On the other hand, Google doesn't have access to the motherlode of your social activity: stuff you post on Facebook itself, data that is closed off to mining from most other companies online. Every time you press the Like button or use one of Facebook's plugins to post a comment, you're telling Facebook something about yourself and your friends. What's more, Facebook's reach keeps extending. Today, many people connect their activity on a host of sites—including Twitter, Flickr, Quora, Amazon, and Yelp—with their Facebook accounts. They do so because it makes intuitive sense to keep one social network—maintaining separate networks on different sites is too much work. If we're sticking to one network, it makes sense to stay where all our friends are—and that's Facebook.
This will be especially true if Facebook adds better tools for maintaining discrete groups within our larger friend network (which it already does quite well). In other words, hey, maybe Facebook already has this social-networking thing all wrapped up. We don't know what the site will look like by 2016; it's possible that, with all the ways it's infiltrating the wider Web, Facebook.com will be just one small part of the Facebook empire. You may be using Facebook wherever you are online—and no other network will matter.
Why is any of this important—why do these Web giants want to catalog your interests and relationships? There's an obvious answer—because doing so allows them to sell ads targeted to you—and a less obvious one: Social signals are becoming the primary organizing structure of the Web. Today most of the links you see online are determined by editors or algorithms—that is, by people who create sites manually, or by Google, which uses computers to guess what you might be interested in. But both these methods are imperfect. The people who create Slate's home page every day are just guessing what you'd like to read. Google, meanwhile, serves up thousands of links in response to your query, and even though it's often right, it's far from perfect. Web companies see social data as the solution to this problem: That trail of Likes you're leaving around the Web forms a picture of your deepest desires. With this picture, sites of all kinds—news sites, shopping sites, travel sites—can tailor themselves to your interests. In five years' time, you and your dad may visit the Huffington Post and not see any stories that overlap. The site will know, based on your social network, exactly what you want to read.
This isn't really a novel idea. "Link analysis" was at the heart of PageRank, the breakthrough algorithm that powered Google's revolutionary search engine. When one site linked to another, PageRank saw the link as a recommendation; the more inbound links a site garnered, the higher it tended to appear in Google. But what's a link? It's one human being's decision to tell other human beings that another page on the Web is important—in other words, a social signal. Google's breakthrough was in recognizing that social signals can be a very powerful way of organizing the Web. It was the start of a $100 billion company.
By analyzing our social relationships in much more detail, Facebook is looking to do something even more revolutionary. Tell me what you think of the Facebook revolution—do you look forward to the social-networking future, or do you fear it? Is Facebook here to stay, or do you think we'll move on to something else? Let me know in the comments below.