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.
Hi Paul
You are probably aware that Tsiolkovsky first speculated on filling Sol space and capturing the full energy of the Sun – Stapledon was not so ambitious. He made up for that with his description of an intergalactic travel attempt which sought to propel a whole star system, but the Life Cloud was first thought of by Tsiolkovsky.
A BOTE calculation tells us that all the carbon in Venus is enough to make about 100 Earth areas of habitat. Conceivably it could be deployed as a multitude of multi-hundred kilometre diamond spheres or an immense one 126,000 km across, filled with gas (close to the Jeans mass if it is though.) Or Uranus and Neptune could each be wrapped in a shell that is supported by gas pressure from below, and supplies a habitat with Earth-like gravity.
Actually one bonus of the nanotube is that, once perfected in manufacture, it can be made in bulk by “just” fusing Jupiter into carbon to make Dyson Shell material, instead of the old iron-grade fusion in “The Next 10,000 Years” by Adrian Berry. That assumes mining the Sun for trace elements isn’t easier and less wasteful than fusing Jupiter into carbon.
Ultimately a Dyson Shell might let us capture a bit more than the 1/(2 billionth) the Eatth intercepts today. Perhaps it will merely be power collectors, or maybe a cloud of habitats. Observing advanced ETIs in action would give us powerful hints as to the best strategy for our long-term future.
The inspiration for Stapledon, I thought, was Bernal’s “The World, The Flesh, and The Devil”:
http://www.qedcorp.com/pcr/pcr/bernal.html
Fred, you may be right about Stapledon and Bernal, but I believe Dyson relied more on Stapledon, though the memory goes back to a Dyson book read so long ago that I could easily be wrong.
?irkovi? talks about Stapledon as well as Tsiolkovsky in his paper, though I hadn’t heard the term ‘life cloud’ before. Isn’t this stuff wonderful to speculate about? ‘A multitude of multi-hundred kilometre diamond spheres’ offers the kind of imagery Stapledon would have appreciated. Love those big thinkers!
I’d recommend a look at Larry Niven’s essay “Larger Than Worlds”, most recently published in the Benford/Zebrowski anthology “Skylife” (an excellent collection!). He ranges from expanded asteroids to a Dyson Sphere that encloses a whole galaxy! Imagine if we spotted something like that!
Hi Fred, James Annis did a study a few years ago on the presence or absence of Kardashev III civilisations practicing stellar husbandry. A few billion stars wrapped in Dyson shells should perturb the normal features of a galaxy as expected from the Virial Theorem. His result: a big negative. But those Low Surface Brightness galaxies just don’t seem right to me…
But those Low Surface Brightness galaxies just don’t seem right to me…
So, how do they show up in IR?
There is an edge-on spiral galaxy about 35 million light years from here
named NGC 5907.
http://www.seds.org/messier/Xtra/ngc/n5907.html
What is interesting about it is that it should have many more bright
stars than it does. It has a lot of what appear to be red dwarfs.
Or maybe they are something else radiating in the infrared….
http://www.ifa.hawaii.edu/~meech/bioast/program/LEINT.1.9.pdf
http://www.futurehi.net/docs/Matrioshka_Brains.html
Hi again
You know I don’t know what LSB galaxies look like in IR – there’s got to be a decent preprint discussing the issue out there.
Larry, that ifa.hawaii link didn’t work for me.
Adam
You know I don’t know what LSB galaxies look like in IR
Apparently, they don’t show a lot of emissions as would be produced by dust, which argues against ensphereing of their stars as a cause of the low brightness.
http://www.aas.org/publications/baas/v31n5/aas195/910.htm
You need things for kids projects so it will be easier for my daugter to find stuff for SETI Institute.