On Thu, Jan 9, 2025 at 4:41 PM Quentin Anciaux <allco...@gmail.com> wrote:
> > > Le jeu. 9 janv. 2025, 22:16, Jesse Mazer <laserma...@gmail.com> a écrit : > >> >> >> On Thu, Jan 9, 2025 at 5:38 AM Quentin Anciaux <allco...@gmail.com> >> wrote: >> >>> Brent, >>> >>> The core disagreement here seems to rest on the role and status of >>> possibilities. In a single-world framework, the unrealized possibilities >>> you refer to have no actual existence or causal link to the realized world. >>> They are simply conceptual tools to calculate probabilities. But this is >>> precisely what strikes me as incoherent: why invoke these possibilities as >>> part of the explanation if they play no real role in shaping the outcome? >>> >> >> I don't see a fundamental problem here, you can interpret it in terms of >> the notion of "hypothetical frequentism" where you are just talking about >> the frequencies that would obtain if an experiment were (hypothetically) >> repeated an infinite number of times, even if such repetitions don't occur >> in reality (assuming some sort of ontological difference between possible >> worlds and the 'real world', a difference which some views like Tegmark's >> MUH or David Lewis' modal realism might deny--personally I'm >> philosophically inclined to a sort of monism that denies a distinction >> between possible and real worlds, as well as denying a distinction between >> mathematical forms and the physical universe, but I don't think the idea of >> making such distinctions is incoherent). >> >> To me there are other reasons for seeing it implausible that "collapse of >> the wavefunction on measurement" should be treated as real rather than just >> a useful approximation, though. One is just that I expect all physical >> phenomenon should be described by some unified set of physical laws, >> applying to small collections of particles and large measuring instruments >> alike; those Copenhagen advocates who treat the collapse as objective don't >> have any sort of mathematical model of the laws governing measurement >> instrument/quantum system interaction to determine when a collapse occurs, >> they just have to put in the notion by hand in an ad hoc way. There are >> also "objective collapse theories" which do try to give a theory in terms >> of some idea like a collapse happening spontaneously whenever a collection >> of entangled particles exceeds a certain mass, but this would actually give >> predictions different from standard QM and seems implausible to me, it is >> an idea worth testing of course. >> >> The other big reason to see collapse as not ultimately real is point made >> by von Neumann that it's actually arbitrary where you place the collapse in >> a series of interactions, it doesn't matter in terms of predictions whether >> it happens when the measuring instrument interacts with the quantum system >> or only when the information about that interaction enters a human >> observer's brain. See the paper at https://www.jstor.org/stable/3541837 >> (readable if you sign up for a free jstor membership) which talks starting >> on p. 123 about von Neumann's principle of "psycho-physical parallelism" >> and on p. 125 quotes von Neumann that this principle requires us to be able >> to show "that the boundary between the observed system and the observer can >> be displaced arbitrarily" and that "this boundary can be pushed arbitrarily >> into the interior of the body of the actual observer is the content of the >> principle of the psycho-physical parallelism" (p. 126 also quotes him >> giving an example involving the measurement of temperature). >> >> I believe one could extend this further and imagine a Wigner's friend >> style thought-experiment where a human experimenter is making a bunch of >> measurements in a box which is perfectly sealed off from interactions with >> the outside world (no decoherence between the contents of the box and the >> outside environment) from some time t=0 until we open it at a later time >> t=T. The person in the box could be doing a series of measurements in the >> electron-double slit experiment for example, in some cases putting >> measuring devices at the slits to see which one the electron went through, >> in other cases not, and recording the outcome of all experiments. If we >> assumed each such individual measurement collapsed the wavefunction, we'd >> get a prediction about the statistics in cases where the electron was >> observed, and how they differed from the statistics when it wasn't >> observed. If on the other hand we assumed everything in the box was >> evolving according to the Schrodinger equation with no collapse until we >> opened the box at t=T, we would get exactly the same prediction about the >> statistics seen in the experimenter's records! Except in this case the >> different statistics when a measuring device was present at the slits would >> be explained in terms of decoherence when the electron became entangled >> with the measuring instrument and records, plus the final collapse of those >> records at t=T. (it seems to me that this is a further reason to be dubious >> of objective collapse theories--it would make this agreement into just a >> 'weird coincidence') >> >> From what I understand the only way we might get different predictions in >> the "every measurement causes collapse" picture and the "collapse of >> records doesn't happen until box is opened at t=T" picture is if there's >> some possibility the records of a measurement could be thoroughly erased, >> with no possibility of reconstructing it from the measured state at t=T. >> This is the type of thought-experiment Deutsch suggested to test MWI >> against "consciousness causes collapse" interpretations, see discussion of >> "Experiment #3" proposed by Deutch, involving a quantum artificial >> intelligence which makes measurements and then has its memory erased, >> starting on p. 15 at >> http://www.columbia.edu/~jpp2139/IssuesInQuantumComputingFD.pdf >> >> Jesse >> > > Jesse, > > The issue with invoking "hypothetical frequentism" in a single-world > framework is that the supposed ensemble of possibilities has no substance. > It’s a purely abstract construct, with no ontological status or causal > influence on the realized history. If only one history exists for all > eternity, this ensemble is not just unrealized—it’s irrelevant. It has no > bearing on the single outcome, no mechanism to "shape" probabilities, and > no connection to reality beyond being a mathematical abstraction. > Well, many philosophers do see mathematical abstractions as having their own kind of reality, either mathematical platonism which grants them ontological status as "abstract objects", or a weaker position called truth-value realism at https://plato.stanford.edu/entries/platonism-mathematics/#TrutValuReal which says there is an objective truth about mathematical statements (at least some of them, since philosophers can be truth-value realists about arithmetic but not questions concerning uncountable sets like the continuum hypothesis) but isn't necessarily committed to explaining this truth in terms of the existence of abstract objects. Do you think this is itself incoherent, that anyone committed to believing in mathematical truth must take a position like Tegmark where any mathematical structure containing descriptions of intelligent beings will be experienced as real by them? To me it seems like a coherent metaphysical position to say these other mathematical universes are "real" in the sense of having objective truths about their mathematical structure but lack some other property like "physical reality" or "conscious experience"--in the latter case they would in effect be like the possible "zombie worlds" imagined by David Chalmers, worlds with the same structure of physical events as ours but lacking any conscious experience. I've read that David Lewis considered this sort of thing a challenge to his own philosophical doctrine of modal realism (which says that in order for there to be facts about counterfactuals, all possible worlds must exist just like ours does)--one could have an "ersatz modal realism" that granted that possible worlds existed as mathematical structures but lacked some other kind of reality possessed by our world (see the discussion on p. 88 of https://sci-hub.se/10.1080/00048400012349371 ). As I said earlier, I have monist inclinations so I personally don't like this sort of solution, since it seems to create a fundamental metaphysical dualism. I remember as a teenager reading Roger Penrose's book Shadows of the Mind, I was particularly struck by his illustration of three interrelated spheres of reality: physical reality, mathematical reality, and the mental reality of conscious experience/qualia (the illustration is reproduced at https://astudentforever.wordpress.com/2015/03/13/roger-penroses-three-worlds-and-three-deep-mysteries-theory/ ). It struck me even then that it would be more elegant if these three domains could somehow be unified or shown to be different ways of looking at a single type of reality, which led me to think about something along the lines of Tegmark's Mathematical Universe Hypothesis before I had read Tegmark (a philosophical paper Tegmark co-authored with Peit Hut and Mark Alford at https://arxiv.org/pdf/physics/0510188 also prominently features Roger Penrose's three sphere diagram and talks on p. 6 about a 'unification' of the spheres, so I wonder if this could have been part of his original inspiration). Nevertheless, I don't see anything intrinsically incoherent about a dualistic view that says both the mathematical and mental spheres have their own reality, and that our particular mathematical structure is uniquely "real" in the sense of giving rise to conscious experiences (or instead of a dualistic view one could also have a 'trialistic' view that says our structure is also uniquely associated with a "physical" reality, though I'm not sure what this would mean separate from the property of giving rise to consciousness, maybe something like the belief in physical 'quiddities' separate from structure that's discussed in the paper at https://sci-hub.se/10.1080/00048400012349371 I cited earlier, and also discussed at https://plato.stanford.edu/entries/russellian-monism/#PhysQuid ). It seems like a viable way to have truths about "possible worlds", and therefore about probabilities for worlds governed by the same laws as ours, without having to accept something like modal realism or the MUH. Jesse > > In this sense, the ensemble in a single-world interpretation is entirely > hollow. It doesn’t exist in any meaningful way, yet it’s used to justify > the probabilities of events in the realized world. This is the core of what > I find incoherent: how can something with no substance or existence play a > role in explaining the realized history? > > In frameworks like Tegmark’s MUH or modal realism, where all mathematical > structures or possible worlds are real, the ensemble is given ontological > weight. Probabilities describe distributions across a real, existing set of > possibilities. But in a single-world framework, the ensemble is nothing > more than a notional tool. It’s invoked as if it has explanatory power, yet > it has no grounding in the reality it’s supposed to explain. > > If the single history is all that exists, the probabilities and > hypothetical ensembles collapse into "it just happened this way." Without a > substantive ensemble, the single-world view relies on something that isn’t > there to explain outcomes, leaving the framework conceptually empty. > > As for collapse, I am not talking precisely about MWI vs collapse, but > single unique history for all eternity vs everthing, many worlds, many > minds. > > Quentin > >> >> >> >> >> >> >>> >>> You argue that they reduce the probability of occurrence for other >>> events. But this reduction is purely formal—an artifact of the mathematical >>> framework, not something grounded in reality. In a single-world view, only >>> the realized history exists, so the "ensemble" of possibilities is entirely >>> abstract. It doesn’t exist as part of reality, which means it cannot >>> influence or interact with it. The "reduction of probability" you mention >>> is simply a mathematical convenience, not a causal mechanism. >>> >>> When you calculated probabilities during the Vietnam War, those >>> calculations had predictive utility, but the unrealized scenarios were not >>> part of reality—they didn’t shape or explain the actual outcomes beyond >>> being conceptual constructs. That’s fine for practical purposes, but when >>> applied to the nature of existence itself, it becomes unsatisfying. The >>> single-world framework uses the language of possibility and probability >>> without giving these notions any real grounding. >>> >>> In a multiverse framework, possibilities are not just mathematical >>> tools—they are ontologically real. Each possible outcome exists within the >>> structure of the multiverse, and the probabilities describe the >>> distribution of outcomes across this ensemble. This provides explanatory >>> depth that the single-world framework lacks because it doesn’t need to rely >>> on nonexistent possibilities to "explain" realized outcomes. >>> >>> Your bridge tournament analogy highlights the difference: in the >>> single-world view, only one table exists, and all the other possible hands >>> are irrelevant—they have no role in shaping the one game that’s played. In >>> the multiverse view, all tables exist, and the hand you’re dealt >>> corresponds to your position in the tournament. The probabilities describe >>> the relative frequency of hands across the tables, not just the abstract >>> chance of receiving one hand. >>> >>> The single-world framework asks us to accept that possibilities exist >>> only in the abstract, with no causal or explanatory role in the realized >>> world. This reliance on nonexistent entities to justify outcomes feels like >>> an incomplete explanation, one that collapses into "it just happened this >>> way." That’s the heart of my issue with it. >>> >>> >>> >>> Le jeu. 9 janv. 2025, 07:33, Brent Meeker <meekerbr...@gmail.com> a >>> écrit : >>> >>>> >>>> >>>> >>>> On 1/8/2025 9:42 PM, Quentin Anciaux wrote: >>>> >>>> Brent, >>>> >>>> The issue I see with a single-world framework is the reliance on >>>> possibilities that have no existence or causal link to the realized world. >>>> In this view, possibilities are entirely notional, they don’t exist >>>> ontologically, and they have no impact on the single realized history. This >>>> makes their invocation seem unnecessary, even absurd, because they don’t >>>> contribute to the reality we observe in any meaningful way. >>>> >>>> But they do. They reduce its probability of occurence. >>>> >>>> >>>> If the only thing that exists is the realized world, why appeal to a >>>> theoretical ensemble of possibilities? >>>> >>>> Because that's what the equations of quantum mechanics produces. We're >>>> not "appealing to them" where taking them into account as things that might >>>> occur. That's why the Born rule assigns probabilities less than one to >>>> them. >>>> >>>> It’s as if the single-world view borrows the language and tools of >>>> probability to describe outcomes but discards the explanatory depth >>>> provided by an actual ensemble. >>>> >>>> I'd say that's looking at it exactly backwards, as though the "tools of >>>> probability" on applied to cases that were really deterministic (had >>>> explanatory depth) and what work is done by the word "actual" in "actual >>>> ensemble". Usually it is an ensemble of possibilities. When you're dealt >>>> a bridge hand no one supposes that all other possible hands are dealt >>>> somewhere else; it is enough that they merely possible. During the Viet >>>> Nam was I calculated the probability of dropping a bridge with a Walleye, I >>>> calculated the probability of a missile failure causing it to hit the >>>> launching aircraft, I calculated the probability of a wayward missile going >>>> out of the range safety boundaries, and dozens of other probabilities. I >>>> was always considering a range of instances and their contrary; but I never >>>> needed to suppose the instances were actually anything more than >>>> possibilities. They didn't have to happen anywhere in any world. >>>> >>>> Without the existence of unrealized possibilities, the concept of >>>> "randomness" seems like a placeholder for "it just happened this way," >>>> offering no real insight into why this one history unfolded. >>>> >>>> No, it's a "placeholder" for it could have happened these other ways >>>> but didn't. >>>> >>>> >>>> In contrast, in a multiverse framework, the ensemble is not merely >>>> theoretical, it has ontological status. >>>> >>>> Yes, it's like a bridge tournament in which all possible hands are >>>> dealt at different tables and then you pick one to sit *at random*. >>>> But wait, that's absurd, we must sit down at every table. And then we must >>>> play every possible card in every possible order. Otherwise we cannot >>>> speak of the probability of making our bid. >>>> >>>> The possibilities exist and have causal relationships within the >>>> broader structure. This provides coherence to the use of probability, as it >>>> describes the distribution of outcomes across the ensemble, not just within >>>> a single, isolated history. >>>> >>>> The single-world framework effectively asks us to accept a universe >>>> where unrealized possibilities are invoked to explain outcomes, yet they >>>> have no actual role in shaping reality. >>>> >>>> Sure they do. If they are things that might possibily happen then they >>>> reduce the probability of something else happening. >>>> >>>> Brent >>>> >>>> This reliance on something that neither exists nor affects the realized >>>> world strikes me as deeply incoherent. >>>> >>>> Quentin >>>> >>>> Le jeu. 9 janv. 2025, 03:14, Brent Meeker <meekerbr...@gmail.com> a >>>> écrit : >>>> >>>>> >>>>> >>>>> >>>>> On 1/8/2025 4:11 AM, Quentin Anciaux wrote: >>>>> >>>>> Brent, >>>>> >>>>> The core of my argument is that in a single-world framework, the >>>>> ensemble of possibilities described by Schrödinger’s equation is only >>>>> conceptual. If only one history is realized, then those "possibilities" >>>>> don’t exist in any meaningful way—they’re theoretical abstractions. In the >>>>> absence of an actual ensemble from which a selection occurs, the notion of >>>>> randomness is a metaphor, not a mechanism. >>>>> >>>>> In the many-worlds framework, every possibility is realized, so the >>>>> "selection" is an emergent phenomenon from within the structure of the >>>>> totality. In the single-world view, however, there’s no actual ensemble. >>>>> Probabilities merely describe the likelihood of the one realized outcome, >>>>> but there’s no underlying framework where those possibilities are >>>>> instantiated. Randomness then becomes a label for the lack of explanation >>>>> rather than a true process. >>>>> >>>>> To say "the single history simply is" and call that random doesn’t >>>>> resolve the issue—it just restates it. Without an ensemble that exists >>>>> ontologically (even probabilistically), the idea of selection collapses >>>>> because there’s nothing to select from. The photon emission you mentioned >>>>> is described by probabilities in QM, but those probabilities don’t >>>>> correspond to real, alternate outcomes in a single-world framework. The >>>>> realized outcome is the only one that exists, and all other >>>>> "possibilities" >>>>> are simply unrealized ideas. >>>>> >>>>> In contrast, in the many-worlds interpretation, the photon’s emission >>>>> in one state is one thread of the total structure, and alternate emissions >>>>> exist along other threads. This gives explanatory power to the >>>>> probabilities, as they correspond to real structures within the ensemble. >>>>> >>>>> But small probabilities explain why things *don't* exist. >>>>> >>>>> >>>>> Regarding your point that probabilities lose meaning in MWI because >>>>> all possibilities are realized—that’s not the case. Probabilities in MWI >>>>> are understood as the measure of the branching structure relative to the >>>>> observer's perspective. They still hold meaning because they reflect the >>>>> structure of the multiverse, not a singular outcome. >>>>> >>>>> What about the one's for which P=0, you could as well say that reflect >>>>> the structure of the multiverse. Will you make an ensemble of them? >>>>> >>>>> >>>>> The single-world view still strikes me as incoherent because it leans >>>>> on the language of probability and possibility but denies their actual >>>>> realization. Without an ensemble, it’s hard to see what randomness truly >>>>> means. >>>>> >>>>> In every other application of probability theory (and for years I >>>>> headed the Reliability Division at Pt. Mugu) the ensemble is only >>>>> notional. It is a the set of possibilities without assuming that they >>>>> exist, in which case they would be actualities. With an ensemble of which >>>>> every member exists, randomness becomes incoherent. >>>>> >>>>> Brent >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Everything List" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to everything-list+unsubscr...@googlegroups.com. >>>>> To view this discussion visit >>>>> https://groups.google.com/d/msgid/everything-list/207aada7-2a8d-4c9e-8490-a25f23eff83a%40gmail.com >>>>> <https://groups.google.com/d/msgid/everything-list/207aada7-2a8d-4c9e-8490-a25f23eff83a%40gmail.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Everything List" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to everything-list+unsubscr...@googlegroups.com. >>>> To view this discussion visit >>>> https://groups.google.com/d/msgid/everything-list/CAMW2kAoJKWzYSjXeRQJCNBiXo2Xbk8VseggxV%3D6rgWL4y6aMFQ%40mail.gmail.com >>>> <https://groups.google.com/d/msgid/everything-list/CAMW2kAoJKWzYSjXeRQJCNBiXo2Xbk8VseggxV%3D6rgWL4y6aMFQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Everything List" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to everything-list+unsubscr...@googlegroups.com. >>>> To view this discussion visit >>>> https://groups.google.com/d/msgid/everything-list/2f860f70-c8af-477a-add2-c7192ab54ed2%40gmail.com >>>> <https://groups.google.com/d/msgid/everything-list/2f860f70-c8af-477a-add2-c7192ab54ed2%40gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Everything List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to everything-list+unsubscr...@googlegroups.com. >>> To view this discussion visit >>> https://groups.google.com/d/msgid/everything-list/CAMW2kAox73KEyv%3DqWUWsCd7pd9wHgm0jwyAPAfv4mkY%3DZkJH7Q%40mail.gmail.com >>> <https://groups.google.com/d/msgid/everything-list/CAMW2kAox73KEyv%3DqWUWsCd7pd9wHgm0jwyAPAfv4mkY%3DZkJH7Q%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Everything List" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to everything-list+unsubscr...@googlegroups.com. >> To view this discussion visit >> https://groups.google.com/d/msgid/everything-list/CAPCWU3KP1ygXnajTScOFOrH7zCMJ%2BozNpZRuwsWcpR6qM_UUYQ%40mail.gmail.com >> <https://groups.google.com/d/msgid/everything-list/CAPCWU3KP1ygXnajTScOFOrH7zCMJ%2BozNpZRuwsWcpR6qM_UUYQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to everything-list+unsubscr...@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/everything-list/CAMW2kAqjPA6Y1BgnBNzr2mXB8fD4A2Pz9cpeH4Ctok%3DuxLv%2Bkg%40mail.gmail.com > <https://groups.google.com/d/msgid/everything-list/CAMW2kAqjPA6Y1BgnBNzr2mXB8fD4A2Pz9cpeH4Ctok%3DuxLv%2Bkg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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