Dustin2

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Many Worlds, One Best Guess

So, decoherence, which implies Many Worlds, is the superior scientific theory because it makes the same predictions with strictly fewer postulates
No. Decoherence as an interpretation is not a scientific theory, it is an ontology. Decoherence as an interpretation does not imply Many Worlds unless the wavefunction is considered to be metaphysically real. That ascription of reality to the wavefunction is not a scientific postulate, it is a metaphysical one. Many worlds does not predict anything -- quantum theory makes the predictions, Many Worlds is an ontology, a reification of that theory.

In any case, my last question was ignored, and I don't suspect that further questions about considering things in a less realistic light will be taken seriously because of the glib dismissal and flippant mischaracterization Eli has given the very serious objections from instrumentalists. But I'm going to throw out another paper on the relational interpretation in the hopes that someone here will take seriously the idea that all of this confusion over which interpretation is the right one comes from an unreasonable committment to bad metaphysics.

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The problem here seems to be a deliberate conflation of "logically equivalent claims" (which are two sets of claims entailing precisely the same set of statements entirely independently of whether those statements are a good or even testable model for a physical pheonomenon) and "physically equivalent states" (which are two ostensibly different states which are the same at every level of examination), or a deliberate conflation of the model of a phenomenon with the phenomenon itself. This conflation is, in either case, completely solipsistic, and arguing with solipsists is futile.

I'll leave the two of you to congratulate yourselves on being both brains in vats and not brains in vats at the same time.

If Many-Worlds Had Come First

I don't see how decoherence is an automatic win for MWI. Decoherence has been used in several different interpretations of quantum mechanics, notably in consistent histories and in certain hidden variable interpretations. Why should we choose MWI before those, particularly since it seems less parsimonious than consistent histories? For that matter, the language of Rovelli and Smolin's relational quantum mechanics very nearly turns decoherence into its own interpretation (if you compare papers on decoherence which shirk the metaphysical interpretation to the interpretation put forward by Rovelli, they're almost identical). Relational quantum mechanics requires much less in the way of grand assertions than MWI and is a natural framework for decoherence, so why pick MWI over relational quantum mechanics?

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Having quantum collapses IS having Many Worlds
Good God, he's even making up his own contradictions now.

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And by the way, Zen master, you still have a contradiction to explain away.

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Throw something over that edge, and it ceases to be.
Sweet Jesus! Observers in asymptotically flat spacetime don't ever see something go over an event horizon. They just see it get pancaked onto the thing. Interestingly, in proper time, you're still probably wrong.

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So there isn't even a theoretical distinction between them.
You were making perfect sense right up to this sentence (I suspect that's because you were just rephrasing something I've already said). That sentence, though, has sadly brought us back to where we started: your perpetual conflation of metaphysics with epistemology. Scientific theories and ontologies aren't the same thing. If you think the latter is baseless, that's probably right, but I'd think that would give you added incentive in making sure that you understand the difference between a model and the reification of that model.

By the way, you still have a contradiction to explain away.

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You aren't paying attention. Theories make predictions, interpretations of theories do not. In any case, suppose we grant you your little maxim. Then, if we can't tell the difference between an interpretation which claims that wavefunctions and their collapses are real and one which explicitly claims that they are not real by experiment, they're equivalent. Your maxim has just given us that wavefunctions are metaphysically real if and only if they are not.

And, in any case, someone who reacts against metaphysical realism should also take the brain in the vat hypothesis seriously, and you have no grounds for saying that something which is measured in all ways to be like a duck is, metaphysically, a duck. And that's fine. I'd agree. But if you don't want to play metaphysics, don't. Don't claim that two different ontologies are equivalent when they clearly aren't. Just don't reify the physical model. Tell anyone who purports to have a reification of a physical theory that they're committing a fallacy of reification and be done with it. You can't have it both ways.

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There is no difference at the level of predictions, because I'm not calling for any new laws of physics beyond QM. It's a matter of what makes sense as interpretation.
The reason for that lack of difference is that every interpretation of a physical theory is an attempt at reifying the theory in some sense. Each interpretation must conform to the theory at every level of examination since the interpretation is an ascription of a certain ontology to that theory, not a modification of that theory. But it isn't the ontology which predicts things, it's the model which we've attempted to reify that does that, so no amount of experimentation is going to reveal any difference between two interpretations of the same theory. Nonetheless, those two interpretations are not equivalent. I cannot find, by way of experiment, any difference between any two interpretations of quantum mechanics, but we need only find one which asserts the metaphysical reality of wavefunctions and one which does not to see that they do not, in fact, entail precisely the same body of claims and are therefore not equivalent.

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'Interpretation' is irrelevant, Bob. If they have identical consequences, they're equivalent no matter what you choose to call them.

You're confusing metaphysics with epistemology AGAIN.

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