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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.

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Comments on this entry are closed.

  • Alex Tolley August 30, 2010, 9:16

    Why the requirement for information to travel to the center? This seems like an “imperialistic” expansion model to me. Life doesn’t work this way, nor has human expansion. If each culture needs to justify its exploration costs with returns, there is no reason why the information trade should extend beyond the local bubble, but with each new star system occupied, a new bubble starts.

    As for the breakdown of replicating probes, I don’t buy that argument either. The trick is to ensure that they are built so that code modifications are not brittle so that the machines would slowly evolve as life has when finding new, open territories. Whether that is desirable is another question.

  • Mark Wakely August 30, 2010, 11:13

    Rather than a bubble or sphere of exploration, it’s easier to imagine a lighting bolt or a crooked tree as more representative of the shape. Advanced civilizations with the new ability to reach neighboring stars would likely start with the closest star systems of interest, then push out from there to the next one of interest and so on, with the occasional “branch” to promising nearby stars. These crooked paths would leave large voids and gaps in the sphere surrounding the civilization’s home planet, places where no stars or no planets deemed worth visiting exist. This lightning bolt or tree shape would likely stop when the next star of opportunity is beyond that civilization’s reach, either due to stretched resources or extreme distance to the next worthwhile star. (Instead of a bridge too far, think of it as a star too far.) At some point one of these “outpost” civilizations might grow enough to resume outward expansion, but the bolt or tree pattern of exploration would likely be the same. Whether or not information would “have” to return to the home world is another matter, but that would have little impact on the pattern. And of course the outpost civilizations might eventually evolve so far apart from their parent civilization as to virtually constitute alien civilizations themselves, but that too is another matter.

  • Michael Gauthier August 30, 2010, 11:24

    Now, I would hate to find the universe devoid of alien civilization, but I think Poul Anderson really missed the mark on this one.

    Like Alex said, human expansion did not mirror an expanding bubble, and neither does life. After all of history, our politicians do not report back to ancient Sumer. Mesopotamia is not the center of our information networks. I would argue that isolation from the center of a civilization, whether caused by geography or time, would give rise to the same process of nation-building and proliferation as Earth experienced in the past.

    Solving the replication issue is conceptually very simple: create “natural” selection. Program every machine to exchange information with another before reproducing. Program each machine to seek desireable traits in a partner. For example, if the prospective mate for a machine is an asteroid miner, the machine would favor the most efficient asteroid miners. The least efficient asteroid miners would fail to pass on their defective data. As strange as it sounds, giving the machines something akin to a social life would solve this issue.

    I wish Poul Anderson’s answer to the Fermi Paradox was convincing, but it is not.

  • Scott G August 30, 2010, 11:58

    Anderson’s bubble/saturation idea an interesting solution to the Fermi Paradox. However, I must say that I find it almost equally likely that at least one civilization has bothered to send a reconnaissance probe here within the last 250 million years or so. (Macroscopic complex life is just so interesting!) Whether we’re being watched right now is another question. I think the likelihood is small, but large enough to investigate it further. I’d really like to see a SETI research-group put a satellite up (~ 2-3 million miles from Earth) and point it back towards us to listen for any hypothetical ET transmissions coming from near-Earth space aimed back towards a home star. Sounds (and is) kind of crazy, but I think it’s likely enough that it would be worth the expense.

  • Pat Galea August 30, 2010, 12:14

    Alex, I share your thoughts on this. In fact, I’ll copy here an email that I wrote earlier this month on this very topic.

    —-

    I find Poul Anderson’s letter interesting, but unsatisfying.

    He says that the replicating probes will ultimately become extinct through mutation and degradation. But why should this be so? If each generation spawns a digital copy of itself, complete with good error correction algorithms, then there is no reason why faithful copies should not be made ad infinitum. He also says that there is no natural selection mechanism, but I don’t understand this. Surely if there are any unsuccessful copies, they will either fail to reach their destination, or fail to reproduce. This is natural selection at work. Only the copies that can reproduce and travel to their destinations will, by definition, be able to spam themselves throughout the galaxy.

    However, faithful copies may not even be the optimal strategy at all. The civilization may emulate nature, creating equivalents of sexual reproduction with all the gene mixing that goes along with it. And perhaps each generation will run virtual environments (in a Queen Bee?) that can try out different mutations and sex combinations in a simulated world before using actual resources to create the next generation.

    His other point about the diminishing returns of probes further out is true but of limited scope. It only applies if you think of the civilization as existing at one central point, with all the data flooding back into the heart. But if the probes are intelligent (or even sentient) enough to be considered members of the civilization themselves, then it is no longer centralized, but a distributed decentralized civilization. Each location they inhabit is the center of their own civilization, rather than an outpost of a distant home.

    But even without this decentralization, Anderson disparages the reception of ancient data, saying that it is of “academic” interest only. But isn’t that true of most data that they will be getting, even from closer probes? I’m very doubtful that our understanding of the cosmic microwave background is going to make a better toothpaste. Maybe one day, but for the forseeable future it is of academic interest. We still want to know, though. Likewise, I can’t see any reason why a civilization would deliberately limit its automatically-reproducing probe explorations. It’s effectively free data, as far as they’re concerned. Von Neumann probes are the ultimate “fire and forget” explorers. And we humans should know!

    [img src=”http://imgs.xkcd.com/comics/advanced_technology.png”]

    http://xkcd.com/387/

  • Erik Anderson August 30, 2010, 13:35

    I generally favor the idea that Earth hosts the only civilized society within the Milky Way Galaxy — or even within the portion of the universe in our past light-cone. But I’m willing to entertain a few alternate solutions to the Fermi Paradox that would allow at least one more M.W. civilization.

    #1) Other habitable planets in our Galaxy are so few and far between, or even impossible to find, that other M.W. civilizations cannot overcome the first hurdles of branching out.

    #2) The distribution of habitable worlds is only dense enough to facilitate migration along the paths of the Galactic spiral arms. Thus, one or more civilizations originating in the Galaxy’s other spiral arm* could now populate the Galaxy at every longitude, yet miss the Solar neighborhood entirely.

    #3) If a Galaxy-wide starburst event was the cause of the “Snowball Earth” episode ~500 million years ago (See: Svensmark & Calder, “The Chilling Stars”) which immediately preceded the Cambrian explosion, then it stands to reason that other habitable worlds across the Galaxy underwent similar episodes simultaneously. This perhaps “synchronized” biological evolution on a Galactic scale, perhaps allowing other civilizations to emerge before the first one conquers all worlds.

    *Note: I take the M.W. to be a 2-armed spiral (not 4-) and the sun’s position to be in one of these arms (not between arms) — see my website link for details.

  • Carl Keller August 30, 2010, 13:41

    Autumn is coming, along with the spectacular early-evening view of Andromeda and Perseus. A clear sky with good-aperture binoculars -50mm are good- will show details in that part of our galaxy which naked eyes and high magnifications will not: the sheer vistas of star associations like Alpha Persei, globulars such as the Double Cluster, and the remoter stellar and nebular populations which merge from individual stars to star clouds.

    If you take some time to let it sink in the scale of what this view holds, the notion of even a very long-lived civilization visiting most of them is a tremendous idea. We can enter space, but conquer it?

    Poul’s comment about degradation over the ages was the subject of Clarke’s 3001. Several readers panned the work, but it brought a fresh view of a thousand years from now by a trusted writer. And his monolith technology was limited to the speed of light, refreshing in these days of Trek and Wars.

  • Scott G August 30, 2010, 15:18

    Regarding Pat’s comment on the error correction algorithms… I suppose it’s also possible for the software that does the error correcting to develop a bug itself — which would require meta-error correction software, and then that would require meta-meta-error correction software, etc.

    And a related point: are Von Neumann probes even possible?? I can’t imagine a probe — however talented — being able to produce an exact copy of itself. I say this because there’s always some other component — machinery/instruments/inspectors — involved in the manufacturing process. Now, would a self-replicating probe have to build the entire factory (and educate it’s workforce) first, in order to reproduce itself? I can see a scenario of a near-self replica, but not an EXACT self replica — which destroys the notion of self-replicating probes conquering the galaxy in the first place.

    One final thought. It seems the Fermi Paradox comes down to this: unimaginable technology versus unimaginable distance. No wonder it’s so hard to guess which one wins out!

  • ad August 30, 2010, 15:31

    Only the copies that can reproduce and travel to their destinations will, by definition, be able to spam themselves throughout the galaxy.

    Pat, does this not imply that mutant self-replicating probes will eventually eat every planet in the Galaxy? Naturally, we should expect to find ourselves on one of the as-yet uneaten planets.

    I am not sure how long this argument would suggest we have to wait before we are eaten.

  • Tulse August 30, 2010, 15:39

    “does this not imply that mutant self-replicating probes will eventually eat every planet in the Galaxy?”

    I believe that is the premise of quite a few science fiction stories.

  • Paul D. August 30, 2010, 16:07

    Probes may not be able to make exact copies of themselves — but they should be able (with exponentially small chance of failure) make exact copies of their programs. Error correcting codes and redundancy should make the chance of mutation arbitrarily small.

  • Eniac August 30, 2010, 16:15

    Mark: The only way expansion could be sparser than a bubble is if the inhabitants of each star system somehow decided to only colonize one other system and then stop. Everything more than that (even just 1.0001 colonizations per system) leads to exponential growth and will eventually fill the entire expansion shell, which grows (sub-exponentially) with the square of distance and time.

    With the greatest respect for Poul, I agree with Alex, Michael, and Pat that he got this one wrong on both counts. However, I think Poul had the insight that the vast distances are not conducive to the formation of large empires or coherent civilizations. I believe there will be so little exchange between individual colonies that the “civilization” we talk about would really just be a collection of completely independent societies minimally linked by a common history and whatever cultural interchange is durable enough to be still relevant after decades long turnaround times. After a few millennia of divergence, the civilizations on adjacent star systems will be so alien to each other that they may as well have descended from different biological mother worlds. Yet, despite this lack of coordination, expansion will proceed spherically, somewhat like the growth of a bacterial colony in a Petri dish.

    I believe self-replicating machines would (and should) be designed to reproduce 100% faithfully, anything else would be reckless. As others have noted, and contrary to Poul’s assertion, this is quite possible with proper redundancy and error-correcting mechanisms. The original builders would (and should) retain the capability to send design updates down the chain, to address unanticipated problems and improve performance over time.

  • Interstellar Bill August 30, 2010, 16:15

    No intelligent race would go to the stars hoping to find habitable planets near enough to colonize. They would go because their own star had been completely enveloped by a Dyson Swarm of mega-Habitats, each with millions of people. They would go to young stars with disks of dispersed matter that could much more easily be made into mega-Habs than could planetary matter. A star of only 10 solar masses could host a 10,000 times bigger Swarm, enough to dominate space out to at least a hundred light years.

    Another thing everybody forgets is that once you’re at relativistic speeds the big cost is to slow down and stop, which means that you might as well go a long ways and beat the competition to the biggest clusters of massive young stars. There’d be no pussy-footing to a few nearby stars and then quitting, no squirting out a few robot probes and gathering data. The biggest stars in the Galaxy would be settled out in a mere million years and the rest in ten more. Then the Magellanic Clouds and M31 would go Dark too.

    The rare metazoan-drenched lifeworld such as this would be highly quarantined, but the Galaxy going Dark as it gets Swarmed is not something that could be hidden from any aboriginals techies on said rare planet.

    If intelligent life is so abundant that there’s one close by for us to talk to,
    then at least one somewhere would have Swarmed its own supercluster, but…
    we see no Galaxies going Dark anywhere in our light cone,
    so therefore….. We Are Alone.
    Get over it.

  • Eniac August 30, 2010, 16:33

    Regarding Pat’s comment on the error correction algorithms… I suppose it’s also possible for the software that does the error correcting to develop a bug itself — which would require meta-error correction software, and then that would require meta-meta-error correction software, etc.

    No, the error correcting software simply corrects ALL the code, including its own. If you build in independent data checks in sufficiently many places along the replication pathway, you can easily reduce the risk of mutation arbitrarily close to zero, say to once every 10^1000 generations.

    And a related point: are Von Neumann probes even possible?? I can’t imagine a probe — however talented — being able to produce an exact copy of itself.

    That’s what von Neumann proved, which is why they carry his name. You may want to browse (or even read) this very excellent book on the subject:

    http://www.molecularassembler.com/KSRM.htm

  • NS August 30, 2010, 17:02

    Here’s a paper that tries to explain the Fermi Paradox using percolation theory (which some posters have touched on):

    http://www.geoffreylandis.com/percolation.htp

  • Eniac August 30, 2010, 17:49

    Pat, does this not imply that mutant self-replicating probes will eventually eat every planet in the Galaxy? Naturally, we should expect to find ourselves on one of the as-yet uneaten planets.

    I am not sure how long this argument would suggest we have to wait before we are eaten.

    Let me give this a try: If voracious self-replicating probes occurred in the galaxy much more often than once every few billion years, our planet would have been eaten long ago. Thus, we probably have to wait another billion years or so until we are eaten. Unless, that is, we build our own. In that case, if we cannot make sure ours will stay away from Earth as food, it could be just a few millennia.

    Seriously, though, properly designed probes would just find a few asteroids or innermost rocky planets to settle on for the long haul and refrain from eating or even nibbling on the rest of the system, in order to avoid angering the natives.

  • Ronald August 30, 2010, 18:17

    You can say of Poul Anderson what you like, but he (indirectly) made me realize something quite relevant with regard to (the fallibility of) self-replicating machines, which many people may overlook: precisely their ability and characteristic to copy themselves exactly and reliably might also be their weakness. Widely varying circumstances require great adaptability and hence (numerous, random) mutations. Self-replicating machines are basically a monoculture. It is precisely the inconsistency of the genetic code, which is at the same time its success, the code varies at random and nature selects for the best adapted. Surely, one could program a certain degree of adaptability, but basically those machines are copy-cats.
    And it remains to be seen whether any machine would ever be as successful in adaptation as molecular carbon-based life.

  • Ronald August 30, 2010, 18:25

    Interstellar Bill: your, more often cited, argument is based on the very unfounded premise that the ultimate goal of any ‘higher’ civilization would be to completely utilize its star’s energy output and/or reach maximum population size, instead of utilizing as much of it as this civilization needs for its other, ‘higher’ purposes, whatever those may be. This is about as logical as it would be for us to use any resource fully, as a goal in itself. This issue has been discussed here before in a few threads on Dyson spheres/swarms and the like.
    Sure, abundant energy is absolutely vital for any civilization, but *maximum* consumption of it as a goal is so 20th century ;-)

  • Curt Sandberg August 30, 2010, 19:47

    IMHO, the arrogance of human thought appears in each and every answer provided to this point. However, I cannot say that my reaction is any better, just perhaps less “homo sapiens-centric”, i.e.,:

    Just as humans dare to express what their religion says about God, what makes any of us unemotionally capable of rationally expressing alien sentiments, goals, desires, physical or mental limitations, etc?

    We, homo sapiens, are irrationally destroying our home planet even as we electronically write our thoughts. We seek continuous growth in wealth, population, and GNP. These are not universal goals — or, at least, I hope and pray that they are not!

    Thus, to a certain extent, for us to state why other advanced civilizations or entities have not made their presence known to us is akin to discussing the numbers of angels capable of being present on the head of a pin.

    While I admit it is fun to pursue the thoughts and goals that would lead to homo sapiens becoming a significant factor in the biological evolution and eventual humanizing of our Milky Way neighborhood, let’s stop wasting our energies on explicitly stating why or why not we do not currently know of other “intelligient entities”.

  • Ron S August 30, 2010, 20:08

    I find it interesting that intelligent machines with self-correcting hardware and software, and with progeny that they can repair or reject based on the fidelity of the transcription, can sit at their computers and type in that this is not possible.

  • Geoff August 30, 2010, 21:34

    Anderson’s data-overload argument may be valid for ordinary stars and planets. But it doesn’t apply to astrophysical objects which are so rare that only a few exist in the whole galaxy. Even if most of a civilization is content to stay within a small bubble, the scientists will want to send probes much farther, to investigate pulsars, O stars, black holes, etc. To assume otherwise is to posit a technological civilization with no interest in science – surely a contradiction.

    Now note that the Earth belongs to just such a class of rare objects…..

  • Robin Goodfellow August 30, 2010, 22:23

    Fermi’s paradox has an easy but unsatisfying resolution: we do not know enough about interstellar civilizations to estimate their behavior.

    It’s the same as the old “problem” of the bumble bee. If you imagine that a bumble bee works by the same principles as a propeller aircraft and you do all the necessary calculations you find out that the bumble bee can’t fly. But what does that mean? That bumble bees can’t fly? Or more that bumble bee flight doesn’t operate by the same principles as conventional winged aircraft? Since we know bumble bees do indeed fly we know the answer (and modern experimentation has ferreted out the true mechanisms behind bumble bee flight). Today we do not have the strong counter-example of a physical reality pointing out that our pre-conceived imaginings about the way interstellar civilizations operate are in error, but that seems to me to be the overwhelmingly likely prospect.

    We have learned much about the universe in the last several centuries, but our ignorance still outweighs our knowledge by leaps and bounds. We are only now acquiring the slimmest of slices of knowledge on the nature and abundance of planets in our stellar neighborhood. The idea that we can confidently estimate the behavior of civilizations many generations more advanced than our own operating within environments we scarcely understand is little more than mental masturbation.

  • bill fish August 30, 2010, 22:37

    If one is talking about space travel, cosmic rays come into play in terms of bringing about errors in the hardware and software.

    I am not very familiar with the Neumann machines. Are the errors assumed to be random and rare? I see the cosmic ray damage being both random and clustered (a fast neutron can leave a long trail of damage).

  • Leonard August 31, 2010, 1:43

    Von Neumann´s probes hipotesis is irrelevant. We all, biological beings, are self-replicants machines! A Von Neumann´s probe is equivalent to an upgrade of our body, but it´s not something radically different, from my point of view.

  • Gary B August 31, 2010, 4:57

    Thanks for the interesting article and posts. I am reminded of two things. The first is that Ray Bradbury, I recall, suggested that all science fiction is actually fashioned of stories about ourselves, because we do not escape our own self-conceptualization and the limitations of human cognition. The second is that Darwin’s observations and subsequent theory suggest that “fidelity of the transcription” is nothing short of untrue as regards nature in general as it evolves. We are a part of that changing nature. Imagine that everyone today would be commenting based on replicated MS-DOS of the earliest sort rather than through their up-to-date PC and Apple software; it would be rather antiquated, I imagine we might agree. A decade from now, the stuff we are using now will called “obsolete.” Therefore the notion that “today” tells us that much about tomorrow might well be specious, however exciting it is to contemplate what all our species’ and machines’ tomorrows will bring. Perhaps those “they” others which have contemplated another cosmological species “out there” might well have concluded something quite other than “explore at all costs.” Or perhaps other forms of life have such different conceptions of life itself that they are not bothering to look for us. I note that Project Icarus has taken its name from a mythic character which failed to achieve the largest objective and fell to earth. How many of our conjectures are Icarus-like? Fermi asks in his paradox for demonstrable, scientifically-validated proof — where are they? Your fine article says, “Where are they indeed.”

    As to the dour comments about “destroying the planet,” I imagine that the planet will be around long, long after the time span from early man to Homo sapiens is passed again. Such commentary is political in tone, and not particularly scientific, as well as perhaps not up to the literary standards of science fiction. We humans have been telling ourselves stories of utter destruction since “being driven out of the garden” and “flood” myths. And that amount of time, compared to the time from early man to today, is but a fleeting moment. To tell such stories of dire warning is a part of early religious thought, as of modern science-fiction. It is not a part of hard science, for the planet and life upon it have been here and likely will be here long after human storytellers have wearied of each newly imagined Armageddon. Several thousand years of tales of panic have usually served to control others, not adequately describe the world of any given time, anyway.

    Let’s ask Fermi’s question again. “Where are they?” A portion of the answer is alreay known. As a part of nature, we as a part of the larger “they” are already here. So we know that much. Now it’s only time to listen patiently while reaching out patiently. If there is another “we” thinking as we do, the proof will be unequivocal. Until then, what jolly fun to dream Centauri dreams and tell our explorer stories to each other, which is so deeply a part of our most human nature. Thanks for the thought-provoking articles and your site.

  • Adam August 31, 2010, 5:29

    Ron S makes a point which needs emphasising – intelligent, self-replicating machines with a deep wanderlust are needed to explore and ultimately colonize the Galaxy… which fits at least some members of our own species. That we might need serious augmentation to achieve the goal should be no impediment to us ultimately adapting ourselves to the task. Why leave it to “machines” which’ll be essentially ourselves remodelled for the task anyway?

  • Ronald August 31, 2010, 5:57

    The simplest and most obvious explanations to the Fermi Paradox still seem to be, at least pertaining to our MW galaxy:
    – Scarcity of (higher) life;
    – Scarcity of intelligent life;
    – Scarcity of technological civilization originating;
    – Scarcity of techno-civilizations surviving;
    – Scarcity of techno civs able to bridge the gap between the stars.

    In increasing order of scarcity, each next step being a subset of the previous, like higher levels in a game. My assumption is that, once a techno civ becomes truly space rafing, i.e. able to travel to other planetary systems, then:
    1) Such a civilization and species become virtually immortal, at least as a source and continuation of new off-shoots;
    2) Such a civilization would always know where the interesting (habitable and actually life-bearing) planets are in the MW and would always be highly interested in those, particularly if they possess higher life.

    There have been a few recent articles here with regard to attempts to estimate/guesstimate the number of habitable planets in our MW galaxy. These varied roughly from 50 – 200 million. That may seem like a lot, but really isn’t, considering the above-mentioned barriers that have to be taken. Particularly the last one, bridging the gap between the stars, may have proven to be too formidable for the undoubdtedly relatively small number of budding intelligences and civilizations. After all, we humans have existed for several hunderd thousand years as an intelligent species and thousands of years as several civilizations. And only very recently we have started seriously considering space travel, even now not being able to get much farther than our own solar system.

    First things first: let’s first and foremost acquire a more or less complete picture of planetary systems in our (part of the) MW and of planetary biosignatures. A very doable target. This may already answer part of the Fermi paradox.

  • Scott G August 31, 2010, 9:32

    Eniac — I still have a serious problem accepting the idea that Von Neumann probes will EVER exist. I don’t doubt that at some point we (or others) will be capable of inventing molecule-sized (and eventually macroscopic) self-replicating machines.

    What I’m arguing is that I do not believe that we can ever encapsulate an entire rocket-ship/spacecraft production complex into one probe. You do realize that a self-replicating PROBE means that it will not only have to reproduce a clone of itself from raw materials, but will also have to build something akin to a Saturn V to propel it’s clones on to other star systems. (And now we’re talking cryogenic, nuclear, electric, or anti-matter propulsion systems — each requiring many additional machines, specialized factories, and storage facilities to produce. Not to mention the other 1-2 million or so parts in a rocket.)

    You see where I’m going with this? If we could compile every piece of machinery, production process, and underlying knowledge involved in producing a functioning/flying spacecraft, we’d have a list 1,000,000+ pages long. I don’t think that anyone has ever proved that THIS is possible. (Not saying that we couldn’t find SOME WAY to do it, but I just don’t ever see us, or any advanced species for that matter, ever undertaking such an extreme engineering feat.) It clearly would not be worth it. Not for us. Not for anyone.

    I think we need to do away with the notion that a lack of Von Nuemann probes implies a lack of intelligent species in the Milky Way. A lack of Von Neumann probes most-likely means that it’s a ridiculous idea that’s so astoundingly complex that no one has ever decided to pursue it.

    PS – thanks for the link; I really do appreciate it and will definitely take a look at it! I want to be convinced otherwise!

  • stephen August 31, 2010, 9:54

    Interstellar Bill said,”If intelligent life is so abundant that there’s one close by for us to talk to, then at least one somewhere would have Swarmed its own supercluster, but… we see no Galaxies going Dark anywhere in our light cone,
    so therefore….. We Are Alone.”

    But maps of galaxies show vast regions in intergalactic space, where there don’t seem to be any galaxies. Maybe that’s where the aliens are, building vast structures.

    Why would they necessarily feel like reproducing? Among human societies, the wealthier groups tend to have fewer offspring, or so I’ve read.

    Aliens might have different feelings about that sort of thing, of course.

    How do we know they aren’t here visiting already? They might have probes disguised as gnats, or bacteria.

    Star Trek’s Prime Directive wasn’t handled very well in the episodes, but the general idea seems plausible enough, aliens not revealing themselves to the beings they’re studying.

  • Greg August 31, 2010, 13:11

    I’ll echo what others have said, thanks for the interesting post! I enjoyed Mr. Anderson books growing up immensely. I do believe Poul has some merit in his idea of a ‘bubble’ of expansion. When the US was being colonized for the first couple of centuries most travel occurring was back to the countries of origin, that would have been the ‘bubble’ as I believe Poul was talking about. Only after the US was established and it was self-sufficient to survive on it’s own were we able to a “bubble” of expansion on our own. Even now look how far have we colonized the solar system? Even though we know there are far more easily accessible resources in the Asteroids than can be gotten at the bottom of a gravity well such as earth. Really why we haven’t is because we don’t have a real pressing need to. No demand for it as yet. I think it will be much like that for other civilizations.

  • Henk August 31, 2010, 15:39

    I agree with some of the above posts that a large civilization would actually consist of many smaller empires due to the lack of efficient communication and therefore inefficiency of centralized goverments. If human history is anything to go by, differences between these empires can escalate into war. planetary biospheres and other habitats are relatively fragile targets that are hard to move and it may therefore be very unwise to advertise your current status and position to the entire universe, parts of your empire, their AI or god knows what may have turned against you years ago, the news may just not have reached you yet. Sure, other civilizations may have more peacefull histories than we have had, and may just get along with eachother, but in general it may be wise to be stealthy, and undetectable.

    I personally think it’s more plausible that the lack of signals indicates that we are alone out here, but it’s always fun to speculate.

  • Eniac August 31, 2010, 16:29

    Scott:

    What I’m arguing is that I do not believe that we can ever encapsulate an entire rocket-ship/spacecraft production complex into one probe. You do realize that a self-replicating PROBE means that it will not only have to reproduce a clone of itself from raw materials, but will also have to build something akin to a Saturn V to propel it’s clones on to other star systems. (And now we’re talking cryogenic, nuclear, electric, or anti-matter propulsion systems — each requiring many additional machines, specialized factories, and storage facilities to produce. Not to mention the other 1-2 million or so parts in a rocket.)

    The way the argument goes is: A self-replicating machine can build itself, it is a small step to have it build most everything else. Why a small step? Because a self-replicating machine is among the more complex and difficult things to build. Comparable, say, to a space shuttle or a star ship in complexity. If you can do one, you can do the others, too, with manageable extra effort.

    How complex it really is remains to be seen, could be more or less than a space shuttle. Most people think, though that the difference is not going to be orders of magnitude, and the gene count of self-replicating organisms is one indicator of that.

    If we could compile every piece of machinery, production process, and underlying knowledge involved in producing a functioning/flying spacecraft, we’d have a list 1,000,000+ pages long. I don’t think that anyone has ever proved that THIS is possible. (Not saying that we couldn’t find SOME WAY to do it, but I just don’t ever see us, or any advanced species for that matter, ever undertaking such an extreme engineering feat.) It clearly would not be worth it. Not for us. Not for anyone.

    I am not sure I understand you. To me, the fact that we actually DO build functioning/flying spacecraft means that we have done just what you seem to be worrying is impossible. For every piece of machinery, production process, and underlying knowledge involved in producing a functioning/flying spacecraft, there is a blueprint, SOP, or book somewhere, you bet. And I am pretty sure if you are, say, a safety inspector, you can actually ferret out any specific piece of that within a few days without undue exertion. The fact that we have lots of spacecraft flying around in orbit says that we can even make the whole thing work together, in its entirety, routinely.

    Yes, it will be difficult to create a self replicating machine, and a million pages may well be a realistic estimate for the size of its specification. However, I think that having the machine will actually make the engineering of any other machines easier than it is now, and the production process MUCH cheaper.

    BTW, a million pages is roughly 1 gigabyte, just about the size of the human genome.

  • Eniac August 31, 2010, 16:37

    Henk:

    I agree with some of the above posts that a large civilization would actually consist of many smaller empires due to the lack of efficient communication and therefore inefficiency of centralized goverments. If human history is anything to go by, differences between these empires can escalate into war.

    In my view the communication problem is so severe that war is completely pointless, if not impossible. It will be hard enough to come up with a reason to fight, and much harder still to fight over the enormous distance, with decades in between strike and counterstrike. Who has the patience, and over what?

  • Eniac August 31, 2010, 17:06

    BTW, a million pages is roughly 1 gigabyte, just about the size of the human genome.

    Some other interesting little tidbits:
    – The size of the U.S. code is estimated at greater than 42 million words.
    – Windows XP has around 40 million lines of code.
    – Some free-living, self-supporting and self-replicating microbes come in at under 2Mb of code and under 2000 genes.

    The last item suggests that 1 million pages of specification may be overkill, really, for an efficient design. And, that the Windows XP and the U.S. code could do with some more brevity. They are not even self-replicating. Luckily.

    Sources:

    http://computationallegalstudies.com/2009/11/08/facts-about-the-length-of-h-r-3962/
    http://en.wikipedia.org/wiki/Source_lines_of_code
    http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GenomeSizes.html

  • Bounty August 31, 2010, 17:50

    I think it’s funny that the ‘paradox’ is sort of self-fufilling, in that if our optimism is correct about how easy it will be to conquer the Milky Way, eventually there will be beacons and aliens all over the place. If it’s not that easy, you have your answer.

  • bigdan201 August 31, 2010, 18:53

    Indeed, the vast distances of space and the limit of c could definitely hold back the expansion of even an advanced alien race. Colonizing large parts of a galaxy is just not easy to do, unless you have technologies like controlled wormholes or foldspace, and they would be expensive in energy.

    It is difficult in general to extrapolate about what aliens would do.. there are certain evolutionary principles that should stay consistent, such as intelligence developing from social and aggressive creatures. And the scientific laws we’ve studied apply elsewhere too. but other than that, extrapolating is very difficult. Imagine an intelligent whale that assumes that there is no intelligent life on land because he’s never heard a whalesong from land.

    This problem of anthropomorphic bias applies not only to extrapolation, but communication.. as I’ve mentioned before. We need to keep our eyes and ears open to as many channels as possible to intercept alien signals. As far as the Fermi Paradox is concerned, the biggest issue is that we simply don’t observe enough of the sky. We can’t say that they’re not there when we aren’t listening to all signals from all of the sky, and we haven’t finished studying all the stars and exoplanets.

    Also, the speed of light delay means that the further they are from us, the longer it will take their signals to reach us. There could be aliens broadcasting 500 light years away, and we’d have no way of knowing (until 500 years from now)

    In conclusion, we simply don’t observe or know enough for the Fermi Paradox to be a dealbreaker.

  • Hank September 1, 2010, 0:12

    ” without any natural selections to winnow out the unfavourable majority”

    I actually don’t know about this- might the less successful machines be less likely to “reproduce?” Even if not, couldn’t the creator of the machine create something to simulate the effect of natural selection? I’m the absolute opposite of an expert, but still this assumption seems to be a bit excessive to me.

    But Mr. Anderson’s point is well taken- we don’t know how hard space exploration will be for an alien intelligence, or even for a more advanced version of ourselves. It could be… “very hard.”

  • Zen Blade September 1, 2010, 13:28

    Wow… looks like I chose a bad end of the month to pack and move…

    Great thread, but a few comments.

    1. This thread could really be broken into numerous sub-threads that might facilitate the varying discussions that are currently on-going.

    2. Paul, I would not assume that all of your audience is hardcore sci-fi/space people. I am not. I had never even heard of Mr. Anderson (outside of the Matrix). Which brings me to number #3.

    3. I don’t know how much of what people post is pure conjecture, opinion, belief without evidence, well-thought, conclusions based upon some data, or other… but a lot of the posts in this thread seem to lie within the conjecture/opinion/belief without evidence “section”.

    I find this annoying. Not because there is conjecture, but because people are using their own conjecture to trash a different opinion, one that is clearly attempting to make a significant point in good faith–even if not perfect.

    End part I

    -Zen Blade

  • Zen Blade September 1, 2010, 13:34

    Begin Part II (self-replicating machines)

    4. Regarding Self-replicating machines: While still computer science, this is also computer biology, potentially. Especially once people start to talk about having these machines reproduce sexually (for lack of a better term). Natural selection is NOT the same as “logical” selection.

    Anyone who would willingly create a new life form, which CAN AND WILL evolve INDEPENDENT of your intentions is playing with fire. None of us is smarter than the process of evolution because evolution tries as many (and eventually all) possible solutions as quickly as possible.
    Anyone who would allow that new organism to evolve in a free and open manner is potentially dangerous.
    Anyone who would allow that organism to go off into space and evolve and essentially “find itself” is not acting responsibly.

    We in the biological/life sciences do enough genetic engineering as it is, and some would like to claim creation of synthetic organisms… Yes, we let loose slightly modified plants, and undoubtedly other organisms in the future… but the creation of something so alien, or the release of an artificial organism into a new environment… that’s just not what an informed sane person would do.

    We are not smarter than random chance. We (collectively) have done countless experiments where it was only after the result that we realized what was going to happen. So, why would anyone sanction the independent releasing of a von Neumann probe…
    either:
    a) they will break down and never serve a purpose
    b) they will evolve and serve their own purpose (perhaps to our detriment)
    c) they will do exactly what we want because we are super smart and super lucky. It’s like how I trained my dog, only then my dog became 1,000,000,000 dogs.

    This is such a dangerous experiment, that even with “suicide programming” I would never want this done in an open environment. There are lots of ways to kill organisms that start to mutate or perform unwanted tasks… but letting these organisms into the natural environment is always a risk… this includes genetically modified plants. Just because something is great today, tomorrow, next year… that does not mean it will be great in 10, 100, 1000+ years.
    There are plenty examples of this occurring throughout human history. We start selecting for trait X, and then later that hurts us a lot because of some disease or some event that makes the inbred population incredibly susceptible.

    -Zen Blade

  • Zen Blade September 1, 2010, 13:49

    Begin part III:

    My thoughts on the bubbles, society, and Fermi paradox.

    I have listed some of my thoughts before, but essentially:

    1. Many people (including me perhaps) are still looking at the Fermi paradox from a pre-contact perspective. Thus, we are trapped in the paradox. If people instead try to look at the paradox from a post-contact perspective, it is no longer a paradox… but there are lots of very “I just want to be friends; you are not very sexy” answers… [in other words, answers that make us sort of sad]

    I think bubbles make a lot of sense. Central authority is not the issue, it is the problem. Without a central authority the time, money, and vision to conduct interstellar exploration/research will not exist. But, the larger the population/expansion of a civilization, the harder it is to keep central authority… Without the authority, we lose the desire/ability to put our collective resources into exploration because we need those resources for short term demands…more profits, lower taxes, education, healthcare, etc… new holobands…

    So, yes, a civilization bubbles into a dozen+ systems near its homeworld… but at that point maybe it has reached its maximum extent. There is no ability to expand further… the population becomes satiated. There is no such thing as continual endless expansion. There are booms and busts. And often whatever went bust does not begin the next boom. The next boom usually begins elsewhere or in a different field/technology…

    That’s my opinion on bubbles. We have seen it occur countless times in our history.

    Regarding my personal thoughts. Who really cares about making first contact…or second contact… or forty-third contact??? Society has a lot of other needs… We like what’s new. So, yeah, 1st, 2nd, 3rd contact would be cool. But after meeting those first few ETs… they would have just as many problems as we already have. Why spend the time/money/resources to find more?
    So, if they are already out there… maybe they just don’t care.

    I am optimistic that intelligent life is out there somewhere. I just am not optimistic that they would feel the need to meet us. Especially if they deal with things such as unemployment, downturns in their economy, physical limitations of expansion, and any number of local issues…

    -Zen Blade
    Sorry for the multiple posts. I thought it would be better to break things up.

  • Eniac September 1, 2010, 14:39

    So, yes, a civilization bubbles into a dozen+ systems near its homeworld… but at that point maybe it has reached its maximum extent. There is no ability to expand further… the population becomes satiated. There is no such thing as continual endless expansion.

    Why is the maximum extent a dozen? Why not a thousand, or one? As I said above, given the communication lag, I consider the maximum extent of any sort of coherent civilization to be a single system. But that does not mean there will not be colonization, it only means each colony will act on its own, without much help from or coordination with its ancestors and neighbors. Those at the boundary will colonize new systems for the same reasons their ancestors did.

    You are right there is no such thing as continual endless expansion, but the limits are external. A colony of bacteria will not stop growing until it completely covers its petri dish and runs out of nutrients. The individual bacteria do not know or care about the extent of the culture, they will multiply wherever there is nutrient. There is no way they could stop after a certain area is covered, even if they wanted to.

    Historically, neither life itself, nor we as its intelligent outgrowth have stopped expanding until the Earth was filled. Some think we are not done, even now…

  • Eniac September 1, 2010, 15:04

    Big Dan:

    Colonizing large parts of a galaxy is just not easy to do, unless you have technologies like controlled wormholes or foldspace, and they would be expensive in energy.

    I disagree. 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.

  • Eniac September 1, 2010, 16:54

    What I’m arguing is that I do not believe that we can ever encapsulate an entire rocket-ship/spacecraft production complex into one probe. You do realize that a self-replicating PROBE means that it will not only have to reproduce a clone of itself from raw materials, but will also have to build something akin to a Saturn V to propel it’s clones on to other star systems.

    The encapsulation of a self-replicating machine into a probe is an interesting problem. The probe will be designed to contain the minimum amount of machinery and provisions needed to bootstrap itself into a full complement of manufacturing hardware using only raw materials. It is an optimization problem with many interlocking decisions. For example, you can include with the probe a furnace for smelting iron. However, these things are heavy. You might be better off building a primitive furnace on location first, using mostly dirt and rock, in addition to more lightweight imported parts. The relationship between probe and full manufacturing facility is like that of a spore and mushroom, with emphasis on small size and economy in the spore, and emphasis on throughput and performance in the mushroom.

    The likely sequence is as follows: The probe is made mostly from “precious” parts and carries “precious” provisions, precious meaning hard to make. Upon landing, the probe will proceed, with its limited abilities, to process a limited set of raw materials into a limited set of different parts, just enough to assemble a larger facility that has a wider range of abilities than the probe. This may go through multiple stages until the full range of abilities has been reached, enough to reproduce the probe and its provisions. An example for a precious part would be microchips. The final stage will have to include a microchip manufacturing facility, but the probe itself needs no such capability. Instead, it needs to carry a supply of chips that will last until the final stage is built.

    I am no aerospace engineer, but I can imagine that 95% of the parts that make up a Saturn V are quite similar to parts you need for a self-replicating machine (think nuts and bolts), so the manufacture of those is already covered. The remaining 5% may need special facilities, but hopefully (or by design) those special facilities can be made from standard parts. You build the special facilities from standard parts, and then build the tricky parts using the special facilities. We know it can be done, because that is how we do things here at home. I think that once you can close the microchip loop, nothing we can build here on Earth is out of reach, including spacecraft.

    Remember that all we can build today ultimately comes from raw materials and started long ago with someone banging rocks together.

    Sorry about the multiple posts, I just can’t get enough of this stuff….

  • Zen Blade September 1, 2010, 17:24

    Eniac,

    Given the ability to communicate and to know of your recent progenitor planet/system, I think one can convincingly argue that newly expanded-into-systems will have a substantial amount of contact and there will be attempts to control/interact with one another… no matter how futile.

    During the periods of colonization/imperialism, distant lands were essentially independent (with different priorities from their motherlands), but each was, more often than not, caught up in the politics and conflicts of their motherland. I don’t think that model can be readily discarded.

    I should add that the independence of each colonized system will largely rest on population/resources/wealth… so, depending on how populated each system can become (relative to the cost to expand the population–food, water, etc…) that will also limit the independence of the system. If a system can only support a small population, but has great resources… it is a genuine colony, controllable and exploitable by the home system.

    My reason for saying “12+” is that I think a relatively small number of colonies will be affordable (if any). The cost of getting even a small population to a habitable, known world will be immense… and this assumes the colony has sufficient supplies and can live on said world without the need for constant support/relief supplies. The cost and will power to conduct such a long term (and risky) mission can undoubtedly be done under some set of circumstances… but I don’t think that number of times is infinite if one considers the quote “the bureaucracy is expanding to meet the needs of the ever-expanding bureaucracy.”

    Look at the US today versus the 80’s and 90’s. When I was a kid we had “biodome” or rather biosphere 2. Now, we talk about nothing but sending machines into space, and the public could not care less.
    Maybe if China decides to inhabit the moon we in the US will do something, but even then, I think we might pass given our money problems.

    -Zen Blade

  • Eniac September 1, 2010, 18:52

    Zen,

    Your arguments make sense if there were resources worth transporting over interstellar distances rather than develop locally. And if it made any sense to “control” a colony when it takes decades to just get a reply to a message. I think neither is the case. Our historic experience is inadequate to derive insight from on this, because even the most remote colonies were always reachable within weeks. However, note that historic colonies mostly became independent within decades despite plentiful communication and interchange.

  • bigdan201 September 1, 2010, 21:02

    I disagree. 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.

    True, you can continue to spread across the galaxy by repeating the steps of colonization. But colonizing a galaxy would take far more time than a star or several stars. And with more time, there is the question of how stable the civilization(s) will be. Even without warfare or social breakdown, there is also the consideration of distances and communication. Would aliens prefer to stay centralized in a certain galactic region?

    There’s much more to be learned about the universe, but that just makes things more interesting imo.

  • Scott G September 1, 2010, 22:32

    Eniac — That’s an interesting formula for a self-replication process. If Von Neumann probes are ever to become a reality, then that’s exactly the kind of thinking we will have to expand upon — eventually in excruciating detail.

    As for the “encapsulation” problem, I suppose there is SOME way to do it since we know that the number of steps required to build a spacecraft + launch vehicle (from raw materials) is finite, not infinite — but does that make it possible to package those into a flyable (and preferably lightweight) interstellar probe? I’m not so sure…

    Basically, I think that manufacturing the hardware on-site (as opposed to software errors) is the real show-stopper with Von Neumann probes. The sheer complexity of the operation will undoubtedly lead to (some) faulty hardware production that, if occurring early in the process, may cascade throughout the remaining production process resulting in non-functioning, or even unfinished offspring probes.

    I’m still convinced that it’ll be easier to accelerate a fleet of interstellar reconnaissance probes to 0.90c than it will be to build a single reliable Von Neumann probe.

  • amphiox September 1, 2010, 23:42

    What I’m arguing is that I do not believe that we can ever encapsulate an entire rocket-ship/spacecraft production complex into one probe.

    That isn’t actually necessary. And we can use the same solution that biology does – namely differentiation and specialization.

    Start with a probe that has intelligence roughly equivalent to a single human being, and a manual dexterity roughly similar to a single bare-handed human. You can send it off alone or with a supply of critical and hard to obtain components/raw materials if you want to be safe and can afford the additional resources.

    When it lands it starts by replicating itself with its supply of critical components and local materials. After sufficient rounds of replication, the progeny differentiate into “workers”, who fashion simple tools out of local materials, no more complex that the stone tools used by early man (and we know that a probe with human level intelligence and human level dexterity can do this). They then use these simple tools to make more complex tools, and repeat this process, up to and including more sophisticated and specialized “workers”, until they’ve built an entire manufacturing complex, with resource harvesting, transport, and refining specialized subdivisions. And we know this is quite possible for probes with human level intelligence and human level dexterity, since it has already been done. Finally the manufacturing complex produces launch vehicles, each equipped with a single generalist probe and the bootstrap critical components, and launches them.

    With some fine tuning and clever engineering, it’s quite probable that the original start-up probe won’t even need to be as sophisticated as a human being. (With a few extra steps, you could probably go all the way down to a probe the size of sophistication of say an ant.)