Everything Is Obvious_ _Once You Know the Answer - Duncan J. Watts [39]
CHAPTER 4
Special People
It may seem hard to believe in a time when “social networking” has become so commonplace an idea that it shows up in everything from feature films to Foster’s beer commercials, but it wasn’t that long ago—as recently as the mid-1990s—that the study of social networks was relatively obscure, pursued mostly by a small cadre of mathematically inclined sociologists interested in mapping the social interactions among individuals.1 The field has exploded in recent years, in large part because fast computers, along with communication technologies like e-mail, cell phones, and social networking sites such as Facebook have made it possible to record and analyze these interactions with great precision, even for hundreds of millions of people at a time. Nowadays, thousands of computer scientists, physicists, mathematicians, and even biologists count themselves as “network scientists,” and new discoveries about the structure and dynamics of networked systems arrive daily.2
SIX DEGREES OF SEPARATION
Back in 1995, however, when I was a graduate student at Cornell studying the synchronization of chirping crickets, all this was in the future. Back then, in fact, the idea that everyone in the world is connected through a giant social network through which information, ideas, and influence might flow, was still sufficiently novel that when my father asked me during one of our regular phone conversations if I’d ever heard of the notion that “everyone in the world is only six handshakes away from the president of the United States,” I assumed it was folklore. And in some sense it was. People have been fascinated with what sociologists call the small-world problem for nearly a century, since the Hungarian poet Frigyes Karinthy published a short story called “Chains” in which his protagonist boasts that he can connect himself to any other person in the world, whether a Nobel Prize winner or a worker in a Ford Motor factory, through a chain of no more than five acquaintances. Four decades later, in her polemic on urban planning The Death and Life of Great American Cities, the journalist Jane Jacobs described a similar game, called messages, that she used to play with her sister when they first moved to New York:
The idea was to pick two wildly dissimilar individuals—say a headhunter in the Solomon Islands and a cobbler in Rock Island, Illinois—and assume that one had to get a message to the other by word of mouth; then we would each silently figure out a plausible, or at least possible, chain of persons through whom the message could go. The one who could make the shortest plausible chain of messages won.
But how long are these chains in reality? One way to answer the question would be to map out all the links in the social network of the whole world and then simply count by brute force how many people you can reach in one “degree of separation,” how many at “two degrees,” and so on, until you have reached everyone. In Jacobs’s day that was impossible, but in 2008 two computer scientists at Microsoft Research got somewhat close when they computed the length of paths connecting pairs of individuals in Microsoft’s 240-million-strong instant messenger network, where being “friends” in this case meant being on each other’s buddy lists.3 On average they found that people were separated by about seven steps—remarkably close to the six handshakes that my father had mentioned. Yet this can’t be the real answer to the question. The characters in Jacobs’s fictional game didn’t have access to this network, so they couldn’t have computed the paths the way the Microsoft researchers did even if they had the computing power to do so. Clearly they must have used some other method to direct their messages. And indeed, according