In a recent article in the journal Astrobiology, Seth Shostak of the SETI Institute explains just how powerful current and planned SETI efforts are compared to what they were only a few years ago. Critical improvements have come from increasing the speed of the search, increasing the sensitivity of the observations, improving the quality and number of targeted star systems, and expanding search strategies beyond the radio range.
In the 1980s the best SETI receiver had tens of thousands of frequency channels, while today’s equipment typically has tens or even hundreds of millions. Sensitivities are increasing as the size of the antennas used in the search grows by roughly two orders of magnitude per century, combined with other technological advances such as low-noise receivers. Recent exoplanet discoveries, especially the detection of planets that are Earth-like in at least some respects, have increased the number and quality of SETI targets. And search strategies have been broadened to include optical detection methods or attempts to detect Dyson spheres.
Shostak says that rather than waiting “for the payoff from multi-billion dollar efforts to churn the sands of Mars or plumb the stygian depths of Europa or Enceladus—rather than drumming our fingers anticipating new telescopes that could sense distant life’s spectral signature,” SETI offers the possibility of short-cutting the search. Finding a radio signal would instantly prove the existence of extraterrestrial life with technology at least as advanced as our own.
But what if technologically advanced life is exceedingly rare? By my own recent estimate (for the upcoming second edition of the Extraterrestrial Encyclopedia), there may be only one other technologically adept civilization in the whole galaxy. If such civilizations are common, would we not have seen some evidence by now?
Given the lack of evidence for technologically advanced life, SETI searches are worthwhile, but at least in my view cannot replace the admittedly tedious effort to find simpler forms of life. Although we anticipate only microbial life existing on the planets and moons of our solar system (at best), those are the only places we’ll be able to visit in the foreseeable future. And we would learn a lot, even from extraterrestrial microbes.