On Friday, February 14, 2025 at 4:21:39 PM UTC-7 Quentin Anciaux wrote:
AG, You're making the classic mistake of conflating what's mathematically rigorous with what's immediately observable. The universal wavefunction isn't a mere hypothesis; it's a direct consequence of applying Schrödinger's equation universally. *I've seen it applied in different specific situations, but what does it mean to* *apply it universally? AG* If you take the equation seriously and reject ad hoc collapses, you get the Many-Worlds Interpretation (MWI). > "If it's not a world, why do advocates of the MWI refer to worlds with > copies of experimenters doing quantum measurements, or maybe flying > insects changing directions?" Because "worlds" are emergent patterns within the wavefunction, not fundamental ontological entities. Just like temperature emerges from molecular motion but isn't a single particle property, "worlds" emerge from decoherence but aren't fundamental themselves. The term "world" is a linguistic convenience, but the reality is just unitary evolution. *Are these worlds physical, in the sense of having energy and containing copies* *of entities in this world, such as people? AG* > "Why should anyone experience superpositions? What would it feel like?" You're already in a superposition; you just don’t experience it as such because measurement entangles you with an outcome, and decoherence suppresses interference. It's like asking why you don’t "experience" being in two places at once when your wavefunction technically spreads over a region. The question misunderstands how observation works in quantum mechanics. > "In a macro experiment like throwing dice, there's no interference, > so what role has decoherence have in this situation or generally?" Decoherence ensures that macroscopic randomness behaves classically. The dice don’t interfere with themselves because they are entangled with countless environmental degrees of freedom. That's decoherence in action— destroying coherence between outcomes so that they evolve independently. > "Maybe 'collapse' isn't a good way to describe what happens when a > measurement occurs. ISTM, that the wf evolves into a delta function > centered at the measurement value. Physically this is what happens, > even though we don't know why." That's just Copenhagen in disguise. The wavefunction doesn't evolve into a delta function unless you force a collapse postulate, which is an artificial addition. Without collapse, all components continue to evolve, just without interference. That’s precisely what the MWI states—nothing more, nothing less. *In the case of the wf representing a horse race, how could it be written to* *account for the uncountable set of possible ways the winner can win? Also,* *since the equation was invented to describe an experiment, what keeps it* *going after the experiment is done? AG * > "I am content to acknowledge that it's an unsolved problem, rather > than postulating other worlds and a universal wf, both of which are > totally undetectable. This can't be compared to a BH which has > something detectable in the region of its horizon." You say "totally undetectable" as if collapse is any more detectable. The difference is that MWI follows directly from the Schrödinger equation without arbitrary assumptions. You claim to be content with an "unsolved problem," but what you call "unsolved" is just an unwillingness to accept the straightforward implications of quantum mechanics. And the black hole analogy stands—if you refuse to acknowledge something just because it's not directly observable, you might as well deny the existence of the singularity inside a black hole. *Singularity inside a BH? You mean mass concentrated in zero volume? Not a* *meaningful concept. Maybe math cannot always be trusted. AG* The math tells us it's there. Just like the math tells us all components of the wavefunction persist. *How does math tell us that? Isn't that your philosophical preference of what* *the math does; how it's interpreted? AG * You're clinging to a philosophical preference, not physics. Quentin Le ven. 14 févr. 2025, 23:48, Alan Grayson <[email protected]> a écrit : On Friday, February 14, 2025 at 1:04:49 PM UTC-7 Quentin Anciaux wrote: AG, A branch is just part of the universal wavefunction evolving under Schrödinger’s equation. It’s not a "world" with clear boundaries but a region of the wavefunction that has decohered, making interference impossible. If it's not a world, why do advocates of the MWI refer to worlds with copies of experimenters doing quantum measurements, or maybe flying insects changing directions? AG You don’t experience other branches for the same reason you don’t experience superpositions, Why should anyone experience superpositions? What would it feel like? AG decoherence isolates them. In a macro experiment like throwing dice, there's no interference, so what role has decoherence have in this situation or generally? AG Saying they "don’t exist" because they’re inaccessible is like denying the other side of a black hole. MWI isn’t excess, it’s just following the math without adding collapse. Maybe "collapse" isn't a good way to describe what happens when a measurement occurs. ISTM, that the wf evolves into a delta function centered at the measurement value. Physically this is what happens, even though we don't know why. I am content to acknowledge that it's an unsolved problem, rather than postulating other worlds and a universal wf, both of which are totally undetectable. This can't be compared to a BH which has something detectable in the region of its horizon. AG Quentin -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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