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In the 1960s Stanley Milgram conducted an experiment to test how many stages it would take to contact a randomly selected 'target' person. If those taking part did not know the target, and it was extremely unlikely that they would, they sent a letter to someone who might be closer to the target. This would continue in a chain until contact was made. The average number of steps required was six, coining the famous phrase "six degrees of separation". The idea has spawned a play of the same name by John Guare and the party game Six Degrees of Kevin Bacon where players are challenged to find the shortest number of film cast lists linking Hollywood actor Bacon to another star.

Subsequent small scale tests have been inconclusive, but Dr Duncan Watts hopes to attract 100 000 people who are willing to test whether the theory is sound.

Researchers hope to explore how social networks are structured and investigate whether parallels can be drawn between human social webs and engineered systems such as computer networks. Just how long are the chains that connect people?

"Broadcasting, where you send all your friends a message and they send all their friends a message and so on, would be a good way to learn where the shortest paths exist," Watts said. "But we'd be creating a computer virus, and we'd get arrested by the FBI. Instead, we're going for a lot of individual chains because, with enough of them, we'll learn how messages move through the social space."

"We'll be able to look at which social dimension people are using," Watts said, "be it work, family, friendship."

By conducting the study online, the researchers are limiting their pool of participants to people with email, but Watts said he did not think that was a problem. "Email is no longer the preserve of the tech elite," he said. ""There are a couple of hundred million people on email, across a number of social dimensions."

To take part, visit the website
website at Columbia University and register. You will then be sent the target person's name, where they live and what they do. Give details of a person you would like to contact, who you believe will take you closer to the target. This could be a friend, family member, work colleague, or any other type of acquaintance. You must have some relationship to the person you choose to email. Any information entered into the site will be kept confidential.