If advanced technological civilizations are out there, how do we go about detecting them? Conventional SETI, beginning in 1960 with Frank Drake’s investigations of Tau Ceti and Epsilon Eridani, has focused largely on the reception of targeted information via radio. More recent optical SETI likewise hunts for beacons from a civilization attempting some form of contact. But it was Freeman Dyson who suggested that if advanced civilizations exist, their very presence should make them detectable.
The Dyson shell is what a civilization running out of living space and energy on planetary surfaces may build. Conceivable in numerous variants (and apparently inspired by Olaf Stapledon’s 1937 novel Star Maker), it is essentially a technology surrounding a star to exploit all its energy output. As summarized in a new paper by Milan Ćirković (Astronomical Observatory of Belgrade), Dyson’s solution serves not only as a way of capturing all energy from the home star, but also as a potential marker for SETI, as the infrared signature of a Dyson shell should be apparent even at great distance.
In his provocative critique of current SETI practice, Ćirković studies other possible manifestations of advanced technological civillizations (ATCs):
Shouldn’t such structures rank high on our priority list for SETI studies? One among many benefits of such targeting is that macro-engineering requires us to make no assumptions about alien cultures and their desire to communicate. SETI today, Ćirković argues, relies on the belief that distant civilizations will want to make contact. But of course we know nothing about such societies, their motives, their disposition toward other cultures. From the paper:
It is indicative that a large portion of the early SETI literature, especially writings of the “founding fathers” consists of largely emotional attempts to make the assumption of willingness (and, indirectly, benevolence) of SETI target societies plausible (e.g., Bracewell, 1975); this is read more like wishful thinking than any real argument (Gould, 1987). To cite Dyson (1966) again: “[M]y point of view is rather different, since I do not wish to presume any spirit of benevolence or community of interest among alien societies.” This, of course, does not mean that the opposite assumption (of malevolence) should be applied. Simply, such prejudicating in the nebulous realm of alien sociology is unnecessary in the Dysonian framework; with fewer assumptions it is easier to pass Occam’s razor.
Which makes abundant sense, especially given the stages of evolution through which civilizations surely pass; the cultural phase that may turn to radio or optical communications could be short indeed. Macro-engineering projects, on the other hand, would offer a much longer window for study. Ćirković again: “On Earth, the very existence of the fascinating discipline of archaeology tells us that cultures (and even individual memes) produce records significantly more durable than themselves. It is only to be expected that such trend[s] will continue to hold even more forcefully for higher levels of complexity and more advanced cultures.”
A Kardashev Type II civilization is one that is able to exploit all the resources of its star; i.e., it is one capable of constructing a Dyson shell. Such a shell, once created, is likely to outlive its creators by vast amounts of time, posing an inviting target for the SETI search. In a similar way, a Kardashev Type III civilization, exploiting an entire galaxy, poses a challenge to extragalactic SETI, although no evidence for such engineering has yet been found in spiral galaxies close enough to be observed in the detail necessary. Just how recognizable such engineering would be remains an open question.
But there are reasons to be optimistic about finding evidence of macro-engineering of some kind in our own and other galaxies. We’ll discuss this tomorrow as we continue this discussion of Ćirković’s work. For now, let me communicate my enthusiasm for his innovative approach to both SETI and the Fermi Paradox. The paper, “Macroengineering in the Galactic Context: A New Agenda for Astrobiology,” available here, will appear as a chapter in Macro-Engineering: A Challenge for the Future, ed. by Viorel Badescu, Richard B. Cathcart, and Roelof D. Schuiling (now in press). It should serve as a wake-up call for SETI theorists facing into the silence that has so far greeted us from the stars. We need new thinking to understand this silence in the context of astrobiology findings that promise a universe abundant with life.