who never appeared with Bacon can be linked indirectly: Penelope Cruz has no common films with Bacon, but she was in Vanilla Sky with Tom Cruise, who appeared with Bacon in A Few Good Men. By mid-2005, Bacon had appeared in films with nearly 2,000 other actors, and he could be linked in six steps or fewer to more than 99.9 percent of all the linked actors in a database dating back to 1892. Bacon’s notoriety in this regard has become legendary, even earning him a starring role in a TV commercial shown during the Super Bowl.

Bacon’s fame inspired the renaissance of a branch of mathematics known as graph theory—in common parlance, the math of networks. Bacon’s role in the network of actors motivated mathematicians to discover new properties about all sorts of networks that could be described with the tools of statistical physics. In particular, modern Baconian science has turned the attention of statistical physicists to social networks, providing a new mode of attack on the problem of forecasting collective human behavior.

In fact, the new network math has begun to resemble a blueprint for a science of human social interaction, a Code of Nature. So far, though, the statistical physics approach to quantifying social networks has mostly paid little attention to game theory. Many researchers believe, however, that there is—or will be—a connection. For game theory is not merely the math for analyzing individual behavior, as you’ll recall—it also proscribes the rules by which many complex networks form. What started out as a game about Kevin Bacon’s network may end up as a convergence of the science of networks and game theory.

SIX DEGREES

In the early 1990s, Kevin Bacon’s ubiquity in popular films caught the attention of some college students in Pennsylvania. They devised a party game in which players tried to find the shortest path of movies linking Bacon to some other actor. When a TV talk show publicized the game in 1994, some clever computer science students at the University of Virginia were watching. They soon



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