The New Approach to SETI Is from the Bottom Up, Rather Than the Top Down
As far as the prevalence of life and intelligence throughout the galaxy goes, the simple fact is we still have no idea. All our estimations and projections continue to be based on a single datum-namely, the life we find around us here on Earth. There are those, such as Peter Ward and Donald Brownlee, who personally see evidence that complex life may be quite rare, even if unicellular life comes about fairly routinely. There are others who see it differently. To give a specific example, routine cosmic catastrophes will, it is claimed, destroy the chances of complex life emerging except in the most unusual cases. Yet, one such catastrophe, at the end of the Cretaceous, was the very reason that high-level intelligence developed on Earth! All of our current hypotheses about the likelihood of extraterrestrial life and intelligence are nothing more than opinions based on inference and one data point. What we must do is continue to look for hard evidence, both locally (within the solar system) and across interstellar distances. Neither optimism nor pessimism is helpful when based on ignorance.
Set against the fact that SETI has not so far received a positive signal are a number of encouraging developments in astronomy and astrobiology. These include the detection, since the mid-1990s, of more than 150 extrasolar planets, and increasing signs from within the solar system that the conditions deemed necessary for the development of life as we know it (water, organics, and a suitable energy source) may arise on multiple worlds around a single star. Astrobiology is in the ascendancy. Mars, Europa, and Titan head a short list of locales in our neighborhood where scientists would not be at all surprised to find extant microbic life. We are detecting increasingly complex molecules in interstellar space and evidence that life might be able to survive trips between worlds aboard meteorites. As I explain in my book Life Everywhere (Basic Books, 2001), terrestrial life, from the outset-not just over the past few hundred million years-has shown a propensity to become increasingly complex and display the rudiments of intelligent behavior.
The rise of astrobiology and of exoplanetary astronomy has offered SETI researchers a new approach which the SETI Institute, in particular, has embraced. That is, it enables the attempt to make contact with other intelligences to be done from the bottom up rather than the top down. Within the next decade, increasingly powerful and sensitive instruments, based on interferometry, will allow us to detect Earthlike worlds that may orbit sunlike stars within a range of a few hundred light-years. These instruments and their successors will enable us then to analyze the light coming from these “alien Earths” to search for biogenic signatures, such as those of molecular oxygen and chlorophyll. If we are successful in demonstrating beyond reasonable doubt that certain known planets are life-bearing, we can then begin to study these worlds more closely to see to what heights their indigenous life has evolved. Are there signs of industrial contaminants in the atmosphere or stray artificially produced EM emissions? When we reach this stage of our investigations, astrobiology and SETI will join forces in an effort to determine if high intelligence is present.
Personally, I feel there’s only a slim chance that any time soon we'll make contact with another race in our galaxy that is at roughly the same technological level as ourselves. I suspect there is a technological window of about 500 years beyond which we would effectively be blind to another intelligent species. The galaxy may be swarming with advanced intelligence that is as invisible to us as satellite communications is to a native in the rainforest. Moreover, our galactic elders, if they exist, far from having any desire to communicate with us, would likely be interested in us only as biological or anthropological specimens. They may also have the wisdom to appreciate that any interference by them in our affairs would have the potential to destroy our culture, just as we in the West have harmed the less technologically advanced races on Earth with whom we've made first contact.