A metallurgist's doubts about self-replicating probes
centauri-dreams.org
centauri-dreams.org
We're along way from self replicating probes. But I would argue were quite capable of autonomous mining, manufacturing and material transport - assuming we can figure out how to refine effectively. If someone wants a cool PhD project and ship an experiment to the ISS, I would argue an ionic or plasma based refining technique designed for micro gravity could be very interesting and very useful
That's a good point. Most bulk industrial processes won't work in zero G. This limits asteroid mining. Breaking off pieces of rock and accelerating them to somewhere, maybe. Building a big wheel and spinning it up to get some gravity, maybe. Materials processing in open space, not so much.
The "seed" to start up an industrial economy might be the size of the industrial base of, say, Israel or North Korea, both of which try to be self-sufficient. We get to find out when someone tries to do something self-sustaining on Luna or Mars.
It may not be like that in practice. But nevertheless, self-reliance is in their stated goals, and North Korea is one of the least "open" states in the world.
I think you can make the case that they "try to be self-sufficient". They do try.
As for Israel, eh, it depends. They certainly don't rely on neighbouring countries.
With space manufacturing the first widget out of a factory costs trillions of dollars. There's also few if any raw materials that are far more abundant in space than here on Earth (at orders of magnitude smaller cost).
I like this part. It gives me chills.
This is, indeed, the exact question one must ask before attempting to build and launch biological Von Neumann probes.
Plus, life can't survive more than a few minutes in space without metal encasings and electronic life support; whereas metal alone only requires life at a much longer time scale. So, while it may be possible to build a fully inorganic self-replicating fleet, it's certainly impossible to build a fully-organic one with any technology or chemistry we know about today at least.
Agreed that metals should unlock wider opportunities in the inner system where solar energy is more abundant. I just don't think it matters much, you need a good place to plant your seed; once you've built up to scale you can then build wherever.
(False that life dies in minutes in space; plus the engineers can invest in even greater error correction than radiodurans.)
What form of life can actually survive (that is, continue living, not just go into some dormant state from which it can later resurrect like a tardigrade) in space for more than a few minutes?
https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...
There's tons of Carbon, Nitrogen and Oxygen in the universe, but very little metals. Heavier elements are much rarer.
Generally speaking the pace of biological activity is a lot slower than industrial ones too. We might make up for the pace with scale, but then you’re back to the hard problem of dependencies and “fuel”.
I’m not sure that the problem of beneficiation changes because the system is biological rather than industrial. Edit: Without carrying whole ecosystems with the probe at least.
That's why my other comment pointed to the autotrophs with the simplest requirements, and the (unknown but complexity-bounded) origin of life.
> pace of biological activity is a lot slower than industrial ones
Bacterial replication times can be under an hour.
What something like E. Coli can do in a well bioreactor is the ideal case, and even then most of what they produce is the bacteria themselves. On Earth this isn’t a problem at all, but as a means of husbanding every joule because you don’t know when or where the next one is coming from, I think it might matter.
It’s also probably a genuinely hard problem keeping your organisms viable without a constant supply of food, a means to get rid of mutants, or some hitherto unknown means of preservation that could handle the extreme time spans involved between “awakenings”.
I think it's pretty extreme to imagine their nth descendants caring about the goals of the parent civilization.
Biological systems require extremely specific environments that aren't space.
Yeah, you can self-replicate (well, not exactly self-replicate), but just think of all the "infrastructure" you need to do that: massive volumes of air and water, all kinds of weird chemicals not found in minerals, a whole biosphere of other stuff, a literal star, etc. And none of that infrastructure is really space-worthy on any reasonable scale for a probe.
If you broke it all down, I bet you'd need a mass/volume at least as big as a more technological probe. And you still need the technological infrastructure to build a vessel to hold it all together.
This isn't insurmountable for a probe. Biology can get stuck in local optima. Humans have the Periodic Table and quantum mechanics. But it means we are on untrodden ground. Refining titanium, today, uses a massive molybdenum-lined reactor operating at 1600 C (2900 F). The alternative processes (FFC and Chinuka) use liquid calcium chloride, mp 773 C. The square-cube law points to enormous energy losses trying to scale these processes down. And that's just one element.
https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...
I'm going to be very pedantic and point out a counterexample: https://en.wikipedia.org/wiki/Scaly-foot_gastropod
- Arthur C Clarke
No, none of the arguments on the article have any implication on the possibility of such a probe. None at all.
There's something to look into at the durability argument. The article has no usable information on it, and it's probably not a showstopper. But again, the only thing on the article is that yes, we don't know how to make one such probe right now.
When we see currently insurmountable problems in creating a piece of technology, it's absolutely possible that we'll never be able to build it. Even if it is theoretically constructible, there is no reason to believe that the way to build it would be found before, say, the sun runs out of hydrogen.
There's absolutely no evidence of that on the article.
The thesis was, “I would like to suggest that the hardest part is the one that gets a single sentence: ‘mines local material and builds a copy.’” And so naturally the points in the article are only trying to support that point.
The closest we get to what this thread is talking about is the concluding remark on the Fermi paradox. Which doesn’t rest on the idea that it’s a practical impossibility; just on the suggestion that it may be hard enough that we can’t just assume civilizations that are in principle capable of building them are likely to actually do it.
If you treat evidence as in the law of excluded middle, then yes. But if you are ready for a probabilistic evidence, then the article is a piece of evidence.
It chains Fermi Paradox, and our lack of knowledge how to do metallurgy in space. They both combined raise probability of impossibility of Von Neumann probes. It is not a proof that rules out Von Neumann probes, but it raises doubts about them.
A lot of computational power can be thrown at the problem in this time. So, the problem should admits no shortcuts, no decomposition into simpler problems, no alternative ways to get similar functionality that allow shotrcuts or decomposition. The result should look like a jumble of atoms that somehow produces the required functionality.
I wonder which problems can admit only this kind of a solution.
We know plenty of actually very simple problems that we would not be able to solve from now till the Sun explodes even if we all of the computers on earth were only doing this. Say, solving a worse case instance of the Knapsack problem for n > 250 items easily fits into this.
If you want to be precise, the complexity class EXP best fits my description (though NP-complete would also be enough). That is, if discovering the required technology to build a self-replicating interstellar probe requires solving an instance of an EXP problem that is not ridiculously tiny, then we would likely never be find out how to build this probe. And no amount of AGI would change this, in this case.
I'm not suggesting that I have any reason for this ridiculously precise scenario to be correct. Just that some technology being allowed by the laws of physics should not be taken to mean that it is actually implementable in any imaginable amount of time, even if we were to assume singularity-style AGI.
Ah, I think I know why I felt it was very unlikely. Engineering constraints should be very "unlucky" so that only the solution works. That is, there's no wiggle room that allows an approximate solution (which is usually simpler to find) to work, even if it would be slightly heavier, costlier, or something of the sort.
For such a tight constraint not to be a coincidence, nature itself would have to be able to solve EXP problems. Which might mean that not all is lost.
ETA: ChatGPT has pointed out that many interesting instances of computationally hard problems are still solvable. For example, see SAT-solvers (SAT is NP-complete).
That is in addition to tight constraints the problem instance should have no exploitable structure.
Over a long enough timescale, though… really, really slow solar trickle charge to a space-capacitor bank? A thousand years’ suns, culminating in a glorious orgy of smelting?
But I still think it's impossible on an asteroid. No nitrogen, very little sunlight, wrong temperature, zero pressure, etc. They are already at their limit on Earth.
Not X, but dramatic Y:
- "But the missing few percent are not marginal; they are precisely the hardest items"
- "is not an engineering detail. It may be the entire problem.
- "the galaxy may be quiet not because nobody tried, but because replication is harder than arithmetic suggests."
as well as at least two other longer "not X, it's Y" type phrases.
Also, melodramatic phrasing like "Replication must outrun degradation — and degradation never sleeps."
Yes, someone could have written these manually, but these particular patterns are the things I notice most commonly in LLM outputs that I don't see in known-human writing.
- crushing
- breaking down with powerful solutions
- blasting
And a self-replicating probe will (initially at least) be a low energy system. I eventually decided that the pathway with the most likelihood of success would be some kind of very slow crushing/grinding machine that can break down ore into separable components, but then you get into a kind of Darwinist explosive combinatorics research rabbit hole: which crusher/grinder, what kind of machine, how to make something that works on different ore types, what mechanical pressure is better?
Conceptualizing something that can sinter and assemble PV cells was pretty easy, there are broad families of chemistries that work and they mainly differ on input temperatures and output efficiencies. Fairly tractable. But mineral extraction... yeesh, it's extremely difficult.
FWIW on the original article: I think the jump from "insulating wires" to "semiconductor fabs" was kind of obtuse. You don't necessarily need Turing complete PCBs or microchips for most (any?) of this.
that is, CC asteroid contain “coal” more or less.
I don’t see a problem with drawing flowsheets for metals like iron, stones like silicon and even BTX chemicals to produce plastics. You cycle syngas and treat resulting H2O and CO2 as precious.
Now I was not thinking of a 500kg “seed” but a factory factory that is packed up in 100 ton loads that builds a sunshade factory by a process like building a ship inside a bottle except inside out.
I did worry about how you handle devolatization at the beginning, like it is precious and maybe even dangerous and it would be real nice to do it all at the beginning but you don’t have the storage tank factory online (thought a lot about storage tanks!)
The plan was to do all this in our solar system to sail sunshades to the Earth-Sun L1 point, the big questions I had was “how do you fix problems when it is hands-off that far away?” (physical twin in cislunar space for one thing!) vs “do you send people who you have to keep alive? can you bring them back? do they turn into Zeons?”
I have thought about the Drexler problem when it comes to Mars colonization and can’t think of a better answer than a synthetic biology platform based on bacteria and possibly yeast which can do versatile if not efficient chemical synthesis from syngas or photosynthesis. You still need flow chemistry, 3-d printing and some more methodologies but the project of “advanced manufacturing” that would enable a small settlement to achieve autakry seems achievable to me and would be essential for interplanetary colonization and helpful in case of forced degrowth.
Also to the authors last point (extremely long time scales causing degradation), it seems like we'd want high thrust capabilities regardless. i.e. maybe a small gravity well doesn't gain us anything, since we'd need big engines to get up to speed anyway.
But I can't see microgravity specifically as a huge challenge. If you can get a probe to another star system, you can probably figure out how to spin it.
In the latter case spinning doesn't get you far.
2. Carbon seems to be brittle.
I don’t see how anyone would expect some kind of self contained probe to be able to do all of that.
Well, there is -- distance.
Also, the regolith is a good electrical insulator.
Also, basic organic compounds are plentiful in space.
What about glass, SiO2?
Whenever I read of von Neumann probes I always thought "How can that even made possible?".
How many AI tells can you count there?
But honestly (see what I did there?) the AI slop is reasonably cleaned up in this piece.
However, the essence of the argument has two deep flaws. One is that the time to complete an interstellar voyage is extremely long and you need some exergy, yada, yada, yada. We could start with sending self-replicating probes to the asteroid belt. There is zero chance that we'll attempt to send self-replicating probes to a different star system before we send them inside our own solar system. And the second error is this:
> Bootstrapping this loop [...] is a chicken-and-egg problem that no study I am aware of has worked through at the level of actual process flowsheets.
The fact that the current technology is not adequate, and nobody even attempted to solve such a problem is a weak argument. Three hundred years ago nobody had "worked through the process flowsheets" of making an injection molding machine, or a 3D printer, or a power drill, yet they are all available now.
This reads as heavily LLM generated/edited to me.
> The closure problem, honestly accounted
> A thermodynamic framing
All of those read like AI, especially considering that the subsections aren't consistent. Some are numbers, some are not, some are framings some are problem juxtapositions.
EM dashes everywhere, AI tells in subheadings, "It's not X it's Y" all over the text of the body. This is clearly AI writen.
Notice also the article has two by lines. At the top it's "by Paul Gilster" at the top of the text it's "by Peter Marinko"
Also note that the "metallugrist" they're interviewing that they claim "his current work explores the thermodynamics of technological civilizations" at Uppsala University, but the university's page for him says he's only involved in Animal Research Ethics Committee
It is Paul Gilster's blog. It looks like all articles there are by him, hence his byline at the top.
In this particular article he writes an introduction talking about self-replication, then says "Right now I want to introduce Peter Marinko, who today weighs in on self-replication and the problems therein", describes Marinko, and then the rest of the text is Marinko's, hence the second byline after Gilster's introduction.
Something similar happens in the next article on the site. Marinko write a length response to comments on the first article. Gilster decided that would be better as a separate article to further discussion: "When Peter wrote recently with his thoughts on reader reactions, I asked him for permission to run it as a regular post rather than a comment, because I think this is a lively question and would like to see us continue to explore it".
So that too is a post by Gilster, and so with his byline, but after an introduction it just run's Marinko's text, so has a second byline for that section.
He does the same thing on this article [1]. He wrote a review a paper, some commenter had interesting thoughts, and Gilster posted an article talking about that, introducing the commenter, and then the rest of the article was the commenter's text. So two bylines, one for the intro and one for the guest text.
It looks like the other articles on the site are just Gilster, and so only have one byline.
[1] https://www.centauri-dreams.org/2026/06/05/observations-on-t...