Bruce, You’re trying to reduce the issue to my supposed "difficulty" with randomness, but that’s not the point. The problem isn’t whether quantum events are random—it’s whether probability has a meaningful foundation in a single-history universe where only one sequence of events is ever realized.
You keep appealing to repeated trials, but even with infinite repetitions, some events with nonzero probability will never occur in the one and only history that unfolds. That’s not a minor detail—that’s a fundamental contradiction in the way probability is treated in a single-world framework. If an event assigned a 30% probability never happens, then its "probability" was meaningless in any real sense. It was never a real possibility, just a number in an equation. Now, regarding the Born rule: You claim that MWI contradicts it, but your argument assumes that every possible branch must exist in equal measure, which is not what MWI predicts. The structure of the wavefunction naturally leads to branches that reflect the Born probabilities because those branches are weighted according to the squared amplitudes. It’s not about equal-counted branching—it’s about the distribution of measure across branches, which naturally results in Born-rule outcomes. Your argument also ignores the fact that in a single-history universe, the Born rule is just an imposed rule with no deeper explanation. Why do probabilities follow this rule in a framework where only one history exists? What forces the realized history to match the expected distribution? If probabilities are just random assignments with no deeper foundation, then their success in predicting experimental results is equally mysterious in a single-history view. MWI provides an actual mechanism for why the Born rule emerges: it follows from the structure of the wavefunction itself. Your argument, on the other hand, assumes the Born rule as a brute fact without explaining why a single realized history should respect it in the first place. That’s not an explanation—it’s just asserting that the math works and ignoring the deeper implications. Le mer. 5 févr. 2025, 22:46, Bruce Kellett <[email protected]> a écrit : > On Thu, Feb 6, 2025 at 9:16 AM Quentin Anciaux <[email protected]> wrote: > >> Bruce, >> >> Quantum mechanics has explanatory power because it provides accurate >> predictions and a framework for modeling reality. The problem isn’t with >> quantum mechanics itself—it’s with trying to reconcile probability with a >> single-history universe where only one sequence of events ever occurs. >> >> In a framework where only one history unfolds, probability is purely >> descriptive—it does not explain why this history, rather than any other, is >> the one that exists. >> > > You seem to have difficulty with the concept of a completely random > event-- one that does not have a 'classical' mechanistic explanation. Sorry > about that, but quantum events have a tendency to be completely random > (within a well-defined probability distribution). > > It assigns numbers to theoretical possibilities that never had a chance of >> being real. You keep asserting that probabilities are meaningful in a >> single-history view, but meaningful in what sense? If a certain event, >> despite being assigned a 30% probability, never happens in the one realized >> history, then in what sense was it ever a possibility? >> > > In the sense that it will happen approximately 30% of the time in repeated > trials. You object to this answer because there can always be > low-probability events that never actually happen in any finite sequence of > trials. I agree, but that is just the nature of probability.... > > In contrast, in a framework where all possibilities are realized, >> probability maintains a clear meaning: it describes the relative measure of >> outcomes across the full set of realized possibilities. In that case, >> probability is tied to something real, rather than just being a tool we use >> to pretend that nonexistent possibilities matter. >> > > Unfortunately, the idea that all possibilities are realized on every trial > is in direct conflict with the Born rule for probabilities. To demonstrate > this, let me spell out a specific example. Consider an experiment on a > two-state system, with a wave function of, say, > > |psi> = a|0> + b|1>, > > where a^2 + b^2 = 1 specifies the normalization of the state. If we now > measure this state according to the variable with eigenstates |0> and |1> > we get two branches, one with outcome '0', and the other with outcome '1'. > Now repeat the experiment in each branch, so we get four branches, with > outcomes '00', '01', '10', and '11', respectively. Repeat this N times and > you find 2^N branches, covering all possible binary sequences. Note that > this result does not depend on the coefficients 'a' and/or 'b' in the above > wave function. So you get the same 2^N branches whatever the coefficients. > > But the Born rule says that the probability that you observe any > particular sequence depends on the squares of the coefficients, and the > number of each coefficient depends on the numbers of '0's and '1's in the > branch you happen to be on. Since, in the multiverse framework, the branch > you happen to be on is random (determined by some self-location probability > -- uniform probability over all branches in this case), it is very > unlikely that the relative numbers of '0's and '1's in your branch happens > to agree with the Born probabilities: In fact the probability that you will > see the Born probabilities vanishes as 1/{2^N }as N becomes large. The fact > that experiments in quantum mechanics universally obtain results that agree > with the Born probabilities is, therefore, inexplicable in the many-worlds > model. > > Bruce > > The fact that quantum mechanics works well does not mean that a >> single-history interpretation is logically coherent when it comes to >> probability. You’re conflating the success of QM with the philosophical >> implications of trying to force probability into a framework where >> unrealized possibilities never had any reality at all. That’s the problem >> you’re not addressing. >> > -- > 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/CAFxXSLQ_67BtMSZAFTjh0EYscnmAm8GVwuMMziM3exCDr-csag%40mail.gmail.com > <https://groups.google.com/d/msgid/everything-list/CAFxXSLQ_67BtMSZAFTjh0EYscnmAm8GVwuMMziM3exCDr-csag%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]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAMW2kAqbs9K0LbKKkMXEAPw4MPGOxscSxwh%2B6HJumcc2re%3DEmA%40mail.gmail.com.
