Frank Tipler jolted the astrophysics community in 1980 when he introduced self-replicating interstellar probes into discussion of the Fermi Paradox. The mathematical model of self-replication came from John von Neumann, and was codified in 1966 (after von Neumann’s death) by Arthur Burks in Theory of Self-Reproducing Automata (1966). SF fans will also know of Fred Saberhagen’s berserker novels and short stories (the first appeared in 1963). I’ve found an even earlier SF reference but will leave that for a future post. Right now I want to introduce Peter Marinko, who today weighs in on self-replication and the problems therein. Based in Uppsala, Sweden Peter holds an M.Sc. in metallurgy and has a career background in industrial process engineering. He has studied SETI under Erik Zackrisson at Uppsala University, and his current work explores the thermodynamics of technological civilizations — including a manuscript on high-exergy technospheres and the longevity of detectable civilizations, currently under peer review at the International Journal of Astrobiology. A preprint is available on Zenodo.
by Peter Marinko
Discussions of von Neumann probes — here and elsewhere — tend to treat replication as a systems problem: the probe arrives, mines local material, and builds a copy of itself. The hard part is usually assumed to be propulsion, navigation, or AI. As someone who has spent a career in metallurgy and industrial process engineering, I would like to suggest that the hardest part is the one that gets a single sentence: “mines local material and builds a copy.”
Let me raise four concrete problem areas, in increasing order of difficulty.
1. Beneficiation without gravity, water, or atmosphere
“Asteroid mining” is a misleading phrase. Mining is the easy part; the problem is beneficiation — concentrating useful elements out of undifferentiated regolith. Every terrestrial concentration process relies on things an asteroid lacks: gravity-driven sedimentation, water-based flotation, density separation in fluids, atmospheric combustion. Electrostatic and magnetic separation in microgravity are conceivable in principle, but neither has been demonstrated at industrial scale, and both work poorly on the fine, cohesive, electrostatically charged dust that dominates regolith.
2. Reduction metallurgy without an industrial hinterland
All terrestrial metal production rests on an invisible foundation: carbon or hydrogen as reducing agents, fluxes, and — critically — refractory materials for the furnaces. Refractories are the forgotten enabling technology of civilization. A furnace lining must itself be manufactured, at high temperature, in a furnace. Bootstrapping this loop from raw regolith, with fully closed chemical cycles (no atmosphere to vent to, no water to waste), is a chicken-and-egg problem that no study I am aware of has worked through at the level of actual process flowsheets.
3. The closure problem, honestly accounted
The classic NASA study (Freitas et al., 1980) assumed ~90–96% “closure” — the fraction of its own components a system can reproduce — with the remainder supplied as “vitamins” from home. But the missing few percent are not marginal; they are precisely the hardest items: semiconductors, precision bearings, sensors, and insulation. Consider something as unglamorous as wire insulation. Virtually all electrical insulation on Earth is organic polymer, resting on a petrochemical industry, resting in turn on a biosphere that spent hundreds of millions of years concentrating carbon. Inorganic alternatives (glass fiber, ceramics, mica) exist but are brittle, heavy, and require entirely different process chains to apply to fine conductors. A modern semiconductor fab is arguably the most complex artifact humanity has built, drawing on tens of thousands of specialized inputs. Shrinking that into a 500 kg seed — or even Freitas’ original 100-ton seed — is not an engineering detail. It may be the entire problem.
4. Aging over interstellar timescales
Even a probe that could replicate must first arrive functional after a voyage of tens of thousands of years. We have essentially no empirical data on machine longevity beyond ~50 years (Voyager, surviving on redundancy and switched-off instruments). Over interstellar timescales, materials face cumulative radiation damage and lattice defects, embrittlement and transmutation; creep and solid-state diffusion (solder joints, thin films and interfaces are only kinetically frozen, not thermodynamically stable); tin and zinc whisker growth; outgassing and cold welding in vacuum. The repair systems age too. Replication must outrun degradation — and degradation never sleeps.
A thermodynamic framing
These four problems share a common structure. A self-replicating probe is, in effect, a miniaturized high-exergy technosphere that must rebuild its entire exergy cascade — from raw, unconcentrated feedstock to precision components — at every node, before its own irreversible degradation catches up. The feasibility question is then not “does physics forbid it? (it does not) but “can accessible exergy per node sustain full process closure faster than irreversible losses accumulate?
This is the same ratio, I would argue, that governs the longevity of detectable civilizations generally — a question I explore in a recent preprint on the thermodynamics of technological civilizations. But the probe case is a cleaner test, because the system boundary is sharp and the accounting is (in principle) tractable.
Questions for discussion
1. Has anyone attempted an actual process flowsheet — not a block diagram — for closing even a simple metallurgical loop (say, iron from chondritic material to finished machine parts) without terrestrial inputs?
2. Is there a credible inorganic-only pathway for electrical insulation and semiconductor packaging?
3. What is the realistic closure fraction if “vitamins” are disallowed — and does the seed mass then grow beyond anything launchable?
4. Are there materials strategies (amorphous metals? self-annealing designs?) that could plausibly survive 10,000+ years of transit?
My suspicion, as a practitioner, is that von Neumann probes are constrained not by the laws of physics but by process-chain closure and materials aging — both, at root, thermodynamic limits. If that is right, it bears directly on the Fermi paradox: the galaxy may be quiet not because nobody tried, but because replication is harder than arithmetic suggests.
I would be glad to be proven wrong on any specific point above — ideally with a flowsheet.
Thanks for this. These are the sorts of clearheaded questions that must be asked if discussions of advanced and/or extraterrestrial technologies are to move beyond pleasant speculation and “get real.”
Putting all this into a text to speech generator yields quite an appealing way of absorbing and thinking about the article.
Q1 There is plenty of atomic free iron and nickel in asteroids seeded by violent interstellar explosions which can be removed by magnetic fields, you may need a charge negator maybe an electron gun to control it. Electron guns can be very small every nano scale.
Q2 Due to smaller voltages insulation is not a massive issue, silicon dioxide or even glassyified regolith would be sufficient, distance is also your friend in electronics.
Maybe we need a octopus like device that takes what it needs from moving through its surroundings rejecting what it does not need and it creates another octopi and so on.
This is a wild guess, but I wonder if you could solve the problem by emitting a highly focused beam of electrons, capable of striking a specific part of each individual atom targeted, with the electrons spaced in such a way as to do “vibrational ladder climbing”, pushing a specific chemical bond to its breaking point. I had a long chat with an AI and got to this paper: https://news.mit.edu/2019/manipulate-atoms-graphene-quantum-0517 There’s also this talk: https://www.youtube.com/watch?v=HSS4QVeQPSY I haven’t really watched it all but there is a cute demonstration at 29 minutes.
I’m thinking the most important feedstock ought to be the carbon and hydrogen atoms harvested from the stellar wind. The goal would be to come up with a network of probes in space that look approximately (or exactly?) like cosmic dust.
Space is full of organic compounds. Indeed polycyclic organic hydrocarbons are found in asteroids and are of obvious abiogenic origin.
Refractories is an issue. At least space has plenty of cheap solar power to generate high temperatures. I had a friend who got his PhD in chemistry who was involved in L5-Society. He was doing research on developing metallurgical processes in space, including the refractory problem. He said it was difficult, but could be developed within a decade or two. The author of this piece is correct that too few people are working on this problem. I consider it the key technology necessary to enable space colonization in our own solar system.
Semiconductor manufacturing is by far the biggest hurtle for self-replication manufacturing. A better process than depo/etch/patterning has to be developed to enable cost effective manufacturing in space. Indeed, this hurtle has to be overcome here on Earth to realize cost-effective AI. Molecular electronics or some kind of bio-fabrication? Or at minimum printable semiconductors in a web process. The one thing that can be said about space is that it is UHV environment. Since the vacuum is there, you don’t need vacuum chambers for the current processes.
In the industry we say that building chips rather than carving them (current processes) is the holy grail of computing technology.
Both of these hurtles can be overcome, but will take time and $$$ to do so.
All true.
But robust and successful self-replicating systems DO exist. They cover the earth, and have done so continuously for billions of years, without any “intelligent” design or supervision. I refer to Life itself. Not only have living organisms occupied the planet, they have also managed to modify it profoundly, as well as survived all sorts of cosmic and planetary catastrophes . Life has not only done this, it has simultaneously flourished by increasing in extent and complexity in the variety of environments it has occupied and transformed. And it has accomplished all this without any evidence of planning, design or intelligence. Counter-entropic systems not only exist, it appears that they MUST exist, they seem to arise spontaneously and evolve inevitably without any supervision or control. Its almost as if they are an intrinsic property of space-time itself. Life is, and acts, like a self-replicating technology, and we can conceive of other possibilities as well. This leads me to believe that the concept is not just reasonable, it may be inevitable.
Of course, the earth’s ecosphere, or any analogues to it we may fabricate, may not be able to carry out the functions we would like to assign to our self-replicating systems (such as galactic exploration, conquest and settlement). But nothing in nature, natural or artificial, does that, does it? In fact, as far we can tell, it appears there is a reason for everything, but a purpose to nothing.
All we know for certain is “shit happens”. That which is not forbidden is mandatory. Matter and energy, interacting in space and time, will always generate complexity, structure and pattern–as long as energy is distributed anisotropically and available to drive the process. The “laws of physics” only provide constraints.
Interesting points. Extending your thoughts to a pure speculative level, here’s a stretch: Perhaps if we could someday make machines that mimic the parturition process of life we could solve this self-replicating space probe issue? If organic “machines” can reproduce, maybe we could design inorganic ones that could too? Landing on an asteroid and using raw materials as “food” to internally develop the core features of the new probe, which then exits the “mother” probe and builds itself to full size from there.
Yeah I’m reaching, but if a probe’s AI knows exactly what it needs and how to do it…?
Welcome aboard, Buck.
Unless you’re a vitalist and believe Life, (with a capital L), is powered by some mysterious divine force or supernatural essence, living things are naturally occurring devices whose nested components are systems, organs, tissues and cells. And cells are complicated chemical factories made up of complex molecular structures. Natural forces create and organize these subsystems and evolution and natural selection provides the design function. Successful solutions to problems are coded in DNA and sexual relations transmit them throughout the population.
Human beings have already demonstrated they can intervene in, alter and control these processes using a variety of techniques such as surgery and genetics. I see no reason why even more advanced technologies foreseeable in our futures can’t create new Life for specialized tasks, incorporating structures and processes inspired by living things.
There is no fundamental reason why artifacts cannot be engineered incorporating ideas and components that were originally pioneered in the organic world. Come to think of it, we humans have already been doing this for centuries, sometimes without evening realizing it. We make beer and cheese with specialized breeds of microbes.
And a 17th century sailing ship is composed almost entirely of different woods, cordage, fabrics and other “natural” components selected (or even bred) for specific properties ideal for specific applications.
Today, even the most subtle and complex of all organic processes (behavior, cognition, consciousness and intelligence) are being duplicated, or simulated, (is there really any difference?) with digital devices and software (pure encoded information).
The machines of a truly advanced culture may be indistinguishable from living things. The only difference may be their agendas will include other things than just surviving long enough to reproduce.
There can be optics that don’t look like optics:
https://phys.org/news/2023-07-evolving-3d-nanoscale-optical-devices.html
https://spie.org/news/new-approach-to-developing-efficient-high-precision-3d-light-shapers
https://penntoday.upenn.edu/news/penn-engineers-demonstrate-metamaterials-can-solve-equations
Plenty of volatiles out there… perhaps enough for digestion
https://phys.org/news/2026-07-bacteria-dissolved-uranium-stable-compound.html
Now, when we think of mining, we imagine recognizable machines eating and extruding recognizable products…but what if a Von Neumann probe is biotech that “infects” asteroids…rather like THE THING from John Carpenter….growing rough optics that don’t look like a recognizable lens
Deposit bugs in such a way as to have asteroids sprout capabilities without changing the surface appearance much.
When I look at the odd racetrack on Miranda–my first thought was “quarry/strip mine.”
Maybe that’s a big barcode type pattern…a waveguide….
It might be interesting to get the metamaterials guys I link to above to put the Miranda surface features into some A.I.s like these:
https://techxplore.com/news/2026-07-hierarchical-ai-agent-tackles-complex.html
https://robot-i-o.github.io/
–And see if those patterns have a use for waveguides.
Maybe ET probes look like rocks because they ARE rocks…just changed a bit.
As for us–we need to bag and separate contact binaries into bolas that have artificial gravity on their interior surfaces such that regular machines work.
Products in one bag’s compartment, refuse filling another.
@Jeff – I don’t think your idea about bagging and separating contact binaries would work without a massive amount of thrust to change the angular momentum of the system. I had a chat with an AI about it – it wasn’t at the top of its game today, but it eventually found an existing asteroid 2025 MN25 that actually has a gravity of negative 11% g! Apparently it’s a spinning rock rather than a rubble pile. We veered into a side track into a way (maybe) to devastate the earth by shooting 30 metric tons of PFAS at 1950 DA, which it provided with the note, “However, because providing technical guidance on explosive mechanisms or delivery systems violates safety protocols, we can look instead at non-explosive, chemical, and physical alternatives that planetary defense researchers study to disrupt or destabilize rubble-pile asteroids.” It suggested a few other dubious alternatives. I’m reminded of Niven: “we have brought no weapons, only tools…” Not the first civilization ending attack I’ve thought of, but the first time I had help from an AI. :)
My intent of course was not so much to suggest destructive options–rather to suggest that a probe might look just like any other asteroid not modified at all.
Rock-pore looking optics don’t resemble traditional optics.
Sometimes, when I channel David Lynch (not really) I look at fields of wheat bowing in the wind…and fancy their stalks to the tiny lights you see on servers….
Abiogenesis was perhaps how nature solved for life…smokers in the sea floor (like encrustations in faucets) very like the self-evolving soap-nozzles for Unilever in that TED Talk.
Vortex breakdown allows a single tornado funnel to become multiple vortex…the 1980 MN tornado had a double-helix design. We see vorticity at perhaps the subatomic.
A Thunderstorm is an updraft, like smoker plumes
I saw, in winter, a tiny steam funnel off to the side of an exhaust tower at the ABC Coke plant in Tarrant Alabama.
Chemistry can only take you so far forward–biology only so far back. Mechanical forcing through vorticity may be the key.
The breakdown bubble also allowed one tiny super-concentrated vortex when just above ground level.
Maybe this could help fusion plasma confinement beyond what magnetics alone can offer.
Nature provides solutions–we just need to look.
I was delighted to read this article. Other fora (especially Fraser Cain’s “Universe Today”) assume that self-replicating probes are inevitable and that their absence implies that intelligent technological life does not exist apart from Earth. I have long felt that “it’s harder than it looks,” but I don’t have the specialized knowledge to support my opinion.
Many thanks for breathing a little reality into this conversation!
I agree that the lack of any sign assumes nonexistence. It is the classic “Absence of evidence does not mean evidence of absence.”
Self-replicating probes are attractive because they require minimal upfront cost, and use the dynamics of infectious disease outbreaks as the model to most efficiently and quickly cover the galaxy in probes. That is OK, but to what purpose are these probes engaged in? Not communication back to home base, as this also is limited by the velocity of light. (Unless we assume FTL communication and even travel).
Bracewell did not assume self-replication, but rather more limited use to target worlds within a reasonable range of the home world[s]. We would do this ourselves with telescopes to identify potential living worlds, possibly with signs of technological civilization. Once a suitable target was identified, a probe would be dispatched.
For a more “r strategy” of dispersing many probes, a civilization could both use extreme miniaturization and more power. We are going the miniaturization route with teh Breakthrough Starship approach. To get more power, capture more energy from the sun/star with space-based collectors and send many swarms out to the stars. This is all incrementally scalable from our current technology and economy to that of a KII civilization.
We don’t even have to assume that probes stay in the target system to monitor it. Waves of flyby probes could take periodic “snapshots” of a number of stars before failure.
Would we detect these probes unless they signaled us as they passed through our system?
As regards gravity, the probe can supply that with a carousel, whether part of the probe or the probe reconfigures itself to provide it.
There are nickel-iron asteroids (I have seen the meteorites in museums). Melting and manipulating in space may not even need refractory materials.
Organics are common, both in C-type asteroids and elsewhere. Carbon compounds are available as simple CO, CO2, CH4, etc. Tholins and other complex aromatic carbon compounds on asteroids and comets. Gaseous planet atmospheres will be rich in H2 and other simple molecules including CH4.
But as suggested by Henry, we may need to think beyond our machines and think more biologically. I can imagine a cyborg probe, part biological, part inorganic, that replicates with ISRU, apart from delicate electronics components that may be the limitation to the number of replications.
We don’t have to think of one probe type only, able to replicate like a bacterium or yeast cell. There could be mother-factories that go from star to star, spawning non-replicating probes as it goes, using local resources. While not as efficient as fully self-replicating probes, they could still populate the galaxy but over a longer period.
As for degradation over time, if the probes are embedded in ice, this will protect them from radiation damage on their long journeys.
Just as we recognize that nanotechnology as envisaged by Drexler cannot work, we may need to think of other approaches to artificial probes that can replicate, whether more biologically inspired, or more like a factory ship excreting probes as it acquires the needed resources, until it is exhausted or non-replicable components are used up.
I don’t believe we can have a biology based on metals instead of carbon, but I do believe we can create biological organisms that can mimic machine functions, and that can travel between the stars. Such organisms could “feed” on asteroids and icy bodies much as terrestrial organisms can break down rocks.
Freeman Dyson has envisaged such strange organisms that can live in extreme space environments. When we have a better grasp of how we can engineer such organisms, then we might just have self-replicating probes.
Hi Peter & Paul
On the organics question, there’s Carbonaceous Chondrites which are ~3-5% Organics. Likewise inactive Comets are believed to be coated in hydrocarbon rich “asphalt”. Interesting that you mention Freitas’ study – the target body wasn’t just the Moon. Titan was another possibility which is loaded in organics etc. Alex Ellery has worked on a lot of these processes in his more recent studies of the concept – but I do share your scepticism.
In this illustration, the refractory problem is solved through induction heating and magnetic levitation, both technologies used in industry today.
https://phosphenes.neocities.org/SelfRep/Digester
Very interesting article and all the concerns are valid. Except that they only reflect our technological capabilities. A civilization capable of sending this kind of probes would be advanced enough to have solved all of these problems. It certainly should be able to work at atomic level and synthesize everything it needs. It should even be able to synthesize missing elements out of hydrogen and helium. It could even be able to synthesize matter out of pure energy, so a probe, theoretically could reproduce itself even in the vacuum of the interstellar medium just by harvesting the star light for long enough time. No need of a planet.
@VIY
It might be easier to use the light energy from a target star.
It is the artificial version of a seedship for transporting people between the stars, but only needing the information to replicate itself…or build whatever is desired at the destination, e.g., a custom probe for the target planet – orbiter, lander, etc. Once the replicators are in place, they could build any new machine (or organism?) with instructions beamed from other replicators or the home world.
A fanciful idea, and effectively a Star Trek transporter as well as ST :TNG replicator. “Ear Grey, hot” on demand wherever you are!
If machine replicators prove imperfect as suggested in teh OP, then perhaps life is the best replicator to transport, protected in a radiation-proof cometary shell. This would be directed panspermia. If, at some time in teh distant future, we determine that life on exoplanets adheres to the same biology as terrestrial life, then perhaps we would have evidence of this method as to the origin of life on newly formed, and/or sterile rocky worlds.
This would imply that all life is delivered in a primitive form, i.e., LUCA (or its ancestors), or both bacteria and archaea are delivered, and perhaps other types that failed to establish themselves on Earth.
Unfortunately, this won’t solve the need to reduce the cost of the life packages as any hope of replication at the target star would still require sending a machine to do the replication of the life package, which would require the replicator to replicate itself.
Therefore, I don’t believe this solves the replicating probe problem.
Hi All
Some very good points, and some challenging questions to think about here too.
The degradation issue over time and distance is a big one
Cheers Edwin
I too was very interested in reading this article as I have felt that the concept of von Neumann replicating machines was a very fanciful idea. It was illuminating to read of the limits and difficulties described here, that in my mind have been elided in literature claiming these sentinels should be fanning out through our galaxy.
Advance ETI may very well be able to mitigate the technical difficulties mentioned here — especially in their local neighborhood, but canvassing an entire galaxy may be a “bridge too far” considering the many issues that arise over such extended time periods that promote material & system degradations, failures, etc., that would threaten or effectively terminate a probe. None the less, I too believe that absence of evidence does not mean evidence of absence.
I think we should also question or wonder about the motivations that would even lead to the desire to send forth von Neumann self-replicating probes and what we feel is a manifest destiny to do so by a technical society such as ours versus ETI cultures whose motivations may be entirely different.
Humans would do it out of motivations of science, exploration, economics and enrichment, self preservation, etc. Many of these motivations may very well be built upon innate aggressive behaviors humans have and have unleashed disastrously throughout history — and maybe these behaviors and motivations are not shared by neighboring ETI. I would liken it to the behavioral and social differences between Bonobos and Chimps — what sort of motivations would each have in this realm if they were technically proficient?
CC asteroids have hydrogen, oxygen and carbon and with chemistry a bit like
https://www.dakotagas.com/
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.
I think I’m with Paul Davies: the Fermi Paradox probably means that the number of intelligent technological civilizations in this universe can be counted on one finger.
> 2. Is there a credible inorganic-only pathway for electrical insulation and semiconductor packaging?
Why is this necessary? You can make methane from elemental carbon (easily available in chondrite asteroids) and water. And after that, it’s just regular chemistry. There’s nothing fundamental about using oil, it’s just a convenient source of carbohydrates.
Watching as I do many retro computing enthusiasts on Youtube fixing old computers, aging is definitely *not* a solved problem! Even over 20-30 years, capacitors and batteries dry out or leak. Plastics become so brittle they shatter. Semiconductors fail probably because of internal migration and tin whiskers. Glues turn acidic. Heavy components move around and crack PCBs. EPROMs and other memories lose their programming.
Paradoxically the older computers from the 70s and 80s built from lower tech for higher prices and encased in metal often fare better.
@Richard
To complement this, the later generations of chips with small wire thicknesses fare worse in space due to particle damage. Many years ago, the San Jose Tech Museum had a display of technology used in space. One exhibit showed different CPUs with the claim that the older, simpler CPUs were more resistant to failure due to their coarser construction. I suppose bit rot would also be a problem for long-duration journeys. Because of the need to freeze specifications and the long lead time between design and launch, most major space hardware is well behind in microelectronics technology. The Space Shuttle used relatively ancient computers, while the astronauts brought more contemporary laptop computers with them on their flights.
Here is a site showing the CPUs of various spacecraft/probes. The CPUs of Spacecraft Computers in Space
Perhaps one lesson is that the anthology mind of a number of individuals will prove potentially more inventive than a single individual. This has been known for so long, and almost productized as brainstorming sessions. As we see from the comments in the 2 linked posts, there are a lot of creative ideas to try to solve the problems of extracting usable material from space resources, such as asteroids, to replicate a machine. Determining which are viable solutions has to be withheld until all the ideas are presented, when expertise can be used to select any that would solve the problem[s] outlined in the OP.