Just for a moment, imagine a universe awash with life, where we humans are not the only intelligent beings around. What might these alien races look like? Could we communicate with them, or even recognise them as intelligent? And what would they make of our violent and dangerous species? Might they take one look, and decide not to bother with such primitive beings? A planetary nursery filled with spiteful, galactic infants. On the other hand, in our imaginary scenario, they may enrich us with scientific knowledge beyond our imagination. Or could an encounter with aliens have a more destructive outcome? It could be a bad day for human kind. But relax, it's just make believe, it could never happen, could it? A mysterious crash in Roswell, New Mexico during the 1940s convinced many that our planet is being visited by space aliens. Crop circles in Britain have only added fuel to the fire. Few scientists doubt that life indeed exists elsewhere, but some believe we're more likely to make ...