Six degrees of Kevin Bacon
"Six Degrees of Kevin Bacon" is a popular game and cultural phenomenon based on the concept of the "small world" theory, which suggests that any two people on the planet can be connected through six degrees of separation. The game involves finding the shortest path between a given actor and Kevin Bacon by identifying co-stars who have worked together in films. This idea emerged from earlier theories about interpersonal connections, notably articulated in the 1929 short story "Chain-Links" by Frigyes Karinthy and further explored through social psychology experiments by Stanley Milgram in the 1960s.
The game gained traction in 1994 when students at Albright College, inspired by several of Bacon's films, created a fun challenge around it. The Internet Movie Database (IMDb) and related websites track these connections, revealing that most actors are surprisingly close to Bacon, typically within three links. The phenomenon has led to broader applications in various scientific fields, where understanding network connections can provide insights into areas like social structures, neural networks, and even genealogical studies. The concept continues to resonate in popular culture, showcasing both the interconnectivity of the entertainment industry and the intriguing nature of human relationships.
Six degrees of Kevin Bacon
Summary: Concepts from graph theory help explain the idea that people, including actor Kevin Bacon, are surprisingly closely connected with each other.
Six degrees of Kevin Bacon is an example of a network showing a high level of interconnection, known as the “small world” phenomenon. In the language of graph theory applied to films, nodes are film actors, and two nodes are connected by an edge if the corresponding actors have appeared together in a film. It is also a game that tests cinematic knowledge. The task is to find the shortest connection between a given actor and Kevin Bacon. For example, John Wayne is two connections from Kevin Bacon. They were never in a film together, so the distance is greater than one. John Wayne starred with Eli Wallach in How the West Was Won, and Eli Wallach starred with Kevin Bacon in Mystic River, establishing a shortest distance of at most length two.
The idea of quantifying distance by interpersonal connections dates at least to a 1929 short story called Chain-Links by the Hungarian writer Frigyes Karinthy, wherein the narrator determines a five-step connection between a riveter at the Ford Motor Company and himself. Almost 40 years later, the social psychologist Stanley Milgram, best known for his experiments on obedience to authority, devised an experiment to quantify interpersonal connections empirically. Letters were given to some 300 participants, each charged with forwarding the letter to an acquaintance who should move the letter toward the intended recipient. Writing in 1969 with Jeffrey Travers, Milgram stated, “The mean number of intermediaries observed in this study was somewhat greater than five; additional research (by Korte and Milgram) indicates that this value is quite stable.” Rounding up, this value became the popular notion “six degrees of separation”—that any two people on the planet are connected by six links. It served as the title of John Guare’s 1990 play and 1993 movie about the confidence man David Hampton. In the play, a character speaks to the audience, “Six degrees of separation. Between us and everybody else on this planet. The President of the United States. A gondolier in Venice. Fill in the names. I find that A) tremendously comforting that we’re so close and B) like Chinese water torture that we’re so close.” Exactly how close people are is something sociologists continue to debate, since the nodes and edges of this network are not precisely known.
Mathematics Networks
There are large networks where the nodes and connections are exactly known, allowing for precise analysis. In a collaboration network, nodes are researchers, and two nodes are connected by an edge if the corresponding researchers worked together on a published paper. As early as 1957, mathematicians determined their “Erdös numbers,” the collaboration distance from Paul Erdös, the most prolific mathematician of recent years, with some 1500 published research papers and more than 500 collaborators. For instance, the author never wrote a paper with Erdös, but Robin Wilson wrote a paper with Erdös in 1977, and the author wrote a paper with Robin Wilson in 2004, so the author’s Erdös number is two. The American Mathematical Society’s MathSciNet electronic publication computes the “collaboration distance” between any two authors in its database of some 500,000 authors and 2.5 million publications.
Film Networks
Of more interest to the general public than mathematicians and their papers, the Internet Movie Database (IMDb, found at imdb.com) includes over 1 million actors around the world and some 250,000 films from the 1890s to titles in production. The Web site OracleOfBacon.org accesses the IMDb and determines the shortest link between any two actors. The network is very tightly connected; it is surprisingly difficult to name any pair of actors even four apart. Consider Kevin Bacon, who has been in over 60 films with over 2200 total co-stars. That is a very small percentage of the total number of actors in the database, but there are over 225,000 actors who, like John Wayne, are co-stars of co-stars of Kevin Bacon. Actors within four links of Kevin Bacon comprise approximately 98% of the database. About 99% of the actors in the IMDb all connect to one another. Finding actors within the last 1% who are five or more from Kevin Bacon is another entertaining part of the game. As of 2010, there are 17 actors with a distance of eight from Kevin Bacon, so that “six degrees” is a misnomer.
Another variant of the game is to determine the actor who is best connected on average. The average every actor’s Kevin Bacon number is 2.980. This number means, roughly, that a randomly chosen actor is within three links of Kevin Bacon. It is interesting to consider which sorts of actors have the lowest averages. John Wayne, with significantly more movies and co-stars than Kevin Bacon, has an average of 3.026 links to the rest of the connected actors. The best-connected actor, as of 2010, is Dennis Hopper, with an average distance of 2.772. The IMDb is regularly updated with new actors and films, and the connection data change accordingly.
Why is it six degrees of Kevin Bacon, and not some other actor? The game was created by students at Albright College in January 1994; they had watched Footloose earlier in the day, then saw a commercial for another Kevin Bacon film, The Air Up There, and a pop culture phenomenon was born. There are similar games based on other large databases, such as baseball players connected by teams, and “six degrees of” remains a very common phrase in society. Kevin Bacon himself used the notion to build a Web-based charity fundraiser, SixDegrees.org. The notion of “small world” networks is being used by scientists in applications as diverse as neural networks of worms, the interconnection of power grids, analysis of the World Wide Web, and genealogical connections.
Bibliography
Grossman, Eric. “The Erdös Number Project.” Oakland University. http://www.oakland.edu/enp/.
Hopkins, Brian. “Kevin Bacon and Graph Theory.” PRIMUS 14, no. 1 (2004).
Watts, Duncan. Six Degrees: The Science of a Connected Age. New York: Norton, 2003.