Six Degrees

June 6, 2017

Are you just six handshakes away from every other person on Earth? Two mathematicians set out to prove we’re all connected.

You have probably heard the phrase “six degrees of separation,” the idea that you’re connected to everyone else on Earth by a chain of just six people. It has inspired a Broadway play, a film nerd’s game, called “Six Degrees of Kevin Bacon”...and even a No Doubt song! But is it true? In the ‘90s, two mathematicians set out to discover just how connected we really are—and ended up launching a new field of science in the process.

Annie holds one of Milgram’s “Letter Experiment” mailings sent to June Shields in Wichita, Kansas. Accessed at the Yale University archives. (Credit: Elah Feder)



A version of psychologist Stanley Milgram’s “Letter Experiment” mailings. “Could you, as an active American, contact another American citizen regardless of his walk of life?” Milgram and his team wrote. They asked for recipients' help in finding out. Accessed at the Yale University archives. (Credit: Elah Feder)


(Original art by Claire Merchlinsky)



  • Duncan Watts, Principal Researcher at Microsoft Research, author of Six Degrees: The Science of a Connected Age
  • Steven Strogatz, Jacob Gould Schurman Professor of Applied Mathematics at Cornell University, author of Sync
  • Andrew Leifer, Assistant Professor in the Department of Physics and the Princeton Neuroscience Institute at Princeton University



  • Read Duncan Watts’ and Steven Strogatz’s breakthrough 1998 Nature paper on small-world networks.
  • Read Stanley Milgram’s 1967 article about his letter experiment in Psychology Today.
  • Watch Duncan and Steve discuss the past and future of small-world networks at Cornell.
  • Watch C. elegans' brain glow! And read more about the brain imaging work happening in Andrew Leifer’s lab.
  • Browse the small-world network of C. elegans’ 302 neurons at wormweb.org.
  • Read Facebook’s analysis of Facebook users’ “degrees of separation.”
  • Just for funsies, a network analysis of Game of Thrones.



This episode of Undiscovered was reported and produced by Annie Minoff and Elah Feder. Editing by Christopher Intagliata. Fact-checking help by Michelle Harris. Original music by Daniel Peterschmidt. Additional music by Podington Bear and Lee Rosevere. Our theme music is by I am Robot and Proud. Art for this episode by Claire Merchlinsky. Story consulting by Ari Daniel. Engineering help from Sarah Fishman. Recording help from Alexa Lim. Thanks to Science Friday’s Danielle Dana, Christian Skotte, Brandon Echter, and Rachel Bouton.


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