Catastrophe Engines: A possible resolution to the Fermi Paradox

by snarles3 min read25th Jul 201522 comments


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The Fermi Paradox leads us to conclude that either A) intelligent life is extremely improbable, B) intelligent life very rarely grows to a higher-level civilization, or C) that higher-level civilizations are common, but are not easy to spot.  But each of these explanations are hard to believe.  It is hard to believe that intelligent life is rare, given that hominids evolved intelligence so quickly.  It is hard to believe that intelligence is inherently self-destructive, since as soon as an intelligent species gains the ability to colonize distant planets, it becomes increasingly unlikely that the entire species could be wiped out; meanwhile, it appears that our own species is on the verge of attaining this potential.  It is hard to believe C, since natural selection favors expansionism, so if even a tiny fraction of higher-level civilizations value expansion, then that civilization becomes extremely visible to observers due to its exponential rate of expansion.  Not to mention that our own system should have already been colonized by now.

Here I present a new explanation on why higher-level civilizations might be common, and yet still undetected.  The key assumption is the existence of a type of Matrioshka brain which I call a "Catastrophe Engine."  I cannot even speculate on the exotic physics which might give rise to such a design.  However, the defining characteristics of a Catastrophe Engine are as follows:

  1. The Catastrophe Engine is orders or magnitude more computationally powerful than any Matrioshka Brain possible by conventional physics.
  2. The Catastrophe Engine has a fixed probability 1-et of "meltdown" in any interval of t seconds.  In other words, the lifetime of a Catastrophe Engine is an exponentially distributed random variable with a mean lifetime of 1/λ seconds.
  3. When the Catastrophe Engine suffers a meltdown, it has a destructive effect of radius r, which, among other things, results in the destruction of all other Catastrophe Engines within the radius, and furthermore renders it permanently impossible to rebuild Engines within the radius.
A civilization using Catastrophe Engines would be incentivized to construct the Engines far apart from each other, hence explaining why such we have never detected such a civilization.  Some simple math shows why this would be the case.

Consider a large spherical volume of space.  A civilization places a number of Catastrophe Engines in the volume: suppose the Engines are placed in a density so that each Engine is within a radius r of n other such Engines.  The civilization seeks to maximize the total computational lifetime of the collection of Engines.

The probability that any given Engine will be destroyed by itself or its neighbors in any given interval of t seconds is 1-e-nλt.
The expected lifetime of an Engine is therefore T = 1/(n λ).
The total computational lifetime of the system is proportional to nT = n/(n λ) = 1/λ.

Hence, there is no incentive for the civilization to build Catastrophe Engines to a density n greater than 1.  If the civilization gains extra utility from long computational lifetimes, as we could easily imagine, then the civilization is in fact incentivized to keep the Catastrophe Engines from getting too close.

Now suppose the radius r is extremely huge, i.e. on the order of intergalatic distances.  Then the closest Catastrophe Engine is likely on the order of r distance from ourselves, and may be quite difficult to spot even if it is highly visible.

On the other hand, the larger the radius of destruction r, the more likely it is that we would be able to observe the effects of a meltdown given that it occurs within our visible universe.  But since a larger radius also implies a smaller number of Catastrophe Engines, a sufficiently large radius (and long expected lifetime) makes it more likely that a meltdown has simply not yet occurred in our visible universe.

The existence of Catastrophe Engines alone does not explain the Fermi Paradox.  We also have to rule out the possibility that a civilization with Catastrophe Engines will still litter the universe with visible artifacts, or that highly visible expansionist civilizations which have not yet developed Catastrophe Engines would coexist with invisible civilizations using Catastrophe Engines.  But there are many ways to fill in these gaps.  Catastrophe Engines might be so potent that a civilization ceases to bother with any other kinds of possibly visible projects other than construction of additional Catastrophe Engines.  Furthermore, it could be possible that civilizations using Catastrophe Engines actively neutralize other spacefaring civilizations, fearing disruption to the Catastrophe Engines.  Or that Catastrophe Engines are rapidly discovered: their principles become known to most civilizations before those civilizations have become highly visible.


The Catastrophe Engine is by no means a conservative explanation of the Fermi Paradox, since only the very most speculative principles of physics could possibly explain how an object of such destructive power could be constructed.  Nevertheless, it is one explanation of how higher civilizations might be hard to detect as a consequence of purely economical motivations.

Supposing this is a correct explanation of the Fermi paradox, does it result in a desirable outcome for the long-term future of the human race?  Perhaps not, since it necessarily implies the existence of a destructive technology that could damage a distant civilization.  Any civilization lying close enough to be affected by our civilization would be incentivized to neutralize us before we gain this technology.  On the other hand, if we could gain the technology before being detected, then mutually assured destruction could give us a bargaining chip, say, to be granted virtual tenancy in one of their Matrioshka Brains.

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22 comments, sorted by Highlighting new comments since Today at 3:26 AM
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Is there any reason we should expect such catastrophe engines to exist?

Seconded. So many layers of specificity, one of which is "exotic physics" ... I have a hard time seeing why it's worth entertaining this idea over any of the other unlikely but less specific theories one could devise.

It's not a contest. And although my explanation invokes unknown physics, it makes specific predictions which could potentially be validated or invalidated, and it has actionable consequences. Could you elaborate on what criteria make an idea "worth entertaining"?

It's not a contest.

But it is. There are only a limited number of ideas we can work on, so we'd better have some reason to think that this idea has more potential than any of the innumerable other ideas we could be working on instead.

There are only a limited number of ideas we can work on

You are right in general. However, it is also a mistake to limit your scope to too few of the most promising ideas. Suppose we put a number K on the number of different explanations we should consider for the Fermi paradox. What number K do you think would give the best tradeoff between thoroughness and time?

The observation of the Fermi Paradox call for some explanation and this is one albeit constructed case.

1) Postulates exotic physics and/or requires a change to the laws of physics to be possible. Low probability.

2) Postulates bad design and something that the builders would work to minimize. Low probability.

3) Postulates additional exotic physics that are likely different from 1) and don't really even make sense giving the vastness of space. Very low probability.

The search space of ideas is incredibly large, and we don't find solutions by picking ideas at random and testing them. Instead, we focus on the ideas that seem most reasonably plausible, and test those first. There are a LOT of ideas that are more reasonably plausible than catastrophe engines as described above.

Given what I know about physics, I actually find "we're the first intelligent technological life in the universe" to be more likely than catastrophe engines.

I mostly agree with you, but we may disagree on the implausibility of exotic physics. Do you consider all explanations which require "exotic physics" to be less plausible than any explanation that does not? If you are willing to entertain "exotic physics", then are there many ideas involving exotic physics that you find more plausible than Catastrophe Engines?

In the domain of exotic physics, I find Catastrophe Engines to be relatively plausible since are already analogues of similar phenomena to Catastrophe Engines in known physics: for example, nuclear chain reactions. It is quite natural to think that a stronger method of energy production would result in even greater risks, and finally the inherent uncertainty of quantum physics implies that one can never eliminate the risk of any machine, regardless of engineering. Note that my explanation holds no matter how small the risk lambda actually is (though I implicitly assumed that the universe has infinite lifetime: for my explanation to work the expected life of the Catastrophe Engine has to be at most on the same order as the lifetime of the universe.)

It is also worth noting that there are many variants of the Catastrophe Engine hypothesis that have the same consequences but which you might find more or less plausible. Perhaps these Engines don't have "meltdown", but it is necessary that they experience some kind of interference from other nearby Engines that would prevent them from being built too closely to each other. You could suppose that the best Matrioshka Brains produce chaotic gravity waves that would interfere with other nearby Brains, for instance.

Personally, I find explanations that require implausible alien psychology to be less plausible than explanations that require unknown physics. I expect most higher civilizations to be indifferent about our existence unless we pose a substantial threat, and I expect a sizable fraction of higher civilizations to value expansion. Perhaps you have less confidence in our understanding of evolutionary biology than our understanding of physics, hence our disagreement.

For the sake of discussion, here is my subjective ranking of explanations by plausibility:

  1. There are visible signs of other civilizations, we just haven't looked hard enough.
  2. Most expansionist civilizations develop near light-speed colonization, hence making it very unlikely for us to exist in the interval between when their civilization is visible and our planet has already been colonized
  3. We happen to be the first technologically advanced civilization in our visible universe
  4. Most artifacts are invisible due to engineering considerations (e.g. the most efficient structures are made out of low-density nanofibers, or dark matter).
  5. Colonization is much, much more difficult than we anticipated.
  6. Defensively motivated "berserkers". Higher civs have delicate artifacts that could actually be harmed by much less advanced spacefaring species, hence new spacefaring species are routinely neutralized. It still needs to be explained why most of the universe hasn't been obviously manipulated, hence "Catastrophe Engines" or a similar hypothesis. Also, it needs to be explained why we still exist, since it would be presumably very cheap to neutralize our civilization.
  7. Some "great filters" lie ahead of us: such as nuclear war. Extremely implausible because you would also have to explain why no species could manage to evolve with better cooperation skills.
  8. "Galactic zoo" hypotheses and other explanations which require most higher civilizations to NOT be expansionist. Extremely implausible because many accidentally created strong AIs would be expansionist.

I ignore the hypothesis that "we are in a simulation" because it doesn't actually help explain why we would be the only species in the simulation.

EDIT: Modified the order

Before we go further:

  • What specific observations and evidence does your idea explain, other than the Fermi paradox?

  • What specific observations and evidence, if we had them, would invalidate your idea?

For the original proposal:


  • A mechanism for explosive energy generation on a cosmic scale might also explain the Big Bang.


  • Catastrophe engines should still be detectable due to extremely concentrated energy emission. A thorough infrared sky survey would rule them out along with more conventional hypotheses such as Dyson spheres.

  • If it becomes clear there is no way to exploit vacuum energy, this eliminates one of the main candidates for a new energy source.

  • A better understanding of the main constraints for engineering Matrioshka brains: if heat dissipation considerations already limit the size of a single brain, then there is no point in considering speculative energy sources.

The fermi paradox is not a paradox. We have not sent out enough signal to be very noticeable, and we do not have the instruments to detect almost any alien signals. Due to signal attenuation, we would be pretty much unable to notice anything further than around 10 lightyears, and even within that range only if the signal was being beamed directly at us. The same problem applies to any aliens, only the paradox there is delayed by a further time problem: the speed of light. We've only been emitting radio for around 100 years, so there's a radius of only 100 light years within which aliens could've detected us and decided to send a signal, and an even smaller 50 lightyear radius in which we might have a chance of noticing it.

We've only been emitting radio for around 100 years

We'we been emitting the presence of oxygen in our atmosphere for about 1 billion years. Every nontrivial alien would notice this.

You don't necessarily spend a bunch of money on sending a contact message to every planet with oxygen.

Why not? Or rather make an expedition there ASAP.

At least. More likely, you have a large colonization plan underway and this planet is in your path anyway.

I think the biggest reason we have to assume that the universe is empty is that the earth hasn't already been colonized.

Regardless of whether ETs are sending signals, presumably we should be able to detect Type II or Type III civilizations given most proposals for how such civilizations should look like.

Implausible premises aside, I'm not convinced this actually resolves the paradox.

The first spacefaring civilization fills the galaxy/universe with Catastrophe Engines at the maximum usable density.

But now the second spacefaring civilization doesn't have any room to build Catastrophe Engines, so they colonize space the regular way. And we're right back at the original problem: either life has to be rare enough that everybody has room to build Engines, or there's lots of life out there that had to expand the non-Engine way but we somehow can't see them.

The second civilization would just go ahead and build them anyways, since doing so maximizes their own utility function. Of course, there is an additional question of whether and how the first civilization will try to stop this from happening, since the second civ's Catastrophe Engines reduce their own utility. If the first civ ignores them, the second civ builds Catastrophe Engines the same way as before. If the first civ enforces a ban on Catastrophe Engines, then the second civ colonizes space using conventional methods. But most likely the first civ would eliminate the second civ (the "Berserker" scenario.)

The second civilization would just go ahead and build them anyways, since doing so maximizes their own utility function.

Then why isn't there an Engine on every star?

The second civ would still avoid building them too close to each other. This is all clear if you do the analysis.

So instead of every civ fillings its galaxy, we get every civ building one in every galaxy. For this to not result in an Engine on every star, you still have to fine-tune the argument such that new civs are somehow very rare.

There are some hypotheticals where the details are largely irrelevant, and you can back up and say "there are many possibilities of this form, so the unlikeliness of my easy-to-present example isn't the point". "Alien civs exist, but prefer to spread out a lot" does not appear to be such a solution. As such, the requirement for fine-tuning and multiple kinds of exotic physics seem to me like sufficiently burdensome details that this makes a bad candidate.

EDIT: Edited my response to be more instructive.

On some level it's fine to make the kinds of qualitative arguments you are making. However, to assess whether a given hypothesis really robust to parameters like ubiquity of civilizations, colonization speed, and alien psychology, you have to start formulating models and actually quantify the size of the parameter space which would result in a particular prediction. A while ago I wrote a tutorial on how to do this:

which covers the basics, but to incorporate alien psychology you would have formulate the relevant game-theoretic models as well.

The pitfall of the kinds of qualitative arguments you are making is that you risk confusing the fact that "I found a particular region of the parameter space where your theory doesn't work" with the conclusion that "Your theory only works in a small region of the parameter space." It is true that under certain conditions regarding ubiquity of civilizations, colonization speed, and alien diplomatic strategy, that Catastrophe Engines end up being built on every star. However, you go on to claim that in most of the parameter space, such an outcome occurs, and that the Fermi Paradox is only observed in a small exceptional part of the parameter space. Given my experience with this kind of modeling, I predict that Catastrophe Engines actually are robust to all but the most implausible assumptions about ubiquity of intelligent life, colonization speed, and alien psychology, but you obviously don't need to take my word on it. On the other hand, you'd have to come up with some quantitative models to convince me of the validity of your criticisms. In any case, continuing to argue on a purely philosophical level won't serve to resolve our disagreement.