Gilles Kepel, an expert on Islam and the Arab world, talks to Sir David about his new book, 'Beyond Terror and Martyrdom', and explains why both George Bush and Osama bin Laden have lost the 'war on terror'. Plus, Steven Johnson talks about his latest book, 'The Invention of Air', which tells the story of the eighteenth century scientist and theologian Joseph Priestley. He talks to Sir David about the relationship between science, religion and politics.