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A Simple Model of Grabby Aliens (arxiv.org)
86 points by ndr 27 days ago | hide | past | favorite | 80 comments

Hanson’s model is an ecological model. It assumes that modeled entities don’t reflect the model and respond to it. With intelligent agents simple ecological modelling may not work. You need to use game theory and strategic thinking.

Assuming intelligent aliens, they know this model.

Assuming stable state alien civilizations, they have countermeasures.

Grabby Aliens might discover immune system against cancer-like civilizations growing without limit. It should hit them early before they are metastasized.

Grabby Aliens might foresee immune system even before they encounter resistance. They might try stealthy expansion, gradual probing first strategy, or modify their behavior in order to survive, .... and so on.

> It should hit them early before they are metastasized. They might try stealthy expansion, gradual probing first strategy, or modify their behavior in order to survive

This essentially is the Dark Forest hypothesis explanation for the Fermi Paradox. Civilizations work to avoid drawing attention to themselves because might be exterminated as potentially cancerous if detected

It's interesting that, under the given assumptions, you can put such tight bounds on the frequency of origination of grabby aliens.

The assumption that seems most unlikely is that civilizations will simply stop expanding when they encounter another one. Even if most civilizations would stop, a single aggressive one would quickly dominate. Especially under the assumption that they can expand at a large fraction of the speed of light, a defender would have little ability to organize a defense before being overrun.

What does a war between two interstellar civilizations look like? If they can accelerate mass to a high fraction of the speed of light doesn’t that mean their first strike weapons are all planet killers? If we assume they still primarily use planets as the sites of their industrial and population centres then doesn’t that mean any systems within striking distance are immediately obliterated by large, dark, unstoppable projectiles travelling at 0.7c? Any point defence you can think of fails when you can easily throw millions of these at a planet. There’s no way to win that game for either side.

If we change our assumptions about whether they live on or even care about planets it becomes a very different story. Who knows if they even need the free energy that stars emit. Most of the interstellar medium is ionized so it may be that it’s much easier to just scoop up gas and dust with magnetic fields than it is to attempt to extract large quantities of matter from planets that are few and far between not to mention gravitationally bound.

while one can postulate that this level of civilization doesn't need planets as habitats, planets with biomass would likely be an important asset as they ease the supply logistics and act as a trampoline for further, faster expansion.

But once your civilization isn’t threatened with complete and sudden obliteration by planet killers, you’re no longer stuck in the prisoner’s dilemma and you’re not necessarily compelled to strike first. It’s a big difference.

You shouldn't assume that an intelligent civilization wouldn't find a weapon of mass destruction that's effective against a non-planet based civilization.

So the utility cost of the betrayal scenario goes from negative infinity to a question mark.

Outer solar systems bodies have water and other volatiles as major constituents. If you want raw material for human bodies, cattle, trees, plastics, that is where most of it is.

And so would interstellar bodies. I’m willing to bet that a large fraction of the mass of a developing solar system gets ejected during the early years of its formation. If you can freely roam among the stars you would probably find everything you need in interstellar space.

miller experiment shows that there's some convergence on certain molecules, it's safe to assume that while every specific biology will differ, the building blocks will look not that far apart, and transforming existing biomass into usable biomass is going to be more energy efficient than transforming raws into usable molecules.

You just described the cold war :) I don't have any larger point, but found it interesting.

What does a war between two nuclear-capable nations look like? If they can nuclear bombs, doesn’t that mean their first strike weapons are all nation killers? If we assume they still primarily use cities as the sites of their industrial and population centres then doesn’t that mean any city within striking distance are immediately obliterated by large, dark, unstoppable projectiles? Any point defence you can think of fails when you can easily throw thousands of these at a nation. There’s no way to win that game for either side.

Perhaps the winning move, like with today's nuclear weaponry, simply not to play.

Or to hide in the Dark Forest instead of announcing yourself to the cosmos.

This does seem to be the logical conclusion of a game theory analysis. Since planet killers can show up without any warning, the only solution is make it impossible to aim your unstoppable weapons, which means you have to be impossible to detect or locate.

So as you said, maybe the solution to the Fermi Paradox is that every surviving civilization is hiding in cloaked habitats within the vastness of intergalactic space.

By the time you can launch a planet-killer, you are no longer tied to your own planet anymore. It requires marshaling an amount of energy far beyond what you could afford to do in a biosphere, and a biosphere is all a planet really has to offer. Two of these civilizations might certainly take a swing at each other's planets, but it wouldn't end the war by any means; at this point the planet may not even account for single-digit percentages of what is going on in the system.

I think if you look ahead at feasible technology, you get self-sustaining pure-space civilizations long before you get civilizations that can launch relativistic planet killers.

(The other problem with the "planet killer" hypothesis, as we've discussed in other HN conversations, is that there's no reason to wait until there's a civilization on the other end to launch one, given how fast they can pop up. As soon as you see life, you should launch one. But Earth has been broadcasting fairly conclusive proof that a civilization with just a bit more tech than we have now is alive ever since the Great Oxygen Catastrophe, yet nobody has killed Earth.)

When some civilization becomes apparent, wouldn’t game theorizing say there’s a free rider problem? Wait for someone else to poke their heads out to handle it, save us the trouble, and maybe learn how we rank in a battle royale?

With nuclear weapons we had MAD - and even if the other side didn’t retaliate, the planet would be ruined by a nuclear war so no one could win.

This is more dangerous. If weapons are absolutely but selectively destructive - I can wipe your planet out quickly before you have time to respond and my planet is just fine - it incentivizes me to attack first and hunt down other potential threats and destroy them before you or they destroy me.

Yes but it also changes your choice of habitat lest someone do the same to you. Remember with clever aiming these weapons have limitless range so there is no such thing as a border conflict and someone could nuke all of your systems. My point is that this strongly discourages solar system based empires and favours mobile space based civilizations. My hunch is that our galaxy is filled with nomadic hard to detect habitats and that that is the natural progression. There’s probably only a brief period of time where technological civilizations remain bound to their original planet and solar system. That’s my answer to the Fermi paradox.

This is basically what I’m saying. With an alternative to unmovable planets, the Dark Forest scenario becomes a bit less likely because the betrayal scenario in the prisoner’s dilemma becomes a lot less extreme.

Why do you say "had"... MAD is still around. There might be less fear about it in the media, but the danger is still present. As defense technology matures, it might make nuclear war winnable for the side that controls a sufficient nuclear defense. Or it might not.

> Even if most civilizations would stop, a single aggressive one would quickly dominate.

Would this affect their model, though? If either of the two civilizations dominates, rather than both being obliterated through mutual destruction, you would expect to see the same thing: that volume of space time is now occupied by a civilization. I’m not sure it matters which one (to their model, of course it would presumably matter to the inhabitants) — and either would be visible and have the effect described in the paper.

That was my read as well, it doesn’t make a difference in terms of the total volume occupied by these “grabby” civs.

Also, one civilization dominating wouldn’t mean that the other one would magically disappear. As a simple assumption, I can imagine the stronger civ expanding into the territory of the weaker one relatively unhindered (in terms of expansion speed). But the weaker civ would still expand outwards as well. If it’s expansion speed isn’t slower, it would continue to grow in absolute size.

Yep, this was my understanding too. It doesn’t change the fact that the area in space and time is now occupied by grabby aliens. The model and diagrams could easily be modified to use some heuristic like allowing older civilizations to take over younger ones when they collide, but it wouldn’t really matter for the purposes of the argument.

The wording 'stop expanding' is confusing. Figure 1 makes it more clear: When two civilizations meet, expansion stops in this direction. In the free directions the civilizations still expand.

As likely is that two grabby expanding civilizations make be so different that thier volumes intercept without conflict. If one only likes warm rocky planets, and the other doesnt bother with solar systems, they might not even see each other as they pass. The "grabbed" volumes would then overlap, mooting this model. Contact would then not be a function or time and speed rather a matter of curiosity and willingness to explore non-desireable parts of one's grabbed space.

> As likely is that two grabby expanding civilizations make be so different that thier volumes intercept without conflict.

Every volume contains only a certain amount of potential free energy that can be used before the end. That’s what you fight over. Dyson Spheres, fusion, antimatter, these are all details. Everybody wants negentropy and it’s a zero sum game.

How could they stop?

If a civilization is spread out in a 10000 light year area and encounters another in one place it seems impossible they could make a collective decision given the amount of communication that it would take.

If that's the case they wouldn't be able to collectively decide to keep expanding either, the decision would have to be made by the parts of the civilization that came in contact with the other civilization.

This implies a lot of things though - let us say we expand to Mars and manage to terraform it somehow - after a few hundred years though Mars has enough of a population that they end up needing new resources (obviously we need some story as to how they expand this quickly, I blame genetic engineering and Hoxar Matos the dictator-general of Mars who commands a billion test tube babies be born and raised by robots in the underground Martian nursery creches).

The model for grabby aliens is that Mars must find somewhere else to expand as they are part of the human civilization - but given human civilization it seems more like splitting the civilization and infighting to get more resources would be the most likely outcome.

> It's interesting that, under the given assumptions, you can put such tight bounds on...

Is it, though? Grant me whatever assumptions I like and I can put tight bounds on anything - as long as it's unfalsifiable, at least.

Your assumption sounds like it favors Star Wars over Star Trek (TOS).

There's going to be a lot of space wars

Indeed, a very inefficient use of limited resources and energy in the known universe. How irrational.

Calling war irrational is irrational.

War is irrational...

If you have limited resourced (no money), but you do have military power, you can invade a neighbor with resources. If a neighbor invades you, you defend yourself.

Neither of those positions is irrational, except maybe the first (maybe), but there's certainly scenarios where it would be your only choice.

It becomes irrational when you develop the capacity for mutually assured destruction.

MAD is grounded in game theory. It is designed to make the only winning move “don’t play”.

It’s hyper-rational.

MAD happened because of a (real, or perceived, I’m unsure myself...) risk of the Soviet Union invading Western Europe - and NATO ended up calculating that maintaining a nuclear deterrence was more affordable and more feasible than resisting a Warsaw Pact invasion using conventional forces. This assumes any kind of Soviet expansionism must be an absolute evil because the position is logically equivalent to “death is a preferable alternative to communism” (to steal a phrase from a video game...) which is patently absurd: it’s rational to prefer reduced standards of living over death, but credible deterrence requires drawing and maintaining a hard-line, even if that line is arbitrarily placed.

...given all of that is due to the risk of aggression from the Soviets, and I believe NATO may have disarmed themselves unilaterally if they didn’t see the SU/WP as a military threat (regardless of ideological threats) - what was making the SU so concerned about NATO military threats? Did the SU still have expansionist designs... or did they actually believe NATO still wanted to liberate/claim Poland long after the 1960s?

I respectfully insist: you are mistaken.

MAD is a formal (i.e. mathematical) model. It is 100%, unequivocally rational. The problem is that this rational process leads to outcomes you and I dislike.

These "bad outcomes" are value judgements. That is, MAD's outocmes don't align with our values. Therefore, the problem with mad (on which we agree!) is based in something extra-rational: values.

Again: you and I agree there is a problem with MAD. Where you are wrong is that the problem is not "MAD is irrational". The problem is "MAD's logical conclusions run afoul of our values".

Mutually assured destruction on a planetary scale does come about rather early in a civilization's history (if we're assuming galactic, or beyond-galactic scales of civilization). But that doesn't really mean it is easy to come about on a galactic or universal scale. Is an enemy destroying a planet or solar system you control really such a big deal when you're battling to control a third of the universe? Even having an entire galaxy destroyed would be like an enemy destroying someone's living room on an earth-scale.

Of course, this is all just making guesses about technology way beyond our current comprehension. Maybe universe-destroying bombs come up rather early in technology on this scale. Who knows.

I read somewhere there's been something like 3000 wars in recorded human history. Seems like a pretty frequent thing. Thru out human history, raiding weaker neighbouring villages for resources, or access to females would be pretty rational behaviour for your villages growth and continuing success of your close genetic relatives.

So much so that parts of Human Male's anatomy seems to be purposely driven for combat and survival. Things like larger muscles, thickness of skull, thickness of neck. Also, societies seem to come together and cooperate, hunker down, in war and conflict. Also seems to me to have some genetic component to that social behaviour.

Only about 50% of men have reproduced through out human history. Raiding a neighbouring village, killing the man, and taking the best women for wives would be a rational though unethical behaviour. Its exactly what the Vikings did.

In fact, there's a growing concern that large and growing percentage of men, currently unattractive to females (internet incels) will lead to radicalization and possibly conflict in the west. As those man try to better their odds of reproduction. Currently they are genetic rejects.

I disagree. Countries and states exist.

I wonder if the inner solar system is a ghetto.

If the base requirement for life is liquid water, then it is a generic property that you find it in most moons and dwarf planets, usually driven by pressure and geothermal or tidal energy. If the under layer is rock instead of ice you could have thermal vent economies like we have in ocean rifts.

In comparison the Earth is a really dry place, the most special thing about it is that the plants support an oxygen economy that might not be necessary for complex life but it sure helps.

Any species that masters interstellar travel is going to know how to cut up something like Ceres or Pluto into hundreds of thousands of miles of shopping malls and apartment buildings and might not find inner solar system bodies that interesting. In fact they might not even have an off-the-shelf landing vehicle that would work on Earth and might spend a few years developing one.

It’s very difficult to tell what environment ‘typical’ aliens evolve in. It seems like Earth is probably a very unusual planet, mainly due to our very large moon which has stripped away so much of our atmosphere. Most planets our size will have atmospheres much more like that of Venus in terms of density at least. Smaller planets might develop atmospheres like ours in terms of density, as Mars did, but won’t be able to retain them for long.

Even a modest increase in Earths gravity, or significantly denser atmosphere would make reaching orbit unviable. I also don’t see how life evolving in liquid voids on outer planet moons, or similar environments, could develop much beyond simple invertebrates or equivalent.

I’m really despairing that spacefaring civilisations are at all likely. Life yes, I think it’s likely to be reasonably common at the galactic level. Intelligent life, sure. But I think we’re fantastically lucky to be in the situation we find ourselves. I know statistics says we’re supposed to most likely be typical, but random chance doesn’t care about how many possibilities didn’t show up. If a lottery has a winner, that ticket won just as much no matter if there were 10 losers or a billion of them.

It’s amusing how we are so improbable yet here we are. It’s like in novels where the book starts at an interesting environment for the protagonist. I often think “this is all pretty unlikely”. But it’s fun for the story and the story is about a protagonist in such a situation so it all works and as readers we can usually suspend disbelief. A similar principle applies to humans. We are incredibly improbable yet here we are doing our thing. I like to imagine other alien civilizations encountering us some day and marveling at how unlikely we are (and they are).

The fact that we find ourselves in such an incredibly unlikely situation, on a planet that seems perfectly designed to harbor life, is probably the best argument for the existence of a higher power.

I can see how that is attractive to people who believe in a higher power, but it’s really a terrible argument because it has no actual explanatory power. Exactly the same argument is used to justify various forms of multiverse for example - more rolls of the dice on types of universe equals a greater chance of us turning up. All it really means is ‘there must be a reason’, but it says nothing about what that reason is. Anything beyond that is just projection.

It's true that such an answer doesn't give any meaningful explanation by itself. But it can motivate us to somehow search for this higher power. I think the Voyager Golden Record is an example of such an action on behalf of mankind.

I think the other way theologically. If you think "God is Great" the majestry of creation known to astronomers is much greater than the theory that earth is 6000 years old and then Adam blew it.

Thus "the Lord has many mansions" and one would expect creativity to be generic in the universe.

This is something that, I think, we all intuitively feel. The big question is: what is the nature of this "higher power"? Is it something external or related to our consciousness?

Agreed. When I learned that bit about the rocket equation and gravity - that just a little more gravity would make all known rocket tech unable leave Earth's atmosphere/gravity - my thoughts of life zipping around the universe dimmed greatly. Maybe we should look at it as our duty to devise ways to 'rescue' other biomes from their gravitational jails? (if only we weren't space orcs.)

I've always thought something like the Skyhook described in Seveneves by Neal Stephenson would be perfect for lifting things off of high gravity worlds where the rocket equation is a deal breaker, provided you were starting in orbit or outside of the gravity well:


Maybe the materials science would still be a deal breaker, but in theory it would be easier to build than a space elevator.

Huh, very interesting. Yes, I wonder where current materials engineering puts us for a maximum length cable. It might be usable to just fly a plane up to it at some point. This also brings to mind capturing an asteroid in LEO. (Surely super dangerous though.)

I can't help but think SpaceX and the rest of us are missing out by targeting places like the moon or mars when there are so many asteroids out there. Maybe some of them could be used as a space station or slowly morphed into a spaceship with higher mass than we could ever launch? (like 1036 ganymed)

If we ever start really living and working in space it seems like we might reach a point where going down into deep gravity wells like Earth or even Mars will be too expensive to be worth it most of the time.

Just because traditional combustion engines can't do it doesn't mean much. More powerful nuclear thermal engines, direct fusion engines, etc are in development. There's other possibilities.

That’s true to a point, but it’s undeniable that as the cost of space technology increases the odds of bothering with it fall, and that the relatively modest changes in the conditions have exponential impact on the costs. A small increase in gravity rules out chemical rockets. Yes nuclear rockets might still be viable at that point, but increase gravity a bit more, or atmospheric density, and those become unviable too. And so it goes. The point is the range of conditions in which space tech is viable is very narrow compared to the range of possible conditions a species might find itself in.

From a human perspective, it's difficult to imagine a civilization that could remain cohesive when its territory is thousands of light-years wide, and therefore separated by time as well as space. Every significant journey is a trip into the future

I’m not so sure about that. What comes to mind is all the successful trading companies of centuries past.

If you mean 17th century trading companies, their sailing ships had one way journey times of six months to one year to practically anywhere in the world. So it's an interesting example, but interstellar distances are usually many times longer: 5 (light) years or 10 years or much more.

I guess that the reason globe-spanning empires and trading companies appeared from about 1600 on was in fact because sailing ships had reduced the travel time enough to allow a cohesive network with some centralized control. Previously, with slower communications, they tended to lose control of the extremities and devolve to looser associations (because the lag was excessive, on the scale of a human life)

There are a lot of stars. Maybe enough to go around.

Anyway, its commonly been theorized that waging war across unimaginable interstellar distances is unlikely or even impossible. Hard enough to seed another system with a spore, much less export capability to wage war.

If could accelerate a projectile to 0.1c you wouldnt bother putting any kind of warhead on it.

Interstellar bombardment of a single planet seems possible but if you had asteroid mining in one solar system or a multi solar system I think the targeting problem is intractable.

Kind of the opposite of 'expansion'. That's essentially 'demolition'. Not going to be anything worth expanding into, after that. Like blowing up a safe generally incinerates the money inside.

This is just the same set of anxieties and hopes, ultimately religious in nature, that surround "superintelligence", except this time projected into space.

Ya I was just thinking that the fact we haven't discovered aliens is strong evidence of new physics. Otherwise we'd see their electromagnetic emissions everywhere.

I tend to think that we're just 1 or 2 discoveries away from a very different view of the universe. The low hanging fruit being stuff like: detecting neutrinos cheaply, having a better understanding of quantum computing/entanglement/etc, knowing how the extra dimensions at subatomic levels work (and how a dimension might be lost/gained or open up sub-universes within black holes), understanding how the electromagnetic/strong/weak/gravity forces converge at high energies and how to modulate one or more with the others, etc.

If we're able to take all that stuff for granted, then the answer is probably that aliens communicate over some kind of encrypted quantum communication channel over something like neutrinos that is very hard to detect. They probably live around energy sources like magnetars and black holes and such so there's no way we'll ever see them against that glare. And their brains have almost certainly been uploaded to a metaverse that we have difficulty imagining, where our whole planet's computation would fit on a microscopic chip of theirs.

I guess what I'm saying is, we might be more likely to find aliens through an altered state than out in space. They're probably here right now waiting for a knock on the door, once we know which door we're looking for. So yes, their superintelligent technology that's indistinguishable from magic to us might as well be religion at this point.

How far exactly do you think normal electromagnetic radiation could be detected from? What percent of the galaxy do you think we could detect an expanse like civilization from?

What would you say are the nonreligious answers to the same question?

I think the answer requires more epistemic humility. You can't anticipate the behavior of a hyperintelligent entity (almost by definition) even if you build it right in your own lab. And about the only thing we know about aliens is that they'll be alien. So right there you have two dimensions of "unknown unknowns" that this analysis sweeps aside.

The pattern that I find distasteful in this kind of thinking is deducing universal rules of complex behavior from a few first principles. A good analogue of this is the Cold War era infatuation with game theory, as it would pertain to nuclear war, or many simple models of economics.

We know that in reality, human beings are quite complex, and their actual behavior bears no relationship to such "first principles" models, no matter how persuasive their authors find them. Yet we have the advantage of being human and understanding our own thinking. The idea that we could be more successful making such inferences from first principles about non-human, hyperintelligent entities, when we can't do it for ourselves, is laughable.

Even such basic questions like "does life always arise from Darwinian evolution" or "what is the physical basis of consciousness" are open. So in a strong sense we know nothing at all about the nature of intelligent life in the Universe, except that it happened at least once, and caused everyone no end of trouble.

Cant help but think this is GPT-3 generated.

More context about the paper: https://www.scottaaronson.com/blog/?p=5253

Scott's post is very good. Don't miss the comments, the paper's author is involved there too.

If it was, it would have to be from Hanson's own writing. No one else talks like him.

I started reading, it seems to pass the smell test for now, will continue reading

The word “till” in the abstract is certainly out of place. I’ve never seen slang like this in a scientific paper.

The word "till" is not slang. From https://www.dictionary.com/browse/till

Till and until are both old in the language and are interchangeable . . .


First recorded before 900; Middle English; Old English (north) til “to,” from Old Norse til “to,” . . .

Well its usage has been beaten out of me for scientific papers, and I’ve never seen it used in the venues I read. Maybe I just need to read more papers.


Till is a perfectly valid, formal word. I was just having this argument yesterday:

Many people assume that till is a misshapen abbreviation of until... However, till is not a shortening of until. It actually predates the longer word.

The above paragraph is from Merriam-Webster:


Good night, good night! parting is such sweet sorrow, That I shall say good night till it be morrow.

I'm neither expert nor elite enough to comment further: https://www.overcomingbias.com/2021/02/experts-versus-elites...

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