Six degrees of separation

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For the game, see Six Degrees of Kevin Bacon. For the film, see Six Degrees of Separation.

Six degrees of separation is the theory that anyone on earth can be connected to any other person on the planet through a chain of acquaintances that has no more than four intermediaries. The theory was first proposed in 1929 by the Hungarian writer Frigyes Karinthy in a short story called Chains. The concept is based on the idea that the number of acquaintances grows exponentially with the number of links in the chain, and so only a small number of links is required for the set of acquaintances to become the whole human population.

By extension, the same term is often used to describe any other setting in which some form of link exists between individual entities in a large set. For example, "see also" links in a dictionary entry may point the reader to other entries in the same dictionary; after following only six such links, the reader could potentially get to any word in the dictionary that has a link to it. In this special case of a dictionary, it is sometimes called the six links rule.

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History

In the 1950s, 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 <math>N</math> of people, what is the probability that each member of <math>N</math> is connected to another member via <math>k_1</math>, <math>k_2</math>, <math>k_3</math>...<math>k_n</math> links?), after twenty years they were still unable to solve the problem to their own satisfaction.

In 1967, American social psychologist Stanley Milgram (see Small world phenomenon) devised a new way to test the theory, which he called "the small-world problem". He randomly selected people from various places in the United States to send postcards to one of two targets: one in Massachusetts and one in the American Midwest. The senders knew the recipient's name, occupation, and general location. They were instructed to send the card 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 it was delivered to the target himself.

Although the participants expected the chain to include at least a hundred intermediaries, 80% of the successfully delivered packages were delivered after four or fewer steps. Almost all the chains were less than six steps. Milgram's findings were published in Psychology Today, and his findings inspired the phrase six degrees of separation. Playwright John Guare popularized the phrase when he chose it as the title for his 1990 play. Milgram's findings were criticized, however, because they were based on the number of packages that reached the intended recipient, which was only about one third of the total packages send out. Further, many claim that Milgram biased the experiment in favor of the successful delivery of the packages by selecting his participants from a list of people likely to have above-average incomes, and thus not representative of the average person. It has been theorised that six is less representative of the true distance between people than of the maximum length a chain can be sustained without breaking down.

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 [1], one of the "Ten Best Web Sites of 1996". Similar programs are still used today in introductory computer science classes to illustrate graphs and linked lists.

In 2001, Duncan Watts, a professor at Columbia University, continued his own earlier research into the phenomenon and 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. Watts' research, and the advent of the computer age, has opened up new areas of inquiry related to six degrees of separation in diverse areas of network theory such as power grid analysis, disease transmission, graph theory, corporate communication, and computer circuitry.

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Play/film

Six Degrees of Separation is also the title of a play and film written by John Guare, based on the true story of David Hampton, a confidence man who bluffed his way into Manhattan high society by claiming to be the son of famous actor Sidney Poitier.

About the play:

It is also the title of episode 1.07 from the SF-drama series Battlestar Galactica.

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Genealogy

The term "six degrees of separation" is often distorted to indicate that six generations is the maximum extent to which everyone in the world is related. This has been disproved in numerous genealogy circles, since six generations translates roughly to 250 years. It has been calculated, more accurately, that the maximum relationship a person living in the modern age can be to someone else, anywhere in the world, is 30-32 generations removed which is roughly 1200 years of ancestry.

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Games

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External links

es:Seis grados de separación fr:Six degrés de séparation it:Sei gradi di separazione (sociologia) ja:六次の隔たり

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