Natalie Wolchover in Quanta:
What’s a physicist doing studying terrorist networks, financial markets and all these other systems?
In all these complex systems, the pieces of the system interact with each other and they evolve over time. And there’s something that a collection of objects like that can do which a handful of coins cannot do. I can throw up a set of coins and it would always come down pretty much 50-50 heads and tails, and there will be a little bit of variance around that — it obeys something called a bell curve. We base so much science on the bell curve. Bell-curve distributions arise when you deal with coins, or any collection where the pieces aren’t connected, like heights of people in a room. However, in most of the systems we’re interested in — the hard problems, be they of science or society — those distributions look very different than bell curves; they’re so-called fat-tail distributions.
Thinking about heights, instead of everybody being 5 feet 10 inches, on average, and maybe down to 4 feet and up to 7 feet, but certainly not 70 feet, with the distributions you get in these complex systems, you can get the 70-foot person. In fact, you can get the 700-foot person. There’s something about the way the pieces interact with each other that makes these extreme events happen: the 700-foot person, the stock market crash, the 9/11. So the interesting question is, is there a general science that can govern and tell us about these extreme behaviors? And if we can understand that for one system, can we transfer that understanding over to another one and therefore do something about it?