They're coming, they're coming. They're all infected, everyone. I can see it, you! You, yeah, you've got the symptoms. Stop sending me invites to play Candy Crush. I don't want to play anymore. And you, yeah, stop liking all those statuses. You're filling up my entire news feed. You've all got it, everyone! Facebook! All right, all right, so Facebook isn't a real infection. Well, at least not in a biological sense anyway. But you may have seen some articles earlier on this year that said that Facebook would lose 80% of its users by 2017. And this is because researchers at Princeton University mathematically modeled the use of Facebook like people modeled the spread of infectious disease. So let's see how they did that. So this one, three volunteers. So can I have the three that I've already brought with me, in fact? Darth Vader, Action Man, and Barbie. I don't know if I know you guys, you should play with these new or younger two, all right? Let's get sensible. All right, so Barbie represents population number one, the susceptible population. Pure, free from Facebook. However, evil lurks close by. Darth Vader represents population number two, infected population, those that use Facebook. And the model describes the interaction between these two and says that the more infected individuals you have, the more you're encouraged to go to Facebook. Come on, join the dark side. And Barbie goes. But never fear. Action Man is near. The greatest here of them all comes and he represents the third population, the recovered population, those that once use Facebook, they saw the light. And so the model describes the interaction between these two and says the more recovered individuals you have, the more friends of yours that say Facebook isn't cool, dude. Don't use Facebook. And so you turn. You become recovered. And once you are recovered, you don't turn back. And that's it, the entire model. Three populations, two interactions. And the researchers use that model to Facebook is currently in a decline phase. And if you fall that line down to 2017, 80% of the user base is gone. So, I have one question for you guys. Where will you be in 2017? Will you be Barbie? Action Man? Free from Facebook? Or will you still be on the dark side? Thank you. Thank you. Barbie, action man, Darth, who wants to go first? You get six out of five for just the use of action man. And actually, having him putting him on the ground, so he's looking out. Yes, he is ready for action. But take this little further. Can you use this kind of modeling? Oh, stop it Quentin. What did you do? Yeah, I know it's cool, right? Can you take this modeling further for epidemics and pandemics, for instance? Of course. So that's where the models came from originally. They are infectious disease models. And the researchers modified it to then show that it can be used for social online networks. So we currently use it at the moment. So infectious disease models are used to work out where we should quarantine people, where we should vaccinate people to get the minimum spread of a disease. So yes, they are used mainly for infectious disease. And what does it tell the entrepreneur tomorrow? You know, the Mark Zuckerberg of tomorrow how to escape the perils that might fall to Darth Vader? It's a good point. So the thing about Mathematical modeling is the model is only as good as the assumptions you make. So whatever assumptions you make about the model, the interactions between the populations, will tell you how general your model can be. And Facebook said that this model was rubbish. So they, in fact, use the same model to show that Princeton wouldn't have any students by 2021. But if the model was actually correct, then Facebook would use that to say, okay, so if my user base goes down by recovered individuals, I need to stop them from being recovered. So then that's how they will start changing and saying, all right, maybe I'll make a Facebook app, I'll buy WhatsApp and Twitter and stuff. And then we'll stop people from moving to being recovered. So that's how you can use models to show. The models actually tell you everything you need to know about how the populations interact. Are you a Facebook user? Or are you recovered? Yes! He infected you, didn't he? Yes. I'm infected. Are you Daph? Come on, you can tell us. I'm not worried. I just wanted to know. I thought it was the case. Well, thank you for a fantastic presentation. We really enjoyed it. Okay, please, we've been hololotless. No tomorrow for Johnny Brooks Barlett, action man, Daph Laider and Barbie.