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shminux comments on [SEQ RERUN] Reductionism - Less Wrong Discussion
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It seems to me that the reductionism as advocated by Eliezer is a poor-quality model. It only works one way: you can potentially trace the 747 all the way down to its subatomic particles, but you cannot construct a particular configuration of subatomic particles that will fly, rather than bark or crawl, using just the laws of QFT. Thus it has no testable predictions (that everything we can see or touch consists of quarks, leptons and gauge bosons is not a prediction, but an observation), just like his other favorite myth, the MWI. He dislikes the term "emergence", and he is entitled to his emotions, but the sad experience is that nuclear physics is no help in psychology, not even after you say "reductionism" three times.
/looks up from reading a study using positron-emission-from-nuclear-isotopes tracing in the brain
I'm sorry, were you saying something?
I think the point was that modeling the brain with enough precision that nuclear physics became necessary to take into account would be intractable and likely not very useful anyway.
But you got the snark thing down, so upvotes for everyone.
Saying "you cannot" is awfully gutsy. Are you familiar with renormalization groups? They're a mathematical tool for getting high-level laws out of low-level laws. The only theoretically unsolved problem I know of between QFT and predicting planes is the prediction of a periodic solid as the ground state of your structural metal, though there are probably a few more.
True, let's say that I'd bet my house on it not being done in my lifetime.
Yes, in the HEP context.
Not quite. You can use renormalization to help explain some of what you observe at lower energies from a HE model point of view. I am yet to see an RNG prediction of a new low-energy effect, though I suppose it might happen for one-level-up problems, but not for any kind of multi-level jumps (do you seriously think that one can potentially renormalize quarks to cognitive biases?)
You are confusing predicting with explaining.
I can't figure out what you're trying to say. Are you saying:
(1) QFT is inherently incapable of explaining the aerodynamics of rigid macroscopic bodies, ever
(2) QFT can do that in principle, but in practice we can't yet justify some of the intermediate steps
(3) QFT can do that in principle, but in practice it's pointless because the higher-level theories already tell you everything about the higher levels
(4) something else?
As I said, explaining != predicting.
Is that my option 3? ETA: I still don't know what your point is. Try s/explaining/predicting in my previous comment.
ETA 2: The meaning of your original comment is what I really don't get. Eliezer is saying that reality consists of elementary particles, not elementary particles and other things. You don't seem to be disagreeing with this, but you're depreciating the proposition somehow. You say it's not predictive, but what is the significance of that? The fact that every natural number has a successor won't help you do arithmetic, but it's still true; and you really can do arithmetic with the larger axiom set of which it is a part. Analogously, the proposition that everything is made of elementary particles is not in itself very predictive, but it is a property of fundamental theories which we use and which are predictive.
What I am saying is that this is irrelevant for higher-level concepts. You can make the same brain out of neurons, or, if you believe in upload, out of bits. It will have all the same cognitive processes, same biases etc. Knowing that the former can be eventually decomposed into subatomic particles adds nothing to our understanding of psychology.
So? What query are you trying to answer?
Are you asking whether we ought to study and understand reductionism? Answer: yes, if we don't get reductionism, we might miss that uploads, etc. are possible.
Are you saying it may not be worth it to learn all the low-level detail, because our higher abstractions aren't all that leaky. Answer: agree for most things, but some require the lower stuff.
Why are you bringing this up?
I thought I had clearly explained it in my original top-level comment: the underlying structure is irrelevant for the entities a few levels removed.
And if it did, it wouldn't matter for atomic physics and up.
I understand what you are saying. Why are you saying it? What is interesting about the idea that higher levels of your map are agnostic to lower level details? What is the query?
To quote the article, "The map is not the territory, but you can't fold up the territory and put it in your glove compartment." Eliezer's point is not that we should discard all our higher level models. Of course you can't feasibly build a working 747 using a subatomic particle model. Of course you need to use higher level models if you want to get any useful work done. His point is that we need to recognise that they are models; that the universe does not really work with different rule sets for different levels.
A street directory of your town isn't actually your town. It is important to understand this, so you don't end up trying to go to your friend's house by jumping up and down on the appropriate page. But that doesn't mean you should throw the street directory away.
Are you saying that such a task would be prohibitively difficult, and presumably not something that is worth the effort, or are you saying that doing this is impossible in principle?
I don't think the renormalization group flow has anything to do with the topic, honestly.
It looked to me like the entire original post was about how you couldn't use lower level laws to extrapolate higher level laws. Renormalization is the only way I know of to do this. Additionally, every comment in this direct thread is about renormalization. I think renormalization is the topic.
Renormalization is a very specific technique, mostly used in HEP, to work around the infinities cropping up into the calculations. It does not let you predict anything about a lower-energy model from the higher-energy one, only to replace "bare" quantities with the renormalized ones.