In a sense, the world wide web is like the largest ever psychology experiment. A psychological marketplace where every day millions of designs, photos and images are uploaded, and tested against millions of behavioural reactions: clicks. The typical psychology or neuroscience experiment in universities is run on around 20 participants, and may take months or longer before it is published. In contrast, the web is working to a radically faster rhythm, running real-time tests, globally, 24/7. Metrics such as social media ‘trending’ lists measure the global psychological pulse, telling us what people are thinking, feeling and desiring around the world.