Brent, The crux of the matter lies in the role and status of the ensemble of possibilities. In a single-world framework, the ensemble is not only notional, but it has no causal or explanatory link to the realized world. While mathematical tools like the Schrödinger equation or probability theory are abstract, they are grounded in physical applications—they correspond to real phenomena or processes. The same cannot be said for a hypothetical ensemble that doesn’t exist in any substantive way. Without grounding, it becomes a hollow construct, invoked solely to justify outcomes in a realized world it has no influence over.
You’ve emphasized that possibilities are just that—possible, not actual. But in a framework where only one history exists for eternity, those possibilities are entirely redundant. They don’t shape the realized history, they aren’t part of reality, and their invocation adds no explanatory depth. The single history simply "is," with probabilities reduced to labels describing abstract mathematical constructs. Contrast this with the many-worlds or everything framework: possibilities are not merely hypothetical—they have ontological status, existing within the structure of reality. Probabilities then describe distributions across actualized outcomes, not abstract notions. This gives coherence to the concept of randomness, as it emerges from the structure of the ensemble rather than being an ad hoc label for "it just happened this way." Your argument about tracing causality until the trail runs cold doesn’t address the core issue. It is precisely because the single-world framework provides no grounding for its ensemble of possibilities that it feels conceptually empty. It leans on notions like probability and randomness, yet denies the existence of the ensemble that gives them meaning. As for moving the goalposts, I’m not demanding an expansive interpretation of MWI; I’m contrasting a single, eternal history with frameworks where all possibilities have a meaningful existence. The Poincaré recurrence you mention might indeed cause worlds to recohere, but such dynamics are consistent with an underlying ensemble—unlike the single-world view, which relies on something fundamentally non-existent to justify its outcomes. If possibilities play no role in shaping reality, then their invocation serves no purpose beyond filling conceptual gaps. That’s the emptiness I’m pointing to, and it’s what makes the single-world framework seem incomplete to me. Le ven. 10 janv. 2025, 06:39, Brent Meeker <meekerbr...@gmail.com> a écrit : > > > > On 1/9/2025 1:41 PM, Quentin Anciaux 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. > > Just like the Schroedinger equation or the mathematics of any other > theory. The connection to reality is in the application. I hope you're > not going to claim that probability theory isn't applicable to anything. > > > 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. > > You're relying on a pun. A set of possibilities that are real and > existing is a set I can write down. But things the possibilities name > don't exist. That's why we call them "possibilities" not actualities. > I've repeated this argument several times now, but you insist on pretending > that possibilities must be something more than just possible: they must > have "ontological weight", which I think is just a fancy way of saying they > *must* exist...contrary to the very concept of "possible". > > > But in a single-world framework, the ensemble is nothing more than a > notional tool. > > Exactly so, and in any other framework to. It is only in the fanciful > world of MWI that possible=actual. > > 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." > > Yes, that's what means for something to be random. > > Without a substantive ensemble, the single-world view relies on something > that isn’t there to explain outcomes, leaving the framework conceptually > empty. > > If you've every tried to trace back all the causal links leading to an > event you would know eventually the trail goes cold and leaves the > framework empty. But probabilistic analyses are not conceptually empty. > Its possibilities are conceived. > > > > 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. > > I think you're moving the goalposts. You don't demand that kind of > expansive extension of MWI. For one thing, if you did, some or even all > separate worlds would recohere per Poincare' recurrence. > > Brent > > > 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. > 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/93f996b4-f4aa-466c-94da-8746f3f0702b%40gmail.com > <https://groups.google.com/d/msgid/everything-list/93f996b4-f4aa-466c-94da-8746f3f0702b%40gmail.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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