According to Milgram's theory, anyone can reach anyone else through a chain of acquaintances no more than six people long.
This idea, known as "six degrees of separation", is a measure of our social networks.
Judith Kleinfeld, a professor psychology at Alaska Fairbanks University, went back to Milgram's original research notes and found something surprising.
It turned out, she told us, that 95% of the letters sent out had failed to reach the target.
Not only did they fail to get there in six steps, they failed to get there at all.
If 95 or 97 letters out of 100 never reached their target, would you say it was proof of six degrees of separation? So why do we want to believe this?"
"The pleasing idea that we live in a 'small world' where people are connected by 'six degrees of separation' may be the academic equivalent of an urban myth," she says. More
I for one, certainly want to believe it. It's a game I play over dinner in Kosovo whenever I meet a new international. We try and find an acquaintance in common, some place we have both worked usually does the trick. Usually we can find several people we have in common as acquaintances or even good friends, though we have never met before. OK it's a small world that we move in doing this work, but not that small.
But the article says that barriers of race and class (and I would think, nationality also) create stronger barriers than social networks. The only reason we have only one degree of separation from our colleagues is that we move internationally amongst groups of internationals, and so the work itself breaks down the barriers between nationalities and place of work.
Social networks are supposed to be unsustainable beyond around 150, a typical size for a village of several families.
But this was probably observed in less developed societies, certainly before telephones and internet. What is the size of a social network when there is a "telephone lady" in the village? This is a mobile phone effectively rented for use by the village, which can be used to contact distant relatives in towns, to find out the prices in nearby markets, or to find out when boats arrive at the coast.
Certainly 150 is a small number of contacts for anyone to keep in their contacts list, these days.