The history of science is replete with ideas that were considered socially, morally or emotionally dangerous in their time. The Copernican and Darwinian revolutions are obvious examples -- radical, brilliant insights that did not so much push the envelope as rip it into shreds. These ideas were dangerous because they challenged our comfort zone. But what are the dangerous ideas of the twenty-first century? Which theories do the world's leading thinkers and scientists regard as too hot to handle -- not because the idea might be false, but because it might turn out to be true? Collecting together the very best contributions to the renowned Edge.org question from the most eminent respondents, 'What Is Your Dangerous Idea?' is another endlessly fascinating and provocative insight into the bleeding-edge of intellectual endeavour.