Complex Adaptive Systems

For my summer reading I’m aiming to catch up on the classics. It’s all about finding the sweet spot of books that make you smarter, but aren’t too boring to bring to the beach. For me that’s usually an Elmore Leonard novel, or – if I can muster the discipline (and that pretty much never happens) – something by a more literary writer. This year, however, I’ve been extra good and have been reading  “Complex Adaptive Systems” by Miller & Page. It’s an introduction to computational models of social systems, and contains a great set of reflections on the use of computation as a tool for building theory + surveys a lot of work I never got around to reading.

I’m not sure I agree with the authors on everything in the book (not really a fan of agent based models in the age of big data), but one section that resonated me is their Physics envy: A pseudo-freudian analysis. They start out the section by writing:

During the late nineteenth century, various “cargo cult” societies emerged in the South Pacific. By the mid-twentieth century, inspired by their experiences during World War II, these societies built elaborate mock facilities, such as airstrips and control towers, in hopes of attracting deliveries of goods similar to those that colonial officials once received. Like these societies, we suspect that much of the current view and apparatus of theory in economics is based on misinterpreted observations and misplaced hopes.

So the tone is set. This sounds a lot like the kind of old-school physicists who tend to see themselves as the lords of the academic jungle. Being a kind of physicist myself, that’s how I grew up, and there’s a certain familiarity to these arguments that reminds me of the halls of the Niels Bohr Institute … and generates a warm, fuzzy feeling when reading stuff like this. My own views have matured a bit since those days, and I’m more in line with Cosma Shalizi’s view (as argued elegantly here and here) that physicists have a bad habit of trying to take up new subject-matter and not learning what’s already known about it …

Thus, it’s a fun start (for a physicist) to see Miller & Page openly – and without any hesitation – comparing economics to a cargo cult. And there is a more serious point coming up next

There is a commonly held perception in economics that its approach to theorizing closely follows the “one” that is used in physics. Indeed, at certain levels, modern economic theory does resemble some parts of physics, where a small set of well-formulated mathematical models is applied to a broad spectrum of the world. However, based on our interactions at the Santa Fe Institute with a fine group of theoretical physicists, we find that this narrow view of theoretical work is far too restrictive to capture either the reality or the potential of what other fields like physics have to offer in terms of ways to approach theoretical questions in the social sciences.

Theoretical physicists are concerned with, and rewarded by, finding insights about nature through the creation of models and the generation of hypotheses. The emphasis here is on understanding nature, not on the tools used to gain this understanding. [my emphasis]

This, I think, hits the nail on its head. That’s precisely what I think is great about physics. And this emphasis on insight and disregard for choice of methodology is the trait that  does distinguishes physicists from scientists from many of the other fields (at least in my experience).

A clarification is in order  here (also just so I don’t sound too much like one of those old-school physicist myself). The thing that Miller & Page focus on is the insight, but I think that’s missing the point a little bit. Every scientific field is about insight – and the search for new insights had better be common to every field of science. What’s special about physics might just be the disregard for the method with which the insight was obtained.

I honestly don’t know other fields (or philosophy of science for that matter) well enough to know if what I’m about to say is true (but random thoughts are what this blog is for, and comments are welcome), but my sense is that most fields are defined primarily defined via the methods they use. For example, if I want to publish in a computer science journal, I have to actually develop new theory that connects to the existing theory in computer science, using the methods of computer science – my sense is that this pattern is true more generally.

The point is drawn even clearer as Miller & Page continue

The premium in theoretical physics is on gaining insight into interesting phenomena. If the insight is there, then there is little desire for mathematical rigor. Consequently, in physics there is a sharp distinction between the mathematical and theoretical branches. Having a good insight and stating a theorem that is not rigorously proved is acceptable behavior. Once, during a talk at the Santa Fe Institute, a well-known theoretical physicist was asked if he could rigorously prove a proposition that he had just made, and his answer was “No, and I don’t need to, but I’m sure someone can.” On first hearing by most economists, this seemingly casual approach to scientific theory is scandalous at best; yet, ultimately it becomes a very productive way to make scientific progress.

While axiomatic rigor is not required for theoretical work in physics, there is still a high premium on good theory—just not on the tools used to develop the theory. Theory must result in insight and withstand testing. [my emphasis]

And perhaps I need another caveat here. I readily concede that are plenty of ‘conservative’ physicists who tend to deem everything that’s not strictly-within-the-boundaries-of-classical-physics as “non-physics”; and who would not think Page & Miller’s work is ‘real physics’. And those same guys might very well be critical towards methods appropriated from other fields, if you were lucky enough to have them review your paper in a physics journal.

But that being said, I do think there’s a tendency for physics to be more inclusive of new methods as long as they get the job done. If I were to name a reason, I’d say maybe it’s because an education in physics already includes  very wide a variety of mathematical tools?

What I’m working on these days probably won’t be classified as physics by most people, but what a background in physics has provided me, is not just a focus on insight over everything else, but a lack of respect for how to build a good theory. As long as you employ the rules of logic & common sense, as long as your work can be reproduced by others, and as long as you’re able to convince most rational beings that you’re right, the details of how you got there are less important.

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Sune Lehmann

I’m an Associate Professor at the Department of Applied Mathematics and Computer Science, at the Technical University of Denmark.

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