Hello and welcome back to Networks Illustrated: Principle without Calculus. In this lecture, we're going to look at the question, why do certain videos go viral on You Tube? Thinking back to the lectures on Amazon and Netflix, we looked at the concept wisdom of crowds. And we saw that under certain circumstances, we could aggregate information coming from a mass of people and come up with a good estimate for some value. The key underlined assumption that was made in the wisdom of crowds, was that people's opinions were independent of one another. So we had independence. What we're going to look at in this and the next lecture, are situations where they're not independent of one another. And rather, everybody can see the public actions of the crowd and hence we have dependence of opinions. A good example of this is when your looking to see whether or not to watch a YouTube video based upon the total view count that video has. And under certain circumstances as well, depending upon the specific situation, we could see how this dependence of information can trigger what's known as an information cascade. [SOUND] Where nobody is looking at their private information anymore, and instead they just following suit with the actions of the public and essentially ignoring their own gut feelings, and hence we're going to see the exact opposite effect of the wisdom of crowds, instead the fallacy of crowds. As a result, in this and the next lecture the overarching principle and theme is going to be that crowds are not so wise. In this space of user-generated content, YouTube has become the dominant sharing site. On the site, we can find videos ranging from lectures on academic subjects, to the music of self-proclaimed quote unquote YouTube artists. More recently, the site has also started a movie rental and purchase business to compete against iTunes and the Studios. So in this lecture, we want to explore the concept of viralization. And in doing so, we're going to recognize how YouTube is a perfect example of dependencies created by information spread. But first, let's take a brief look at the timeline behind YouTube's rapid growth. YouTube was founded in February 2005 at the hands of three former PayPal employees. From it's inception, the site grew at a rapid pace. For instance, by July 2006, it had 65,000 videos and about 100 million views it was getting daily. And just a few months later in November 06, it was acquired by Google for 1.65 billion. And of course the increase in YouTube view counts kept going. For instance by October 2009, it broke 1 billion daily views. This graph right here shows the views per day in billions. So in October 2009 we had it breaking one, one billion views. May 2010 it broke, two billion. By, what, next year May 2011 it had gone up to three billion. And January 2012, it hit the 4 billion mark. An interesting thing to note here is that, the amount of people that are watching the site, or the amount of people that are on the site, is going to influence the amount of content that you have on the site. because as more people are going on the site, more of them are going to be incentivized probably to make content. And the more content you have on the site is going to in turn influence the amount of people on the site which is going to influence the amount of content and so forth. And what's known as a positive feedback with them. We'll look at this more in this lecture as opposed to negative feed back loops that we, looked at before. So by winter 2013, YouTube had over 1 billion unique monthly viewers, with over 4 billion views per day. Further, there is roughly 72 hours of content uploaded each minute. So every minute it gets 72 hours worth of watching time. Which means that in 1 day there is about 12 years of content. So, if you think about that, what that's implying is that, each day, YouTube gets enough content that you'd have to take 12 years of your life to watch all the content that was uploaded in that day, which is pretty remarkable. YouTube's also the second largest search engine that we wouldn't normally think of it as a, as a search engine, it means that, the second largest number of queries are entered into YouTube. And that's of course, behind Google itself as the largest. And Alexis ranked YouTube as the third most visited website behind Google, which is the first most visited website, and Facebook which is the second most visited website. So from all of this and seeing how popular YouTube has become, it's really become somewhat of a viral phenomenon on itself, and we'll turn our attention to viralization next.
