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Musings on a Living Cosmos

George Dvorsky’s ongoing series on the Fermi Paradox, which appears on his Sentient Developments site, is drawn from a recent conference presentation about the implications of Fermi’s question. ‘Where are they?’ indeed, and what factors could explain our inability to find other sentient life forms? Two parts have already run, and I commend them to you. Dvorsky presents a thorough backgrounder on why the ‘great silence’ is puzzling, and goes on to discuss the things we can be sure that advanced extraterrestrial intelligences do not do. This by way of examining assumptions that may flag wrong directions in our thinking.

The first of these statements is interesting: “Advanced civilizations do not advertise their presence to the local community or engage in active efforts to contact.” At least, we might say, in any ways that we’ve so far been able to determine, and it should be fairly straightforward for an alien species that does want to make itself known to us to manage the feat. Dvorsky discusses this in terms of so-called ‘Bracewell probes.’

Think of the Arthur C. Clarke 2001 scenario, ‘sentinel’ probes waiting for an intelligent species to arise and then communicating with it. Such a probe, if in our own Solar System, should have been activated by now, given the amount of electromagnetic noise we’ve been making for the past century. But as Dvorsky says: “We know that no such object exists in our solar system or within a radius of about 25 to 50 light years.”

Nonetheless, the idea that a listening probe should be programmed to activate a communications channel relies on human assumptions. I’m reminded of Freeman Dyson’s statement: “It is unscientific to impute to remote intelligences wisdom and serenity, just as it is to impute to them irrational and murderous impulses. We must be prepared for either possibility.” In other words, watch what you bring to the discussion that is based on things we take for granted. Having no experience whatsoever with alien intelligences, we can’t know whether they would want to meet any cultures they observed or simply catalog and study them. A communicating Bracewell probe is only one of many possibilities.

Gregory Matloff and Anthony R. Martin have written interestingly about the possibility of artificial objects being found in the Kuiper Belt (see the earlier Centauri Dreams story An Infrared Hunt for Artificial Kuiper Belt Objects). Such an infrared search might reveal hypothetical ‘sentinel’ probes that chose to remain silent. So while we can indeed say, with George Dvorsky, that we see no active attempts to contact us, there may well be reasons for such a silence — I suspect this is exactly where Dvorsky is headed with the next installment of his Fermi series.

Another statement also catches the eye: “Advanced civilizations do not engage in any kind of megascale engineering or stellar re-engineering that is immediately obvious to us within our light cone.” Here the key words are ‘immediately obvious’ (Dvorsky knows exactly what he is doing here; he argues with the skill of a trained jurist). The question posed is whether we would be able to recognize the engineering of civilizations a billion years older than our own in the first place. Dvorsky again: “We see no clusters of perfectly aligned stars, nor do we signs of Kardashev III civilizations utilizing the energy output of the entire Milky Way.”

Andromeda galaxy

True, but is this what we would expect to see? Perhaps not. Dvorsky accepts Charles Lineweaver’s work on planet formation in the early Milky Way, including the notion that Earth-like planets first formed up to nine billion years ago. With this as assumption, the average terrestrial planet in the galaxy is 1.6 billion years older than the Earth, and Dvorsky notes that three-quarters of Earth-like planets in the galactic habitable zone should be older than Earth. Would a civilization billions of years older than our own be capable of engineering that we might not even recognize as such?

Image: M31, the Andromeda galaxy. Is it possible that the engineering of cultures billions of years older than our own might not be apparent to us? Copyright and Credit: Robert Gendler (robgendlerastropixs.com).

It is not illogical to assume the answer is yes. Some years back, I was doing an interview with Michio Kaku and made a confident statement that we ‘knew that no Kardashev type III civilizations existed in the intergalactic neighborhood,’ to which Kaku responded with disbelief. Why should I think I knew what alien technologies would be like given the time frames we were talking about? His point was that we would be no more likely to recognize such engineering, based on our own assumptions, than an ant colony would be to understand that the superhighway running past nearby was an artifact and a sign of a superior intelligence.

In any case, read through Dvorsky’s list of the things advanced civilizations do not do. It’s stimulating stuff meant to rattle our preconceptions. Why sentient beings might choose other paths is the next topic on Sentient Developments. If I had to guess, I would say that intelligent life is incredibly rare, with perhaps no more than ten civilizations active at any given time in the Milky Way. That would also explain Fermi, I suppose, though not in ways I’m comfortable with. I think all of us hope for and would like to hear reasons to expect more.

Related: Marko Horvat (University of Zagreb) has calculated how likely we are to pick up alien civilizations based upon their lifetimes. Horvat’s figures make radio detections seem highly unlikely. One assumption is that the likelihood of continous beacons that broadcast to specific stars for decades or centuries at a time (much less millennia) is low. That makes detecting unintentional electromagnetic leakage more likely than picking up beacons aimed at us, but also far more difficult.

A key factor: Civilizations presumably move beyond radio and TV toward methods that are all but undetectible in terms of extraneous transmissions. Here, Horvats discusses this in terms of the number of civilizations (Nac) that can occupy the same volume of space at each moment in time:

The highest probability of contact is achieved in the scenarios with many alien civilizations that have comparably short life spans and long usage of radio communications. At the same time, our listening techniques have to be near perfect. The reasons behind this optimum probability are understandable; compared with their lifetime, civilizations always have relatively short radio-communication status. If there are a lot of them, in other words – if they die rather quickly and are replaced with new civilizations, then, at every point in time, there is a fair number of them that are using the radio. Long-lived civilizations pass their radio-communication status and still remain in Nac but are undetectable by radio. In some respect, they are occupying a place in Nac where some younger and radio active civilization might sit.

It is somewhat paradoxical that we should be opportunistic for short-lived alien civilizations, when at the same time, we want to learn more about them.

Table 2 in the appendix here makes for some interesting mulling. The paper is Horvat, “Calculating the probability of detecting radio signals from alien civilizations,” International Journal of Astrobiology 5 (2006), pp. 143-149 (abstract).

Comments on this entry are closed.

  • philw August 7, 2007, 12:36

    Given that the avg Earthlike workd is 1.5 gigayears older and we’re in the younger third of worlds, we should look at Fermi statements this way…

    No technical civilization that has EVER existed has populated the galaxy with Von Neuman probes that re-engineer visited solar systems

    No technical civilization that has ever existed has made interstellar engineering projects that we can discern from natural phenomenon.

    and so on.

    Point being that some of these FERMI exclusions must apply to each and every society that has ever existed, not just 99% in order for them to explain the great silence. If there are 10 or whatever # of technical civs extant in the Milky Way today, each and every one throughout their long history must have eschewed Von Neuman probes, cosmic engineering beyond their solar system and so on.

    I’m starting to give more thought to total exclusion explanations like the following. These all turn our common space cadet assumptions on their heads.

    1. Maybe life itself was a unique occurance. We have no conclusive evidence to disprove this. I’ll avoid repeating that sentence after each of the following.

    2. Maybe the evolutionary events leadg to an intelligence with a technophile twist is so improbable, no other galactic life form has evolved it.

    3. Maybe interstellar flight is so impractical and resource expensive that it’s impossible such that the other tech civs have never done it.

    3. Maybe Von Neuman automatons are not possible to build. Maybe AI can’t be done.

    I suspect that something in the Drake/Sagan view of the galactic population assumption chain is seriously wrong.

  • ljk August 7, 2007, 14:14

    While we have made progress of a sort in our views on alien life and
    SETI since its flowering days in the 1960s, we certainly haven’t had
    much progress in terms of optimism.

    For example, look at what this astronomer named Michael Rowan-Robinson
    has to say regarding extraterrestrial life:


    Now you might think that a fellow who had a true understanding of
    how vast and numerous things are in the Cosmos would not put down
    the idea of ETI simply because it hasn’t bothered to say Hello to us
    yet; but no, he gives this as one of the big reasons why he thinks
    there is no intelligent life beyond Earth. Surprising and disappointing.

    It seems like a growing trend to me at least. I have noticed a lot of
    forums and even published books that, while advocating a brighter
    future for humanity via nanotechnology et al, assuming few to none
    when it comes to ETI. Obviously arguing that we live in a galaxy
    with 400 billion stars 100,000 light years across is not making an
    impression even on those who are educated on the subject.

    My view on this: It is a combination of fears…

    Fear that one’s colleagues will not take you seriously (and deny grants) if you
    profess belief in little green men, despite decades of progress in astrobiology.

    Fear that you will be lumped in with the UFO crowd (okay, that’s a legit one).

    Fear that there are more powerful and knowledgable beings in the Cosmos,
    beings that if they don’t attack Earth might still bring us down just by being so
    darn superior. After all, we have been God’s Chosen Ones for ages; it’s tough
    to give up a gig like that to a bunch of strange strangers.

    Fear that one is not being scientifically rigorous enough. After all, it is true
    that we have no solid evidence of alien life of any kind, despite knowing about
    hundreds of exoworlds, extremophile life, complex molecules in the Universe, etc.

    Plus there’s that old Fermi Paradox that keeps getting trotted out every time
    this subject comes up. How come THEY haven’t visited US? Aren’t we the
    most visible and important things in all existence?! Ya think just a few other
    cultures out there have/had the same thoughts on that topic?

    To me it is not very scientific at all that we have done so little searching for
    ETI in so few places and declare them non-existant. Sorry that the human
    race has such a short attention span and life, but combing 400 billion stars
    with our currently technology is going to take a while – and it is entirely
    possible that the really advanced ones don’t live anywhere near the
    visible star systems.

    So I say we must ignore the doubters and the fringe nuts and keep searching.

    Remember it was the guys who said humans would never fly who only
    talked while the Wright Brothers went out and built their airplanes.

  • Quasar9 August 7, 2007, 14:57

    One thing I find hard NOT to impute on any ‘other’ advanced civilisations or lifeforms, is their destructive capacity.
    After all as nature has demonstrated on earth it is survival of the fittest, and that usually translates to the meanest and most dangerous or lethal.

    Of course thinking in human terms, it would be difficult NOT to impute to any other civilization, the will & desire to demonstrate their military and technical superiority – as evidenced on earth, through out human history.

    And hence the legitimate interest of the military in any developments in space, and the very earthly preponderance of thought of ‘defensive’ weaponry. Though really a battle in space is a little absurd – there would be no life jackets for survivors to any ship sunk, nor parachutes to abandon an aircraft heading for the ground.

    However it is worth noting that the advances needed for space travel will mean that we will first need to develop new forms of energy – and shields for the aircraft – and these very technologies will produce weaponry.

    But an advance civilization simply looking at ‘us’ for observational purposes, and being able to resist the temptation to overtake the world – just because they can so to speak – would be hard to swallow. Unless of course we are talking of small ships with few crew who have lost the ability to return.

    But let us be realistic, and let me reverse the question, if we could send a small ‘spy’ ship anywhere in space where there was life – and it could return with information of untold riches – and presuming that if we can build a small ship we can also build an intergalactic cruiser, or aircraft carrier or nuclear sub (money really is no object in the advanced economies of this day & age).

    Would the aliens be safe, or would be just hunt them down like prey or boil them like lobsters – and take their lands & resources. Or is it a pre-requisite for space travel to be an advanced civilisation & not to be predatory One.

  • Kurt9 August 7, 2007, 14:59

    The key flaw in thinking about the behavior of alien civilizations is the assumption that such a civilization is monolithic with group think. The argument that they do not communicate with us because we are too dumb or the zoo hypothesis assumes that every single individual within such a civilization would practice such behavior. There are stone-age tribes in the Amazon. Your average Joe six-pack has no interest in contacting them. Same for your typical Wall street banker and silicon valley entreprenuer. However, there ARE some individuals who go down there and observe and contact them.

    The same is true for singularity or transcendence arguments. Most people will go through the singularity, but many individuals will choose not to. This is also the flaw with arguments that they “learn to live within their limits” and do not seek to expand into intersteller space. SOME individuals would not share these goals and would seek to expand into intersteller space.

    The presumption of all of these arguments is that all of the individuals comprising such an advanced civilization would share the exact same attitudes and goals. Within our own civilization, you have all kinds of people with all kinds of differing personal goals and styles. The variation in personal attitudes, values, and choices seems to increase as our society develops. Is it not likely that as a civilization develops, that the variation and diversity of individual attitudes and choices will increase within an alien civilization as well?

    Is there any reason why this would not be the case?

  • Theo Stauffer August 7, 2007, 15:03

    Wonderful article, Paul! Again, as I have posted before, I agree wholeheartedly that the idea of a galaxy teaming with civilisation is in need of review. I think that perhaps civilisations may only remain in their evolved form for a short period once reaching the ability to modify life itself, and then “evolve” rapidly into biomechanical and then perhaps purely energetic life forms, which leave no physical traces.

    We would never see such a civilisation, as they would probably not be planet or biosphere bound.

    Of course, perhaps our moon is what makes the earth almost unique, in that it acts as a motor of life. Perhaps we should be looking for earthlike planets with large scale tidal interaction.

  • Theo Stauffer August 7, 2007, 15:09

    Sorry about the extra post: I would just like to add that I think we are being somewhat overeager to find alien civilisations. We have only had this capability to look for ETI for the briefest, tiniest amount of time, historically speaking. Radio almost a century, and good telescopes about three or four times that long. The galaxy is enormous and the distances are gigantic, and the energy requirements are astronomical, not too mention that what with cosmic radiation, the universe and space are not exactly welcoming to intelligent life as we know it.

    Maybe some patience?

  • Quasar9 August 7, 2007, 15:11

    “It is not illogical to assume the answer is yes. Some years back, I was doing an interview with Michio Kaku and made a confident statement that we ‘knew that no Kardashev type III civilizations existed in the intergalactic neighborhood,’ to which Kaku responded with disbelief. Why should I think I knew what alien technologies would be like given the time frames we were talking about? His point was that we would be no more likely to recognize such engineering, based on our own assumptions, than an ant colony would be to understand that the superhighway running past nearby was an artifact and a sign of a superior intelligence.” Amen.

    Great post, one needs to explore not just the Universe, but the Mind.
    Not just what we are capable of, but what we may be capable of …

    The ISS, the Space Shuttle, cheap Transatlantic flights, the Internet and mobile video phones would be as alien to a civilization on earth two thousands years ago – as the thought of interplanetary travel or even intergalactic travel might be to us today. Let us not forget that even at the speed of light there are few places (outside our solar system) we could visit for our annual holidays.

  • Athena August 7, 2007, 16:26

    Although these thought experiments are useful and need to be revisited every time new data come to light, they are also burdened with enormous numbers of assumptions. We are limited by both our knowledge and our intrinsic perceptions. So I, for one, am not particularly concerned about the Great Silence. Whether extraterrestrial civilizations are friendly and/or capable of mutual understanding are very different questions, of course.

  • andy August 7, 2007, 18:19

    This reminds me of something I mentioned on another post: an odd coincidence: the estimate of the median age of terrestrial planets and the estimated maximum habitable lifetime of an Earth size planet both give roughly the same number: around 6.5 billion years. Not saying it’s an explanation or anything (for a start, super-Earths would presumably last rather longer)

    As for what Fermi is telling us, it means we can rule out some of the least probable scenarios, of shouty aliens in virtually every star system or watchprobes scattered throughout the galaxy, or perfect radio-triggered xenocidal von Neumann killing machines infesting the entire galaxy.

    Also it would appear to cast doubts on the views of the Holy Transhumanist Cult of Singularity in that we build some kind of AI and suddenly start chewing up the scenery and building megastructures like Dyson swarms and suchlike. Some of the assumptions are rather naive (exponential growth extrapolated indefinitely), and it may well be that Singularity doesn’t happen, but like other developments, computer technology starts to plateau below the level of rapidly self-advancing AI (perhaps due to fundamnetal limitations of physics). Or it may be that Singularity is not a good event to be around, and the Divine Utopia of Posthumanism is wishful thinking. It may well be that the “after human” future is literally that: after the humans have gone extinct.

    The Fermi paradox is only a problem if you both believe in the existence of alien technological civilisations and you believe in the transhumanist ideal Singularity. Remove one of those two assumptions (I would personally be inclined to suggest that Singularity is the problematic one: it seems from observations that habitats for alien life are widespread but experience suggests that technology does not exponentially increase forever, but slows down and plateaus), and the Fermi paradox is not such a big deal.

  • david August 7, 2007, 20:08

    What is needed for an intelligent technological species to arise? I can easily conceive of situations where it would be so rare that only one in a trillion star systems would give rise to such a species.

    I can also conceive of situations where there might be several hundred such species in the galaxy.

    What I cannot conceive of is any reason why they would make their presence known. They would know more about humanity than we know about ourselves. They would have long ago sent probes to every star system of the galaxy, probes that would have monitored the status of the system they were in continuously. They would have watched the evolution of life on this world for the last x years including the evolution of homo sapiens. Assuming they, such aliens, exist.

    Where are those probes? If there were several million such probes in orbit, each the size of a grain of sand, we wouldn’t know about it. There would be no reason to make them larger than that, and many reasons not to. They could even be hooked into the internet and actually talk to people. Unlikely, but possible.

    There is also no reason to assume such von neumann type machines are impossible. We already have self-replicating machines here on earth. It’s called life and can vary in size from the blue whale to single celled organisms.

    Currently we are speculating from a near total lack of knowledge on which to base our beliefs. All we know is roughly the number of stars in the galaxy and the percentage of each type. We know some of them have planets but nothing beyond that.

    Could we even rule out a sizable fraction of the dark matter in the universe being habitats for aliens? Total absorption of all energy for power with just gravity to show where they are at?

    When considering the areas of the galaxy where life such as our might arise what is the frequency with which those stars move and down as they circle the galactic core and thus suffer mass extinctions such as the earth does? Is the frequency greater or less than that of the solar system. Or how many remain in the north side of the galactic core within the shock wave and thus would not be able to develop large land dwelling life at all.

    So many question I want to scream. If humanity survives and continues as a technological species one day we will pick a large asteroid and plant a factory on it. It will replicate and start building those probes and we may end up being the aliens observing someone. One can hope anyway.

  • Ron S August 7, 2007, 21:06

    There is no Fermi paradox.

    Ok, that’s a nicely provocative statement, but one that I believe has merit. What we have is, say, the Drake equation – one equation with many unknowns (and probably unknown unknowns) – which various folks try to wrestle into submission with assumptions and biases on the variables, and occasionally with actual data (already noted by david, Athena and other commenters). These are all interesting and thought-provoking speculations that help us to think through the problem. The danger is when someone makes the step of promoting the speculation to a conclusion based on (an unjustifiable) confidence in those assumptions and biases.

    When you do this and find that the reality does not match the conclusion, there is the shout of “paradox!” What we have here is not a paradox but rather a paucity of empirical data, unjustified biases and delusional prediction.

    This is somewhat analogous to the twins paradox in relativity. It’s not a paradox but rather a difference in results from applying pre-1905 and post-1905 physics to a seemingly straight-forward problem. There’s no paradox, just an indication that one or both theories are wrong. Similarly all these ETI theories are perhaps wrong.

    At the danger of an overly long post, I have a couple of other observations.

    1. I find the Kardashev civilization categorization misleading. Do more advanced civilizations have this enormous and increasing need for energy? Much of future development could be in increased technological complexity rather than scale. These include AI and doing away with biological bodies. Suddenly travel, commerce and social interaction on a wide scale is not so energy intensive. There is also less survival necessity in harnessing more planets and suns, though there may be other reasons. There may be new physics waiting for us to discover, such as non-simply connected spacetime, that make the enormous energy budget for interstellar travel obsolete.

    2. I find the idea that we could be the only intelligence, or even life-bearing locale, in the galaxy or universe hard to accept. Pick a probability, any probability, for our being here. It has to be greater than zero (obviously, but not 1 except in hindsight). Now assign a probability of zero to every other conceivable point in the sample space. This makes for a peculiar probability distribution function; it’s more of a delta function, and this would be peculiar indeed for a macroscopic phenomenon such as life. More likely it’s greater than zero everywhere in the sample, though much lower than on Earth in part of the sample, and possibly higher in another part of the sample. Even if Earth does have the highest probability a reasonable, and I think justifiable application of statistics says that the probability of 2 or more intelligences is still non-zero and may in fact be not much less than the probability of life on Earth. I even went so far as to calculate this some months back using (cringe) a few statistical assumptions.

  • philw August 7, 2007, 22:03

    Astronomer Michael-Rowan-Robinson did NOT say there is no intelligent life beyond Earth as alleged by ljk. He did say this, “Personally I think that while there may be primitive life on extrasolar planets, I do not think there is a profusion of extraterrestrial intelligence. Given that there has been such an immense time period during which other civilizations could have existed, the fact that “they” don’t seem to be signalling to us and that they’re not visiting us suggests to me that for some reason they are not common.”

    I do agree he blithly cites reasons that aren’t especially cogent, but it’s an abstracted brief interview, not a paper. Seems that anytime folks dispute the revealed truth from Sagan et. al. decades ago that the galaxy is likely ‘teeming’ with civilizations, the faithful attack the heretics. ETI belief is just that, belief. Proponents of incredible yet unobserved phenomena deserve skepticism. Agnosticism in our ignorance is warranted.

  • ljk August 8, 2007, 0:12

    Don’t worry, Phil, neither of us will probably live long enough
    to find out the real answer, so both our paradigms will remain

    But mine’s cooler.

  • Kurt9 August 8, 2007, 1:26

    I think George Dvorsky is too quick to dismiss the Rare Earth Hypothesis (yes, that REH thing that you guys seem to hate here). It appears that part of the REH is being discredited (required steller metalicity for terrestrial planet formation and, thus, the limited galactic habitable zone). However, the most significant aspect of the REH, which is the necessity for plate tectonics and their connection to having a large moon formed by an improbable impact, remains standing in my opinion. If this turns out to be correct, then the number of complex life harboring planets in the galaxy is likely to be 10,000 to 1,000,000 time less common than is generally thought. If true, this would certainly account for the Fermi paradox.

    The REH could be wrong here as well. However, the instrumentation to test this will not be available for another 2 decades or so. Darwim might be able to answer this.

    I still think the study of the origin of Venus is imperitive to resolving this issue. It is possible that any Earth-sized world that lacks plate tectonics may end up a venus instead and that a large moon is necessary to generate and sustain the plate tectonics. More study of Venus (it IS in our solar system, so we can actually get there easily, compared to going to the stars) is necessary to answer this question.

  • philw August 8, 2007, 12:26

    I agree with ljk, sadly we most likely won’t live long enough to know unless that singularity happens soon and I upload with Hans Moravec & co. I too like the cool paradigm. Just taking a counter conventional space fan position for the fun & intellectual exercize. I really DO feel that probably some of our assumptions are faulty.

  • philw August 8, 2007, 12:32

    A 1st tentative step in testing the rare Earth hypothethis will be the results of Kepler, due to fly in late 2008 and return results within 3 years. If Kepler does NOT find the statistically expected quantity of terrestrial sized planets in stable HZ orbits, we’ll know that something is rare about our solar system.

    Then Darwin, TPF or some other all YET TO BE FUNDED instrument will be needed to search for spectroscopic evidence of excessive reactive gasses in the atmospheres, indicative of biological activity. Somewhere in the mid-late 2020s.

  • Kurt9 August 8, 2007, 13:24

    philw is right. The remaining part of REH will not be confirmed or rejected for another 20 years. In the meantime, analysis of Venus could be useful. The connection between plate tectonics, global resurfacing events, and the need for the large moon need to be established (or, hopefully, disproven). More specifically, if Venus’s lack of plate tectonics is because of a lack of water (as someone has suggested here before) or is because it lacks a big moon.

    I think we will not have any of these answers for another 20 years or so.

  • ljk August 8, 2007, 14:43

    Maybe Venus had plate tectonics at some point, but massive
    volcanism “fused” its continents together.

    Perhaps having a large moon nearby to keep a planet’s
    crust active and broken up is the key?

  • ljk August 8, 2007, 15:44

    I often feel like we are all standing on the shore of an ocean
    arguing over whether or not there are any fish in those big waters.

    We need to get in our boats, grab our poles, tackle boxes, and
    nets and sail out there, or we will remain on the shore debating
    forever. I am not expecting or waiting for the fish to come to us.

  • ljk August 8, 2007, 15:49

    The latest installment – The Fermi Paradox: Possible solutions
    and next steps, here:


    To quote:

    The past 40 years of scientific progress has forced a re-evaluation of humanity’s potential. We appear to be headed for a transformation that takes us away from biological existence and towards a postbiological, or digital existence. Our future visions must take this into account. As Milan Cirkovic and Robert Bradbury have noted, we need to adopt a digital perspective (pdf).

    Why leave the local system when everything can be accomplished at home? Localized existence may hold promise for all the aspirations that an advanced intelligence could conceivably conjure.

    Specifically, advanced intelligences may engage in computational megaprojects and live virtual reality existences. It would be an existential phase transitioning into virtual space such that interstellar colonization would never emerge as a feasible option or experiment.

    For example, advanced ETI’s may construct Jupiter (pdf) and Matrioshka Brains. A Jupiter Brain would utilize all the matter of entire planet for the purpose of computation, while a Matrioshka Brain (a kind of Dyson sphere) would utilizes the energy output of its parent star.

    Determining an upper bound for computational power is difficult, but a number of thinkers have given it a shot. Eric Drexler has outlined a design for a system the size of a sugar cube that would perform 10^21 instructions per second. Robert Bradbury gives a rough estimate of 10^42 operations per second for a computer with a mass on order of a large planet. Seth Lloyd calculates an upper bound for a 1 kg computer of 5*10^50 logical operations per second carried out on ~10^31 bits – this would likely be done on a quantum computer or computers built of out of nuclear matter or plasma [see this article and this article for more information].

    More radically, John Barrow has demonstrated that, under a very strict set of cosmological conditions, indefinite information processing (pdf) can exist in an ever-expanding universe.

    This type of computational power is astounding and defies human comprehension. It’s like imagining a universe within a universe — and that may be precisely be how it’s used.

  • george scaglione August 8, 2007, 15:58

    ljk if i may say so and with no pun intended what you have said above “holds alot of water”! i am speaking of the 2 postings immediately above.thank you very much your friend george

  • andy August 8, 2007, 17:06

    First off, to clarify on the tectonics: the problematic part of the process appears to be subduction: rift valleys seem to be common features on many planets.

    The water idea for tectonics does hold quite a lot of weight. For a start, water lowers the melting point of mantle materials, which makes it easier to melt and hence to move around, secondly it increases the mass of the plate (on account of the fact you have more stuff in there). In fact, there are studies which have done computer modelling that show that dry lithosphere does not fail in the right way to subduct. So the fact that Venus does not have plate tectonics is not surprising, because the planet is extremely dry.

    So if that’s the entire story, we don’t have to worry about plate tectonics as a factor for habitability because planets which support liquid water at their surfaces ought to have plate tectonics.

    The interesting question is whether Venus ever had plate tectonics, back when the Sun was less luminous and before it lost all its water (did it ever have oceans, or was the planet too hot even under a lower-luminosity Sun?). That question requires doing detailed geological surveys, seismometry, etc. in an extreme environment. This is made more difficult because the runaway greenhouse likely occurred billions of years ago, and the planet has suffered massive volcanism since then, which would be a good way to obliterate traces of previous tectonic structures. But if it is found that Venus once had oceans but no plate tectonics, it would suggest that something else had to initiate the process rather than just a hydrated lithosphere.

  • philw August 8, 2007, 20:29

    As someone in the computer field I do not equate Moore’s law extrapolations of computational ability with magical events to come as do Kurzweil et. al. We saw a similar expectation of wonderous things via computation when Minsky et. al. in the 70s hyped the false dawn of imminent AI and in the 80s with Drexler’s nanotech era. How many times do we have to learn that trend extrapolations are not laws of physics and the future is most always NOT what we expect it to be? That could actually be a very good thing.

    DISCLOSURE: I have nanotech investments

  • Luther R. August 8, 2007, 23:40

    I love that some people note the failure of a 40-year effort to detect signals using a technology we won’t be using a century from now as some kind of evidence that a 15 billion-year universe is barren of ETI. It’s also quite amusing the conclusions drawn from the seeming lack of Dyson spheres and other obvious structures, even though (to my knowledge) no one has attempted to look for them, and we would have no clue what to look for even there were a massive effort. Nevermind the fact that such objects would probably not be luminous, making it just an eency bit difficult to see them across the galaxy.

    And even if we had perfect remote sensing equipment capable of pan-galactic resolutions, what are people expecting to see from technology? Smooth, shiny, angular grey and black things? I mean, do we build cities to resemble what an ancient civilization thought the gods would build? Are our skylines dominated by golden palaces and domes? Even if we were handed a perfectly clear photograph of an alien structure, scientists would just spend forever trying to tweak their theories of natural phenomena to explain it, because any stretch would seem preferable in their minds to thinking it was constructed. It’s exactly the same thing that happened with the Mars meteorite. Life was and remains the most plausible explanation, but there’s an emotional resistance to the idea among many scientists every bit as strong as the Saganite desire for it to be true. Nothing short of an Independence Day moment, a clear and unambiguous radio signal specifically directed to us, or a photograph of an obvious Death Star-like structure would convince the scientific community that evidence is sufficient for ETI. And since none of that is ever going to happen, they’re never going to conclude that it exists.

    We just have to accept the fact that uniqueness is virtually impossible in an ordered physical universe, and respect that we live in a delightfully weird and bizarre cosmos.

  • ljk August 9, 2007, 1:42

    Not too long ago some searches for Dyson Shells were conducted.

    Read here for the details:


    I agree that 4 decades of sporadic searches in a galaxy 10 billion
    years old and declaring no one else is around is quite premature.

  • Athena August 9, 2007, 11:59

    As a scientist who also happens to think there is life elsewhere (including advanced lifeforms), I must disagree with one point that Luther R. makes. The reason that scientists bend over backwards to exclude any explanation arising from natural phenomena is so that the proof is ironcast. Especially where extraterrestrial life is concerned, this has to be so because the consequences of such a finding would be so momentous.

  • Kurt9 August 9, 2007, 18:23


    Establishing that a large moon is not necessary for the existance of plate tectonics is key to refuting the rest of the REH. Unfortunately, a survey of Venus to determine if the place had plate tectonics is going to be very difficult, to say the least, given that there has been several “resurfacing” events since that time. Needless to say, the environmental conditions are not exactly favorable for such research, either.

    Mars might be worth studying for this (and a lot easier environment to work in) but its small size was probably sufficient to prevent it from ever having any plate tectonics.

    The only other approach is Darwin or TPF, which will not be available for another 20 years. If Kepler finds lots of Earth-sized planets in HZ orbits, I think funding for Darwin or TPF will be more forth-coming. If Kepler fails to find such planets, then a least one portion of the REH is true and Darwin/TPF is unlikely to be funded.

    In any case, it will be 2010-2011 before we have an answer to this question.

  • Theo Stauffer August 10, 2007, 17:34

    In reply to Kurt9’s comment on investigating Venus as a counter example to earth, i.e. one without a large moon and its resultant motor-of-life effect on earth via tides:

    I don’t think Venus is a good example of what an average planet in or near the habitable zone could be like, because Venus’ very strange retrograde rotation could very possibly also be the result of some almighty collision similar to the one that formed the moon. In other words, that scenario could also be much more common than we have thought.

  • Ron S August 10, 2007, 23:40

    The tidal force (gravitational gradient) of the Sun is about 1/2 that of the Moon. Sounds like that’s pretty strong. Is it enough to drive tectonics if there’s no large moon? Tectonics is also, for a time, perhaps a long time, also driven by gravitational compression heating dating from the planet’s formation. For Venus the Sun’s tidal force should be comparable to that of the Moon’s effect on Earth although the longer rotation period mitigates that to a (large?) degree.

  • andy August 11, 2007, 4:36

    As far as I am aware, Venus is pretty much expected to end up with its current retrograde spin state as a result of chaotic evolution and its dense atmosphere. No need to invoke a giant impact for that. Doctoring the spin on Venus

  • laoem August 11, 2007, 23:36

    Not too long ago some searches for Dyson Shells were conducted.

  • Kurt9 August 12, 2007, 2:44

    Ron S and Andy,

    At least according to the Wiki article, the paleomagnetism in parts of Mars’s crust suggests that Mars did have plate tectonics several billion years ago. Since there is no evidence that Mars ever had a large moon in its past. This suggests that the REH may be wrong about the connection between plate tectonics and the large moon. Further investigation of Mars is needed to confirm this.

  • Michael T August 18, 2007, 15:17

    A thought occurred to me that might support REH. I have been reading about the so-called “Snowball Earth” hypothesis. Now if it is true, the conditions for thawing would indeed be a rare occurrence. According to this notion, extreme volcanic activity caused the release of enormous amounts of green house gases allowing to the planet to warm and thus thaw. Now if it wasn’t for this fortuitous event we would likely not have had have the Cambrian explosion allowing life to evolve in its multitude of forms. For billions of years the planet was quite content with simple organisms and then bam! I finds this story, if true, extraordinary. I mean what are the odds??????

  • ljk August 28, 2007, 12:10

    The Universe: Search for ET

    KurzweilAI.net August 28, 2007


    Ray Kurzweil, SETI senior
    astronomer Seth Shostak, and other
    experts will be featured on The
    “Universe: Search for ET,” kicking
    off a new series on the History
    Channel, “The Universe,” Tuesday,
    August 28 at at 9:00pm, 8:00
    Central. “In a galaxy filled with one
    hundred billion stars, in a universe filled
    with a hundred billion galaxies–are


  • Adam August 28, 2007, 16:02

    Hi Michael T

    Normal volcanic activity caused the greenhouse gas build-up that ended the Snowball episodes according to the models, so there’s nothing especially novel about them except the extreme conditions – from -50 C to +50 C. Geologists are still arguing whether the whole planet was covered or whether the equatorial oceans were open, so it’s still an open issue.

    What triggered it is interesting as prior to about 1000-800 million years ago most of the land was still underwater. The continents drained off around that time with an explosion of plant life and erosion that drew down a lot of CO2 thus starting the deep-freeze. Quite an event.

  • george scaglione August 29, 2007, 9:13

    hello ljk, maybe i’m crazy…not impossible,but universe is i thought a series that has been running for quite a while already.as i see it a copy of cosmos but not near as good. saw that episode yesterday and it was indeed very good but not great – in my opinion.anyhow, respectfully your friend george

  • ljk September 12, 2007, 10:32

    Will Super Smart Artificial Intelligences Keep Humans Around As Pets?

    Reason Online September 11, 2007


    By 2030, or by 2050 at the latest,
    will a super-smart artificial
    intelligence decide to keep humans
    around as pets? Will it instead
    choose to turn the entire Earth,
    including the messy organic bits
    like us, into computronium? Or is
    there a third alternative? These
    were some of the questions pondered
    by the 600 or so technosavants
    meeting in the…


  • ljk December 10, 2007, 11:24

    Earliest galaxies had building blocks of life

    NewScientistSpace Dec. 8, 2007


    The universe might have been
    hospitable for life 500 million
    years earlier than we thought,
    according to researchers at the
    University of Texas in…