Even in a small world, there’s room for disagreement:

You probably don’t know Judith Kleinfeld. She’s a psychologist at the University of Alaska in Fairbanks, and you can contact her by calling the university switchboard or finding her e-mail address online. But could you get to her through some extension of your own social network—by mailing a letter for her to a friend who might know someone who knows someone who knows her?

Who cares?

Judith Kleinfeld does, for starters. She’s part of a growing cadre of scientists reviving the so-called small-world problem, a social-cum-mathematical conundrum formulated in the last century to characterize the interwoven webs of acquaintance among friends, neighbors, colleagues, and kin. In the mid-1960s the legendary social psychologist Stanley Milgram asked randomly selected citizens of Kansas and Nebraska to try to connect with social “targets” in Massachusetts by mailing letters to likely intermediaries. The average number of links between strangers turned out to be surprisingly small. Milgram claimed we’re all connected, on average, by half a dozen interpersonal avenues— a numinous network popularized by the phrase “six degrees of separation.” Discover