The plurality of worlds: A synergistic approach to the question of the search for extraterrestrial intelligence (SETI)

Abstract

If intelligent life is a common occurrence in the Galaxy, then many civilizations should have arisen which by now are far in excess of mankind in both their age and their capabilities. It is to be expected on technical grounds that some of these should have crossed the threshold of their home planetary system and ventured out into interstellar space. In a time that is short when measured against astronomical timescales, such civilizations could have colonized the planets orbiting every suitable star in the Galaxy. As the Solar System is relatively young in the Galaxy, there should nevr have been a time in our history when mankind was not aware of the presence of such civilizations. And yet, we apparently see no signs of intelligent life in the Galaxy other than ourselves! This paradox—first expressed by Enrico Fermi 40 years ago—is today still relevant to discussions on the possible existence of intelligent life in the Universe and the methods of searching for signs of such life. This article explores arguments prompted by the paradox in more detail. It is concluded that the different aspects have only one self-consistent resolution—mankind is unique in the Galaxy. It is hoped that elaboration of some key concepts will cause the discussions to refocus on the paradox that Fermi identified so many years ago.