This year marks the fiftieth anniversary of the first serious scientific attempt to detect signals from an alien civilisation, using a radio telescope at Green Bank in West Virginia. The title of Paul Davies’s homage to all the effort that has succeeded this pioneering work derives from the fact that nothing has yet been heard from ‘out there’ – at least, nothing that can be interpreted as a sign of an intelligent technological civilisation. But the silence is only eerie, as Davies makes clear, if there are sound reasons for thinking that there ought to be many other civilisations in our galaxy broadcasting messages at radio wavelengths. As Davies also makes clear, this assumption is so full of holes that it should be no surprise that the search has proved fruitless. ‘As a scientist,’ Davies admits, ‘my answer [to the silence] is that we are probably the only intelligent beings in the universe.’ But as a human being, he ‘can think of no more thrilling a discovery than coming across clear evidence for extraterrestrial intelligence’.

That is the point of what is now known as the Search for Extraterrestrial Intelligence (SETI). It is reasonably cheap, taking advantage in most cases of spare time on existing radio telescopes, and relying on funding from individual benefactors (including the Microsoft billionaire Paul Allen) for such dedicated