Since Dec. 4, 2009, Google has been personalized for everyone. So when I had two friends this spring Google «BP,» one of them got a set of links that was about investment opportunities in BP. The other one got information about the oil spill. Presumably that was based on the kinds of searches that they had done in the past. If you have Google doing that, and you have Yahoo doing that, and you have Facebook doing that, and you have all of the top sites on the Web customizing themselves to you, then your information environment starts to look very different from anyone else’s. And that’s what I’m calling the «filter bubble»: that personal ecosystem of information that’s been catered by these algorithms to who they think you are.