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Six degrees of separation: where the idea comes from
“Six degrees of separation” is the idea that any two people are linked by a short chain of acquaintances. It started as fiction, became an experiment, and is now a measurable property of networks.
A short story, 1929
The Hungarian writer Frigyes Karinthy published a short story called “Chains” (Láncszemek) in 1929. In it, a character bets that he can link any person on Earth to himself through no more than five acquaintances. The phrase “six degrees” did not exist yet, but the idea did.
Milgram's letters, 1967
In the 1960s the psychologist Stanley Milgram tested the idea. He asked people in the American Midwest to get a letter to a target person in Massachusetts, passing it only to someone they knew personally who might be closer. Most letters never arrived, but those that did took around five intermediaries on average. Milgram described the work in a 1967 article, “The Small-World Problem”.
A play, a film and a party game
The phrase itself was popularised by John Guare's 1990 play Six Degrees of Separation, later a 1993 film. In 1994 three college students turned the idea into a game: Six Degrees of Kevin Bacon, linking any actor to Bacon through shared films.
What the data says now
In 1998 the mathematicians Duncan Watts and Steven Strogatz showed in Nature how “small-world” networks arise: mostly local connections plus a few long-range shortcuts make the whole network surprisingly close. Large social networks have since been measured directly. A 2016 Facebook Research analysis found that people on the platform were separated by an average of about 3.5 degrees.
Short paths are not only about people. Brands, films, sports teams and historical figures are linked in the same way, which is what makes a game like CHAINED possible: there is almost always a short route — the puzzle is finding it.