launched a research project that spawned a Web page providing instant calculations of how closely Bacon was linked to any other actor. (You should try it—go to The 1,952 actors directly linked by a common film appearance with Bacon each have a “Bacon number” of 1. Another 169,274 can be linked to Bacon through one intermediary, giving them a Bacon number of 2. More than 470,000 actors have a Bacon number of 3. On average, Bacon can be linked to the 770,269 linkable actors in the movie database1 in about 2.95 steps. And out of those 770,269 in the database, 770,187 (almost 99.99 percent) are linked to Bacon in six steps or fewer—nearly all, in other words, are less than six degrees of separation from Bacon.

So studies of the Kevin Bacon game seemed to verify an old sociological finding from the 1960s, when social psychologist Stanley Milgram conducted a famous mail experiment. Some people in Nebraska were instructed to send a parcel to someone they knew personally who in turn could forward it to another acquaintance with the eventual goal of reaching a Boston-area stockbroker. On average, it took a little more than five mailings to reach the stockbroker, suggesting the notion that any two people could be connected, via acquaintances, by less than “six degrees of separation.” That idea received considerable publicity in the early 1990s from a play (and later a movie) of that title by John Guare.

From a scientific standpoint, the Bacon game and Guare’s play came along at a propitious time for the study of networks. The six-degrees notion generated an awareness that networks could be interesting things to study, just when the tools for studying networks fell into scientists’ laps, in the form of powerful computers that, it just so happened, were themselves linked into a network of planetary proportions—the Internet.


When I was growing up, “network” meant NBC, ABC, or CBS. Later came PBS, CNN, and ESPN, among others, but the basic idea stayed the same. As the world’s cultural focus shifted from TV

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