Six Degrees of Kevin Bacon

Kevin Bacon

Pick an actor, then find the shortest route through cast lists from that actor to a movie with Kevin Bacon. You can play a similar game with Spotify, by finding the shortest number of clicks to reach from artist A to B. The Kevin Bacon game has gained fame as Six Degrees of Kevin Bacon. Why is this relevant?

Interconnections

The game is based on interconnection, and specifically, the six degrees of separation theory.

The idea is that any two people in the world are separated by at most six handshakes, or more accurately, steps of social connections. So, how do you link to Kevin Bacon? Well, you should know somebody, who knows somebody, who knows somebody, up to six times until you reach Kevin Bacon.

Of course, that sounds nice, but is it true? At the very least there is a mathematical foundation. If you take an interconnected graph of N nodes, with K interconnections per node, the result for 6 billion nodes and 30 interconnections per node does indeed yield a value of 6.6 – which would round to 7. That disregards the 10% of the population deemed to young, but okay, it more or less fits theoretically. See here for some details.

Shortcomings

The distribution in the graph as described above isn’t overly realistic. For example, a completely isolated tribe of people will void the whole theory. We know such tribes of people still exist, mostly in the Amazon.

Still, the idea is nice, and has merit, especially in our interconnected modern world. For example, I learned last year I’m only two steps removed from John Scalzi,which makes me that much closer to getting a book published (I wish). So, yeah, this doesn’t do anything in practice, unless you manage to leverage your connections somehow.

Anyway, we know the model doesn’t play nice with things like iron curtains and isolated tribes, but how well it fits with the real world is hard to find out. Research has yielded that the actual interconnectedness for Facebook users is only 3.57, see here. So, it seems to hold up pretty well. If every person in the world knows somebody who knows somebody who’s on Facebook, we’re only at 5.57, and I wouldn’t call that a stretch.

So whoop-di-bacon what?

We’re all six degrees away from Kevin Bacon. So what?

Mostly it isn’t relevant at all. However, it does help you understand just what ‘exponential rate’ means.

One area where this can become relevant is, say, a viral pandemic. Yup, I couldn’t resist dragging Covid-19 into this post, but I’ll try to keep it to a minimum.

The takeaway of the six degrees of separation theory is that you’re at best only six handshakes away from getting Covid-19, and probably less. The Netherlands has banned handshakes for this reason, and has since yesterday pretty much shut down society. And with cause, as you can now mathematically see.

Luckily, the six degrees of separation assumes 30 interconnections per node, which would translate to every person infecting 30 others. This number is only 2 or 3, thankfully, and should go down because of all the quarantines and hygiene measures – as long as we keep following them, that is.

Conclusion

We’re all separated from Kevin Bacon by only six social connections. The same goes for people like Trump, and -naturally- me. It’s a small world after all. And that has it’s upsides, and it’s downsides.

Author: Martin Stellinga

I'm a science fiction and fantasy writer from the Netherlands