So, there's been a number of places in which the sixth degree of separation concept has come up in popular culture. And we can look at a few of those here. One is the TV show, Six Degrees of Martina McBride in which six aspiring country artists were basically given the task to connect themselves to Martina McBride using six steps or less. And those who were able to do that, and the winners of that challenge were offered a studio session with Martina McBride and also a chance at a record deal. Another one is the six degrees of Kevin Bacon, which is interesting. Basically it studies the, the network of acting relationships among actors. So Kevin Bacon is a famous actor, if you ever heard of him before. And basically the idea is that they believe that Kevin Bacon's basically acted with so many different people that it would be interesting to see how far away different actors are in terms of their relationships. So the idea here is that basically if you're, if, if some, someone's one's an actor and here's, you know, Kevin Bacon or someone else basically someone that you've acted with you would be connected a link with directly. So if I had been in a movie with this person that means that we have a direct link. Okay, so maybe that person has then acted with Kevin Bacon. So they have a direct link. So that would mean, if I don't have a direct link to Kevin Bacon in that case, that this, this node here, would have a Bacon number of two. basically, that's what it's called. It's called a Bacon number. And this person who's acted directly with Kevin Bacon would have a Bacon number of one. So, basically, it's, it's just looking at how far away people are from Kevin Bacon. And this is, also illustrates the network of acting relationships. So, you can, you could do this with a whole bunch of different types of networks. And so you can go to this website here, oracleofbacon.org, and you can type in any actor or actress's name and you can figure out what their Bacon number is. Here's just an example from another famous actor Matt Damon. And Matt Damon actually has a Bacon number of two. So Matt Damon in 1996 acted with Sean Astin. And Sean Astin was in White Summer Water in which he acted with Kevin Bacon. So, Sean Astin has a Bacon number of one, because he's connected directly to Kevin Bacon. And Matt Damon is connected to Sean Astin who's connected to Kevin Bacon, with a Bacon number therefore of two. So, this is basically the number of cops here is two. Another famous example is the Erdos number. Basically, this is more in the academic realm. The famous mathematician Erdos. People say, well, Erdos had so many, so many math papers that the question is how far away are you in terms of co-authorship relationships on math papers from the mathematician Erdos. And so the idea here is that in this case this is movie acting relationships. Movie acting. And you can define a similar network obviously, it's just you're looking at a different property here. In this case you're looking at co-authorships. Authorships. [SOUND] So here two math authors or authors of math papers are connected if they've ever co-authored a paper together. So if you look at their paper, if you look, if there is some paper exists that basically has both of them as being co-authors on the paper, then that means that they have a co-authorship link of just one with one other. So if Erdos is here, and this is some mathematician, and this person's connected directly to Erdos and this person's connected to this person who's connected to Erdos, then that means that the Erdos number there is two. And it can similarly propagate back. So if someone is connected to this person, who's there connected to this person, who's connected to Erdos, then that's Erdos number of three. Now of course, this is only look at the shortest path distance, right? So, if this person was, for instance, connected directly to Erdos, then the Erdos number would not be three, it would be one. But so you have to take just the shortest path. And you can go to this link here if you want to look more at how the Erods number's defined. Another example is Facebook. Okay, so the average degree of separation on Facebook you've probably heard the number 4.74 before. That was computed in November of 2011, and this is looking at a different type of relationships, this is looking at friendships. Friendship relationships. And so what this is saying is that on average it would take one person in terms of friendship relationships, so you'd say okay here's the person that we've picked that we want to get to, okay. So someone else is connected to this person. Someone's connected to this person. And maybe I'm connected to this person, whose connected to this person. And so my shortest path link here is four. And if you do that over all the different combinations in November 2011, you would have gotten 4.74. And that number may be updated soon. From 2008, that number was 5.28 hops, and you see it actually dropped in 2011, it went down to 4.74. And there's many other examples, as well. You can Google and go find a lot of examples in which people have observed this sixth degree of separation phenomenon in popular culture.