He found that each chain averaged six links, with the final member of the chain being the target itself. The result become popularized through the phrase "six degrees of separation," which became part of both sociology dogma and pop culture, and was the name of a popular 1990 play by John Guare.
A popular parlor game, hosted online by the University of Virginia in Charlottesville, involves finding the shortest route between any given thespian and actor Kevin Bacon. Links are made by appearing in a movie with Bacon, or with someone has appeared with Bacon, and so on.
Among all actors, living and dead, the average number is close to three. No actor has been found to be more than 10 degrees of separation from Bacon.
Proving Milgram
The notion that millions of people are connected by just a few short steps seems obvious in today's digital world where e-mail viruses can shut down half of the world's computers in a click.
But very little empirical research has been done to actually understand the small world network theory.
For their Columbia University project, Watts, who is the author of Six Degrees: The Science of a Connected Age, and his colleagues chose 18 targets, including an American professor at an Ivy League University, an archival inspector in Estonia, an Indian technology consultant, a policeman in Australia, and a veterinarian in the Norwegian Army.
Participants, who found out about the experiment primarily through media stories, were given the name of a target and information about the target's work and location. They were then asked to send a message to someone they knew—and ask them to pass on the message—with the aim of ultimately reaching the target.
"We knew that people who participate in a study like this are often people who are at work, sitting in front of a computer with a few minutes to spare," said Watts. "We designed the program with that in mind."
One chain started with an e-mail from a British military officer, jumped to a finance executive in Uganda, on to an art student in Moscow, then a student in Novosibirsk, Russia, before landing in the inbox of its target, another student in Novosibirsk.
Watts found that successful chains more often involved professional ties than personal ties.
"Weak ties are disproportionately responsible for social connectivity," he said. One explanation for this may be that close friends know the same people as the person who is sending the message.
Watts admits that his project may not be an accurate reflection of the connectivity of the world's entire population. There are, after all, only about 100 million e-mail users. While North America and Western Europe were heavily represented in the project, Africa was not.
Small World Network Models
A separate project, based at Ohio State University in Columbus, is also identifying social structures of e-mail communication networks. Its goal is to create a social map of the Internet to reveal how different types of people are connected and how information moves through society.
"The types of goods that flow through the network—information, ideas and viruses—depend on the social connection between people," James Moody, who is leading the Ohio State project, wrote in an e-mail.
"If we can identify how these networks are shaped, we can better understand information flow, promoting the things we want (information, ideas) and preventing the things we don't want (computer viruses)." Researchers hope the results of their studies will help shed light not only on how people are connected, but on how diseases spread, how people find jobs, how to build better computer networks, and how the global economy operates.
People are indeed connected in principle, but whether or not they are connected in practice depends on their motivation to pursue the search.
"A lot of the world is accessible to you," he said. "If you're determined, you will find what you're looking for as long as you're tenacious about it."
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