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Vulcans, Daleks, Martians, Grays - our culture is pervaded by alien beings from distant worlds – some benevolent…most not so much. In our galaxy alone, there should be tens of billions of planets harbouring life, but we have not heard any broadcasts or seen any flashing lights from distant civilisations.

Based in Silicon Valley, California, chief astronomer for SETI (the Search for Extraterrestrial Intelligence), Seth Shostak, has devoted his career to searching for signs of alien life. In this programme he tackles this fundamental question about whether we are alone in the universe.

Sixty years ago, the journal Nature published a paper suggesting the best way to search for alien life was by listening for radio signals. Within months, Frank Drake had begun scanning nearby star systems and SETI was born. Seth talks to Frank about whether his lifetime’s effort has been worthwhile.

He speaks to Jill Tarter, inspiration for Jodie Foster’s character in the movie Contact, hears about a major new listening project and visits a lab where techniques are being developed to monitor light communications from distant worlds.

Seth also talks to a scientist devising techniques to send messages to ET, which could bring aliens calling… but not necessarily in a good way. One theory suggests that aliens may have been watching Earth for years and have decided we are best avoided.

(Photo: A human astronaut making first contact with a Reptoid Alien being. Credit: Education Images/UIG via Getty Images)