Sunday, September 23, 2012

Algorithms, AI, and Emergence

The story about why Google overtook AltaVista is a fascinating one. Up until Google, there were two ways of accessing web pages. The first was Yahoo!'s portal approach, in which a single authority determines the web pages worth viewing, and you trust the experts to have done their work. You want to read sports news? Go to Yahoo! and then the Sports category.  Simple.

Lightning fast!
The obvious problem is that the experts at Yahoo! might have missed something. For this reason, I always preferred AltaVista (or WebCrawler, before that), which used an indexing approach, similar to an index in the back of a book. AltaVista used simple programs to search for key terms in a page's text and metadata and then aggregate that data in a way that later could be easily matched and ranked according to search terms you fed it.

AltaVista was better than the alternatives for a few years, but it had trouble determining relevance. If you're searching for a recipe with certain ingredients, you don't want just any recipe; you want the best recipe. If you want to read about last night's game, you don't want just anyone's commentary; you want the best commentary.

Enter Google's PageRank algorithm. PageRank takes authority into account, like Yahoo!, but it doesn't require a single source of information, like AltaVista. Pages that have more links to them are ranked higher than ones that don't. And the pages that link to these pages give an even higher ranking if many pages link to them. PageRank lets you find what the most important people are talking about.

.304 (at the center) is the highest page rank in this contrived example

It's a bit more complicated than this, but what is revolutionary here (and I use the term revolutionary sparingly, unlike, ahem, Apple) is that Google's algorithm did not try to reproduce the intelligence of the web that was already out there. Instead, it tried to capitalize on the accumulated intelligence of millions of individuals who had made a simple choice: to link to or not link.

Linking is a binary action that, when accumulated into a large network of linked pages, allows for an emergent kind of intelligence. Emergence happens when a simple set of rules add up to something greater than their parts. Ants, for example, are very stupid individually, but when they signal to each other using pheromonic rules that have evolved, some very complex behavior emerges. Similarly, neurons in themselves have no intelligence. They can either fire or not. But when you have a few hundred billion of them, you're on your way to self-consciousness. Markets too display emergent phenomena when the buying and selling of millions of people shape the direction of societies.

PageRank is just one of a few algorithms that have begun to capitalize on emergence. For decades, it was assumed that language translation software would have to know the rules of grammar of the source and destination language in order to decode and encode meaning appropriately. This was a miserable failure. The success of modern translation algorithms is that they use statistics to compare millions of existing translated documents. The algorithm knows that, for example, it has seen 'Je suis' much more frequently than 'Je es'.  It doesn't need to know anything about grammatical rules.

An ant fugue
The problem with algorithms like PageRank is that they are parasitic upon an existing emergent system, whether it is a network of linked pages or a network of translations. The algorithms themselves are not emergent. They require human maintenance and tweaking, and they lead to people gaming the system. PageRank spawned web spam, in which people post links to sites in order to increase their ranking. This is why it's now only one of 200 or so indicators of rank for Google. The whole point of Gödel, Escher, Bach is that intelligence cannot be decomposable into a set of rules. Algorithms like PageRank are still just that.

While we've made some tremendous advances in machine learning by fitting algorithms to emergent systems, the future of AI can't be algorithmic. It can't be only a set of rules. But it might be a set of rules that, when used in aggregate, lead to emergent and artificial intelligence. What set of rules could be this flexible? Perhaps only the binary links of neural networks.

3 comments:

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