The science behind the smile. Interview by Gardiner Morse

Only recently have we been able to apply science to one of the world's oldest questions: "What is the nature of happiness?" In this edited interview, the author of the 2006 best seller Stumbling on Happiness surveys the field. Gilbert explores the sudden emergence of happiness as a discipline, reviews the major findings (including the mistakes we all make in predicting how happy or miserable we'll be), and examines the role of happiness in productivity on the job. He describes what makes us truly happy-it's not a promotion or a new house-and sketches out a "happiness diet" that emphasizes small, routine efforts. Looking forward, Gilbert discusses the breakthrough work of his colleague Matthew Killingsworth, whose iPhoneenabled real-time surveys of people's moods are providing an ultra-high-resolution picture of how our emotional states shift from minute to minute. A sidebar by Killingsworth offers a preliminary look at his findings and their implications for our personal and workplace lives.