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"@Caledonian: If it is an old and trivial insight, why do most scientists and near all non-scientists ignore it?"

They don't. The mismatch between you and them is that they're busy thinking about something else at the moment. I like the rule Turney gave above: "Doubt everything, but one at a time, not all at once." Of course, a single person can't follow that rule completely (there's not enough time in a lifespan to doubt EVERYTHING), and most people pick the wrong things to doubt or are lazy in applying the rule.

Of course, that rule's going to get in the way of reaching truth in some cases (some falsehoods come in self-reinforcing pairs both of which must be doubted in order to falsify either, and some things can't profitably be denied even for the sake of argument), but that's the case with any process, and this is something we've known since Goedel.

This kind of confuses me about this series... If all he was telling us was that Science is a powerful set of rules, and that therefore it can't eliminate all contradictions nor state all facts, I'd simply agree with him. But he seems to be saying that Bayesianism is different from Science, that somehow applying it instead of Science will have better results. It seems to me that both are processes, and both have blind spots.

Something just clicked for me. I mean, regarding the subject of the original post. There is a true dilemma, and in that dilemma, the choices of a pure Bayesian will look crazy to a Scientist, and vice versa.

The hard difference between Science and Bayes is that Bayes does not require a model; Science does. Bayes simply predicts probabilities; Science attempts to establish a model that explains the probabilities.

Thus, a Bayesian won't care about the quality of the model he's given, EXCEPT that it must not be complex (a nonexistent model will work just fine).

MW (like all the others I've seen) is a lousy model, so science is not satisfied with it; but to a Bayesian, the quality of the model is irrelevant, so a Bayesian can accept the model or ignore it and not even ask for something better.

I'm definitely sounding like I disapprove of this pure Bayesian thinking. I'm starting to see that science plus bayes is more complex than bayes alone (which is a win for pure Bayesian thought), but I'm still not sure that not being able to make models is a good tradeoff for pure simplicity.

"The latter, since there are no Garden of Eden patterns in physics."

Thank you for your excellent job of communicating (and the GoE link decreased possible ambiguities, too).

How do we know that there are no Garden of Eden patterns? That is a very interesting claim. In attempting to reverse-engineer it, I remembered that according to quantum theory, each wavefunction is nowhere zero. Thus, any collection of particles could tunnel into place over any distance in any organization you could possibly specify. Is that the key to the proof?

At any rate, I'm "sticking to my guns" about many-worlds not affecting the desirability of average utilitarianism. The sum over all direct results of my actions over all worlds is still overwhelmingly determined by already determined macroscopic causes not known to me, NOT by as-yet undetermined quantum decoherences splitting worlds; my probability computations are dominated by unknowns, not by unknowables.

I'm not arguing that average utilitarianism is wrong; I'm just saying that MW doesn't seem to appreciably affect its desirability.

Nick, thank you for the post. It almost answered my question -- I just need to make sure I'm not totally misreading it.

"But, yes, every outcome is real in some world."

When you say "outcome" do you mean "every outcome of quantum processes", or do you mean "every event"? Do you mean "every possible result of physical processes" or do you mean "every configuration regardless of physical antecedents"?

As a specific example, is there a world where one human was born of a virgin, performed miraculous healings, prophesied his own death and resurrection, rose from the dead after being buried in a tomb for three days and three nights, was seen by 500 people, and ascended some 40 days thereafter -- and do you attribute the existence of this world entirely to quantum decoherences splitting the worlds (i.e. if you believed in God you'd have to answer 'no')?

Let me pull the money quote from the article:

"The tradition handed down through the generations says that a new physics theory comes up with new experimental predictions that distinguish it from the old theory."

This is superficially correct, but I think it's irrelevant. Quantum theory is already a theory with well-established laws. None of the contending interpretations of those laws -- many-worlds, collapse, hidden-variables, and so on -- are theories, and none of them propose new laws (suggesting that there might be a law we don't know doesn't count). They're all attempts at models, and they all suck. Models should have explanatory power; none of these add any explanatory power.

The real reason some people don't care about Many Worlds isn't that they're irrationally wedded to Copenhagen (although some people are). It's that both Copenhagen and MW suck so badly that the only way to stick to one is to be irrationally wedded to it. Back when all we had was Lorentz' equations there were tons of possible ways to explain them; as soon as Einstein proposed a fruitful model all of the other explanations vanished (well, as soon as the fruitfulness became obvious).

I feel that I'm equivocating, though. I used the term 'fruitful', which hides the meaning "producing experimental results". I suppose that makes me a devotee of Scientism as opposed to Bayesianism. I have much reading to do on this site, and I'm thrilled to have the opportunity. Thanks for interacting with us.

"If the exact physical state is underdetermined by the problem description, then there will be separate branches of the wavefunction for each possible state, although they might have diverged arbitrarily long ago. So, yes."

Are you seriously proposing that my use of ambiguous language splits the universe? This is unbelievable. I understand how incoherency would split the universe, but how can ambiguous language do that? How about false information -- if my bank tells me that my paycheck came in, is there an alternate world where my paycheck in fact DIDN'T come in?

I just don't buy this. I think I get the quantum MW model; it makes a certain kind of sense. What I don't get is how it enables you to claim that there are any number of worlds that you want! I think you can only claim a quantum split where there is actually decoherence, and that the splits will contain only events which had a nonzero "quantum probability" in that decoherence.

There may be a world in which my paycheck didn't actually come in to my bank -- but the explanation for that lack is NOT "because I just imagined it", or "because it's the negation of something that did happen"; rather, it's because of some specific quantum decoherence which could eventually result EITHER in my paycheck arriving or NOT arriving.

What am I missing?

"That's Occam's razor, not Science. The scientific method >is taken to suggest< that an untestable theory is of no use."

Watch that passive voice -- unless you're going to actually claim that the scientific method suggests that, I don't care what someone somewhere took it to suggest.

The scientific method doesn't suggest anything. It's a method, not a philosophy. As a method, it gives you steps to follow. A hypothesis is untestable; a theory's been tested. A model integrates theories. MW is a model.

"What's more, Occam's razor isn't some unmutable natural law: it's just a probability - the simplest explanation is >usually< the right one, and so why not start there and move up the ladder of complexity as required: that way, you can cover the most likely (all other aspects being equal) explanations with the minimum amount of work."

Occam's razor is part of science, not to be distinguished from the rest. Without it, there's absolutely no way to distinguish experimental results from lab noise -- without it the "best explanation" for an unexpected but reproduced experimental result might be "sorry, I must have messed something up, and the guy attempting to reproduce my results must have messed the same thing up in the same way to get the same result."

You're right that it has to be applied as a rule of thumb, but it's also fundamental to science as a reductionist pursuit.

"The most important implication is that the scientific method can break down."

I don't understand how this is a consequence of MW. We've always known that the scientific community can and does break down. The scientific method breaks down even theoretically (if you use K-complexity to assess it). And I'm not even sure that the MWI situation is a breakdown... It seems there are more than two interpretations (it's not just collapse versus many-worlds).

"There are some minor ethical implications of many-worlds itself (e.g., average utilitarianism suddenly becomes a lot more appealing) but mostly, it all adds up to normality."

Question: Does every event with two possible/plausible outcomes result in two distinct worlds? I don't think that's the case -- it seems that multiple plausible outcomes also result from an ambiguous problem description (even if the situation is actually completely deterministic). It seems that the primary source of multiple outcomes in ethics is not the same as the source of multiple worlds in quantum theory -- therefore you can't sum across the multiple worlds of quantum theory to get an ethical probability of 1.


"Computer programs in which language? The kolmogorov complexity of a given string depends on the choice of description language (or programming language, or UTM) used."

They only depend to within a constant factor. That's not the problem; the REAL problem is that K-complexity is uncomputable, meaning that you cannot in any way prove that the program you're proposing is, or is NOT, the shortest possible program to express the law.

I'm trying to comprehend how this is a dilemma... Science supposedly teaches that for any two theories that explain the same data, the simplest one is correct. Bayes can't talk about explaining data without invoking the science that collected the data... Can he?

It would seem that the theory of science includes Bayesian theory.

On the other hand, the practice of science requires either exhibiting evidence for theories or testing falsifiable theories. Many Worlds can trivially be falsified by actually finding a collapse, while its main distinguishing feature cannot be directly demonstrated. Thus, science focuses on searching for a collapse.

So... I still don't see the contradiction.

I also have to speak up in favor of metaphysics -- one poster claimed he'd take Science over Metaphysics anytime. Does he realize that that statement is itself metaphysical? Science cannot determine whether Science has priority over other things, and metaphysics by definition has priority over physics.

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