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Probing the Galaxy: Self-Reproduction and Its Consequences

In a long and discursive paper on self-replicating probes as a way of exploring star systems, Alex Ellery (Carleton University, Ottawa) digs, among many other things, into the question of what we might detect from Earth of extraterrestrial technologies here in the Solar System. The idea here is familiar enough. If at some point in our past, a technological civilization had placed a probe, self-replicating or not, near enough to observe Earth, we should at some point be able to detect it. Ellery believes such probes would be commonplace because we humans are developing self-replication technology even today. Thus a lack of probes would indicate that there are no extraterrestrial civilizations to build them.

There are interesting insights in this paper that I want to explore, some of them going a bit far afield from Ellery’s stated intent, but worth considering for all that. SETA, the Search for Extraterrestrial Artifacts, is a young endeavor but a provocative one. Here self-replication attracts the author because probing a stellar system is a far different proposition than colonizing it. In other words, exploration per se — the quest for information — is a driver for exhaustive seeding of probes not limited by issues of sustainability or sociological constraints. Self-replication, he believes, is the key to exponential exploration of the galaxy at minimum cost and greatest likelihood of detection by those being studied.

Image: The galaxy Messier 101 (M101, also known as NGC 5457 and nicknamed the ‘Pinwheel Galaxy’) lies in the northern circumpolar constellation, Ursa Major (The Great Bear), at a distance of about 21 million light-years from Earth. This is one of the largest and most detailed photos of a spiral galaxy that has been released from Hubble. How long would it take a single civilization to fill a galaxy like this with self-replicating probes? Image credit: NASA/STScI.

Growing the Idea of Self-Reproduction

Going through the background to ideas of self-replication in space, Ellery cites the pioneering work of Robert Freitas, and here I want to pause. It intrigues me that Freitas, the man who first studied the halo orbits around the Earth-Moon L4 and L5 points looking for artifacts, is also responsible for one of the earliest studies of machine self-replication in the form of the NASA/ASEE study in 1980. The latter had no direct interstellar intent but rather developed the concept of a self-replicating factory on the lunar surface using resources mined by robots. Freitas would go on to explore a robot factory coupled to a Daedalus-class starship called REPRO, though one taken to the next level and capable of deceleration at the target star, where the factory would grow itself to its full capabilities upon landing.

I should mention that following REPRO, Freitas would turn his attention to nanotechnology, a world where payload constraints are eased and self-reproduction occurs at the molecular level. But let’s stick with REPRO a moment longer, even though I’m departing from Ellery in doing so. For in Freitas’ original concept, half the REPRO payload would be devoted to self-reproduction, with a specialized payload exploiting the resources of a gas giant moon to produce a new REPRO probe every 500 years.

As you can see, the REPRO probe would have taken Project Daedalus’ onboard autonomy to an entirely new level. Freitas’ studies foresaw thirteen distinct robot species, among them chemists, miners, metallurgists, fabricators, assemblers, wardens and verifiers. Each would have a role to play in the creation of the new probe. The chemist robots, for example, were to process ore and extract the heavy elements needed to build the factory on the moon of the gas giant planet. Aerostat robots would float like hot-air balloons in the gas giant’s atmosphere, where they would collect the needed propellants for the next generation REPRO probe. Fabricators would turn raw materials (produced by the metallurgists) into working parts, from threaded bolts to semiconductor chips, while assemblers created the modules that would build the initial factory. Crawler robots would specialize in surface hauling, while wardens, as with Project Daedalus, remained responsible for maintenance and repair of ship systems.

I spend so much time on this because of my fascination with the history of interstellar ideas. In any case, I don’t know of any earlier studies that explored self-reproduction in the interstellar context and in terms of mission hardware than Freitas’ 1980 paper “A Self-Reproducing Interstellar Probe” in JBIS, which is conveniently available online. This was a step forward in interstellar studies, and I want to highlight it with this quotation from its text:

A major alternative to both the Daedalus flyby and “Bracewell probe” orbiter is the concept of the self -reproducing starprobe. Replicating spacefaring machines recently have received a cursory examination by Calder [4] and Boyce [5], but the basic feasibility of this approach has never been seriously considered despite its tremendous potential. In theory, each self -reproducing device dispatched by the launching society would become an independent agent, slowly scouting the Galaxy for evidence of life, intelligence and civilization. While such machines might be costlier to design and construct, given sufficient time a relatively few replicating starprobes could search the entire Milky Way.

The present paper addresses the plausibility of self-reproducing starprobes and the basic parameters of feasibility. A subsequent paper [10] compares reproductive and nonreproductive probe search strategies for missions of interstellar and galactic exploration.

Hart, Tipler and the Spread of Intelligence

These days, as Freitas went on to explore, massive redundancy, miniaturization and self-assembly at the molecular level have moved into tighter focus as we contemplate missions to the stars, and the enormous Daedalus-style craft (54,000 tons initial mass, including 50,000 tonnes of fuel and 500 tonnes of scientific payload) and its successors, while historically important, also resonate a bit with Captain Nemo’s Nautilus, as spectacular creations of the imagination that defied no laws of physics, but remain in tension with the realities of payload and propulsion. These days we explore miniaturization, with Breakthrough Starshot’s tiny payloads as one example.

But back to Ellery. From a philosophical standpoint, self-reproduction, he rightly points out, had also been considered by Michael Hart and Frank Tipler, each noting that if self-replication were possible, a civilization could fill the galaxy in a relatively short (compared to the age of the galaxy) timeframe. Ultimately self-reproducing probes exploit local materials upon arrival and make copies of themselves, a wave of exploration that would ensure every habitable planet had an attendant probe. Thus the Hart/Tipler contention that the lack of evidence for such a probe is an indication that extraterrestrial intelligence does not exist, an idea that still has currency.

Would any exploring civilization turn to self-replication? The author sees many reasons to do so:

There are numerous reasons to send out self-replicating probes – reconnaissance prior to interstellar migration, first-mover advantage, insurance against planetary disaster, etc – but only one not to – indifference to information growth (which must apply to all extant ETI without exception). Self-replicating probes require minimal capital investment and represent the most economical means to explore space, interstellar space included. In a real sense, self-replicating machines cannot become obsolete – new design developments can be broadcast and uploaded to upgrade them when necessary. Once the self-replicating probe is established in a star system, the probe may be exploited in various ways. The universal construction capability ensures that the self-replicating probe can construct any other device.

Probes that can fill the galaxy extract maximum information and can not only monitor but communicate with local species. Should a civilization choose to implement panspermia in systems devoid of life, the capability is implicit here, including “the prospect of exploiting microorganism DNA as a self-replicating message.” Such probes could also, in the event of colonization at a later period, establish needed infrastructure for the new arrivals, with the possibility of terraforming.

Thus probes like these become a route from Kardashev II to III. In fact, as Ellery sees it, if a Kardashev Type I civilization is capable of self-reproduction technology – and remember, Ellery believes we are on the cusp of it now – then the entire Type I phase may be relatively short on the way to Kardashev Types II and III, perhaps as little as a few thousand years. It’s an interesting thought given our current status somewhere around Kardashev 0.72, beset by problems of our own making and wondering whether we will survive long enough to establish a Type I civilization.

Image: NASA’s James Webb Space Telescope has produced the deepest and sharpest infrared image of the distant universe to date. Known as Webb’s First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail. Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb’s view for the first time. This slice of the vast universe covers a patch of sky approximately the size of a grain of sand held at arm’s length by someone on the ground. If self-reproducing probes are possible, are all galaxies likely to be explored by other civilizations? Credit: NASA, ESA, CSA, and STScI.

Early Days for SETA

The question of diffusion through the galaxy here gets a workover from a theory called TRIZ (Teorija Reshenija Izobretatel’skih Zadach), which Ellery uses to analyze the implications of self-reproduction, finding that the entire galaxy could be colonized within 24 probe generations. This produces a population of 424 billion probes. He’s assuming a short replication time at each stop – a few years at most – and thus finds that the spread of such probes is dominated by the transit time across the galactic plane, a million year process to complete assuming travel at a tenth of lightspeed.

Given this short timespan compared with the age of the Galaxy, our Galaxy should be swarming with self-replicating probes yet there is no evidence of them in our solar system. Indeed, it only requires a civilization to exist long enough to send out such probes as they would thenceforth continue to propagate through the Galaxy even if the sending civilization were no more. And of course, it requires only one ETI to do this.

Part of Ellery’s intent is to show how humans might create a self-replicating probe, going through the essential features of such and arguing that self-replication is near- rather than long-term, based on the idea of the universal constructor, a machine that builds any or all other machines including itself. Here we find intellectual origins in the work of Alan Turing and John von Neumann. Ellery digs into 3D printing and ongoing experiments in self-assembly as well as in-situ resource utilization of asteroid material, and along the way he illustrates probe propulsion concepts.

At this stage of the game in SETA, there is no evidence of self-replication or extraterrestrial probes of any kind, the author argues:

There is no observational evidence of large structures in our solar system, nor signs of large-scale mining and processing, nor signs of residue of such processes. Our current terrestrial self-replication scheme with its industrial ecology is imposed by the requirements for closure of the self-replication loop that (i) minimizes waste (sustainability) to minimize energy consumption; (ii) minimizes materials and components manufacture to minimize mining; (iii) minimizes manufacturing and assembly processes to minimize machinery. Nevertheless, we would expect extensive clay residues. We conclude therefore that the most tenable hypothesis is that ETI do not exist.

The answer to that contention is, of course, that we haven’t searched for local probes in any coordinated way, and that now that we are becoming capable of minute analysis of, for instance, the lunar surface (through Lunar Reconnaissance Orbiter imagery, for one), we can become more systematic in the investigation, taking in Earth co-orbitals, as Jim Benford has suggested, or looking for signs of lurkers in the asteroid belt. Ellery notes that the latter might demand searching for signs of resource exploitation there as opposed to finding an individual probe amidst the plethora of candidate objects.

But Ellery is adamant that efforts to find such lurkers should continue, citing the need to continue what has been up to now a meager and sporadic effort to conduct SETA. I’m going to recommend this paper to those Centauri Dreams readers who want to get up to speed on the scholarship on self-reproduction and its consequences. Indeed, the ideas jammed into its pages come at bewildering pace, but the scholarship is thorough and the references handy to have in one place. Whether self-reproducing probes are indeed imminent is a matter for debate but their implications demand our attention.

The paper is Ellery, “Self-replicating probes are imminent – implications for SETI,” International Journal of Astrobiology 8 July 2022 (full text). A companion paper published at the same time is “Curbing the fruitfulness of self-replicating machines,” International Journal of Astrobiology 8 July 2022 (full text).


Comments on this entry are closed.

  • tesh July 12, 2022, 9:51

    Could lurkers be in plain sight? For example, in the form of sparrows or minnows or ants or any common biological lifeform (or indeed even a combination of those).

    • Robert July 12, 2022, 12:53

      “These creatures you call mice, you see, they are not quite as they appear. They are merely the protrusion into our dimension of vastly hyperintelligent pandimensional beings.”

      ― Douglas Adams, The Hitchhiker’s Guide to the Galaxy

      • Paul Gilster July 12, 2022, 19:12

        A favorite quote!

        • Jeff Wright July 14, 2022, 4:40

          Saturn has hydrocarbon sea moons and ice rings to hide swarms-but Miranda either has been….or would lend itself to, strip-mining…any natural geology a cover. I can just see drones rising above the ring plane.

  • Harold Shaw July 12, 2022, 14:15

    Social explanations for the Fermi Paradox don’t have to be universal. We would get the same results from a 1:1 ratio of social explanations to societies. Occam’s razor has no place being applied to social explanations.

    Applying Occam’s razor to our lack of evidence is also suspect. It simply moves complexity to the mechanism for producing space faring peoples.

    We can not reliably predict self-replication to continue past the lifetime of space faring people simply by pointing to the definition of self-replication. One of the most secure and simplest approaches to controlling self-replication is to make replication dependent on a signal from the people who sent them.

    In the context of a universal constructor, humanities presence makes it impossible to generalize that the evidence for probes in the Solar system will conform to an average. We should expect the probe to configure evidence for itself according to the value function of its sender.

    Or its own value function. It is impossible to allow for molecular universal constructors without allowing for spaceship people. It would take only one people to cross the paper thin boundary between self-replicating probes and spaceship people to fill the observable universe with a truly space faring civilization. Evidence of this people could be very hard to detect.

  • Alex Tolley July 12, 2022, 14:56

    Probably because it reflects my own opinions and biases, I really liked the Ellery paper, even though it was overlong.

    The widely used assumption of replicators traveling at 0.1c filling the galaxy could be at odds with some propulsion technologies at the end of the paper. It seems pretty clear that the most accessible propulsion technology is a light sail, but even a highly efficient one will only reach maybe 125 km/s after a sundiver maneuver. That is 4.2E-4 c. Assuming galaxy filling time = 2R/velocity (R – galaxy radius), then
    t = 480 million years. [And still much faster than star hopping through close encounters]. This is a long time, but well within the age of the galaxy and the emergence of intelligence in older star systems and I don’t think invalidates the author’s argument that ETI does not exist in the galaxy.

    That replicators will be everywhere either now or will be when we launch them supports my belief that the dominant form of technological capable intelligence in the galaxy will be machine-based.

    I see no reason why replicators cannot also be the mechanism for panspermia. [What if that is their main task and they decamp from the system after the biosphere is established?]

    Regardless of whether replicators will be used to colonize the galaxy, it is clear that replicator machines would be ideal for terraforming or preparing the planets and moons of our system for human habitation. While O’Neills may be the best way for humans to colonize space, the lack of a requirement for gravity and a pressure hull would allow machine space platforms to dwarf those of the O’Neills. Imagine vast, spider web frames as the basic platform, with specialized pressure/artificial gravity sub-structures needed for some industrial processes. And what better anchors to hand space elevators to transport cargo between Earth and the platform?

    In the companion paper (mostly biology) there is the lo-tech idea that memory is best made as the old magnetic core memories. .
    I trust that the 3D printing technology can sufficiently reduce the size to dimensions closer to chip technology.

    Whether these replicators look like advanced forms of our current industrial ecosystem (very much the approach of P K Dick’s autofacs or become more biologically inspired, it seems to me that they should have a very important role to play in the future, both within our system, and probably the galaxy.

    • Robert July 14, 2022, 12:34

      “I see no reason why replicators cannot also be the mechanism for panspermia. [What if that is their main task and they decamp from the system after the biosphere is established?]”

      Yes, and if time wasn’t a big concern they could be tiny and blown by the solar winds. This has the advantage of not only accelerating the machines but automatically decelerating them in the target star systems which would be any stars in their path. Humanity could conceivably be able to do this within a century or two (if allowed to do so!).

      • Jeff Wright July 17, 2022, 4:02

        Four days before the Great Daylight Fireball, Earth was struck by a solar event that set off mines in Vietnam.

        I wonder if that was a bracewell that glitched and came in too low.

  • Henry Cordova July 12, 2022, 16:56

    What if there are no lurkers? What if intelligent, long-lived species have already determined that the Galaxy is probably populated with other intelligent long-lived species so there’s really no point in expending resources to locate and study them? This is especially the case if their own research has suggested that they are so separated by space and time that their encountering one another is highly unlikely anyway?

    Maybe this desperate need to demonstrate we are not alone is a purely human response to our own religious pathologies and superstitions. Maybe they don’t care.

    Sure, anything is possible. But it is unlikely any rational species is going to invest massive resources in searching for something it knows exists, but is unlikely to find.

    As to Mr Tesh’s comment that lurkers may be disguised as a local, common life form on our own planet, again, it can’t be ruled out, but it is also highly unlikely. We have not encountered any creature that cannot be fitted into the existing Terran evolutionary tree of life. I suppose a truly advanced civilization could engineer an artificial taxon that could be disguised to appear Terran, to have evolved from birds or fish or insects. But it could never guarantee that life forms evolving here wouldn’t be able to eventually expose the intruder and follow the trail to its originators.

    Self-replicating probes have a fundamental flaw: not only must they be able to reproduce, that implies they must be able to evolve to adapt to unexpected circumstances and environments. This means that whatever initial programing is installed by their creators may unexpectedly change into something strange, different, perhaps hostile.

    Any civilization irresponsible enough to turn some potential Saberhagen Berserker loose on the cosmos deserves to be immediately exterminated. They are, by definition, not very good neighbors.

    The point is, although it is pretty safe to say ETI may be capable of pretty amazing things, that doesn’t necessarily mean it has to.

  • Christian G July 12, 2022, 17:02

    Paul, it occurs to me an interesting challenge would be to design a probe with current tech and see how hard it would be to find using the telescopes we have available. Have you heard of any studies like that?

    And I’m sorry, I don’t find, “Unless we observe aliens doing this one specific thing we have never attempted, cannot do with present tech levels, and may not be able to currently detect, then aliens do not exist,” a convincing argument.

    • Peter E July 14, 2022, 12:43

      To first order, I don’t think we could do it. There is an absolute crapload of stuff even in Earth orbit. We could definitely see something meter-scale orbiting Earth, but could we distinguish it from all the other satellites? Lots of countries have military satellites with classified orbits. We would have a a hard time parsing out what’s a lurker even for large scale satellites, unless we have really good imaging capabilities so we can see the structure of the satellite.

      But there could also be alien chipsats floating around, sent out by something akin to Breakthrough Starshot. We have even less hope of finding those, because there’s a huge amount of space junk out there at the centimeter scale.

      It gets worse as you leave Earth orbit and look further out, because your radar power falls off, and an optical telescope will have a hard time catching a chip doing a 0.1c flyby.

  • Dimjo July 12, 2022, 17:42

    If one were to design the program, wouldn’t one consider: 1. It can’t be one size fits all. One would have to presume their probe will eventually encounter intelligence of varying levels of technologies, and the consequences of such encounters. Avoidance protocols would be in place. One would have to incorporate some pretty sophisticated software and quantum computer level hardware. 2. Consider the possibility that the probes themselves may eventually evolve intelligence. And would they cease replication, (for various reasons), leading to us concluding there are none? Or become a post biological intelligence? Their lurker tech may be “invisible” to us as the sparrows and minnows mentioned above. If they have lurkers, their tech will adapt and evolve to take advantage of our tech, piggybacking on everything everywhere, on this planet. Are all hackers on this planet from this planet? It might be slowed down by quantum computing and communication, but we really don’t know that it will. The point is, as our tech evolves it makes it easier to watch us, and it makes us realize how much more difficult it is for us to see them.

  • Robin Datta July 12, 2022, 21:38

    “Ultimately self-reproducing probes exploit local materials upon arrival
    and make copies of themselves
    “… that is indeed the basic idea.

    However, the integrated circuits that make the microprocessors are close to the current limits of nanotechnology, and downscaling their manufacture may be quite problematic. A more detailed (but still simple) description of the issues involved in the manufacture: How CPUs and Processors are Made for Smartphones, Laptops, and Desktops – YouTube.

    • Alex Tolley July 13, 2022, 8:08

      The author has proposed far more lo-tech versions for this. He suggests fairly crude neuromorphic brains built from wires and even valvales[!], also, chemical approaches are possible. As I commented, a companion paper has suggested memories are created with magnetic memory cores. All this is crude and massive, but by reverting to 1950s-1960s technology, all doable with 3D printers and some wiring help.
      The author has suggested that something far closer to microchip technology may be printable, but if not, there is this fallback approach.

      I would just put on skeptical spectacles for the moment or allow for future improvements in replicator technology or chip design to solve that problem.

  • David Horacek July 12, 2022, 23:35

    I don’t think that the difference between galactic exploration and colonization is so big. Imagine your design of a self-reproducing probe. Now imagine giving that probe this one extra task: create an abiogenesis lab where a simple living cell is created, and then successive generations of it are modified until a non-trivial subset of terrestrial life (including human life) is built from archived genetic data. If the probe can already self-replicate, what extra stuff would it need to also do the abiogenesis? I suspect it’s no extra stuff at all, apart from the lots of AI code and the genetic data itself. But suitably packed, data weighs almost nothing. If we send out self-reproducing probes, we should insist that we always tack on this “oh and wherever you stop, also make O’Neill cylinders and fill them with Earth life” functionality. If we can’t spare the few grams of mass that the data storage would require, we should at least program it to build a giant receiver, point it at already-colonized systems and then receive the data by laser link. I honestly think that once probes stop to observe and reproduce, the building of life basically happens for free.

  • Martin Alfredsson July 13, 2022, 8:31

    Lets say its possible for an advanced civilisation, biological or machine, to build self-replicating probes. They may have ways to cope with failure in replication and unforseen events. If the Milky way is 100,000 ly wide (it might be more) their point of origin is probably 50,000 ly from us. With 10% c speed probes that means that any information they get about us will take (ideally) 500,000 + 50,000 to get back to them.
    We don’t send probes out there with no real chance of getting information back. Proxima flyby with no data return?

    While self-replicating probes sound interesting all they would be able to do, on a galaxy scale, is to spread our DNA and possibly the history of a long forgotten civilication in a far corner of the galaxy.

    So why lurkers?

    • Alex Tolley July 13, 2022, 10:53

      So why lurkers?

      We have no idea of the longevity of advanced civilization[s]. We also need to think more about a patchwork of local civilizations arising by colonization or ab initio. Having a galaxywide “internet” of surveillance sensors would be a useful hedge against predator species that might arise.

      Secondly, if galactic “greening” was a program, lurkers would make sense to continue to monitor progress. They may be dead once the local biosphere has been successful but see above.

      We shouldn’t assume lurkers are like our intelligence-gathering devices for control. They might be gathering data for general use, like public webcams. Was it Nielsen in a prior post suggesting that a galactic encyclopedia would be a good legacy to pass on? How better than to fill that encyclopedia with local data on for each system. A few billion years of data for possibly many millions/billions of systems would be a treasure trove for each new civilization to discover.

  • Neil Stahl July 13, 2022, 12:25

    1. Is it not possible that the reason we don’t see replicators is that some advanced species has taken upon itself to search out replicators and destroy them? Or the civilizations that start them.

    2. Surely for any long-term lurker the main problem would be energy. For a really advanced civilization it might not amount to much but for us, e.g. trying to hide a lurker in our asteroid belt solar power would work but solar panels would be rather visible and eventually would be hit by a passing rock. Nuclear power is shorter term than we would surely want a lurker to last. And anything that generates much heat would stand out like a sore thumb.

  • wdk July 13, 2022, 20:57

    In this week with the JWST coming on line, our attention is drawn to an increasing plethora of observable galaxies. They have variety, true; but I don’t see evidence of galaxy wide alterations due to some systematic exploration and/or exploitation. … Unless I missed some significant reports.

    Maybe decades ago, one could have interpreted a quasar observation as such, but not now.

    Now if self-replicating devices were mailed from star to star in a small package, that would reduce their presumed impact. But one might also suspect that some aliens would use large packages and some use small.
    And in either case, the production pyramid to produce the interstellar probe in concepts we understand would be significant. lf the star systems of a galaxy look like they have artificial circumstellar disks, we know they are in the Kardeshev civilization producing business.
    And if self -replicating probes have to mine one planet in a star system extensively to get to the next, then the mining would leave industrial scars across the galaxy. In order to leave the village and pack the bags…

    In the case of interesting planets which actually have exo-biology, the arrival of such a replicating device would be a dangerous turning point in local history. There might not be a convenient mining resource except the world described to make the next jump. But OK, I take my own bait: Maybe that’s how we got the asteroid belt?

    But thus far, unless the JWST changes things significantly, we don’t see evidence like that.

    Given that, we could assume that galactic or interstellar civilizations are rare or near non-existent, or that galactic civilizations end up doing business or routine commerce in some other way.

    But then again, if there is such, and to the unitiated like ourselves, it would appear as though the aliens had walked through a door suspended in the air, there would be reasons for anxiety if we are all connected that way as well. Beside the fright of a genuine alien encounter, it might be that the occupants on the other side have a significant pressure differential on their home world – or it is toxic.
    The hinges on the door might break or the aliens might neglect to shut the door. Getting linked to the right (?) galactic explorer, a certain
    atmospheric uniformity could result. E.g., Beware of Mini-Neptunes.
    They’re united.

    • Ron S. July 14, 2022, 8:11

      “I don’t see evidence of galaxy wide alterations due to some systematic exploration and/or exploitation.”

      You’re seeing the universe as it was billions of years ago. That is early for any engineering by a purported ET since they would not yet exist. The probability (such as it is) would grow over time. For that reason the highest likelihood to find that evidence is here, now.

  • Roger B July 13, 2022, 21:26

    Maybe ETI have no need to send probes through out the galaxy, as they are exemplary stewards of their worlds, living in harmony and not needing to move beyond their planet. It amuses me that we assume ETI shares our motivations, ambitions and desires when they may not – even though they may be technologically advanced.

    Alternatively, maybe we have already detected ETI’s probes – right here on earth – in the form of UAPs and yet we haven’t a clue on how to analyze, assess or meaningfully study them. As difficult as it has been to study and characterize UAPs, similarly probes placed in the space around earth may be equally difficult to detect let alone characterize.

  • Harold Shaw July 14, 2022, 8:27

    The premise of the paper is solid. We should expect the footprint of exploration to be larger than the footprint of colonization. We should also expect more civilizations to engage in exploration than colonization.

    Imo, the major flaw of this paper is the conclusion and his grandiose claim that others must prove him wrong. Ellery extends his conclusion that we are alone to several million galaxies. This would require something much more complex than the rare Earth hypothesis. Perhaps something more complex than the hypothesis that a space faring people gathering information adjust their posture within the home system of another space faring people. There are a host of reasons to do so, ranging from diplomacy to avoiding a path to runaway replication through tampering. Ellery is using Occam’s broadsword or battering ram to reach his conclusion.

    If other space faring people exist in any number, the field of SETI is a soft science like ecology or sociology where variables, interactions and feedback proliferate.

  • Mike Serfas July 14, 2022, 21:13

    Does the galaxy have an immune system? Let’s find out…

    “You move to an area, and you multiply, and multiply, until every natural resource is consumed. The only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. A virus. Human beings are a disease, a cancer of this planet, you are a plague, and we are the cure.” — Agent Smith, The Matrix

    • tesh July 15, 2022, 11:38

      I completely disagree with the notion that more and more power is required the more of you there is, and, that the power grab and sustained expansion is achieved by physical expansion and cultivation of new space.

      Maybe the silence is because we aren’t currently able to dial in yet OR it is really a silent universe. Either way, it seems it is easier for a civilisation to “go inward” rather than out if an understanding of everything is achieved. My feeling is that the understanding of everything can be achieved well before the need to inhabit and know everywhere.

      Once you know everything there is to know within a particular square micron, what is the advantage in expansion? Why not use your knowhow to down load to a more interesting virtual world or make your own (more interesting) universe?

      Beyond that I get the impression that the whole lurker debate is tinged by our(?) “infant” view point and highly parochial in perspective. As well as the disconnect of space and time, why would another civilisation bother – beyond the our current infatuation with voyeurism.

      • Alex Tolley July 15, 2022, 13:17

        Once you know everything there is to know within a particular square micron, what is the advantage in expansion? Why not use your knowhow to down load to a more interesting virtual world or make your own (more interesting) universe?

        Alternatively, why climb Everest when you could simulate it in VR? Some people want reality. Those who want to know “everything” will want to explore the universe to find out, rather than retreat into a VR (Holodeck) environment. The complexity of the universe is likely to be far greater than any imagined universe and therefore to explore it is important to those minds.

        Are you arguing for a solipsist viewpoint, rather than an outward engagement in reality? Which civilization would have the advantage when the expansionist and solipsist ones meet?

  • Jer July 16, 2022, 14:03

    Truly wonderful article encompassing many compelling ETI and pre-exo-solar-exploration Thought Experiments. I am (currently) finding the paper a slog, but hope to persevere as this is from my alma mater (thoroughly unrelated major, many decades earlier – ho hum, but I feel that late 20thC optimism). Also, the unexpected trove of Vanuxem Lecture materials (and its ilk) from the early 70s, that spawned from this review, astounding.

    Unfortunately, I must disagree fundamentally with its most basic premises and assumptions:
    — “… [reasons to send out probes] …but only one not to – indifference to information growth (which must apply to all extant ETI without exception)….” I don’t necessarily believe that a civilization is a consistent, mostly-homogenous entity with singular (or few) projects, goals, and endeavours; typically manifest by obvious, grand, communal projects provided mainly through its vast resources. The great increases of exo-solar knowledge may, and likely would, come from its most ardent explorers and individualistic endeavours, likely an infinitesimally-tiny part of the overall ‘civilization’s’ resources, skills, or current knowledge – possibly not even generally shared internally.

    — self-replication tech (or even its recognizable path) off earth is imminent. I have to plead near-total-ignornace and a true intimidation in undertaking a literature review of this goliath subject, but the idea that a probe/ self-contained system could access raw materials likely many orders of magnitude of its own mass, primarily available from areas likely a significant portion of a moon/ planet/ solar system radius away (from the probe and its other raw components), and coordinate/assemble/promote forward the next step of its daughter-clone with acceptable error, to be insanely unlikely, above a singular or minimal success, even over many orders of magnitude of the universe’s current age, for a mere few iterations.

    — a pattern of widespread diffusion is the likely preferred mission goal. As I believe that all significantly advanced civilizations (slightly less than K1, but above us) would almost-all necessarily become decentralized and therefore just the base (but still very advanced) technology infrastructure to enable its population’s individualistic, post-scarcity, functionally-immortal, component-citizens (likely mostly non-biological) to do their own thing, likely leave the home Civ hub and do the equivalent of explore, this kind of probe mission would be a low priority – and a widespread scatter, less important still.

    Though, I do like the idea that an ultra-efficient, all-in-one-box factory system would become popular among the explorers and travellers as they journey to points of interest (rather than general diffusion).
    I also feel that the type of efficiency and self-reliance encouraged by this technology could indeed provide very reduced earth scarcity, more successful solar and exo-solar missions, and an approach to cis-lunar habitation beyond NASA’s Artemis and related stuff.

    On pros and cons, an excellent addition to the discipline’s academic Literature.

  • Henry Cordova July 16, 2022, 15:13

    Speaking of the JWST photo…

    The PBS science program NOA did a special on the Webb Telescope last night. Most of it was stuff that’s already been released and that we all are familiar with, such as the project’s antecedents, history, its development, construction and future capabilities. They also showed the ‘first light’ images that were released yesterday.

    The show was a pretty good intro to the telescope, the people who built it, and the people who will use it. But most important, it goes into just what an ambitious project this was. NASA and its collaborators went for broke, they truly aimed at the stars. They took enormous risks, and, hopefully, it appears they have paid off. I know if I had been in charge of this program I would have opted for something a lot more conservative, a lot less audacious. The Webb’s creators are to be congratulated not just for their vision and their wisdom, but for their courage. The entire project was a career-wrecker, there were a million places where it could have gone south–the “single points of failure”. It’s not only the technology, but the organization, the management, the collaboration with our many international technical allies and friends, the whole shooting match. It was our generation’s Stonehenge, our Pyramids, our Panama Canal, our Parthenon. It may very well turn out to be our finest hour.

    I salute these guys, they swung for the fences when I bet their every instinct was to hope for the walk, the bunt, or at most, to settle for the base hit. I am so proud of them, and of my country. At a time when it looks like the American Century is starting to unravel, when everything about this nation seems to be in danger of coming apart, Webb is all the proof we need America can still KICK ASS!

  • Michael Fidler July 19, 2022, 21:50

    X-Rays Could Carry Quantum Signals Across the Stars Hypothetical interstellar civilizations could employ such signals for lossless long-distance communication.


  • Michael Fidler July 20, 2022, 2:51

    The future can arrive in sudden bursts. What seems a long way off can suddenly jump into view, especially when technology is involved. That might be true of self-replicating machines. Will we combine 3D printing with in-situ resource utilization to build self-replicating space probes?


  • ljk July 26, 2022, 15:52

    If ETI are visiting other star systems and using their resources such as planetoids to make copies of themselves, etc., they should be very careful where they step in certain cases…


  • ljk July 27, 2022, 11:10

    Before we Develop Self-Replicating Machines to Explore the Universe, we Should Figure out how to Turn Them off Again

    JULY 26, 2022


    In 1948/49, famed computer scientist, engineer, and physicist John von Neumann introduced the world to his revolutionary idea for a species of self-replicating robots (aka. “Universal Assemblers”). In time, researchers involved in the Search for Extraterrestrial Intelligence (SETI) adopted this idea, stating that self-replicating probes would be an effective way to explore the cosmos and that an advanced species may be doing this already. Among SETI researchers, “Von Neumann probes” (as they’ve come to be known) are considered a viable indication of technologically advanced species (technosignature).

    Given the rate of progress with robotics, it’s likely just a matter of time before humanity can deploy Von Neumann probes, and the range of applications is endless. But what about the safety implications? In a recent study by Carleton University Professor Alex Ellery explores the potential harm that Von Neumann Probes could have. In particular, Ellery considers the prospect of runaway population growth (aka. the “grey goo problem”) and how a series of biologically-inspired controls that impose a cap on their replication cycles would prevent that.

    Professor Ellery is the Canada Research Chair in Space Robotics & Space Technology in the Mechanical & Aerospace Engineering Department at Carleton University, Ottawa. The paper that describes his findings, titled “Curbing the fruitfulness of self-replicating machines,” recently appeared in the International Journal of Astrobiology. For the sake of this study, Ellery investigated how interstellar Von Neumann probes could explore the Milky Way galaxy safely by imposing a limit on their ability to reproduce.

    Full article here: