This was of course a great contribution Cocconi and Morrison made in 1959. They calculated what you could actually detect with existing radio telescopes over very large distances, and it turned out that the results were surprising; that you could detect our present day radio transmissions if they were transmitted from here to some place else in the galaxy and if the aliens at the other end had a similar telescope receiving the signal; that even with our present equipment you could communicate over thousands of light years, in fact not quite all the way across the galaxy but over a substantial part of the galaxy. So it was technically within reach to communicate with aliens over these enormous distances. So they proposed that we actually listen for the aliens. If there are any extraterrestrial intelligences they might be transmitting on the radio and we might be able to hear what they're saying. So that was the Cocconi-Morrison proposal and... which I thought was a brilliant idea and it made sense from every point of view. The beauty of it is that it doesn't cost much to implement, so right away Frank Drake in the first year started a search programme at Green Bank with the existing telescope, actually listening. He didn't hear any aliens, but he proved the feasibility of it and it was an extremely cheap programme. I mean he... his total expenses were a few thousand dollars just for a little bit of detecting equipment and data processing, and that's all he needed. And from that beginning it has continued now for 40 years, so there is a very active programme going on. Particularly there is a programme in Massachusetts led by Paul Horowitz which is listening for radio signals on about half a billion channels, so it's increased in its data processing power by factors of billions since Frank Drake. But still the equipment is quite cheap and the running costs are small, so this is actually all being done with private money, it's not funded by the government, so it's one of the most cost effective things you can do in the whole of astronomy in a way. If we did discover any aliens of course, it would be an enormous... revolution in our whole way of thinking. So I'm 100% in favour of this searching for the radio signals.