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Former featured article candidateMany-worlds interpretation is a former featured article candidate. Please view the links under Article milestones below to see why the nomination was archived. For older candidates, please check the archive.
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August 1, 2005Featured article candidateNot promoted

Theory not mentioned here

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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.

Literature and alternate histories

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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)[reply]

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)[reply]
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)[reply]
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:
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
I changed the paragraph to attribute this point of view to Deutsch. Johnjbarton (talk) 22:32, 30 November 2023 (UTC)[reply]
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)[reply]
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)[reply]
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)[reply]
Within the MWI community it is consensus. cheers, Michael C. Price talk 23:09, 30 November 2023 (UTC)[reply]
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)[reply]
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)[reply]
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)[reply]
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)[reply]
Yes, we could have Wuthering Heights, not as a fact, but as something attributed to Gribbin. For Sobel, we cannot do the same. Of course, neither is a good illustration of MWI. In the text, we would not invent our own example either. Jähmefyysikko (talk) 13:57, 1 December 2023 (UTC)[reply]
Also, following your suggestion, I reread WP:IMAGEOR. It says that captions are treated equally with the main text. Here the problem lies within the captions, not with the figure itself, which is fine to use in For Want of a Nail (novel), where it is not associated with MWI. Jähmefyysikko (talk) 14:50, 1 December 2023 (UTC)[reply]
And if you read the caption you will see that Sobel is not cited as an example of a MWI alternate history, but to illustrate the general point about the butterfly effect and branch points in history. It then goes on to say "everything" (explicitly following Tegmark and DeWitt) is covered by MWI, and it is left to the reader to connect the dots. cheers, Michael C. Price talk 15:05, 1 December 2023 (UTC)[reply]
If one takes two unrelated statements and juxtaposes them in order to imply a conclusion not present in the sources, then this constitutes WP:SYNTH, even if the logical connection is not explicitly stated (but is obvious enough). And butterfly effect is not discussed in the article, so introducing it requires some reference. Jähmefyysikko (talk) 15:27, 1 December 2023 (UTC)[reply]
Actually I think what matters is whether the butterfly effect has ever been mentioned in the context of for want of a nail.
BTW, a Deutsch uses the examples of Roma Eterna and Fatherland. cheers, Michael C. Price talk 15:51, 1 December 2023 (UTC)[reply]
The word "butterfly" appears once in "For want of a nail : if Burgoyne had won at Saratoga" by Sobel, Robert, 1931:
... Niles was “the best butterfly collector Mexico has ever seen, but this is no recommendation for the presidency.”
See https://archive.org/details/forwantofnailifb0000sobe/page/134/mode/2up?q=butterfly Johnjbarton (talk) 16:44, 1 December 2023 (UTC)[reply]
https://tvtropes.org/pmwiki/pmwiki.php/Main/TheButterflyEffect cheers, Michael C. Price talk 17:14, 1 December 2023 (UTC)[reply]
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)[reply]
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)[reply]
The untestable claim is old and hackneyed, and dealt with elsewhere. cheers, Michael C. Price talk 19:31, 30 November 2023 (UTC)[reply]
I made this series of edits. I concur with many of the criticisms above. Having content about a specific work of fiction/alternate history is WP:OR and WP:UNDUE, giving credence to an unscientific claim that it could be real. I also reorganized the section to not have so many (now overlapping) subheadings and tiny separate paragraphs, and, crucially for this matter, adding a source from Sean M. Carroll in which he debunks the common misconception that human decisions can be thought of as quantum events, with equally existing worlds for each outcome. Crossroads -talk- 01:43, 18 February 2024 (UTC)[reply]
The edit comment " Ugh, not this 'MWI means some fiction is real' silliness again " indicates you are pushing your own views of absurdity and not going with the sources. Both Deutsch and Gribbin are claiming exactly that, namely that some fiction is realised in MWI. The wholesale removal of the section without discussion is not justified. cheers, Michael C. Price talk 04:07, 18 February 2024 (UTC)[reply]
I'll grant that my edit summary, in shock over seeing that map return, was a bit much, but to be clear, I did not remove that section entirely. I retained this: David Deutsch speculates in his book The Beginning of Infinity that some fiction, such as alternate history, could occur somewhere in the multiverse, as long as it is consistent with the laws of physics.[92][93]. Anything more than this is undue weight - this idea exists solely as a rather brief mention in two popular-science works and both times is attributed to one man (Deutsch); it is not a scientific discovery or consensus in the peer-reviewed literature or even found there at all. It is those latter sources Wikipedia articles usually go by. Gribbin, as stated above by another editor, appears to simply be repeating and explaining Deutsch's idea without necessarily endorsing it - he specifically attributes the idea to him. In addition, as made clear by Ladyman and Ross, and Carroll (as mentioned above), just because humans can imagine something being plausible on a very coarse level doesn't mean it's actually consistent with the universal wavefunction. Given these factors, I think adding the one sentence I quoted is more than fair, but beyond that is undue (and relating the map to this topic remains OR in any case). Crossroads -talk- 23:57, 18 February 2024 (UTC)[reply]
Good discussion and I agree. Johnjbarton (talk) 01:27, 19 February 2024 (UTC)[reply]
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Many-worlds interpretation

The many-worlds interpretation (MWI) is a philosophical position about how the mathematics used in quantum mechanics relates to physical reality. It asserts that the universal wavefunction is objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe. In contrast to some other interpretations of quantum mechanics, the evolution of reality as a whole in MWI is rigidly deterministic  and local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s. According to this interpretation: in the "Schrödinger's cat" paradox, every quantum event is a branch point; the cat is both alive and dead, even before the box is opened, but the "alive" and "dead" cats are in different branches of the multiverse, both of which are equally real, but which do not interact with each other

Illustration credit: Christian Schirm

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Questioning the removal of "Debate whether the other worlds are real"

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Hello everyone! Before I begin, full disclosure, I'm very inexperienced with editing or talking about editing on Wikipedia and am not a subject-matter expert. My background is in philosophy and psychology. I recall visiting this page a while ago and reading about what I considered to be some very important philosophical implications of the theory in the "Debate whether the other worlds are real" section. I went back to see when the edit was made to remove it (15 September, 2023) and found the corresponding talk page, and I'm not sure I fully understand why it was removed. I saw that User:Michael C Price and User:Johnjbarton were the main people discussing it. I saw some flaws in it discussed but nothing that immediately seems to me to justify the outright deletion of it. Is it possible I could get some clarification on why this was done? I was just disappointed to find it gone because for me, the philosophical implications of MWI are extremely important. - PillageMe (talk) 04:47, 27 July 2024 (UTC)[reply]

The discussion that preceded that deletion was archived. At the risk of misrepresenting the contributions to that discussion, I believe the content was considered non-scientific in an article about a scientific topic. The presentation amounted to various opinions and interpretations of opinions. For reference, this is the deletion edit. Johnjbarton (talk) 05:00, 28 July 2024 (UTC)[reply]
Ah, I missed that part of the conversation because the title in the talk page didn't mention the section by name. Thank you for pointing me to it. I'm not sure if it's appropriate to reopen conversation on it, but I'd like to risk it and say that it seems to me that the page is both philosophical and scientific. The first sentence of the lede itself says that it is "a philosophical position about how the mathematics used in quantum mechanics relates to physical reality." However, without that section, this page comes off as mostly devoid of directly philosophical content. There are lots of philosophical words used such as "objective" and "subjective" with little philosophical explanation (beyond the link to the page on philosophical realism). Without the section in question, a huge question remains open: what does it mean that the many worlds are objectively real? Would it not be better for the page to be more strongly a mixture of the science involved and its philosophical implications so as to avoid this gap? Perhaps I am just overly immersed in philosophy, but it seems like an especially glaring gap in the page's content.
- PillageMe (talk) 12:15, 28 July 2024 (UTC)[reply]
I'm afraid I must agree with Johnjbarton. That section was simply listing the beliefs of people. This is worthless. Now a section that would actually describe the arguments about whether the worlds are real would belong in this article. Tercer (talk) 12:52, 28 July 2024 (UTC)[reply]
That's reasonable. I'm completely with you in that it should definitely be filled out more than it was. But because the section was about the debate I think filling it out with at least some of what was there originally (listing what people think) is also good. I did personally find it useful and valuable to gain a little insight into what experts think because I tend to like to base my opinions on said expert opinions. One tentative suggestion I'd like to put forward for discussion is modifying the "Speculative implications" section to have both more philosophical substance and some returning content from the old section. Renaming that section to "philosophical implications" might be appropriate as well. "Speculative" is technically accurate but also has some negative connotations that I don't think are fully appropriate in this case. I'd also like to hear from Michael C Price because of his past involvement with this subject and how much he has contributed to this page. My understanding is that he and most contributors to this page have backgrounds in the sciences, not so much philosophy, so I think I may be able to help on this front if I am welcome. Quantum physics in general is immensely important for metaphysics, and I like when philosophy bases itself on science as much as possible. Also, in philosophy spheres quantum physics is extremely frequently brought up in relation to determinism in particular, and I'm hoping to get some better interaction between the scientists and philosophers here, since it is in both of our courts.
- PillageMe (talk) 04:45, 29 July 2024 (UTC)[reply]
I would oppose reviving the old content. It was not philosophy, just opinions and not even first hand opinions.
As I recall there are several top-notch philosophical treatments of MWI including by Tim Maudlin. However any presentation needs to be balanced and organized around the principles discussed. Most philosophical treatments of scientific topics are very long and nuanced: they don't summarize in wiki pages very easily and secondary sources are less common. Johnjbarton (talk) 15:22, 29 July 2024 (UTC)[reply]
I agree that it wasn't itself philosophy, but it was information about what people think about philosophy. I think information about what people think about philosophy is useful precisely because of how difficult it is to summarize philosophy in a Wiki page. My proposal is to bring back some of it in combination with a difficult and necessarily imperfect summary.
- PillageMe (talk) 12:57, 30 July 2024 (UTC)[reply]
You are correct that my background is in hard science not philosophy. The debates section was getting a bit tangled so I didnt mind its removal too much, although I do think it is a valid subject for inclusion, since there are many people who incorrectly insist the worlds within MWI are not intended to be real.
I think the lede's first sentence is a just flim-flam and the old version should be restored. I will merge the first and second sentences. cheers, Michael C. Price talk 07:49, 20 August 2024 (UTC)[reply]
That's fair enough, and I like your changes. It now reads as being much clearer that these worlds are 'real' according to MWI. I think some greater elaboration upon what this means would be helpful somewhere in the article, but maybe the average reader would take that for granted and see it as pedantry. Let me know what you think because I may work on such additions if it's supported. My only question now is if there is actually no real debate regarding whether all of the worlds are 'real'. In my recollection, Hawking (most notably) talked about how he essentially just uses MWI instrumentally, without affirming all of the metaphysical implications.
- PillageMe (talk) 08:32, 5 September 2024 (UTC)[reply]

What is meant by "uncountable"?

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In the Introduction, it says this: "The many-worlds interpretation implies that there are most likely an uncountable number of universes." What is meant by "uncountable" in that sentence? Does that sentence mean that the number of universes is larger than aleph-null, the cardinality of the natural numbers (see uncountable set)? 19:56, 25 September 2024 (UTC) Mksword (talk) 19:56, 25 September 2024 (UTC)[reply]

The source on that sentence is
  • 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.
I found nothing in that article about "universes" or counting them. Or multiverses, etc. What I did find was on page 108 that source quotes Everett:
  • ‘‘We have a strong desire to construct a single all-embracing theory which would be applicable to the entire universe.’’
I would interpret that plainly: one universe. In my opinion the multiverse conjecture is a separate concept from Everett's quantum model. But multiverse believers disagree of course.
I'm sure there is a reference for that sentence and which might explain "uncountable". I don't know if it would explain "most likely an uncountable", whatever that can mean.
I will remove the unverified ref and hopefully someone will fix it. Johnjbarton (talk) 20:20, 25 September 2024 (UTC)[reply]
Ok I found a footnote that cites a Physics Today article:
  • To the remark of Podolsky: “It looks like we would have a non-denumerable infinity of worlds”, Everett answered: “Yes.”
The article is
That article is a summary of a 1964 conference chaired by Podolsky. The article says
  • Hugh Everett flew to Cincinnati from Washington to present his relative-state formalism.
I found nothing else about Everett and nothing about the quote above. The article did say:
  • "In order that each main participant might feel free to express himself spontaneously in the spirit of the limited portion of the conference, Chairman Podolsky adopted the policy that references to remarks made by the participants during the conference were to be checked with the persons who said them for approval prior to publication.
which suggests there is a proceedings somewhere. Johnjbarton (talk) 20:44, 25 September 2024 (UTC)[reply]
I don't think this is a proper source. Many-Worlds is not a religion, and Everett is not a prophet. That he said "yes" to a question at a conference is irrelevant. We do have a source which actually studied the question, Ref. [15]. It concludes that the number is undefinable.
That aside, I don't think "non-denumerable infinity" helps any reader. This is obsolete jargon, what people say today is "uncountable infinity". Tercer (talk) 09:19, 26 September 2024 (UTC)[reply]
I completely agree that the conference transcript source is lame and I believe there are better ones. However ref 15, which is
  • Wallace, David (2010). "Decoherence and Ontology, or: How I Learned To Stop Worrying And Love FAPP". In Saunders, S.; Barrett, J.; Kent, A.; Wallace, D. (eds.). Many Worlds? Everett, Quantum Theory and Reality. Oxford University Press. arXiv:1111.2189.
says on page 15:
  • "As such, the question “how many branches are there?” does not, ultimately, make sense."
This matches my take that the real-many-worlds concept is distinct from the historical role of Everett's work on physics. It doesn't support an infinity which is what we need for the sentence. And I don't want to change the sentence significantly as I am unable to discern the gap between Many Worlds and religion.
I did restore the wikilink that points to the same page as uncountable infinity. Hopefully someone will find a third alternative. Johnjbarton (talk) 15:12, 26 September 2024 (UTC)[reply]
I have a vague memory that this point is addressed in Byrne's biography of Everett. XOR'easter (talk) 21:40, 26 September 2024 (UTC)[reply]
If you can't discern between Many Worlds and religion you shouldn't edit this article at all. Tercer (talk) 10:15, 27 September 2024 (UTC)[reply]
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