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  • So where is everybody?

    Posted by ken on September 14th, 2004 (All posts by )

    The age of the Earth is approximately five billion years. That’s an awfully long time. I see no evidence that the evolution of sentient creatures on this planet took place faster here than it possibly could anywhere else. We get more cosmic radiation than some other places, and much less than others. The course of biological evolution was drastically altered several times by catastrophic impacts with extraterrestrial bodies; I don’t see any reason to believe that these impacts were timed to minimize the time required to evolve sentient life.

    Thus, if this galaxy were destined to develop one other sentient race in its entire history, I’d give at least even odds of it having occured already. If it were to develop many other sentient races over the course of its entire history, odds approach certainty that at least one of them evolved a long time ago.

    “Long time” as in hundreds of millions or billions of years ago.

    A race that evolved to spacefaring stage as recently as 100 million years ago anywhere in our galaxy would have to be spreading outward at less than 1/943 lightspeed; any faster, and they’d have settled our solar system by now. One hundred million years of technological advancement seems unlikely to end in drives that can only do a small fraction of lightspeed. Even at 1% of lightspeed, that other spacefaring race would have had to evolve and acquire spaceflight less than 10 million years ago, the blink of an eye in the grand scheme of things.

    So where is everybody? Why was this planet empty when we evolved? The most plausible (and most pessimistic) explanation I can think of is that the problem of maintaining a good government and a free society long enough to develop civilian spaceflight doesn’t have a workable solution.

    In total, I can think of only a few good reasons. One, intelligent creatures don’t exist anywhere else in this galaxy and never did. Two, they don’t want to go anywhere near star systems; perhaps they have a method of converting “dark matter” to regular matter and tend to look for concentrations of dark matter rather than stars and planets. Or three, intelligent aliens exist, but they never become starfaring for some reason.

    The first possibility seems ludicrous, at least to me. There’s just too many stars in this galaxy, and too much time has gone by. I find the second more plausible But the third possibility, that intelligent creatures never become starfaring, is more than a little frightening and chillingly plausible to my mind.

    If intelligent creatures are common, and none of them ever become starfaring, then whatever is stopping them should also affect us. Carl Sagan, among others, speculated that the development of nuclear weapons was the dead end; if so, we might be in the clear. Alternatively, if the development of cheap and abundant antimatter production happens before the development of good space habitats that can be widely separated, then small groups or even individuals can acquire the means to destroy their civilizations, and at least among humans there’s a small fraction (but frighteningly large in absolute numerical terms) that would eagerly do so if they could. But we’d have space habitats already if we hadn’t made some disastrous political decisions over the past century, so I don’t think it’s anywhere close to universal that antimatter production will come first.

    To find another factor, let’s take another look at humanity. Humanity is not, of course, a single civilization. Human beings have formed thousands of civilizations since our race came into existence, most of them either falling to the sword or decaying and falling on its own. Humanity apparently went tens of thousands of years (or maybe > 100,000 years, depending on just when real, honest-to-God humans as opposed to more-or-less human-appearing animals first walked the Earth) without developing any civilizations past the tribal stage. Since we have so many examples of civilizations to look at, and since nearly all of them failed long before reaching the spacefaring stage, perhaps that is what happens to aliens – some never develop civilizations, others develop them but fail to sustain them long enough to reach the stars.

    To get to the stars, your civilization has to endure long enough to develop the requisite technology. Not only must it endure, it must continue to be governed by the correct policies to facilitate technological development and economic growth generation after generation for centuries. Let the government go wrong during this time, and the drive to the stars stagnates.

    The government is going to have to stand by as large numbers of respectable and even high and mighty people find themselves made completely redundant and unemployed by new technology – not once, but several times. The government is going to have to stand by as upstart nobodies, foreigners, and other riffraff become wealthy beyond anybody’s wildest dreams with the new stuff and take away lots of other people’s livelihoods – repeatedly. The government is going to have to resist the overwhelming temptation to raid the society’s capital for loot, either for the ruler and his family or for the “welfare” of the voters, and the perhaps greater temptation to take over and micromanage the productive enterprises in order to steal the credit for all the technological advancement going on. The government is going to have to resist demands by respectable people to prevent their jobs from being “destroyed” or “exported”, to prevent their tasks from being changed and their lives from being turned upside down – and resist those demands again and again and again for hundreds of years straight. It will have to resist the demands of busybodies to stop young people from being corrupted, made soft, and otherwise led astray by all the changes being wrought. It will have to refrain from asserting the authority to demand that the people working on new technologies ask permission before they can sell it, demand that people ask permission before they can buy it, or otherwise insert appeasements of the authorities as a necessary step before every incremental step of development. It will have to stand back as people do all sorts of nutty things, sometimes hurting themselves in the process, as they work out the right way to do things that no one’s ever done before.

    The record of human societies shows that sustaining such an unswerving, centuries-long dedication to the necessary laissez-faire policies on the part of the governing classes, regardless of who those governing classes are, is extremely problematic, at least among human beings. Assuming aliens aren’t that much different from us, I could easily see a galaxy populated by hundreds or thousands of sentient species, all of which find their civilizations stagnating and falling before they can escape their home planets. Which in turn would, if true, strongly suggest that there isn’t a good way to straighten out our own government and prevent the eventual collapse of our own civilization before we build any spacecraft.

    I really hope there’s a lot of aliens out in the dark matter…


    19 Responses to “So where is everybody?”

    1. chris Says:

      Remember though…just because they could spread out from any point at a certain speed, they could not spread out in any kind of high density, uniform would be random directions into space and once you talk about distances the size of even our galaxy, then the probabality of coming to our specific planet or even solar system is still very small…and keep in mind we ARE out in an isolated corner of the galaxy. And nothing says they haven’t…if you were millions of years advanced beyond us and travelling to other solar systems and planets was trivial then perhaps you wouldn’t always stop and say hello to every technologically/socially challenged planet you came across…

    2. Varenius Says:

      There’s also the possibility that other races exist which have the technology to be spacefaring, but have no interest in using it. It’s a mistake to assume that nonhuman races would necessarily think the way we do.

      You also need to consider how technological advancement might change the nature of a society and the desires of its members. Say the wildest dreams of the transhumanists come true and we develop a society with no material limits at all and people who live almost forever. One potential outcome of that could be a society in which any idealistic values are abandoned and people reproduce rarely, leading to a very small and self-absorbed human race. Grand schemes for space colonization are unlikely to have any appeal for such a people. Sure, the occasional joyride around the galaxy to stave off the crushing boredom, but not the type of romantic vision that excites the people of our time. So in addition to the technological obstacles, there might also be this “ennui barrier” that races have to make it past to spread out in the universe.

    3. Conrad Says:

      Humans have a written history that only goes back a few thousand years. That is not a sufficient sampling interval with which to make such a judgment.

      If humans pass through a technological “singularity”, it is likely that artificial intelligence controlled probes would be sent out toward a large number of interesting star systems. As for population, artificial wombs with in vitro fertilization, cloning, genetic engineering of germlines, and any number of technological fixes for low birthrates would be utilized.

      Even if elderly humans were able to upload their minds into some sort of machine reservation for human intelligences, there would probably be plenty of capable embodied humans working within an ever expanding useful middle age, to pursue mankind’s age old goals of SMI2LE. Timothy Leary did not invent the concept. Ancient religions did–and who knows what may have inspired them?

    4. Shannon Love Says:

      I personally like the singularity theory. After reaching a certain level of technological advancement a civilization would be come inexplicable to us.

      Its quite possible that aliens are right in front of our faces but we don’t recognize them. A stone age human viewing New York would not recognize it as human construction. He would not even think about something like radio waves, much less have the technology to detect them with.

      Likewise, we assume that the universe we see through our telescopes represents natural phenomenon when we might be looking at some kind of giant construction project.

    5. John Farren Says:

      Well. Look at the history of life on Earth.
      Life appears to get going about 3.5 billion years Before Present, but multicellular life not until about 2by BP.

      How inevitable is multicellular development?

      Then, spread of megafauna onland, not till c.400my BP.
      And genus Homo arrives only c 2.5my BP.
      Despite slow increase in brain sizes of ‘top’ megafauna, considering amphibians, reptiles, theropods, dinosaurs, birds and almost all mammals, there does not seem to be any inevitable drive to sapience over 397.5my of more or less flourishing land life.

      Are forms with hand-like forelimbs (or equivalent), a necessary precursor to sapience? That might leave other specialised forms unlikely to reach this stage.
      And if a ‘monkey-analogue’ is a necessary pre-sapient stage, the environmental/evolutionary twists needed to get beyond the monkey stage to hominids (or equivalents) may be another bottleneck.

      Then transitions in genus Homo to Homo Sapiens.
      And the cultural development of humanity: hunter gathering for most of our species history, then agriculture, then literate/urban/’crafty’ but often traditionalist and/or hierarchical civilisations, then scientific/technical ‘take-off’.
      What likelihood of a somewhat different species ‘stabilising’ at earlier stages?

      And all the time the possibility of the whole line being terminated by climatic shift, vulcanism, asteroid impact.

      My conclusion: life may well be common, perhaps very common, but sapience massively less so (say 0.001% of all terrestrial planets with life?), and scientific/technological civilisations very, very rare indeed.

      And then you’ve got possible expansion/stability dilemma with high-tech civs:
      Too much expansion, you might eat up the resources of your home world or system before you go interstellar.
      Too much stability, maybe you never even bother with interstellar exploration (is abstract curiosity enough of a drive? for non-humans?). How many might just decide to make do with the (vast) resources of a single maximally developed system for billions of years?

      Similarly, potential of either atomic/bio-genetic/nanonic/robotic tech to destroy a species, or surveillance/control countermeasures to lock it in stasis.

      And let’s not even start on the ‘Singularity’…

      Humans as the only potentially expansive sapient civilisation around in the Galaxy would not suprise me too much.

      In the end, we still don’t know anywhere near enough to tell. Hence the need for SETI (despite my pessimism on a positive result: a growing negative would still be valuable data), and extrasolar planetary astronomy, and hopefully eventually interstellar probes (may I live to see the day!).

    6. Varenius Says:

      Conrad writes:

      As for population, artificial wombs with in vitro fertilization, cloning, genetic engineering of germlines, and any number of technological fixes for low birthrates would be utilized.

      But that’s assuming people will care about low birthrates. I was imagining the situation as a voluntary choice, not a matter of circumstance.

      My point is simply that we should not assume too much about either the thinking and motives of alien races or the future path of the human race.

    7. Captain Mojo Says:


      I think you discount possibility #1 far too readily. Just looking at our own planetary history, intelligent life took 4 billion years to evolve, and was by no means destined to magically produce it when our particular branch of the primate family popped up 10 million years ago or so (~0.2-0.3 % of life’s history).

      Why did the apes evolve? I’m no evolutionary biologist so I can’t give you a firm answer, but you can be damn sure it was a freak event.

      Our hominid ancestors were on the brink of extinction for almost their entire existence. The existence of modern Homo Sapiens was also a freak event, and our escape from the doorstep of oblivion during the last 100,000 years of ice ages was also unlikely.

      The development of agriculture? Metal working? The industrial revolution? It could be argued that, once we had our big juicy brains (which was the really unlikely part), all these things were inevitable (although I do find each remarkable). The development of the adaptive, expansionistic, tool using ape species we lovingly call Homo Sapiens ~150,000 years ago was truly miraculous.

      Unfortunately, our one data point in regards to life and evolution is goofy as all hell. There’s no way the earth-moon system (with a large moon relative to planet size) is common in planets throughout the galaxy. Plate tectonics may also be rare. Venus, despite being earth-like in mass, doesn’t have plate tectonics at all (although Venus has its own ‘issues’). Our magnetic field may also be uniquely powerful. These three factors alone would radically change the course of evolution on a planet.

      It’s impossible to discuss this topic without making wild guesses on the probabilities involved. The Drake Equation, although still guesswork, is a useful tool for trying to quantify those guesses in a methodical way. The link has an online calculator that you can use to play around with the variables in the equation (using values I thought reasonable, I came up with a likelihood of 0.165 ‘communicating civilizations’ per galaxy. Your mileage may vary).

      Addressing a more general point, by following your logic that we should assume the vast numbers of star systems guarantees large numbers of intelligent species, we should also assume that, among the large number of intelligent species, at least one would develop economically viable space faring technology before us. As you point out, with the time-scales we’re discussing, such a civilization would quickly overrun much of the galaxy.

      The only firm facts in this discussion are a) we are not slaves to Kodos and Kang (unless they’re being very subtle about it), and b) we have yet to definitively detect intelligent signals from extra-solar sources. You are correct in that, if intelligent life is common, we need an explanation as to why it hasn’t spread throughout the galaxy.

      I used to buy the Sagan nuclear dead-end stuff, but the more I think about it, the less it makes sense (plus Sagan was big ol’ pacifist lefty). Does anyone really think even a full-scale nuclear war would wipe out humanity on this planet? Hell, we faced something worse ~100k years ago, and came out. Sure it might knock us back 10,000 (or 50,000) years, but that ain’t squat over the long haul. If there were enough civilizations out there, at least one would survive the nuclear age and conquer the galaxy.

      I don’t buy the ‘Technological Singularity’ argument either. No matter how advanced a civilization is, it needs to generate enough energy to function. A truly advanced civilization, no matter how efficient, would have spectacular energy requirements, and we would almost certainly be able to detect their massive power sources (Matter / Antimatter, system-scale solar collectors like dyson spheres, etc…). They ain’t out there. Magical power sources? Maybe, but we’d still see something.

      I find it a simpler explanation that, while life itself is likely to be common throughout the universe, the bottleneck on space faring species is in the development of tool-using intelligence, and not the refinement of technology through subsequent cultural and economic development. We may be the first, at least in this galaxy.

      Of course, the state of our knowledge about extra-solar planetary systems, as well as the origins of life, are so primitive that this whole topic is mental masturbation, enjoyable and thought provoking, but with no immediate conclusion or end point.

    8. James R. Rummel Says:

      This discussion is moot until and unless we get out there and put some boots on the ground. That might or might not happen. We’ll just have to muddle along and see.


    9. Captain Mojo Says:

      Curses! Looks like John made most of my points first.

      Also, the Drake Equation link I was referring to is here.

    10. Lori Says:

      Who says that an intelligent being has to be anything like human? It may have been a ‘freak’ accident that we evolved the way we did, but is ours the only means to intelligence? Also, it should be considered that all technologies may be in place for these ET’s to travel here and contact us, but who says they want to?

    11. Tom Bridgeland Says:

      I generally back the thoughts of John Farren, and would like to add the factors internal to Homo Sapiens itself. We are just barely able to maintain advanced civilasation ourselves. Imagine if we were just a bit more docile and dog-like than we are. A human race made up of more followers and fewer leaders, with no go-it-alone types, might be very unlikely to develope technology higher than the craft level. Ditto humans who were further in the opposite direction, all independant, loners who could barely cooperate beyond a single group hunt.

      Or suppose our territorial nature was screwed a bit tighter. We would be spending every second watching our nearest neighbor.

      There are not many species that could jump the internal barriers to developing advanced technological societies.

      Even if life is very common, a debatable point itself, and if intelligence is common, technological society would still be very rare.

      Since no life is likely to be much older than life on Earth, it may be we are close to the cutting edge.

    12. Captain Mojo Says:

      I think in a point related to some of what Chris, Varenius, and Lori mentioned, is what we mean by “intelligent”. In discussions like this I always try to explicitly limit the definition to very anthropomorphic terms. This definition would have the following properties:

      -Tool using
      -Self aware (fuzzily defined, “I know it when I see it”)
      -Capable of symbolic thought (read mathematics and logic)

      There are a number of non-human ways this could evolve (a hive mind for example), but in all cases, the species would build stuff and use some form of mathematics to understand the universe that we could also understand. Communication with such a species might be difficult but would be at least possible.

      “Intelligences” outside of this definition are certainly possible, but irrelevant to the discussion, as the chances of us being able to communicate with, or even detect their intelligence, are slim. When something is that alien, we would probably be lucky to even recognize it as life.

    13. Robert Schwartz Says:

      It seems that we have ignored our mandate here. As the Chicagoboyz and under the pictures above one of which is of Enrico Fermi, who was a professor in the Divison of Physical Sciences, in the 1940s and 50s.

      It was Mr. Fermi, who when presented with the case for ETs, asked the question: “where are they?” The argument presented by the OP, is therefore often referred to as the Fermi Paradox.

      I tend to be on Fermi’s side.

      Among the parameters in the equation that need to be defined are the number of planets available for life. Most of the extra Solar plantes discovered so far have been gas giants bigger than Jupiter, closer to their primaries than Mercury. Not candidates for Life as we knowit. habitale planets maybe very rare.

    14. Stevely Says:

      I don’t buy the ‘Technological Singularity’ argument either. No matter how advanced a civilization is, it needs to generate enough energy to function. A truly advanced civilization, no matter how efficient, would have spectacular energy requirements, and we would almost certainly be able to detect their massive power sources (Matter / Antimatter, system-scale solar collectors like dyson spheres, etc…). They ain’t out there. Magical power sources? Maybe, but we’d still see something.

      I think you assume far too much when you see “we’d still see something.” How can you know that? How are you so sure that whatever we observe (which, you can be sure, is but the tiniest fraction of what there is to be observed in the universe) can be readily identified as the signature of power use by an intelligent species? There are so many possibilities, so many variables that blanket statements like yours are unsupportable. What if a civilization 1000 or 5000 light years away built a Dyson sphere around a star to harness its energy output? We’d be totally unable to see the star, and it’s not certain that we would be able to detect the waste energy produced by this hypothetical civilization’s activity at such a range, or even if we saw the waste heat and light that we would be able to resolve it precisely enough to know it for what it was.

      For really advanced civilizations, we must come to grips with the idea that beings very far in advance of us would be as unintelligble and unknowable as we are to slugs. And civilizations much closer to us are not likely to be able to leave strong enough signs for us to detect at stellar distances.

      IMHO, there is simply far too many unknowables for anyone to pronounce strongly on this subject one way or another. Not that we should stop looking – I strongly support SETI – but we should be humble about our chances.

    15. Ken Says:

      Sorry, I forgot to give props to Mr. Fermi, who first publicly posed that question. I didn’t originate the question, just took some stabs at some plausible answers.

      “Remember though…just because they could spread out from any point at a certain speed, they could not spread out in any kind of high density, uniform would be random directions into space and once you talk about distances the size of even our galaxy, then the probabality of coming to our specific planet or even solar system is still very small.”

      I don’t think so. Remember that these are technologically advanced creatures with lots of resources to play with. They’ll have excellent medical care, long lifespans, and probably multiply like rabbits, given the low probability that anyone would worry about population pressure until they had actually come within sight of filling up every star system they could reach Even though the most advanced nations on Earth have low birthrates (which admittedly might itself be a bottleneck if it’s a common phenomenon… having the most successful members of your race selected against in evolutionary terms doesn’t give your race very bright prospects for going forth and multiplying across the galaxy…) I don’t see any reason why that will necessarily persist more than a century or so. Surely subpopulations with higher birthrates will outbreed subpopulations with lower ones and be more heavily represented as time goes on.

      Which means that, assuming that they like to hang around stars as much as we do, our hypothetical aliens would fill up every star system on their way outward in short order, at least on the timescales we’re talking about, and our own star system and planet would have been crawling with aliens throughout our history.

      I guess I should qualify the kind of creatures I’m talking about. I’m talking about intelligent creatures; they’re “intelligent” in the sense that they are at least theoretically capable of improving their technology over time to the point of building spacecraft given a suitable government, and “creatures” in the sense that they are animals that need to eat something and probably feel themselves driven to reproduce, which means that they compete for resources, expand their population, and find striking out into areas where there’s a lot of resources and no competition an exceedingly worthwhile activity, assuming they can pull it off.

      Either no such creatures exist (other than here), they’ve got a better place to get resources than star systems, or they can’t get off the ground for some reason.

      “Most of the extra Solar plantes discovered so far have been gas giants bigger than Jupiter, closer to their primaries than Mercury. ”

      That’s because our long-range telescopes are still kind of crappy. When looking across interstellar space, huge planets close to their suns are the only kind of planets our telescopes can detect, so of course we’re not finding anything else.

    16. Captain Mojo Says:


      Dyson spheres are not impossible to detect, they will radiate in infrared. Here’s an interesting article on some SETI guys searching for the big behemoths. I don’t know how far their methodology would be useful, so you may be right that such objects several thousand light-years away would be impossible for us to detect with present technology,

      More broadly, you are absolutely correct. I can’t argue with magic technology. Maybe some alien has zero point energy or something, and is completely silent on the radio spectrum. Maybe they’d be creatures of “pure energy”, who’ve achieved complete spiritual purity and don’t want to sully themselves with our primitive race. Maybe they’re already here and spend their time eating strawberry ice cream and anally violating rednecks. I can’t prove any of it’s impossible. I can only say I’ve seen no evidence of it.

      I think the technology issue, though, isn’t really important in regards to the Fermi Paradox. Fact is, we could conquer the galaxy using near-current technology if we were willing (and collectivist enough) to spend enough resources on the first few colony ships. Once you’re out of the home system, it’s just a matter of time, and there’s been plenty of time already for all these potential aliens. All it would take is for one species over the past billion years to go expansionistic, just one, and we would be living on an ancient colony world.

      And I’m not seeing any decaying statues to bug eyed monsters anywhere around here…

      Despite what I’ve just written, I agree that our raw understanding of the universe is poor, and strong pronouncements are unwise.

    17. Michael Hiteshew Says:

      “Any sufficiently advanced technology is indistinguishable from magic.” -Arthur C. Clarke

      What makes us believe we are capable of detecting these civilizations, if they exist? Any civilization *MUST* fall into one of three categories WRT to ours:

      1. Less technologically advanced.
      2. Equal.
      3. More technologically advanced.

      We are currently only searching for civilizations broadcasting (I believe) in the radio spectrum. If we define #2 as being those civilizaions that have at least achieved radio technology, then, by definition, we will not detect those in category #1.

      Radio is radiated energy. Its strength diminishes according to the inverse square rule. Move away twice the distance and the intensity of the measured energy is (1/2)^2 (one half, squared) or only 1/4 of the previous intensity. Move away to interstellar distances and the energy intensity of a low or medium power source quickly approaches zero. Only radio sources that start with truly immense levels of power are still clearly detectable.

      The exception is those radio energy sources that have been focused in a particular direction. Instead of spreading out in an ever-expanding sphere, their energy is all directed in a single direction and will retain high energy levels over much longer distances depending on the amount of blocking/interference/attenuation the signals encounter and the quality of the initial focusing. Spacecraft use directional parabolic radios for this reason. However, those signals are focused towards Earth and so only detectable from one direction. This also allows them to be broadcast at very low power levels; about ten watts. There are also millions of available frequencies on which to broadcast. All of which argues against our detecting category #2 civilizations with current radio search methods.

      As for searching for category #3, I refer you to the above quotation.

      Finally, regarding the ‘Where are they?’ question, which I’ll rephrase as ‘Why aren’t they here?’, I’ll say this:

      1. The only civilization type that could possibly arrive here on Earth from interstellar distances are those in category #3. What fraction of all intelligent life existing in our galaxy is that?

      2. What fraction of the land mass of the galaxy does the Earth represent and how long would it take even a highly advanced civilization moving through the galaxy to stumble upon us?

      3. What if an early bloomer civilization stumbled upon us a million years ago and simply cataloged us and moved on?

    18. rvman Says:

      Michael’s comment brings a question to mind – how far away could we detect ourselves? Obviously, more than 100 light years out, we couldn’t (our “signals” couldn’t have gotten that far, yet), but less trivially, even 10 LY out, could we “detect” ourselves? We haven’t discovered “earthlike” planets – how close would a star have to be for an earthlike planet or a Sun-like system to have a discernable signature with current technology? 20 LY? 100? There are only a handful of stars, relatively, that close. We just days ago found a jupiter-like planet at jupiter-like distances in a system 40+ LY away – Earth has far less detectible effect than Jupiter does. Mostly we’ve found big(14x Earth min) stuff close in – because we don’t yet have the tech up and running to find small(earth sized) stuff anywhere.

      A Dyson Sphere could be “dark matter” or a “micro black hole” or something else dark to us, or a Pulsar-like thing if we happen to be in roughly the direction of its waste-energy disposal system. A dark-matter based civilization could look like a gently glowing nebula. Look at what our waste would look like from space, then consider what a civilization spreading in interstellar space might look like from here. In order to identify advanced civs, we’d have to know what to look for, otherwise we might see the effect, think “odd natural phenomenon”, identify a natural “cause”, and move on. This assumes their emissions are even in a “frequency” we are even looking for. Or are bright enough to be detected – extreme energy efficiency just might be a prerequisite for interstellar expansion, we just don’t know.

      It could easily be that races go interstellar, but then end up in steady state due to population expansion stablizing. Even if aging is solved, it is possible the accident/suicide rate could equal the birth rate of a very advanced, very low birth rate species. Why continue to expand, if you haven’t filled your own territory? They could be out there and a) view earth as too dangerous to settle/make contact with(we don’t know if microbes from space would affect us, maybe ours would affect them, War of the Worlds-style), b) haven’t come this way (we are rather out on an arm of the galaxy), or c) don’t use or avoid stars, once they are out from their own system. After all, life evolved in the depths of the ocean – we don’t still live there. Humanity evolved in East Africa, but we wouldn’t want to live there, necessarily. Once we have space stations, we may not need or want planets. (Gravity wells may be expensive.)

    19. Watertreat Says:

      A couple of idle thoughts the comments here have given rise to.

      SETI seems to me to be a dicey and reckless excersize given what often results in two disparate cultures rubbing up against each other. I’m thinking that the American Indians would have regretted advertising their existence to the Europeons.

      Regarding the possible presence of more developed beings among us I’m struck by the possible reverse relationship by the words “dog” and “god”. I imagine that we would no more understand the works of such creatures than my dog understands where I go, what I do, and how I obtain that can of dog food….I may be a god to him. I may understand an advanced being (god) about as well as the dog understands me.