I recently read an article called "Complex Systems, Artificial Intelligence and Theoretical Psychology" by Richard Loosemore. The argument it makes goes something like this:
1. A "complex system" (referring to complex systems science) is one that displays behavior that cannot be predicted analytically using the system's defining rules. (This is called, in the paper, a global-local disconnect: the local rules that play the role of the "physical laws" of the system are disconnected analytically from the global behavior displayed by the system.)
2. The mind seems to be a complex system, and intelligence seems to be a global phenomenon that is somewhat disconnected with the local processes that create it. (Richard Loosemore argues that no real proof of this can be given, even in principle; such proofs are blocked by the global-local disconnect. However, he thinks it is the case, partly because no analytical solution for the mind's behavior has been found so far.)
3. The mind therefore has global-local disconnect. Richard Loosemore argues that, therefore, artificial intelligence cannot be achieved by a logical approach that attempts to derive the local rules from the list of desired global properties. Instead, he proposes an experimental approach to artificial intelligence: researchers should produce and test a large number of systems based on intuitions about what will produce results, rather than devoting years to the development of single systems based on mathematical proofs of what will produce results.
I agree with some points and disagree with others, so I'll try to go through the argument approximately in order.
First, I do take the idea of a complex system seriously. Perhaps the idea that the global behavior of some systems cannot be mathematically predicted seems a bit surprising. It IS surprising. But it seems to be true.
My acceptance of this idea is due in part to an eye-opening book I recently read, called "Meta math: the quest for omega", by Gregory Chaitin.
Chaitin's motivation is to determine why Godel's Theorem, proving the incompleteness of mathematics, is true. He found Godel's proof convincing, but not very revealing: it only gives a single counterexample, a single meaningful theorem that is true but mathematically unprovable. But this theorem is a very strange-sounding one, one that nobody would ever really want. Perhaps it was the only place where math failed, or perhaps math would only fail in similarly contrived cases. Chaitin wanted some indication of how bad the situation was. So he found an infinite class of very practical-sounding, useful theorems, all but a handful of which are unreachable by any formal logic! Terrible!
Perhaps I'll go through the proof in another post.
Chaitin shows us, then, that there really are global properties that are analytically unreachable. In fact, in addition to his infinite class of unreachable-but-useful theorems, he talks about a global property that any given programming language will have, but which is analytically unreachable: the probability that a randomly generated program will ever produce any output. This probability has some very interesting properties, but I won't go into that.
I think the term Chaitin used for math's failure is somewhat more evocative than "global-local disconnect". He uses the term "irreducible mathematical fact", a fact of mathematics that is "true for no reason", at least no logical reason. Notice that he still refers to them as mathematical facts, because they are true statements about mathematical entities. As with other mathematical facts, it still seems as if their truth would be unchanged in any possible world. Yet, they are "irreducible": logically disconnected from the body of provable facts of mathematics.
So, math sometimes cannot tell us what we want to know, even when we are asking seemingly reasonable questions about mathematically defined entities. Does this mean anything about artificial intelligence?
Another term related to global-local disconnect, this one mentioned in the paper by Loosemore, is "computational irreducibility". This term was introduced by Stephan Wolfram. The idea is that physics is able to predict the orbits of the planets and the stress on a beam in an architectural design because these physical systems are computationally reducible; we can come up with fairly simple equations that abbreviate (with high accuracy) a huge number of physical interactions. If they were not reducible, we would be forced to simulate each atom to get from the initial state to the final result. This is the situation that occurs in complex systems. Unlike the "mathematically irreducible" facts just discussed, there IS a way to get the answer: run the system. But there are no shortcuts. This form of global-local disconnect is considerably easier to deal with, but it's still bad enough.
It's this second kind of irreducibility, computational irreducibility, that I see as more relevant to AI. Take the example of a planning AI. To find the best plan, it must search through a great number of possibilities. Smarter AIs will try to reduce the computation by ruling out some possibilities, but significant gains can be made only if we're willing to take a chance and rule out possibilities we're not sure are bad. The computation, in other words, is irreducible-- we'll have a sort of global-local disconnect simply because if we could predict the result from the basic rules, we wouldn't need the AI to find it for us.
So it seems Loosemore was right: intelligence does seem to involve complexity, and unavoidably so. But this sort of irreducibility clearly doesn't support the conclusion that Loosemore draws! The global-local disconnect seems caused by taking a logical approach to AI, rather than somehow negating it.
But there is a way to salvage Loosemore's position, at least to an extent. I mentioned briefly the idea of shortcutting an irreducible computation by compromising, allowing the system to produce less-than-perfect results. In the planning example, this meant the search didn't check some plans that may have been good. But for more complicated problems, the situation can be worse; as we tackle harder problems, the methods must become increasingly approximate.
When Loosemore says AI, he means AGI: artificial general intelligence, the branch of AI devoted to making intelligent machines that can deal with every aspect of the human world, rather than merely working on specialized problems like planning. In other words, he's talking about a really complicated problem, one where approximation will be involved in every step.
Whereas methods of calculating the answer to a problem often seem to follow logically from the problem description, approximations usually do not. Approximation is hard. It's in this arena that I'm willing to grant that, maybe, the "logical approach" fails, or at least becomes subservient to the experimental approach Loosemore argues for.
So, I think there is a sort of split: the "logical" approach applies to the broad problem descriptions (issues like defining the prior for a universal agent), and to narrow AI applications, but the "messy" approach must be used in practice on difficult problems, especially AGI.