Six degrees of separation is the idea that anyone on the planet can be connected to any other person on the planet through a chain of acquaintances that has no more than five intermediaries.   If you take a person here in Fort Collins and a randomly chosen person in Salt Lake City, you would need at most five intermediaries to connect them!

The theory was first proposed in 1929 by the Hungarian writer Frigyes Karinthy in a short story called "Chains."   In the 1950's, Ithiel de Sola Pool (MIT) and Manfred Kochen (IBM) set out to prove the theory mathematically.   Although they were able to phrase the question (given a set N of people, what is the probability that each member of N is connected to another member via 1, 2, 3...n links?), they were still unable to solve the problem after twenty years of trying.

In 1967, American sociologist Stanley Milgram devised a new way to test the theory, which he called "the small-world problem."   He randomly selected people in the mid-West to send packages to a stranger located in Massachusetts.   The senders knew the recipient's name, occupation, and general location.   They were instructed to send the package to a person they knew on a first-name basis who they thought was most likely, out of all their friends, to know the target personally.   That person would do the same, and so on, until the package was personally delivered to its target recipient.

Although the participants expected the chain to include at least a hundred intermediaries, Milgram found that the number of intermediaries to get each package delivered ranged from two to ten, with five being the most common number.   Milgram's findings were published in Psychology Today and inspired the phrase "six degrees of separation."   This helps to explain how confidential information, rumors, and jokes travel so rapidly through a population.   How many times have you been sent the same e-mail???

John Allen Paulos, in his book Innumeracy, states that if "the target is well-known, the number of intermediaries is even smaller, especially if you have a link with one or two celebrities.   How many intermediaries are there between you and President Reagan?   Say the number is N.   Then the number of intermediaries between you and Secretary General Gorbachev is less than or equal to (N + 1), since Reagan has met Gorbachev.   How many intermediaries between you and Elvis Presley?   Again, it can't be bigger than (N + 2), since Reagan has met Nixon, who has met Presley.   Most people are surprised when they realize how short the chain is which links them to almost any celebrity."

Playwright John Guare popularized the phrase, six degrees of separation, when he chose it as the title for his 1990 play.   Although Milgram's findings were discounted after it was discovered that he based his conclusion on a very small number of packages, six degrees of separation became an accepted notion in pop culture after Brett C. Tjaden published a computer game on the University of Virginia's Web site based on the small-world problem. Tjaden used the Internet Movie Database (IMDB) to document connections between different actors.   Time Magazine called his site, The Oracle of Bacon at Virginia, one of the "Ten Best Web Sites of 1996."

In 1993, Will Smith and Sockard Channing starred in a movie called, Six degrees of Separation.   Stockard Channing as Ouisa Kittredge says in the movie, "I read somewhere that everybody on this planet is separated by only six other people. Six degrees of separation between us and everyone else on this planet."   She goes on to say, "Everyone is a new door opening into other worlds. Six degrees of separation between us and everyone else on this planet.   But, to find the right six people..."

In 2001, Duncan Watts, a professor at Columbia University, recreated Milgram's experiment on the Internet.   Watts used an e-mail message as the "package" that needed to be delivered, and surprisingly, after reviewing the data collected by 48,000 senders and 19 targets (in 157 countries), Watts found that the average number of intermediaries was indeed, six!

In 2003, there was a television movie called the Six degrees of Separation.   In this documentary, a Londoner, Lucy Leveugle, sets forth to test the "six degrees of separation" theory as she seeks to find how many people separate her and a herdsman living in outer Mongolia.


The Kevin Bacon Game

Craig Fass, Brian Turtle and Mike Ginelli came up with the game Six Degrees of Kevin Bacon.   They wrote a letter to TV talk-show host Jon Stewart, who invited them on his show to demonstrate the game. From these humble beginnings, a Web site arose, a book was published and a nationwide cult-fad was born.

The game is based on the concept that we are all connected by six or fewer stages of circumstance or acquaintance.   They hypothesized that Kevin Bacon might be the center of the universe, at least when it comes to connecting actors.   Although never a big box-office draw, Bacon has been in a significant number of films. The boys discovered that if you use Bacon as an end point, you can link him in six degrees or less to almost any other performer.

For instance, Kevin Bacon links to Kevin Costner in one swift link: Both were in JFK.
Julia Louis-Dreyfus of TV's Seinfeld, however, takes all six steps to make a chain:
She was in Christmas Vacation with Randy Quaid, who was in Major League II with Tom Berenger, who was in Shattered with Greta Scacchi, who was in Presumed Innocent with Harrison Ford, who was in Raiders of the Lost Ark with Karen Allen, who was in Animal House with Kevin Bacon.