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Six Degrees of Kevin Bacon

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I know a guy, who knows a guy,
who knows a guy, who knows a guy,
who knows a guy, who knows... Kevin Bacon!

This is a pop-culture game, whose title is a mondegreen of Six Degrees of Separation, in which it is said that anyone in the entertainment business can be linked through their film roles to the actor Kevin Bacon within six steps.

In other words, pick a random actor. Any actor. Now think of someone they've ever been in a movie with. Now think of a chain of such individuals, each of whom has been in a film with a different person, until you reach somebody who's been in one with Kevin Bacon — and thereby link to the man himself, in as few steps as possible. For example: George Clooney was in Ocean's Eleven with Matt Damon, Matt Damon was in The Departed with Jack Nicholson, and Jack Nicholson was in A Few Good Men with... Kevin Bacon. Voilà.

Mathematicians have extrapolated this phenomenon and given it a name: "Bacon Number", which sounds like one of those impossibly high numbers with dangerous implications for the future of the Universe but is in fact incredibly low. In the example above, Clooney has a Bacon Number of 3: three degrees of separation from the target individual. Damon has a Bacon Number of 2, and Nicholson has the lowest attainable Bacon Number of 1. Kevin Bacon, himself, has the unique Bacon Number of 0.

Every actor has a Bacon Number, even voice actors.note  Most players agree that the game should be limited to feature-length films; some vary on whether or not to include animation or documentaries.

And it's not just actors, per se. As implied in the first paragraph above, you can play it with literally anybody who's ever appeared in a film. Try, oh, Andy Warhol. He made an uncredited cameo in Tootsie, starring Dustin Hoffman, who was in Sleepers with Kevin Bacon — giving Warhol a Bacon Number of 2. David Letterman? Same. He was in Man on the Moon, as was David Koechner who acted alongside Bacon in My One And Only. Or how about a man who was literally on the moon? Buzz Aldrin appeared in Transformers: Dark of the Moon, as did John Malkovich, who was in Queens Logic with KB. That's a Bacon Number of 2 for Aldrin too. And so on.

There is a whole website, The Oracle of Bacon, dedicated to this that is found here. The site's algorithms originally used the IMDb for tracing its web of connections, before moving to Wikipedia and finally The Movie Database (TMDB).

For applications in fiction, see One Degree of Separation.

Center of the Hollywood Universe

Whisper it, but there isn't really anything special (in this context) about Kevin Bacon — bar his name's happy resemblance to the word "separation".

Anybody who's been in Hollywood for any length of time will, the chances are, represent their own Ground Zero in a comparable network of radiating interconnections. There are a few key factors: appearing in large casts, and/or with people who themselves have acted alongside a whole lot of other people, are quick ways of establishing a significant number of close connections. Long-term, featuring in a diverse range of productions will broaden the web of possible links.

Certainly, the most connected person in acting is not Mr Bacon. Research by people who found it important enough to do so discovered that the "Center of the Hollywood Universe" shifts over time — but typically it will be someone who has appeared in many, many films over a considerable period. During the latter part of his long life and prolific career, for instance, Christopher Lee was credited on IMDb as being this. As of July 2023, the center of the Hollywood universe has shifted to Samuel L. Jackson, who with a mean score of 2.89828 degrees of separation is fractionally more closely linked to everyone else on average than Eric Roberts is, by a mere 0.0041 degrees. Bacon himself isn't even all that high on the list, typically ranking among the top 600 centers of the Hollywood universe but a fair way behind the likes of, say, Christian Slater, Vinnie Jones, Gary Busey or Diane Keaton.

As a fun diversion, note that as soon as an individual acts with someone whose heyday is a long way removed from their own then they will, at a stroke, be connected to a host of actors from decades earlier or later at just a degree or two of separation. For instance, silent-era icon Buster Keaton appeared, late in life, in a 1960 film of The Adventures of Huckleberry Finn with child actress Patty McCormack — who, 48 years later, appeared in Frost/Nixon with... Kevin Bacon, giving Keaton a Bacon Number of just 2. In 1989 Bacon starred in The Big Picture, in which he appeared with June Lockhart (b.1925), who made her film debut in A Christmas Carol (1938), which featured Lionel Braham (b.1879) as the Ghost of Christmas Present.note  Lockhart's most recent credited film role was in 2016; Braham's first was in 1915. In 2023's Leave The World Behind, meanwhile, Bacon played the father of 10-year-old Alexis Rae Forlenza — who, born in The New '10s, therefore has just 3 degrees of separation from actors born in the 1870s...!

Average Bacon Number

Researchers have demonstrated (true story!) that almost everyone has a Bacon Number less than 10, due to Kevin Bacon at one point or another appearing in movies with people who've appeared in movies with people who've appeared in movies (... etc.) with people who've appeared in, mathematically speaking, almost every film on the planet. The Oracle of Bacon claims that 21 persons on TMDB have Bacon Numbers of 10, the highest listed, but does not say who they are.

The perhaps surprising thing is that the average Bacon Number across every single person in the database, no matter how obscure, is just a little under 3.1. When you stop to think about it, though, it quickly becomes apparent why.

Over the several decades of his career Kevin Bacon has appeared in productions which, put together, feature over 2100 distinct co-stars — by which we mean everybody with even a tiny onscreen role in them. Even if they never shared a scene with him, each and every one of them has a Bacon Number of 1.

And between them those couple of thousand people link to a couple of hundred thousand other people who have acted in films with at least one of them, but not with Bacon himself — each of whom therefore has a Bacon Number of 2. Then at one step further removed, there are over 680,000 actors who have at some point appeared alongside one (or more) of those #2s although never alongside a #1 or Bacon himself, making a B.N. of 3 tremendously common.

Now here's the interesting bit. Beyond that, since the possible routes back to Bacon increase exponentially, the number of people with a B.N. of 4 immediately drops sharply to back around the 250,000 mark... and at a B.N. of 5 it collapses to only 32,000, then at 6 to barely 5000 and at 7 to less than a thousand individuals. Because, naturally, once you've got around 1 million more closely connected actors already accounted for, and can map every pathway between them, it swiftly becomes almost impossible for a film actor to have never worked with anyone in the business who's ever worked with anyone who's worked with anyone who's worked with anyone who's worked with Kevin.

Ironically, Kevin Bacon did not have anything at all to do with the movie Six Degrees of Separation.note 

This is all just a silly game, of course. Yet those mathematics associated with it have genuine real-world implications — see the bottom of this page.

Similar numbers in other fields

Scientists also have a similar ranking called the Erdős Number, based on co-authorship of mathematical articles with deceased mathematician Paul Erdős. Inevitably there's a combination, the Erdős-Bacon number, based on adding the two together. Thanks to the documentaries, and occasional extra work on math-related films, some mathematicians have EB numbers as low as 3. More surprising are actors who attack the problem from the other side. Danica McKellar (Winnie from The Wonder Years and bona-fide mathematician) and Natalie Portman (wrote a psychology paper at Harvard with an Erdős link) each have Erdős-Bacon numbers of 6. (This ties them with Richard Feynman.)

There is also now the Sabbath Number, based on how many collaborations it takes to get from a given musician to Black Sabbath. Then, of course, musicians who've appeared in films have Sabbath-Bacon numbers, and a surprising number of math-geeks turned musos have Sabbath-Erdős numbers. Then, there's the Sabbath-Bacon-Erdős number. The lowest known Sabbath-Bacon-Erdős number is 8, famously held by physicist, The Simpsons guest star, and Pink Floyd guest vocalist Stephen Hawking. Neuroscientist Daniel Levitin and inventor Ray Kurzweil have the same number as well.

Chess players have a Morphy number, for Paul Morphy, and Go players have a Shusaku number, centered on Honinbo Shusaku. Both of those players died in the late 1800s, but if you're interested in a Stiglitz number of 1, economist Joseph Stiglitz is still alive and publishing.

In professional sports, players are generally connected through teammates, not by playing against other players. Ice hockey has the Sillinger number, named after journeyman Mike Sillinger. Baseball players have the Miñoso number, after Minnie Miñoso, who played in five different decades.

Thanks to Crossovers, even fictional characters aren't exempt from this phenomenon. For video game characters, there's the Ryu number. For TV show characters, there's the Tommy Westphall number.

On a less specific level, the aforementioned serious research into this phenomenon actually has some importance for fields like sociology and epidemiology. In the modern global world, any living or recently deceased person on Earth can apparently be connected to any other person by an astoundingly short chain of connections. For example, in 2019-2020, the COVID-19 Pandemic spread from China to distant tribes on other continents within a couple of months, simply because statistically there are going to be a handful of people in every major city with a particularly short chain of physical connections to that tribal village.

Alternative Title(s): Degrees Of Kevin Bacon, Bacon Number