A recent workshop at Ohio State raises a number of interesting questions regarding what is being referred to as ‘high energy SETI.’ The notion is that places where vast energies are concentrated might well attract an advanced civilization to power up projects on a Kardashev Type II or III scale. We wouldn’t necessarily know what kind of projects such a culture would build, but we might find evidence that these beings were at work, perhaps through current observations or, interestingly enough, through scans of existing datasets.
Running June 23-24, the event was titled “Bridging Multi-Messenger Astronomy and SETI: The Deep Ends of the Haystack Workshop.” ‘Multi-messenger astronomy’ refers to observations that take in a wide range of inputs, from electromagnetic wavelengths to gravitational waves, from X-rays through gamma ray emissions. Extend this to SETI and you’re looking in all these areas, the broad message being that a SETI signature might show up in regions we have only recently begun to look at and may have prematurely dismissed.
Notice that such ‘signals’ don’t have to imply intended communication. We might well turn up evidence of advanced engineering through astronomical plates taken a century ago and only now recognized as anomalous. This kind of search is deliberately open-ended, acknowledging as it does that civilizations perhaps millions of years ahead of us in their history might be far more occupied in their own projects than in trying to talk to species in their infancy.
As I mentioned in SETI at the Extremes, Brian Lacki (Oxford University) and Stephen DiKerby (Michigan State) have produced a white paper on the workshop, an overview that puts the major issues in play. The high-energy bands that we have been talking about recently have seldom been explored with SETI in mind, given the natural predisposition to think that life would be something rather like ourselves, and certainly not capable of existing on, say, a neutron star. High-energy SETI pushes the idea of astrobiology into these realms anyway, but equally significant, makes the point that whatever their makeup, advanced aliens might exploit high-energy sources whether or not they had evolved on them. Thus these energy resources become SETI targets, in the hope that activity affecting them will throw a signature.
Image: The area around Sgr A* contains several X-ray filaments. Some of these likely represent huge magnetic structures interacting with streams of very energetic electrons produced by rapidly spinning neutron stars or perhaps by a gigantic analog of a solar flare. Scattered throughout the region are thousands of point-like X-ray sources. These are produced by normal stars feeding material onto the compact, dense remains of stars that have reached the end of their evolutionary trail – white dwarfs, neutron stars and black holes. Because X-rays penetrate the gas and dust that blocks optical light coming from the center of the galaxy, Chandra is a powerful tool for studying the Galactic Center. This image combines low energy X-rays (colored red), intermediate energy X-rays (green) and high energy X-rays (blue). Credit: NASA/CXC/UMass/D. Wang et al.
Let’s acknowledge our ignorance by recognizing that the motivations of any off-Earth civilization are unknown to us, and for all our logic, we have no notion of what such a culture wants to do. It’s a helpful fact that technosignature searches don’t require futuristic off-planet observatories. Reams of observations have been recorded that have seldom if ever been actively mined. Thus high-energy SETI, exotic as it is, can proceed with existing materials, even as ongoing astrophysical research continues to produce new data that add to the mix.
As the authors note, high-energy radiation has many sources, from nuclear processes, from gamma ray emissions and neutrinos to relativistic particles, which include not only cosmic rays but particles thrown out by jets and the interaction of electrons and positrons. We can study compact sources like neutron stars and black holes (ideal for energy extraction) and relativistic flows from energetic transients. Gravitational waves might be used to bind together elements of a galactic network. How exactly might ETI modify any of these?
It’s natural to ask whether X-ray astronomy has implications for SETI. Bursts of emission using X-rays for communication, exploiting less diffraction and the ability to produce tighter beams, might be detected if aimed specifically at us, making something like a flash at these frequencies from a nearby star an anomalous event worth studying. Or consider signals more general in nature:
Non-directional X-ray communication can be effected by dropping an asteroid onto a neutron star [4]. When it hits, it releases a burst of energy detectable at interstellar distances. The cosmos also has a number of compact high-energy “signal lamps”. X-ray binaries (XRBs) are systems with a neutron star or black hole accreting from a donor star, having luminosities of up to 105 suns. Even a kilometer-scale object passing in front of the hotspots of an XRB can easily modulate its luminosity, serving as a technosignature [4, 16]. A subplanetary-scale lens is potentially capable of creating a brief flash visible even in nearby galaxies without any power input of its own. Credit: NASA/CXC/UMass/D. Wang et al.
We don’t have a handle on how to use neutrinos for communication, although there have been experiments along these lines given the ability of neutrinos to pass right through obstacles and thus probe, for example, the oceans of icy moons. But perhaps we can home in on industrial activities, which as the authors point out, could involve not just energy collection to power scientific experiments but interstellar propulsion through antimatter rockets. The interactions between a relativistic spacecraft and the interstellar medium could become apparent through gamma rays, while X-ray binaries might show oddities in their proper motion indicative of their use as stellar engines.
This possibility, studied at some length by Clément Vidal under his ‘stellivore’ concept, stands as a particularly detectable phenomenon:
What are the limits of life, broadly defined? At the very least, complex processes require a thermodynamic gradient to feed them. In his reflections on the future of the cosmos, Dyson suggested that this is the only absolute requirement, and that long after the stars have gone out, life could still thrive in the chilly atmospheres of cooled compact objects [7]. A contemporary test of this admittedly extreme idea might be found with today’s compact objects. The accretion hotspots of XRBs have some of the greatest sustained power densities around in the contemporary universe. If thermodynamics really is the only prerequisite factor for complexity and ETIs can withstand the incredibly hostile environments, they may find the energy gradients in XRBs attractive [29].
If we look not at the stellar but the galactic level, the actual lack of X-ray binaries could be a marker, with the deficiency being a sign their energies are being exploited to some purpose. For that matter, high-energy flare activity from an individual star or the source of a gamma ray burst may point us at locations where an advanced civilization can use its technologies to deflect these energies to avoid the threat. If we push speculation to the extreme, we’re talking once again about Robert Forward territory, wondering whether environments like neutron stars can sustain their own kinds of life.
Image: HEAO-1 All-Sky X-ray Catalog: Beginning in 1977, NASA launched a series of very large scientific payloads called High Energy Astronomy Observatories (HEAO). The first of these missions, HEAO-1, carried NRL’s Large Area Sky Survey Experiment (LASS), consisting of 7 detectors. It surveyed the X-ray sky almost three times over the 0.2 keV – 10 MeV energy band and provided nearly constant monitoring of X-ray sources near the ecliptic poles. We’ve been examining high-energy targets for quite a while now and have numerous datasets to consult. Image credit: NASA.
Several things to keep in mind as we consider ideas that are on the face of things fantastic. First, the very practical fact that high-energy SETI need not be expensive, given our growing sophistication at using machine intelligence to analyze existing astronomical data (I’ve always nursed the wonderful idea that some day we’ll make a SETI detection and it will be corroborated by a century-old astronomical plate taken at Mt. Wilson Observatory). Second, existing facilities monitoring things like gamma ray bursts and detecting neutrinos are capable of full-sky monitoring and are doing good science. Our search for high-energy anomalies, then, takes a free ride on existing equipment.
So while it’s completely natural to find this approach well outside our normal ideas of astrobiology, their improbable nature should elicit a willingness to keep our eyes open. It would be absurd to miss something that has been in our data all along. And filtering incoming data as an add-on investigation into astrophysical processes may turn up anomalies that advance high-energy physics even if they never do resolve themselves into a SETI detection.
The paper is Lacki & DiKerby, “Possibilities for SETI at High Energy,” submitted for 2025 NASA DARES [Decadal Astrobiology Research and Exploration Strategy] RFI and available as a preprint.
Are not these phenomena always going to be ambiguous in nature?
Think of our Earth being observed from afar. Would pre-civilizational humans settings grass fires to flush prey be interpreted as either a natural fire or a human artifact. Similarly with slash and burn agriculture. Could a hydrogen bomb used in space be distinguished from a solar flare? Can the slow dimming of a star as a Dyson swarm was constructed be distinguished from a natural phenomenon, such as a dust cloud passing through the line of sight of the star?
While it is true that we cannot know the motivations of ETI, the need to detect some mega-engineering artifact seems associated with our industrial growth period. The Victorian era was redolent with building big, and often futuristic cities and transport systems were depicted in magazines. The developed, post-industrial nations seem generally to have passed this phase, and we see it mainly in developing nations as they exercise their capabilities, whether extremely tall or large structures in the Middle East, or huge engineering projects in the Far East and China.
Maybe we may see it again, perhaps with vast solar power satellites, both beaming power to Earth as well as shading the Earth to mitigate global heating. But notably, the Western nations are not seriously contemplating such ideas anymore, despite decades of ideas and designs. I suspect any such projects will be instigated by China.
Will ancient, mature ET civilizations be interested in such projects, or will they be a passé idea?
Once we looked for signs of G*d or the G*ds in the skies, interpreting extreme weather or astronomical events as such signs. Are we still doing the same with these high-energy astronomical observations? We can rationalize that we are doing science by testing hypotheses of possible ETI presence through massive engineering, particularly as SETI, looking for radio and optical signals, has so far turned up nothing. We had a recent post that was an attempt to hypothesize [quite effectively] an ET power beam rather than a natural phenomenon. Freeman Dyson was well known for suggesting looking for big, obvious signs. Not just his habitat swarms, but also for macrolife, such as fish rather than unicellular organisms, on Europa or in orbit around it.
Today, we don’t think of interstellar beamed sails as vast constructs kilometers in extent, but rather 1 gm sails, perhaps no more than 1 m^2, and a payload of a complex chip and sensors. Even our crewed spaceships on deep space missions have been reduced in size to robotic probes. [Musk’s SpaceX Starship being an aspiration to counter this trend.]
Maybe mature civilizations are long-lived because they do not have such mega-engineering desires, but are more like the pre-West arrival by focusing on the small. If so, then failure to detect RTI does not imply non-existence, but simply a gentler, and certainly non-grabby approach, to living.
“Maybe mature civilizations are long-lived because they do not have such mega-engineering desires…”
That may very well be the case. But those of us determined to detect intelligence in the cosmos tend to be technologically inclined; and technology is the only way we can detect those intelligences because it is the only way they can make their presence known across interstellar distances.
Its just another way of saying we look for our lost keys near the streetlights because that’s the only way we could find them in the dark. Or to put it another way, our prayers to God are guided by the assumption that He exists, and that He is not totally indifferent to our existence.
A successful SETI discovery will justify our suspicion they must be just like us, because we cannot imagine ourselves being any way other than we are.
I’ve been fascinated by the search for extra terrestrial civilizations for as long as I can remember, but I have become much more pessimistic about our chances of actually finding one as I near the end of my life. Am I wiser now, or just older?
Yes.
My education and environment were in relatively secular England. While the state religion, the Church of England, was extant, it was clearly dying. The religious believers were anomalies. This was also happening in Northern Europe.
The US remains an anomaly with believers at rates that of much poorer countries, like Turkey, despite its wealth.
I don’t want to make a connection between religion and that most SETI work seems to be US-based, because other factors are involved, but it could be a contributing factor. It is easy to find articles both supporting and denying that there is some religious strains behind SETI. Movies about alien invasions often seem to have a religious component as a subplot – nakedly in the case of “Contact” (and far more so in the book, although Sagan takes the side of rational science, but keeps the door open at the very end.
Cherry-picking UK science fiction, Fred Hoyle does not invoke any religious ideas in The Black Cloud or the 2 Andromeda novels, Clarke does not ascribe any religious connection to aliens in any of his novels from Childhood’s End through to Rendezvous with Rama, and Nigel Kneale’s various tv series, especially the 4 Quatermass series only has religion in the last and that is to dismiss it as a delusion. The only classic religious sci-fi that comes immediately to mind is Olaf Stapledon’s Star Maker.
It is rational to search for ETI, yet it seems that continued disappointment with success is always excused – too few samples, too short a time. Are bigger radio telescope arrays for SETI, e.g. Allen Telescope Array, our version of building bigger cathedrals? Will we end up building the equivalent of Bob Silverberg’s Tower of Glass?
If humanity ever does get proof of ETI, it would be interesting to observe how different national populations, with different adherence to different religions, interpret the discovery. Sadly, or perhaps gladly, I don’t expect to be around.
An intriguing article discusses technosignatures from the pre-space age found in archived data;
“This is a preprint of a paper now under review. We first tried in 2022, but it was too early for the journals. Years later, with better methods, we gave it another go. The key question has been: are the transients real, or plate defects? Well, there seems to be a clear deficit of transients in the Earth’s shadow. If correct, that demonstrates they’re highly reflective objects with flat surfaces (think mirrors, glass…) — and transients are sunlight glints. And it seems there may be a few more of them than we initially thought.”
https://www.researchgate.net/publication/394040040_Aligned_multiple-transient_events_in_the_First_Palomar_Sky_Survey?
I recall a CD post of this sometime ago. It is an original idea to look at images before we cluttered the sky with satellites and other junk, and now even worse with satellite swarms.
However, photographic plates are just instant snapshots, with either transients or streaks (for moving objects against the stars). What we need is videos of transients to detect tumbling, as well as spectrographic data to help with identification.
Clarke wrote a short story about a transient that an astronaut thought was a dead spacecraft in “Passer-by,” written sometime after 1957.
Is it possible that specular reflection was bright enough for a photographic plate to capture an ISO?
What kind of power would copper coils around a magnetar put out?
“What kind of power would copper coils around a magnetar put out?”
If you have the extraordinary amount of energy it would require to travel to a magnetar and *then* build a gargantuan facility to harvest its energy, you don’t need the magnetar.
Hi, Alex
Photographic plates are the result of time exposures, from several minutes to several hours. Very faint or fast-moving objects may or may not show up. Slower, brighter objects often do. As an astronomy student, I spent many hours staring at plates under a microscope with a blink comparator or measuring engine doing astrometric work and searching for variable stars, etc. Especially near the ecliptic, they were often littered with the oblong images of asteroids creeping across the star fields, like little fuzzy caterpillars. They were so numerous in some areas they were a nuisance! Knowing the telescope, location, length of the exposure, and the time and date it would be possible to determine the brightness, angular motion and direction of these objects to a great accuracy. We just ignored them because we had different research priorities.
The good news is that thousands of these plates exist and are warehoused and thoroughly documented in astronomical institutes. Some were taken to monitor certain objects or areas, others were just “patrol plates” available to anyone who was interested in that particular part of the sky at that particular date and time. Look up the Harvard Patrol Plates, or the French Carte du Ciel project. This sort of routine photography has been going on for over a century, there must be thousands of plates, perhaps millions, in the archives, and most have never been inspected by human eyes. No doubt AI could be trained to look for transients.
There are many gaps in this record, but it does cover areas all over the sky, and many areas have been observed multiple times, sometimes with both blue and red sensitive emulsions. No doubt much of this work is automated and digitized these days, but an enormous amount of data covering most of the 20th century is available, just waiting to be looked at.
If objects have been visiting our solar system from distant reaches of the galaxy we may already have a detailed record of some of them, perhaps in a 100 year old glass plate in a manila envelope stashed away in some observatory basement in eastern Europe. These plates are never thrown away, they are irreplaceable, because ancient data can be compared with modern imagery of the same area to see if anything has changed.. They are an invaluable treasure.
@Henry
If as you say, many/most of these photographic plates have never even been looked at, then they deserve to be digitized and fed to algorithms to exactly match overlapping areas and look for transients and other interesting phenomena.
The examples Henry linked to are all pre-1957, so there is not a single satellite or piece of rocket hardware to contaminate the image with false positives. However, when zooming into the images, some became very granular, like looking at popcorn, so I assume that is the individual grains. The rings of Saturn looked like those in the movie Pilot Pirx’s inquest as the spaceship navigated the rings that looked like a wall of ragged foam blocks.
It is certainly a treasure to mine and see if anything interesting turns up.
I think I read that the plates from some of these [smallish] telescopes could detect 11th-magnitude stars. How do they compare with pre-space age plates from the 200-inch Hale telescope? Can you put that in context in terms of objects in the solar system?
@Alex
Just because a scope is newer, or bigger doesn’t necessarily mean its better. It depends on what it is designed for. The resolution of an image depends LINEARLY on the size of the objective lens, but how faint an object it can see is a function of the area, that is, the SQUARE of the aperture. In addition, image sharpness also depends on how accurately the lens or mirror is figured.
The big modern reflectors can see extremely faint objects because they are “light buckets”, designed primarily for spectroscopy or photographing faint extended nebulae. They often have poorly figured mirrors because of cost. By the end of the 19th century, smaller refractors were already being designed as “diffraction-limited”, that is, the images were as sharp as the laws of optics allowed for their aperture. In addition, the size of the plate and the grain size of the emulsion had to be considered.
A century ago, one of the leading applications was astrometry, where sharp photography which could be examined under a microscope and geometric uniformity throughout the plate were essential. On the other hand, the big American reflectors had notoriously blurred imagery (the Hale 200 inch was notorious for this), but they worked just fine at doing spectroscopy on faint objects, which is what they were designed for. Reflectors also have other problems, like the diffraction spikes on point source imagery caused by the supports for secondary mirrors suspended in the light path. But then again, Palomar could go as deep as 21st magnitude!
It is possible to have deep AND sharp images but that means highly accurate parabolas on big objectives, and that gets expensive. Mirror and lens grinding costs go up as the CUBE of the aperture.
There are other issues, as well. A “slow” focal ratio (aperture/focal length) or “speed” of a lens or mirror makes it easier and cheaper to grind an objective accurately which is why old refractors have long skinny tubes and modern reflectors are short and stubby. Of course, long and skinny means the addition of supports and braces to prevent bending. The thickness of a lens, and the number of components (to cancel out color distortion) means the NUMBER of surfaces which have to be precision-ground goes up. That is not a problem with a reflector.
The worlds largest refractor is the 40 inch at Yerkes Observatory.
All these factors interact, as well as the clarity of the atmosphere, in complex ways, so telescopes are usually designed for specific applications. But there is always pressure to make an expensive telescope so it is suitable for multiple applications, which is of course a contradiction. Like firearms, race cars and sailboats, the final product is usually an engineering compromise. And if you want to make it light and robust enough to work in a spacecraft, the problem quickly becomes more complicated, and much, much more expensive.
I’m afraid I’m not knowledgeable enough on this topic to give you more quantitative information for the application you describe.
@Henry,
Let me ask a slightly different question. Is the emulsion on a photographic plate the limitation on useful resolution, or is it the telescope itself? Now I appreciate this could be a “depends on the telescope” design, but are the Hale or Yerkes telescopes pushing the capability of the plate, or are the telescope optics the limit, with more resolution capability than the plate?
We have all probably been alive long enough to see that even with a high-end smartphone camera that the resolution is now on a par with 35mm film (and better than with the smaller film sizes of pocket film cameras). Professional digital cameras must have excellent image quality. A remarkable technical feat. Massive digital arrays on telescopes must be a good as traditional photographic plates, before noise and “graininess” in either system become problematic. Software processing of digital images can also clean them up, removing defects, as well as other tricks.
As for film vs digital imaging from space, I always remember the movie “Ice Station Zebra” where the US and USSR teams were fighting to retrieve a film capsule dropped into the Arctic from a spy satellite. So 1960s. So quaint.
At the focal plane, the emulsion grains were much smaller than the resolution limit of the telescope, so your answer is the optical system is the limiting factor. But other factors come into play, such as small tracking errors in the clock drives that compensated for earth rotation.
During a time exposure, the star is scintillating (twinkling) due to the atmosphere, so the image is blurred. The image does a sort of Brownian motion dance on the plate (or your retina). This occurs to some extent even during nights of excellent “seeing”. Normally you don’t notice this because the effect is only apparent under magnification (you are looking at the plate through a microscope). If you are using the telescope visually, you can often see the image moving around and pulsating due to turbulence in the atmosphere. The atmosphere degrades the image resolution much more than the optics or the emulsion size. This is why observatories are built on mountain tops in areas where the “seeing” is better, or out in space (if possible!). “Seeing” is the limiting factor. On a good night, if you look at a bright object like the moon through an amateur scope you can see this, it looks like you are looking through water.
When I was using a plate measuring engine microscope the grain size was about a micron and the stellar images looked like globular clusters–big blobs of black dots (the plates were negatives). The idea was to measure each star in the crosshairs several times and later the measurements were averaged by the computer. Each single measurement was accomplished by placing the crosshairs in the center of the blob, pressing a foot pedal, and the x and y would be punched into an IBM card. Then you would back off and measure again. With the brighter stars, the blobs would be so big it was very difficult to find the center. But that was back in the 1970s, nowadays, the process is automated by electronic scanners (flying spot digitizers). These were experimental and under development back then, but I understand they have replaced the graduate student slave labor. I doubt plates are still used at all, its all digital detectors now. But the old plates we’re talking about can still be compared with new data if you can properly model all these effects in your software.
The latest technology involves shining a laser into the atmosphere and having detectors monitor the scintillation of the laser dot in the sky, and using adaptive optics (actually distorting the mirror shape mechanically) to partially compensate for the atmospheric turbulence.
Designing a telescope to maximize the resolution of extrasolar visitor images so it approached the physical limits imposed by optics would probably require some pretty sophisticated engineering.
>or the French Carte du Ciel project.
Here is one of these maps preserved at the Paris Observatory
At the bottom of the sheet is written:
“map comprising 2,340 stars; reproduction of a 3-exposure photograph taken on January 23, 1903, at 8:42 a.m. TM (=Meridian Time?) in Paris.”
https://bibnum.obspm.fr/ark:/11287/Zz8x3#?c=&m=&s=&cv=&xywh=-334%2C-78%2C2552%2C2337
the project :
https://en.wikipedia.org/wiki/Carte_du_Ciel
and a lot of plate here :
https://public.aip.de/historical-sky/en/
The Carte du Ciel offers some important lessons on how scientific hubris and ill-founded ambition can have unexpected consequences, even disastrous ones.
About a century ago, French astronomers realized how important a systematic mapping of the entire sky, using the best technology available at the time and the vast resources of the French astronomical establishment, could be. But the project was overly ambitious and expensive, and promised to be quickly eclipsed by other astrophysical technologies being developed, and it consumed the technical, financial and administrative resources of the astronomical community for decades. Observatories all over the world were enlisted to help while France assumed leadership of the effort.
The project was never completed. A great deal of useful data was collected and catalogued, but a comprehensive and consistent photographic database of the entire sky was never assembled. Other, less elaborate, efforts taking advantage of new technology soon replaced it, and the project died a natural death long before it was finished. Efforts like the Palomar Observatory Sky Survey (POSS) proved much more useful in meeting the needs of the fast-developing astrophysical community, and were also modifiable and expandable and able to take advantage of new technologies coming available.
Unfortunately, French astronomy never fully recovered from the hemorrhage of resources and talent initiated by the CdC, and that nation’s leadership in the science was surrendered to the astrophysical requirements better served by the big American reflectors such as the Hooker 100″ and the Hale 200″ with their vastly superior spectroscopical capabilities. The ultra precision uranography delivered by the French photographic project was simply not as useful to modern science as the ability to go another 10 or so magnitudes deeper with the wide field 60″ Schmidt camera at Palomar. That is the technology that eventually took over, and the French astronomical community never fully recovered.
Much good data was collected by CdC, and it is still being utilized in several lines of research such as the one we are discussing here. But the original promise of this project was never fully realized.
https://en.wikipedia.org/wiki/Carte_du_Ciel
a few more astro observation plates from the late 19th century :
https://bibnum.obspm.fr/ark:/11287/7q7z4
Zooming in on these old picture (which are of high quality because the lens glass was pure and the night was certainly darker than it is today) gives a kind of vertigo.
It also raises the question of what the technology used tells us and, above all, how we interpret what we see :
https://bibnum.obspm.fr/ark:/11287/spBGq#?c=&m=&s=&cv=&xywh=-1031%2C0%2C6158%2C5335
Reflections: so there’s Clarke’s The Sentinel, but I’m trying to remember the author and title of a short story where an astronaut on the moon takes a hike up a distant hill toward a sparkly object. He discovers it’s artificial and covered in eye pieces or apertures of which some work for human senses.
Dang this senior moment, but In a search for the story I ran across this 2016 CD post!
https://www.centauri-dreams.org/2016/12/05/thought-experiment-the-asteroid-belt-astronomical-telescope/
Three things about the linked item below…
One. A species that isn’t even a Kardashev Type 1 society yet and has barely left its home planet is trying to figure out how civilizations that can build megastructures around stars or do this for an entire galaxy operate.
Two. If they can build such things, they will have figured out the bugs long before as well.
Three. Just because current humans have trouble dealing with such vast concepts doesn’t mean other minds who have a much wider and longer appreciation for the real scale of the cosmic do as well.
https://www.msn.com/en-us/news/technology/humans-may-only-have-41000-years-to-catch-signs-of-aliens-before-they-fade/ar-AA1JAeX5?ocid=BingNewsVerp
One more thing about Dyson Shells/Swarms/Spheres: Just because Freeman Dyson envisioned them originally as dwelling places for humanoid species does not mean that is their only possible function.
As usual, Orion’s Arm shows many other possibilities for Dyson Swarms that are slowly catching on with contemporary science:
https://www.orionsarm.com/eg-article/4845fbe091a18
I also thank Robert Bradbury for expanding my thinking on the concept in the 1990s:
https://en.wikipedia.org/wiki/Matrioshka_brain
Or we are like termites that think alien ETI termites would build termite columns to space.
If they can build such things, they will have figured out the bugs long before as well.
Maybe. A species that built a Dyson swarm, which subsequently went extinct, may not be able to create a system that is eternal and able to avoid all random hits. To avoid comets and ISOs, the swarm would have to remain active and able to dodge any such body for millions or billions of years. I’m not saying that Lacki is right, just that it may be a big assumption ETI can eliminate eventual disasters, even when teh star expands.
It depends on what you mean by “dealing with”. Science fiction seems to have no trouble with cosmic concepts. But my comment on your first point also applies. Why should ETI do things that we pre-Kardashev I species think is a grand idea? We are trapped in our culture, which thinks of industrial civilization expansion. Building physical structures on ever grander scale. Triumphantly shouting to the planet (and cosmos) – “Behold my works, and stand in awe!”.
This paper on high energy SETI and the last CD blog post “SETI at the Extremes” made me recall this paper from 1992 by Guillermo A. Lemarchand:
http://www.coseti.org/lemarch1.htm
I know every generation needs a refresher but let us not keep reinventing the wheel as well. I am also aware that SETI is only recently and finally getting out of the “radio messages sent by altruistic aliens from their home planet” paradigm. After all, it took over thirty years for the SETI mainstream to accept Optical SETI and for reasons that had little to do with the technologies involved.
From the Wipedia entry: Matrioska Brain:
I highly recommend this anime. It is very imaginative and exceeds the ideas of most sci-fi authors on the subject.
As for building one, or as Stross’s Accelerando works through a future of turning all mass into computronium, our wild-eyed LLM hyper-scalers seem to be intent on starting the process. Meta’s “Zuck” is proposing a computational facility, to train and serve LLMs, the size of Manhattan! (And you can bet he will not be powering it with wind turbines anytime soon.)
>advanced aliens might exploit high-energy sources whether or not they had evolved on them.
I find that this sentence in the text encourages us to think about energy: ultimately, what purpose does it serve in the universe? Why would an ETI want to appropriate it? Why this source of energy and not another? How would it do so? Overall, energy is used to modify one’s environment, so perhaps by looking at the problem from the opposite angle, we can deduce some things?
To what extent does a civilization (terrestrial or otherwise) need energy? If it is self-sufficient, perhaps we will never detect it. Could it be that a change in energy levels is the clue to “their” presence? Just an idea…
To riff on Ellie Arroway from Contact, “If there is no one to use the energy available from stars, that seems like an awful waste of energy”.
From a biology POV, life uses all the available energy it can and converts into into living organisms, which make up ecosystems, and a biosphere. Energy is converted to information that begets more information as life evolves. Humans are now a minuscule part of the universe that allows the universe to view and understand itself. I believe that is a very positive view of using energy, even if it has been only biology doing this for the past 4+bny years until a few millennia ago.
If humanity could harvest the solar output to convert its radiation to information, I would welcome this. There are dangers, of course, but increasing life is a worthwhile goal.
Consider sterile, lifeless worlds. Is it better to leave them sterile or to clothe them in life to evolve new organisms?
Suppose the most energetic sources are inimical to life. Then intelligence to harness technology to allow life to take hold seems worthwhile.
Where I part company with those who want to harness energy purely to create an expansion of an intelligent, technology-using species is that there seems little point in doing this with the sorts of technology we use. Our technology is brittle and is used primarily to benefit humans, and the biosphere be damned. Somewhere, our ape-brains were led astray, thinking of short-term benefits and personal aggrandizement. Yes, we do build some fabulous technological artifacts, but our mega-engineering projects seem only to increase the human benefits of the economy. If only what we did included our natural world as stakeholders.
Having said that, I don’t want our entire galaxy to become a garden, perhaps filled only with technological artifacts or manicured gardens. In that regard, I can empathize with Ann Clayborne’s Red Mars faction in KSM’s Martian trilogy, even as I was mostly sympathetic to the scientists and technologists represented by “Sax” Russell, who were terraforming Mars. At least in this fictional case, there was a compromise, leaving the high-altitude locations untouched and maintaining a lower-than-Earth atmospheric pressure.
I dislike Asimov’s Trantor, and Star Wars’ Coruscant, both planet-spanning cities, as impressive, but overwhelming, as Ancient Rome.
For humans, at least, it appears we need to be connected to Earth. Whether we can truly survive long-term off-planet is to be determined. I suspect we will either need to bring along the species to maintain our microbiomes, or we will need to be engineered to do without them. Our equivalent to Asimov’s Spacers will not be sterilized humans, but more probably humans with nanobots and other enhancements to maintain our bodies in alien environments.
All things in moderation. Harvest the energy of some stars, but not all of them, for increasing our technological capabilities, but balance this by “greening” sterile worlds to create new “wilderness” for the future. Keep increasing the information content of the galaxy (and the universe), as a legacy for the future.
As for longevity of life, I think starlifting to reduce the energy emitted by stars to extend their lives may well be worthwhile. Certainly do this for the large, hot stars, to prevent them from all quickly burning out, but leave enough to ensure the debris of supernovae is continued to be produced.
Now if ETI have airports (and spaceports) too…
https://astrobiology.com/2025/07/how-airports-could-help-aliens-spot-earth.html
How Airports Could Help Aliens Spot Earth
By Keith Cowing
Press Release
Royal Astronomical Society
July 9, 2025
The average total power of individual airport radar systems, averaged over one-hour intervals as seen from Barnard’s Star. — Royal Astronomical Society
Radar systems used by civilian airports and military operations are inadvertently revealing our existence to potential advanced alien civilisations, new research shows.
The study explored how hidden electromagnetic leakage might look to extraterrestrials up to 200 light-years from Earth, if they had state-of-the-art radio telescopes like our own. Theoretically, it also suggests this is how far we would be able to look to spot aliens who have evolved to use a similar level of technology.
Preliminary results revealed at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham show how worldwide aviation hubs such as Heathrow, Gatwick and New York’s JFK International Airport give off clues to our existence.
By carefully simulating how these radar signals spread out from Earth over time and space, the researchers looked at how visible they would be from nearby stars such as Barnard’s Star and AU Microscopii.
In the upper panel, the animation shows the average total power of individual airport radar systems, averaged over one-hour intervals. The lower panel reveals the total power of airport radar leakage radiation as a function of time, plotted over a 24-hour period in the direction of Barnard’s Star. — Royal Astronomical Society
This animation reveals the same average total power of individual airport radar systems and total power of airport radar leakage radiation as would be seen from AU Microscopii. — Royal Astronomical Society
They found that airport radar systems, which sweep the skies for airplanes, send out a combined radio signal of 2×1015 watts, enough to be picked up as far as 200 light-years away by telescopes comparable to the Green Bank Telescope in West Virginia.
To put that distance into context, the nearest potentially habitable world beyond our solar system is Proxima Centauri b, which is 4 light-years away. That would still take a spacecraft using current technology thousands of years to get there.
Military radar systems, which are more focused and directional, create a unique pattern – like a lighthouse beam sweeping the sky – have an accumulated peak emission reaching about 1×1014 watts in a given field-of-view of the observer.
Radar systems used by civilian airports (like this at Heathrow) and military operations are inadvertently revealing our existence to potential advanced alien civilisations because of the hidden electromagnetic leakage they emit. Mick Lobb / Radar scanner – Heathrow / CC BY-SA 2.0 Licence type Attribution (CC BY 2.0)
This, lead researcher Ramiro Caisse Saide at the University of Manchester said, would look “clearly artificial to anyone watching from interstellar distances with powerful radio telescopes”.
“In fact, these military signals can appear up to a hundred times stronger from certain points in space, depending on where an observer is located,” the PhD student added.
“Our findings suggest that radar signals – produced unintentionally by any planet with advanced technology and complex aviation system – could act as a universal sign of intelligent life.”
He said the research not only helps guide the search for extraterrestrial civilisations by identifying promising technosignatures, but also deepens our understanding of how human technology may be seen from space.
“By learning how our signals travel through space, we gain valuable insights into how to protect the radio spectrum for communications and design future radar systems,” said co-researcher Professor Michael Garrett, of the University of Manchester.
“The methods developed for modelling and detecting these weak signals can also be used in astronomy, planetary defence, and even in monitoring the impact of human technology on our space environment.”
Caisse Saide, a PhD student, added: “In this way, our work supports both the scientific quest to answer the question ‘Are we alone?’ and practical efforts to manage the influence of technology on our world and beyond.”
Astrobiology, Astronomy, SETI, Technosignature, CETI.
We are a noisy species. We also have had biosignatures on Earth going back perhaps four billion years. We have been crying into the presumed wilderness in virtually every direction for a long time now.