Six Degrees of Separation

In the previous chapter, we considered how social networks can serve as conduits by which ideas and innovations flow through groups of people. To develop this idea more fully, we now relate it to another basic structural issue — the fact that these groups can be connected by very short paths through the social network. When people try to use these short paths to reach others who are socially distant, they are engaging in a kind of “focused” search that is much more targeted than the broad spreading pattern exhibited by the diffusion of information or a new behavior. Understanding the relationship between targeted search and wide-ranging diffusion is important in thinking more generally about the way things flow through social networks.

As we saw in Chapter 2, the fact that social networks are so rich in short paths is known as the small-world phenomenon, or the “six degrees of separation,” and it has long been the subject of both anecdotal and scientific fascination. To briefly recapitulate what we discussed in that earlier chapter, the first significant empirical study of the small-world phenomenon was undertaken the social psychologist Stanley Milgram [297, 391], who asked randomly chosen “starter” individuals to each try forwarding a letter to a designated “target” person living in the town of Sharon, Massachusetts, a suburb of Boston. He provided the target's name, address, occupation, and some personal information, but stipulated that the participants could not mail the letter directly to the target; rather, each participant could only advance the letter by forwarding it to a single acquaintance that he or she knew on a first-name basis, with the goal of reaching the target as rapidly as possible.