Six Degrees of Separation? Really?

We’ve all heard that saying, “Six Degrees of Separation”, meaning that everyone on earth is connected by a maximum of 6 person to person links. What most people don’t know, though, is where this notion came from, and that it’s not exactly true.

• Item: My friend, Sasha, a musician in London, knows three (3!) people I know on a first name basis: an economist in Boulder, CO, a research engineer in Princeton, NJ, and a German psychologist (though she may actually live in London — but London and its environs have 12 – 14 million residents). To my knowledge, none of these people knows each other. What’s going on?

“Six degrees of separation” came from an experiment done by Stanley Milgram, the psychologist, in the 1930s. It is said that he gave 300 random Nebraskans an envelope and told them to send that to someone they knew on a first name basis, who they thought could get it to a particular stockbroker in Boston, with instructions for them to do the same, and that the envelopes got there in an average of 6 steps. That’s not entirely true. The average of all 300 envelopes was 6 mailing legs to get to the target — but Milgram gave 100 of those envelopes to people in Boston, 100 of them to blue chip investors, and only 100 to random Nebraskans. And of the 100 given to the random Nebraskans, only 18 got to the target! But Milgram was on to something.

• Item: Last weekend, I went to a hypnotherapy class in Oakland, CA, which had 5 participants besides me. At lunch, I discovered that one of them, an attorney in Sydney, Australia, is a good friend of, and sometime attorney for, the my one friend in all of Australia. What’s going on?

Or perhaps you’ve heard of the game, Six Degrees of Kevin Bacon, where players try to tie a given actor to Kevin Bacon in as few steps as possible, based on the movies they’ve acted in together. So if an actor has worked in a movie with Mr. Bacon, he has a Bacon number of 1, if an actor has worked with an actor who has worked with Mr. Bacon, she has a Bacon number of 2, and so on. As you can see in the table below, using data from the internet movie data base, www.imdb.com, which has over 500,000 actors, the vast majority of actors are within 3 degrees of separation from Bacon, and virtually all are within 4 degrees:

Cumulative
Bacon Percentage
Number of Actors

1 .3
2 24.1
3 84.9
4 98.8

The book, “Six Degrees”, by Duncan Watts, from which the above data is abstracted, is all about “small world” networks, looking at networks as different as movie actors and the power grid from a mulitdisciplinary approach. After considering several models and research from the 1930’s onward, he concludes that “As long as individuals are more likely to know other people like them, and — crucially — as long as they measure similarity along more than one social dimension, then not only will short paths exist between almost anyone almost anywhere, but also individuals... will be able to find them.” And other research suggests that the two most powerful dimensions to explore are geographical connections and professional ones.

• Item: A few weeks ago, I went to an NLP training in Novato, CA. The trainer, from NJ, turned out to have grown up a few blocks from me, and to have been a patient of my (MD) father’s. What’s going on?

So it’s reasonable that you’ll be connected to anyone, anywhere in very few steps, and that you’re most likely to find them by asking where they’re from and/or what they do for a living. But I’m still not sure that explains what’s happening to me.