Six degrees of separation refers to a theory that all people on Earth are connected to one another by no more than six separate individuals. A theory that parallels the idea that “it’s a small world,” six degrees of separation maintains that through a series of connections or steps, all people have the potential to know one another on a first name basis through mutual acquaintances.

The theory of six degrees of separation has been examined through research for proof that the theory holds true. Milgram’s Small World Experiment, a study conducted by Stanley Milgram, a researcher of social psychology at Harvard University, is perhaps the most famous such experiment. Though Milgram reportedly never used the term six degrees of separation, his experimental findings did somewhat support the theory.

Milgram’s Small World Experiment began in the late 1960s. He conducted various experiments that involved sending informational packets from one starting individual to an ending individual, neither of whom personally knew each other. The packets contained rosters where participants in the study passed on the packet and then listed their names and mailed postcards to researchers at Harvard for tracking purposes. The results of Milgram’s experiments, though not exactly scientific, concluded that those packets that reached the targeted recipients had an average path length of five to six people.

A similar study to prove six degrees of separation was conducted in 2001 by Professor Watts at Columbia University. This modern day experiment was performed using email messages at the packet that was passed along. His findings also concluded that the average number of people within a given chain was six.

Though there is no solid scientific evidence that the six degrees of separation theory is correct, it, along with the small world phenomenon, remains an area of interest to social researches. Six degrees of separation is a theory that has also received attention in popular culture including the famous play of the same name written by John Guare, which was adapted into a screenplay for the 1993 film starring Will Smith, Stockard Channing, and Donald Sutherland.