What causes paranoia? That’s a tough question to answer, and for at least a couple of reasons. For one thing, there’s no simple explanation. Paranoia, like so many psychological experiences, is the result of a complex interaction of numerous factors—as we’ll see over the course of the next three chapters. But there’s a bigger, more fundamental problem. How can we accurately and scientifically observe paranoid thinking? Paranoid thoughts don’t pop into our heads out of the blue. They’re generally our attempt to make sense of something we’ve experienced—perhaps a colleague ignored us at lunch or someone looked at us oddly on the bus. We can ask people about their paranoid thoughts, but how do we get at the truth of the situation? How do we even know for sure whether their thoughts are genuinely paranoid? Perhaps the colleague ignored us because our existing paranoia makes us reluctant to socialize. Or perhaps our fears are a legitimate response to a threatening situation. Maybe the guy on the bus really was looking for trouble. Any rigorous, scientific study of paranoia would need to expose a statistically significant number of people to exactly the same experience to see which of them reacted in a paranoid way. Once you had these data, you could start probing to see whether there was anything distinctive about the paranoid group. But how on earth can we arrange for hundreds of people to experience exactly the same everyday event in laboratory conditions? It’s impossible, right? Actually, there is a way, and it’s one we used in a groundbreaking recent experiment. That way is virtual reality. In the summer of 2006, we sent a leaflet to all households local to King’s College London. The leaflet announced a study of virtual reality at the college and invited people to participate. In the end we recruited 100 men and 100women of varying ages from 18 to 77, and from very diverse socioeconomic backgrounds. The mix, in fact, was pretty representative of the UK as a whole. We didn’t tell the volunteers that we were researching into paranoia until we’d completed the experiment.