SETI - The Search For Extraterrestrial Intelligence It is now just over 40 years since Guiseppe Cocconi and Philip Morrison in their seminal paper on the Search for Extra-Terrestrial Intelligence in the science journal Nature pointed out that, given two telescopes the size of the then newly built Lovell Telescope at Jodrell Bank (see the photo), it would be possible to communicate across interstellar distances. They suggested that perhaps a search for any signals from another civilisation might be attempted and to this end, observed that a suitable frequency band in which to search might be that around the 21 cm (1420 MHz) Hydrogen line - a frequency that would be known to any advanced civilisation. The first search - Project OZMA They also provided a list of suitable candidate stars - those like our Sun which would be hot enough and live long enough for an advanced civilisation to arise from their (hoped for) solar systems. In this list were Tau Ceti and Epsilon Eridani, the latter at the centre of some interest recently as a companion planet has been detected in orbit around it! It was these two stars that were targeted in 1960 by Frank Drake and his colleagues using a highly sensitive receiver on the 85-ft Tatel Telescope at Greenbank in West Virginia in what was the very first SETI search - called Project OZMA. No signals were detected except those from a very high flying aircraft, probably the then top secret U2 spy plane! No detections yet Many efforts have been undertaken in the meantime, but so far, no unambiguous extraterrestrial signals have been captured. Should we then, after 40 years, be disheartened? No! To be honest, it is only recently that we have been capable of having a realistic chance of detecting a signal, and even then from only our near neighbourhood in the Galaxy. Advanced civilisations would have to be very common indeed, and deliberately wishing to make their presence known to us for us to have had a high probability of detecting them so far. The search is only just beginning in earnest. How common are civilisations? It is perhaps, a little ironic, that just as our capability for detecting extraterrestrial signals has reached a high degree of sophistication we are beginning to suspect that advanced civilisations may not be as common as had been previously thought. Carl Sagan believed that there might be perhaps one million other advanced civilisations in the Galaxy. It was felt that should simple life arise on a planet, evolution would drive it towards increasing intelligence. However, this may not necessarily be the case, and if the time scale for the development of our own advanced civilisation is a guide, there may not be many planets where conditions remain temperate for a sufficient time. Few doubt that simple life forms will be very common within the Galaxy but it may not be often that they get the chance to develop into an advanced civilisation as we have. At the moment, radio searches like SERENDIP and PHOENIX are our only chance of detecting other life outside our own solar system. More recently, optical searches have also been started. Let us hope that some day they might be successful for it would surely be one of the most exciting discoveries ever made. But if, after many years of using even more advanced receivers and a new generation of large telescopes, no signals are found we may well come to the realisation that our planet Earth and our human race are, if not unique (for we could never be sure of that), then at the very least rare and very special. Perhaps that would be an even more valuable thing for us to know.

The Lovell Telescope at Jodrell Bank, United Kingdom