When Princeton sociology professor Matthew Salganik was a doctoral student at Columbia, he got interested in blockbusters — specifically, he got curious about the role of social influence in determining the success of music, art, and books.  He and his coauthors set up an ingenious experiment: they created a website where people could listen to songs by unknown artists, then decide whether they wanted to download particular songs to their private library. Participants were randomly assigned to different virtual rooms. In some rooms, people saw only a list of songs, while in others they could see how many times a song had been downloaded. Altogether the researchers created eight rooms — parallel worlds, really — which allowed them to study not just the role of popularity, but also the role of chance, in the creation of hits.