Search for intelligent life: reassessing SETI

The article, "SETI Requires a Skeptical Reappraisal," by Peter Schenkel, and three responses by astronomers Jill Tarter, David Morrison, and David Darling that appeared in our May/June 2006 issue brought, as expected, a large reader reaction. Here is a sampling.

Editor

Regarding Peter Schenkel's "Skeptical Reappraisal" of SETI, a few corrective historical notes may be helpful.

Schenkel writes that Frank Drake, Carl Sagan, and other SETI pioneers estimated that "a million advanced civilizations probably exist in the galaxy." It is true that one can find isolated quotations to that effect in the SETI literature, although for some reason, Schenkel cites none at all. But this view was characteristic neither of Drake nor Sagan, nor of the SETI community as a whole. Their habit was to quote a wide range of values, from a million communicative worlds down to two or three, noting that the outcome depended on which data one plugged into the Drake equation.

The most sensitive term of the equation turned out to be average life span of civilizations: if the median life span were long, there might be many civilizations at a given time; if it were short, we might indeed be alone. As we can hardly expect to know the average life spans of civilizations until we have access to some sort of galactic history book, they cautioned, all such estimates remained speculative, even if we happened to be right about every other parameter. This was responsible science, not starry-eyed romanticism.

Schenkel describes the Drake equation as "incomplete" and urges that it be revised, but he never explains what he thinks is missing from it. If one accepts, say, his assertion that the earth is more unusual than had been thought--not that this position, based largely on post hoc reasoning, is particularly persuasive--all one needs to do is to alter the term in the equation which quantifies the fraction of all planets deemed "earthlike."

Researchers in the field have been wresding with such matters for decades without finding it necessary to declare their tools inadequate to the task.

Schenkel makes much of the fact that no extrasolar planets resembling the earth have yet been found. But he neglects to mention that the detection techniques employed to date in almost all such searches are mass-dependent--i.e., they can readily detect Jupiters but are virtually blind to Earths. To reason that they reveal an absence of Earths is like dragging a net with a foot-square mesh through the seas and concluding from the resulting evidence that all fish are at least a foot long.

Because we know so little about extraterrestrial life, SETI has long constituted a kind of screen onto which we risk projecting our predispositions. Schenkel, for his part, once believed that our world, "beset by problems," could solve them by consulting "a civilization more advanced than ours"--a notion that certainly qualifies as romantic and optimistic, inasmuch as we have little idea of what we might actually learn from such contact.

Now, he maintains that we need to "demystify" SETI by correcting its "early optimistic estimates," and he takes it upon himself to pardon Drake and Sagan for putative lapses that he condescendingly characterizes as "understandable and profoundly human." But the "optimistic estimates" he decries were never more than part of an ongoing dialog during which Drake, Sagan, and their colleagues remained, in the main, alert to the very hazards that Schenkel has now discovered. They justify neither revising the tools of the trade nor rewriting its history.

Timothy Ferris

University of California,

Berkeley

Rocky Hill Observatory

Glen Ellen, California

Peter Schenkel's article on SETI was thoughtful, but it resurrected one poor argument against ET visitation: if I were an alien, I'd behave thusly; since we haven't caught them behaving thusly, they aren't around. But their behavior might not be based on determinants comparable to ours.

ET visitors would have an advanced technology, perhaps old enough to have surpassed our own by several orders of magnitude. They live in the same physical universe, but actually knowing just how mass deforms spacetime or the ultimate nature of electromagnetism and gravity might enable them to manipulate or bypass universal constants. It could certainly make their experiences, and interrelated values, interests, and priorities, very different from ours.

Elephants and cetaceans seem to use complicated verbal communications. We haven't been able to decipher them (or even perceive their subsonic and ultrasonic extremes very well), despite these large-brained mammals' sharing some of our environment and much of our genome. ET's might have even less in common with us. We shouldn't be surprised if alien approaches turn out to be--well, alien.

Jon Hauxwell

Hays, Kansas

Peter Schenkers "realistic and sober view" of SETI is interesting and thought-provoking, but overly pessimistic. His view reminds me of the similarly negative view intelligent-design creationists hold toward prebiotic chemistry. And for the same reason: both Schenkel and the creationists are stuck in the present, implying that if scientists haven't succeeded by now (either discovering extraterrestrial intelligence or creating life in a test tube), it's unlikely they ever will.