023 (UTC)

Tegmark explicitly agrees with Deutsch, so this is not helpful. I shall restore the additional refs. cheers, Michael C. Price ^talk 23:13, 30 November 2023 (UTC)

John Gribbin uses the example of Harry Potter as a magical work in fiction which is not realised, in his Royal Society award-winning book, Six Impossible Things. cheers, Michael C. Price ^talk 23:44, 30 November 2023 (UTC)

Besides, Deutsch is an advocate of MWI, and often makes very bold claims about it. Those cannot be taken to represent any kind of scientific consensus about the interpretation. Jähmefyysikko (talk) 20:15, 30 November 2023 (UTC)

Within the MWI community it is consensus. cheers, Michael C. Price ^talk 23:09, 30 November 2023 (UTC)

So far, we have only heard this claim from Deutsch. A slightly longer quote from Gribbin: Deutsch has pointed out that according to the MWI, any world described in a work of fiction, provided it obeys the laws of physics, really does exist somewhere in the Multiverse. There really is, for example, a Wuthering Heights world (but not a Harry Potter world).. Jähmefyysikko (talk) 07:55, 1 December 2023 (UTC)

No, the Wutherheights and Harry Potter is Gribbin's own synthesis. He is agreeing with Deutsch, but it is his own example.

Please don't use a topic merge as an excuse to delete such content again. It was in the article for years. I get that you think it "gaudy" - well let's try to improve it, not delete it. cheers, Michael C. Price ^talk 10:38, 1 December 2023 (UTC)

Gribbin devotes only half a paragraph of his popular science book for fictional universes. For the extreme interpretation that all alternative universes are realized in some branch, he cites Deutsch. The way I read it, he merely illustrates Deutsch's idea with Wuthering Heights and Harry Potter, and neither agrees or disagrees with him. In fact, since he says so little about the issue, citing him in support is WP:UNDUE weight.

And again, how are Refs. [6] (DeWitt) and [95] (Tegmark) relevant for the fictional universes? It seems incorrect to attribute such ideas to DeWitt and Tegmark, if they never explicitly articulated them. Please point out a specific place in the reference if I am wrong.

The fact that the figure you added in 2009 was in the article for some years after its initial addition is not really an argument for it, as it had also been absent from the article for multiple years now. The caption is original research (WP:IMAGEOR), as there is no source which states that Sobel's universe is realized in some branch of the Multiverse without WP:SYNTHESIS. If we remove the original research from the caption, the figure is not connected to the article. Why should we have it, when it is also very ugly? To improve its appearance would require it to be completely redrawn. Jähmefyysikko (talk) 13:27, 1 December 2023 (UTC)

I suggest you re-read WP:IMAGEOR, because it is explicitly encouraging editors to introduce images. "Original images created by a Wikipedian are not considered original research, so long as they do not illustrate or introduce unpublished ideas or arguments". The idea here, of alternate histories being actualized, has been published, so that is really the end of the argument. Or are you going to argue that we can have an image based on Wuthering heights, but not for want of a nail? cheers, Michael C. Price ^talk 13:45, 1 December 2023 (UTC)

One may also use the Ladyman & Ross reference to argue against the idea that all fictional universes would necessarily be realized. They say: So although on the Everett interpretation, there is more to reality than the actuality that meets the eye, it is still the case that the actual (in the non-indexical sense) universal wave function rules out some possibilities, and hence that not all the modal structure of the world is realized. So, even if some fictional universe would be allowed by the laws of physics, it is not necessarily contained in the actual universal wavefunction. Jähmefyysikko (talk) 13:42, 1 December 2023 (UTC)

The claims of MWI are untestable and therefore equivalent to miracles. We should present them similarly, independent of our personal opinions. Johnjbarton (talk) 18:14, 30 November 2023 (UTC)

The untestable claim is old and hackneyed, and dealt with elsewhere. cheers, Michael C. Price ^talk 19:31, 30 November 2023 (UTC)

The butterfly effect claim is WP:OR

The current article makes this claim in the caption for a figure:

A map from Robert Sobel's novel For Want of a Nail, an artistic illustration of how the butterfly effect – in this example the branching or point of divergence from our timeline's history is in October 1777 – can profoundly alter the course of history.

The connection between this classical effect in nonlinear systems and the branching in the many-worlds interpretation of quantum mechanics is not referenced.

Here is a contrary reference: “The Quantum Butterfly Noneffect” in SA Space & Physics Vol. 3 No. 6 (December 2020) "A familiar concept from chaos theory turns out to work differently in the quantum world."

Now there may be scientific work showing that MWI's model matches the butterfly effect, in which case both points of view could be represented. To me such a presentation of opposing points of view belong in quantum chaos or butterfly effect. Johnjbarton (talk) 03:47, 1 December 2023 (UTC)

Irrelevant to the effect on macroscopic, non-linear history. As they say, "To what extent the no-butterfly effect might apply in the macroscopic world of our lives is an open question," cheers, Michael C. Price ^talk 04:07, 1 December 2023 (UTC)