Probably we (as in Facebook users) are part of the largest psychological experience in history. With the billion users and trillions of actions, the computers a

Probably we (as in Facebook users) are part of the largest psychological experience in history. With the billion users and trillions of actions, the computers at Facebook have an unprecedented opportunity to make experiments on us to see what makes us tick. Take notifications as an example. Not that hard to think that there could be some machine learning system trying to find the best possible notification pattern to lure back a user who has not visited Facebook for a while. On Facebook scale you can run large number of tests in reasonable small time frame and still get pretty good number of observations for each test. Similar thing could be applied to quite many things on Facebook. Most of the things they want to optimize are easy to measure. Like how often we check the site, how much time we spend there, how many times we click ads and so on.