The remains of hurricane Alberto didn’t seem terribly menacing as they approached North Carolina, and much of the state got no more than a good soaking. But here in Raleigh we were inundated with over 7 inches in a short period of time, leaving Centauri Dreams with a flooded office. I’m back online, but only just, and there is still a lot of cleaning up to do. Please bear with me and expect things to get back to normal in a day or so.
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.
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 ?irkovi? (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, ?irkovi? 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, ?irkovi? 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. ?irkovi? 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 ?irkovi?’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.
As we move up the frequency ladder toward optical communications, each step takes us closer to the kind of data traffic we’ll need for deep space missions into the Kuiper Belt and beyond. The idea is to pack as much information as possible into the signal. A stream of data transmitted from an antenna spreads at a diffraction rate that is determined by the wavelength of the signal divided by the diameter of the antenna. Higher frequencies, then, give us a much narrower signal, alleviating bandwidth crowding. And a laser communications system makes fewer demands upon a spacecraft’s power sources than radio.
So watch developments like the recent experiment performed by the Japan Aerospace Exploration Agency (JAXA) with interest. The agency carried out a successful optical test using laser beams between its ‘Kirari’ satellite (also known as the Optical Inter-orbit Communication Engineering Test Satellite) and a mobile ground station in Germany. The downlink occurred with the satellite at about 600 kilometers altitude and lasted for three minutes.
We have much to do to iron out a laser communications infrastructure, but demonstrating communications with a mobile station on Earth points to a newfound flexibility in these operations. Lasers will give us data rates a hundred times faster than current radio systems, and will offer mission planners the ability to pack more and more high-resolution tools onto their vehicles for uses such as synthetic aperture radar and hyper-spectral imaging that are far more demanding than photographs. And someday, lasers will carry data from our first dedicated interstellar probes as they close on nearby stars.
When the British Interplanetary Society’s Daedalus designs were being created in the 1970s, the scientists and engineers involved quickly realized that interstellar dust would become a problem for a vehicle traveling at 12 percent of light speed. That led to shielding concepts involving materials like beryllium, boron and graphite. But what of concepts like Robert Forward’s vast lightsails? If dust posed a problem to Daedalus on its way to Barnard’s Star, surely a huge lightsail was even more threatened, there being no effective way to shield it.
Forward himself suggested an answer in a 1986 letter to the Society’s journal. His optimum sail materials (still far beyond our capabilities) would be much thinner than the diameter of the interstellar grains the starship would likely encounter. The result: such materials would pass right through the sail, creating a hole about as big as themselves. For work within the range of nearby stars, Forward believed, interstellar dust would not pose a significant problem, an assumption that, as far as I am aware, has yet to be modeled in any laboratory experiments.
But we’re learning more about interstellar dust through space-based observatories like the Spitzer Space Telescope. Space dust is believed to be composed of the same essentials from which the Earth is made: carbon, silicon, magnesium, iron and oxygen, and a further assumption has long held that this material was produced by red giants as they aged. That assumption is now challenged by observations of a supernova in the spiral galaxy NGC 628, findings that begin to fill in our knowledge of interstellar materials. They suggest that supernovae are significant contributors to dust clouds between the stars.
In the case of supernova 2003gd, infrared measurements taken 500-700 days after the supernova event by the Spitzer Space Telescope show that solid dust particles in an amount equal to 7000 Earth masses had formed. “2003gd is, quite literally, the smoking gun,” says Doug Welch (McMaster University). “These carbon and silicon dust particles which form from the supernovae blast make possible the many generations of high-mass stars and all the heavy elements they produce. These are elements which make up the bulk of everything around us on Earth, including you and me.”
Observational work like this will one day have to be supplanted by missions to take in situ readings of what spacecraft encounter outside the heliosphere. The Innovative Interstellar Explorer (IIE), a NASA Vision Mission study now being developed, is one possibility, although payload constraints make dust measurements in its earliest designs problematic. Another possibility: a second-generation mission like Claudio Maccone’s FOCAL, which might one day piggyback a suite of instruments aboard an observatory designed to make use of the lensing properties at the Sun’s gravitational focus. Missions to nearby stars are in our future, but there is a vast amount of science to be done just outside the Solar System.
For those interested, Forward’s correspondence on lightsail shielding appears in the Journal of the British interplanetary Society 39, p. 328 (1986). A. R. Martin discussed shielding for Daedalus in “Bombardment by Interstellar Material and Its Effects on the Vehicle,” Project Daedalus Final Report (JBIS, 1978), pp. S116-S121. The recent findings on supernovae appear in Sugerman, Ercolano, Barlow et al., “Massive-Star Supernovae as Major Dust Factories,” published in the June 8 Science Express edition of the journal Science.
