Charles Stross recently on possible future great filters:
So IO9 ran a piece by George Dvorsky on ways we could wreck the solar system. And then Anders Sandberg responded in depth on the subject of existential risks, asking what conceivable threats have big enough spatial reach to threaten an interplanetary or star-faring civilization. … The implication of an [future great filter] is that it doesn’t specifically work against life, it works against interplanetary colonization. … much as Kessler syndrome could effectively block all access to low Earth orbit as a side-effect of carelessly launching too much space junk. Here are some example scenarios: …
Simplistic warfare: … Today’s boringly old-hat chemical rockets, even in the absence of nuclear warheads, are formidably destructive weapons. … War, or other resource conflicts, within a polity capable of rapid interplanetary or even slow interstellar flight, is a horrible prospect.
Irreducible complexity: I take issue with one of Anders’ assumptions, which is that a multi-planet civilization is … not just … distributed, but it will almost by necessity have fairly self-sufficient habitats that could act as seeds for a new civilization if they survive. … I doubt that we could make a self-sufficient habitat that was capable of maintaining its infrastructure and perpetuating and refreshing its human culture with a population any smaller than high-single-digit millions. … Building robust self-sufficient off-world habitats … is vastly more expensive than building an off-world outpost and shipping rations there, as we do with Antarctica. …
Griefers: … All it takes is one civilization of alien ass-hat griefers who send out just one Von Neumann Probe programmed to replicate, build N-D lasers, and zap any planet showing signs of technological civilization, and the result is a galaxy sterile of interplanetary civilizations until the end of the stelliferous era. (more)
These are indeed scenarios of concern. But I find it hard to see how, by themselves, they could add up to a big future filter.
On griefers (aka “berserkers”), a griefer equilibrium seems to me unstable to their trying sometimes to switch to rapid growth within a sufficiently large volume that they seem to control. Sometimes that will fail, but once it succeeds enough then competing griefers have little chance to stop them. Yes there’s a chance the first civilization to make them didn’t think to encode that strategy, but that seems a pretty small filter factor.
On simple war, I find it hard to see how war has a substantial chance of killing everyone unless the minimum viable civilization size is large. And I agree that this min size gets bigger for humans in space, who are more fragile there. But it should get smaller for smart robots in space, or on Earth, especially if production becomes more local via nano-factories. The chance that the last big bomb used in a war happens to kill off the last viable group of survivors seems to me relatively small.
Of course none of these chances are low enough to justify complacency. We should explore such scenarios, and work to prevent them. But we should work even harder to find more worrisome scenarios.
So let me explain my nightmare scenario: general non-diminishing prey. Consider the classic post-apocalyptic scenario, such as described in The Road. Desperate starving people ignore the need to save and build for the future, and grab any food they can find, including each other. First all the non-human food is gone, then all the people.
Such situations have been modeled formally via “predator-prey dynamics”:
These are differential equations giving the rates at which counts of predators and prey grow or decline as a function of each other. The standard formulation has a key term whereby prey count falls in proportional to the product of the predator count and the prey count. This formulation embodies an important feature of diminishing returns: the fewer prey are left, the harder it is for predators to find and eat them.
Without enough such diminishing returns, any excess of predators quickly leads to the extinction of prey, followed quickly by the extinction of predators. For example, when starving humans are given easy access to granaries, such granaries are emptied quickly. Not made low; emptied. Which is why granaries in famines are usually either well-protected, or empty.
In nature, there are usually many kinds of predators, and even more kinds of prey. So the real predator-prey dynamic is high-dimensional. The pairwise relations between most predators and preys do in fact usually involve strongly diminishing returns, both because predators must usually search for prey, and because some prey hiding places are much better than others.
If the relation between any one pair of predator and prey types happens to have no diminishing returns, then that particular type of prey will go extinct whenever there is a big enough excess of that particular type of predator. Since this selects against such prey, the prey we see in nature almost all have diminishing returns for all their practical predators.
Humans are general predators, able to eat a great many kinds of prey. And within human societies humans are also relatively general kinds of prey, since we mostly all use the same kinds of resources. So when humans prey on humans, the human prey can more easily go extinct.
For foragers, a key limit on human predation was simple distance. Foragers lived far apart, and were unpredictably located. Also, foragers had little physical property to grab, wives were not treated as property, and land was too plentiful to be worth grabbing. These limits mattered less for farmers, who did predate often via war.
The usual source of diminishing returns in farmer war predation has been the wide range of protection in places to hide; humans have often run to the mountains, jungle, or sea to escape human predators. Even so, humans and proto-humans have quite often driven one another to local relative extinction.
While the extinction of some kinds of humans relative to others has been common, the extinction of all humans in an area has been much less common. This is in part because, when there has been a local excess of humans, most have focused on non-human prey. Such prey are diverse, and most have strongly diminishing returns to human predation.
Even if humans expand into the solar system, and even if they create robot descendants, we expect our descendants to remain relatively general predators, at least for a long while. We also expect the physical resources that they collect to constitute relatively general prey, useful to a wide range of our descendants. Furthermore, we expect nature that isn’t domesticated or descended from humans to hold a decreasing quantity of useful resources.
Thus the future predator-prey dynamic should become lower dimensional than it has been in the past. To a perhaps useful approximation, there’d be only a few kinds of predators and prey. Which raises the key question: how strong are the diminishing returns to predation in that new world? That is, when some of our descendants hunt down others to grab resources, how fast does that task get harder as fewer prey remain?
One source of diminishing returns in predation is a diversity of approaches and interfaces. The more different are the methods that prey use to create and store value, the smaller the fraction of that value a predator can obtain via a simple hostile takeover. This increases the ratio of how hard prey and prey fight. As many have noted, in nature prey fight for their lives, while predators fight only for a meal. Even so, nature still has plenty of predation. Even if predators gain only part of the value contained in prey, they still predate if that costs them even less than this value.
As I said above, the main source of diminishing returns in predation among foragers was travel cost, and among farmers it was the diversity of physical places to run and hide. Such effects might still protect our descendants from predator-prey-dynamic extinction, even if they have only one kind of predator and prey. Alas, we have good reasons to fear that these factors may less protect our descendants.
The basic problem here is our improving techs for travel, communication, and surveillance. We are steadily able to move bits and people more cheaply, and to more cheaply and accurately watch spaces for activity. Yes moving out into the solar system would put more distance between things, and make them harder to see. But that one-time effect will be quickly overwhelmed by improving tech.
A colonized solar system is plausibly a place where predators can see most any civilized activities of any substantial magnitude, and get to them easily if not quickly. So if we ever reach a point where predators fight to grab civilized resources with little concern to save some for the future, they might be able to find and grab pretty much everything in the solar system. Much as easy-access granaries are quickly emptied in a famine.
Whether extinction results from such a scenario depends how small are minimum viable civilization seeds, how obscure and well protected are the nooks and crannies in which they might hide, and how many of them exist and try to hide. Yes, hidden viable seeds drifting at near light-speed to other stars could prevent extinction, but such a prey-collapse scenario could play out well before such seeds are feasible.
So, bottom line, the future great filter scenario that most concerns me is one where our solar-system-bound descendants have killed most of nature, can’t yet colonize other stars, are general predators and prey of each other, and have fallen into a short-term-predatory-focus equilibrium where predators can easily see and travel to most all prey. Yes there are about a hundred billion comets way out there circling the sun, but even that seems a small enough number for predators to careful map and track all of them.
Worry about prey-extinction scenarios like this is a reason I’ve focused on hidden refuges as protection from existential risk. Nick Beckstead has argued against refuges saying:
The most likely ways in which improved refuges could help humanity recover from a global catastrophe are scenarios in which well-stocked refuges with appropriately trained people help civilization to recover after a catastrophe that leaves a substantial portion of humanity alive but disrupts industrial and agricultural infrastructure, and scenarios in which only people in constantly-staffed refuges survive a pandemic purposely engineered to cause human extinction. I would guess that, in the former case, resources and people stocked in refuges would play a relatively small role in helping humanity to recover because they would represent a small share of relevant people and resources. The latter case strikes me as relatively far-fetched and I would guess it would be very challenging to do much better than the largely uncontacted peoples in terms of ensuring the survival of the species. (more)
Nick does at one point seem to point to the scenario that concerns me:
If a refuge is sufficiently isolated and/or secret, it would be easier to ensure that everyone in the refuge had an adequate food supply, even if that meant an inegalitarian food distribution.
But he doesn’t appear to think this relevant for his conclusions. In contrast, I fear that a predatory-collapse scenario is the most likely future great filter, where unequal survival key to preventing extinction.
Added 10a: Of course the concern isn’t just that some parties would have short term orientations, but that most would pursue short-term predation so vigorously that they force most everyone to put in similar effort levels, even if they take have long-term view. When enemies mass on the border, one might have to turn farmers into soldiers to resist them, even if it is harvest time.