SETI, the search for extraterrestrial intelligent life, has held a privileged position in science for decades. A discipline without a subject, SETI has nonetheless attracted a talented group of dedicated researchers. But the lack of results is starting to prompt questions and, yes, even doubts.

Why does anyone even think there might be intelligent life out there? It's all about faith and probability. Faith that the processes that led to the origin of life here on Earth should operate anywhere in space where the conditions are right. Probability then takes over, leading to calculations about the number of planets that might eventually host an intelligence at least as acute as that of humans'.

Years ago, Frank Drake, the leader-emeritus of SETI, concocted something called the Drake equation, which was an attempt to estimate just how many intelligent civilizations there might be out there. The starting point was the number of stars in the galaxies (many, many zeroes). Each subsequent term in the equation whittled that gargantuan number down by posing further conditions. Of those stars, how many might have planets? How many of those planets might actually harbour life? And, in the end, how many intelligent civilizations with the technological capacity to signal us arose and are still out there?

You'd think there wouldn't be many, but you'd be wrong. Because the initial number in the equation is so huge, the number of intelligent civilizations was initially calculated to be something like a million in our Milky Way galaxy alone — give or take.

Calling this an equation is to mislabel it slightly, because really only the first term — the number of stars in the galaxies — is even roughly known. Everything from then on is a guess. We are getting closer to an idea of how many planets those stars have, and how many of those planets might be habitable, but that's still a long way from having a good handle on the idea.

Now, some skeptical voices are being heard. In the May/June issue of the Skeptical Inquirer, political scientist Peter Schenkel takes issue with the optimistic numbers yielded by the Drake equation. I don't buy his first argument, that if they were really out there, we should have found them by now. (It's an old question. The legendary physicist Enrico Fermi actually asked, "Why haven't we heard from them?" back in the 1940s.) But the search is really just beginning.

The fact that it is 46 years and counting since we started listening seems tiny to me compared with the times and distances we're considering.

But Schenkel also suggests that there's evidence that we are pretty special, even in a chemistry/physics way. The sun is just the right age and distance, the outer planets protected us from the asteroid bombardment early in the life of the solar system, and even dramatic extinctions, like that of the dinosaurs, created opportunities for other living things.

But others suggest that the reason we haven't been in contact with others is that they're simply not interested in us. Schenkel finds this unbelievable, claiming that any species that calls itself intelligent must also have that drive and curiosity that leads humans to explore the Earth, travel into space and listen for the signs of others. (We began sending our own messages in the form of music, speech and symbols on spacecraft at least 30 years ago.)

This notion of the curious, out-reaching alien clashes nicely with the ideas of evolutionary psychologist Geoffrey Miller, who suggests in Seed magazine that the tendency to look inward, not out, would actually be bred in technologically advanced civilizations — in fact, it is happening right now with ours. Miller writes: "Aliens don't blow themselves up; they just get addicted to computer games." His point is that technology is able to provide virtual versions of real-life things that we choose because — at least in real life — they promote survival.

But the virtual version is more vivid and compelling. Miller cites tasty foods giving rise to fast food; sexy mates to the porn industry.

He goes on: One hundred years ago, gadgetry enhanced real life: electric lights, air conditioners, zippers. Today, it's all about TV, the Internet, virtual reality.

Miller suspects that alien civilizations that followed roughly the same developmental line as we have eventually disappeared into their made-up worlds and died out, too absorbed in technology to reproduce.

So, we have to work fast. Find one other civilization like us, one that is still interested, before the technological vortex sucks us in, too.

Jay Ingram hosts Daily Planet on the Discovery Channel.