Finding evidence of large-scale ‘macro-engineering’ projects around other stars may be our best chance of detecting other civilizations. So says Milan ?irkovi? (Astronomical Observatory of Belgrade) in a paper discussed here yesterday. But what would make us think such structures exist? Recent microlensing projects have found evidence of objects around distant stars — we can detect their lensing effect and separate it from that of the parent star. We naturally assume these are planets, but could they be artificial habitats or other system-wide engineering projects?

In the absence of direct evidence, we can only speculate, but it seems a not unreasonable assumption that a fraction of advanced technological cultures evolve to the Kardashev Type II stage, capable of controlling the entire energy output of their stars. ?irkovi? relies on recent work by Charles Lineweaver, whose studies of the ‘galactic habitable zone’ show that Earth-like planets within it would be on average 1.8 billion years older than Earth, plus or minus .9 billion.

Which triggers this, from the paper:

Applying the Copernican assumption naively, we would expect that correspondingly complex life forms on those others to be on the average 1.8 Gyr older. Intelligent societies, therefore, should also be older than ours by the same amount. In fact, the situation is even worse, since this is just the average value, and it is reasonable to assume that there will be, somewhere in the Galaxy, an inhabitable planet (say) 3 Gyr older than Earth. Since the set of intelligent societies is likely to be dominated by a small number of oldest and most advanced members…we are likely to encounter a civilization actually more ancient than 1.8 Gyr (and probably significantly more).

And ?irkovi? points out that 1 billion years ago, even simple animals lay far in Earth’s future. What chance would we have of communicating with a civilization that far in advance of our own? Such creatures are unlikely to have a pressing need to communicate with us. But if we are unlikely to encounter a communications beacon, we have a reasonable chance of finding evidence of transiting artificial objects, antimatter-burning signatures, Dyson shells or other clearly artificial structures. In many cases, these would be long-lived objects more susceptible to discovery than a transient beacon.

Couple this logic with breakthroughs in astrobiology, from the discovery of extremophile organisms in deep ocean hydrothermal vents to the evidence of organic compounds in meteorites, the experimental verification of the survival of microorganisms under conditions of cometary or asteroidal impact, and the increasingly interesting work on panspermia theories dealing with life’s origin.

Life, in other words, ought to be out there. And one reason we have not yet found it may be that we continue to assume extraterrestrial civilizations will be something like us. ?irkovi? questions the notion, and notes recent work on the possible evolutionary development of postbiological intelligence (we might have to re-consider infrared searches for Dyson shells, for example, adjusting for the lower temperatures that might be more efficient for completely computerized, non-biological civlizations). Not all artifacts are necessarily the result of biology, and limiting our assumptions makes us less likely to find them.

All of this gives good reason to expect a better answer to the Fermi Paradox than ‘we are alone.’ Especially compelling in this notion is that ?irkovi? is arguing for a reassessment of our time frames, criticizing conventional SETI as far too conservative in its expectations of the kind of technological civilization we might expect to encounter. Moving into the Lineweaver era, we contemplate civilizations potentially hundreds of millions of years older than our own, if not more. Perhaps we are better served by looking for the signatures of technological civilizations at work rather than directed messages from them.

“The end of our foundation is the knowledge of causes, and secret motions of things; and the enlarging of the bounds of human empire, to the effecting of all things possible.” So said Francis Bacon in his New Atlantis (1626), quoted by ?irkovi? at the beginning of this paper. The effecting of all things possible seems to be a theme of human technology, and it is likely a theme of civilizations around other stars. By their engineering you shall know them, and perhaps in no other way. In any case, “Macroengineering in the Galactic Context,” available here, is bracing reading that holds the feet of conventional SETI to the fire. Don’t miss it.