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Dyson Shells and the Astrobiological Imperative

Finding evidence of large-scale ‘macro-engineering’ projects around other stars may be our best chance of detecting other civilizations. So says Milan Ćirković (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. Ćirković 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 Ćirković 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. Ćirković 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 Ćirković 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 Ćirković 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.

Comments on this entry are closed.

  • qraal June 14, 2006, 9:48

    Hi Paul

    Cirkovic mentions Matrioshka Brains as a plausible end state of technical reconstruction of a star system – an Intelligent system on a supra-stellar scale. Truly an awesome entity and potentially ‘immortal’.


  • ljk June 15, 2006, 11:27

    For those who want the details on this incredible concept,
    see here:


    And for an idea of what our galaxy may be like with such
    beings, see here:


  • qraal June 19, 2006, 9:11

    Hi Larry

    One thing with that first discussion is its naive assumption that such a Brain would be a unitary Being, with no recognizable role for smaller conscious and independent entities within. Personally I think that ignores the nature of holoarchies which subsume the levels ‘below’ them and have their own unique features.

    Personally I think consciousness is a quantum process of the brain’s EM field and that’s what gives up the sense of unitary perception. I am dubious about such quantum consciousness being feasible on the scale of Matrioshka Brains, though quantum communications might allow something at a whole new scale.

    That being said even our own brains are believed to develop ideas and thoughts through a vigorous selection process, almost like an ecosystem or economy in minature. Perhaps then a Brain would be composed of all those ‘lower’ levels, and yet still have an emergent, unitary ‘Self’. After all the human race, as it is, can be likened pretty easily to a vast neural network. That it might be ‘literally true’ oneday – if it isn’t already – shouldn’t be so strange.


  • Robert Bradbury July 3, 2006, 14:47

    The correct link for papers regarding Matrioshka Brains is NOT the FutureHi.net site, that is an illegal copy and will be removed in the future.
    The correct link is:
    or the Wikipedia entry which contains a good, though limited discussion.

  • ljk April 4, 2008, 10:53

    The incidence of mid-infrared excesses in G and K giants

    Authors: Mark H. Jones

    (Submitted on 3 Apr 2008)

    Abstract: Using photometric data from the 2MASS and GLIMPSE catalogues, I investigate the incidence of mid-infrared excesses (~10 microns) of G and K stars of luminosity class III. In order to obtain a large sample size, stars are selected using a near-IR colour-magnitude diagram. Sources which are candidates for showing mid-IR excess are carefully examined and modelled to determined whether they are likely to be G/K giants. It is found that mid-IR excesses are present at a level of (1.8 +/- 0.4) x 10^-3.

    While the origin of these excesses remains uncertain, it is plausible that they arise from debris discs around these stars. I note that the measured incidence is consistent with a scenario in which dust lifetimes in debris discs are determined by Poynting-Robertson drag rather than by collisions.

    Comments: Accepted for publication in MNRAS. 13 pages, 5 figures, 2 tables (1 landscape table)

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0804.0521v1 [astro-ph]

    Submission history

    From: Mark Jones [view email]

    [v1] Thu, 3 Apr 2008 10:44:56 GMT (445kb)


  • ljk October 4, 2009, 14:23

    The Daily Galaxy: Great Discoveries Channel – Could a 1.8 Gigayear Technology Gap Exist? (The Weekend Feature/A Galaxy Classic)

    Could a 1.8 Gigayear Technology Gap Exist? (The Weekend Feature/A Galaxy Classic)

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    There are an estimated 250 billion (2.5 x 10¹¹ ) stars in the Milky Way alone, and over 70 sextillion (7 x 10²² ) in the visible universe, and many of them are surrounded by multiple planets. Meanwhile, our 4.5 billion-year old Solar System exits in a…