The Logic of Life by Tim Harford

Author:Tim Harford
Language: eng
Format: mobi, epub
ISBN: 9781588366825
Publisher: Random House
Published: 2008-01-15T06:00:00+00:00

SCHELLING’S CHESSBOARD MODEL suggests that transformations such as Fifteenth Street’s should be impossible: Things always fall apart, people always give in to their prejudices, and small anxieties lead to big divisions. But Schelling’s model is not a forecast, just an illustration of the kind of unexpected transitions that can emerge from individual interactions. Its successors, sophisticated simulations using modern computers with hundreds of thousands of decision makers rather than a chessboard with forty checkers, often find the same sort of sudden transitions, but not necessarily to the worst possible outcomes.

One model was developed by a political economist who was then at the Brookings Institution, just a few blocks away from Whole Foods and the Fifteenth Street attack. Ross A. Hammond developed his model in 2000, at a time when the Washington, D.C., community around him was becoming safer at a dramatic rate. Perhaps it was this startling transition that inspired him to develop models of artificial societies that move from a corrupt, crime-ridden state to being the most genteel, law-abiding communities.

Hammond’s computer creates a simple world populated by artificial people. Watching it work is a little like watching speeded-up footage of a Schelling chessboard. Little patterned tiles cascade down the screen, each representing a person and each with a color that shows how each person is acting. And how do they act? The computer randomly pairs up people each “day” (actually, many times a second). The computer gives them a simple choice: Act honestly or act corruptly. If both sides of the pair act corruptly, both enjoy a kickback; if only one side acts corruptly and the other honestly, the crook will go to jail.

The magic of the computer model is in seeing how quickly the artificial world can change. At first, it is populated by self-interested crooks, with a few honest citizens sprinkled among them. The few honest citizens don’t respond to incentives; irrationally, if heartwarmingly, they always act honestly. The crooks do respond to incentives, being corrupt or honest depending on whether they believe the other side will reciprocate. The chances of honesty being the best policy are quite small at first, and many days go by with corruption thick in the air and the honest folk unable to stem the tide.

But when Hammond’s crooks fear that even other crooks will decide to act honestly, they will do the same. That fear of an outbreak of honesty can spring up suddenly as the result of a few random events, a few honest citizens clustered together creating the impression of a legal crackdown. After a long period of pure corruption, Hammond’s model displays a change even more dramatic than Schelling’s: Suddenly, very quickly, everybody in the world decides to be honest. The moment the process starts it is impossible to stop: Offering a corrupt deal becomes irrational and suddenly the world is full of crooks who have decided that honesty is the best policy. It is a self-fulfilling decision. The cascade of tiles on the computer screen changes color abruptly as honesty breaks out everywhere.

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