Was Einstein wrong? One of the few things the lay person understands, or thinks they do, about relativity is that things can't go faster than light. Because if they do they travel backwards in time. So when scientists at Cern Europe's top physics laboratory, recently claimed that particles they fi red had broken the ultimate speed limit their peers were sceptical. In this film, Professor Marcus du Sautoy explores one of the most dramatic scientific announcements for a generation. In clear, simple language he tells the story of the science we thought we knew, how it is being challenged, and why it matters.