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Rethinking SETI’s Targets

Have you ever given any thought to intergalactic SETI? On the face of it, the idea seems absurd — we have been doing SETI in one form or another since the days of Project Ozma and without result. If we can’t pick up radio signals from nearby stars that tell us of extraterrestrial civilizations, how could we expect to do so at distances like M31’s 2.573 million light years, not to mention even the closest galaxies beyond? Herein lies a tale, for what intergalactic SETI exposes us to is the baldness of our assumptions about the overall SETI attempt, that it is most likely to succeed using radio wavelengths, and that it may open up two-way communications with extraterrestrials. It’s the nature of these assumptions that we need to explore today.

The Visibility of a Galactic Culture

Let’s suppose, for example, that Nikolai Kardashev’s thoughts about types of civilizations are compelling enough to put to the test. A Kardashev Type III civilization is one that is able to exploit the energy resources not just of its home star but of its entire galaxy. So unimaginably beyond our present capabilities is a Kardashev Type III that we scarcely know how to describe it, but it is within the realm of reason that signs of astro-engineering on this scale might be detectable in at least nearby galaxies if such a civilization had gone to work on them. And indeed, James Annis has made such a study, concluding that neither our Milky Way nor M31 or M33, our two large, neighboring galaxies, has been transformed by the work of a Type III civilization.

Image: M33, the Triangulum Galaxy. We’ve only begun to investigate whether nearby galaxies like this one might show signs of astro-engineering on a gigantic scale. Civilizations a billion years or more older than our own might be capable of feats detectable from great distance. Credit: Adam Block/NOAO/AURA/NSF.

It should hardly be necessary to point out how preliminary such results are, and how rare such studies have been. What’s striking about Annis (and related work by Richard Carrigan and P.S. Wesson) is that these scientists are pursuing ideas that are well outside the SETI mainstream. There is a new paradigm here, one that operates without any notion of ‘contact’ and subsequent exchange of ideas between civilizations. It is a search for artifacts, for artificial structure and signs of engineering. It is all about discovery. And just as we can have no two-way conversation with Mycenaean Greece as we dig for information about the era of Agammemnon, we may with this stellar archaeology discover something just as unreachable but likewise well worth the study.

Toward a Dysonian SETI

In a recent paper, Robert Bradbury, Milan Ćirković (Astronomical Observatory, Belgrade) and George Dvorsky (Institute for Ethics and Emerging Technologies) consider whether intergalactic SETI may be an example of what they call a ‘Dysonian’ approach to SETI, one that is a ‘middle ground’ between the traditional radio-centric view (with contact implications) and the hostile reaction of SETI detractors who see no value in the enterprise whatsoever and think the money better spent elsewhere. The nod to Freeman Dyson is based on the latter’s conjecture that a truly developed society would surmount the limits of planetary living space and energy by building a Dyson shell, capturing most or all of the energy from the star near which it lived.

A Dyson sphere immediately changes the terms of SETI because it is in principle detectable, but unlike nearby radio signals (either from a beacon or as unintentional ‘leakage’ from a civilization’s activities), a Dyson shell might be spotted at great astronomical distances through its infrared signature. Carl Sagan was one of the first to pick up on the idea and ponder its implications. Dyson was much in favor of attacking the question in a disciplined way, using our astronomical tools, as he once wrote, “…to transpose the dreams of a frustrated engineer into a framework of respectable astronomy.” And here again, we have seen attempts, especially by the aforementioned Richard Carrigan, to study infrared data for signs of such Dyson constructs.

The new direction in SETI that the three authors of the new paper champion is one that employs a broader set of tools. Rather than limiting itself to radio dishes or dedicated optical facilities, it broadens our workspace for extraterrestrial civilizations to include astronomical data that can be gathered in tandem with other research projects, scanning a far wider and deeper field. In the authors’ view, Dysonian SETI also takes into account new developments in astrobiology and even extends into computer science and the possibility of post-biological intelligence. They advocate a Dysonian SETI drawing on four basic strategies to supplement older methods:

  • The search for technological products, artifacts, and signatures of advanced technological civilizations.
  • The study of postbiological and artificially super-intelligent evolutionary trajectories, as well as other relevant fields of future studies.
  • The expansion of admissible SETI target spectrum.
  • The achievement of tighter interdisciplinary contact with related astrobiological subfields (studies of Galactic habitability, biogenesis, etc.) as well as related magisteria (computer science, artificial life, evolutionary biology, philosophy of mind, etc.)

The expansion of SETI into these areas would not replace ongoing SETI methods but would significantly expand the overall process in line with the great goal of learning whether other intelligent beings share the galaxy and the nearby universe with us. The paper offers more fruitful speculation than I can fit into a single entry, so we’ll be looking at these ideas over the course of the next few days. If there really is a Great Silence, to use David Brin’s phrase, these authors argue it’s one that we can only ponder usefully if we broaden our search toward the potentially observable achievements of cultures far more advanced than our own. That study has only recently begun.

The paper is Bradbury, Ćirković and Dvorsky, “Dysonian Approach to SETI: A Fruitful Middle Ground?” JBIS Vol. 64 (2011), pp. 156-165.

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Comments on this entry are closed.

  • GreenTom January 23, 2012, 10:57

    I wonder how much of this has been unintentionally done already. I’ve thought for a while about how Dyson spheres/clouds would look to us, and I think if they were common, we’d see some population of stars off the main sequence at higher magnitude/lower wavelength than models predict.

    I don’t know how complete our current infrared star surveys are, but imagine they would let us set some upper bound on the frequency of Kardashev Type II civilizations.

    At a lesser level, would highly space-faring Type I civs show up as, essentially, unusually dusty systems with our current sensors? Not sure how we could distinguish a system full of primordial dust/rocks/comets from one full of structures. Do current planetary formation and evolution models predict the dustiness changing over time? Might be reasonable to expect younger systems to have more dust, so a > a few GYr old star with what looks like a thick asteroid belt might be a candidate.

  • Richard BW January 23, 2012, 11:05

    Looking forward to hearing more about this paper, Paul. But for what it’s worth there is another area where SETA (Search for Extraterrestrial Artefacts) could bear fruit – and that is right here in our solar system.

    It’s not unreasonable to think that, within a suer-conservative 1,000 years, humanity will have the technology (a) to make self-replicating machines, and (b) to send such a machine (perhaps the size of a sugar cube) to a nearby star… Where it would make copies of itself, launch itself to say 10 nearby stars – where each probe would create ten more copies and launch them to ten more stars…

    There would be a limit to how far such probes could meaningfully penetrate whilst still transmitting data back to the parent civilisation – but data acquisition is only one of many possible reasons for creating such probes. It might be a more effective form of data *transmission* than huge radio beacons, for example. Or, if the probes contained a store of entangled particles, with half of each entangled pair remaining home, the act of finding such a probe would immediately tell the parent civilisation that there was someone else out there…

    A few years ago I wrote an article for JBIS about this. I included a modification of the Drake equation – a thought experiment – aimed at quantifying how likely it is, given a technological civilisation out there, that there might be examples of their technology right here in our solar system. Perhaps it would be dead tech – could be billions of years old, even – but that’s still evidence we are not the only intelligence ever to have arisen in the universe.

    And that evidence could be within a few AU of Earth.

    That’s quite a thought!

    Richard

  • Ron S January 23, 2012, 12:04

    Doing the search is probably a good idea, even though I expect either a null result or some momentarily-intriguing false positives. The reason I feel this way is that I find the whole rationale behind the Kardashev scale to be unrealistic, being that it little better than an extrapolation of human civilization of a certain type and at a certain point in time. The need for extraordinary amounts of controlled energy input (and output) to support a large civilization is not necessarily true. No doubt there will be great works that will involve large scale energy use and transport, though probably not for routine societal needs. I could be wrong.

    I also cringe a bit at criticisms of radio SETI since we really have little choice, if we pursue SETI at all, but to use the tools that we have. If ETI uses a mode of communication we neither have nor suspect there is little we can do about it, for the present.

  • torque_xtr January 23, 2012, 15:06

    I guess no one Dyson sphere exists in the nearest part of our Galaxy, since the ball glowing in thermal infrared, but with bolometric luminosity of orange dwarf (assuming 90% energy conversion efficiency) would be blazingly prominent on WISE images, or any other infrared sky surveys. But I wonder what would it be if such one is discovered. A “black box” some jillion light-years away, possibly with some weird spectral lines… We would know at least one civilisation has made it and not destroyed itself in nuclear war or who knows how else (which is surely optimistic), but not much more.

  • Nick January 23, 2012, 15:10

    It’s great to see some people doing some real SETI work instead of obsessing over a communications method that briefly dominated the previous century. The key to this kind of endeavor is to forget about the specific structures that might exist (e.g. the various variations on Dyson spheres) and think about what we would actually see — surfaces. Surface engineering has some very specific but universal goals, especially involving thermal and optical efficiency (for heat radiation, illumination, reflection, etc.)

    The universal quest for efficiency should lead to some very blatant spectroscopic signatures. For example the most efficient illumination methods create a very improbable narrow and sharp spike at certain wavelengths. Surface coatings contain some very improbable chemicals for thermal reasons (e.g. skyscraper windows, satellite covers, etc. often contain millions of times the natural proportions of gold).

    It’s not that ETI will necessarily or even probably use the same surface materials we use (e.g. gold), but whatever superior surface materials they discover are likely to be just as or more improbable looking vs. just seeing dumb nature at work, and for some engineering reasons we can expect to be universal.

    One difference from archeology is that we are probably more likely to see freshly maintained than long-decayed surfaces.

  • Paul Gilster January 23, 2012, 15:55

    Richard BW writes:

    A few years ago I wrote an article for JBIS about this. I included a modification of the Drake equation – a thought experiment – aimed at quantifying how likely it is, given a technological civilisation out there, that there might be examples of their technology right here in our solar system. Perhaps it would be dead tech – could be billions of years old, even – but that’s still evidence we are not the only intelligence ever to have arisen in the universe.

    Yes, the authors of this paper get into SETA as well, as it might be practiced in our own system, though probably not at the level of detail as your paper does. Please give me the citation so I can look your paper up, and thanks for bringing it into the discussion.

  • Eniac January 23, 2012, 16:30

    @Richard:

    There would be a limit to how far such probes could meaningfully penetrate whilst still transmitting data back to the parent civilisation

    Limit? What limit? It seems to me that we only need to be able to bridge the gap between stars, any further distances will be no problem as we can relay information from star to star, in the manner of an interstellar Internet, if you will.

    I am afraid entanglement will not provide a means of instantaneous communication, but even without, the amount of information gathered would quickly increase with the radius of propagation, providing a torrent of material to Earth-side researchers. The limit, in as far as there is any, will be the boundaries of the galaxy. There will be a gap in information when there is nothing more to discover here and the nearest extragalactic target has not yet been reached.

  • Bob January 23, 2012, 16:50

    Since you brought it up…SETI should broaden the search way beyond electromagnetic signals and take a serious scientific look at the possible evidence for contact past and present rather than a wholesale rejection
    of such possibilities based on apriori assumptions.

  • Nick January 23, 2012, 17:27

    Ron S: “I also cringe a bit at criticisms of radio SETI since we really have little choice, if we pursue SETI at all, but to use the tools that we have.”

    SETI people (with some great exceptions named above, and other astronomers who quietly think about these issues in their spare time) aren’t using the tools available, namely the vast amounts of spectroscopic data we have gathered about other galaxies. This data is many orders of magnitude more likely to result in a positive discovery than listening for a communications method (radio) that only makes sense over short distances when one hasn’t come up with anything better (and in less than a century we’ve already come up with many better, e.g. lasers).

    As a general response to some other comments, the search for artifacts in our own galaxy is misguided. The existence of any artifacts at all in a galaxy (with the exception of our own improbably young civilization) would make it likely that substantial fractions of the visible surfaces of the entire galaxy will have been converted into artifacts — probably according to universal principles of surface physics and efficiency as discussed above, which would result in blatant spectroscopic signatures. Other galaxies provide a sample space over 100 billion times larger than our own galaxy to search for these artifacts.

  • Rob Henry January 23, 2012, 20:01

    Eniac asks “Limit? What limit?” in response to Richards “There would be a limit to how far such probes could meaningfully penetrate whilst still transmitting data back to the parent civilisation”

    Richards statement does not make sense in relation to the limits of a single probe. The real problem is the cost each additional transmitting probe places on those probes that are already transmitting, such that the marginal befit of further exploration falls so rapidly as to reduce interest in continuing the process. The hypothesis is that the wave of exploration thereafter is so dramatically slowed, as to take billions of years to cover the whole galaxy if only one system in it remains inhabited. The idea is that this is meant to explain why they are not already here.

  • Eniac January 23, 2012, 23:04

    A few years ago I wrote an article for JBIS about this. I included a modification of the Drake equation – a thought experiment – aimed at quantifying how likely it is, given a technological civilisation out there, that there might be examples of their technology right here in our solar system. Perhaps it would be dead tech – could be billions of years old, even – but that’s still evidence we are not the only intelligence ever to have arisen in the universe.

    And that evidence could be within a few AU of Earth.

    That’s quite a thought!

    I completely agree. And I would go further: More likely than dead artifacts, we should be seeing living descendants right here in our solar system. Once life takes hold, it is not eradicated easily. In the very unlikely event of complete extinction, chances are another ETI arrival will bring extraterrestrial life right back in (relatively) short order.

  • Ron S January 24, 2012, 0:24

    Nick: “SETI people (with some great exceptions named above, and other astronomers who quietly think about these issues in their spare time) aren’t using the tools available, namely the vast amounts of spectroscopic data we have gathered about other galaxies. This data is many orders of magnitude more likely to result in a positive discovery than listening for a communications method (radio) that only makes sense over short distances when one hasn’t come up with anything better (and in less than a century we’ve already come up with many better, e.g. lasers).”

    As I said, I have no problem with the search if there is the interest, just that I don’t expect much to come of it. I think you are wrong to say “many orders of magnitude more likely” since this is simply a guess that cannot be quantified to any probability measure with confidence. Better to do both, assuming interested investigators with the necessary resources.

    Lasers are better in some ways, not in others. Using one pretty much effectively requires a directed transmission of exquisite pointing precision, and therefore that constrains the search to the subset of ETI that would explicitly target us. We don’t know enough to say whether the benefit of lasers more than compensates for the reduced subset of ETI candidates, as opposed to more conventional RF. Again, with interest and resources it, too, can be pursued.

  • Interstellar Bill January 24, 2012, 1:19

    How about examining so-called ‘subluminous galaxies’
    as normal galaxies except that all the stars are
    partially obscured by Type II civilizations?
    Perhaps for some reason Type II can’t be full.

    Given the mere mega-year temporal scale of Galactic Conquest,
    we’d expect to observe only complete Type III signatures,
    after which they’d star- up all their gas and dust in, say, 100 Myr,
    so we’d be looking for star-only galaxies.

    A Type III implies significant interstellar commerce, so:
    Could we see the launch lasers of another galaxy?
    An edge-on galaxy would have far more lasers
    pointed our way than a face-on,
    but then it becomes harder to tell it’s subluminous.
    Since the lasers are held in a constant direction for years,
    and every star should have hundreds of lasers,
    what’s the probability of us seeing just one?

  • Nick January 24, 2012, 2:52

    @torque_xtr: We would get some very interesting information from spectroscopy of the molecular or other physical nature of the surfaces of a civilization millions of years older than us, even in a distant galaxy, should it have modified a substantial fraction of the surfaces of that galaxy in some consistent ways. In particular, we may get from these spectra very valuable clues on how to do very advanced surface and illumination engineering. Which might also teach us some news things about physics and chemistry in general.

    @Rob Henry: I’m still not sure I quite follow Richard BW’s argument, which seems to contain some dubious economic assumptions. In particular, it seems to assume some limit on how cheap probes and interstellar transport can be. I do like the general idea of applying economic arguments, though, as economics along with Darwinian selection are likely to form the most universal bases of motivation.

    The probable economics are that cheap propellant will give us cheap interstellar travel. The transport costs between stars can easily fall to a few cents per kilogram. With the important caveat that interstellar trips take millenia, and speeding them up increases their (energy) costs by a square of the velocity. Which brings up the applicability of compound interest in such a calculation (see below).

    Also, I don’t see any basic limit to how efficient the manufacturing of probes can be. Manufacturing costs for a very wide variety of goods have been falling on average by about 2-5%/year since the Middle Ages , and I don’t see why such progress couldn’t continue for many millenia into the future.

    If a one-tonne interstellar probe only costs an ETI*minute worth of labor to make and one more to transport to the next star, it won’t take much of scientific, curiosity, or any other preference to motivate it. Mere slight differences in planetary size, orbit, chemistry, and so on, in the new solar system would presumably be worth at least a few minutes of labor cost to some ETI to gather petabytes of up-close measurement data that can’t be gathered any other way.

    Similarly the costs of transporting an entire self-sufficient economy between stars will eventually be a miniscule fraction of the income of its inhabitants.

    A more plausible argument for the “civilization stuck in their home solar system forever” model might be made based on time preferences: that no intelligent species, including ourselves, prefers to spend significant amounts on projects that won’t pay off for many millennia (and in interstellar travel the cost of making them pay off sooner increases as the square of the time savings). Nevertheless, given that such projects will probably eventually be doable for a few ETI*minutes of labor, the very existence of this forum and others where a few unusual people expend many hours discussing the far future argues against such a thoroughgoing dominance of short-term motivations.

    (Observe BTW that applying a compound interest rate to interstellar travel costs is basically equivalent to making a time preference argument. Market interest rates only reflect _average_ time preferences and thus can’t be considered universal for similarly low-cost projects).

  • The Void January 24, 2012, 3:34

    Has anyone ever proposed to look for extant civilizations using some form of spectroscopy or other means?

    It seems to me a lot of thinking and research has gone into to looking for living civilizations at our level of technology (radio SETI), just beyond our level (optical SETI), well beyond our level, (infrared searches for Dyson Spheres, Dyson Shells, Galactic or Extra-Galactic level engineering,) etc.

    But with the Fermi Paradox seemingly unanswered why do we not look for failed civilizations??

    Beyond looking for “funeral pyre” Benford Beacons I can think of a number of other things which could befall a civilization which might be detectable at interstellar distances with some future advance in astronomical data collection.

    Looking for astro-archeology of extant civilizations could be anything from looking for signs of past (or current) nuclear conflagration, looking for the atmospheric signal from a formerly habitable planet with an artificially induced runaway greenhouse effect, perhaps the signature of a self-replicating nano-machine meltdown (ie: the “grey goo” scenario), potential victims of an interstellar disassembler (ie: a terrestrial planet being dismantled by a species alien to that star system), the gamma ray signature of large quantities of antimatter coming into contact with matter on a planetary surface, the ionization over time of a terrestrial planet’s atmosphere due to some form of technology, the list could go on but you see what I am getting at. Perhaps more investigation needs to take place on just what is detectable at interstellar distances?

    Sagan when he talked about SETI with skeptics in Congress in the 80s during the Cold War often referred to the factor L in the Drake Equation and the very real possibility that SETI may not have heard anyone because L is low due to species wiping themselves out in atomic conflict.

    So a good study of what it would take to detect such a civilization (presumably less intelligent than we have been -so far-) would be in the spirit of Carl Sagan. What would the signal be from a global nuclear conflict both as it happened and 100s or thousands of years later? How long would a “nuclear winter” exist and be detectable? What other potential long term (ie: billion year or more) effects would be detectable from a nuclear conflict?

    All good questions in my mind.

    Discovering such extant civilizations could very well serve to increase the L factor of our own civilization by providing a cautionary tale of ones who didn’t make it.

    The investigation into how to detect such civilizations might also bear fruit in providing technologies or yielding techniques for discovering existing, living civilizations who have been previously undetectable.

    Your thoughts?

  • Mephane January 24, 2012, 4:01

    I am in with the lot who considers the entire Kardashev scale to be not much more than an interesting thought-experiment. Just like a Dyson Sphere is physically just not feasible (though a Dyson Swarm might be), I would not expect to find any civilization to consume and/or manipulate the energy output of an entire galaxy.

    I see this as a misconception which resulted from projecting our own development, or hopes for it – i.e. constant or accelerating economic growth – into a distant, hypothetical future. I would find it much more likely that at some point, in order to create any long-term sustainable civilization – which would be required for a culture to live long enough to reach other stars or galaxies – there would likely have to be a point in their development where economic growth ceases to have any importance, and instead scientific growth, i.e. gaining more and more knowledge, is the prime imperative.

    Thus I don’t even think that never-ending expansion to other stars or galaxies would be a common long-term goal among star-faring civilizations. Sure, they’d spread out, but I would be very surprise if we were ever to find any culture spanning an entire galaxy. Much more likely, they might occupy a tight packet of space around their home star, and the further out the more sprinkled their colonization efforts become, with minor outposts, lone settled (maybe terraformed) planets here and there.

    The incentives to expand into space are clear – the dangers of remaining constricted to a single star system, or even a single planetary body – are too high in the long run, but after reaching a certain point spreading out further might not be necessary, maybe not even desirable at all.

  • Anthony Mugan January 24, 2012, 5:32

    Widening out the range of criteria being considered with regards to SETI / SETA / SETV is a wise development. The incommensurability problem highlights the extreme difficulty of extrapolating from human psychology to predict the motivations of entirely alien species, should any actually exist (which I suspect is highly probable although by no means absolutely certain).
    Added to that is the challenge of attempting to imagine just what sort of technology might be available to a civilisation millions or possibly even billions of years older than ourselves. We certainly haven’t reached an end in our quest for a fundamental understanding of physics so the imponderables become considerable. The earlier point by Ron S makes the point well that we tend to extrapolate our current technology in our assumptions around this, which is understandable but will probably not turn out to be right.

    We do need to make progress from where we are at and with the tools at our disposal, as others have commented above already. What is particularly encouraging is that this process of thinking more widely about what might be available evidence is likley to continue as our own understanding of physics and astrobiology develops. I very tentatively (and this is most definately not a thought out concept, just a thought that occurred as I read the main article and the posts above) wonder about a sort of anthropic argument. If there isn’t any current evidence of the type of large scale engineering such as Dyson spheres etc. (accepting we haven’t looked very hard yet) and we assume for the moment that advanced ETI actually are present, for the sake of a thought experiment, does that tell us anything about the type of technology they may be using for energy production (or any other aspect of technology for that matter)…? Some of the immature theories discussed in Marc Millis’ recent book on possible propulsion systems come to mind but that is only intended as a tentative possible example….

    This approach leads to potentially testable predictions along the lines of (purely as an example):
    If advanced ETI exist and are capable of interstellar travel and are using technology along the lines of (e.g. vacuum or metric engineering or insert whatever technology is being considered) then we would predict observations of (space time distortions with certain characteristics or insert whatever prediction) etc etc.

    Highly unlikely that any one specific test would come out positive for the reasons discussed above, but sooner or later we may get lucky, or run out of ideas to test, in which case my assessment on the probability of ETI would need to change pretty radically!

  • spaceman January 24, 2012, 5:32

    Super-civilizations capable of undertaking vast astro-engineering projects, such as Dyson spheres are exciting to contemplate and worth looking for, but what about the origin of life in other places in the cosmos–since if the origin of life is a one-time affair, then we are it and super-civilizations do not exist. For so long I took for granted the notion that life should be widespread in the Universe, though after having finished Paul Davies’s “The Eerie Silence” I can’t help but wonder if there is no other life–not even microbes–outside of our solar system. Without an origin of life elsewhere, then the search for signatures of super-civilizations will obviously fail.

    The steps that led to the emergence of life are obviously physically possible otherwise we would not exist. However, perhaps it took a series of extremely unlikely independent events to bring about the primitive entities who took on the characteristics of what it means to be a living organism. If the origin of life is easy, then why has it not happened multiple times on our own planet?

    Just like the origin of life may not have occured more than once on Earth, maybe the unlikely steps did not occur any other place in the Universe. As dismal as this prospect may be, it goes a long way toward explaining the Fermi paradox: we have found no evidence of intelligent life because there is only one example of life period in the Universe and it’s on our planet. This is why I will be on the edge of my seat if and when the first telescopes are launched to find signs of life in exoplanet atmospheres.

  • A. A. Jackson January 24, 2012, 8:50

    Someone, I can’t remember who rephrased Clarke’s third law as:

    Any sufficiently advanced technology is indistinguishable.

    I think the Kardashev scale goes Type VI now, if one includes multiverses.

    I love Dyson and Kardashev’s quantification of H.G. Well’s BIG THINKS.

    But this is just physics and engineering physics.
    It tells me nothing about the character of a civilization with that kind of command of an instrumentality of that order.
    Even human, post human, post biological ‘civilization’… has a horizon of predictability that cannot be formulated.
    No one has a nonlinear equation of the social-economic-political characterization of future human cultural evolution.
    I want to see the Lyapunov exponent for the phase space of human cultural evolution. Sure I know the number of civilizations is probably large enough and the time dead sure is, that phase space is huge.
    Predictability of what an advanced ancient civilization will do , is of now, indeterminate.

    Reference:
    Dick, S. Jj. 1996, The Biological Universe:
    The Twentieth Century Extraterrestrial Life Debate and the Limits of Science, Cambridge Universe Press

  • Eniac January 24, 2012, 9:48

    The real problem is the cost each additional transmitting probe places on those probes that are already transmitting, such that the marginal befit of further exploration falls so rapidly as to reduce interest in continuing the process.

    This sounds almost like you are supposing that exploration of a self-replicating swarm of probes will be limited by the bandwidth of the network used to transmit the data back? Given self-replicating probes to begin with, what keeps us from making arbitrarily large swarms of them around any star between here and the expanding frontier, to increase network bandwidth to whatever is needed to transmit all the data? And that data flow, for sure, will increase rather than “fall rapidly”, at least until half of the galaxy is explored. At worst, there will be a limit to the bandwidth between nearby stars and Earth, which would level out as a constant data rate, but certainly not “falling rapidly”. As for cost, I do not see how that factors in given self-replicating probes.

  • Doug M. January 24, 2012, 11:01

    I’m a little surprised that nobody has yet mentioned that we’ve already been looking for Dyson spheres in our stellar neighborhood. For, oh, a decade or so now.

    It’s the Fermilab Dyson Sphere Search Program, and it’s been running on and off for years. Shoestring budget, grabs time on scopes when it can, but they’re totally serious about it. They got a slab of time on IRAS a while back, and used it to do a search of nearby stars — see “IRAS-based whole-sky upper limit on Dyson Spheres” (2008) by Richard Carrigan, http://stacks.iop.org/0004-637X/698/2075.

    Summary: they’ve looked at a bunch of stars within 50 ly of us, searching for signatures that would match hypothetical Dyson spheres with internal temperatures between 80 and several hundred K. (So, if there was a Dyson sphere built by methane breathers, or one at 200 C, they’d still have found it.)

    Results, entirely negative — they didn’t find anything. There don’t seem to be any Dyson spheres within 50 ly of us.

    Richard Carrigan is the go-to guy on this. He has a website with links to all the search work so far. It updates maybe once every year or two — this isn’t something that is moving forward with blinding speed — but if you’re interested, go check it out.

    Doug M.

  • Bob January 24, 2012, 14:22

    “And indeed, James Annis has made such a study, concluding that neither our Milky Way nor M31 or M33, our two large, neighboring galaxies, has been transformed by the work of a Type III civilization.”

    I would like to turn the concept of the Dyson Sphere inside out. Suppose we actually do live in a galaxy where a Type III (or nearly so) civilization exists.
    If they were wise and benevolent, they might isolate and protect infant civilizations such as ours. They could built a large Dyson Sphere to create the near perfect illusion of the galaxy before their mega-conversion. Think of the scenario of the movie ‘The Truman Show’.

    So, assuming this as at least a possibility, how does that change the argument? How could we tell if we were living inside a massive isolation and near perfect simulation sphere? If we were, then that discovery might be the test to be welcomed into the greater galactic civilization. Any thoughts?

  • Nick January 24, 2012, 14:22

    @The Void: those are all very interesting speculations. And spectroscopy will indeed be the main useful tool as I have proposed. There may be a near-infinity of such possible technologies that we can imagine, almost all of them with a correspondingly small probability of occurring. So I suggest we invoke Occam and Popper and stick to hypothesizing about what we will actually be able to see: namely emissions and reflections from engineered surfaces and the outputs of various illumination and energy processes. For example, lasers have been proposed for various purposes (esp. transportation and communications). We don’t have to come anywhere close to being able to listen in on a laser conversation to be able to tell that it is a laser (an incredibly artificial-looking spike on the spectrum) rather than a natural phenomenon. If the denizens of a distant galaxy make ample use of lasers, LEDs, or even more efficient quantum radiation devices for any purpose (i.e. if it’s even a very small but significant fraction of the total luminosity of the galaxy), we have the means to easily discover this. The testable hypothesis need only be, that a certain small fraction of the luminosity of a galaxy does or does not take the form of spectrum spikes that are not produced by any natural phenomenon. The exact nature of the devices or surfaces, beyond what we can infer from the spectral signatures, should, per Occam and Popper, not overly concern us.

    In fact we have petabytes of spectroscopic data on other galaxies and I don’t doubt that many astronomers, inspired to their profession by alien-filled SF, have been quietly looking over this data for signs of artificiality for many decades now. Of course, this process might benefit greatly from being brought more into the open.

    There is a major problem in thinking about this in terms of archaeology: the carefully engineered surfaces of nearly all unmaintained artifacts will soon decay into more natural-looking states due to radiation, micrometeors, etc. We will have a far greater likelihood of finding signatures of artificiality from freshly maintained surfaces and live working radiation devices.

    @spaceman, that scenario is certainly possible, although it’s the last thing that astrobiologists, who depend for their funding on the supposed probability of life right next door, will want to admit.

  • Nick January 24, 2012, 14:34

    The Kardashev system does seem to leave people with the wrong impression, that there must be some monolithic galactic-wide civilization for its denizens to collectively gather and use most of the stellar energies in their galaxy. This is wrong. For most of the visible surfaces of a galaxy to have been engineered:

    * There is no need for the inhabitants of the different star systems to be of the same culture, or to trade, or even to communicate (although I suspect they’d do some of the latter).

    * There need be no civilization-wide starship program. There is only the need for a desire among a very small subset of the population of a given star system, with very long time preferences, to move their homes to the next star system over. Starships will be very cheap (see my analysis above), it is only the needed patience that may be scarce.

    As Malthus (inspiring Darwin) once observed, the tendency for life to expand to its limits is well-nigh universal:

    “Throughout the animal and vegetable kingdoms Nature has scattered the seeds of life abroad with the most profuse and liberal hand but has been comparatively sparing in the room and the nourishment necessary to rear them. The germs of existence contained in this earth if they could freely develop themselves would fill millions of worlds in the course of a few thousand years…… Wherever therefore there is liberty the power of increase is exerted…”

    To argue that the _opposite_ of this Malthusian/Darwinian imperative operates _everywhere_ in the universe strikes me as extremely absurd. The technological details are a matter of speculation, but if this imperative universal to life on earth operates in any advanced civilization in any of the tens of billions of galaxies on which we can take detailed spectra, we will soon find out.

  • Paul Gilster January 24, 2012, 14:42

    Doug M writes:

    I’m a little surprised that nobody has yet mentioned that we’ve already been looking for Dyson spheres in our stellar neighborhood. For, oh, a decade or so now.

    For those wanting more information on Richard Carrigan’s work on Dyson spheres, here are two write-ups, or search ‘Carrigan’ in the archives:

    https://www.centauri-dreams.org/?p=12153

    and this:

    https://www.centauri-dreams.org/?p=11237

  • ljk January 24, 2012, 15:08

    Doug M. said on January 24, 2012 at 11:01:

    “It’s the Fermilab Dyson Sphere Search Program, and it’s been running on and off for years. Shoestring budget, grabs time on scopes when it can, but they’re totally serious about it. They got a slab of time on IRAS a while back, and used it to do a search of nearby stars — see “IRAS-based whole-sky upper limit on Dyson Spheres” (2008) by Richard Carrigan, http://stacks.iop.org/0004-637X/698/2075.”

    That is the other problem with current SETI: It has to get most of its time on professional instruments like a dog waiting for its master to drop some crumbs from the dinner table.

    Discovering whether or not other intelligences exist in the Universe and seeing what we can learn from and about them is one of the most important endeavors that the human species should be conducting. But even when we finally have a dedicated SETI system like the ATA, it is now hanging on month to month on the support of handouts.

    Definitely says something about humanity. And SETI has been treated like this by scientists and public officials alike, since its earliest days, so the blame cannot be laid simply on the current economic situation.

  • Bill B. January 24, 2012, 15:52

    @Bob,
    Your comment about a reverse Dyson sphere errected by a benevolant type III civilization to shield us, contain us, or study us, gets me thinking along the lines of ‘Ancestor simulation’, some ideas I have read by Nick Bostrom. Assuming any civilization has a chance of reaching a type II civilization or a singularity it would be far more likely to exist in one of an infinite number of ancestor simulation civilizations than to exist in the real original beginings of that civilization. When looking at the Fermi Paradox, what would be more interesting for any advanced civilization to simulate in their computers than the idea of the very first galactic civilization or the first civilization in the whole universe? Such a simulation would be a popular study and could happen endless times by endless civilizations, but could only happen rarely (galactic first) or once (universal first) in the ‘real’ universe.

  • Chris T January 24, 2012, 17:45

    ljk – Who made you arbiter of what should be most important to humanity?

    Topic – I am glad to see some movement away from listening to the radio spectrum. The odds of the method succeeding were incredibly low to start with.

  • Alex Tolley January 24, 2012, 17:48

    @Bob
    They could built a large Dyson Sphere to create the near perfect illusion of the galaxy before their mega-conversion. Think of the scenario of the movie ‘The Truman Show’.

    I think that an answer was provided by Stephen Baxter [IIRC]. The processing power to main the simulation to account for different observations of our probes and technology eventually overwhelms the simulation. In the story, this breakdown exposes the real universe, not the simulated empty one.

  • Rob Henry January 24, 2012, 18:24

    Eniac asks “As for cost, I do not see how that factors in given self-replicating probes.” And I would agree that the cost of production is close to zero, but there is a cost in sending them out earlier than you can receive the information. This includes flagging your existence to other ETI’s before it is possible to communicate with them, and being overloaded with information that is tens of millions of years out of date.

    However your point that this excess information could be stored (and processed) in a diffuse interstellar network, then (presumably) accessed when necessary looks devastating to the cause. Remember that the cause is that almost every ETI who ever used this system would be similarly retarded.

    To try to recover a presupposition that allow radio SETI to be a worthwhile cause perhaps we could postulate that until recently our galaxy was hostile to the development of higher life. Or perhaps some facet of physics that is more advanced than our own might do the trick.

    Imagine that faster than light communication is possible, but to preserve causality only one such net per ETI civilisation is possible. In such a case it is much easier to imagine neutral zones between these galactic empires in which humanity must currently reside. These could be due to them being communicatively isolated or having incomprehensible and varying law and legal status, or they could be left because all acknowledge that it is just too tempting for new colonists to join their home network and cause massive disruption to an alien one. Between these empires radio communication would make sense.

    All that may sound unusual, still, the strangest thing of all is that radio SETI seems to have been well establishes already, so let’s see if we can find a reason that would give logic to their approach.

  • A. A. Jackson January 24, 2012, 19:36

    @Nick
    “To argue that the _opposite_ of this Malthusian/Darwinian imperative operates _everywhere_ in the universe strikes me as extremely absurd. The technological details are a matter of speculation, but if this imperative universal to life on earth operates in any advanced civilization in any of the tens of billions of galaxies on which we can take detailed spectra, we will soon find out.”
    Can you cite an authoritative quantitative analysis that a Malthusian ‘imperative’ is the predictable outcome of us as a complex technological civilization? (I think we leave Darwin out this , that theory is much more sophisticated than Malthus.)
    For centuries one could use history as a gauge of the future. That no longer holds true. If the future of our technological future does not hold a dead end for us then by the very nature of how it differs from the past makes it unpredictable.

  • Eniac January 25, 2012, 0:57

    @Mephane:

    Thus I don’t even think that never-ending expansion to other stars or galaxies would be a common long-term goal among star-faring civilizations. Sure, they’d spread out, but I would be very surprise if we were ever to find any culture spanning an entire galaxy. Much more likely, they might occupy a tight packet of space around their home star, and the further out the more sprinkled their colonization efforts become, with minor outposts, lone settled (maybe terraformed) planets here and there.

    Do you really believe those “minor outposts” you speak of will remain that forever? Will they not grow into full-scale civilizations of their own, with the ability and eventual desire to colonize unoccupied neighboring systems?

    You are right that it is extremely unlikely there will be any common long-term goal among civilizations, or a culture spanning the entire galaxy. I believe you are wrong in implying that this will be a barrier to expansion. The lack of long-term planning, coordination, culture, or intelligence has never prevented bacteria from filling a Petri dish, or trees from filling the Earth. It will not prevent us from filling the galaxy. Perhaps something else will, but at least for me, it is very hard to come up with a plausible scenario for that.

  • Nick January 25, 2012, 4:16

    A. A. Jackson, if your are arguing that the laws of Malthus and Darwin no longer apply — or even worse that they no longer apply anywhere in the universe to any advanced species — the burden if proof is clearly on you, not me, to demonstrate why advanced civilization would everywhere and always take such a U-turn from the previous 4 billion year history of life.

  • Mephane January 25, 2012, 4:16

    If the origin of life is easy, then why has it not happened multiple times on our own planet?

    As far as I know, there is the idea that this indeed happened, and just one form eventually outperformed all of the others and went to extinguish them, just like naturally selection has entire species going extinct, it could just as well have entirely different forms of life go extinct, too. If this would happen in the earliest stages, it might be impossible to find any traces of it on our planet – though maybe one day it might be possible to observe it on some young exoplanet, who knows.

    Obviously, this is just an idea, as without any way to falsify it, cannot be made into a serious theory. But the bottom line is – the existence of just one basic type of life and DNA etc. on Earth is not sufficient proof that there cannot be other types, but only that what we have here is most likely the one best adapted to this planet.

  • Anthony Mugan January 25, 2012, 6:02

    @ AA Jackson and Nick

    re the discussion on Malthus
    The idea that populations would tend to expand whilst resources to do so exist, which is the essence of Malthus’ idea (he didn’t factor in changes in competitiveness from changes to the species itself, competitors or the environement) was pretty standard bio-geography when I was at university 25 years ago. This has never been an area I have stayed close to, so don’t intend to spend time digging out specific references but one has only to look at what has happened to human populations (or any animal population where predation get reduced for whatever reason) to see the basic point is clear.

    As in any model Malthus is a simplification – he was concerned that humans would hit the limits of food production fairly quickly from when he was writing in the 18th Century. Changes to the wider environment (i.e. technology in this case) have impacted on that. In essence a lot of what we see in biological systems as random events derive from at one level fundamental biochemistry, and therefore from physics, interacting with the wider environment in ways that can be modelled mathmatically. Whilst there is a strong stochastic element in eactly which mutations, environemtal events etc etc happen and at what times, the overall system shows some fairly consistent patterns of behaviour as people like Malthus, Darwin and many other (including complexity theorists more recently) have shown.

    Assuming life elsewhere actually exists and is DNA based and in environments not totally disimilar to earth many of these emergent features of biospheres should recurr (obviously a number of ‘ifs’ in that statement!) – not an exact replication of course, but the tendancy for a species that isn’t suffering significant predation and has technology at its disposal to increase in number might be predicted to be very common. In the more developed world, however other factors (economic cost of children and the opportunity and education to take advantage of relevant technology) have led to a levelling out of population growth in these countries. This may eventually occurr world wide and so may therefore be a factor which limits the wider application of a purely Mathusian approach for advanced civilisations.

  • Securis January 25, 2012, 9:30

    I really like the idea that the Red Square Nebula is a sign of a Kardashev Type II civilization building a Dyson sphere:

    http://www.projectrho.com/rocket/weirdastronomy.php#id–Red_Square_Nebula

    And just another thought: If ETI managed interstellar travel is there any possibility we could detect their (supposedly) hot exhaust?

  • ljk January 25, 2012, 11:48

    Do not forget NGC 5907. The astronomers say this sprial galaxy has an unusually high amount of red dwarf stars, or at least that is how they are explaining the large number of dim objects detected there.

    We true SETI fans know what is really going on: Artilects or their equivalents are converting NGC 5907 into a collection of Dyson Shells/Jupiter Brains. As usual, the idea of an entire stellar island of billions of suns being turned into an energy source for massive and highly advanced machines is always frightening to the tiny organic creatures that still think digital watches are really neat things.

    See here:

    http://atomicrockets.posterous.com/dyson-shells-a-retrospective

    Relevant quotes from the above article:

    “Dyson Shells are implausible or impractical only if you envision them as true spheres or primitive human habitats. And some science fiction writers, by stretching their imagination to include engineering methods such as force transfer using high speed circulating fluid streams, have described plausible Dyson Spheres [25]!”

    and:

    “Unexplained or incompletely studied astrophysical phenomena such as odd star populations of the galaxy NGC 5907[42] or the asymmetry of increases and decreases in the brightness of long-period variable stars[43] provide us with a number of locations that may be studied for signs of Dyson Shells.

    “If we free ourselves from anthropocentric perspectives and combine the ideas of Dyson, Minsky and Suffern as well as the technological progress of recent decades, we can envision advanced civilizations at the limits of physical laws. Observations directed towards stars decreasing in visual magnitude or searching for stellar occultations by large cold dark objects, merit serious consideration as future strategies in optical SETI.”

  • Rob Henry January 25, 2012, 17:23

    I’ve notice that about half of all commenters here seem to hold 3 implicit assumptions.

    1) All ETI’s have very similar characteristics to each other but not necessarily to us.
    2) All ETI civilisations lack internal variation derived by the individualistic thinking that is characteristic of our society
    3) All ETI civilisations hold their current outlook for billions of years.

    When the rest of us here statements such as, ETI’s might be more interested in philosophical matters rather than startravel*, it sound like gobbledegook, but at least by my revealing of their hitherto hidden assumptions we can, for the first time, begin to see where they are coming from.

    *I gave a statement not yet expressed here because I don’t want this to refer to any one commenter

  • Eric January 26, 2012, 2:32

    @A. A. Jackson

    The tendency to replicate and spread seems pretty straightforward if you imagine a population with diversity / variability in its behaviors, and if there is some degree of fidelity in the inheritance of those behaviors.

    Let’s say 99% of a population like home, 1% is interested in colonizing. A small fraction of that 1% actually succeeds in colonizing. The successful colonists will learn to be better at colonizing, and will have behaviors / motivations that favor colonization, being a self-selected group. That group at the new colony will then have a population mix that is say 80% stay-at-homers, 20% colonizing (for example).

    Now iterate a few million times, and pretty soon, you get a population that is almost all nomadic at frontier regions, and will remain so (expanding) so long as new open territories exist and colonization can proceed successfully. Behaviors will change behind the wave of colonization as the frontier fills up and closes, and colonizing behaviors in settled regions will become less common in populations. [Note, the specifics about why colonization does or does not happen do not matter, the only thing we’re modeling here are tendency to spread, versus tendency not to spread.]

    The problem about thinking about aliens is that we tend to forget variability in behavior and how such variability shakes out over long time scales. Dyson swarms or no, I think the Fermi Paradox is pretty profound.

  • ljk January 26, 2012, 10:22

    Some good points there, Rob Henry. This is similar to what we often see in Star Trek, where humanity can have all sorts of cultural and racial variety, but most of the aliens they meet are neatly divided into just a few groups, if at all.

    If we assume that very advanced ETI could and would build large space-based telescopes (Robert Bradbury said they could be as large as our Moon – I think we should at least stopped being shocked by such ideas), they could observe most of the galaxy without ever having or wanting to leave home, being able to see Earth in detail. This would also essentially solve the issue of interstellar travel and having to interact with other intelligences.

    http://abcnews.go.com/Technology/story?id=98221&page=1

    Dipping into the Star Trek well, there was an episode from The Next Generation series where an advanced species explored the galaxy by sending out probes that would bring samples of other intelligences to them! One assumes they are capable of dealing with any problems that might arise if they grabbed a species that wasn’t very happy with the situation – and there are a lot of nasty beings in the ST universe.

    http://en.memory-alpha.org/wiki/The_Nth_Degree

  • Eniac January 26, 2012, 13:21

    @LJK:

    If we assume that very advanced ETI could and would build large space-based telescopes (Robert Bradbury said they could be as large as our Moon – I think we should at least stopped being shocked by such ideas), they could observe most of the galaxy without ever having or wanting to leave home, being able to see Earth in detail. This would also essentially solve the issue of interstellar travel and having to interact with other intelligences.

    Are you serious? You must understand that, no matter how large the telescope, there is always a next step to want to do. Dig into the dirt, dive into the ocean, or put a specimen under a microscope, any number of things. In fact, if anything, I would submit that the motivation to send a probe (or go) increases with the size of telescopes. Would you go as far as saying Kepler is detrimental to our ambitions for an interstellar probe?

  • Nick January 26, 2012, 15:42

    Eric, that’s a really great point. Not only would the the principles Malthus and Darwin observed that have held for 4 billion years of the history of life tend to continue to hold in at least a significant fraction of advanced civilizations, but a Darwinian selection effect as you describe will continue to act on the genes and culture (or whatever information succeeds in in advanced civilization to what we call genes and culture in ours) , meaning only a small fraction of the original home world inhabitants need to be adventurous to result in a galaxy full of adventurous beings.

    And that only needs to happen on a small fraction of home worlds to result in many blatantly artificial galaxies out of the 100 billion we can see in our sky, if such home worlds occur at rates anything close to one per galaxy or higher.

  • Nick January 26, 2012, 16:20

    Eniac, as you well observe, telescopic observation hardly satisfies all scientific motivations. Not to mention that science is only one out of a million possible motivations for traveling beyond the home planet.

    Not only are these hypothetical concoctions of the traditional SETI imagination, like other fantasy races, shy and clever at hiding, they are also so preposterously one-dimensional in their motivations that they could never even reach the pages of fiction. And these characteristics are supposed to apply to practically all of the tens of trillions of races supposedly in our galactic neighborhood!

  • ljk January 26, 2012, 17:16

    Eniac said on January 26, 2012 at 13:21:

    “Are you serious? You must understand that, no matter how large the telescope, there is always a next step to want to do. Dig into the dirt, dive into the ocean, or put a specimen under a microscope, any number of things. In fact, if anything, I would submit that the motivation to send a probe (or go) increases with the size of telescopes. Would you go as far as saying Kepler is detrimental to our ambitions for an interstellar probe?”

    LJK replies:

    I am not saying or trying to stop an advanced ETI from sending out interstellar probes just because they have superscopes to examine the galaxy with. I was just giving some plausible reasons why we have not yet come across any alien probes, though how hard would it be for a sophisticated species to hide their technology from us? Sprinkle nanotech or femtotech all over Earth and would any human have a clue it is there? Or just hide in the Planetoid Belt or over the lunar farside.

    I would never say anything detrimental about Kepler. It has done and is doing a great and much-needed task. Kepler’s only faults are its limited sky survey and the fact that it cannot examine the exoworlds it finds in the kind of detail that some of our more sophisticated (and currently shelved) space telescope plans could do, to say nothing of what a much more advanced technological intelligence might build.

  • ljk January 27, 2012, 10:42

    New mathematical study reveals that our Galaxy should have been colonized by now

    Sentient Developments – George Dvorsky – January 21, 2012

    A recent article in the Economist alerted me to a recent paper by Thomas Hair and Andrew Hedman that profoundly reaffirms the conundrum that is the Fermi Paradox, an observational problem that is sometimes referred to as the Great Silence.

    What’s fascinating about the Hair and Hedman paper is that they are not cosmologists or astrobiologists, but rather mathematicians—and it is through the lens of number-cruching that they sought an answer to the question of how long it would take a civilization to colonize its local region given a specific set of parameters. And their findings are disturbing: No matter how they reworked the numbers, they came to the same conclusion: the Galaxy should be colonized by now.

    Full article here:

    http://www.sentientdevelopments.com/2012/01/new-mathematical-study-reveals-that-our.html

  • Nick January 27, 2012, 14:48

    “profoundly reaffirms the conundrum that is the Fermi Paradox”

    Mathematicians call it proof by contradiction. Logicians and philosophers call it the argument _ad absurdum_, as Eniac described in another thread. There is no “paradox” or “conundrum”.

  • Eniac January 30, 2012, 1:04

    @LJK, from that article:

    So, the next time somebody smugly shrugs off the Fermi Pardox by suggesting that “it takes too long to colonize the Galaxy” or that “there hasn’t been enough time,” or that “the Galaxy is too big,” tell them to shut-up and read this paper.

    Yeah, finally: Reason!

  • Daniel Alman February 16, 2012, 14:17

    Would our astronomers and scientists be able to distinguish a type 3 civilization from a type 2 or visca versa. How would be able to know that a type 3 civilization isnt really multiple type 2 civilizations.

  • ljk February 25, 2012, 17:37

    Ignoring 500 Billion Galaxies: Mathematics vs Common Sense in the Debate About the Probability of Extraterrestrial Life

    Daily Galaxy, February 23, 2012

    Carl Sagan said that “extraordinary claims, require extraordinary evidence.” In a stunning display of mathematical logic vs common sense, David Spiegel of Princeton University and Edwin Turner from the University of Tokyo published a paper last summer that turns the Drake equation upside down using Bayesian reasoning to show that just because we evolved on Earth, doesn’t mean that the same occurrence would necessarily happen elsewhere; “using evidence of our own existence doesn’t show anything” they argue, “other than that we are here.”

    What Bayesian reasoning overlooks, of course, is the inconvenient fact that there are some one trillion galaxies in the known universe and some 50 billion planets estimated to exist in the Milky Way alone and some 500,000,000 predicted to exist in a habitable zone.

    Spiegel and Turner point out that basing our expectations of life existing on other planets, for no better reason that it exists here, is really only proof that were are more than capable of deceiving ourselves into thinking that things are much more likely than they really are.

    Full article here:

    http://www.dailygalaxy.com/my_weblog/2012/02/comment-of-the-day-ignoring-500-billion-galaxies-mathematics-vs-common-sense-in-the-debate-about-the.html

  • ljk February 29, 2012, 11:27

    Check out this bit of artwork depicting how far our radio signals have gotten into the galaxy:

    http://www.planetary.org/blog/article/00003390/

    The answer is not very far at all on a cosmic scale. And most of those radio signals would be too weak to pick up anyway, plus they will eventually fade into the natural cosmic radio background.