In a mathematically perfect universe, we would be less than dead; we would never have existed. According to the basic precepts of Einsteinian relativity and quantum mechanics, equal amounts of matter and antimatter should have been created in the Big Bang and then immediately annihilated each other in a blaze of lethal energy, leaving a big fat goose egg with which to make stars, galaxies and us. And yet we exist, and physicists (among others) would dearly like to know why.