As we enter an era of molecular manufacturing and ubiquitous computing, it becomes increasingly difficult to imagine what form an extraterrestrial presence might take. I'm personally convinced that the UFO phenomenon, bizarre as it initially seems, conforms to at least some of the "acceptable" criteria for a Bracewell-type probe. If I'm right, then the electromagnetic bias evidenced by our radio searches takes an abrupt and unwelcome backseat to something far stranger.
If our solar system is host to an ET intelligence, argue transhumanist pundits, it's unlikely we'll meet flesh-and-blood aliens. Metallic interstellar spaceships with biological passengers made sense to pre-computer audiences, but the reality-bending potential of the Silicon Age has cautioned theorists from expecting anything so blatant as the arrival of a "mothership." It's more likely that our first meeting with ETI will involve a novel form of artificial intelligence -- perhaps even the encoded persona of the ETs themselves. (It's worth noting the possibility that the fabled signal awaited by SETI researchers may turn out to be a practical blueprint instead of a mere greeting. In Carl Sagan's "Contact," the blueprint provides humanity with a transportation device, but perhaps it's just as reasonable to expect instructions for building an "alien-making machine": certainly an elegant solution to crossing the void in a messy, energy-intensive spacecraft.)
