Six Degrees: Urban Myth?

In the first issue of Psychology Today, back in May 1967, Stanley Milgram described the familiar "small world" experience:

"Fred Jones of Peoria, sitting in a sidewalk cafe in Tunisia, and needing a light for his cigarette, asks the man at the next table for a match. They fall into conversation; the stranger is an Englishman who, it turns out, spent several months in Detroit. 'I know it's a foolish question; says Jones, 'but do you by any chance know a fellow named Ben Arkadian? He's an old friend of mine, manages a chain of supermarkets in Detroit...'

'Arkadian...Arkadian...' the Englishman mutters. 'Why, upon my soul, I believe I do! Small chap, very energetic, raised merry hell with the factory over a shipment of defective bottle caps'

'No kidding!' Jones exclaims, amazed.

'Good lord, it's a small world, isn't it?'"

Milgram's small-world experiment took this idea a step further: His subjects could reach anyone in the country, maybe anyone on the planet, through a chain averaging just a few people.

In the intervening decades, Milgram's findings have slipped away from their scientific moorings and sailed into the world of imagination. The "six degrees of separation" between any two people has been adopted by the intelligentsia, and it has turned up in the media, movies and on Web sites.

But Milgram's startling conclusion has scanty evidence. The idea of six degrees of separation may, in fact, be plain wrong—the academic equivalent of an urban myth.

The Experiment

The question of how people are interconnected had long been a diversion among mathematicians: If you randomly choose any two people in the world, how many acquaintances would be needed to link them? Researchers Ithiel de Sola Pool at the Massachusetts Institute of Technology and Manfred Kochen of IBM collaborated on mathematical models over the past years, but never felt they had broken the back of the problem.

But Milgram believed he had made substantial progress, if not solved the problem outright. Rather than theorize, Milgram experimented. He asked "starters" from places such as Nebraska to mail a folder to a target person in major cities, such as Boston. The starters had to get the folder to someone they knew on a first-name basis. That person was to send the folder to someone closer to the target, and so forth. Incredibly, Milgram reported that it took only five people in six jumps to get the folder from the starter to the targeted stranger.

I had always regarded Milgram's work as one of the great counterintuitive studies in the social sciences and wanted to replicate it. To do so, I tracked down the details of the small-world study in Milgram's papers at the Yale archives.

What I found was disconcerting. Very few of his folders reached their targets. In his first, unpublished study, only three of 60 letters—5 percent—made it. Even in Milgram's published studies, less than 30 percent of the folders got through. Since then, only a few replications that actually spanned cities have been done. Of these trials, few folders made it through, especially across class and race boundaries.

Perhaps people didn't bother sending the letters on. That was Milgram's explanation. But that seems unlikely. The folder was not a simple chain letter, but an official-looking document with heavy blue binding and a gold logo. If the subjects knew how to reach the targets, they probably would have.

Inconclusive Evidence

There is some evidence that Milgram might be right despite his own research. Duncan Watts, Ph.D., at Columbia University, and his colleagues have created mathematical models that show how a small world could work. Random connectors in a network, such as especially sociable people who have friends across subcultures, can vastly decrease the distance between points in a network. This research has spurred interest in other fields such as disease transmission.

It is just as likely, though, that Milgram was wrong. But if we don't live in a small world after all, why do people find this idea so easy to believe? My research suggests that first, the belief that we live in a small world gives people a sense of security. And small-world experiences that we encounter naturally buttress people's religious faith as evidence of "design."

There is also a difference between what we mean by a small-world experience and what mathematicians mean. We are not talking about the chances of connection between two people taken at random. We are talking about the chances of meeting a person who knows someone from our past. Over a lifetime, these chances are high, especially for educated people who travel in similar networks.

And when an especially unlikely connection occurs, the world does feel small, whether or not the scientific evidence agrees.