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In Context #7 (Spring, 2002, pp. 19-23); copyright 2002 by The Nature Institute

The Lure of Complexity (Part 2)
Stephen L. Talbott

(This is the second part of a two-part essay. The first part appeared in our Fall, 2001 issue and is available here.

Anyone who lives in an earthquake zone knows that mild earthquakes are much more common than powerful, devastating ones. What you might not expect, however, is that a simple, straight-line mathematical relationship known as a "power law" tells you what percentage of earthquakes will exceed any given energy. Even more surprisingly, you can derive the same sort of law showing what percentage of cities will be larger than a given size. Or what percentage of fjords in Norway will exceed a given length. Other power laws occur when you look at word-usage patterns in texts, global temperature variations, the occurrence of traffic jams, stock market performance, and (as discussed in part 1) avalanches in artificially constructed sand piles.

In each of these domains any attempt at causal analysis leads you to the complex, nearly unanalyzable interplay of countless factors. (Try to tabulate all the reasons why individuals migrate