Steven Strogatz, Cornell University

NOTE: Originally published in the New York Times, this op-ed appeared on March 4, 2003. Reprinted by permission of the author.

Last week newspapers and magazines devoted tens of thousands of words to the 50th anniversary of the discovery of the chemical structure of DNA. While James D. Watson and Francis Crick certainly deserved a good party, there was no mention of another scientific feat that also turned 50 this year—one whose ramifications may ultimately turn out to be as profound as those of the double helix.

In 1953, Enrico Fermi and two of his colleagues at Los Alamos Scientific Laboratory, John Pasta and Stanislaw Ulam, invented the concept of a “computer experiment.” Suddenly the computer became a telescope for the mind, a way of exploring inaccessible processes like the collision of black holes or the frenzied dance of subatomic particles—phenomena that are too large or too fast to be visualized by traditional experiments, and too complex to be handled by pencil-and-paper mathematics. The computer experiment offered a third way of doing science. Over the past 50 years, it has helped scientists to see the invisible and imagine the inconceivable.

Fermi and his colleagues introduced this revolutionary approach to better understand entropy, the tendency of all systems to decay to states of ever greater disorder. To observe the predicted descent into chaos in unprecedented detail, Fermi and his team created a virtual world, a simulation taking place inside the circuits of an electronic behemoth known as Maniac, the most powerful supercomputer of its era. Their test problem involved a deliberately simplified model of a vibrating atomic lattice, consisting of 64 identical particles (representing atoms) linked end to end by springs (representing the chemical bonds between them).

This structure was akin to a guitar string, but with an unfamiliar feature: normally, a guitar string behaves “linearly”—pull it to the side and it pulls back, pull it twice as far and it pulls back twice as hard. Force and response are proportional. In the 300 years since Isaac Newton invented calculus, mathematicians and physicists had mastered the analysis of systems like that, where causes are strictly proportional to effects, and the whole is exactly equal to the sum of the parts.

But that’s not how the bonds between real atoms behave. Twice the stretch does not produce exactly twice the force. Fermi suspected that this