Talk:Many-worlds interpretation/Archive 8

The current article uses lots historical references outside of the history section.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 ${\displaystyle |\psi \rangle }$  which belongs to a Hilbert space ${\displaystyle V}$  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Tegmark is seriously outdated.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)

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)

The "Equivocal" section begins with Ladyman and Ross weighing the pros and cons of MWI. This makes sense as an example of "equivocal". But the Feynman paragraph is not similar. It has two references. One is a pseudo-science book that cites an unpublished poll supposedly by a political scientist, L David Rabi. (The poll reports Gell-Mann as giving the same answer as Feynman, but Gell-Mann is not a Yes.) Two is an offhand remark by Feynman commenting on someone else's interest. The section quoted starts out: "In fact the physicists have no good point of view. Somebody mumbled something about a many-world picture, and that many-world picture says that the wave function ~ is what's real, ... It's possible, but I'm not very happy with it. So, I would like to see if there's some other way out,..." Does that sound like "yes" or even weighing the idea pro/con?

Richard Feynman publish many books on QM and discussed QM in many public lectures: he had plenty of opportunity to discuss MWI but did not. James Gleick never mentions Everett or MWI in "Genius: The Life and Science of Richard Feynman." Gleick mentions that Feynman rarely read other peoples work. Feynman was passionately interested in his own views of quantum mechanics. Rather than equivocal Feynman was disinterested. Johnjbarton (talk) 16:52, 3 December 2023 (UTC)

Feynman also at least once rejected the notion of 'universal wavefunction' when Wheeler brought up the Everett interpretation up in the 1957 Chapel Hill conference. (Chapel Hill report, p.270) But since it is just a single remark, I wouldn't use this to put him into the 'Rejection' bin either. I agree that we do not need to invoke Feynman here if he did not write anything about this topic. Jähmefyysikko (talk) 17:27, 3 December 2023 (UTC)

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)

Ok let's check your reference. Oh, you don't have one. So we have no idea if there is any connection between the butterfly effect and MWI other than your personal assertion. Johnjbarton (talk) 16:46, 1 December 2023 (UTC)

I've re-removed the picture and caption; more explanation in the "Literature and alternate histories" section above. Crossroads ^-talk- 01:39, 18 February 2024 (UTC)