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There are situations in which holding a false belief (or theory) about the world is actually rational; and, conversely, situations in which holding a true belief (or theory) is irrational. Our Pleistocene ancestors, for example, had only their raw senses with which to observe the sun going up and down each day.

As a result, given the data available to them, adopting a geocentric model of the solar system (or the entire universe, as in Aristotle) was actually more reasonable than espousing the heliocentrist alternative. Science is, indeed, an enterprise that employs a highly intuitive basic methodology -- in its simplest form, “look and see” -- yet it often produces highly unintuitive results -- e.g., actually, the earth rotates around its axis while revolving around the sun!

In other cases, there is simply a dearth of relevant data to arbitrate between competing hypotheses, in which case refraining from forming any strong opinion about the subject matter is usually most reasonable.

For example, natural philosophers as far back as the 5th century B.C.E. debated the existence of atoms: some held that matter is composed of “indivisible” basic constituents, while others -- the “continuum theorists” -- held that elements like fire and earth were continuous in nature. But there was, until the 19th century arrived, a void (so to speak) of empirical data to substantiate either position. Making any strong claims about the existence of atoms was thus unwarranted.

The point is that, as far as I can tell, scientists engaged in the Search for Extraterrestrial Intelligence (SETI) are in a rather similar epistemic predicament: there simply aren't enough data points to make any strong claims about whether ETIs exist or not, whether ETIs are (if they exist) benevolent or malevolent, and so on.

To use a Kuhnian neologism, SETI is in something like a “pre-paradigmatic” stage of development, one marked by a conspicuous lack of consensus. Thus, while all scientific theories, no matter how secure at a given moment, are in principle open to revision (for all we know, paleontologists may discover a “pre-Cambrian rabbit” next week and thus have to revise evolutionary theory), one must be especially tentative and circumspect when the science is as incipient as SETI.

This being said, Stephen Hawking has recently argued that we ought not to be transmitting messages into space -- the cosmic equivalent of shooting a flare into the sky, or sending a smoke signal -- because an encounter with extraterrestrials would likely have (Hawking claims) catastrophic consequences; that is, consequences of “existential” proportions.

In Hawking's words: “If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans.” Indeed, as the pious explorer himself once wrote: “Let us in the name of the Holy Trinity go on sending all the slaves that can be sold.” And so the population of Indians in northern Mexico dwindled from 10 million to less than 1 million.

In response, George Dvorsky has written a thought-provoking article in which he argues that “it doesn't really matter [whether messages are transmitted or not] because in all likelihood no one's listening and no one really cares. And if I'm wrong, it still doesn't matter -- ETIs will find us and treat us according to their will.”

I am, in fact, inclined to agree with Dvorsky. The absence of evidence for ETIs appears to be good evidence for the absence of ETIs. But, crucially, just because I -- and many respectable theorists as well -- happen to believe this doesn't mean that transmitting signals is permissible. Why?

(1) As already stated, SETI is a nascent field of inquiry. I once saw Daniel Dennett give a talk in which he claimed that memetics hasn't yet burgeoned into a mature science because the field just recently got its Drosophila: the Internet! In certain respects, SETI doesn't even seem this well-off. Thus, for all we know there is a perfectly sensible explanation for a completely “silent” universe that's also saturated by ETIs that have not yet noticed us; after all, despite our own profound dominance of the biosphere, we are still discovering new species all the time (such as “lungless” frogs and “ninja slugs” in Borneo).

Maybe, then, the aforementioned explanation lies just beyond the horizon of actual -- or even possible -- human understanding. We should thus refrain from saying, as Dvorsky does, “Here's the deal, people” and “So there you have it.” No one on either side of the debate ought to be that confident, at least not at present (I confidently say).

Furthermore, consider Dvorsky's subthesis that “extrapolating biological tendencies to a post-Singularity intelligence is asinine.” But the very idea that, as Dvorsky elsewhere puts it, aliens visiting us would have (e.g.) “survived a technological Singularity event” itself involves an extrapolation of our own (peculiar?) experience with technology -- an experience prognosticated to culminate, at some future point, in an historically singular event of which many are still highly skeptical.

We have here the equivalent of the N = 1 problem in ALife: all we have is one history of technology from which to infer the technological development of another possible civilization. Thus, any claim about aliens experiencing a Singularity, or developing nanotechnology, and so on, must be sensitive to such epistemic limitations.

(2) Given that it is not unreasonable at present to think that a visit from aliens could effectuate an eschatological disaster, Active SETI researchers are confronted by a moral problem: the possible consequences of alien contact could affect the entire human population, yet the decision to transmit such signals is being made “unilaterally” by a relatively small fraction of the population. (A similar issue arises with, for example, unilateral geoengineering: a single country injecting sulfur dioxide into the stratosphere would have global affects, but without global approval. This would be an ethical violation of one's rights.)

Until we can make probabilistic claims about the benevolence of aliens with far more certitude, it seems fair to request -- as David Brin recently has -- that “arrogant fools [stop] blaring into space 'on our behalf' without at least offering the rest of us the courtesy of first openly consulting” experts like Hawking. “Heteronomy” (in the sense of one individual's will dominating another's) ought to be avoided.

In sum, no one should be too sure about any view pertaining to the existence or disposition of ETIs -- or even about the sorts of advanced technologies they possess. Thus, while I find the proposition that we tellurian bipeds with big brains are aberrations in a cold and otherwise lifeless universe rather compelling, I also recognize the special fallibility of this and other such hypotheses. Indeed, SETI is not only a (fallible) science but a rather nascent one as well, and this combination of attributes has the effect of raising the probability that any particular “xenological” hypothesis will end up being shown incorrect, or at least incomplete, by future research.

And, secondly, there is an important moral issue concerning the right of a small group of Active SETI researchers to make decisions for all of humanity (without consulting “all of humanity,” or its representatives, first). At the very least, I believe, we should refrain from shooting off any sidereal flares until a reasonable consensus among the relevant experts is reached -- no matter how sure theorists like Dvorsky (or myself) are about the ultimate safety of such activities.

The history of science is, after all, replete with brilliant scientists who expressed absolute confidence in the truth of theories that were subsequently shown to be rubbish. (Although I myself am a convinced scientific realist, there is something to be said for theses like Larry Laudan's “pessimistic meta-induction.”) And while in many cases the consequences of such error were not significant (personal embarrassment, a minor delay in scientific progress, etc.), it behooves us SETI enthusiasts to be especially careful as long as a sufficient number of scientists like Hawking think the consequences of alien contact might be both bad and global -- or “transgenerational” [PDF] -- in scope.