in praise of simplicity
In her keynote at PyCon a few minutes ago, Adele Goldberg just mentioned Mitch Resnick’s book Turtles, Termites and Traffic Jams. I wrote a review of the book for the Complexity journal in 1994 or 1995:
There is an important trade-off between realism and understanding in the construction of models of complex systems. At one extreme, a model may be so realistic that it allows no increase in understanding of the modeled system. At the other, the model may be precisely understood but be so divorced from reality that this understanding cannot be related back to the original system. The construction of a model requires that difficult choices be made about what aspects of a system should and should not be modeled, and about how abstractions, simplifications and generalizations are to be justified and implemented. Any unchecked tendency to include more than is absolutely necessary can soon result in a model that, at least aesthetically, feels somehow bloated. It is easy to underestimate the difficulty involved in these decisions, and in the requirements of good judgement and taste in the construction of models.
It was with great pleasure then that I read Mitchel Resnick’s “Turtles, Termites, and Traffic Jams: Explorations in Massively Parallel Microworlds” (1994, MIT Press). Resnick’s StarLogo system achieves a balance between simplicity and realism that it would be difficult to improve on. This is an accomplishment in itself, but Resnick takes us much further. His StarLogo is not a single model, but a platform for exploring a wide range of decentralized systems. The StarLogo system deals so effectively with the trade-off between realism and understanding, that at times one tends to forget it is an issue.
The most provocative situation in modeling, and a sure sign that a model has dealt with the trade-off well, occurs when an apparently simple model produces unexpected results. At these times, the potential for increased understanding is at its greatest. The probability of explaining the surprising results is high, because the model is apparently simple. The decentralized systems constructed and described by Resnick repeatedly produce surprises of this kind. The delightful simplicity of StarLogo makes it possible to understand what is happening, and why our expectations were incorrect. These systems, few and far between, offer the highest returns for the effort we must invest to understand and use them.
In five short chapters, Resnick guides us through thinking about centralized and decentralized mindsets, the StarLogo system, and reflections on psychology and education. The “Explorations” chapter describes simulations (or, as Resnick prefers, stimulations) of Slime Molds, Artificial Ants, Traffic Jams, Termites, Turtles, Frogs, Forest Fires, Geometry and Recursive Trees. Resnick guides us through the thinking behind the construction of these simulations, presents alternative ideas for their construction, and argues well for decentralized views of these systems. Resnick offers the reader challenges, surprises, insights, and simple heuristic guidelines that he developed as a result of these explorations. It is remarkable that Resnick includes the entire StarLogo programs for these systems in the text of the book. The code, only once slightly over two pages in length, is clear, instructive, and incredibly simple.
Resnick’s book is a little treasure. Though much of the book is presented in the context of high-school education, any temptation to discount it on this account should be resisted. Resnick has something to teach us all. If it has a failing, it is the modesty of its presentation and claims, which may retard its recognition in “higher” academic circles. Virtually every aspect of this book should be instructive to researchers involved in agent-based modeling and simulation, especially to those in biology and artificial life. To the many scientists interested in agent-based computational modeling who are, however, not computationally inclined, read this book. It is an example of someone getting a set of deceptively difficult problems absolutely right. There are many ways in which to appreciate “Turtles, Termites, and Traffic Jams.” It is an important book.
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