American Scientist

To the Editors:

I carefully read Howard Smith’s article “Questioning Copernican Mediocrity” (July–August). I found the premise of the title interesting, due to the significance of the Copernican revolution, which indeed “demoted” the Earth from the center of the Solar System and the universe, to an ordinary planet revolving around an ordinary sun.

There are three points of debate that I raise over Dr. Smith’s article: First, the article seems to make a water-rich environment essential for the evolution of a carbon-based life-form and ultimately intelligence—meaning no other type of life-form is considered. Second, the article seems to make an anthropogenic argument that if we encountered other intelligence, we could see it and communicate with it. Third, the article spends many words arguing for the existence or nonexistence of extraterrestrial intelligence based on distance and time; in other words, Dr. Smith assumes that the only method of communication is via electromagnetic signals propagating at the speed of light, which raises the additional issue of whether we will be able to receive either electromagnetic or other signals generated by an alien intelligence.

Dwain Butler
Vicksburg, MS

Dr. Smith responds:

Dr. Butler asks about the possibility of intelligent life forms based neither on carbon nor water. Maybe they could exist somewhere, but there is no authority I know of who thinks that silicon, for instance, comes close to carbon in its suitability, and the same goes for water. So, such aliens are expected to be even rarer than conventional ones. I briefly mention some of the difficulties in my other articles. The bottom line is that no one has figured out in the slightest what quantitative possibility to assign such strange creatures to develop; it could certainly be nil. My article attempts a quantitative estimate of whether or not “mediocre” and speculative beings (why not civilizations hidden underground on Mars?) are excluded because they are limited so far to the realm of human imagination. In a similar vein, if we encounter some beings but do not recognize them as such, then surely they—as far as we are concerned—are the same as nonexistent and we are still alone. As for communication, any forms we can conceive of will use the force carriers: photons most likely, but perhaps gravitons or other bosons, or perhaps pressure waves (sound) locally. We have good detectors, and they are getting better, so unless an alien signal is intentionally hidden in some faint or noisy frequency band, it seems to me we could in principle detect it. The exciting recent discovery of gravitational waves demonstrated that even they travel at the speed of light.