The Surprising Science Behind The Six Degrees Of Kevin Bacon

By Debra Kelly on Sunday, November 29, 2015
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“Well, on my planet, we have a legend about people like you. It’s called ‘Footloose.’ And in it, a great hero, named Kevin Bacon, teaches an entire city full of people with sticks up their butts that, dancing, well, is the greatest thing there is.” —Star-Lord, Guardians of the Galaxy (2014)

In A Nutshell

Six Degrees of Kevin Bacon was a party game based on the idea that Kevin Bacon had been in so many movies with so many co-stars that he could be linked to anyone else in Hollywood through only a maximum of six people. When mathematicians started looking at the formulas behind that theory, they cracked the code on something bigger and started on their way to proving that it works for all of us. According to the formula, anyone on the planet can be linked to anyone else in the same way, and it’s the same way that other networks—like the spread of disease or the latest best seller—act as well.

The Whole Bushel

Way back in the 1990s, playing Six Degrees of Kevin Bacon was an actual thing, where participants would try to link any celebrity back to Kevin Bacon through a chain of movies and co-stars. If there’s anything that seems less likely to contain a real, scientific, and potentially world-changing principle, we can’t think of it off-hand. But now, researchers are finding that there really is something to the “six degrees of separation” idea, and that it doesn’t just work for Kevin Bacon.

It works for anyone.

At least, in theory. The research comes from mathematician Steven Strogatz and PhD student Duncan Watts. They started out trying to answer a very odd question: Why do all the crickets in a group chirp at the same time?

Deciding that it must have something to do with the network that existed within cricket society, they took a look at an online version of Six Degrees of Kevin Bacon to see if there was any sort of mathematical breakthrough they could take away from the game. And there was, a formula that could be applied to the links between people. Essentially, Kevin Bacon was just one hub in a whole world of hubs, a person with a huge number of connections that makes it possible to connect anyone to anyone else with a shockingly low number of connections.

The idea is nothing new, and it actually started with psychologist Stanley Milgram. Milgram is better known for his experiments in goading people into thinking they were delivering a lethal shock to others and then seeing if they would just keep going, but he also made a failed attempt at figuring out just how closely people were connected.

He started out by picking random people and sending them a letter. The letter contained a name and instructions to either send it to that person or to send it to another person that they thought might know the ultimate target. And even though it failed pretty miserably (in large part because most people couldn’t be bothered to participate), he still coined the phrase “six degrees of separation.”

Watts attempted the experiment again, using 60,000 people and email. Once the results were in, he found that it took an average of five to seven emails for the message to reach the final, random target.

They also tried another variation in conjunction with the BBC. Forty packages were handed out to random people around the world, and they were told to get the package to a man named Marc Vidal in Boston. While only three of the packages made it (they think that the others disappeared because again, people just couldn’t be bothered), they did it in an average of six steps. One of the packages that made it was given to a woman named Nyaloka Auma, who lived in a remote Kenyan village.

The resulting science that was built on the back of Six Degrees of Kevin Bacon is the science of networks, and it’s more than connecting a DC socialite with a Tibetan monk. They’re starting to find that other networks act in much the same way. The spread of a highly infectious disease can piggyback along on the same sort of network connections, and they’ve also looked at phenomena like the popularity of Harry Potter and the strange economic history of the tulip market in Europe.

And they’re not the only ones that have found the patterns. In 2008, Microsoft started analyzing their instant messenger conversations, which involved around 180 million people and billions of conversations. They found that, on average, people could be linked to anyone else through 6.6 acquaintances.

Show Me The Proof

BBC Magazine: How Kevin Bacon sparked a new branch of science
The Guardian: What a small world—or is it?
io9.com: Stanley Milgram’s Chain Letter Experiment