Aliens abound on the movie screens, but in reality we are still trying to find out if we share our universe with other sentient creatures. Intelligence is very difficult to define, and impossible to directly detect over interstellar distances. Therefore, SETI, the search for extraterrestrial intelligence, is actually an attempt to detect evidence of another distant technology. If we find such evidence, we will infer the existence of intelligent technologists. For the past 50+ years, the SETI community has had a very pragmatic definition of intelligence - the ability to build large transmitters! SETI searches to date have looked for radio or optical signals coming from distant civilizations as a way to detect a technology across the vast distances that separate the stars. As our own technology matures, we will try other means of searching, and we will certainly improve upon the searches that we are already conducting. The Kepler spacecraft and goundbased searches have now discovered thousands of planets orbiting other stars - it may be the case that all stars have planetary systems around them. We have not yet uncovered Earth 2.0, our twin, although we think that event is imminent. And when we do, we will surely wish to know whether anybody lives there. For the near term, SETI may be the only way to find out.
Guiseppi Cocconi and Philip Morrison ended their 1959 seminal paper on SETI with the statement, "The probability of success is difficult to estimate; but if we never search, the chance of success is zero." At the SETI Institute and at other facilities around the globe, we are searching. Prof. Morrison also described SETI as "the archeology of the future"; we should not underestimate the importance of the search for helping us to achieve our long future. As astronomers we tend to forget the privileged perspective of the cosmos that we share. This big picture view is one that sees the Earth as a single entity, ignores artificial, national boundaries, and trivializes the differences among humans. Getting the world actively involved in SETI may be a first step in promoting the global cooperation that will be required to find technical solutions to the problems that threaten our future as Earthlings.
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