Aliens and intergalactic spheres of influence

Over the years, I’ve done a lot of posts speculating about alien civilizations. My take is generally that while extraterrestrial life may be prevalent in the universe, complex life is rare, and intelligent civilization producing life is profoundly rare.

This seems evident from our own history, where simple life appears to have started as soon as it could on Earth, but complex life took billions years to get off the ground and needed numerous prerequisite developments. A civilization producing species only evolved once among 8.7 million different species, and required a highly improbable sequence of events.

There’s also the Fermi paradox, which asks if alien civilizations are common, then where is everyone? Taken together, it leads to the profoundly rare conclusion. That means our nearest neighboring civilization is likely very far away, far enough that there hasn’t been enough time for them to reach us yet, likely hundreds of millions or even billions of light years away.

This means it’s possible that, due to the expansion of the universe, we may never get a chance to meet them. If we do, it will likely be some distant vanguard of human expansion into the universe, or our AI progeny, that eventually meets their vanguard or AI progeny, probably millions or billions of years in the future.

It turns out Robin Hanson thinks along similar lines, although in far more detail. Scott Aaronson did a post this weekend on Hanson’s theory about alien civilizations, which Hanson himself has detailed in a series of blog posts. His estimate of the distance to our nearest neighbor is one to four billion light years. I don’t fully understand how he narrows it down to that range, but it seems plausible enough.

Hanson discusses the idea of a “grabby civilization” (GC), one that is aggressively expansionist and appropriates resources in the universe for its purposes. This is in contrast to other quieter civilizations that may be in harmony with nature or something and not be very noticeable. But a GC should be very noticeable, building Dyson swarms around the majority of stars in galaxies, making those galaxies less visible, except in the infrared range, or perhaps other megaprojects we haven’t conceived of.

We don’t see signs of a GC (at least not conclusive ones). But Hanson points out that the light of their alterations may not have reached us yet. Depending on how fast such a civilization can spread, that light may not reach us too far ahead of the civilization itself. In other words, there is both an expanding sphere of influence for the GC, and an expanding sphere of detection. A GC able to expand at near the speed of light may not have a sphere of detection much bigger than its sphere of influence.

Of course, this is on cosmological time scales. A civilization expanding from an origin a billion light years away, that expands at 99% the speed of light, would still have its effects visible to us 10 million years before they arrived. But it would mean they had already appropriated everything in that direction.

Hansen thinks a more likely scenario is, assuming we don’t destroy ourselves, we become a GC ourselves and start expanding. This brings us back to the scenario I mentioned above, where our vanguard meets theirs, half a billion years from now on Hanson’s estimate. My assumption had always been that it would be a surprise event for the two vanguards, but if Hanson is right, they should see each other approaching in advance through their visible effects.

It’s worth noting that expansion throughout the universe would likely not be straightforward, but would often involve following cosmic filaments around intergalactic voids. We might imagine humanity’s vanguard splitting from each other in many directions, and then meeting again on the other side of a void. But hundreds of millions of years could have passed in the interim. How different might the factions have become over that period? Those factions might be almost as alien to each other as anything else they might meet in the universe.

In both cases, you have to wonder what happens when two GCs, or even two factions of the same GC, meet like that. It might be natural selection on a cosmological scale. Even if some encounters are friendly, it’s not hard to imagine many of them won’t be. And it’s not like either side would be able to coordinate a consistent policy across disparate meeting points since all communications could only happen at the speed of light.

Hanson also notes that the time span for expansion is limited. The local Virgo supercluster is expected to become causally separated from the rest of the universe by 150 billion years from now. Eventually, the local group will itself become isolated from the rest of Virgo. We’ll be able to see the rest of the universe for trillions of years, but the light will only be from the first 150 billions years or so. In other words, we might eventually see the effects of many more civilizations than we ever have the chance to meet.

Hanson imagines different civilizations sending out information about themselves into the wider universe. Some may try sending information physically, all in an attempt to tell their story to a wider universe, while there’s still time.

Once the various islands of the universe have become isolated from each other, there remains a long future, as everyone watches the rest of the universe become increasingly more red shifted, and bizarrely, time dilated. A long time to review the stories they may have received. In later ages, the idea that there was once a wider universe could become the stuff of distant legend.

Of course, all of this assumes this type of expansion is possible. Or if possible, that it’s possible fast enough for civilizations to come into contact with each other. It might be the expansion is possible, but only practical at 5% of the speed of light, which might put us back into the mode of never encountering each other. Although it shouldn’t prevent us from seeing their effects.

What do you think of Hanson’s idea of grabby civilizations? Should we become one as a defensive precaution? Or hunker down as a quiet one and hope for the best? I’m usually dismissive of the idea of Earth as a backwater in our galaxy, but on an intergalactic scale, the local group actually is a backwater. Maybe we shouldn’t call attention to ourselves?

98 thoughts on “Aliens and intergalactic spheres of influence


    This is a common misconception. People talk about the improbability of us produced by evolution. But, if you look at the improbability of any of us as an individual, it is immensely unlikely. Going back, generation after generation, your ancestors had to survive long enough to have children who survived. The odds are immensely negative about your creation. By evolution doesn’t give a flying fart about you. If you hadn’t been born, somebody else would have been. When you look at the probability of evolutions creating some “new species” the odds are fantastically high. When you look at “life” surviving major catastrophes (the entire earth freezing, huge vulcanism, massive asteroid strikes, etc.) the odds are very, very high for survival . . . changed by still evolving.

    Similarly there may be billions of galactic civilizations right now and we probably wouldn’t know it. If there were all of these, spread out in the universe as we understand it now, how far apart would they be on the average? They would still be immensely spread out. A civilization only 200 light-years from us (our galaxy is roughly 100,000 light-years wide) which was searching for exoplanets, would see Earth as it was 200 years ago. What part of earth in roughly 1900 would be visible? Our pollution from out industry might be detectable, but radio was in its infancy, etc. Even if this civilization “discovered” us and decided to make the trip, how long would that trip take. At half the speed of light, an immense velocity, it would take close to 500 years. At the rate we are going, will we still be here in 500 years? Would that other civilization take the trip knowing that their information is at least 200 years old?

    I can’t imagine life is rare. If life isn’t rare and evolution is a thing (it is), then intelligent life elsewhere is virtually a given, but spread out over the vast distances and spread out in time over billions of years, the odds on any of us getting together or even communicating is infinitesimally small. Of course, we may find a way out of this trap in physics yet undiscovered (It’s a warp drive, Captain!) but with the current state of affairs, Fermi’s paradox is as misguided as Olber’s paradox was.

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    1. The thing is, if there are billions of civilizations, and if interstellar travel of any type is possible, they should have been here long before humanity ever evolved. It’s been estimated that even if they are only able to travel at 1% of the speed of light, a civilization should be able to colonize the entire galaxy in 100 million years. Certainly not all civs would be interested in doing that, but it only takes one.

      I’m definitely not saying life is rare. But complex life probably is moderately rare. As for a civilization producing intelligence, if you study the evolutionary record, we are the result of numerous unlikely events. It’s possible we almost went extinct multiple times. If we had, no civilization would have developed, and there’s no other species that looks likely to produce one. The best hope would be other primates. Remember, producing a civilization needs not just intelligence, but an appendage equivalent to the hand.

      Olber’s paradox was misguided? I think it demonstrated that the then current idea of a static unchanging universe was unfeasible. It required a universe with a beginning, and the expansion of space helped too.

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    2. I think the probability of me existing in the universe is quite likely. If I compare my existence to everything that I come across, the infinity of things that I can come across in the universe puts my single existence is highly unlikely, but that’s just because I am excluding myself in my ability to know of these other things. But the fact of the matter is it’s probably most likely that I have a risen in the universe and will continue to arise in the universe is highly likely, whereas anything else becomes increasingly more unlikely. 😁


  2. The laws of physics lead inevitably to nuclear and atomic structure, which lead inevitably to simple and then complex chemistry, which seems very likely to lead inevitably to cellular life. So far, so mechanical.

    Once life gets started, evolution kicks in and you can debate how likely this is to produce multicellular or intelligent life, but with billions of years and unbelievably numerous instances to work with, it is very hard to believe that intelligent life only happens once in the universe. But the universe is a big place, and observations tells us that civilisations are rare.

    Perhaps civilisations inevitably destroy themselves, in which case we are all screwed, but not all game theory ends in lose-lose. Some civilisations must surely endure, however bad the odds. Key, I believe, is whether a civilisation reaches escape velocity before something causes their demise, and expansionist (grabby) civilisations are most likely to do this. This is what the game of Monopoly teaches us.

    So, if we survive, we’re most likely to meet a grabby kind of ET, and, as you say, a post-biological kind, as these must be the grabbiest of all, because they are engineered to be that way.

    Your article is very interesting, Mike. You’re right that a meeting between two alien civilisations is likely to be not a surprise at all. Both sides will literally see it coming. Game theory doesn’t suggest a good outcome. And two civilisations with a common origin but separated by millions of years – as you say, they may be chalk and cheese.

    The universe is a very violent and destructive place at a physical level. Life is a mere perturbation, but at its own scale, just as violent, and there’s nothing we can do to change it. Thanks, evolution! We can become peace-loving vegans in search of intergalactic harmony, but when those Martians land, they’re gonna zap us with their ray-guns and kick our butt. Game over.

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    1. Thanks Steve. Good points. The earlier developments do seem inevitable. But as each development builds on the other, the possibility for variance increases.

      By the time we get to humans, the possibility evolution would have produced us again if the clock were turned back to the beginning seems infinitesimal. Of course, it can be argued that intelligence and dexterity could find other paths, and that’s definitely true. But it only happened once here in 4 billion years. It’s not hard to imagine the entire history of life on Earth playing out with it never happening.

      And the observational evidence seems to indicate that either intelligent life is rare, it virtually always destroys itself, or interstellar travel (much less intergalactic travel) is impossible. I suppose it’s also possible that everyone transcends to a level we can’t currently comprehend, but that’s a major postulate we have no evidence for.

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  3. Did you notice that Scott Aaronson has a post out on this topic.

    I’ll repeat a comment I made there.

    I think there are two major factors overlooked in most considerations of alien civilizations.

    1- Many species hide themselves with camouflage in one way or another. Hiding yourself is a sound strategy especially if you can’t be certain of your ability to cope with unknown predators, but it is also a sound strategy if you are the predator. We would probably be well-advised to hide or disguise our own presence rather than advertising it. If other civilizations have adopted this strategy, we would not likely know of their presence even if they were among us.

    2- Lifespan could be a critical factor in how civilizations evolve. For one thing, exploration of the cosmos makes little sense for an individual unless the individual is able to live long enough to outlive the vast timeframes required for exploration. I’m dubious of von Neuman probes being desirable or workable except perhaps for initial explorations. Second, advances in biology and medicine are likely to create eventually a species with the ability to extend life virtually forever. Things would need to change drastically in such a civilization. I think likely the birth rate would need to drop to zero. No more children or only an extremely small controlled number. As the civilization spread out, the population density itself would become less and the amount of resources required to sustain small settlements or outposts would be very small. This would also be very congruent with a hide and camouflage strategy.

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    1. I actually mentioned and linked to Aaronson’s post. It’s what clued me into this.

      For 1, if that were truly a feasible strategy, I could see some, perhaps many, doing something like it. But hiding our thermodynamic footprint is virtually impossible. And mathematically, there’s just nothing that stands in the way of a civilization having a probe in every solar system in the galaxy. Long term, I don’t think hiding is really an option.

      On 2, I suppose if we achieve an extended lifespan before reaching the stars, we might settle into a zero population growth habit. But once we do reach the stars, and have unlimited space and resources, I wonder how long that would last. The biological imperative seems to be to expand to fill the available space where energy is available. It would only take a minority faction among us to restart it. So even if 99% of the species eschews reproduction and expansion, the other 1% can still expand exponentially.

      That last point applies to just about every other theory on how there could be large numbers of civilizations. The factor that keeps them away and hidden has to be true with 100% consistency, with no exceptions (or profoundly few exceptions). That seems unlikely.


      1. If your civilization is small, hiding is certainly an option. And you do underestimate the technological feasibility of hiding thermodynamic signatures. Stealth aircraft do that. The Klingon cloaking device – surely feasible maybe even on enormous scales for a sufficiently advanced society. Actually there was an Star Trek episode with a cloaked planet.

        On 2, immortality and reproduction might be compatible. But why would a civilization with customs and science that involved immortality and controlled reproduction toss it aside in favor of massive consumption and exploding growth with risks of exposure? I think your human-centric bias is leading you to think that every intelligent creature will be as stupid as we are.


        1. From everything I’ve read, actual thermodynamic waste heat isn’t nearly as easy to dismiss as a lot of science fiction implies. The Expanse actually did this a bit more realistically (at least in the books). It has ships that are able to hide their waste heat (when not under thrust), but only for a limited time, since it builds up, eventually endangers the ship itself, and has to be dumped.

          I think what you’re calling human-centric bias is actually biological bias, the biological imperative to expand as wide as possible. Why would a civ switch to consumption and growth? Why not? Remember, grabby civs are pretty hypothetical right now. It’s not hard to see most civs deciding there’s no one else out there and not worrying about it. At least until the light starts to come in showing their existence, but by then, it’s way too late.

          And again, remember, even if only a minority of civs do this, that’s enough, assuming they’re not so far away that it’s irrelevant to us.

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          1. Nope. It’s human-centric I would contend.

            We humans find ourselves with rapidly increasing technology, population, and resource consumption and are threatening the collapse of eco-systems. We think alien civilizations to be bigger versions of the same. It is like we are seeing ourselves in a carnival mirror, distorted, stretched, but essentially human in all the ways we are modern technological humans.

            What drives expansion is usually population growth or resource contention from population growth. There have been explorers, of course, but they don’t settle down. The ones who settle only move on when they exhaust resources but, in human history, that has been largely because of population growth. Reduce the human population to 10,000 immortals, add some robots for the grunt work, and imagine what sorts of reorganizations would occur.

            The idea that will be groups that wouldn’t go along with the plan is conceivable. But that assumes several things. A group would break off from an established civilization with guaranteed immortality. The civilization would allow the group to break off. The group that broke off and resumed expansionistic behavior would not eventually come up against population and resource constraints that would lead to its collapse.


          2. Imagine an immortal society of 10,000 people. Now imagine millions of years pass. No one in that civilization is going to want to do things differently? Ever? And even if the civ successfully suppresses that urge, it will be successful every time it comes up, bar none? And this will happen with every other civ that arises in the universe, again bar none?

            I think if the option to expand exists, at least some faction will always eventually do it, because they can. It might turn out that the option isn’t feasible, but if it is, I have a hard time imagining that it’s never exercised.


          3. Think of totalitarian societies. Ant societies. The Borg. You are projecting a lot of American and free market type of views onto alien life. It’s unlikely any expansionistic civilization will survive long-term. So even if some group broke off from civilization it probably wouldn’t last.

            You can’t imagine what sorts of social structures and norms might come to be in a society of relatively small numbers with extremely long life times.

            It is odd is there is widespread speculation about alien civilizations destroying themselves through war, resource depletion, or something else. Yet the entire expansionistic meme is based on multiple civilizations over thousand of star systems being able to avoid self-destruction.

            I think the only way expansion would happen would be with a deliberately small footprint and highly organized society.

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          4. It is slightly amusing to argue, however, that an alien civilization who could travel about and settle all over the galaxy might be stymied in their development of a cloaking device.


          5. They’d also likely be stymied in their ability to develop a perpetual motion machine. Unless they find a way around the laws of thermodynamics. But if we bring in new physics, all bets are off.


          6. Or let’s say we wanted earth to appear uninhabited by intelligent life.

            Start with only 10,000 people.

            Remove above ground artifacts, destroy most artificial satellites

            People live almost entirely underground and heat is deflected back into the earth. What is above ground is wrapped and camouflaged with tree, grasses, and vines. Food is engineered fungus, artificial meats. Communication is underground or point to point for long distance so nothing leaks into space. People might also live in a relatively small area so long distance communication would be unnecessary.

            Most of the planet is wild and untouched by humans.

            I would think earth would resemble much what it looked like 10 million years ago to any casual visiting aliens – a vibrant ecosystem with a lot of diversity but nothing close to a civilization level intelligence.


          7. Certainly if an entire civilization devotes itself to keeping a small energy footprint and living underground, they may escape notice. We certainly wouldn’t be able to see such a civilization from a distance.

            Of course, if a GC comes along, it wouldn’t save them if the GC converts their entire solar system into a Dyson swarm. They might be better off hiding in a rogue planet deep in interstellar space. Or just being out in the open and hoping the GC is benevolent.

            Of course, a GC that is currently benevolent may not always be benevolent. In a universe of GCs, it seems best to be a GC, or at least part of one.

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          8. Still the question would be whether GCs could exist for long without collapsing.

            That is where I have my doubts. I’m doubting the premise that such a civilization would even escape its own planet without transforming into something different.

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          9. Once a GC has spread over a substantial number of star systems, what do you think would bring down the whole civilization, or perhaps more accurately, the entire family tree of civilizations? I can imagine a virus of some type (biological or informational) causing a lot of damage, but the speed of light limit would offer some protection.

            I do agree that leaving its own planet would inevitably result in transformation. I think spreading into space is a lot more like animals spreading to land than Europeans colonizing other continents.


          10. You’re right to add “family tree” because it is hard to see how a single cohesive civilization could be maintained over thousands of light years. So it is really a question of the child civilizations, how they behave, and what becomes of them.

            Any child system could fail or fail to spread because of unchecked AI, exhaustion of resources before it could spread, internal strife, a planetary system catastrophe, no suitable new systems near enough, or contact with another civilization that stops it from spreading. If we are assuming there will be sophisticated expansionistic civilizations, there is no reason to assume there wouldn’t also be opposite sort of civilizations that would check them or exterminate them if necessary.

            A child system might also simply lose interest in expanding or finds its own challenges so daunting it couldn’t mount an effort.

            I guess there might always be some branches that would survive and propagate, but the lines that survive might be very unlike the original progenitor. So there would be no guarantee that whatever drove the original civilization on expansion would persist in the child civilizations.

            If we assume continued technological progress, it could simply become that the rationale for expansion vanishes. If you can extract all of the energy you will ever need from a black hole or empty space or [fill in the blank] , for example, then there is no reason to go anywhere else.

            But I still think we are projecting a lot of human-centric views on these civilizations. We seem to be looking at them through a narrow lens of rockets and energy generation and usage with no thought to what might be happening at the biological and social organization level. When we develop a feasible propulsion system that can transport hundreds of people at 25% the speed of light, what will our capacity for life extension and genetic manipulation look like. What will we have evolved into?


          11. Definitely each of these child civs would be different. and different branches would evolve away from each other. As I noted in the post, different wings of the GC might be as alien to each other as anything they may encounter with a completely different origin.

            There are all kinds of reasons any particular child civ might fail. You list a lot of them. But even if only a small percent survive and want to expand, the expansion will continue. Since we’re talking about something that is exponential, even if large portions of the GC fail, it wouldn’t stop expansion. (Including expansion into regions that have failed.) That doesn’t mean there might not be dark ages during those times of failure.

            I don’t agree on the human centric part. Of course, as humans, we can never completely guarantee we’re free of anthropomorphism. But we have plenty of examples in biology, of very non-human species expanding to fill any available niche. I don’t think it’s problematic to see that at least some other biospheres would produce similar systems.

            I will acknowledge that if the transition is to AI systems, we’re entering a phase we have no examples of yet. But even here, we return to the point that if only a tiny minority want to expand, the expansion still happens.

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          12. Whether it would be exponential would be highly dependent on the failure rate. If only one child survives and propagates, it certainly wouldn’t be exponential. It certainly wouldn’t result in anything like a sphere encompassing more and more in all directions. Even if it is several it might only result in expansion into one or two regions especially if the regions tended to have more favorable systems. For a biological analogies, even when species expand they usually don’t expand everywhere equally but instead expand into favorable niches. Also, the more profitable areas for expansion might actually be where they came from. So the children might end up expanding back into the progenitor parts of the galaxy with potential for conflict and war.

            Even after expansion, the progenitor civilizations could fail so instead of a large ever-growing sphere you end up with isolated pockets of civilizations

            The idea of a minority deciding to expand probably isn’t as easily accomplished as you seem to think. It is one thing for a group of a few hundred people to pack up their gear and head out from the homeland on earth but it might be quite a bit more costly to pack up a space ship with enough stuff to survive the years of a journey and to reestablish a new civilization a few hundred light years away.

            However, the original post I think may be assuming something different than these sorts of scenarios. It seems it could be thinking not so much of a civilization gradually fanning out across the galaxy in stages but rather a civilization that reaches a sort of technological max that would enable it to expand at near light speed in all directions. If something like that is possible, it would seem to me likely they are already here and hidden from us.

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          13. It depends on how long it takes civilizations on average to arise and how far apart they are. Here’s where I’d like to understand Hanson’s estimates a bit better. Why 1-4 billion light years away, instead of 100 million, 10 billion, or 100 billion?

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          14. Frankly I haven’t invested that much time in trying to understand the model but isn’t the estimate based on the age of the earth and the fact they aren’t here yet. That would assume that they really aren’t here but I would argue they could easily be here and maybe have been here for millions of years but hiding. Anyway, if you buy into the idea at all, I think that would be as likely a conclusion as any other.


          15. His model does take as data points that they’re not here and that we haven’t detected them yet. He describes it as having three parameters: the expansion rate of a GC, the number of what he calls “try-try” steps in the “local great filter” for producing the GC, and the third is some kind of constant that modifies the second for overall filter strength. But he quickly loses me in the details.

            It seems like that first parameter could be changed to their expanding sphere of detection, which would always be at the speed of light, at least if Hanson is right about how detectable they should be. So even if they can only expand at 1% c, their detectability still expands out at c.

            While it’s conceivable they could be here and hidden, we can postulate anything as long as we stipulate that it’s undetectable. But it seems like the simpler explanation is that they’re just not here yet.


          16. I hadn’t seen that one, but I’ve definitely seen stuff like it, and even engaged in similar speculation myself. We can’t rule out that we’re not like monkeys oblivious to the significance of the buildings and vehicles we’re crawling over.

            On the other hand, I always think about this point from Isaac Asimov.

            Ah, but must all kinds of intelligence be the same, or even similar, or even recognizable? Might not a boulder be as intensely intelligent as we are, or more intensely, but be so in a completely unrecognizable way?

            If that is so, there is nothing to prevent us from saying that every individual object in the entire Universe is as intelligent as a human being, or more intelligent than one, but that in the case of every single one of those objects, the nature of the intelligence is so different from ours as to be unrecognizable.

            If we can successfully maintain that, all argument stops right there and there is no room for further investigation. We must set limits, if we are to continue. In searching for nonhuman intelligence, we can reasonably limit ourselves to such intelligence that we can recognize as such (even if only dimly) from reproducible observations and by using our own intelligence as a standard.

            Asimov, Isaac. Extraterrestrial Civilizations (p. 8). Random House Publishing Group. Kindle Edition.


          17. Use lasers to dump your waste heat into intergalactic deep empty space, with a very narrow focus. Cross your fingers and hope that the grabby guys didn’t invest in a huge array of intergalactic void probes in anticipation of just such an action.

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          18. Converting waste heat into a laser beam sounds cool. Unfortunately it is forbidden by the laws of thermodynamics. Waste heat is exactly what the name implies – waste. It cannot be converted into a useful form of energy (and a laser is definitely useful), otherwise you have a perpetual motion machine.

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          19. Does that still hold if the system in question (waste disposal) is receiving additional energy from somewhere? In other words, an isolated system can’t lower its entropy, but a system with new energy coming in can. Is this different from that?


          20. If more energy is being supplied, then yes, you can produce a laser beam. In thermodynamics, this is called work. But now you have even more waste energy to deal with! Eventually any system however efficient generates heat, leading to a temperature rise, and hot objects emit black body radiation.

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          21. You could have a (coherent, even, I think) beam of very low frequency photons carrying very high entropy waste heat. The problem for my idea then becomes that this puts a limit on the maximum free-energy consumption rate of your civilization. But then, presumably only non-greedy civilizations would be interested in such hiding-away measures in the first place?


          22. It does put a limit. You can always add new lasers, but each addition increases the chance of detection. Although the method might work for something like a cloaked warship, as long as it isn’t under thrust or firing weapons. The time would still be limited, but probably far less limited than if the ship is just bottling up all the waste heat.


          23. I’m afraid your laser, if it worked at all, would generate more waste heat than it could emit. David Brin famously made a similar mistake in his novel Sundiver.

            There is also the problem, if you think about how lasers work, of getting it to work at all. Waste heat, almost by definition, cannot be moved around or used. The operation of lasers involves changes in energy levels, and I’m afraid the notion of “coherent waste heat” is not, itself, coherent.

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          24. The thing about definitions is that you have to be careful that the one you’re using matches the topic at hand. One man’s waste is another man’s treasure. The hiding civ is throwing away what you would call treasure, i.e. free energy, in order to safely dispose of (what all would call) waste.

            Interestingly, according to this laser engineer, the maximum theoretical efficiency of a laser is arbitrarily close to 100%. Of course, he isn’t talking about using the laser as an air conditioner (aka heat pump in reverse), so maybe that would be different. I suspect that the latter would just be the Carnot efficiency, but I haven’t thought it through.


          25. They’re talking about the efficiency of lasers, how much of the energy put into the lasing comes out as light. That particular thread is talking about high-energy lasers, which would be the opposite of what’s considered here. Even low energy lasing involves energy and waste heat, pretty much by definition, isn’t energy we can leverage.

            One problem with it working is the wavelength of the photons involved. It’s hard to get things to lase at 10 km wavelengths.

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          26. The peak wavelength of CMB radiation is 1.9mm. So: maser. When the hiding civ disposes of heat they’ll need to sacrifice some otherwise-useful work. I think that implies choosing a shorter wavelength? – but preferably not much shorter. Of course, the wavelength either gets longer as the universe ages, or their refrigeration system gets further and further from its maximum theoretical efficiency. But they don’t need to hide forever, just until the threats have likely gone over the cosmic horizon.


          27. OK, forget the laser. I can’t find any way to use a thermal gradient to directly induce a population inversion. Instead, just use geometric optics to direct the emission in a preferred direction, and use ordinary heat pumps to heat the photon-dumping element.


          28. Your car engine’s “waste heat” is only waste from the point of view of that extremely inefficient internal combustion process. That it can be used to heat your car, cook food, or cause severe burns, shows it’s not the waste heat we mean here.

            We’re talking about, for instance, the heat energy imparted by your car to the road surface as the car passes over it. This comes both from tire friction and heat radiated from the car (unless the road is already much hotter, then the road heats the car).

            The only way to capture such low-level heat is with something much colder (which had to be chilled, which generated heat), and all you end up with is equalizing the heat to ambient. True waste heat is actually very cold, relatively speaking.

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          29. I don’t know Wyrd. It seems like, short of a black hole, no form of waste is going to be so entropic that, in principle, it can’t be transformed with enough fresh energy. Of course, any transformation is going to involve producing more waste than is taken in. Entropy always increases.

            But for waste heat to leave the system, there has to be a gradient of some type, and it seems like the gradient could be set up to control where the waste heat goes, at least to some extent. That too takes incoming energy, but it’s not obvious to me it would necessarily generate more waste than is radiated away. Although I can buy that something like a laser might.


          30. If we pour energy into a high entropy system, all we do is transfer energy to that system (losing some in the process). Now that system has slightly less energy than we started with, and we’ve generated more waste heat.

            The gradient for waste heat is outer space, which is cold enough to produce that gradient. Low-frequency photons radiate it away.

            As on The Expanse we can use energy to heat pump some cold we can use to sink our waste heat, but also as on The Expanse it ultimately cooks us. The only way to move heat is by creating more heat. Thermodynamics is a losing game!

            Liked by 2 people

          31. But I don’t. My thought is that if you invest some work, the amount of directed energy can exceed the amount of work. Much as, if you expend some work in a heat pump, the number of joules delivered into your house from the wintry environment can exceed the work.


  4. If intelligent life can happen here, it can happen elsewhere. While the odds are probably very small of it happening, that does not mean it is impossible. Given the vastness of the universe, even with such small odds, it is highly likely other intelligent tool users are out there somewhere.

    That vastness of the universe, with its incredible, incomprehensible scale, with its incomprehensible number of galaxies, multiplied by the incomprehensible number of stars, multiplied by the incomprehensible number of planets, strongly suggests we are not alone.

    But that vastness also means we are so far away it isn’t likely we will ever know of each others existence. And if we did, it’s unlikely we could ever communicate, let alone meet. Light years are just that, how far you could get at the speed of light in one year. We can’t get anywhere near light speed and even if we could it would take 4 years to visist the closest star. It would take 2.5 million years to visit the galaxy Andromeda at light speed.

    If there was a known intelligent species within Andromeda, and we wanted to visit, and could, there may be nothing left of that species or its solar sytem by the time we could get there. A lot of things can happen in 2.5 million years. (The fact that we are on a collision course could drop that estimate a bit.) I sincerely doubt our own survival on earth would survive a crewed mission to Andromeda.

    I think we have to be satisfied knowing that life is out there somewhere. But the idea we could visit is a pipe dream. Unless there comes a tech that can defy the laws of physics as we know them.

    Liked by 1 person

    1. Thanks shelldigger. And welcome!

      I agree with most of what you write. Although I’m a bit more optimistic that we could someday encounter them. But it’s also not hard to imagine scenarios where it will never be true. It could be that Hanson’s estimates are too optimistic, and they’re beyond the visible universe. Or even if they aren’t, the limitations from energy and entropy might make the distances just too immense.

      Even if we do ever encounter them, “we” might amount to our AI offspring. Indeed, it seems like the first encounter would likely be between automated craft from both civilizations, which may not have the intelligence for any meaningful interaction.


      1. 🙂

        Someday, would be nice. But I have my doubts. But to say contact is impossible is begging to be proven wrong 😉

        The distances is the problem. Unless someone else has figured out light speed travel, or FTL even, or some way of bending space/time and punching through. Or, some weird thing we haven’t imagined yet, those distances to me seem insurmountable. Which is what drives my negativity on the issue. Magic, unfortunately is only an option for the religious.

        Even if a solution to high speed travel was found, there are still many hurdles to be overcome. Survivng years of irradiation, as well as basic sustainability, in space, would be high on the list.

        Now the meeting of AI’s has a better chance of success I’d think. But as you mention interaction would be difficult. Likely any interaction would be interpreted wrongly, and badly, if it were possible at all. Just knowing we encountered something that wasn’t ours would sure make news though.


        1. I do think a knowledge of the history of statements about what is impossible should make us very careful with the i-word. I minimize my use of it. We don’t know what we don’t know.

          But I agree that the distances make the idea of biological humans traveling that far very remote. Short of new physics, I’m not convinced humans will necessarily leave the solar system, much less the galaxy. If we do, it won’t be in human form anymore. But that’s a different topic.

          For the meeting itself, it depends on just how much intelligence goes into the probes on the frontier, and how seriously anyone thinks the possibility is of actually encountering anyone else. If we’ve gone hundreds of millions of years without any such encounter, it might be considered impossible. By the time their presence can be detected, there may not be enough time to change the programming of the leading probes.


  5. A Follow-up on Previous Comment

    Re “His estimate of the distance to our nearest neighbor is one to four billion light years.” If this estimate is right, there is no more, on average, than one civilization per galaxy. While the galaxies are spread out *less* than the stars within a galaxy are, the distances between galaxies are far, far greater than the distances between starts within a galaxy.

    A 1-4 billion light year separation in distances is a 1-4 billion year difference in time. If another civilization were to become aware of us, it could only do so from 1-4 billion years ago in time. Neither they nor we would exist at any time in the future when our civilizations came into contact.

    People seem to underestimate these separations on space and time.


    1. There are actually about 60 million galaxies within one billion light years, so if the nearest civ is one billion light years away, and they’re all one billion light years from each other, that’s maybe one civ per 10 million galaxies. Although we might imagine civs are a bit denser toward the center of a supercluster. (We’re on the edge of our local supercluster, Virgo, which itself is just a branch of the overall Lanikea supercluster.)

      You’re being pretty pessimistic about our long term prospects. I can’t argue against that. We may well destroy ourselves. But if we do manage to colonize other solar systems before we do that, it becomes hard to see us completely going extinct. Although in that far future, we might have evolved into something (probably several somethings) we’d consider as alien as any actual aliens by then.


    2. Hey Steve! 🙂

      Yes, again the distances is the problem. You are correct in the time reference. It took life on earth 3.5 billion years to come up with intelligent enough primates to get to the moon. If we can use that as a baseline (and that’s doubtful, but for kicks let’s do it anyway,) any life that is equally developed would have to have reached the same level of tech we are at right now at the very least, to be able to detect our presence. Most likely they would have to be further along tech-wise to do it. As we are thus unable to do that ourselves.

      Bottom line is, it would be very difficult, for intelligent enough life, to be looking for extraterrestrial life, and find each other, along the same timeline.


  6. You likely remember my simple math model… Premise: At least five “unlikely” serial events (habitable world, moon, RNA, multi-cell, etc) are necessary for intelligent life to start asking questions about what it all means. Each of those events has at least 1-in-10^4 odds. The likelihood of all five, then, is just 1-in-10^20.

    Noting there are roughly 10^12 stars in the Local Group, reasonable odds suggest we’re alone for quite some distance in asking those questions. 10^12 ≪ 10^20

    Alien civilization is almost certainly science fiction. Speaking of which, I’m reading John Scalzi’s The Interdependency trilogy. Pretty decent space opera. (He has his own version of Avasarala. A foul-mouthed no-BS woman in a position of power.)

    Liked by 2 people

      1. I like to think I’m a realist. 😉

        You don’t feel, that for us to be here, there weren’t in our history at least five events for which the odds were at least 1-in-10,000? Everything that happened along the way had lower odds?

        Liked by 1 person

        1. I like to think I’m a realist too. Not gonna argue numbers here, because we both know this is speculation, but I only counted four events in your list, unless “etc” is an event. In which case, I don’t know what kind of probability I’d attach to “etc” ever happening 😦


          1. The list is suggestive, not exhaustive. The premise is simply that there were five events necessary for which 1/10000 odds are reasonable; nothing more complicated than that.


    1. I do remember it. That calculation would leave room for maybe a hundred civilizations in the observable universe, but separated by distances that would make it very unlikely we’d ever come into contact with each other, particularly for us on the edge of our local supercluster. Although like Steve, I think there’s room for more optimism in some of the estimates, but not enough for civs to be anywhere close.

      I read The Interdependency and enjoyed it, although I didn’t find it to be Scalzi at his best. But as always, he’s an easy and quick read. Kiva is sort of a young version of Avasarala, but with gasoline poured on the lack of inhibition.


      1. Of course such a simple math model is extremely crude, but a Fermi estimate seems appropriate for the ultimate Fermi question. 🙂 The model only points out how odds stack up and what that implies.

        Totally agree on all counts about The Interdependency! I do think the Flow is a clever gimmick for the story he wants to tell. As if the British Empire could no longer use the ocean.


        1. I think a Fermi estimate is basically what the Drake equation tries to do. And the Fermi paradox is only a paradox for people who insist on optimistic estimates all down the line. For the rest of us, it’s more of a constraint on the outcome. Although I think we’ve concluded that the equation needs to consider a much broader population than just our galaxy.

          The Flow is definitely a clever gimmick. I’ll wait until you’ve finished before discussing what about the series I thought could have been done better.


          1. Yeah, the Drake equation is the most famous Fermi estimate of all. obviously I’ve come to think the usual assignment of coefficients there is wildly optimistic. It’s possible we’re something of a freak of nature.

            Liked by 1 person

    2. I think I mentioned this before, but when providing odds, I think you need to include a time period. One in ten thousand odds seems small, unless you’re talking about 1/10,000 per year, which is not small odds given a million years.



      1. As I replied last time, we’re talking about singular events: the location of a nascent solar system, gas giants in the outer system, the exact nature and consequences of the collision with Theia, the oxidation of the atmosphere, the formation of RNA, or of multi-cellular life.

        The probability distribution is over all the possible paths for a planetary system, and the die have, in fact, been thrown billions of times in this galaxy. But a simple string of odds shows it might take many, many orders more throws to come up something like Earth Human. Copernicus aside, we may be very rare.


  7. My intuition is basically the same as yours. We’ve talked about this before: how microbes are very common, multicellular organisms are very uncommon, and intelligent life is super rare. But how common is common and how rare is rare are still open questions in my mind.

    I’ve read a few articles now about the limitations of current SETI research. SETI researchers have surveyed some parts of the sky more thoroughly than others, for example, or follow-up research doesn’t happen due to funding cuts—that sort of thing. And then there’s the WOW! signal. Since no one was able to pinpoint an exact point of origin for the signal, it’s been difficult to do follow-up research on what might have caused it.

    I don’t want to dip into conspiracy theory talk with this, but I think it’s plausible to say that the reason we haven’t detected another civilization out there is because we haven’t been looking hard enough. Intelligent life is still sure to be very, very rare. I’m just not sure how rare is rare.

    P.S.: I absolutely want to do a Sciency Words post on “grabby civilization” now.

    Liked by 1 person

    1. We’re definitely on the same page.

      I do think SETI works in a universe where interstellar exploration is essentially impossible, at least on a large scale, or so monstrously difficult that no one bothers. It’s not a possibility I like, but it remains a viable one. It might be that the combination of energy cost, entropy, and radiation from the interstellar medium, are just too difficult to overcome.

      If that’s the case, then there’s plenty of logical space for civilizations out there we haven’t yet detected, maybe as close as a few thousand light years away. (Assuming they show the effects Hanson talks about, we should have seen them if they were closer.)

      One big issue for SETI is that a lot of the communication may be in the form of lasers, lasers that wouldn’t be pointed in our direction. We’d only be able to detect them if we happen to be within the path of one of them. There may be a vast interstellar internet, which we can’t join until we find a local ISP.

      You definitely should do that Sciency Words post! I also think you’d enjoy Hanson’s posts.

      Liked by 1 person

  8. Fun to speculate. Sci-Fy is nothing if not fantastical speculation.

    There are so many facets to the concept of ETs. I’ve made the circuit numerous times and always circle back to analyzing the one place in the universe where we know life, electro-magnetic-manipulating-life, exists. My collection of unique properties of our aggregate system continues to grow. Here’s an odd one to fathom: how would humanity have built a civilization (much less a tech-civ) without trees? Think of all the uses of trees/wood that we’ve leveraged through the ages and how, without it or its analog, we’d been shit outta luck.

    Regarding the topics your raised, one issue I see is the presumptive claim that civilizations are thought of as singular units of intent. If the Chinese, North Koreans, Russians, or Muskians wanted to alert the Universe as to our existence — who’s to stop them? All you need is one filthy-rich Bezos to buck the “let’s hide out in our backwater galactic spiral-arm” trend and the gig would be up.

    Grabby civilizations? We’ve been technologically capable for like a nano-second of galactic-time, and capable of collective organization for a blink of an eye. Beyond the deal-breaking improbability of our existence (2^70, in my opinion) there’s the shear unhealthiness of space outside of our precious “pale blue dot”. Let’s face it, the Universe wants you, me, everyone — dead. (“Want” is strong word here, after all, everyone knows the Universe is Absurd.) All we need to do is wait around for another nano-second or two and POOF! There goes life on Earth. Ask me again about our odds in about 10,000 years.

    Liked by 1 person

    1. It is fun to speculate. And totally fine, as long as we remember it’s speculation.

      Our dependence on trees may go even deeper. Consider how primates evolved. Would we have the body plan we do without the need to navigate among tree branches? Then consider the sequence of trees thinning in Africa that forced some of the primates back unto the plains. And that high grass on those plains may have made walking upright adaptive. Now consider if neither trees nor grass had ever evolved.

      Definitely civs would likely not operate with one intent. And that would be exacerbated once one is spread out among interstellar or even intergalactic distances. What one branch might do could be radically different from what another branch does. The question is what the average actions of such a civ would amount to.

      It’s definitely possible we’re just hairless apes with delusions of grandeur, playing with forces that will eventually destroy us.

      2^70 seems pretty pessimistic. If that’s the case, then the next nearest civ would be far outside our observable universe, and we’ll never know about them.

      The universe definitely “wants” us dead. In that light, I think our biggest mistake might be to sit in one place too long and give it an easy target. Our chances might be better if we’re spread out, assuming spreading out is possible.

      Liked by 1 person

      1. Trees/wood: Although I agree that trees undoubtedly contributed to our evolution, there’s the whole “cooking gave us the option to grow a bigger brain,” theory too (see: Catching Fire (not the teen-pop-story). I tend to allow the probability that some alien species could have acquired an intellect near enough to our own, with our without trees. However, fire (and not for cooking). Without ample wood for combustion for the smelting of metals – no tech-civ.

        Here’s another one that nobody thinks about: beasts of burden (and not to eat). Without the horse, donkey, or oxen (or their equivalent) humans would have been unable to cultivate and transport sufficient surplus food to provide for the specialization of skills required to build a tech-civ. No surplus food, no spare time to develop metallurgy, chemistry, science of any kind, written languages, and so on.

        These are just two of the ^70 that any other alien race would have needed to create an equivalent tech-civ. Now, I admit that there might be alternative paths to a tech-civ. But, I know of only one actual tech-civ, and without those two rarely considered dependencies (not to mention the ~68 others), we would not be here having this conversation.

        Liked by 2 people

        1. I definitely don’t discount those things. They just add to the number of factors that had to come together to produce us. Fire in particular requires a land based animal. And the beast of burden thing made a difference between human civilizations. The Americas didn’t have good beasts of burden, which was among the many things that retarded their progress in comparison to the old world.

          On the alternate paths, that’s true. And our imagination is probably limited by our experiences in our own biosphere. But definitely a sequence of unlikely events has to be replaced by an alternate sequence of unlikely events.

          Liked by 1 person

    2. “…one issue I see is the presumptive claim that civilizations are thought of as singular units of intent.”

      A common SF trope! I refer to it as “Collective Species Insanity” this notion that an entire intelligent species would act with a singular will. (Niven’s Puppeteers are a good example.)

      Liked by 2 people

  9. There is also an issue of control. Is EC centrally controlled or not? How a decision to go out, or to hide made or would be made? So far on Earth, we have a lot of competing fractions. In technologically advanced civilization a lot of such competing fractions could make their own decisions about what to do with an outside Universe. Even with one original civilization that could increase the presence of civilization signals or expansions in space enormously.

    Liked by 1 person

    1. Definitely. I think at the level of an overall civilization, we’re talking about the overall actions of all the factions. So some factions may well decide to go Buddhist, be one with nature, and never be part of the expansion. But if only a minor faction of the civ decides to be expansionist, the civ overall ends up being expansionist. Most likely there would be multiple factions expanding in different directions, not all friendly with each other.

      Liked by 2 people

  10. I think you know where I stand on this. There can be only one. But that pretty much applies to a galaxy. So I agree with most everything in your post, and Hanson’s articles seem to provide some explanatory math. But I do have a few extra comments.

    1. We talk about grabby civilizations, but eventually it only takes a grabby individual, like Musk. (He shot a car into space, for Christ’s sake.) The cost of creating small, intelligent robots will continue to decline. It’s only a matter of time before an individual can create the Neuman probes and start shooting them at stars.

    2. You mention expansion around the empty spaces between galaxies. The question is, if you’re on the edge of this space and you’re shooting probes at all of the galaxies, you’re shooting some straight across the space at the galaxies on the other side as well as the ones closest to you. So each galaxy will get an initial probe long before the sphere of control works it’s way around the edges.

    3. Aaronson’s commentary included my pet peeve: the sun burning up the earth in a billion years or so. My response is, of course, why would we let that happen? Given a few million years to work on it, could we not learn how to engineer and maintain our sun for longer than that? I bring this up here, because that sort of engineering project might be hard to hide. And it’s not just Dyson spheres. Say, the sun is set to expand because it is running out of hydrogen. What if we go collect hydrogen from a few nearby stars? What would we think if we saw jets of hydrogen from multiple stars all pointed towards a single star? Or if we simply saw a few stars in a cluster which simply have a lot less hydrogen than they should? Or something like that.

    4. I think someone needs to work out the math of the Neuman probes. Say in 100 years we can build a Probe and send it off at 50% light speed. Then in the next thousand years we improve the tech and can send one at 80%. Then in the next 1000 yrs we get to 95%. Which of these will get to the edge of our galaxy first? Should we just wait until we get to 95% before we start? Should we send one every ten years, just in case?

    5. What’s the second thing your probe does when it reaches the edge of your galaxy. The first thing is to send probes at other galaxies. The second thing is to set up a system to catch probes from other galaxies.

    [lots of fun to think about]

    Liked by 1 person

    1. Interesting comments James!

      There can be only one? Does that apply to all grabby civs? If so, that’s a pretty stark outlook. (It might be true, but still, stark.)

      1. Definitely it doesn’t take the whole civ. A grabby leader might well do it. Of course, a grabby leader needs at least some grabby followers.

      2. I actually mentioned galactic voids, which are immense gaps between clusters, superclusters, and chains of galaxies. These voids have few galaxies in them. The distances are immense, typically over a hundred million light years. Sending a probe straight through would require that it maintain its integrity for that period with no source of energy. (If we want to hide from a GC and can pull it off, making it to one of the scattered galaxies in such a void might be a good place to hide. On the other hand, if we can make, they probably can too.) It’s worth noting the the local group is on the edge of such a void, given the clever name: Local Void.

      3. We could do that, but it would probably just be a lot easier to move to another star. Or, if we’re sentimental, move the Earth to another star. (There’s a Chinese movie call “The Wandering Earth” that has that premise.)

      4. Someone once tried to work out a framework for deciding when the optimum time would be to launch an interstellar mission. But definitely, early waves of probes might be passed up later by later ones. The issue is, once the probes are moving out near light speed, it becomes nearly impossible to stop them, at least in any coordinated manner. That might be an argument for making them intelligent enough to understand when they might need to stop, such as running into another civ.

      5. Good point. A probe coming in to a galaxy or solar system is pretty vulnerable. Anyone already in that location has many advantages. The only advantage the incoming probe has is its kinetic energy, which isn’t trivial, but it needs to know what to hit, and from a distance, that might be tough to figure out.

      [ 🙂 ]


      1. Okay, comments on comments:
        First, by “there can be only one”, I only mean within a given galaxy because a grabby C is gonna take the whole thing before another gets there.

        On the whole, I have a very optimistic view. I don’t think there will be significant conflict when grabbies meet. As I just said, any given galaxy will be essentially free or taken. I don’t think there will be any motivation to try to take one that is already taken.

        1. Just wanna reiterate: I don’t think it will even take a leader. It will just take an individual.

        2. I mentioned the void *because* you mentioned it. But you seemed to be missing the point, which is the probes will be sent at every visible object at the highest speed of current tech. How empty the void is will determine how much maintenance it might need.

        3. You have no sentimentality? When global warming raises the level of the oceans, are people just gonna leave the low-lying cities? Are we just gonna give up on ideas like carbon-capture and just say “yep, it’s gonna get warmer, best to start scoping out places higher up”?

        4. If it were me, I would program the probes to start cooperating with whatever civ they might find, setting up communication channels, etc.



        1. I could actually see two civs coming in on opposite sides of a galaxy and that ending up being border territory. But the dynamic you describe might well hold for individual solar systems.

          2. My point was that having probes survive a journey through an intergalactic void would be far more challenging than having them survive the normal distances between galaxies. Of course, that itself is far more challenging than surviving between stars within a galaxy, so who knows.

          3. I do, but I’m not sure how long term a solution throwing more hydrogen into the sun would be. Keep doing it and eventually we’d have a blue giant on our hands, which would then end as a supernova instead of a red giant. Eventually the Earth has to be moved, if we’re sentimental. Of course, also eventually Earth’s core will freeze and tectonics cease, followed by the loss of the magnetosphere and exposure to radiation, so sentimentality might eventually have to be satisfied by VRs of old Earth.

          4. Sounds good to me. I wonder if future entrepreneurs will have the foresight to do that.


          1. 1. Re: two civs reaching a galaxy at same time: It’s certainly possible, but I think the odds would be like the odds of two sea-faring civs discovering/expanding into Hawaii at the same time.

            2. Why would travel across a void be “far more challenging”? We shot Voyager out of our system with approx. no maintenance and it’s still working. What do you think would be the challenge?

            3. [You’re not expecting me to come up with the actual solution to Sun maintenance, are you?]
            [And did you just say the equiv. of “Well, we may be able to engineer our way out of our Sun expanding, but we can’t engineer our way out of almost certainly easier problems, like losing our magnetic shielding”?]

            4. I’m hopeful that it will become understood that cooperation is necessary for successful civ. in the first place, and only cooperative civs. are gonna get out into space at all.

            [told you, lots of fun]


          2. 2. On Voyager, they were launched in 1977 with plutonium power sources that will last as long as radioactive decay provides sufficient heat. Over the decades, various instruments have had to be turned off as the power waned. They’re now running on a bare minimum. The probes couldn’t do today what they could in the 1980s. Sometime over the next decade, they won’t have enough power for any instrument, including communications. They will likely die sometime before 2030.

            Now imagine if they had to survive for centuries? Millenia? Eons? In interstellar space, probes might be able to use something like the Q-drive to continue powered operation, but it depends on the interstellar medium. The intergalactic medium is expected to be far sparser. And an intergalactic void would be the sparsest place in the universe.

            It’s conceivable that a void probe might be able to do something with the CMB, but we’re talking about 2.7 K. Most of its instruments would have to lay dormant. For a hundred million years. And then start working again when the probe finally enters a galaxy. That’s a long time to sit at near absolute zero while being bathed in that steady CMB, and then just start working again.

            3. So if you’re going to propose solutions, you should be prepared to at least acknowledge the issues with those solutions.
            How would you propose to fix a frozen Earth core?

            4. Maybe. I’m not sure the expansionist spirit is consistently going to be compatible with all around cooperation.


          3. 2. Don’t forget we’re talking about launching these probes at near light speed which will reduce the subjective time of the probe somewhat.

            3. Fair enough, and I had thought somewhat about the problem about dumping hydrogen into the sun. At some point you’d have to start kicking stuff out as well. But again, an engineering problem.

            Re: frozen earth core — is that something we need to fix? I think it would be straight forward to just put a radiation shield in space. Alternatively, we could just dig down to the center of the earth and build our own generator there, given it won’t be as hot as it is now. I think I might be okay with tectonics ceasing, making long term real estate investments less risky.

            If the whole thing only extends the usable life of the earth by a billion years or two, I’d say it was worth it.



          4. 2. Good point. I don’t know why I was forgetting about relativity. Although it’s no panacea. If the probe is flying at 99% of c, it has a gamma of about 7, that reduces the inflight transit time through a 100 million light year void to around 14 million years. Get it up to a gamma of 7000 (99.999999% of c), and the flight time drops to around 14,000 years.

            The constraint here is the amount of energy needed, which is appalling just to get to gamma 7. Gamma 7000 requires 1000 times that amount (ignoring fuel weight, which makes it exponential). Another constraint is that as we get closer and closer to c, the CMB in the direction of travel turns into a destructive gamma ray bath. The probe now needs substantial shielding. (Which adds to the weight and energy costs.)

            On the other hand, that conceivably could make the CMB a much more usable energy source to allow the probe to continue functioning for long periods of time.

            So if the initial acceleration and later deceleration energy requirements can be solved, it might be doable. Still far more challenging than hopping between galaxies inside a cluster or filament.

            3. I suspect long term, the best solution might be to virtualize the whole thing. Then it can be copied and ported wherever needed until heat death.


          5. Okay, so maybe you don’t shoot a probe at *every* galaxy on the far side. Maybe you just pick a few and spend a few stars, or black holes, to get to those as fast as possible. As your immediate neighbors become populated, they can do the same.



          6. I guess it depends on how badly we want to “quickly” get across the void. We know we’ll get there eventually if we just take the easier paths. What might get us in the void are the sparse galaxies within it.


  11. I don’t think two arms of an expanding civilization that meet up after long separation need to have radically different values. I think there’s a good chance an advanced civilization stabilizes its values.

    By the time interstellar travel is reasonably well developed, I expect a civilization to know the basic laws of physics like the back of their tentacles. They would also know all the body-plans they could genetically and robotically engineer themselves into, including which ones were optimal for space travel and for various classes of planets. They would have advanced AIs to help figure all these things out. And, importantly, AIs would be able to enforce any rules that were made about genetic and robotic engineering. Including especially, rules against creating rogue AIs. Rogue AIs would be those which are likely to control vast swathes of resources in ways the civilization does not approve of. (If the rogue AIs win, they become the new arbiters of approval.) One way or another, it seems to me, some set of values – some ideas about what sorts of lives are worth living and reproducing – dominates the civilization, probably before it can spread to more than one or a few solar system(s).

    If our own psychology is remotely representative, this value structure must disallow evolution for pure reproduction’s sake: that would destroy everything that we value. Sentience as we know it is not needed for reproduction. Von Neumann probes without any people would be prodigious reproducers. That is an obvious, and let’s hope not too easy, failure mode to fall into. Blind evolution got us the values we have now, but if we let it continue, blind evolution will take them away. And I mean “values” in both senses: value-beliefs and -attitudes, and also, values meaning valuable things.

    Liked by 1 person

    1. I don’t know. I think any civilization is going to change over time, at least if it’s still alive and vital in any significant way. And one spread out over millions of light years will see its different wings diverge. Even if they’re optimizing for their current environment, environments vary. For example, the metallicity of a particular galaxy, or the concentration of matter in different regions of the universe, could conceivably have operational effects and constraints on their values,

      I’m also not sure that evolution can be permanently suppressed. Eventually entropy always wins and errors creep into the system, leading to unplanned mutations. Over billions of years, I think we’d see evolution. Where it would go is the question, but I can’t see it as guaranteed that it would necessarily preserve intelligence.

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      1. So here’s a question for you – do you suppose that a set of values could be encoded in a finite memory? If so, wouldn’t it be possible to build a set of machines that (A) periodically error-check themselves and (B) enforce those values? Note that the values could allow for innovation, as long as the innovations don’t violate certain prohibitions.

        I actually have considerable doubt about my first sentence above. But as the computationalist/functionalist that you are, you can’t, without abandoning those views. Or else I’ve horribly misunderstood you for a while now.

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        1. Computation happens in physical systems, and such systems are always subject to degradation, unexpected or unwanted changes from the environment. (Technically these could be seen as input, just not input we want.)

          We can set up protocols to minimize errors, but no system will be perfect. Eventually errors, defects, degradation, will get through. Of course, conceivably we could set up something with so much shielding, redundancy, and checking that the probability of an error is low enough not to arise until after all the stars burn out, but we’re going to have to dedicate a lot of overhead to it, to the extent that virtually all of a sublimely vast system would be dedicated to preserving some relatively small nugget of information. (I suspect there’s not enough energy in the accessible universe to build anything to retain its integrity past heat death.)

          I don’t see anything incompatible here with computationalism or functionalism, except perhaps for strawman versions.

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          1. I think error-checking is more powerful than you give it credit for. As in, a modest amount of redundancy can push the odds very far. I am not a computer scientist though. Does Scott Aaronson do ask-me-anything?

            The non-computationalism would be if you disagreed that a value system could be represented in finite memory. A variant of consciousness-is-beyond-the-algorithm, only with values in place of consciousness.

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    I didn’t fully grasp the magnitude of those numbers until I realized Andromeda is only 2.5 million light years away. The notion of a “civilization” spanning across galaxies seems pretty absurd no matter what kind of model you have. What commonality would one end of the “civilization” have with another end if they were 500 million light years away from each other? How would they even qualify as belonging to the same civilization? Unless there is FTL communication. Or wormholes. If we are down a rabbit hole like that then why limit the civilization to some concentric sphere in space. It would be likely the universe has already been seized by the GC and it is controlling everything.


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    1. I think portions of the civilization that are near each other would communicate and preserve some similarities. But that was my point about separated branches running into each other after hundreds of millions of years. They’d likely be as alien to each other as anything else they might run into.

      All the discussion from Hanson is in terms of STL (slower than light), both for travel and communication. If FTL is possible, then I think it’s safe to say that our nearest neighbors are far beyond the observable universe. Or, as we discussed above, so incomprehensibly strange we can’t even recognize them and, at least for now, effectively don’t exist for us.

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