Six Degrees of Separation

Podcast Transcript

You may have noticed, on occasion, that friends you have from totally different parts of your life sometimes know each other.

It often comes as a surprise, but it actually shouldn’t. It turns out that the world is highly connected via personal relationships.

In fact, it has been suggested that any two people in the world are only six degrees apart from each other via friends of friends of a friend.

In some special cases, this can actually be measured and can even make for a fun game.

Learn more about the Six Degrees of Separation theory and its connection to Kevin Bacon on this episode of Everything Everywhere Daily.

Most of you might be familiar with the Six Degrees of Kevin Bacon game, also known as just the Kevin Bacon game.

The game is pretty simple. You need to find the shortest path between an actor and Kevin Bacon based on the movies they both appeared in.

For example, Sir Lawrence Oliver was in the 1979 movie Dracula with Frank Langella, who was in the 2008 movie Frost/Nixon with Kevin Bacon.

Shirley Temple was in the 1942 film Miss Annie Rooney with June Lockhart, who was in the 1989 film The Big Picture with Kevin Bacon.

I’ll be coming back to the Kevin Bacon game in a bit, but this is just a well-known version of a similar theory that was developed in the early 20th century: The Six Degrees of Separation Theory.

The Six Degrees of Separation theory is the idea that any two people on Earth are connected by at most six social connections. Put another way, you could reach anyone in the world through a chain of no more than six acquaintances, where each link is a “friend of a friend.”

The concept can be traced back to early 20th-century thinking about networks and human connections. The Hungarian author Frigyes Karinthy first popularized it in a 1929 short story collection called Everything is Different.

In his story “Chains,” he speculated that advances in communication and travel had so shrunk the world that everyone was linked through only a handful of connections.

It was one of the few predictions from this period that was remarkably prescient.

The theory gained academic attention in the 1960s with the “small-world experiment” conducted by social psychologist Stanley Milgram.

You might remember Stanley Milgram from a previous episode on the Milgram Experiment. The Milgram Experiment, you might remember, was a test to see how far people would go when they thought they were shocking other people to follow instructions.

The question he was trying to answer was: if you pick two random people in the United States, how many intermediate acquaintances would it take to connect them?

Milgram carried out the experiment in 1967. He recruited about 300 participants from Nebraska and Kansas and asked them to help forward a folder to a designated target person: a Boston stockbroker named Howard Milgram, who was no relation to Stanley.

The rules were:

Participants could not mail the folder directly to the target.
They had to send it only to someone they personally knew on a first-name basis.
Each recipient, in turn, would follow the same rule, forwarding it closer to the target.

Each folder contained instructions, a roster sheet to track its path, and a postcard for recipients to return to Milgram so he could track progress even if the chain broke.

The results were striking, though also messy. Out of roughly 300 starting chains, only about 64 successfully reached the target. For those who did arrive, the average length of the chain was about five to six intermediaries.

This is where the phrase “six degrees of separation” originates, though Milgram himself did not use that wording. He instead concluded that people live in a “small world,” meaning that social networks are much more tightly interconnected than intuition would suggest.

The experiment, while groundbreaking, has been criticized.

The study had a high attrition rate. Most chains never reached the target, raising questions about the robustness of the results.

It also had a strong sample bias. Participants were mainly middle-class Americans from limited geographic areas, which might not generalize to broader or more diverse populations.

On the flip side, people may not have been strongly motivated to keep forwarding the letters, and thus, the experiment may have underestimated social connectivity.

Despite these issues, the concept held enormous intuitive appeal and sparked decades of research in sociology, mathematics, and network science.

One problem was that there wasn’t a theoretical framework to explain the small-world connections among people.

The work by Australian researcher Duncan Watts and American Steven Strogatz’s in the late 1990s transformed Milgram’s intuitive “small world” finding into a precise mathematical framework, opening up an entirely new field in network science. Their 1998 paper, Collective dynamics of ‘small-world’ networks, published in Nature, is one of the most influential studies in modern complexity science.

Watts and Strogatz proposed a simple, elegant model.:

Start with a regular lattice with each node connected to its immediate neighbors.
Randomly rewire a small fraction of the edges, creating “shortcuts” across the network.

The result was a “small-world network” with two key properties:

High clustering, like a regular lattice.
Short average path length, similar to a random graph.

This meant that you could preserve the local “cliquishness” of real social groups while still allowing long-distance links that drastically shortened the distance between any two nodes.

One of the things that radically transformed this field of research was social media.

Social media sites such as Facebook, Twitter, and LinkedIn made it possible to measure the distances between people without having to resort to experiments.

Studies have repeatedly shown that average distances between any two users are indeed surprisingly short, often three to four steps, making Milgram’s intuition prescient.

In fact, if you ever look someone up on LinkedIn, it will show you the number of links you are from them, including what people connect you.

While this had been a field of academic study, what brought this into the popular consciousness was the Six Degrees of Kevin Bacon game.

In 1994, three college students from Albright College in Pennsylvania, Craig Fass, Brian Turtle, and Mike Ginelli, were watching television when they noticed that Kevin Bacon seemed to appear in, or be connected to, a huge number of movies.

They joked that “Kevin Bacon is the center of the universe,” and began challenging each other to link any actor to Kevin Bacon through co-stars. They formalized it into a parlor game where participants tried to connect an actor to Kevin Bacon in six steps or fewer, each step being a film in which two actors appeared together.

The game was mentioned on The Jon Stewart Show in 1994, and it rapidly spread as a pop-culture phenomenon. This was his short-lived late-night show on MTV, not his Comedy Central Show.

Kevin Bacon himself was initially bemused, but eventually embraced the idea, even collaborating with the creators on a book and appearing on shows where the game was played. In later years, he founded the charitable website SixDegrees.org, which uses the concept of interconnectedness to promote social good.

The game is a direct parody and application of the Six Degrees of Separation theory. Just as Milgram’s social experiment demonstrated that people are surprisingly close in a social network, the Bacon game shows that actors in Hollywood form a tightly knit network where most are only a few “degrees” apart from each other.

Because Kevin Bacon had a prolific and diverse career, working across genres and with many co-stars, he became an ideal hub for the experiment.

In the Kevin Bacon game, everyone who can be linked to him is given a Bacon Number. Kevin Bacon himself has a Bacon number of zero, as he is the font from which all connections flow.

If you appeared in a movie with Kevin Bacon, then you have a Bacon Number of 1. For example, in the recent remake of The Toxic Avenger, Kevin Bacon is the villain and The Toxic Avenger is played by Peter Dinklage, giving him a Bacon number of 1.

If you didn’t star in a film with Kevin Bacon, but you starred in a film with one of his co-stars, then you have a Bacon Number of 2, and so on.

It is surprisingly difficult to find a regularly working actor with a Bacon Number greater than 3.

Who, you might wonder, has the highest Bacon Number? This was difficult to find, but the best answer I could find was General William Rufus Shafter, an American general during the Spanish-American War and recipient of the Medal of Honor. He has a Bacon Number of 10.

William Rufus Shafter appeared in the Surrender of General Toral in 1898 with Confederate General Joseph Wheeler.

Joseph Wheeler appeared in General Wheeler and Secretary of War Alger at Camp Wikoff in 1898, with Union Army General Russell Alexander Alger.

Russell Alexander Alger appeared in President McKinley’s Inspection of Camp Wikoff in 1898 with President William McKinley.

William McKinley was in President McKinley and Escort Going to the Capitol in 1901 with Nelson Miles, who was also a Union General.

Nelson Miles was in The Indian Wars in 1914 with Buffalo Bill Cody.

Buffalo Bill Cody was in Buffalo Bill’s Wild West and Pawnee Bill’s Far East in 1910 with showman Major Gordon W. ‘Pawnee Bill’ Lillie.

Pawnee Bill’ Lillie was in In the Days of the Thundering Herd in 1914 with actor Wheeler Oakman.

Wheeler Oakman appeared in Flash Gordon’s Trip to Mars in 1938 with Jerry Gardner.

Jerry Gardner was in Natural Born Killers in 1994 with Pruitt Taylor Vince.

…and Pruitt Taylor Vince appeared in 24 Hours in 2002 with Kevin Bacon.

Many of those early films weren’t films as we would consider them today, but they were films that were released.

This got me wondering if I had a Bacon number, and it turns out that I do. I have a Bacon Number of 5.

In 2007, I appeared in a documentary as myself with my friend Haley Chamberlain. The documentary was titled 50 States in 50 Days.

In 2015, Haley was in a small film called The Telephone Game with Jesse LaVercombe.

Jesse LaVercombe was in the 2019 film Chubby with Mark Ingram, who was in Sesame Street: Sing Yourself Silly! with John Candy, who was in She’s Having a Baby with Kevin Bacon.

Once the Internet Movie Database was created, researchers wanted to know if Kevin Bacon was, in fact, the center of the acting universe. They plowed through all the data to check every relationship with everyone to see who had the lowest average score.

When they first checked, the center of the universe was actor Rod Steiger. The reason he had such a high score was that he appeared in a wide variety of movies, a lot of movies, and had a long career.

However, this has changed over time as more movies have been released. The Oracle of Bacon calculates this periodically, and the new center of the acting universe, as of January 2025, was……Eric Roberts.

He is followed by Michael Madsen, Willem Dafoe, Samuel L. Jackson, Harvey Keitel, and Danny Trejo.

The Kevin Bacon game isn’t the only game in town.

The Erd?s number was created as a way to measure a mathematician’s “collaborative distance” from the prolific Hungarian mathematician Paul Erd?s, who authored or co-authored more than 1,500 academic papers.

The rules are the same as the Kevin Bacon game, but instead of appearing in a film, the links are made via co-authoring academic papers.

From mathematics, you can link to any number of fields, including physics, biology, and economics.

For example, Albert Einstein has an Erd?s number of 2, and Milton Friedman has an Erd?s number of 3.

Of course, someone has taken this to the next step and developed the Bacon-Erd?s Number, which is the sum of your Bacon and Erd?s numbers.

Very few people have them because not many academics are in movies and vice versa.

Mathematician Daniel Kleitman has a Bacon-Erd?s of 3 as he co-authored a paper with Erd?s himself, and briefly appeared in Good Will Hunting with Mini Driver, who was in Sleepers with Kevin Bacon.

Other people with a Bacon-Erd?s Number include Danica McKellar, Natalie Portman, Colin Firth, Kristen Stewart, and, of course, Carl Sagan.

There is one other number I’ll mention, which is a bit different than the others, the Morphy number.

Paul Morphy was arguably the greatest chess player of the 19th century. Your number is based on the distance you are from Morphy, based on who you’ve played a game of chess with.

This is different from the Bacon or Erd?s Numbers because it connects people through time. Every generation gets a higher number as time goes on. For example, Garry Kasparov has a 4, and Magnus Carlsen has a 5.

This is how very early Christian communities in the first or second centuries established authority, based on the connection to Jesus. In this system, the apostles would have a score of 1, the people whom the apostles trained and made bishops would have a score of 2, etc.

The bishops, especially in key sees like Rome, Alexandria, and Antioch, were seen as custodians of the authentic teaching because of their short chain of succession back to the apostles. This concept apostolic succession still underpins Catholic, Orthodox, and Anglican understandings of church authority today.

You would be surprised how fast you can link yourself to people around the world. In the course of my travels I met people who had totally unexpected connections to people that I knew.

It turns out that Disney had it right. It’s a small world after all.