The Drake equation revisited

If these conclusions are correct, then the SETI project (Search for ExtraTerrestrial Intelligence) and the funding and attention given to it are absurd. SETI is based on serious misconceptions about the likelihood of alien intelligence and about our chances of communicating with it. In the light of our arguments in this chapter, let us reconsider the factors in the Drake equation. So far as R* (the rate of formation of stars compatible with the development of life), fp (the fraction of those stars that have planetary systems) and ne (the number of planets orbiting each of these stars that has a life-supporting environment) are concerned, recent investigations have provided some clues. R* and fp probably have fairly high numerical values, but ne is probably low. It is difficult decide whether fl (the fraction of these planets on which life actually appears) is a reasonably high number or close to zero. It depends on the likelihood of the origin of life, about which opposing views can be held, as we have seen. However, we can be sure that fi (the fraction of life-bearing planets on which intelligent life evolves) is vanishingly small, and fc (the fraction of civilisations that develop an advanced technology emitting detectable radio signals) is effectively zero. The factor L is accordingly irrelevant. Serious omissions from the Drake equation include the fraction of planets developing intelligent life on which human intelligence evolves (again, this is almost certainly close to zero), and the components of fi, which include the probabilities of developing eukaryotes, multicellularity and animal-like forms - collectively very low.

No doubt this will prove an unpopular conclusion, so let us suppose that we are wrong. Suppose, despite all reason to the contrary, we discovered an extraterrestrial intelligence with advanced technology and found a way of signalling to it. News that we were not alone in the universe might be reassuring, depressing or uninteresting, depending on our point of view (compare the various responses to the ALH84001 story). But what could we gain from such a discovery? The notion that we could usefully exchange ideas with hypothetical intelligent aliens is ridiculous. Consider: if we had a time machine that enabled us to exchange ideas with our own forebears three or four centuries ago, what could they gain from us or us from them? How could we possibly convey (for instance) the ideas of quantum physics, modern evolutionary theory, molecular biology, modern art, high-technology warfare, commercial pop music or the internet to Newton and his contemporaries? And at what level could we hope to grasp, or to respect, their way of thinking about the world? The comprehension barrier on both sides would be too great. How incomparably more difficult would it be to exchange ideas with an entirely alien culture from an entirely alien world? It is wholly implausible.

So much, alas, for the most enduring and entertaining theme in our science fiction literature.

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