You didn't quite say 'choose what is true', I was just pointing out how closely what you wrote matched certain anti-epistemologies :-)

I'm also saying that if you think the other worlds 'collapse' then your intuitions will collide with reality when you have to account for one of those other worlds decohering something you were otherwise expecting not to decohere. But this is relatively minor in this context.

Also, unless I misunderstood you, your last point is not relevant to the truth-value of the claim, which is what we're discussing here, not it's social benefit (or whatever).

I observe the usual "Well, both explanations offer the exact same experimental outcomes, therefore I can choose what is true as I feel".

Furthermore, thinking in the Copenhagen way will constantly cause you to re-remember to include the worlds which you thought had 'collapsed' into your calculations, when they come to interfere with your world. It's easier (and a heck of a lot more parsimonious, but for that argument see the QM Sequence) to have your thoughts track reality if you think Many-Worlds is true.

As for the Naval Gunner, the point is that he would be right in other fields than fundamental physics. In weather forecasting long term forecasts using coarser models are actually more accurate than those using fine meshes, because of the chaotic behaviour at smaller scales.

I don't quite agree here. It's true that chaotic interactions and floating point multiplication errors mean that long-running fine-grained maps are less accurate than long-running coarse-grained maps, but it seems cleaner to consider that a fact about computer science, not meteorology.

Thanks for pointing to the more recent EY post, which I look forward to reading. No time tonight.

I would actually recommend Hands vs. Fingers first if you haven't read it yet. It's shorter and may be more directly relevant to your interests.

It is often claimed that the the Uncertainty Principle of quantum mechanics [10] makes the future unpredictable [11], but in the terms of the above analysis this is far from the whole story.

The predominant interpretation of quantum dynamics on LessWrong seems Many Worldism. I think it would make sense to address it shortly.

So, shortly, these are the important things to consider:
* in some systems small errors grow to large errors;
* our measurements cannot be completely precise;
* there is some kind of randomness in physics (random collapse / indexic uncertainty of many-world splitting).

Therefore even the best possible measurement in time T1 may not give good results about time T2. Therefore exactly determining the future is not possible (unless we have some subsystem where the errors don't grow).

In hindsight, my presentation in this article was suboptimal. I clarify in a number of comments on this thread.

The common thread that ties together the quantitative majors example and the Penrose example is "rather than dismissing arguments that appear to break down upon examination, one should recognize that such arguments often have a nontrivial chance of succeeding owing to model uncertainty, and one should count such arguments as evidence."

In the case of the quantitative majors example, the point is that you can amass a large number such arguments to reach a confident conclusion. In the Penrose example, the point is that one should hedge rather than concluding that Penrose is virtually certain to be wrong.

I can give more examples of the use of MWAs to reach a confident conclusion. They're not sufficiently polished to post, so if you're interested in hearing them, shoot me at email at jsinick@gmail.com.

"having different descriptions at different levels" is itself something you say that belongs in the realm of Talking About Maps, not the realm of Talking About Territory

Why do we distinguish “map” and “territory”? Because they correspond to “beliefs” and “reality”, and we have learnt elsewhere in the Sequences that

my beliefs determine my experimental predictions, but only reality gets to determine my experimental results.

Let’s apply that test. It isn’t only predictions that apply at different levels, so do the results. We can have right or wrong models at quark level, atom level, crystal level, and engineering component level. At each level, the fact that one model is right and another wrong is a fact about reality: it is Talking about Territory. When we say a 747 wing is really there, we mean that (for example) visualising it as a saucepan will result in expectations that the results will not fulfil in the way that they will when visualising it as a wing. Indeed, we can have many different models of the wing, all equally correct - since they all result in predictions that conform to the same observations. The choice of correct model is what is in our head. The fact that it has to be (equivalent to) a model of a wing to be correct is in the Territory. In short, when Talking about Territory we can describe things at as many levels (of aggregation) as yield descriptions that can be tested against observation.

at different levels

What exactly is meant by “levels” here? The Naval Gunner is arguing about levels of approximation. The discussion of Boeing 747 wings is an argument about levels of aggregation. They are not the same thing. Treating the forces on an aircraft wing at the aggregate level is leaving out internal details that per se do not affect the result. There will certainly be approximations involved in practice, of course, but they don’t stem from the actual process of aggregation, which is essentially a matter of combining all the relevant force equations algebraically, eliminating internal forces, before solving them; rather than combining the calculated forces numerically.

...the way physics really works, as far as we can tell, is that there is only the most basic level—the elementary particle fields and fundamental forces

The way that reality works, as far as we can tell, is that there are basic ingredients, with their properties, which in any given system at any given instant exist in a particular configuration. Now reality is not just the ingredients but also the configuration - a wrong model of the configuration will give wrong predictions just as a wrong model of the ingredients will. The possible configurations include known stable structures. These structures are likewise real because any model of a configuration which cannot be transformed into a model which includes the identified structure in question is in conflict with reality. Physics is I understand it comprises (a) laws that are common to different configurations of the ingredients, and (b) laws that are common to different configurations of the known stable structures. Physicalism implies the belief that laws (b) are always consistent with laws (a) when both are sufficiently accurate.

...The laws of physics do not contain distinct additional causal entities that correspond to lift or airplane wings

True but the key word here is “additional”. Newton’s laws were undoubtedly laws of physics, and in my school physics lessons were expressed in terms of forces on bodies, rather than on their constituent particles. The laws for forces on constituent particles were then derived from Newton’s laws by a thought experiment in which a body is divided up. In higher education today the reverse process is the norm, but reality is indifferent to which equivalent formulation we use: both give identical predictions.[Original wording edited]

General Relativity contains the additional causal entity known as space-time curvature, which is an aggregate effect of all the massive particles in the universe given their configuration so is not a natural fit in the Procrustean bed of reductionism. [Postscript] Interestingly, I've read that Newton was never happy with his idea of gravitation as a force of attraction between two things because it implied a property shared between the two things concerned and therefore being intrinsic to neither - but failed to find a better formulation.

The critical words are really and see

Indeed, but when you see a wing it is not just in the mind, it is also evidence of how reality is configured. It is the result of the experiment you perform by looking.

.. the laws of physics themselves, use different descriptions at different levels—as yonder artillery gunner thought

What the gunner really thought is pure speculation of course, but this assumption by EY raises an important point about meta-models.

In thought experiments the outcome is determined by the applicable universal laws – that’s meta-model (A). In any real-world case you need a model of the application as well as models of universal laws. That’s meta-model (B). An actual artillery shell will be affected by things like air resistance, so the greater accuracy of Einstein’s laws in textbook cases is no guarantee of it giving more accurate results in this case. EY obviously knew this, but his meta-model excluded it from consideration here. Treating the actual application as a case governed only by Newton’s or Einstein’s laws is itself a case of “Mind Projection Fallacy” – projecting meta-model (A) onto a real-world application. So it’s not a case of the gunner mistaking a model for reality, but of mistaking the criteria for choosing between one imperfect model and another. I imagine gunners are generally practical men, and in the field of the applied sciences it is very common for competing theories to have their own fields of application where they are more accurate than the alternatives – so although he was clearly misinformed, at least his meta-model was the right one.

[Postscript] An arguable version of reductionism is the belief that laws about the ingredients of reality are in some sense "more fundamental" than laws about stable structures of the ingredients. This cannot be an empirical truth, since both laws give the same predictions where they overlap so cannot be empirically distinguished. Neither is any logical contradiction implied by its negation. It can only be a metaphysical truth, whatever that is. Doesn't it come down to believing Einstein's essentialist concept of science against Bohr's instrumentalist version? That science doesn't just describe, but also tells? So pick Bohr as an opponent if you must, not some anonymous gunner.

I don't think so, since the information I would be comparing in this case (the "file contents") would be just a reduction of the information in two regions of space-time.

And under determinsim, all the information in any spatial slice will be reproduced throughout time. Hence the false positives.

OK, not strictly "conserved", except that I understand quantum mechanics requires that the information in the universe must be conserved

..absent collapse..

But what I meant is that if you download a file to a different medium and then delete the original, the information is still the same although the descriptions at quark level are utterly different.

But a 4D descriptions of al the changes involved in the copy-and-delete process would be sufficient to show that the information in the first medium is equivalent to the information in the second. In fact, your problem would be false positives, since determinism will always show that subsequent state contains the same information as a previous one.

In the context of the mind-body problem, the contentious claim of emergentists is that mental properties can;t be reduced to physical properties in principal. There could be any number of in practice problems involved in understanding complex systems in terms of their parts. No actual reductionists think that all sciences should be replaced by particle physics, because they understand these in-practice problems. The contentiousness is all about the in-principle issues.