Believe it or not, the world's population rolls along a similarly shaped mood curve--at least, according to Twitter they do. A study in the latest issue of Science magazine describes the findings of sociologists who analyzed the tweets of over 2.4 million people worldwide. "People are most upbeat around breakfast time. Their mood deteriorates over the course of the day and then rebounds in the evening," says co-author and Cornell sociology professor Michael Macy, who notes that people's moods are brightest on Sundays. "It could be that the elevated mood on the weekends is because they did not get woken up by an alarm clock, which would have disrupted their natural sleep patterns." As Harvard psychologist Dan Gilbert tells The Times, Twitter only knows if you're happy if you show it. “Tweets may tell us more about what the tweeter thinks the follower wants to hear than about what the tweeter is actually feeling," said Gilbert. "In short, tweets are not a simple reflection of a person’s current affective state and should not be taken at face value." They can however, keeping track of mood data can be converted into money as this newly minted Twitter-based hedge fund has shown.