An unexpected e-mail from a US university over the coming months may not be spam 鈥� it could be from scientists investigating a fascinating social phenomenon.
According to urban folklore, everyone in the world knows everyone else via just a few intermediaries 鈥� an effect summed up by the phrase 鈥渟ix degrees of separation鈥�.
The number six emerged from an experiment performed in 1967 by the social psychologist Stanley Milgram, who sent packages to several hundred randomly selected people in America鈥檚 Midwest, with the aim of getting them delivered to target people in Boston.
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Each recipient was given some details about the target, such as their name and profession, and was asked to send the package to a personal acquaintance whom they believed was more likely to know the target personally. Milgram discovered that on average the packages reached their targets after passing through astonishingly short chains, typically comprising just six people.
Small world
In 1998, mathematicians Duncan Watts and Steven Strogatz at Cornell University showed that Milgram鈥檚 finding can be explained by the 鈥渟mall world effect鈥�, in which just a handful of people with very diverse friends can 鈥渟hort circuit鈥� otherwise huge networks of acquaintances.
But attempts to replicate Milgram鈥檚 findings have had mixed results 鈥� and in any case, the original experiment fell far short of proving that the 鈥渟ix degrees鈥� effect holds true for the whole world. So a team at Columbia University is now using the internet to attempt a global version.
Instead of a postal package, they are inviting people to use their network of acquaintances to get an e-mail message to targets spread across the world. According to Watts, who devised the experiment, e-mail is ideal for testing Milgram鈥檚 claim as there are well over 100 million e-mail users worldwide.
Only e-mails between genuine acquaintances will be deemed to complete a chain. People will not be allowed to short-circuit the sequence by just looking up the target鈥檚 e-mail address.
Chain mail
Watts has set up a website giving details about how to take part, and how to volunteer to act as a target. 鈥淚deally, we鈥檇 like to have, say, 100,000 people, each trying to reach around 20 targets,鈥� he says.
The team is keen to have as many people take part as possible, not least because they suspect people鈥檚 mistrust of unsolicited e-mail might otherwise scupper their experiment.
Early tests show that barely one in four e-mails are being passed on. With such a high rate of attrition, many thousands of people would have to take part to give much chance of even one chain of acquaintances reaching the target if Milgram鈥檚 six degrees apply worldwide.
鈥淧erhaps people can鈥檛 be bothered to pass them on 鈥� or perhaps Milgram was just wrong,鈥� says Watts. 鈥淓ither way, we need lots of people to take part so we can tell.鈥�