Bruce, You’re making a distinction between single-event probabilities and repeated trials, but you’re not addressing the core issue: in a single-history universe, probability is only ever descriptive, not explanatory. You claim that if an asteroid has an 80% chance of impact but doesn’t hit, then the 20% chance was simply realized. But this explanation is entirely retrospective—it tells us nothing about why this history, rather than any other, is the one that unfolded.
You say, "assuming the calculations were accurate, then there certainly was an 80% chance of hitting, and a 20% chance of missing." But in what sense was that 80% ever real? In the only history that exists, the asteroid never had an 80% chance of hitting—it always had a 100% chance of missing because that’s what happened. The probability was just a number assigned before the event, with no actual force in determining the outcome. In a multiverse framework, probabilities are grounded in actual distributions across histories. The 80% means that in 80% of branches, the asteroid hits, and in 20%, it misses. This gives probability an explanatory role—it describes the structure of reality, not just an arbitrary number assigned to something that never had a chance of happening. You claim that MWI has no way to connect probabilities to the wavefunction, but that’s false. The structure of the wavefunction naturally assigns measure to branches, and those measures correspond to the squared amplitudes of the coefficients—the Born rule emerges from this structure. You keep asserting that probabilities in MWI are meaningless because "all possibilities happen," but that’s only true if you ignore the fact that measure matters. Not all branches are weighted equally, and the frequencies of outcomes reflect those weights. The issue isn’t whether we can calculate probabilities in a single-history world—it’s whether those probabilities have any real ontological meaning. You claim that in a single-history world, probabilities "just work," but that’s not an explanation. It’s just a way of pretending that numbers assigned before an event have some deeper reality when, in truth, they don’t. In the end, the only thing that exists is the one history that happens, and everything else was just an illusion of possibility. Quentin Le jeu. 6 févr. 2025, 00:39, Bruce Kellett <[email protected]> a écrit : > On Thu, Feb 6, 2025 at 11:05 AM Quentin Anciaux <[email protected]> > wrote: > >> Bruce, >> >> Let’s take your own argument about probability and push it to its logical >> conclusion. You said that if something with a 30% probability doesn’t >> happen in a given set of trials, that just means the prior probability >> estimate was wrong. Fine. Now, let’s apply that logic to a real-world >> scenario. >> >> Imagine an asteroid is heading toward Earth, and based on all available >> data, models predict it has an 80% probability of impact. Yet, somehow, it >> doesn’t hit. By your reasoning, this means that the 80% estimate must have >> been wrong—because in the single-history universe, only what actually >> happens matters. The probability was just a number assigned to something >> that never had any reality. >> > > You have changed the nature of the problem. In the first instance it was > that an event of probability 30% would never happen in a series of trials. > I countered by saying that if it didn't happen in, say, 100 trials, then > the initial probability estimate was wrong. > > The asteroid case is different in that there is only ever one trial. If > the chance of hitting is calculated to be 80%, and it doesn't hit. That > merely means that the 20% chance of missing is realized. It does not imply > that the initial estimates were wrong -- it merely implies that the earth > was lucky. You have confused single event probabilities with repeated trial > probability. > > But this raises an obvious problem: what is probability even describing in >> a single-history framework? If probabilities are supposed to quantify real >> possibilities, yet some of them never happen despite high probability >> assignments, then those probabilities were meaningless from the start. The >> asteroid example makes it clear—if a highly probable event doesn’t occur, >> it wasn’t a real possibility in any meaningful sense. It was just a >> mathematical expectation that reality never fulfilled. >> > > Single event probabilities are not the same as probabilities in a series > of trials. You are just confusing things. > > In a multiverse framework, this isn’t an issue because the probabilities >> describe actual distributions of events across different branches. There >> exist branches where the asteroid hits and others where it doesn’t, and the >> 80% probability corresponds to the fraction of branches where impact >> occurs. But in a single-history framework, that 80% was just an empty >> number—nothing ever "happened" with 80% likelihood because only one outcome >> was ever real. >> >> Your argument boils down to saying, "Probability theory tells us what we >> should expect, but if reality doesn’t match, then the prior probability was >> wrong." But this means probability has no independent explanatory power—it >> is just a bookkeeping trick that retroactively adjusts itself to match what >> already happened. That’s not an actual explanation of events; it’s just a >> way of pretending probability still means something when it clearly doesn’t >> in a single-history world. >> > > In fact, what we assume is the Born rule which says that the probability > of a particular outcome is just the absolute square of the corresponding > coefficient in the wave function. > > Many worlds theory does not have any comparable way of relating > probabilities to the properties of the wave function. In fact, if all > possibilities are realized on every trial, the majority of observers will > get results that contradict the Born probabilities. > > So tell me: in a single-history universe, if the asteroid doesn’t hit >> despite an 80% probability, was it ever actually an 80% chance event? Or >> was that probability just an illusion, describing something that was never >> going to happen in the only history that exists? >> > > Yes, assuming that the calculations were accurate, then there certainly > was an 80% chance of hitting, and a 20% chance of missing. It happened that > the 20% chance was realized in this one-off trial. Whis is not to say that > that would be the outcome in repeated trials of the same event. > Unfortunately, repeats of unique events are seldom possible. > > Bruce > > -- > 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 [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/everything-list/CAFxXSLSFvd4UHR8yMaa%2BtkRdc5d7_X7edp1Vpez-1iyc5EkyPA%40mail.gmail.com > <https://groups.google.com/d/msgid/everything-list/CAFxXSLSFvd4UHR8yMaa%2BtkRdc5d7_X7edp1Vpez-1iyc5EkyPA%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 [email protected]. 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