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Is there life beyond our planet? That is a question which occupies the astrophysicist Paul Davies. He spends a lot of his time involved in the search for extra terrestrial intelligence and chairs an international group which would help to decide the world's response if aliens ever got in touch with us.

But after 50 years of scientists looking for life beyond earth using radio telescopes, there has been nothing but a deafening silence. Jonathan Charles asks him whether it is time to accept that there is no-one else out there.