Facebook just not a social site it much more Facebook running science experiment on user's .
The PNAS company today revels a paper in which they tell that Facebook manipulating user's and they don't know about it. Company saying that experiment run along week and it affect nearly 700K user's of Facebook. This Experiment is about carrying out motion online in other word's Facebook checking our updates like positive or negative thinking.
The News Feed of 690K user's are in this experiment like pupates of Facebook for a week. Facebook checking that these user's have some change in their thinkin after this experiment or not.
Facebook later said about this experiment that the user who getting positive post is thinking better and the user who getting negative post are not affected in this experiment and mostly still viewing the post's.