Melvyn Bragg examines the history of what we know about the origins of the universe. Some four hundred years ago in Rome, one Giordano Bruno was burnt at the stake for his belief in other inhabited worlds - it’s a possibility which has fascinated scientists, writers, artists and the general public for centuries - and any consideration of the origins of life and matter on other planets, and indeed this one, inevitably raises huge questions. Do other worlds exist? How did our planet come into existence? How can we know anything at all about the origins of life and matter so many billions of years ago, and how has our thinking on these - amongst the deepest of questions - changed over the 20th century? Are we any closer to knowing whether other worlds exist and how our own planet came into being? And does the knowledge we have about these things change our perception of ourselves and our position in the universe?With Professor Sir Martin Rees, Astronomer Royal and Royal Society Research Professor in Astronomy and Physics, Cambridge University; Professor Paul Davies, theoretical physicist and Visiting Professor at Imperial College, London.