# Idea for what the Great Filter could be **URL:** \ **Category:** Great Debates\ **Created:** [April 28, 2017, 3:57am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417 "2017-04-28T03:57:42Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 1, 2017, 2:33am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/61 "2017-05-01T02:33:52Z")
> [@wolfpup](#): > > IOW, your exponential growth assumes a consistently systematic pattern of expansion, which may be extremely unrealistic even if you allow many millions of years for it to happen. The point of the exponential growth thing was to give an example of how there has been sufficient time. There are other examples like self-replicating drones. Of course you can shoot any of them down with ad hoc speculation. > [@](#): > > I took a peek at [the Wikipedia article](https://en.wikipedia.org/wiki/Fermi_paradox) on the Fermi paradox, and while the arguments against it are of varied degrees of plausibility, there are several that deal with cost and motivation; for instance: Sure, but again this does seem to concede the original point about space being so vast and SoL in itself being enough of a barrier to contact. If you’re saying _Well there must be some reason why we haven’t seen ET_, then of course I agree. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 1, 2017, 2:52am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/62 "2017-05-01T02:52:03Z")
> [@Stranger\_On\_A\_Train](#): > > The notion that communicating with an extraterrestrial species which shares no evolutionary history, cognitive structure, or possibly even basic chemical structure would be an “easy problem” is so absurdly dismissive and, in your terms, “a bad extrapolation”, it would seem that you are projecting some unfounded personal belief rather than any hypothesis grounded in reason or plausible analogue, such as communication with dolphins or whales which are far closer to us in cognitive structure than we could expect any extraterrestrial life to be. The hypothetical alien species also has no evolutionary history of interstellar travel. They have demonstrated an ability to solve countless incredibly difficult and abstract problems _nothing like_ those encountered in their natural habitat. It’s laughable to me that such a species could be swimming in data about human language, which as I say is clearly structured, not like the random and vague clues nature serves up, and just be utterly stuck. And they must be utterly utterly stuck for your point to have any relevance to a discussion about the Fermi paradox: if a species even becomes aware that another species is _trying to_ communicate, then that’s already a sufficient level of understanding for the Fermi Paradox to be a problem again. > [@](#): > > The Fermi paradox and this Great Filter hypothesis also assumes that an intelligent species would ultimately achieve interstellar civilization and grow to fill all available space and use all resources it could access. I disagree. We only need to posit a species spending a minute fraction of their resources on exploration. And as I just said in my previous post, yes there must be some explanation(s) why we don’t see ETs. We all agree about that. This doesn’t make the Fermi Paradox “wrong”, or making incorrect assumptions; the whole point is to discuss these explanations. At this time, we can’t say for sure which one(s) are true. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 1, 2017, 4:10am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/63 "2017-05-01T04:10:08Z")
> [@Mijin](#): > > The point of the exponential growth thing was to give an example of how there has been sufficient time. There are other examples like self-replicating drones. > Of course you can shoot any of them down with ad hoc speculation. > > … > > Sure, but again this does seem to concede the original point about space being so vast and SoL in itself being enough of a barrier to contact. > If you’re saying _Well there must be some reason why we haven’t seen ET_, then of course I agree. You’re either not quite getting my point, or are trying to obfuscate it. The only point demonstrated by the exponential growth thing is that _ **math works** _, which is not really an especially profound point. It does _ **not** _ demonstrate that the vastness of space and time are irrelevant – they are in fact central to the discussion. The simple point here is the following. The greater the distances in space that are involved in reaching other destinations, the greater are the resources and the more exotic the technologies required to reach them, at some point requiring incredible commitments stretching across eons and thousands of generations and perhaps consuming the resources of entire planets. Meanwhile we, the humble human species who only invented radio in the previous century and practical computers toward the latter half of it, have already sent our space emissaries all over the solar system, and if there were Little Green Men on Mars, by this point we’ve sent so much earthly stuff over there that by this time they’d be fearing an all-out invasion! IOW, distance matters, profoundly and absolutely, and for the spread of an intelligent species through interstellar distances, you have to make some very specific assumptions about how an alien species will behave, not just over any short term of technological development, but over a very long term of the evolution of its civilization and its species. The greater the distances, the more critical this set of special assumptions becomes, and the less likely it is that it will happen – not for any profound reason, but just because of the number of factors that have to simultaneously be in place for a very long time. This is how you have it backwards. I readily concede that the math works – I submit that the more meaningful challenge is for your side of the argument to show _ **that the assumptions work** _, or else we can consider the absence of any evidence of extraterrestrial intelligence thus far to be quite a plausible outcome quite consistent with lots of it actually being out there. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [May 1, 2017, 6:12am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/64 "2017-05-01T06:12:49Z")
> [@wolfpup](#): > > You’re either not quite getting my point, or are trying to obfuscate it. It’s weird you start your post like this, then concede the simple point I was making later on. Is my style is too adverserial or something that you feel the need to imply bad faith on my part while agreeing with me? > [@](#): > > It does not demonstrate that the vastness of space and time are irrelevant – they are in fact central to the discussion. Apart from Strawman McStrawey, is there anyone who believes that the distances involved are not a significant issue, and do not present immense challenges for a species? As I said, the distances are usually mentioned in the set up of the Fermi Paradox because it’s the very important context of the discussion. > [@](#): > > I readily concede that the math works – I submit that the more meaningful challenge is for your side of the argument to show _ **that the assumptions work** _, or else we can consider the absence of any evidence of extraterrestrial intelligence thus far to be quite a plausible outcome quite consistent with lots of it actually being out there. I’m making no assumptions (though yes I’m making some inferences; such as that a species that can build interstellar spaceships can solve complex abstract puzzles). Nor making any claim about how common life is (apart from saying \>= 1 planet). All I’m saying is that Fermi’s Paradox is a perfectly reasonable drawing together of the various hypotheses for why we have not seen evidence of ETs yet, and that it is unsolved. That all the various hypotheses are somewhat debatable and largely based on speculation at this time. It’s like the OP: if he were to throw the burden of proof back on me then of course I cannot demonstrate that wood is a common form of organic material in the universe. All I can say is that at this time I have no reason to think that. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [May 1, 2017, 10:34am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/65 "2017-05-01T10:34:22Z")
> [@wolfpup](#): > > I agree that it’s plausible that there are older and therefore likely more advanced civilizations than ours, but I was referencing the earlier cited paper that hypothesizes that we may be one of the first, which is one possible answer to the paradox. Of course, however, the paper makes the assumption that life is possible around low-mass stars (red dwarfs of 0.1 solar masses), and thus, we find ourselves in unusual circumstances—which is a contentious assumption. Furthermore, even if we’re ‘among the first’, this could easily mean that there are hundreds of civilizations hundreds of millions of years older, given the scales involved. > [@](#): > > But personally I subscribe to the idea that in terms of the extremes of the chronology of intelligent life, we’re most likely in the most populous part of the bell curve. That, on the other hand, probably isn’t true: as far as the universe goes, with an expected lifespan in the trillions of years, we’re almost surely among the ‘early birds’ in some sense—otherwise, we should expect that life dies out for some reason soonish, leaving our galaxy an empty wasteland for the next couple of hundreds of billions of years. > [@](#): > > Point taken, and I should retract that part about “… to do nothing but propagate itself from star to star …”, but IME some strong points remain about the necessary long-term motivation for them to do this – even if this exploration urge is intermittent, we still have to make a whole lot of assumptions including the fact that they will keep wanting to build starships and move on to the next stellar system even after a hundred thousand years and unimaginable technological and cultural evolution. Why would they? I think that’s getting things backwards. After all, we don’t need for all of the civilizations to propagate themselves through the galaxy for all of their existence—we need for one to do so a small fraction of the time. And given this, I think it’s more reasonable to ask—why wouldn’t they? What’s the reason they—here meaning all of them, all of the civilizations that have arisen in the time since it first became possible for them to do so—just looked at the stars and went, nah, why bother? I grant that it may be the case that at a certain point in the history of a civilization, the urge to explore is just lost (or edited out, or overruled, or whatever). But that’s in itself something that asks for an explanation—after all, our own image of ourselves doesn’t foresee anything like this; basically all of our speculative future scenarios include a human civilization that’s taken to the stars as soon as they could. Nobody seems to think that we’ll achieve the necessary level of technological maturity, and then just sit tight on our asses. So why would every single other mature civilization do so? (Again, the emphasis here is on the _every single_ part: it’s readily imaginable that some, or even a majority, of civilizations just don’t bother; but for _all of them_ to do so seems to cry out for explanation.) Regarding wikipedia’s explanations, they’re all really just ways to avert the question—yes, it may be too expensive to colonize the galaxy—but why? What’s the factor that drives up the resource needs so much that to a million-year-old advanced industrial civilization, it’s not just a pittance? And likewise, why isolate? And why would _all of them_ isolate? Sure, maybe some go off to play The Sims for all of eternity, but why doesn’t there seem to be a single one interested in exploring the real world? I think that if that’s the case, then there is a real answer to be had that would either tell us a lot about intelligence, or about the real world; and that’s the answer I’m looking for, not ‘maybe something unknown does something unforeseeable’. Because the latter is trivially the case: after all, we don’t see a galaxy teeming with life, so something must have prevented that from happening. > [@Stranger\_On\_A\_Train](#): > > First of all, your assumption that non-human animals have no sentience is [not shared by animal psychologists cognitive scientists](http://www.livescience.com/39481-time-to-declare-animal-sentience.html). It is widely recognized and well established that all mammals, most aves, and many other distantly related species such as octopuses have degrees of sentience, and communicate with one another in often surprisingly sophisticated ways. > > The notion that communicating with an extraterrestrial species which shares no evolutionary history, cognitive structure, or possibly even basic chemical structure would be an “easy problem” is so absurdly dismissive and, in your terms, “a bad extrapolation”, it would seem that you are projecting some unfounded personal belief rather than any hypothesis grounded in reason or plausible analogue, such as communication with dolphins or whales which are far closer to us in cognitive structure than we could expect any extraterrestrial life to be. I can’t speak for **Mijin** , obviously, but I think what he’s talking about is usually termed as the difference between ‘general intelligence’ and ‘narrow intelligence’ in AI circles. We have narrow AI for a lot of applications: chess, go, jeopardy, and so on. We don’t have any artificial general intelligence (AGI), i.e. no universal problem solver. Here, ‘universal’ can be read in the same way as in ‘universal Turing machine’: such an AGI can solve, in principle, any problem a narrow intelligence can solve. From this, it also follows that all such general intelligences are equivalent: what problem one can solve, another can, likewise. So there isn’t going to be a difference in principle between us and another generally intelligent extraterrestrial species; we can communicate with one another in much the same way a PC and a Mac can. However, there is a difference in principle between us and (to the best of our knowledge, all) other animals: for any given narrowly intelligent animal, there are going to be problems that we can solve, but they can’t. Also, I think **Mijin** is using ‘easy problem’ in analogy to the easy problems in the philosophy of mind (as opposed to the ‘hard problem’ of consciousness): that is, figuring out how brains create behavior. There is no problem of principle there: existing methodology is virtually certain to ultimately figure things out. Likewise, there is no problem of principle in communication with generally intelligent aliens. > [@](#): > > The Fermi paradox and this Great Filter hypothesis also assumes that an intelligent species would ultimately achieve interstellar civilization and grow to fill all available space and use all resources it could access. This is certainly what bacteria do, and to a certain extent even we do so, but an advanced species may have other agenda beyond physical expansion. Of course, it may not follow this drive. But then, there ought to be some reason for not possessing it: this is what the Fermi paradox asks for. After all, that every advanced civilization just randomly decides to sit on its hands (tentacles, fins,…) and not bother is implausible. Recall that we don’t need for _every_ civilization to be expansionist all the time; we simply need one, and only for a comparatively short time. So that any one species doesn’t take to the stars isn’t implausible (although, as already mentioned, we certainly seem to expect of ourselves that once we can, we will); but that all of them decide not to implies that either there are relatively few of them, or there is a reason that they all follow the same course of action. Both possibilities ask for further explanation. > [@](#): > > The notion that all intelligent life would seek to exploit resources, build giant structures, and send messages everywhere seems to be as much grounded in the conquistador tradition of European colonization as any kind of basic philosophy. The problem is, again, that this is a fine argument that _not all_ species will follow this kind of behavior; but in order for this to be an answer to the Fermi paradox, you need to argue that _none_ of the species so far have pursued this course. This is a much harder case to make, and almost certainly will need some new insights. Of course, it could be that the reason for the Fermi paradox is the Fermi paradox: every species on the verge of interstellar travelling capacities asks itself, but where are they? And infers that there must be a reason that they just don’t yet understand why nobody else ever colonized the galaxy; and thus, being the cautious sort of species after having survived nuclear power, they decide to play it safe and better leave things out there alone. 😉 ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [May 1, 2017, 1:12pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/66 "2017-05-01T13:12:32Z")
I think it’s a combination of 1. Shagnasty’s point about space being really super duper big. It’s only quite recently that we’ve managed to even prove other solar systems have planets. There are stars I can actually name where the distance to them is, frankly, little better than a guesstimate. For all we know there’s a dozen intelligent, advanced civilizations in the Milky Way, but we’re just too far apart to hear each other. Parts of the Milky Way are probably too obscured to ever be heard at all - we will never, ever detect an advanced civilization on the opposite side of the galaxy from us. And of course a neighbour more than 100 LY away can’t have heard us by now. We ourselves have not been broadcasting anything long enough to be detected outside of a relatively small radius. 1. It is worth noting that not only is intelligent life a rarity on this planet - only one species has gotten to technology - but **multicellular** life is a recent innovation and is still the minority partner in our enterprise. Life on Earth was single-cell from approximately 4.2 billion years ago to about 1.5 billion years ago - so ;life appeared very quickly (well, relatively speaking) after Earth was formed, but life really prefers to stay simple. Even today, most life is simple. You notice the complicated life forms becuase you are one, and you can see cows and dogs and mice and birds. You don’t notice that there’s a gazillion bacteria, virii, amoebas and stuff in your house. We have no other examples to draw from but this suggests two things; one, that biogenesis might be reasonably common if the conditions are right (but planet likes Earth, around a sun like our Sun, are not that common) and two, that life really does prefer to keep it simple. 1. Even if intelligent life CAN arise, there are a thousand things that could keep it from inventing powerful radios. [QUOTE=Stranger On A Train] First of all, your assumption that non-human animals have no sentience [/QUOTE] I hate to be picky on this, but all animals are sentient. Regrettably, “Star Trek”'s use of this word has caused it to be commonly misused. “Sentient” means to be possessed of the ability to sense and perceive. Mice are, obviously, sentient. A better word for what we’re talking about in this thread would be “intelligent” or “sapient.” I personally find it kind of weird anyone would deny some animals have some degree of consciousness. I mean, you can’t possibly have a dog and not know it’s aware. My dog can’t do long division, but he is sure as hell aware of his own existence. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [May 1, 2017, 1:55pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/67 "2017-05-01T13:55:32Z")
> [@blindboyard](#): > > Fire isn’t enough on its own, but if you can’t do fire, what can you do? You can’t smoke, but you can still drink. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [May 1, 2017, 4:22pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/68 "2017-05-01T16:22:16Z")
> [@wolfpup](#): > > First of all the possibility of life requires precursors that take time to develop. The universe may be very old but its life-bearing epoch is less so; we don’t really know how much less, but at the very least second-generation stellar systems with heavier elements and stars with lifetimes long enough to allow life to evolve are necessary. Not really. The first generation stars which cook up some of the useful elements during their lifetime and the rest of the useful elements during their death are by necessity the ones that are big enough to have have short lifetimes, some only a few million years. (Current thinking is that the very first stars, called [Population](https://en.wikipedia.org/wiki/Stellar_population#Population_III_stars) [III](http://astronomy.swin.edu.au/cosmos/P/Population+III), were _very_ big, thus lived and died _very_ fast.) So there have been metals available for building Population II and Population I stars for almost as long as there have been stars. The [oldest known planet](https://en.wikipedia.org/wiki/PSR_B1620-26_b) is around 12.7 billion years old, little younger than the universe itself. So planet _production_ has no problem for most of the age of the universe. Whether the radiation environment was survivable enough to allow intelligent life to evolve is a different issue–planets back then would have to deal with more and closer supernova, quasars, and various other sources of planet-killing levels of radiation than we have in these calmer times. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [May 1, 2017, 6:15pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/69 "2017-05-01T18:15:59Z")
It should be noted that while we’ve delineated stars into Population I (metal-rich), Population II (metal-poor), and Population III (formed only from primordial hydrogen and helium), these “generations” are not distinct and are overlapping. In material rich regions supermassive stars with very short lifetimes of tens of millions form and go supernova, producing the elements heavier than iron and nickel by core collapse nucleosynthesis, while smaller, slower burning stars produce larger volumes of intermediate atomic weight elements in large amounts. Our solar system (and presumably stars and planets that formed in the same region) have a good mix of these elements, but the suffiicent elements for the CHONPS-based biology may have been found in some regions in abundance suffiicent to support the development of life. Our own solar system is comprised of material from at least ten different nucleosynthesis sources (some possibly from extragalactic sources), and we’re out in the suburbs of our galaxy. It is statistically and evidentially unlikely that Earth is the first place in the galaxy where the conditions for life like ours could arise unless there is something special about life that we are missing, and that ignores the potential for life-like systems formed from something other than the carbonaceous-nitrogenous chemical basis of life on Earth. On the issue of why we don’t see evidence of vast interstellar civilizations, I’ll reiterate that we don’t even know what to look for or what motivations and means an extraterrestrial civilization would have. Would they be explorers in space, sending physical probes to every star system by propulsive means of conventional momentum transfer or exotic physics of wormholes and space warps, or would they be more interested in exploring the inner depths of the subatomic world and possibly dimensions and interactions that are only hypothetical to our current understanding of nature? Would they construct vast obviously artifical structures visible from thousands of light years distance, or would they prefer more subtle or apparently (to us) natural formations intended to produce a cosmic environment congruent with their nature? The presumption that they should be beaming detectable radio signals at one another despite the limitations (we could not detect our own emenations at more than a few hundred ligt years distance even with the most sensitive technology intentionally tuned to look for transmissions) would be like primitive natives expecting the US Navy to use smoke signals or campfires for communication, being completely unaware of the existence of electromagnetic transmission. As I noted upthread, communication by coherent gravity waves makes far more sense for a vast, galaxy-spanning civilization (or perhaps means even more exotic) which could have us awash in communications we are not capable of detecting, much less decyphering. On the topic of language being an “easy problem” for an advanced alien species to solve, I’ll just point out that our cerebral cortex–the ‘advanced’ part of the brain responsible for higher cognition and reasoning–is heavily structured around language as we use it, and basic linguistic similarities across widely seperated human languages strongly suggests that how our language is structured reflects essential mechanics of cognition. For instance, every human language has a distintion beween ‘me’ and ‘you’, possessive versus demonstrative or objective, discrete counting, et cetera. An alien intelligence and cognitive system would presumably be structured around whatever system of communication that they use (presuming they are a discrete and social form) and may have an unimaginably different form, perhaps not even recognizing concepts such as integers or ownership. Their view of the world and themselves may be so fundamentally different that they cannot conceive of the basic concepts underlying our language, and this alone may prevent effective communication even if they can figure out that pushing air theough meaty flaps at different pitches is some from of communication. There is the tendency when approaching the question of what form and practices an extraterrestrial intelligence might take to reason from the specifics of our own experience to the general, and it is understandable because we have this single data point from which to guess what an alien might be like. But an objective assessment of the vast ways life and cognition could independently arise suggests that we can really assume almost nothing beyond nasic chemistry and physics, and even in those we should be prepared to be surprised how a novel organization of mechanisms could give rise to unexpected complexity. It is a fallacy to assume that alien life would be like us in any material way or that communication is a mere matter of concept translation or conversion from spoken word to flahshing lights or electrial signals. Even life on Earth, coming from a common evolutionary tree, has come up wiht bizarrely diverse solutions to problems of survival, reproduction, social organization, and communication in ways that we’re continually surprised by, and we share a common fundamental unit of inheritance and continuum of environment. When it comes to extraterrestrial life we pretty mich can’t assume anything except that our expectations are likely to be wildly off base. Stranger ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [May 1, 2017, 6:42pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/70 "2017-05-01T18:42:21Z")
> [@wolfpup](#): > > This. I think the most likely reason that “we do not observe exponentially expanding interstellar civilization” is that there would have to be an extremely unlikely chance encounter in an unimaginably large four-dimensional spacetime in order for us to observe anything at all. I look at it this way; suppose there were only three people on Earth, spread around more or less evenly, possessed of nothing more than the barest of hand tools needed to survive. We’ll put one in China, one in Botswana, and one in Venezuela just to give you a visual. None are specifically aware of the others; would they ever find each other? Not a chance in hell. Space is _much_ more spread out than that. Stranger makes a neat point about how other intelligent species could be so different we don’t recognize them, but the truth is we probably wouldn’t find them anytime soon **even if they were all human beings** , or, Star Trek style, variation on human beings. If there are five Earth-like civilizations in this galaxy - and I mean humanoids who breathe atmospheres just like us, speak like we do, and play soccer and baseball and watch reality TV shows - we are never, ever finding them, unless we are just unbelievably lucky. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [May 1, 2017, 7:12pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/71 "2017-05-01T19:12:01Z")
Another thing to consider is that while life is statistically either so rare that Earth is essentially unique or so common that it can be found almost anywhere that has hydrocabon compunds in a liquid substrate, intelligent life and industrial civilization (or the alien analogue thereof) is a complete unknown. We’ve only had an industrial society capable of directly controlling electromagnetic forces for useful purposes for les than two centuries. We don’t know if we’ll survive or die out through natural catacalysim (large meteroite impact, massive geophysics disaster) or self-destruction, but if we do survive and advance we almost certainly aren’t going to be transmitting videos to one another across interstellar space for the next ten million years while remaining the same essential species and civilization. As we advance our understanding of nature and find the means to directly control nuclear and gravitational forces the way we do electricity today, we’ll most certainly change and transform, not only in our technology and our physical bodies (which are very poorly suited to any kind of space habitation or exploration) but in our agendas and motivations as a civilization. We can barely even imagine what the human species (or more likely, its successors) will look like on eons much less how alien civilations with comparable abilities will expand and interact, or how common they may be in a form that would even be comprehensible to us. Stranger ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [May 1, 2017, 9:44pm UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/72 "2017-05-01T21:44:48Z")
The critical flaw with the “technologically advanced slowpoke naval gazers” hypothesis above is that it ignores evolutionary pressure. Maybe the alien species of naval gazers originally is mostly naval gazers. But after a million years or so, one group of them finally get around to building a starship and going to the next star over. That subgroup probably contains traits (cultural or genetic) that make the subgroup contain a smaller percentage of naval gazers. So it might, on average, take 100k years before that group has a subgroup feel like leaving the new star. And so on and so forth until the mutated species is nothing but hard charging, interstellar explorers who want to expand as much as they can as fast as they can. As for the aeons long journey it would take - since even with antimatter fuel, you’re probably looking at trip times of decades and then you need more decades to build the infrastructure to build a new ship and fuel it at the destination star - so what? No species that does something like this is going to be anything but biologically (or technologically) immortal. However they do it, they will have a way to preserve exactly the memories and personalities of the prominent members of their species such that information is not lost over time. (there are many ways to accomplish this) Only a truly idiotic and stupendously selfless species would do something like “generation ships”. No, they would wait til they have the technology such that the crew and backers of the first starship get to _personally_ be alive to see the gains from arriving at another star. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 2, 2017, 12:35am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/73 "2017-05-02T00:35:15Z")
> [@SamuelA](#): > > …you’re probably looking at trip times of decades … You misspelled “tens of thousands of years, maybe millions”. Which is how long it would likely take to travel between star systems with habitable planets with any conceivable technology. Most of them are a lot more than tens of _ **light-years** _ apart. In general, wow, what a lot of fantastical assumptions all strung together to make this stuff happen! Which brings me to a point I wanted to make anyway, that I think maybe a good way to sum up the disagreements about the so-called Fermi paradox is to look at definitions and first principles. A “paradox” in essence is “a statement, proposition, or situation that seems to be contradictory, but in fact is or may be true”. The Fermi proposition is thought to be paradoxical because our understanding of the universe in general, and calculations like the Drake equation in particular, make it plausible that intelligent life is quite abundant in the galaxy, yet we’re apparently not seeing it, neither indirectly nor, as it were, in person. This seems to demand an explanation. Where I think some of us disagree is in where the most plausible explanation lies, and the above fantastical assumptions are a good illustration of plausibility or lack thereof. To lift a quote from a book on a completely different topic, “[In science,] simplicity is held to be a marker of intrinsic probability, of truth. It is complex realities that are thought to stand in need of explanation, not simple ones.” My argument is that the vast distances between any stars, let alone between stars harboring planetary systems hospitable to life, and the unimaginable travel time and resources required to reach them, offers the basis for _ **the simplest set of reasons** _ for why civilizations would not attempt it on a large scale or be able to maintain it for the requisite number of millions of years. Conversely, ISTM that the proposition that a civilization would do so is a proposition that requires an unlikely concatenation of very complex assumptions about their motivations, technology, and extremely long-term persistence across vast spans of space and time. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [May 2, 2017, 12:55am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/74 "2017-05-02T00:55:27Z")
> [@wolfpup](#): > > You misspelled “tens of thousands of years, maybe millions”. Which is how long it would likely take to travel between star systems with habitable planets with any conceivable technology. Most of them are a lot more than tens of _ **light-years** _ apart. > **[Antimatter rocket](https://en.wikipedia.org/wiki/Antimatter_rocket)** > > Onia > An antimatter rocket is a proposed class of rockets that use antimatter as their power source. There are several designs that attempt to accomplish this goal. The advantage to this class of rocket is that a large fraction of the rest mass of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher energy density and specific impulse than any other proposed class of rocket. > Antimatter rockets can be divided into three types of application: tho... The decades travel time is a straightforward engineering problem. Step 1, you need self replicating factories. We may have those within the lifetimes of most of the readers of this forum. Step 2, you put self replicating factories on other objects like the Moon Step 3, you turn the entire Moon and the other moonlets of our solar system into mining debris and machinery. This is a simple extrapolation of the capabilities of self replication. Step 4, you use your industry, which is millions of times what earth has now, to build the antimatter production plant and the starship itself. There’s a few ways that might work, using stupendously large lasers and particle accelerators, to get reasonably efficient production of positrons and antiprotons. You then fuse the resulting particles until it’s a heavy element like iron and thus easy to contain in the tanks on a starship. Note that experiments on earth have shown that pair production can be done, and that we have various fusor devices right now that work (you don’t need net energy) and work without physical contact with the gas you are trying to fuse. Step 5, you use your industry to make a relativistic launch apparatus to get the starship up to cruising speed without consuming onboard fuel. Cruising speed is at least 10% of the speed of light. You get it up to speed by either just building a mass driver that can do it or you have it ride a pellet beam. This is feasible, but if it’s more expensive than carrying more onboard fuel, you don’t do it. Step 6, it cruises until it’s time to decelerate, then decelerates. On paper this would get you to a nearby star in 40 years or less, but I think the antimatter engine would have very low net thrust because of all the waste heat you need to dispose of in order for your ship not to melt. Deceleration alone might take decades. Nevertheless, it’s a blink in the cosmic eye and at the next star, you have a self replicating factory and you start the process from the beginning from there. Your “species” are intelligent entities who exist as electronically emulated beings in boxes on the ship, basically. They are immortal and are copied without error as part of the process. They are at least as intelligent and mentally flexible as humans but can think thousands or millions of times faster when needed. As their personalities are mostly fixed, they will not change their minds about expanding across the universe. You may think this is a stretch on top of a stretch. I cannot convince you otherwise, because while _everything_ I just sketched out is currently thought to be possible, it’s not like I can build the stuff mentioned above until a point in the future when it’s possible. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [May 2, 2017, 12:59am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/75 "2017-05-02T00:59:50Z")
Ah…so magic. ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [May 2, 2017, 1:01am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/76 "2017-05-02T01:01:17Z")
> [@Grey](#): > > Ah…so magic. If you can point to a flaw or bit of speculation known to current science, let me know. I will point out one weakness - no one has demonstrated \*efficient \*production of antimatter. Best methods are stupidly wasteful. So it might not be practical to fuel a starship. Everything else is hard science. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [May 2, 2017, 1:18am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/77 "2017-05-02T01:18:09Z")
Presuming that spacecraft can’t go any faster than a Voyager probe is asinine. New Horizons is traveling at about .067% of the speed of light; we could improve on that by a factor of 20 _with tech we could build now_ if we were determined to. With even modestly optimistic technological advancement- not “Star Trek”, more like “The Expanse”- we could do 5% of the speed of light. With conceivable tech anything from 20% to 50%. Even if life-bearing planets are rare, it only takes one to achieve interstellar travel. After that all the barren systems that would never develop life on their own get colonized either by self-reproducing mining machines, artificial habitats, or where possible planets get eco-formed to support life. Exponential growth isn’t some aberrant feature of western society- it’s the basis of all life on Earth and all evolution on Earth: everything grows and reproduces as much as it can. And colonizing species become adapted to colonization: as long as there’s an untapped frontier it’ll get expanded into. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [May 2, 2017, 1:23am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/78 "2017-05-02T01:23:56Z")
> [@SamuelA](#): > > If you can point to a flaw or bit of speculation known to current science, let me know. I will point out one weakness - no one has demonstrated \*efficient \*production of antimatter. Best methods are stupidly wasteful. So it might not be practical to fuel a starship. > > Everything else is hard science. You’ve just said that there can exist a fixated, imortal species capable of a dust to rockets industrial capacity wanting to migrate every few hundred years. You’ve also argued that they’ll travel at a significant fraction of C (let’s say .5) So roll the clock back 10,000,000 years with a starting point on the other side of the galaxy. If they travel 20 light years every 500 years they should have a current colonization wavefront of 400,000 light years from their point of origin. But our galaxy is 100,000 light years wide and we’re sadly alien free. So something in your argument is far more difficult than you allow. 1. Closed cycle self replicating factories capable or boot strapping a civilization is wrong 2. Velocities at significant fraction of C are difficult due to technical limits and/or ablation due to the inter stellar medium 3. Fixated/imortal a species are unlikely 3a. Species, once electronically immortal have any interest in exploring a physical reality. 4. Long lasting technical civilization are difficult to maintain ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 2, 2017, 2:06am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/79 "2017-05-02T02:06:10Z")
> [@SamuelA](#): > > If you can point to a flaw or bit of speculation known to current science, let me know. Here’s one. Every single one of such long-term technological prognostications has been wrong, and it’s been about our own species, let alone totally alien ones. Every single one. It’s generally been wrong by greatly overestimating some technological advances, greatly underestimating others, and totally missing some of the most fundamentally revolutionary ones. Where are all the flying cars and regular passenger rockets to other planets? OTOH, who a century ago could have predicted the microchip or the ubiquity of modern computers or the smartphone or artificial intelligence? With that track record, what are our chances of correctly predicting the goals and technological trajectories _ **thousands of years ahead for a completely alien species** _? ---
**Author:** ![SamuelA](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@SamuelA](https://boards.straightdope.com/u/SamuelA)\ **Post date:** [May 2, 2017, 2:16am UTC](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417/80 "2017-05-02T02:16:58Z")
> [@Grey](#): > > You’ve just said that there can exist a fixated, imortal species capable of a dust to rockets industrial capacity wanting to migrate every few hundred years. You’ve also argued that they’ll travel at a significant fraction of C (let’s say .5) > > So roll the clock back 10,000,000 years with a starting point on the other side of the galaxy. If they travel 20 light years every 500 years they should have a current colonization wavefront of 400,000 light years from their point of origin. > > But our galaxy is 100,000 light years wide and we’re sadly alien free. > > So something in your argument is far more difficult than you allow. > > 1. Closed cycle self replicating factories capable or boot strapping a civilization is wrong > 2. Velocities at significant fraction of C are difficult due to technical limits and/or ablation due to the inter stellar medium > 3. Fixated/imortal a species are unlikely > 3a. Species, once electronically immortal have any interest in exploring a physical reality. > 4. Long lasting technical civilization are difficult to maintain Well, #1 is what human beings _are_, so I can dismiss that argument as it is not correct. #2 is something that can be estimated, the interstellar medium should have a predictable density. This is the strongest argument so far. #3 is wrong, digital systems can do this, dismissing this argument. #3a is wrong, evolution prevents this. #4 is wrong, digital systems can do this, dismissing this argument. Anyways, we’re talking past each other I suspect. I know #1 is correct because living cells are self replicating factories. The megaplexplex in Shenzhen is a self replicating factory that can turn rocks into machines, so clear that argument is incorrect. Digital systems need not decay, error correction can trivially maintain data states past the expected lifespan of the universe. And evolution means that if there is a pool of different beings, and just _once_ someone builds the _first_ starship, that’s it. The universe should be full of such beings. Remember, the starship is crewed by beings who have a digital state and thus will never not want to stop expanding. They won’t lose their technology because of error correction (damage that doesn’t flat out destroy most of the ship can be repaired with no loss of information). They need only gain access to rocks with a wide variety of elements and they can continue the cycle forever. (and can probably just make any element they need via fusion if they have to, albeit very slowly, if they have access to a star) Why are we alien free? I can’t say for certain. I just think that the probabilities are strongly leaning away from any theory that posits advanced beings who _can_ make von neuman starships yet who aren’t doing it. [Previous page](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417.md?page=3) [Next page](https://boards.straightdope.com/t/idea-for-what-the-great-filter-could-be/785417.md?page=5)