I’m catching up with a lot of papers in my backlog, prompted by a rereading yesterday of David Kipping’s 2022 paper on the Wow! Signal, the intriguing, one-off reception at the Big Ear radio telescope in Ohio back in 1977 (Kipping citation below). I had just finished checking Abel Mendez’ work at Arecibo, where the Arecibo Wow! project has announced a new analysis based on study of previously unpublished observations using updated signal analysis techniques. No huge surprises here, but both Kipping’s work and Arecibo Wow! are evidence of our continuing fascination with what Kipping calls “the most compelling candidate for an alien radio transmission we have ever received.”
They also remind us that no matter how many times this intriguing event has been looked at, there are still new ways to approach it. I give the citation for the Mendez paper, written with a team of collaborators (one of whom is Kipping) below. Let me just pull this from Mendez’ statement on the Arecibo Wow! site, showing how the new work has refined the original Wow! Signal’s properties:
Location: Two adjacent sky fields, centered at right ascensions 19h 25m 02s ± 3s or 19h 27m 55s ± 3s, and declination –26° 57′ ± 20′ (J2000). This is both more precise and slightly shifted from earlier estimates.
Intensity: A peak flux density exceeding 250 Janskys, more than four times higher than the commonly cited value.
Frequency: 1420.726 MHz, placing it firmly in the hydrogen line but with a greater radial velocity than previously assumed.
Leading Mendez (University of Puerto Rico at Arecibo) to comment:
“Our results don’t solve the mystery of the Wow! Signal. “But they give us the clearest picture yet of what it was and where it came from. This new precision allows us to target future observations more effectively than ever before…. This study doesn’t close the case,” Méndez said. “It reopens it, but now with a much sharper map in hand.”
Image: Comparison of the previously estimated locations of the Wow! Signal (gray boxes) with the refined positions from the Arecibo Wow! Project (yellow boxes). The signal’s source is presumed to lie within one of these boxes and beyond the foreground Galactic hydrogen clouds shown in bright red. Credit: PHL @ UPR Arecibo.
Homing in on interesting anomalies is of course one way for SETI to proceed, although the host of later one-off detections from other locations (none evidently as powerful a signal as Wow!) doesn’t yield optimism that one of these will eventually repeat. A sweeping beam that by sheer chance swept across Earth from some kind of ETI installation? Works for me, if only we had repeating evidence. In the absence of it, we continue to dig into existing data using new techniques.
We can also proceed with targeted searches of nearby stars of interest both because of their proximity as well as the presence of unusual planetary configurations. The TRAPPIST-1 system isn’t remotely like ours, with its seven Earth-sized planets crammed into tight orbit around an M8V red dwarf star, but the fact that each of these transits makes the system of huge value. Now a team led by Guang-Yuan Song (Dezhou University, China) has used the FAST instrument (Five hundred meter Aperture Spherical Telescope) to search for SETI signals, delving into the frequency range 1.05–1.45GHz with a spectral resolution of ~7.5Hz. No signals detected, but the scientists plan to continue to search other nearby systems and do not rule out a return to this one. Citation below.
The Factors Leading to Technology
The frustration over lack of success at finding an extraterrestrial civilization is understandable, so it’s no surprise that theoretical work explaining it from an entirely opposite direction continues to appear. As witness a new study just presented at the EPSC-DPS Joint Meeting 2025 in Helsinki. Here we’re asking what factors go into making a technological society possible, assuming an evolutionary history something like our own, and probing whether changes to any of the parameters that helped us emerge would have made us impossible.
All this goes back to the 1960s and the original Drake Equation, which makes a loose attempt at sizing up the possibilities. Manuel Scherf and Helmut Lammer of the Space Research Institute at the Austrian Academy of Sciences in Graz paint a distressing picture for those intent on plucking a signal from ETI out of the ether. Their work has focused on plate tectonics and its relationship with the critical gas carbon dioxide, which governs the carbon-silicate cycle.
CO2 is a huge factor in sustaining photosynthesis, but too much of it creates greenhouse effects that can likewise spell the end of life on a planet like ours. The fine-tuning that goes on through the carbon-silicate cycle ensures that CO2 gets released back into the atmosphere through plate tectonics and volcanic emissions, recycling it back out of the rock in which it had been previously locked. Scherf pointed out to the EPSC-DPS gathering that if we wait somewhere between 200 million and one billion years, loss of atmospheric CO2 will bring an end to photosynthesis. The Sun may have another five billion years of life ahead, but the environment that sustains us won’t last nearly as long.
Indeed, the researchers argue, surface partial pressures and mixing ratios of CO2, O2, and N2 likewise affect such things as combustion, needed for the smelting of metals that underpins the growth of a technological civilization. Imagine a planet with 10 percent of its atmosphere taken up by CO2 (as opposed to the 0.042 percent now found on Earth). This world produces a biosphere that can sustain itself against a runaway greenhouse if further away from its star than we are from the Sun, but it would also require no less than 18 percent oxygen (Earth now has 21 percent) to ensure that combustion can occur.
If we do away with plate tectonics, so critical to the carbon-silicate cycle, we likewise limit habitable conditions at the surface. So we need this as well as enough oxygen to provide combustion to make technology possible. In other words, we have astrophysical, geophysical, and biochemical criteria that have to be met even when a planet is in the habitable zone if we are hoping to find lifeforms that have survived long enough to create technology. Rare Earth?
Scherf and Lammer weigh these factors against the amount of time it takes technology to emerge, assuming that the longer an ETI civilization exists, the more likely we are to observe it. Here I don’t have a paper to work with, so I can only report the conclusions presented at the EPSC-DPS conference, which are stated bluntly by Scherf:
“For 10 civilizations to exist at the same time as ours, the average lifetime must be above 10 million years. The numbers of ETIs are pretty low and depend strongly upon the lifetime of a civilization.”
I can also fall back on a 2024 paper from the same team discussing these matters, which delves not only into the question of the perhaps rare combination of circumstances which allows for technological civilizations to emerge but also our use of the Copernican Principle in framing the issues:
…our study is agnostic about life originating on hypothetical habitats other than EHs. Any more exotic habitats (e.g., subsurface ocean worlds) could significantly outnumber planets with Earthlike atmospheres, at least in principle. Finally, we argue that the Copernican Principle of Mediocrity cannot be valid in the sense of the Earth and consequently complex life being common in the Galaxy. Certain requirements must be met to allow for the existence of EHs and only a small fraction of planets indeed meet such criteria. It is therefore unscientific to deduce complex aerobic life to be common in the Universe, at least based on the Copernican Principle. Instead, we argue, at maximum, for a combined Anthropic-Copernican Principle stating that life as we know it may be common, as long as certain criteria are met to allow for its existence. Extremophiles, anaerobic and simple aerobic lifeforms, however, could be more common.
Image: An artist’s impression of our Milky Way Galaxy, showing the location of the Sun. Our Solar System is about 27,000 light years from the centre of the galaxy. The nearest technological species could be 33,000 light years away. Credit: NASA/JPL–Caltech/R. Hurt (SSC–Caltech).
All of which illuminates the paucity of data. We could say that it took four and a half billion years for technology to emerge on Earth, but that is our only reference point. We also have no data on how long technological societies exist. It is clear, though, that the longer the survival period, the more likely we are to be present in the cosmos at the same time they are. For there to be even one technological civilization in the galaxy coinciding with our existence, ETI would have to have survived in a technological phase for at least 280,000 years. I think that matches up with the case Brian Lacki has been making for some time now, which emphasizes the ‘windows’ of time within which we view the cosmos.
But Scherf adds this:
“Although ETIs might be rare there is only one way to really find out and that is by searching for it. If these searches find nothing, it makes our theory more likely, and if SETI does find something, then it will be one of the biggest scientific breakthroughs ever achieved as we would know that we are not alone in the Universe.”
Image: This graph shows the maximum number of ETIs presently existing in the Milky Way. The solid orange line describes the scenario of planets with nitrogen–oxygen atmospheres with 10 per cent carbon dioxide. In this case the average lifetime of a civilization must be at least 280,000 years for a second civilization to exist in the Milky Way. Changing the amount of atmospheric carbon dioxide produces different results. Credit: Manuel Scherf and Helmut Lammer.
I’ll note in passing that Adam Frank (Rochester Institute of Technology) and Amedeo Balbi (University of Rome Tor Vergata) have analyzed the question of an ‘oxygen bottleneck’ for the emergence of technology in a recent paper in Nature Astronomy. The memorable thought that if there are no other civilizations in the galaxy, it’s a tremendous waste of space sounds reasonable only if we have fully worked out how likely any planet is to be habitable. This new direction of astrobiological research tells me we have a long way to go.
The Mendez paper is Mendez et al., “Arecibo Wow! II: Revised Properties of the Wow! Signal from Archival Ohio SETI Data,” currently available as a preprint but submitted to The Astrophysical Journal. The Kipping paper from 2022 is Kipping & Gray, “Could the ‘Wow’ signal have originated from a stochastic repeating beacon?” Monthly Notices of the Royal Astronomical Society, Volume 515, Issue 1 (September 2022), pp.1122-1129 (full text). Thanks to my friend Antonio Tavani for the heads-up on the Mendez paper. The paper on the FAST search of TRAPPIST-1 is Guang-Yuan Song et al., “A Deep SETI Search for Technosignatures in the TRAPPIST-1 System with FAST,” submitted to The Astrophysical Journal and available as a preprint.
The Scherf and Lammer presentation is titled “How common are biological ETIs in the Galaxy?” EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-1512. The abstract is available here. The same team’s 2024 paper on these matters is “Scherf et al. “Eta-Earth Revisited II: Deriving a Maximum Number of Earth-Like Habitats in the Galactic Disk,” Astrobiology 24 (2023), e916 (full text). The paper from Adam Frank is Frank & Balbi, “The oxygen bottleneck for technospheres,” Nature Astronomy 8 (2024), pp. 39–43 (abstract / preprint).
And I want to be sure to mention Robert Gray, Kipping’s co-author on his 2022 paper, who devoted years to the study of the Wow! Signal and was kind enough to write about his quest in these pages. If you’re not familiar with Gray’s work, I hope you’ll read my An Appreciation of SETI’s Robert Gray (1948-2021). I only wish I had gotten to know him better. His death was a loss to the entire community. David Kipping’s fine video covering his work with Gray is available at Cool Worlds. Keith Cooper also explicates this paper in One Man’s Quest to Investigate the Mysterious “Wow!” Signal.
(Hi, Paul. Hope you are well!)
The conclusion of Lammer, Scherf and Sproß seems reasonable. The required extreme longevity of ETI is often taken by optimists as a given. Sometimes under the assumption that advanced civilizations will know how to prevent their own demise. Sometimes under the naive(and oft repeated) thesis that a migration to the stars will somehow prevent or massively delay the demise of the ETI.
It’s easy to plug in generous values for each parameter and imagine a galaxy buzzing with ETIs. But as soon as you apply realistic constraints like the rarity of Earth like atmospheres in the sense the authors define, or the fragility of technological civilizations, the product of probabilities collapses fast.
The single biggest determinant of how many coexisting ETIs exist isn’t how many habitable planets there are, but how long civilizations last. If the average longevity is short (thousands of years), the galaxy could have hosted miriad civilizations that never overlap with us. If longevity is long (hundreds of thousands to millions of years), then overlap becomes plausible, but the extreme longevity requires a number of dubious explanations to achieve.
The SETI community often leans toward optimism ala “absence of evidence isn’t evidence of absence”. But that only works up to a point. Papers like Lammer’s are important because they remind us that the numbers are not actually our friends when the calculations are made with less wishful values.
Common counterarguments attempting to extend the ETI longevity window often invoke interstellar migration and or a transition to a post-biological existence.
But Fermi’s paradox cuts deeper especially if longevity and migration are common.
If advanced civilizations can last for hundreds of thousands to millions of years, or migrate, or build machine colonies, then we should expect a galaxy full of detectable signatures. Transmissions, engineering projects, artifacts. Thus far(grasp the straw!), nothing. Detection methods will improve, then you’ll see, we are told. Yet, the fact remains, so far, we do not. The fact that we see nothing makes one of two possibilities more likely. Those trajectories (post-biological, star-faring) are either much less likely than we imagine or civilizations that achieve them all deliberately avoid detectable activity.
And this loops back to the point of wishful thinking. While the public and parts of the research community often lean toward hopeful extrapolation, the empirical silence plus the hard numbers in this paper suggest less fanciful grounds for that silence. As sobering and unpalatable as it may seem, the Galaxy is probably* empty of co-existing technological civilizations right now.
The irony is sharp. If civilizations are fragile and short-lived, the numbers explain the silence. There is no “overlap”. If civilizations are long-lived and expansionist, the silence is inexplicable(or only explicable with very presumptuous assumptions about ETI mentalities).
The conclusion is both depressing and liberating. Depressing because the hope of “neighbors” fades. Liberating because it divests the mind of what amounts to a collection of wishful assumptions – ones that seem more aligned to science fiction tropes ala Star Trek. I would love to be proven wrong. But in the absence of evidence, I won’t invoke any pseudo-scientific analogs to a magic wand.
Excellent points, well made, summarizing some very widely held conclusions.
And I would fail any attempt to argue the point, were it not for one, single, fact: that the Universe is so colossally large that the tiniest of odds become altogether probable. And the flip side of this point: Distances, like numbers, are colossal as well, leading me to nearly conclude a heartbreaking fact: yes, they are out there; and no, we shall never meet them.
Optimists and pessimists both use the same generalized requirements for space faring intelligence; given time, a SFI will fully explore the requirements for all possible body plans and modes of living. This final state for SFI is independent of the planetary requirements for SFI to emerge. Any number of hard-steps will produce the same outcome. Applying Occam’s razor to the number of hard-steps is straight forward, “n-1” hard-steps are fewer than “n”. It is much harder and perhaps in coherent to apply Occam’s razor to body plans and modes of living. In the history of evolution on Earth and humanity we see a tendency towards more complex body plans and modes of living. The assumption that we share a Fermi question volume with a SFI with body plan and mode of living outside our extremely limited field of view is justified and arguably simpler than the assumption that the planetary requirements are too numerous. The rare Earth hypothesis may be true, but is unarguably built on an anti-Occam’s razor philosophy.
The prediction that we must see super structures or more precisely, the generalized dependence of SFI on an infrastructure commons, requires some hard to accept assumptions. The set of all possible body plans and modes of living does not include traits that allow SFI to be independent from the hive or that hive life is the intrinsic demand for SFI.
If the Scherf et al paper is correct, then habitable, Earth-like worlds are very rare. This suggests that searching for biosignatures will result in almost entirely null detection cases.
Even worse, SETI may never receive a radio/optical message. The last image in teh post suggests that for just 2 civilizations in the galaxy, us and one ETI, technological, communicating civilizations have to be extant for at least 10,000 years, almost as long as there have been civilizations on Earth, and that is the optimistic case.
If technological artifacts last considerably longer, much like the Egyptian pyramids lasted much longer than the dominant Egyptian civilization, then perhaps we should look for technosignatures rather than hoping for a message or transient energy beam.
We know that early civilizations (i.e., humans living in cities and no longer nomadic) existed about 10 millennia ago. Human cultures are perhaps 10x longer, based on rock carvings and paintings. This makes our Industrial Revolution technological civilization almost an eyeblink in comparison. Clearly, if we could detect intelligent species or civilizations that were pre-modern technological, then the window opens up from centuries to millennia. Our civilization, even at our current level of technology and population, will exhaust fossil carbon fuels fairly quickly, no more than a few centuries at best. Had we only maintained small, localized civilizations, we might even have only needed renewable forests as fuels, allowing these civilizations far longer to exist. How much development these small civilizations can manage is debatable, but clearly, progress was very slow and incremental until our industrial age.
If our civilization is going to have a long future, then we will have to successfully transition to space-based solar energy as our primary, long-term energy source if we continue to expand our economy and spatial distribution. This would seem to be the case for other similar civilizations, whether they send messages or not. Can we detect them? But note that the Scherf analysis suggests that our galaxy might only have one other extant civilization if such civilizations survive for 100,000,000 years! (When dinosaurs ruled the Earth.) For biosignatures, these may only exist for 1 in 10,000 or 100,000 worlds. If so, we will really need to be able to narrow down our search. Would any of the current techniques be able to manage this on a reasonably economic basis, or will we need to be able to do this by “casting a net” on patches of the sky to survey thousands of stars simultaneously, much like Kepler did for transiting planets, and Gaia for astrometry?
If communicating civilizations are extremely rare, it does suggest that the Wow! signal and other transients were probably not signals or power beams, and that either RFI or natural phenomena were the cause.
In my more cynical moments, I think of these transients as being interpreted at ETI as similar to seeing rare phenomena as signs of the supernatural, something that seems almost baked into humanity’s cognition. (And Avi Loeb is “Asking questions” about whether 3I/ATLAS also could be an alien spaceship. Is this really science?)
A counterargument to my suggestion that transients are unlikely to be signs of ETI based on the Scherf analysis of life and civilizations is to turn the Fermi Question on its head. If the transients are signs of ETI, then this implies that ETI is far more common than we suppose. Maybe there were very few civilizations, but at least one spread through the galaxy, populating the stars, extending the extant number of civilizations by uncoupling the L term from the Drake equation that assumes civilizations are bound to their home world or system. This assumes that interstellar travel by any means to seed star systems with “new life and new civilizations” is both possible and has been done.
This seems analogous to sci-fi stories where an STL ship arrives at its destination star, only to find an Earth civilization that arrived on a faster ship welcoming the travelers. We may be like those STL crews, assuming the galaxy is almost empty of ETI, only to find that ETI[s] have already spread throughout the galaxy before us. Hopefully, they are friendly, and we have passed the test to join their Federation.
Perhaps we should abandon the “Dark Forest” meme entirely and go with “Empty Desert”.
David Kipping has made 2 “Cool Worlds” YouTube videos on the Dark Forest in the last 3 months. He doesn’t buy the idea either, mainly because ETI would know about us without our attempting to signal them using telescopes, as we are doing.
I would go further and suggest that if ETI were out there, not only would they know the Earth is living, but they may have left probes in our system to monitor the Earth. Those probes may have AIs to respond to us at some time, as proxies to eliminate the latency of lightspeed communication, or have FTL communication technology we know nothing about.
But the simplest explanation seems to be that extant ETI is very rare in the galaxy, and maybe we are alone. There may be other ETI civilizations in all the billions of galaxies in the observable universe, but we are all so far apart that without FTL communication, there is no point in sending signals.
The unreasonable likelihood of being.
Origin of life, terraforming, and AI.
Abstract
The origin of life on Earth via the spontaneous emergence of a protocell prior to Darwinian evolution remains a fundamental open question in physics and chemistry. Here, we develop a conceptual framework based on information theory and algorithmic complexity. Using estimates grounded in modern computational models, we evaluate the difficulty of assembling structured biological information under plausible prebiotic conditions. Our results highlight the formidable entropic and informational barriers to forming a viable protocell within the available window of Earth’s early history. While the idea of Earth being terraformed by advanced extraterrestrials might violate Occam’s razor from within mainstream science, directed panspermia—originally proposed by Francis Crick and Leslie Orgel—remains a speculative but logically open alternative. Ultimately, uncovering physical principles for life’s spontaneous emergence remains a grand challenge for biological physics.
https://arxiv.org/pdf/2507.18545
I find it hard to believe that a civilization could exist on a planet with a moon that is 400 times smaller than its sun and 400 times farther away, just to create total solar eclipses. Additionally, this moon is the largest in relation to its planet compared to other nearby celestial bodies.
The chances of such a scenario occurring seem incredibly slim—one in a billion, or even one in a trillion.
What we should focus on instead is how many planets might have been terraformed to support intelligent life. In a million years, we might use AI to seed the galaxy and create life on these worlds. We could then return to these planets when there is intelligent life capable of communication.
The game is closer to what 2001: A Space Odyssey was implying. So, how many nearby planets have already been cooked to perfection???
What one might also ask are:
1. Are the “cooked” planets bearing life with the same or different biology to Earth?
2. Is Earth one of those “cooked” planets?
3. If we do detect biospheres with what appears to be terrestrial-like biology, is that due to artifice or natural causes?
I couldn’t follow the method of the arXiv paper you referenced, although the author raises the same question others have raised about whether the calculated emergence of LUCA might imply panspermia rather than a local abiogenesis.
I have always liked that line in “Aliens” when Van Leuwen, chairman of the Interstellar Commerce Commission, calls the terraforming projects “shake and bake” colonies. It perfectly evokes the simplicity of baking with packaged cake mixes for a planet-scale terraforming project.
In the Alien franchise reboot, the “engineers” are seeding worlds with their form of life.
In ST:TNG, the highly improbable existence of so many humanoid races is explained by an ancient race that was seeding the galaxy. No explanation of how evolution managed to tread a path to such similar humanoid species, in so similar a time frame, is given. “Handwavium”?
Natural scientists would prefer an abiotic genesis for life on Earth. If the evidence makes this an untenable hypothesis, this makes abiogenesis a more difficult problem. If another origin of terrestrial life is needed, then what? Natural panspermia, directed panspermia, Tom Gold’s “alien garbage” hypothesis (which relates to “Roadside Picnic”), and/or alien seeding? As with the “who created G*d?” question, so such hypotheses push back the question of how life originated elsewhere, something we cannot yet, or ever, test. If life is ubiquitous, possibly even in our system, then if the biology is different, this strongly supports the abiogenesis hypothesis. If life on exoplanets is the same, or very similar to terrestrial life, then the mechanisms of abiogenesis become a more interesting question, and will compete with other explanations. The answers will be far more complex and interesting than “42”.
1/137 as the universal key.
“It would be less unsettling if the relationship between all these important concepts turned out to be one or three or maybe a multiple of pi. But 137?” The number 137, according to Lederman, “shows up naked all over the place”, meaning that scientists on any planet in the universe using whatever units they have for charge or speed, and whatever their version of Planck’s constant may be, will all come up with 137 because it is a pure number. Lederman recalled that Richard Feynman had even suggested that all physicists put a sign in their offices with the number 137 to remind them of just how much they do not know.
In the Bohr model, the innermost electron of an atom with Z = 137 would be orbiting just below the speed of light, and the next element (Z = 138) would be “impossible”. Since the Bohr model does not include either quantum mechanics or special relativity, the fact that it breaks down in this regime is not unexpected. However, such large atoms (if their nuclei were stable) could be expected to behave rather differently from a naive extrapolation of trends in the periodic table. For a finite nuclear volume, the limit is raised to about Z = 172.”
https://homiinstitute.blogspot.com/2021/06/why-137-is-most-magical-number-in.html
“Potential for Interstellar Communication: Some physicists, like Richard Feynman and Laurence Eaves, have suggested that this number is so fundamental that it could serve as a signal to other intelligent species in the universe, indicating advanced scientific understanding.”
The “Copernican Principle of Mediocrity” gets my pedantic heart pumping. It is impossible to use the Copernican principle to predict the distribution of Earth like planets. It simply states that there aren’t any special and fundamental laws and privileges applied to our view from Earth. The principle of mediocrity demands a sample be randomly chosen. Since it is impossible to randomly chose the planet we are standing on, it delivers an error message when used to predict the distribution of Earth like planets. As long as we confine the category from which we chose Earth to “planets where space faring intelligence is possible”, we can maintain a firmer, though not perfect, claim to a randomly chosen sample. When used correctly, the principle of mediocrity is crucial to the claim that Earth is broadly representative of planets where SFI can emerge. It still can’t be used to predict distribution.
The “Anthropic-Coperinican Principle” is a bit of an oxymoron and the claim that how common something is depends on the distribution of its necessary conditions is a basic axiom of probability and I’m skeptical it warrants a special SETI version. Pedantry aside, if Earth’s complexity is broadly representative of the necessary conditions, SFI will be rare.
I am still an optimist. The volume of space implied by Fermi’s question is much larger than the Milky Way. It could span thousands of galaxies. I am also unconvinced we should equate SFI with infrastructure or even civilization. With two basic assumptions, SFI could outgrow both. Intelligent conscious beings would adopt bodily form factors and modes of living that maximize conscious experience. As well, any competition for resources would encourage body plans and modes of living that maximize competitive advantage. SFI should exist at the cutting edge of what is technologically possible. I can’t claim to know what that is, but imho, space ship people with universal constructors for bodies describes the minimum threshold. Maximum threshold may be super massive black holes for bodies and a population density of one SF person per galaxy.
Not to belabor the point, which I am, but establishing whether there is/was life on Mars is going to be quite telling in terms of a baren universe or otherwise. The recent findings by one of the rovers is intriguing and the sooner we get there to study it, the less unclear the picture may become.
1. Are the deposits indeed remnants/byproduct of life?
2. Is it still there?
3. If still present, is it Earth like or not??
4. Multi- or uni-cellular?
5. Either way, what constrained it?
If life can form on two planets in one system then the filter is beyond the formation of life itself. If the cooking conditions are right, it will form or at least take.
Earth is closer than we think to evolving complex life forms! https://www.nature.com/articles/s41586-025-09425-w A simple colonial organism such as a humans has a complex cell genome, but the same 1.5 gigabytes of data is copied 37 trillion times within the organism. However, in this newest publication, we see one species of ant has been able to clone and maintain the genome of a related species, used to produce domesticated workers with hybrid vigor, for five million years. If an intervention permits the planet to continue its evolutionary trajectory for some billions of years, this suggests Earth might yet attain an ecology where the flower can produce the bee, and perhaps eventually, where complex organisms are capable of drawing on yottabytes of archived genetic data to efficiently modify their structure and function to match their current situation.
As I was taught in high school mathematics class, an infinite number of curves pass through a single data point.
Well put!
As a data point, I could use the infinite curves passing through me (don’t judge) to predict I am absolutely unique. And I would be right. I would also fit comfortably within the set of all, equally unique, humans.
For what it’s worth, the Broca’s Brain curve passes through your data point as well.
What I want to know is the trajectories of any focal lines Earth crossed.
Draw lines from Earth at its WOW location and which star was directly across at that moment
We don’t have to abandon the Copernican principle that Earth is “not special;” we just have to change the scale. E.g. our galaxy has one supermassive black hole. Is that special? No; most galaxies have supermassive black holes. But the scale is one per galaxy.
Similarly, I regret to say, the density of space-faring civilizations may be one per galaxy. Or one per 100 galaxies. But the Copernican principle holds.
I think the discussion is better served by stressing what “special” means in the context of the Copernican principle. It has a vital function in the philosophy of science and when we over generalize the scope of “special”, SETI discussions become detached from that function. Copernicus’s model for our solar system eliminated the assumption that the Earth possessed a fundamentally unique place in the universe. The meaning of “special” that emerges from this model only applies to laws and processes, not outcomes.
Perhaps applying the principle to an analogy will make this more clear. Let’s map habitability to a lottery. The set of number choices will represent possible planet traits: star type, distance from star, type of core, percentage of water, etc. Someone’s selection of numbers represents an individual planet. The winning lottery number represents what is needed for a space faring intelligence to emerge.
The Copernican principle establishes the assumption that everyone has access to the same set of numbers and is using the same random number selector. That’s it, that is all it can do. What is does is still vitally important. We can confidently assume that a lottery ticket with the correct numbers has won.
We can’t use it to make any predictions about how many won. That is determined by the ratio of total numbers to how many numbers a person can choose. If the set of numbers contains one number and everyone can choose one number, everyone wins. With a set of two numbers, and a choice of one, we would predict 50% winners; 4 to 1, 25%. The only impact the Copernican principle is having on the distribution of winners is as a common, first principles play field and rule set where second order considerations play out.
With regard to Paul’s reference to the Arecibo Wow! project, they also have a planned public participation project for those willing to install a receiving system and monitor for the same and similar signals. I hadn’t heard of it until now, so perhaps some of you haven’t either.
It looks easy enough to join the network, though I wonder whether it can accomplish much. The aim is to vastly increase monitoring time since professional instruments are busy doing other things.
Here’s a direct link for those interested: https://phl.upr.edu/wow/outreach
Thanks Ron.
Antennas for the 1421 MHz frequency can be easily constructed especially since they are relatively small : a satellite dish and horn antenna are ideal, but one can also use wire mesh, a tin can, etc. Careful attention must be paid to the wiring (connections and shielding).
https://lweb.cfa.harvard.edu/~npatel/hornAntennaAASposterPDF2.pdf
https://hackaday.com/tag/1420-4058-mhz/
BTW An idea crossed my mind as I was reading the comments: what if the fact that we are so isolated in space and time is a kind of protective measure? A bit like the safety feature on electrical outlets. Just an idea to look at the problem from a different angle ;)
Fred F5CEY
So who is isolating us? And why? And how? Are there a collection of beacons surrounding our solar system warning away anyone who might be able to approach the Sol system directly, or even try to contact us via distant communication methods?
Is the Prime Direct a real thing out there? If centuries of UFO reports have any truth to them at all if they are the product of ETI visitations, then one has to wonder about that.
I would say the interstellar distances alone provide enough protection from all but the most determined species. The natural barrier works both ways, of course. We certainly aren’t very serious about doing interstellar travel ourselves, as this news item attests…
https://www.scientificamerican.com/article/the-quiet-demise-of-breakthrough-starshot-a-billionaires-interstellar/
We are isolated. It takes a radio signal to be one million watts of power just to make it to the nearest star. The idea that we have been listened to since the invention of radio and TV is false because not any of those signals makes it to a distance of even one light year due to the attenuation of radio signals and inverse square law of electromagnetic radiation and the inverse square law. There same is true of any signals we have already sent to other star systems. They won’t even make it to a four light year radius. We are further isolated by the fact that not any of our telescopes can see an Earth like planet past one hundred light years, the JWST. A star shade might change that and that will change when ELT won’t be completed and operational until 2030. Until then we are almost blind to oxygen spectra.
I think the idea that interstellar travel is too difficult for spacecraft to travel on a regular basis is rather obsolete now. Everything is forced into that idea so which until recently included SETI, but if we consider UFO’s, then the wow signal really could still have come from nearby although I will admit that radio astronomers might not want to believe that without an intelligent signal. If a UFO came down right in clear view of radio astronomers and hovered right over the radio telescope and sent a wow signal and quickly left, then one might consider it to be a terrestrial fake. My point being that they the ET’s s don’t have to land or make an intelligent signal make themselves known. There are many reasons why they would not, but it is their technological freedom to be able to do that is a freedom of choice to contact or not contact and not ours. That I we hope will change in the future. This of course is ego humbling to an isolated civilization and world with a false sense of superiority over the rest of the galaxy, an idea that has been in several science fiction films.
Surviving for millions of years would require a refined understanding of self-interest. True altruism is possible but self-interest including positive sum collaboration must be our mediocre assumption.
For a sufficiently aged SFI, collaboration with a younger peoples such as humanity won’t deliver any new information about the laws of nature, material science or anything we would consider “hard science”. Only our cultural assets would have any value. This would include things like phlogiston, ideas we come up with as we stumble towards the true nature of reality. In a virtual environment, playgrounds and mental health facilities could be built on phlogiston or Platonic solids. The Mona Lisa and the poems of E E Cummings could be a mind altering drug or weaponized.
Contact and collaboration will unavoidably change how a young peoples does science and culture. The cost of observing is similar to discovery; with von Neumann probes it is identical. Imho, no contact or collaboration is a rational application of self-interest and easy to generalize.
Outlier motivations could exist but 100% of the probability, everything besides the non-zero potential, they intersect with us emerges from the distribution of outliers. The absence of an outlier within a finite field of view does not create a paradox. This particular outlier would have to be willing to decrease the value finding strategy of their peers. This is a complicated outlier. Since the younger peoples will eventually force contact, the outlier could just take a nap until then.
What constitutes “hard science”. Physics and chemistry, only? Everything else is mediated on local conditions, even mathematics might only straddle the already known by ETI. Almost all our areas of study and entertainment are effectively “cultural” and would be worth adding to the Encyclopedia Galactica, if only to add to the data set. Even for humanity, cultural information about ETIs might be very valuable, possibly even more so than new “hard science”. certainly understanding how a civilization could survive for millions of years would be worth its weight in “gold-pressed latinum”. It might even be quite depressing to learn that FTL communication and travel were impossible, that we had discovered almost all of physics and chemistry, and what was undiscovered was only of marginal value. (What if FTL communication was possible, but so difficult and expensive that the ETI didn’t use it?) ;-)
I can also see that cultural information may be more valuable for ETI if it wasn’t contaminated by contact. This is rather like the value of studying fauna and flora in their natural state, and not tamed or domesticated in gardens, zoos, circuses, or as pets. Best ETI study us with hidden probes and surveillance technology, and remain out of contact. Less a “zoo hypothesis” and more like maintaining Earth as a “wilderness, or reserve zone”.
The philosophy of Realism posits that the world is, well real. It exists independently of perception and the mind. By “hard science”, I am referring to the empirical understanding of reality. Idealism posits the world is fundamentally mental, an extension of our minds. When I look at what exists, I see a combination of the two. Every SFI should be able to discover the empirical nature of reality.
Even if we assume the hard case for Idealism, an SFI would maintain economic comparative and competitive advantage by avoiding contact. We could even make the case that avoiding contact is for the greater good. The longer a young SFI remains isolated the more idealistic assets are available to the whole population which includes itself.
SFI are more complex than the paper clip maximizers assumed by Dyson and most pessimists. Surviving and thriving as conscious beings into deep time isn’t going to look like factory farming your people.
@Harold
I think you need to unpack that statement. Trade between Earth and the SFI should increase the size of both economies. Our respective cultural assets are valuable and would stimulate growth in their consumption and study. Obviously, any new “hard science” that we get would be to our advantage if we could exploit it. We have millennia of history to show that trade is beneficial, from flints and shells to studio-produced movies.
The overall, averaged benefits of free trade depend on the scale we measure the average and on what is considered beneficial. Globalization has unarguably disadvantaged some sectors. Even the most staunch advocates of free trade like Krugman admit that everyone would have benefited from policies that mitigated the uneven distribution of advantage. More apropos to this discussion, restricting free trade has been a successful strategy for economies transitioning from agrarian to industrialization. The restrictions provide time for their industrial sectors to mature before competing in a free trade environment.
A galactic/inter-galactic encyclopedia is a succinct model for deep time economics where we can consider scale and benefits. The scale is however many agents, including the encyclopedia who can read and write entries. The average benefit, total potential value created, is simple to understand – unique entries are directly proportional to potential value creation. Assume the encyclopedia includes an entry for universal constructors and Turing complete machines. Everyone with read permission could build any realistic or idealistic asset. Everything would have non-zero value; phlogiston, miasma theory, alchemy, etc.
My hypothesis depends on the answer to two questions.
Does the encyclopedia require permission to write entries? Objectively, the answer must be no. We would need to assume a code of ethics that prevented the encyclopedia and other agents from observing and sharing.
Would a people create phlogiston, miasma theory, alchemy, etc if they were given combustion, germ theory, chemistry, etc ? Imo, no.
With the goal of maximizing unique entries, when is the optimal point to grant a young space faring intelligence read permission? The question remains even if we assume the young SFI will eventually discover the encyclopedia and will be able to create unique variants of existing entries.
Interesting article, as is the Wikipedia pages on Milner and the Breakthrough Initiatives (this last hasn’t been materially updated since 2022.23.)
If I had to guess, he spent any of his money on other projects that captured his attention. It wouldn’t surprise me if the assessment of his wealth were exaggerated. The promises of funding were just that, more vapor than reality. There is something rather obscene that he spent so little on Breakthrough Starshot (and his other initiatives), yet spent $100 million on a house in Silicon Valley appraised at $50 million. Sounds similar the the suspected money laundering that Trump managed for an oligarch in FL selling a property for vastly more than it was worth.
Any funding without a financial ROI can be fickle, whether public or private monies. The promise of ROI is the motive to maintain the funding flow. Just ask OpenAI’s CEO, Sam Altman.
An excellent documentary on the Wow! Signal…
https://www.youtube.com/watch?v=TjQUucV83w4
This is not a simple galaxy to live in. It may take hundreds, or thousands of years or even longer to find anyone to talk to. They may be on holiday and not answering their phones or just trying to get away from the kids. Who knows. We will have to expect this to be the longest project we will ever undertake and possibly not doable at all.
Is there a galaxy that is simple? And if it is not chaotic does that also mean that planets and life may not form as easily? Is a bit of wild activity that price one must pay for life to come about?
A couple of seasons ago Centauri Dreams had some discussion about the sun as a gravitational lens and the GR properties that made 550 AUs out from it a possible means to collimate an EM beam as well as collect information from other targets. We also had some deliberation about whether this signal should be perceived as “fixed base” since the sun was not exactly the center of the solar system but perturbed by the planets ( Jupiter especially).
Our discussions stemmed from the idea of a device being constructed at 550 AUs to act as a telescope with fixed orientation and solar wandering would have posed some problem. But on the other hand, the concept might have allowed collection of solar energy and transmission of it off as a collimated beam at that same target point. But whether such a lens were natural or artificially constructed here, it is quite possible that the same could or could have happened elsewhere – and the WOW signal might have been such an artifact.
One problem with the GL as a communication device was that everything was moving. Orbiting at 550 AUs, the sun and Jupiter around its center of mass, etc.
Though the suns circular path velocity was less a fraction of a kilometer per second, the rotation rate amplified out at 550 AU radius. So, it might not be out of the question that a a GL of such nature formed elsewhere in the Galaxy propagating a radio signal in this direction and then shifted away. Nearby a radio pulsar perhaps?
If the signal were sent in such manner by sentient creatures, I would suspect that it was not meant for us. But they don’t appear to be alarmed that we intercepted some of it – or so far…
But the development did beg re-examining intelligent life in the galaxy and whether it could arise often enough to contact any contemporaries. That was kind of like asking Chou En-Lai about the impact of the French Revolution of 1789: “Too early to tell.” It was not quite 200 years ago then, but Chou would not be available to comment for much longer after the inquiry.
On this “other hand”, communication between stars in the galaxy might be augmented now and then. When they form they are close together so much of life’s precursors or early stages might be commonly held. Then Alpha Centauri or Sirius will not maintain their distance from Sol forever. The stars drift away but also drift closer. A million years hence, it might be interesting to consider how close some stars might drift toward our own. And correspondingly, stars with life like ours across the galaxy. I don’t think this gets much examination in discussions of the Drake equation.
Over the next 100,000 years, several stars appear destined to approach to about 3 light years away from the Earth.
https://beyondearthlyskies.blogspot.com/2013/04/nearest-stars-past-present-and-future.html
Proxima and Alpha Centauri, Ross 248 and Gliese 445. About 20,000 to 40,000 years from now looks like a better window if we are still dithering over our interstellar vehicle designs. I don’t have data beyond 100,000 years ahead, but it is within the realm of possibility that over a million years the interstellar transit problem and technology could build a bridge to some other star or stars. Less than a light year? Well, if we don’t visit them, maybe they will visit us.
The exchange in our case might be a little fanciful, but a lot of the WOW discussion above is taking an even longer and wider view anyway. Even if faster than light drives are not possible for intellects such as ours, over a million year interval, somewhere in the galaxy if others similar to ours find themselves in similar circumstances, they could make a transit from one star to another. Or island. Like pineapples originally arriving in Hawaii.
Discussing motivation or means, we often use the Drake equation to identify obstacles, means, likelihoods and populations. For communicating across the galaxy with other intelligences, there has to be at both ends an acknowledgment that there is something like the galaxy, Perhaps messengers from somewhere in the galaxy have communicated with us in past, but the concepts were so alien that they were not recorded in a manner which identified them as such. Then on the other hand, it is possible that alien intelligence resides on worlds where something like the galaxy cannot be easily perceived. We have a window to the galaxy at several bands in our perception, When clouds clear at night we can see it even with our eyes. Other worlds might not allow this: e.g., a Hycean world for example where astronomical perceptions simply might not arise. Or a Jovian world. Not easy to escape either. But what with the volumes provided within, why would they necessarily be concerned?
To connect back to the WOW signal, maybe one of the entities mentioned above sent us the signal inadvertently.
Does charity – and SETI – begin at home?
https://arxiv.org/abs/2510.00082
[Submitted on 30 Sep 2025]
Technosignatures of Self-Replicating Probes in the Solar System
Alex Ellery
We explore a much-neglected area of SETI: solar system techno-signatures. As our cursory solar system exploration consolidates into commercial industrialisation, it is crucial that we determine what to look for and where.
We first consider the rationale for interstellar self-replicating probes and their implications for the Fermi paradox. Whether for defensive or exploratory reasons, self-replicating probes are a rational strategy for Galactic investigation.
We determine that self-replicating probes will systematically explore the Galaxy by tracking resources of sufficient metallicity. We focus on the resource requirements of a self-replicating interstellar probe that may have visited our solar system.
After considering asteroid resources, we suggest that evidence of asteroidal processing will be difficult to discern from natural processes given the constraints imposed by self-replication. We further determine that the Moon is an ideal base of manufacturing operations.
We suggest that nuclear reactors, such as the Magnox reactor model, can feasibly be constructed from lunar resources which will have left isotopic ratio signatures of Th-232/Nd-144 and/or Th-232/Ba-137.
We further suggest that in anticipatory economic trade for resources, a self-replicating probe may have left artefacts buried with asteroidal resources on the Moon.
Such gifts would be detectable and accessible only once a threshold of technological sophistication has been achieved. An obvious gift in trade for the resources utilised would be a universal constructor.
Comments: 31 pages
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2510.00082 [astro-ph.IM]
(or arXiv:2510.00082v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2510.00082
Focus to learn more
Submission history
From: Alex Ellery [view email]
[v1] Tue, 30 Sep 2025 05:26:59 UTC (810 KB)
Jane Goodall passed away on October 1, 2025. It may be comforting to know she will live on for perhaps billions of years in the form of her image on the Voyager Interstellar Record, where two golden copies are now plunging their way attached to the twin deep space probes into the wider Milky Way galaxy.
This article displays her image on the Record first, doing field research:
https://www.nationalgeographic.com/photography/article/10-national-geographic-photos-on-voyager-that-explain-earth-to-extraterrestrials
This site has all the Record images, greetings, and music, but you have to click through a few layers to get to them. Goodall’s image in number 60:
https://goldenrecord.org/
https://astrobiology.com/2025/10/artificial-broadcasts-as-galactic-populations-i-a-point-process-formalism-for-extraterrestrial-intelligences-and-their-broadcasts.html
Artificial Broadcasts as Galactic Populations: I. A Point Process Formalism for Extraterrestrial Intelligences and Their Broadcasts
By Keith Cowing
Status Report
astro-ph.GA
October 7, 2025
Artificial broadcasts from extraterrestrial intelligences (ETIs) are a hypothetical class of celestial phenomena. Unlike known astrophysical objects, the societies that generate them may be able to replicate on galactic scales through interstellar travel. Different galaxies could thus have drastically different populations, with abundance variations of many orders of magnitude.
I present a probabilistic formalism to treat this shared history, in which societies and their broadcasts are described by distributions over basic properties like lifespan and energy released. The framework contains a hierarchy of objects related by a tree structure.
Discrete societies, the sources of broadcasts, are organized into potentially interstellar “metasocieties.” The population of each type of object is represented by a random point process in an abstract parameter hyperspace, a “haystack.”
When a selection like an observation draws a sample, the point process is thinned. Given assumptions of interchangeability and independence, observables are modeled with compound Poisson random variables. I present an example of how selection bias can favor sampling longer-lived objects.
I rederive the Drake Equation for societies in the limit of no expansion. When interstellar replication is present, however, the mean number of detected broadcasts can depend quadratically on stellar mass, suggesting a search strategy favoring large galaxies.
Brian C. Lacki
Comments: Published in ApJ; 51 pages, 9 figures, 10 tables, 3 appendices
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2405.04646 [astro-ph.GA] (or arXiv:2405.04646v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2405.04646
Focus to learn more
Journal reference: ApJ 966, 182 (2024)
Related DOI:
https://doi.org/10.3847/1538-4357/ad11f2
Focus to learn more
Submission history
From: Brian Lacki
[v1] Tue, 7 May 2024 20:09:23 UTC (1,371 KB)
https://arxiv.org/abs/2405.04646
Astrobiology, SETI
https://bigthink.com/starts-with-a-bang/alien-life-stephen-king/
Starts With A Bang — October 7, 2025
The search for alien life must heed this lesson from Stephen King
In 2025, Earth remains the only planet where life is known to exist. Without a second example, “The Stand” has a vital lesson to teach us.
Key Takeaways
Although it’s easy to speculate about the abundance of alien life, inhabited planets, or spacefaring civilizations, among the thousands of known worlds, the only one we’re certain has ever had life on it is Earth. Many assume that, if it happened here, it certainly happened elsewhere, and likely happens elsewhere frequently: life, its sustained presence on a world, the emergence of complexity, and intelligence.
But all of these are mere assumptions, unjustified by the data we currently have. Stephen King recognized the fallacy of this reasoning, and laid out in his epic novel, “The Stand,” what evidence we need to draw an informed conclusion.
A very nice infogram here…
https://bigthink.com/wp-content/uploads/2021/11/exoearth-spectra.jpg?resize=1024,949
A quote from the article, in case you are starting to feel alone in the galaxy…
The prospect of detecting and characterizing the atmosphere of a true Earth-like planet, i.e., an Earth-sized planet in the habitable zone of its star, including both red dwarf and more Sun-like stars, is within our reach. With a next-generation coronagraph, a large ultraviolet-optical-infrared mission could find dozens, or even hundreds, of Earth-sized worlds to measure.
And yet, despite the lack of any signs of life out there despite all the ways that we’ve looked so far, there are good reasons to believe that the galaxy is actually a very life-friendly place. The raw ingredients for life — the heavy elements that lead to the formation of rocky planets, organic molecules, and living creatures — are ubiquitous throughout the plane of the Milky Way: where most of its stars reside. Most of the known stars have comparable heavy element fractions to those found in the Sun, and when we’ve looked at newly forming stellar systems, they tend to produce planet-forming disks.
Over 80% of the stars, based on our surveys, are suspected to have planets. Earth-sized planets are common around stars at all distances, and Earth-sized planets at the right distances from their parent stars to support liquid water on their surfaces (assuming they have Earth-like atmospheres) are anticipated to be common: present in between 1-10% of all star systems. Sun-like stars, as well, are common, representing between 1-10% of all stars. We know of many such stars, some of which are strongly suspected to have planets, right in our own backyard, such as Tau Ceti, Alpha Centauri A, Epsilon Eridani, 61 Cygni, and Epsilon Indi. Although there are many others, these five stars are all located within a mere 12 light-years of Earth.
https://astrobiology.com/2025/10/artificial-broadcasts-as-galactic-populations-ii-comparing-individualist-and-collective-bounds-on-broadcast-populations-in-single-galaxies.html
Artificial Broadcasts as Galactic Populations: II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies
By Keith Cowing
Status Report
astro-ph.GA
October 8, 2025
Current and forthcoming constraints on radio line broadcasts in M31 (left) and three example Virgo cluster ellipticals (right), assuming that all broadcasts in each galaxy have the same EIRP ℓ. The G17 observations of M31 exclude the red shaded region, while example future observations with FAST and GBT are in blue and green, respectively. Solid shading applies to individualist constraints when δM = 0, and hatched shading is for the noise confusion limit at high δM (vertical for M49, diagonal for M31 and M87, horizontal for M59). — astro-ph.GA
The search for extraterrestrial intelligence includes efforts to constrain populations of artificial broadcasts in other galaxies.
Previous efforts use individualist methods, searching for single broadcasts with high signal-to-noise ratio. These would be detected as observables with extreme values. This approach is limited to very bright broadcasts and also is subject to confusion, where a large number of broadcasts blend together to form a noise continuum. The mean value of the total emission provides an additional collective bound: the luminosity of the transmitters is no higher than the galaxy’s observed luminosity.
Using the framework developed in Paper I, I evaluate how confusion affects individualist searches. I then compare individualist and collective approaches for radio broadcasts from the Milky Way, M31, and three Virgo Cluster elliptical galaxies. For current observations, confusion blurs narrowband radio broadcasts together in the Virgo ellipticals when there is one broadcast per gigahertz per 1000 stars.
The collective bound implies fewer than ∼106(ℓ⎯⎯⎯⎯/1013W)−1 L-band broadcasts per star gigahertz GHz in the Milky Way and is about 10 and 400 times stronger in M31 and M59, respectively. Applying the collective bound to the far-infrared–radio correlation yields constraints on radio broadcast populations in star-forming galaxies throughout the Universe. The collective bound allows us to rule out large regions of broadcast population parameter space even for distant galaxies. It also imposes constraints on gamma-ray, neutrino, and gravitational-wave broadcasts in the nearest galaxies.
Brian C. Lacki
Comments: Published in ApJ; 48 pages, 8 figures, 5 tables, 4 appendices
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2405.04651 [astro-ph.GA] (or arXiv:2405.04651v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2405.04651
Focus to learn more
Journal reference: ApJ 966, 183 (2024)
Related DOI:
https://doi.org/10.3847/1538-4357/ad11f1
Focus to learn more
Submission history
From: Brian Lacki
[v1] Tue, 7 May 2024 20:16:21 UTC (984 KB)
https://arxiv.org/abs/2405.04646
Astrobiology, SETI
https://astrobiology.com/2025/10/artificial-broadcasts-as-galactic-populations-iii-constraints-on-radio-broadcasts-from-the-cosmic-population-of-inhabited-galaxies.html
Artificial Broadcasts as Galactic Populations: III. Constraints on Radio Broadcasts from the Cosmic Population of Inhabited Galaxies
By Keith Cowing
Status Report
astro-ph.GA
October 9, 2025
Any population of artificial radio broadcasts in a galaxy contributes to its integrated radio luminosity.
If this radio emission is bright enough, inhabited galaxies themselves form a cosmic population of artificial radio galaxies. We can detect these broadcasts individually or set constraints from their collective emission.
Using the formalism in Paper I and II, I set bounds on the artificial radio galaxy population using both of these methodologies. Measured radio source counts set limits on radio broadcasts across the radio spectrum, including the first Search for Extraterrestrial Intelligence (SETI) constraints at ~250 GHz.
I compare these with commensal limits from background galaxies in the fields of large SETI surveys. The field limits are more powerful, but generally only over a limited luminosity range and for frequencies with dedicated SETI surveys.
The limits are weaker when broadcasts clump into discrete hosts that are themselves extremely rare. I find that the abundance of Kardashev Type III radio broadcast populations is less than one in 10^17 stars, about one in a million large galaxies. I also examine limits for a power-law distribution in broadcast luminosity.
Brian C. Lacki
Comments: 40 pages, 13 figures, 6 tables, submitted to PASP
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2508.00249 [astro-ph.GA] (or arXiv:2508.00249v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2508.00249
Focus to learn more
Submission history
From: Brian Lacki
[v1] Fri, 1 Aug 2025 01:28:40 UTC (1,653 KB)
https://arxiv.org/abs/2508.00249
Astrobiology, SETI
Review: Reinventing SETI
Modern efforts to search for evidence of extraterrestrial civilizations started 65 years ago but have come up empty. Jeff Foust reviews a book that argues now is the time to rethink our approaches to those searches, including turning away from efforts to look for radio signals.
Monday, October 13, 2025
https://thespacereview.com/article/5076/1
Some quotes from the review linked above and my responses, labeled My Reply…
Loeb’s persistence in the face of data came to mind when reading the new book Reinventing SETI, although perhaps for reasons neither Loeb nor the book’s author, John Gertz, intended. Sixty-five years after Frank Drake conducted the first modern SETI effort, Project Ozma, Gertz argues in the book that the SETI field is in need of a reboot, turning away from traditional radiofrequency searches that have, so far, found no signs of civilizations beyond Earth.
My Reply: While I do not think we should turn away from Radio SETI, as it is still a viable option, I agree with the reviewer that we need to really expand on current searches, both in scope and numbers. After 65 years we are still conducting largely token and sporadic searches in only a few wavelengths.
People also need to realize that much of the data collected by SETI in the last few decades has not been properly analyzed due to staff and funding shortages.
Gertz comes to the topic as both an outsider and an insider. He is not a scientist, he acknowledges, but instead a businessman (his claim to fame, he notes in the book, is that he owns a company called ZORRO Productions that holds the rights to Zorro, the TV and movie character). However, he is also an amateur astronomer who became involved with the SETI Institute, joining its board and serving as its chairman, allowing him to see how SETI is practiced today.
My Reply: It is good to have an “outsider’s” perspective on SETI and astrobiology. Even science professionals in the relevant fields can become pigeonholed as well as succumb to peer pressure by their less open-minded colleagues. SETI has suffered from these factors since before it began.
Gertz also wonders whether any alien civilizations would make concerted efforts at transmissions, lest they draw attention to themselves by other, more predatory species. He adamantly opposes any efforts to transmit messages, known as Active SETI or Messaging to Extraterrestrial Intelligence (METI), devoting one chapter to an almost angry rebuttal of the concept: “I regard METI as dangerous, arrogant, delusional, unethical, unscientific, illegal, quasi-religious, cultic, and not merely foolish but downright stupid!” Got it.
My Reply: I get why many humans might fear intelligent beings from other worlds – not just because science fiction and popular culture have been inundating us with hostile conquering aliens since at least H. G. Wells 1897 novel The War of the Worlds, but also from our own very real history of people from relatively advanced societies conquering and destroying those belonging to what they see as inferior cultures.
At the same time, the situation is not quite the same as our history. For one, we do not know if any of these possible aliens even exist. On the other hand, we know all too well of humans past and present who want to exploit their fellow species members and worse right here on planet Earth. Such aliens would likely be very, very far away, unless they are hiding in our Sol system right now. Which leads me to this next quote…
He is in favor of alternative approaches, thinking that any extraterrestrial civilizations might eschew bits for atoms: probes sent to various solar systems to monitor any life there and be ready to communicate with it—or, maybe, extinguish it if it’s perceived as a threat. Those probes could be nodes in an interstellar network, he adds. “How do we know that every asteroid is in fact an asteroid and not one of these large transmitters? We don’t,” he writes.
My Reply: If there are ETI in our Sol system and they wanted to destroy us in one fashion or another, they could do so and rather easily at that. We have little in the way of stopping such an attack. If they wanted to do something as relatively simple as drop a few planetoids on us to clean us off Earth’s surface, we could not stop such an assault even though we have been talking about it for a while.
So, while I am not saying we should not be concerned regarding conquering aliens or not bother to do anything about this, for now we should be far more concerned about the very real humans living on this planet now who want to – and are – doing great harm to their fellow humans and home.
The other space race: why the world is obsessed with sending objects into orbit
Published: October 2, 2025 at 10:50 am EDT
https://theconversation.com/the-other-space-race-why-the-world-is-obsessed-with-sending-objects-into-orbit-265264
To quote…
Beyond the race for scientific, commercial and military purposes, there is another space race of a more curious sort. A race to be the first to send various objects up there. But why?
In December 2024, Buddhist monks from Japan attempted unsuccessfully to send a small temple on board a satellite into orbit. The rocket did make it more than 110km from Earth, making it the first time the Dainichi Nyorai (the Buddha of the Cosmos) and the mandala were transported into outer space. The monks hope to try again in the future.
The space temple is only about the size of a medium Amazon delivery box, and covered in protective gold tinted foil. Buddha sits in a special compartment on top. The idea is that, with a growing number of Japanese people living outside of Japan, prayers for departed loved ones could be beamed up to the Buddha as he passes overhead.
https://astrobiology.com/2025/10/wind-power-as-a-technosignature-on-m-dwarf-planets.html
Wind Power As A Technosignature On M-dwarf Planets
By Keith Cowing
Status Report
Research Notes of the AAS
October 20, 2025
We suggest that the large-scale deployment of wind turbines on an M-dwarf planet could produce observable technosignatures.
Motivated by observations of hypersonic wind velocities on WASP-127 b, we note that the atmospheres of such planets could serve as vast reservoirs of energy for an extraterrestrial civilization.
A large-scale deployment of wind turbines in a hypersonic environment would produce heated shock waves in the hypersonic stream, cause strong frictional heating from the rotation of the blades, and be a source of infrared radiation.
We mention possible scenarios that could lead to the deployment of wind turbines on a gas giant and also note that similar features could exist on terrestrial M-dwarf planets.
The idea that aerodynamic peculiarities could be a technosignature is worth keeping in mind as ground- and space-based exoplanet observations continue to improve.
Wind Power as a Technosignature on M-dwarf Planets, Research Notes of the AAS (open access)
https://iopscience.iop.org/article/10.3847/2515-5172/ae13a7
Astrobiology, SETI
https://astrobiology.com/2025/10/seti-post-detection-protocols-progress-towards-a-new-version.html
SETI Post-Detection Protocols: Progress Towards A New Version
By Keith Cowing
Status Report
astro-ph.IM
October 17, 2025
The International Academy of Astronautics (IAA) SETI Committee has long provided guiding principles for responding to a potential detection of a SETI signal.
The foundational Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence, first formulated in 1989, has been widely recognised by the international scientific community.
A supplemental set of draft protocols addressing the possibility of a reply to an extraterrestrial signal was prepared in 1995 by the IAA SETI Permanent Committee, with both documents presented in a position paper to the UN Committee on the Peaceful Uses of Outer Space in 2000.
In keeping with the evolving landscape of SETI research, the IAA Declaration of Principles was streamlined and updated in 2010. Recognising the need for continued adaptation, the IAA SETI Committee established a Task Group in 2022 to re-examine the protocols in light of recent advances in search methodologies, the expansion of international participation in SETI, and the increasing complexity of the global information environment.
The Group recognises the living document nature of the protocols, which will require ongoing refinement to remain relevant and effective in a rapidly changing world. A draft revised Declaration of Principles was presented at the IAC 2024 in Milan, and initial feedback was received from the community, particularly members of the IAA SETI Committee.
Since then, we have continued to seek broader community input in a structured process, refining the proposed updates based on further discussions and consultations. A Revised Declaration of Principles, is presented here.
Michael A. Garrett (University of Manchester, JBCA, UK and Leiden Observatory, NL), Kathryn Denning (Dept of Anthropology, York University, Toronto, Canada), Leslie I. Tennen (Law Offices of Sterns and Tennen, Phoenix, Arizona, USA), Carol Oliver (Australian Centre for Astrobiology, School of Biological, Earth, and Environmental Sciences, University of New South Wales, Australia)
Comments: 9 pages, 1 figure. Manuscript presented at the 76th International Astronautical Congress (IAC), Sydney, Australia, 29 September – 3 October 2025, IAC 2025 congress proceedings, Paper ID 99704
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Popular Physics (physics.pop-ph)
Cite as: arXiv:2510.14506 [astro-ph.IM] (or arXiv:2510.14506v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2510.14506
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Submission history
From: Mike Garrett
[v1] Thu, 16 Oct 2025 09:52:17 UTC (383 KB)
https://arxiv.org/abs/2510.14506
Astrobiology, SETI, Technosignature
What would it mean if we were able to ‘speak’ with whales?
https://aeon.co/videos/what-would-it-mean-if-we-were-able-to-speak-with-whales
Posting the introduction of the video about speaking with whales, I love the fact that the organization conducting this research is called CETI !
This is what SETI was called before they settled on SETI, except it meant Communications with Extraterrestrial Intelligences. When they realized that actual two-way communications between star systems might take longer than expected, if at all, they went with the safer Search for ETI. Now we are being even more cautious by looking for their technological activities.
What would it mean if we were able to ‘speak’ with whales?
Until the 1950s, when ‘whale songs’ were first captured by US underwater surveillance systems during the Cold War, whales were widely thought to be mute. This discovery changed how humans view these creatures and influenced how we treated them, helping to drive campaigns for whaling bans and long-term conservation efforts.
In this conversation, hosted by the cosmologist Janna Levin at Pioneer Works in New York City, the biologist David Gruber and the comparative anatomist Joy S Reidenberg discuss how our understanding of whale communication has developed over the decades.
This includes Gruber’s work as the founder and president of Project CETI (Cetacean Translation Initiative), which is using emerging technologies to decode sperm whale communication, and may one day make an interspecies dialogue possible.
Video by Pioneer Works
16 October 2025
https://astrobiology.com/2025/10/a-cost-effective-search-for-extraterrestrial-probes-in-the-solar-system.html
A Cost-Effective Search for Extraterrestrial Probes in the Solar System
By Keith Cowing
Status Report
astro-ph.IM
October 22, 2025
For centuries, astronomers have discussed the possibility of inhabited worlds – from Herschel’s 18th-century observations suggesting Mars may host life, to the systematic search for technosignatures that began in the 1960s using radio telescopes.
Searching for artifacts in the solar system has received relatively little formal scientific interest and has faced significant technical and social challenges. Automated surveys and new observational techniques developed over the past decade now enable astronomers to survey parts of the sky for anomalous objects.
We briefly describe four methods for detecting extraterrestrial artifacts and probes within the Solar System and then focus on demonstrating one of these. The first makes use of pre-Sputnik images to search for flashes from glinting objects. The second method makes use of space-borne telescopes to search for artificial objects. A third approach involves examining the reflectance spectra of objects in Earth orbit, in search of the characteristic reddening that may imply long-term exposure of metallic surfaces to space weathering. We focus here on a fourth approach, which involves using Earth’s shadow as a filter when searching for optically luminous objects in near-Earth space.
We demonstrate a proof-of-concept of this method by conducting two searches for transients in images acquired by the Zwicky Transient Facility (ZTF), which has generated many repeated 30-second exposures of the same fields.
In this way, we identified previously uncatalogued events at short angular separations from the center of the shadow, motivating more extensive searches using this technique. We conclude that the Earth’s shadow presents a new and exciting search domain for near-Earth SETI.
Beatriz Villarroel, Wesley A. Watters, Alina Streblyanska, Enrique Solano, Stefan Geier, Lars Mattsson
Comments: Published in MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)
Report number: staf1158
Cite as: arXiv:2510.17907 [astro-ph.IM] (or arXiv:2510.17907v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2510.17907
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Related DOI:
https://doi.org/10.1093/mnras/staf1158
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Submission history
From: Beatriz Villarroel
[v1] Sun, 19 Oct 2025 15:00:24 UTC (25,158 KB)
https://arxiv.org/abs/2510.17907
Astrobiology, SETI
https://www.universetoday.com/articles/galactic-empires-may-live-at-the-center-of-our-galaxy-hence-why-we-dont-hear-from-them
Galactic Empires May Live at the Center of our Galaxy, Hence Why We Don’t Hear from Them
By Matthew Williams
October 26, 2025 at 01:57 AM UTC | Uncategorized
For over half a century, scientists have struggled to answer Fermi’s time-honored question: “Where is Everybody?” Answering this question is extremely difficult, partly because of the data-poor nature of the Search for Extraterrestrial Intelligence (SETI) itself, due to a historical lack of funding and resources.
However, there are also the inherent assumptions involved that make it difficult to arrive at a simple answer. The way “Fermi’s Paradox” is framed (by its chief proponents, Michael Hart and Frank Tipler), it is assumed that advanced civilizations will naturally seek to expand beyond their home planet and colonize other star systems.
But many researchers have criticized this outlook, emphasizing the difficulties of establishing footholds in environments entirely “alien” to them (e.g., Percolation Theory and the Aurora Hypothesis). There’s also the problem of General Relativity (GR), which establishes that faster-than-light travel is not possible without the existence of exotic physics that is yet unknown to us.
In a recent paper, a team of researchers considered several scenarios in which a civilization could expand in a relativistic Universe and concluded that it could be done within (what can be reasonably assumed to be) a civilization’s lifetime.
The study, titled “Redshifted civilizations, galactic empires, and the Fermi paradox,” was conducted by Chris Reiss, an Independent Researcher, and Justin C. Feng, a postdoctoral researcher at the Central European Institute for Cosmology and Fundamental Physics (CEICO) at the Institute of Physics of the Czech Academy of Sciences. As they argue, the rules of General Relativity, combined with a little input from the Kardashev Scale and some other theories related to SETI research, allow for the existence of a Type II Civilization inhabiting the galactic core region, and could also explain why we haven’t heard from them.
Go to the link above at top to see and read the full article.
The paper here:
https://arxiv.org/pdf/2510.00377