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Poul Anderson’s Answer to Fermi

Enrico Fermi’s paradox has occupied us more than occasionally in these pages, and for good reason. ‘Where are they,’ asked Fermi, acknowledging an obvious fact: Even if it takes one or two million years for a civilization to develop and use interstellar travel, that is but a blip in terms of the 13.7 billion year age of the universe. Von Neumann probes designed to study other stellar systems and reproduce, moving outward in an ever expanding wave of exploration, could easily have spread across the galaxy long before our ancestors thought of building the pyramids.

Where are they indeed. Kelvin Long, one of Project Icarus’ most energetic proponents, recently sent me Poul Anderson’s thoughts on the subject. I probably don’t need to tell this audience that Anderson was a science fiction author extraordinaire. His books and short stories occupied vast stretches of my youth, and I still maintain that if you want to get not so much the tech and science but the sheer wonder of the interstellar idea, you can tap it in its pure form in his writing. Poul was also the author of Tau Zero, the novel which gave our Tau Zero Foundation its name, and we’re delighted to have Karen Anderson, Poul’s wife, as a valuable part of the organization.

In a letter to the Journal of the British Interplanetary Society in 1986, Anderson sketched the reasons why Fermi was asking his question, citing the von Neumann probes mentioned above, and noting that while interstellar travel was likely hard enough that civilizations practicing it might be rare, all it takes is one to eventually fill the galaxy with its artifacts. He found the notion that Fermi could be answered by saying we are the only high-technology civilization unlikely, but his reason for writing was to offer an entirely different suggestion based on practicality.

Let’s assume a stable civilization arises that achieves extremely long lifespans, if not physical immortality — this may be too big an assumption, but there are those arguing that our successors may be a form of artificial intelligence for whom this could apply. Such a civilization naturally would explore its neighborhood, moving out to local star systems and gradually spreading beyond. Anderson saw this as a problem: The farther from home you go, the longer it takes you to return information. The galaxy itself is 100,000 light years wide, he noted, and that means most information would be utterly outdated by the time it spread throughout the disk.

And what of this self-replication idea? Anderson saw problems there too:

…self-replication would probably already have broken down. Quantum mechanics alone guarantees gradual degradation of the programmes, an accumulation of ‘mutations’ generation by generation — without any natural selections to winnow out the unfavourable majority — until ultimately every machine is useless and every line of its descent extinct.

Can we conjecture a kind of self-healing technology that extends to fixing these errors to maintain the integrity of the expansion? Perhaps, but the data flaw remains paramount:

…long before this has happened, the sphere of exploration will include so many stars that the data flow from them saturates the processing capacity of the present civilisation. After all, with some 1012 stars in the Galaxy, a small fraction amounts to a huge number. Moreover, while they may fall into categories with predictable properties, we are learning in our own back yard that every planet any of them may have is a world, replete with mysteries and surprises. Every life-bearing planet offers endless matter for research, especially since the life will always be changing, evolving.

In short, Fermi’s ‘they’ are not here because they are kept too busy within a few score light-years of their various homes.

If Anderson is right, then we can imagine a galaxy in which technological civilizations arise here and there, each of them gradually filling a sphere of exploration and colonization until a kind of equilibrium is reached and there is no practical advantage to pushing further. Earth, then, could be seen as being in the spaces between such civilizations, not yet aware of their existence, preparing over the next few centuries to begin its own expansion to nearby stars.

Is the galactic population sufficiently dense that such ‘bubbles’ of expansion ever meet? Or is SETI our only chance to confirm the idea that the galaxy has brought forth other technological civilizations? If the latter, we may know them only by the whisperings of their local traffic, exchanging information and perhaps speculating as we do about still more distant suns.

Anderson’s letter appeared in JBIS Vol 39 No (7 July 1986), p. 327.


Comments on this entry are closed.

  • amphiox September 2, 2010, 0:01

    If the von Neumann probes are subject to replication infidelity (ie mutation), then they will automatically become subject to natural selection.

    And if that happens they will become vulnerable to motive decay. Variants that retain the original programming are going to be at a disadvantage compared to mutants that ditch parts of the original code in favor of just replicating. Probes that devote resources to replicating, exploring, relaying information back home, and traveling to new star systems are going to be outcompeted by mutant probes that devote all their resources to just replicating blindly. Probes that retain error-correction mechanisms are going to lose to probes that dump the error-correction in favor of putting more resources into just replicating. Probes that retain the capacity to communicate with home for software upgrades designed to eliminate such mutations will lose out to mutants who simply ditch the capacity to communicate with and be manipulated by home.

    The expansion front may well peter out into a shell of “dead-end” systems filled with probes that are highly efficient at infecting those systems, but without the capacity to leave it. With sufficient time, the descendents of these probes may well become completely indistinguishable from naturally evolved lifeforms.

  • Ronald September 2, 2010, 4:47

    Eniac: “Colonizing the entire galaxy is just as easy (or hard) as colonizing the first neighboring system. After that first step, you just have to do the same thing over and over again. There is no resource to run out of, because you use local resources only. You know you can, because that’s what you did the first time.”

    How true! This means it all comes down to the (average) distance between two neighboring inhabitable systems (I deliberately say systems instead of planets, because I want to avoid the discussion of colonizing planets versus asteroids and Oort cloud/Kuiper Belt like objects here).
    Once you know how to sail the sea you can travel to any overseas country.

    The average distance between two neighboring inhabitable systems might well be several tens of lightyears.

    Anyway, for now it doesn’t make any difference to us, because we are still like a primitive tribe trying to reach the moon by climbing mountains.

    But once we manage to master some form of ‘considerable-proportion-of-lightspeed-velocity-propulsion’ (by means of nuclear fusion and/or light/laser/mag sails) in combination with some form of hibernation/suspended animation/life-extension, the difference between an average of 3 and an average of 30 lightyears between systems may prove to be highly significant. Like to people using rather basic sailboats the difference between crossing the Channel, the North Sea or the Atlantic.

    Brings me to the following observation: the most promising and enticing systems for promotion of space travel and space colonization by intelligent inhabitants may then be (very) wide binary systems of suitable (solar type?) stars, such as Zeta 1 and 2 Reticuli or 16 Cygni A and B, provided that each of the components has some habitable or at least terraformable property.

  • ljk September 2, 2010, 7:13

    Humanity still has a tough time realizing and accepting this one truth: That we are not the most visible or important thing in the Universe.

    I am not saying we don’t matter at all, but neither are we the whole reason for existence.

    Knowing we weren’t the center of the Sol system/Universe since the time of Copernicus (Yes I know about Aristarchus but he was hardly widely accepted) still hasn’t gotten across to the majority of people. Maybe when we start colonizing space in earnest.

  • Zen Blade September 2, 2010, 8:28


    Regarding historic colonies, that’s not accurate. It wasn’t “weeks”. It was “months” or possibly even a year to go between far off colonies. Roundtrip to the east indies and then back to europe took well over a year. I’m not sure of the exact travel times, but traveling from England to west India was ~7000 miles… [they didn’t have cars or motor boats] assuming you stopped at Egypt and traveled across the isthmus before the canal was built. Australia and southeast asia were even farther. The Americas were not as far, but they were also far more entangled by European affairs.

    So, I see a real conundrum here. If a colony is easily reachable or controllable, then it may be quickly populated and may quickly develop. But, at a cost of certain independence. However, if a colony is not easily reachable/controllable, then its growth/development is likely to be slower. If we had a historian, we could probably determine if this speculation holds true, but it does at least seem plausible. By the 1800’s the Americas had numerous factions derived from European settlers/conquistadors/explorers, and independence movements were appearing throughout. Portugal even relocated its crown to Brazil during the Napoleonic time period.

    Also, with regards to resource acquisition/cost, I think one has to assume that by the time we have substantial colonizing efforts outside of this system, if we find a good world, WE WILL WANT the resources on that world.
    The Spanish treasure fleets, which operated on a large scale from the mid 1500’s until the late 1700’s, traveled to the Americas, to the east indies, and essentially across the entire globe bringing gold and other riches back to Spain. You can argue it was not as expensive as space travel… that’s true. But if space travel is so expensive, then one might argue that traveling to set up a colony is also PROHIBITIVELY expensive. A colony that never returns anything to the homeworld is…???
    Who is going to fund that? I ask this from a practical perspective.

  • Eniac September 2, 2010, 9:04

    If the von Neumann probes are subject to replication infidelity (ie mutation), then they will automatically become subject to natural selection.

    Very true. With replication fidelity, you have created a tool. With evolvability, you have created life. A form of life that can devour entire planets. Not good.

    Luckily, it is not hard to ensure replication fidelity. Plus, I believe it takes extra effort to make a mechanical system that can change randomly and still work. The latter is a prerequisite for evolution, and must be strictly avoided for von Neumann probes.

  • Eniac September 2, 2010, 9:47

    But if space travel is so expensive, then one might argue that traveling to set up a colony is also PROHIBITIVELY expensive. A colony that never returns anything to the homeworld is…???
    Who is going to fund that? I ask this from a practical perspective.

    You have hit the nail on the head. Assuming there are no aliens to visit, there is no way you can bring riches back from interstellar space. The only way to use the resources of another system is to go there. Looking for real estate, not gold. You cannot bring real estate back, so there will never be a return to the homeworld, except for the satisfaction to have “spread your seed”. The motivation will be that, or simply to go where no-one has gone before. If this motivation is strong enough to overcome the barriers, colonization will happen,repeatedly, until the galaxy is filled. If it is not, then we will not colonize the stars, at all. I do not claim to know which, but I am pretty sure there is no in between.

    Note that, because of the independence of colonized star systems enforced by isolation, only some of them need to maintain this motivation to colonize for expansion to continue. Those that don’t, or those that destroy themselves or decay, will simply leave more space to (re-)colonize for the others. For expansion to stop short in the manner that has been suggested, every single colony, without exception, needs to lose the motivation or ability to colonize, permanently, in spite of a tradition of doing so. This is not likely.

  • Bob Earley September 2, 2010, 11:41

    Why should highly advanced alien civilizations (or future human civilizations) _want_ to colonize at all? Why should they want to forever increase their population, their exploitation of those populations and natural resources, even if this were possible? It’s a fantasy of “science” fiction writers — trying to project the “glories” of our past (the rise and fall of the Roman Empire, the conquest of the Americas, Westward expansion, etc.) beyond earth; their social conservatism and nostalgia combined with a lack of imagination and unbounded, unrealistic optimism for technological advancement. Global warming ought to get us thinking about past motivations and behavior, their consequences, what is or is not sustainable, what does or does not contribute to the quality of life _in the long run_; and what it means to be or become an advanced civilization.

  • Zen Blade September 2, 2010, 13:29


    I think you forget to include the rate of failure… not every attempted colonization will succeed. Many/most? will fail or perhaps not be able to grow beyond a small and inconsequential footprint.

    Based on your post, I might argue that you would find very, very small outpost colonies by those few individuals who wish to go out and explore AND have the means to finance a small expedition.

    I’m not sure what the current criteria are for considering “survival” of a family line, but I remember reading the Seven Daughters of Eve a number of years ago (beginning of grad school). I also read some related books/articles at the time that discussed the number of daughters required to survive and have their own offspring in order to give a high probability that the maternal line would continue. I want to say the number might have been three… but that was a long time ago.
    The point being: the original homeworld would likely have to send out more than 1 colony ship per sustainable colony world. And after that success, the colony world itself would have to send out multiple colony ships in order to generate at least 1 sustainable colony world. And not only does that colony need to be sustainable. It needs to produce 1 or more additional colony ships.
    Assuming this premise is correct, then the selection criteria of what system to colonize will not necessarily match the criteria required for that world to later become a good world for launching its own colony ships.

    It is conceivable, maybe even likely, that colonizing will “peter out” quite quickly regardless of the practical concerns of a large society/culture/population. Personally, I think the practical concerns of a large society/culture/population are more important, but for the sake of this current discussion, I am disregarding them.

    -Zen Blade

  • Eniac September 2, 2010, 16:34

    Zen: Perhaps we just have different time scales in mind. Of course colonization may fail. But if it doesn’t, it eventually leads to a whole new society, as likely as not with similar motivations and better technological capabilities.

    America took less than 500 years to grow beyond the motherland. For an interstellar colony, without the benefit of significant immigration and trade, it may take much longer . All I am saying is, it does not matter how long it takes, or how often it fails. If it ever succeeds at all, it will continue and eventually cover the galaxy.

    The “petering out” you mention seems a remote possibility to me. There will not be much of a “larger society”, because of the lack of interaction between different systems. Other factors, such as advancing technology and gain of experience lower the barriers and are in favor of colonization. I do not know a good factor that would go the other way. “We are fifth in the line, why have a sixth, there is no point?” “New star systems are boring, we have so many old ones to read about, we know it all?” Possibly, but neither sounds very convincing to me. And remember, it has to take hold in every single system in order to stop expansion.

    Perhaps a plausible scenario would be some unavoidable stage in technological advancement that renders colonization moot, such as the singularity. The singularity is scheduled to occur well before even the first colonization could succeed, so it is not really relevant here. I suppose you could imagine other, more long term developments that would inhibit colonization, but I myself have a hard time at that. It would have to be something positive, because if it was destructive, people would see it happening in the other colonies and strive to avoid it for themselves.

  • Eniac September 2, 2010, 17:40

    I’m not sure what the current criteria are for considering “survival” of a family line, but I remember reading the Seven Daughters of Eve a number of years ago (beginning of grad school). I also read some related books/articles at the time that discussed the number of daughters required to survive and have their own offspring in order to give a high probability that the maternal line would continue. I want to say the number might have been three…

    All maternal and paternal lines eventually die out, except for one. We all have one common female ancestor, and one common male ancestor, but they lived at different times and did not know each other. This is a fascinating topic, but most of the fascination has to do with the peculiarities of sexual reproduction.

    Here, a better biological analogue is microbial growth, which is quite simple and only limited by external factors.

  • Zen Blade September 3, 2010, 7:40


    Regarding ancestors… that’s not exactly accurate. We have a “last common ancestor”. That is simply a definition of being evolved from the same individual, but we have many different ancestors.
    There is always a last common ancestor, but after that point, not all lines die out. There is a struggle and mixing of various lineages. That was the whole point about the “daughters” of Eve. The author claimed that were seven surviving maternal lineages in Europe (maybe middle east also, I forget the entire geographic extent).

    I don’t think we can say that colonization is limited predominantly by external factors. I think internal factors are very relevant, and I don’t think microbial growth is necessarily a better analogy. One reason is that microbes do tend to be limited by primarily external factors… yet, our colonization of space has slowed (dramatically?) since the 1970’s. We had people on the moon. Currently, it would take 5-10 years to get a program in place to send us back to the moon. I’m not sure what the external factor was/is that has caused this retrograde in our colonizing ability. However, I can think of numerous internal factors including a desire for prestige, a sense of nationalism, expanding scientific knowledge about space (leaps and bounds) /curiosity/industrial base. All of which have experienced at least a partial downturn or an outright decline in recent decades.
    **The general public is NOT anywhere near as interested in science as those of us who visit this website. It is sad, but true.

    Don’t fall for the singularity tripe. Doomsday cults are dangerous things.

    -Zen Blade

  • Eniac September 3, 2010, 12:07

    Zen, I think you are mixing up something about the ancestors. Check out this for explanation: http://en.wikipedia.org/wiki/Mitochondrial_Eve

    Quite clearly, if there is a matrilineal ancestor (Eve) common to all of us (as the article correctly states), then hers must be the only surviving line. If there was another surviving line (i.e. that of one of Eve’s contemporaries), its now living members would not be matrilineal descendents of Eve. But we all are, thus there cannot be such a second surviving line.

    The same goes for the Y-chromosomal Adam.

  • Eniac September 3, 2010, 12:44

    Zen: Of course there are internal factors. I am just saying that these internal factors are not likely to be biased against colonization in colonies, as opposed to the mother world. So, if the mother world colonized, the colonies, after they grow to reach the capability, are likely to do so as well. On their own, without asking for approval from anyone else.

    If the above is not true, there will be no growth at all. If it is true, there will be unrestrained growth.

    The only way to have growth for a while and then stop is some sort of collective decision to stop colonizing at a certain point, and collective decisions of any kind are very difficult with the communication delays involved. The mother world may very well decide that “enough is enough”, but how are they going to convince every single one of the frontier worlds?

    You are right about the sad state of public perception of space, but these are just temporary mood swings, tiny blips in the face of history, and even tinier on the galactic time scale we are contemplating.

    And I share your opinion about the singularity, more or less. ;-)

  • Zen Blade September 3, 2010, 15:18


    I still think you are being overly optimistic about expansion. I think it will take a major concerted effort. We will need to be single-minded AND resolute in that single-mindedness in order to finance a successful effort. If that single-minded fails, even for a brief period, I believe that any colonial effort will fail or be halted to such an extent that it will need to be restarted from scratch.

    That is why I view internal factors as far more relevant than external factors. We must 1. achieve a single-mind with regards to the time and energy required to colonize; and 2. we must maintain that mindset for a substantial period in time… maybe as long as a generation or two.

    I think smaller scale efforts could be financed/supported by a subset of the population, but I doubt how successful those efforts would be without substantial ongoing support and “reinforcements”.

    Now, all that being said… if we find little green commi-nazis in space, I think we could sustain the war forever.

    Regarding lineages, yes there is a last common ancestor (Eve or Adam, for example). BUT, after that point all descending daughters (generic term, not necessarily female) will begin to differentiate and compete against one another. At that point, there are multiple lineages. Some will go extinct, others will thrive and perhaps even replace the previous last common ancestor of the surviving population, but that is not a guarantee.

    Think about this in terms of tribes or clans competing for the same hunting ground or the same foraging ground, and later the same farms, minerals, cities, etc…

  • Eniac September 3, 2010, 18:00

    It is perfectly fine if you say it is too difficult to colonize. Then the whole argument is moot, because there will not even be a bubble. What I object to is to say it happens many times (proving it is not too difficult), yielding many inhabited worlds (the bubble), and then suddenly everyone agrees to stop. Why? It just doesn’t strike me as plausible, especially if the worlds are all independent, as lightspeed isolation would make them.

    The sub-lines you are talking about are all part of Eve’s line. By “other” lines we mean those descending from Eve’s contemporaries, which have necessarily all died out (or else Eve wouldn’t be Eve).

  • bigdan201 September 4, 2010, 4:07

    Space colonization is the future, and it’s the best insurance policy for our species.

    Colonizing the solar system will start with industry/commerce such as mining planets/asteroids for resources. That will be the next major stage in history.. but we’ll colonize the solar system long before we establish a presence around other stars. Interstellar travel and colonization will happen eventually, but the distances are just so vast that it will not be for a long time. Certain events could provide much more motivation and change the timeframe.. such as finding an earthlike exoplanet, or identifying extremely valuable resources in another system that can’t be found here.

    Even if we don’t need to go to other stars for certain resources, that doesn’t mean people won’t be willing to go. Throughout history, people have shown their willingness to travel great distances and settle far from home.. and I don’t expect space to be a different story. Once reaching space becomes economic and efficient, and a way is opened to settle on other worlds, many human motivations will push us to other planets and eventually other stars. Whether it is pure wanderlust, or escape from persecution, or wanting to split away from the old society for other reasons, there will be great motivation for space colonization.

  • Bob Earley September 4, 2010, 14:08

    From the comments, not the posts, I’d think, What this site needs is a colonoscopy. Nothing but gung-ho colonists here. And they’re full of what?


    Show me the science or the technology that’s going to make some dot on the moon, Mars, anywhere off-earth, as habitable as Antarctica or the ocean floor. Show me how you’re going to pay for it. Show me.

    Because if we can’t maintain a biosphere on earth, especially if we can’t help but wreck what we’ve got now, how in the world are we going to sustain life off-earth? Don’t get me wrong, I’m all for it. I just don’t buy into any SFnal Santa Claus.

  • Eniac September 4, 2010, 23:28

    There is one very big difference between space and Antarctica or the ocean floor: Space is a lot bigger than Earth. That can make all the difference, because it offers a way out, ultimately, not just a niche.

  • intercostal September 5, 2010, 23:37

    The difficulty is getting the mass there, not habitability. We could do a ‘dome city’ (well, underground would be better…) on, say, the Moon. It’s simply a matter of replicating the natural ecological cycling of air, water, nutrients… (Water being the tricky part. The air is fairly simply done.)

    Actually, ‘test colonies’ in inhospitable parts of Earth would be a good proof-of-concept. I’d pick the Atacama Desert or Bonneville Salt Flats over Antarctica, though, since the waste-heat from such a colony might cause ice melting and stuff, and there’s the whole long-polar-night issue, too.

  • Bryan September 6, 2010, 1:50

    I think Anderson’s made a number of errors and oversimplifying assumptions in the quoted material above.

    Re von Neumann machines, two points. Firstly if you don’t want them to mutate it’s a perfectly straightforward to add as much error-checking rigor to their genome-replication routines as one desires. No “perhaps” about it, this is a well-explored area of computer science. And secondly, if von Neumann machines do start to mutate, they certainly _will_ be operated on by natural selection. Those whose mutations prevent them from leaving descendants will be supplanted by those without those mutations. Why would this not be the case?

    Re the “data flow” problem… well, who cares? Even if there really are fundamental bandwidth issues that will limit the flow of information back to the homeworld I don’t see why that would make any difference to an outlying colony’s decision whether to plant a colony yet farther out. _They_ won’t have a problem receiving information from their new neighbor. And it’s possible that these considerations won’t be relevant at all. Anderson seems to be assuming that the only important motivation for sending out colonies is to retrieve information for those sending out the colony ships, an assumption that I see no reason to make.

    Ultimately, whatever specific motivations and justifications that a civilization may have for sending out colony ships isn’t all that relevant. What’s important is that there will be lots of different motivations, some of which result in colonies being planted and some of which won’t. It’s incredibly short-sighted to assume that all civilizations throughout all of time and space will share just a single point of view on this.

  • Eniac September 6, 2010, 23:51

    Bryan: Very well said. I agree completely.

  • CP September 7, 2010, 20:19

    In his novel “Accelerando” (and in an earlier form, the shorter work “Scratch Monkey”) Charles Stross posits another explanation for the Fermi paradox: Life ultimately creates intelligent machines, which create more intelligent machines, which ultimately convert the entire mass of their home system into “computronium” (i.e., the theoretical arrangement of matter that is the most optimal possible form of computing device for that amount of matter), which provides the processing power/platform on which these super-intelligences will run.

    Once life looks like this, it’s very hard to get it to move outside its system. If a super-intelligence is running on a large amount of computronium, the energy required to move that mass becomes prohibitive. Moving the information is likewise difficult from the standpoint of bandwidth.

    So per Stross, the reason that civilizations don’t become interstellar is that intelligence rapidly bootstraps its way into a state that simply can’t be moved. Individual stars hosting intelligences of this kind might have specific types of spectral characteristics that would be detectable if we knew what to look for, but the pattern wouldn’t necessarily spread to the local environment in the same way that we might expect from colonization of von Neumann machines.

    The counter-argument to that view is that super-intelligences running on large amounts of computronium might still send “seeds” (lesser intelligences supported by less massive substrates) to neighboring stars.

  • tesh September 8, 2010, 5:07

    CP September 7, 2010 at 20:19

    on similar lines, it is just as likely we will go “inwards” as apposed to going “outwards”. Why would we not “travel” into an artificial/synthetic universe rather than the supposed real thing. We could create more and more complex versions, into which we could travel, until the complexity matches the observed “real” thing and then we could explore for ever or create a more complex or different versions.

  • Ronald September 8, 2010, 6:10

    @CP: though interesting, this theme is quite common and a bit of a cliché, also often mentioned here on this site in different versions, a civilization ultimately withdrawing into itself, introvert, even ‘uploading’ of intelligence/consciousness from organic into computers and the like.

    My basic objection against that is not only that it is highly speculative, about as speculative as the whole idea of singularity and ‘uploading’, but even more so because it arrogantly determines an ultimate goal for a ‘higher’ civilization: maximum computing power, even if that means entirely depending on and submitting to artificial power and intelligence.

    This may seem a bit more civilized than another well-known variety of such speculation, namely that the ultimate goal of any higher civilization would be maximum energy harnessing, expressed as Dyson spheres/swarms and the like, but it is just as speculative, anthropocentric and even time/culture based (energy and computing power as limiting factors are sooo late 20th/early 21st century).

    Truth is that we simply do not know what the ultimate goals of another, much higher developed, civilization are, what makes them tick. What they would really (REALLY) want to achieve once their long-term survival is reasonably guaranteed.

    For that is the only issue that I boldly dare mention as the most likely and immediate goal of any civilization: long-term survival. It is a law of nature and self-evident, any species and civilization not adhering to this quickly becoming extinct.

    For that reason also, I doubt whether any self-respecting civilization would just withdraw into an advanced state of technological navel-staring. Very risky and very naïve: a planet-wide highly developed techno-civilization may be very stable in itself (and working in information technology myself I even dare doubt that), but is also very (VERY) vulnerable to long-term stochastic (chance) extinction events. I would expect any such civilizations to at least strife to become multi-planet, even multi-planetary-system, as quickly as possible, since this is one of the surest ways of long-term survival (risk-spreading).

    After that, all bets are off, with regard to ‘higher’ (i.e. beyond survival) goals. When we look at ourselves, and particularly at very successful retired people whose Mazlov pyramid is almost completely fulfilled, we might get an idea of what at least our own intelligence seems to ultimately enjoy: studying, travelling, gardening and so.

    Though admittedly just as speculative, I just like this idea at a galactic, or even intergalactic, level: a higher civilization, whose long-term survival is well guaranteed, going around a galaxy observing, studying and seeding its life on lifeless planets, the Eternal Gardeners.

    In this respect also, the potentially truly dangerous aliens aren’t those that have reached that level, but those that are still in some advanced stage of struggle for survival, for which purpose they consider they need more habitable planets.

  • Ronald September 13, 2010, 5:18

    Also see the later thread on star clusters and (the absence of) hot Jupiters(https://www.centauri-dreams.org/?p=14297&cpage=1#comment-83778).
    Open star clusters of approximately the same age and metallicity as our sun, such as particularly M67, might be the best place to expect envelope/bubble-like expansion of a civilization, because of the relative proximity of other sunlike stars and planetary systems.

  • ljk January 27, 2012, 10:59


    by Dr. Robert A. Freitas Jr.

    Isaac Asimov’s Science Fiction Magazine 8 (September, 1984):30-44.

    Note: This web version is derived from an earlier draft of the paper and may possibly differ in some substantial aspects from the final published paper.

    In his Viewpoint article, “The Fermi Paradox,” last Issue, Stephen L. Gillett argued that the theory of a universe populated by aliens was untenable. This month we present Dr. Robert A. Freitas Jr.’s defense of the right to posit the extraterrestriaI’s existence.

    The author has performed three SETI searches, two of them the first ever to look for Interstellar probes in Earth orbit, the third a standard radio search, but at an unusual frequency. He is currently completing a book on extraterrestrial life, called Xenology.

    Have you ever seen a lemming? I must admit I haven’t, at least not in the pelt. I hear they live in the Scandinavian highlands and the North American tundra.

    Only problem is-I’ve just figured out they can’t exist!

    Full article here:


    To quote:

    “Of alien planetary or solar system cultures, or small galactic civilizations we can know next to nothing. We can only see out along the galactic plane a few kiloparsecs because interstellar gas and dust obscure the view.”

  • ljk February 29, 2012, 11:52

    Eric M. Jones did some research on the validity of the origin of the Fermi Paradox, namely that the great physicist Enrico Fermi one day during a discussion at lunch at Los Alamos in 1950 asked “Where is everybody?” in terms of alien visitors to Earth.

    Here is the paper: