Kevin Bacon, It’s a Small World, and Staying Home

Six degrees of Kevin Bacon. Six degrees is a game movie fans play, based on classic psychology research, and important for understanding the need to self-isolate.

The six degrees of Kevin Bacon is a game for people who really know movies. The idea is to find the shortest route from Kevin Bacon to another actor. You do this by looking at movies with Kevin Bacon and finding the other people in those movies. Then consider the movies those people were in. Find the people in those films and keep going. The goal is to find a chain of people and movies linking Kevin Bacon to a particular actor—preferably the shortest route. Here’s the first critical aspect of this: the chains from Kevin Bacon to other actors are short. Usually only a few actors and movies are needed. At most you only need 6 movies—thus the six degrees of Kevin Bacon. He’s only six steps from almost every other actor.

Now you should cue up the theme song from the famous Disneyland ride, It’s a Small World. The Kevin Bacon game is based on the Stanley Milgram’s research on the small world problem (Milgram, 1967; Travers & Milgram, 1969). In the research, people are challenged to find a way to connect to another person; maybe someone in your city or someone in another state. They did this by using the mail—yes, snail mail through the postal service. Take a card and send it to someone who would hopefully get the card to the person or at least a step closer to the target person. The goal is to find a short path. Find someone who gets closer, check if that person knows someone who might know the other person, and finally find a connection to the critical person. When Milgram’s team conducted this research, they found that most chains were surprisingly short. The chains generally involved between four and six people. Our connections mean that it is a small world.

In a more recent replication, Backstrom and colleagues (2012) did this on the internet with social media, using Facebook. They did not ask people to send a message. Instead they looked at the entire social network to find the connections. This mirrors old research looking at social networks in schools. And the finding is essentially the same. Our connections through the social network are vast. On average, any one person is separated from any other person by only five steps (actually 4.75). Again, it doesn’t take many links to get from any one person in the world to another. It’s a small world.

By now, you should have the famous song from that Disney ride repeating in your head. It’s a small world, after all. The links from one person to another generally create short chains. For that matter, you and I probably know each other, or at least we are indirectly connected. You undoubtedly know someone, who knows someone else, who is a friend of another person, who works with someone, who went to school with another person, who may know me. We’re connected. It is a small world.

But here’s the misleading part of the small world problem and the Kevin Bacon game. We think of these connections as chains. The connections run from one person to another person through a straight chain of other people. But in reality, the chains occur because they are single paths on incredibly wide sets of a connection. And this is why we should self-isolate during the COVID-19 pandemic.

Why self-isolate? Because it is a small world. Because you aren’t only standing next to and shaking hands with that person. You’re standing next to and shaking hands with everyone that person has interacted with in the last two weeks. You aren’t just touching that surface; you are touching everyone else who has touched that surface recently. In this small world fashion, the spread of the coronavirus becomes exponential. It’s because our human interactions are exponential. Here’s the simple math. Maybe you had close contact with three different people in the last 24 hours; that doesn’t seem like much exposure risk. But if they each had interactions with three people in the previous 24 hours, suddenly you have indirect contact with nine people. Run through six degrees of separation, and you’re connected to 2,187 different people. And that’s with only a very small number of contacts—three per person. Increase to four contacts for each person, through six degrees of separation and you’re connected to 16,384 people. And if you went out to a bar last weekend, maybe you interacted with 10 people or surfaces. Take those 10 contacts through six degrees of Kevin Bacon, and you have contact with 1 million people.

These numbers get scary when you then go visit an elderly relative or someone else at higher risk. And you aren’t just visiting your older relatives, you are exposing them to all those people and all those surfaces. Viruses travel by the connections of one person to all of their contacts. We spread the virus by interacting with others. We put people at risk precisely because we are connected. Because it’s a small world. Usually that’s a good thing. And we are all Kevin Bacon, connected to everyone else in the world through only a few degrees of separation.

By the way, Kevin Bacon is aware of the six degrees game and the small world problem. He has used it in the past to support charities. Now, he is using it to encourage people to stay home. Here’s a link to an article about his efforts to make people aware that it is a small world and that they should stay home.

He started a hashtag for social media: #IStayHomeFor. The idea is that you aren’t staying home to just keep yourself healthy. You are staying home to keep someone else healthy. You know someone who is at greater risk than you. Maybe an elderly relative or a co-worker with health complications. We should stay home not for ourselves, but for those friends and family members. I’m staying home for my mom. She’s in an assisted living center. She has Alzheimer’s and other health complications. She is clearly high risk and I haven’t seen her for three weeks. I’m staying home because I simply hope to see my mom again after this pandemic. I hope to hug my mom again.

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