AC Grayling discusses the science behind the search for extra terrestrials with Seth Shostak, Chief Astronomer at SETI Institute in the USA.
It is a scientific endeavour which is 50 years old this year and, in a public event at the Wellcome Collection in London, they explore the science of radio waves as well as the likelihood and implications of contacting the little green men.
In 1959 a letter to Nature magazine called for some serious science on trying to find life forms on other planets, and an experiment began to search nearby solar systems for radio wave activity.
Far from being an esoteric backwater for cosmologists, SETI as it has become known, has attracted the financial support of Nasa, the public backing of a phalanx of Nobel Prize winners over the years, and universities and scientific institutions are ready to lend the expertise and provide funding for a search which now involves almost every country on earth.
With a trillion planets in our own galaxy, so the thinking goes, and water now found on Mars, the moon and several other places in our solar system, there is a strong probability that life - intelligent life - exists elsewhere out in the deep dark blue.