Six Degees of Separation

kevin bacon

kevin bacon

In the latter part of my university career I met someone from another part of the country who had taken an entirely different degree course at roughly the same time as me, but whom I’d never bumped into at university itself. In fact, it wasn’t until we both ended up working in a small town in the USA by sheer coincidence that we mat in the first place. What was odd though was that we seemed to know a lot of the same people. And, if we didn’t know the same people we knew people who knew them and so on.

At the time, neither of us had heard of the six degrees of Kevin Bacon, or the whole concept of degrees of separation, idea. In fact this was 20 years ago and I don’t think that game had even been invented. We thought we’d stumbled on a new theory and began extrapolating wildly about how with just a few connections everyone in the world might be interconnected. This was at a time before even web 1.0 too, let alone web 2.0, so the whole idea of extensive online networking was yet to be born.

Anyway, we still keep in touch and are occasionally dumbfounded by the apparently supernatural connections that seem to crop up on a regular basis. For instance, my friend was chatting in a pub with a group of friends and some “new” people in the social circle a few years back. Conversation turned to travel, my friend mentioned her job in the USA, and one of the new people in the circle mentioned knowing someone who had done the same job, at roughly the same time. The new person my friend later related was my wife’s sister and those two are now best friends. A similar coincidence occurred to my own sister who met someone “new” to her social circle (again, in a pub, is there a theme here, do you think?) who turned out to know both me and my friend from some other place. I could go on…

Anyway, as many people will know this idea of everyone in the world being connected within so many friends, relatives, and acquaintances was already well known even 20 years ago and well before Kevin Bacon started acting. Seemingly, it was Guglielmo Marconi, developer of radio communication, who in his 1909 Nobel speech is thought to be the first person to suggest the magic number 6 (actually 5.83) as being somehow pertinent in connecting everyone together, although he was referring to a network of radio stations to provide global coverage.

In Stanley Milgram’s so-called “small world experiment”, he attempted to measure the connectivity of Americans to determine whether there was a separation factor. Although he never referred to the “six degrees of separation”, Milgram did discover that only a small number of connections is needed to interlink the entire population. It turns out that, as with a network, such as the World Wide Web, there are several large hubs, people or portals with a huge number of connections on which the connectivity of all those billions of websites and people hang.

Six Degrees of Separation

It’s quite unlikely that without the advent of electronic communication, we would find the connectivity between all 6,647,380,082 people to be such a small number. I was musing on this subject while adding a new friend to my LinkedIn and Facebook accounts. I have not been very active on LinkedIn and have just 31 connections on that online networking site. However, those 31 contacts have a total of 2700+ connections of their own, and if I move along the degrees of separation another notch, there would be 171,000+ contacts of contacts’ contacts. Just four degrees of separation would bring me into contact with almost 20 million people, five degrees would be almost 2 billion.

Within 6 degrees of separation I could connect with 200 billion people, which is obviously going to require at least one new address book. If you’ve got more LinkedIn contacts than my small cluster, just think how many people you could connect to…oh…wait a minute…

There is, however, a theory, well supported by anthropology, that our brains were wired by evolution to cope with a mere 150 close contacts. That’s 150 people you’d know and “love”. The theory may explain why hunter-gatherer villages topped out at around that population size, why certain groups, such as the Hutterites, split their communities once they reach this size, and have done for centuries, and maybe even why fighting groups work best at fewer than 200 members. You simply haven’t got the brain power to really care about more than that number of people, because you wouldn’t be able to keep track of all the relationships between the group members if there were more.

Maybe it’s time to trim down those friends lists if you’ve got several thousand twitter contacts. You can only really call close a limited number of people, according to this theory. That said, humans are still evolving, maybe there will be some reproductive advantage to having thousands of virtual friends should environmental pressures change in coming years. By the way, I’m yet to find a personal connection with Kevin Bacon.

12 thoughts on “Six Degees of Separation”

  1. what about networking, six degrees at the cellular level? Does it offer the opportunity of prediction?

  2. There’s one guy isn’t there who already does that with his life…keeps everything…maybe he’s at IBM, I cannot remember his name. Thanks for the link though, nice predictions…

  3. Regarding our earlier discussion here, on whether our brains can handle connecting with more than 150 people at a time. I was saying that soon technology will be able to help us with these types of tasks and others. Well, it may be sooner than we think.

    IBM is creating an audio/video image device that stores everything we see and here and downloads it to the computer when it can be categorized, bookmarked, replayed, etc.

    Check out the article:

    Hard to imagine, but certainly possible!

    Take care,
    Bradley (@OutsideMyBrain)

  4. I didn’t find my copy of his book, but searching for a quote from it online, I did come across this interesting post from

    “In 1967, American sociologist Stanley Milgram devised a new way to test the theory, which he called “the small-world problem.” He randomly selected people in the mid-West to send packages to a stranger located in Massachusetts. The senders knew the recipient’s name, occupation, and general location. They were instructed to send the package to a person they knew on a first-name basis who they thought was most likely, out of all their friends, to know the target personally. That person would do the same, and so on, until the package was personally delivered to its target recipient.
    Although the participants expected the chain to include at least a hundred intermediaries, Milgram found that the number of intermediaries to get each package delivered ranged from two to ten, with five being the most common number. Milgram’s findings were published in Psychology Today and inspired the phrase “six degrees of separation.” This helps to explain how confidential information, rumors, and jokes travel so rapidly through a population. How many times have you been sent the same e-mail???”


  5. I’ll have to dig out my copy of Innumeracy – Paulos explains this phenomenon pretty well in that book if I remember correctly.

  6. @Bradley It is curious isn’t it…that we all have sooooo many virtual friends these days, but our brains may really only be able to cope with the numbers one would have in a small, small village. As to the Kevin Bacon game, here’s a little secret those who tout it don’t tend to reveal: it works for almost any Hollywood actor.

  7. David,

    I just met you through @jimconnolly. You bring up an interesting point about how many people we can actually connect with, with that limit being around 150. Hmmm… that blows out most people on Twitter then. LOL

    However, perhaps in the future, there will be some sort of software that enables us to better connect with a larger number of people. Twitter certainly seems to helping to push that number a little higher.

    Like you said, interesting concept regardless of the actual numbers, because it all works on the law of averages anyway. Kevin Bacon may only be seperated from you by 2 or 3 degrees, granted you choose the correct 1st degree. Hence the platforms like Twitter, Facebook and Linked in create those paths for us allowing us, if we choose, to persue relationships with people who are a friend, of a friend, of a friend, of a friend.

    Thanks for the food for thought!


  8. Jack, the whole idea of us being connected by however many degrees of separation, 5, 6, 7, is a purely hypothetical construct. It is not entirely verifiable but a statistical average. The bigger the number though, the more chance of more people being connected via that number of other people.

    The WSJ blog has this to say about it:

    As to just how special is Kevin Bacon, an aspect of that actor’s position in the network of movies is that it is not very different from any other prolific actor. The game would work just as well for Meryl Streep, Jeff Bridges, Dustin Hoffman or many others. In fact, there is the possibility that one could find a “hub” individual with 5 degrees.

    Fascinating idea regardless of how the numbers add up.

  9. Recently I read an article in Wall Street Journal that noted there were researchers who have figured out that seven connections would reach the entire world. This is in contrast to Kevin Bacon’s six degrees of sepearation. I did not keep the article nor did I note who the researchers were. Have you read or heard about this theory or know an actual fact?

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