Seth Shostak: Alien life is not so far away

From a speech by the astronomer to the 54th International Astronautical Congress in Bremen, Germany

When will scientists succeed in proving the existence of other thinking beings? It turns out that, even given the wide range of assumptions inherent in the search, a rather definite prediction can be made as to when our radio telescopes will pick up the faint squeal of an alien transmitter. These dates range from 2014 to 2027.

The estimate depends upon two things: the suspected number of technological civilisations in the galaxy and the rate at which our radio telescopes are sifting for signals. The first has been optimistically gauged by Carl Sagan as a million or more. A less ebullient judgment by the Search for Extraterrestrial Intelligence (Seti) Institute pioneer Frank Drake is 10,000. We assume that the truth lies somewhere within this range. If so, the nearest alien society is between 200 and 1,000 light-years distant.

How long will it take our radio telescopes to scrutinise all the likely star systems within this range? The speed of Seti experiments has improved following Moore's Law, according to which the amount of computing power purchasable per dollar doubles each 18 months. The Allen Telescope Array, a new radio instrument currently being built by the Seti Institute and the University of California, Berkeley, which can be used full-time for Seti observations, will likely experience this exponential improvement for the next several decades.

When the estimated search space and telescope speed are combined, one can easily predict the first detection: it will occur within two dozen years. Although Seti searches are sometimes referred to as multigenerational projects, our estimate suggests that this isn't the case: success is within the foreseeable future.