WORLDS AND COMPLEX SYSTEMS
B y their very nature, complex systems resist analysis by decomposition. It is just not possible to study, say, the human immune system or a stock market by breaking it up into individual parts-molecules or traders-and looking at what these parts do in isolation. The very essence of the system lies in the interaction among all its parts, with the overall behavior of the system emerging from these interactions. So, by throwing away the interactions, one also throws away any hope of actually understanding the workings of the system. The problem is that, until very recently, there was no way of studying these sorts of systems as complete entities, since to do experiments with stock markets, immune systems, rainforest ecosystems, and the like was too expensive, too dangerous, or just plain too difficult. But the arrival of cheap, powerful, widespread computing capability over the past decade or so has changed the situation entirely.
I want to examine the way in which the ability to create surrogate versions of real complex systems inside our computing machines changes the way we do science. In particular, emphasis will be laid on the idea that these so-called "artificial worlds" play the role of laboratories for complex systems, laboratories that are completely analogous to the more familiar laboratories that have been used by physicists, biologists, and chemists for centuries to understand the workings of matter. But now we have laboratories that allow us to explore information instead of matter. And since the ability to do controlled, repeatable experiments is a necessary precondition to the creation of a scientific theory of anything, the argument will be made that, for perhaps the first time in history, we are now in a position to realistically think about the creation of a theory of complex systems.
By more-or-less common consensus, Galileo is credited with ushering in the idea of controlled, repeatable, laboratory experiments for the study of physical systems. And as such experiments are an integral part of the so-called scientific method, it is no exaggeration to say that Galileo's work formed a necessary precondition for Newton's creation of a workable theory of systems composed of interacting particles,