Because we so often talk about finding an Earth 2.0, I’m reminded that the discipline of astrobiology all too easily falls prey to an earthly assumption: Intelligent beings elsewhere must take forms compatible with our planet. Thus the recent post on SETI and fireflies, one I enjoyed writing because it explores how communications work amongst non-human species here on Earth. Learning about such methods may lessen whatever anthropomorphic bias SETI retains. But these thoughts also emphasize that we continue to search in the dark. It’s a natural question to ask just where SETI goes from here. What happens if in all our work, we continue to confront silence? I’ve been asked before what a null result in SETI means – how long do we have to keep doing this before we simply acknowledge that there is no one out there? But a better question is, how would we ever discover a definitive answer given the scale of the cosmos? If not in this galaxy, maybe in Andromeda? If not there, M87?
In today’s essay, Nick Nielsen returns to dig into how these questions relate to the way we do science, and ponders what we can learn by continuing to push out into a universe that remains stubbornly unyielding in its secrets. Nick is an independent scholar in Portland OR whose work has long graced these pages. Of late he has been producing videos on the philosophy of history. His most recent paper is “Human Presence in Extreme Environments as a Condition of Knowledge: An Epistemological Inquiry.” As Breakthrough Listen continues and we enter the era of the Extremely Large Telescopes, questions like these will continue to resonate.
by J. N. Nielsen
What would it mean for humanity to be truly alone in the universe? In an earlier Centauri Dreams post, SETI’s Charismatic Megafauna, I discussed the tendency to focus on the extraterrestrial equivalent of what ecologists sometimes call “charismatic megafauna”—which in the case of SETI consists of little green men, space aliens, bug-eyed monsters, Martians, and their kin—whereas life and intelligence might take very different forms from those with which we’re familiar. [1] We might not feel much of a connection to the discovery of an exoplanet covered in a microbial mats, which couldn’t respond to us, much less communicate with us, but it would be evidence that there is other life in the universe, which suggests there may be other life yet to be found, which also would mean that, as life, we aren’t utterly alone in the universe. This in turn suggests the alternative view that we might be utterly alone, without a trace of life beyond Earth, and this gets to some fundamental questions. One way to cast some light on these questions is through a thought experiment that would bring the method of isolation to bear on the problem. I will focus on a single, narrow, unlikely scenario as a way to think about what it would mean to be truly alone in the universe.
Suppose, then, we find ourselves utterly alone in the universe—not only alone in the sense of there being no other intelligent species with whom we could communicate, and no evidence of any having existed in the universe’s past (from which we could experience unidirectional communication), but utterly alone in the sense that there’s not any sign of life in the universe, not even microbes. This scenario begins where we are today, inhabiting Earth, looking out into the cosmos to see what we can see, listening for SETI transmissions, trying to detect life elsewhere, and planning missions and designing spacecraft to extend this search further outward into the universe. This thought experiment, then, is consistent with what we know of the universe today; it is empirically equivalent to a universe positively brimming with other life and other civilizations that we just haven’t yet found; at our current level of technology and cosmological standing, we can’t distinguish between the two scenarios.
There is a cluster of related problems in the philosophy of science, including the underdetermination of theories, the possibility of empirically equivalent theories, theory choice, and holism in confirmation. I’m going to focus on the possibility of empirically equivalent theories, but what follows could be reformulated in terms of the others. What is it for a theory to be underdetermined? “To say that an outcome is underdetermined is to say that some information about initial conditions and rules or principles does not guarantee a unique solution.” (Lipton 1991: 6) If there’s no unique solution, there may be many possible solutions. Empirically equivalent theories are these many possible solutions. [2]
The discussion of empirically equivalent theories today has focused on the expansion of the consequence class of a theory, i.e., adopting auxiliary hypotheses so as to derive further testable consequences. We’re going to look at this through the other end of the telescope, however. Two theories can have radically different consequence classes while our ability conduct observations that would confirm or disconfirm these consequence classes is so limited that the available empirical evidence cannot distinguish between the two theories. That our ability to observe changes, and therefore the scope of the empirical consequence class changes, due to technologies and techniques of observation has been called “variability of the range of observation” (VRO) and the “inconstancy of the boundary of the observable.” (discussed in Laudan and Leplin 1991). Given VRO, there may be a time in the history of science when the observable consequence classes of two theories coincide, even while their unobservable consequence class ultimately diverges; at this time, the two theories are empirically equivalent in the sense that no current observation can confirm one while disconfirming the other. This is why we build larger telescopes and more powerful particle accelerators: to gain access to observations that can decide between theories that are empirically equivalent at present, but which have divergent consequence classes.
Returning to our thought experiment, where we began as we are today (unable to distinguish between a populous universe and terrestrial exceptionalism)—what do we do next? In our naïveté we make progress with our ongoing search. We build better telescopes, and we orbit larger and more sophisticated telescopes, with the intention of performing exoplanet atmospheric spectroscopy. We build spacecraft that allow us to explore our solar system. We go to Mars, but we don’t find anything there; no microbes in the permafrost or deep in subterranean bodies of water, and no sign of any life in the past. But we aren’t discouraged by this, because it’s always been possible that there was never life on Mars. There are many other places to explore in our solar system. Eventually we travel to interesting places like Titan, with its own thick atmosphere. We find this moon to be scientifically fascinating, but, again, no life of any kind is found. We send probes into subsurface liquid water oceans, first on Enceladus, then Europa, and we find nothing more complex in these waters than what we see in the astrochemistry of deep space: some simple organic molecules, but no macromolecules. Again, these worlds are scientifically fascinating, but we don’t find life and, again, we aren’t greatly bothered because we’ve only recently accustomed ourselves to the idea that there might be life in these oceans, and we can readily un-accustom ourselves as quickly. But it does raise questions, and so we seek out all the subsurface oceans in our solar system, even the brine pockets under the surface of Ceres, this time with a little more urgency. Again, we find many things of scientific interest, but no life, and no other unexpected forms of emergent complexity.
Suppose we exhaust every potential niche in our solar system, from the ice deep in craters on Mercury, to moons and comets in the outer solar system, and we find no life at all, and nothing like life either—no weird life (Toomey 2013), no life-as-we-do-not-know-it (Ward 2007), and no alternative forms of emergent complexity that are peers of life (Nielsen 2024). All the while as we’ve been exploring our solar system, our cosmological “backyard” as it were, we’ve continued to listen for SETI signals, and we’ve heard nothing. And we’ve continued to pursue exoplanet atmospheric spectroscopy, and we have a few false positives and a few mysteries—as always, scientifically interesting—but no life and no intelligence betrays itself. Now we’re several hundred years in the future, with better technology, better scientific understanding, and presumably a better chance of finding life, but still nothing.
If we had had some kind of a hint of possible life on another world, we could have had some definite target for the next stage of our exploration, but so far we’ve drawn a blank. We could choose our first interstellar objective by flipping a coin, but instead we choose to investigate the strangest planetary system we can find, with some mysterious and ambiguous observations that might be signs of biotic processes we don’t understand. And so we begin our interstellar exploration. Despite choosing a planetary system with ambiguous observations that might betray something more complex going on, once we arrive at the other planetary system and investigate it, we once again come up empty-handed. The investigation is scientifically interesting, as always, but it yields no life. Suppose we investigate this other planetary system as thoroughly as we’ve investigated our own solar system, and the whole thing, with all its potential niches for life, yields nothing but sterile, abiological processes, and nothing that on close inspection can’t be explained by chemistry, mineralogy, and geology.
Again we’re hundreds of years into the future, with interstellar exploration under our belt, and we still find ourselves alone in the cosmos. Not only are we alone in the cosmos, but the rest of the cosmos so far as we have studied it, is sterile. Nothing moves except that life that we brought with us from Earth. Still hundreds of years into the future and with all this additional exploration, and the scenario remains consistent with the scenario we know today: no life known beyond Earth. We can continue this process, exploring other scientifically interesting planetary systems, and trying our best to exhaustively explore our galaxy, but still finding nothing. At what threshold does this unlikelihood rise to the level of paradoxicality? Certainly at this point the strangeness of the situation in which we found ourselves would seem to require an explanation. So instead of merely searching for life, wherever we go we also seek to confirm that the laws of nature we’ve formulated to date remain consistent. That is to say, we test science for symmetry, because if we are able to find asymmetry, we will have found a limit to scientific knowledge.
We don’t have any non-arbitrary way to limit the scope of our scientific findings. If any given scientific findings could be shown to fail under translation in space or translation in time, then we would have reason to restrict their scope. Indeed, if we were to discover that our scientific findings fail beyond a given range in space and time, there would be an intense interest in exploring that boundary, mapping it, and understanding it. Eventually, we would want to explain this boundary. But without having discovered this boundary, we find ourselves in a quandary. Our science ought to apply to the universe entire. At least, this is the idealization of scientific knowledge that informs our practice. “On the one hand, there are truths founded on experiment, and verified approximately as far as almost isolated systems are concerned; on the other hand, there are postulates applicable to the whole of the universe and regarded as rigorously true.” (Poincaré 1952: 135-136) Earth and its biosphere are effectively an isolated system in Poincaré’s sense. We’ve constructed a science of biology based on experimentation within that isolated system (“verified approximately as far as almost isolated systems are concerned”), and the truths we’ve derived we project onto the universe (“applicable to the whole of the universe”). But our extrapolation of what we observe locally is an idealization, and our projecting a postulate onto the universe entire is equally an idealization. We can no more realize these idealizations in fact than we can construct a simple pendulum in fact. [3]
We need to distinguish between, on the one hand, that idealization used in science and without which science is impossible (e.g., the simple pendulum mentioned above), and, on the other hand, that idealization that is impossible for science to capture in any finite formalization, but which can be approximated (like the ideal isolation of experiment discussed by Poincaré). Holism in confirmation, to which I referred above (and which is especially associated with Duhem-Quine thesis), is an instance of this latter kind of idealization. Both forms of idealization force compromises upon science through approximation; we accept a result that is “good enough,” even if not perfect. Each form of idealization implies the other, as, for example, the impossibility of accounting for all factors in an experiment (idealized isolation) implies the use of a simplified (ideal) model employed in place of actual complexity. Thus one ideal, realizable in theory, is substituted for another ideal, unrealizable in theory.
Our science of life in the universe, i.e., astrobiology, involves these two forms of idealization. Our schematic view of life, embodied in contemporary biology (for example, the taxonomic hierarchy of kingdom, phylum, class, order, family, genus, and species, or the idealized individuation of species), is the idealization realizable in theory, while the actual complexity of life, the countless interactions of actual biological individuals within a population both of others of its own species and individuals of other species, not to mention the complexity of the environment, is the idealization unrealizable in theory. The compromises we have accepted up to now, which have been good enough for the description of life on Earth, may not be adequate in an astrobiological context. Thus the testing of science for symmetries in space and time ought to include the testing of biology for symmetries, but, since in this thought experiment there are no other instances of biology beyond Earth, we cannot test for symmetry in biology as we would like to.
Suppose that our research confirms that as much of our science as can be tested is tested, and this science is as correct as it can be, and so it should be predictive, even if it doesn’t seem to be doing a good job at predicting what we find on other worlds. We don’t have to stop there, however. If we don’t find other living worlds in the cosmos, we might be able to create them. Exploring the universe on a cosmological scale would involve cosmological scales of time. If we were to travel to the Andromeda galaxy and back, about four million years would elapse back in the Milky Way. If we were to travel to other galaxy clusters, tens of millions of years or hundreds of millions of years would elapse. These are biologically significant periods of time, by which I mean these are scales of time over which macroevolutionary processes could take place. Our cosmological exploration would give us an opportunity to test that. In the sterile universe that we’ve discovered in this thought experiment, we still have the life from Earth that we’ve brought to the universe, and over biological scales of time life from Earth could go on to its own cosmological destiny. In our exploration of a sterile universe, we could plant the seeds of life from Earth and seek to create the biological universe we expected to find. The adaptive radiation of Earth life, facilitated by technology, could supply to other worlds the origins of life, and if origins of life were the bottleneck that produced a sterile universe, then once we supply that life to other worlds, these other worlds should develop biospheres in a predictable way (within expected parameters).
It probably wouldn’t be as easy as leaving some microbes on another planet or moon; we would have to prepare the ground for them so they weren’t immediately killed by the sterile environment. In other words, we would have to practice terraforming, at least to the extent of facilitating the survival, growth, and evolution of rudimentary Earth life on other worlds. If every attempt at terraforming immediately failed, that would be as strange as finding the universe to be sterile, and perhaps more inexplicable. But that’s a rather artificial scenario. It’s much more realistic to imagine that we attempt the terraforming of many worlds, and, despite some initial hopeful signs, all of our attempts at terraforming eventually die off, all for apparently different reasons, but none of them “take.” This would be strange, but we could still seek some kind of scientific explanation for this that demonstrated truly unique forces to be at work on Earth that allowed the biosphere not only to originate but to survive over cosmological scales of time (the “rare Earth” hypothesis with a vengeance).
If the seeding of Earth life on other worlds didn’t end in this strange way (as strange as the strangeness of exploring a sterile universe, so it’s a continued strangeness), but rather some of these terraforming experiments were successful, what comes next could entail a number of possible outcomes of ongoing strangeness. Leaving our galaxy for a few billion years of exploration in other galaxies, upon our return we could study these Earth life transplantations. Transplanted Earth life on other worlds could very nearly reproduce the biosphere on Earth, which would suggest very tight constraints of convergent evolution. If origins of life are very rare, and conditions for the further evolution of life are tightly constrained by convergent evolution, that would partially explain why we found a sterile universe, but the conditions would be far stronger than we would expect, and that would be scientifically unaccountable.
Another strange outcome would be if our terraformed worlds with transplanted Earth life all branched out in radically different directions over our multi-billion year absence exploring other galaxies. We would expect some branching out, but there would be a threshold of branching out, with none of the biospheric outcomes even vaguely resembling any of the others, that would defy expectations, and, in defying expectations, we would once again find ourselves faced with conditions much stronger than we would expect. In all these cases of strangeness—the strangeness of all our engineered biospheres failing, the strangeness of our engineered biospheres reproducing Earth’s biosphere to an unexpected degree of fidelity, and the strangeness of our engineered biospheres all branching off in radically different directions—we would confront something scientifically unaccountable. Even though we have no experience of other biospheres, we still have expectations for them based on the kind of norms we’ve come to expect from hundreds of years of practicing science, and departure from the norms of naturalism is strange. All of these scenarios would be strange in the sense of defying scientific expectations, and that would make them all scientifically interesting.
These scenarios are entirely consistent with our current observations, so that a sterile universe with Earth as the sole exception where life is to be found is, at the present time, empirically equivalent with a living universe in which life is commonplace. However, the exploration of our own solar system could offer further confirmation of a sterile universe, or disconfirm it, or modify it. If, as in the preceding scenario, we find nothing at all beyond Earth in our solar system, this will increase the degree of confirmation for the sterile universe hypothesis (which we could also call terrestrial exceptionalism). If we were to find life elsewhere in our solar system, but molecular phylogeny shows that all life in our solar system derives from a single origins of life event, then we will have demonstrated that life as we know it can be exchanged among worlds, but the likelihood of independent origins of life events would be rendered somewhat less probable, especially if we were to determine that any of the over life-bearing niches in our solar system were not only habitable, but unambiguously urable. [4]
If we were to find life elsewhere in our solar system and molecular phylogeny shows that these other instances of life derive from independent origins of life events, then this would increase the degree of confirmation of the predictability of origins of life events on the basis of our present understanding of biology. The number of distinct origins of life events could serve as a metric to quantify this. [5] If we were to find life elsewhere in the solar system and this life consists of an eclectic admixture of life with the same origins event as life on Earth, and life derived from distinct origins events, then we would know both that the distribution of life among worlds and origins of life were common, and on this basis we would expect to find the same in the cosmos at large. An exacting analysis of this maximal life scenario would probably yield interesting details, such as particular forms of life that appear the most readily once boundary conditions have been met, and particular forms of life that are more finicky and don’t as readily appear. Similarly, among life distributed across many worlds we would likely find that some varieties are more readily distributed than others.
If the solar system is brimming with life, we could still maintain that the rest of the cosmos is sterile, reproducing the same scenario as above, but the scenario would be less persuasive, or perhaps I should say less frightening, knowing that life had originated elsewhere and was not absolutely unique to Earth. Nevertheless, we could yet be faced with a scenario that is even more inexplicable than the above (call it the “augmented Fermi paradox” if you like). If we found our solar system to be brimming with life, with life easily originating and easily transferable among astronomical bodies, increasing our confidence that life is common in the universe and widely distributed, and then we went out to explore the wider universe and found it to be sterile, we would be faced with an even greater mystery than the mystery we face today. The dilemma imposed upon us by the Fermi paradox can yet take more severe forms than the form in which we know it today. The possibilities are all the more tantalizing given that at least some of these questions will be answered by evidence within our own solar system.
It seems likely that the Fermi paradox is an artifact of the contemporary state of science, and will persist as long as science and scientific knowledge retains its current state of conceptual development. Anglo-American philosophy of science has tended to focus on confirmation and disconfirmation of theories, while continental philosophy of science has developed the concept of idealization [6]; I have drawn on both of these traditions in the above thought experiment, and it will probably require resources from both of these traditions to resolve the impasse we find ourselves at present. Because science and scientific knowledge itself would be called into question in this scenario, there would be a need for human beings themselves to travel to the remotest parts of the universe to ensure the integrity of the scientific process and the data collected (Nielsen 2025b), and this will in turn demand heroic virtues (Nielsen 2025) on the part of those who undertake this scientific research program.
Thanks are due to Alex Tolley for suggesting this.
Notes
1. I have discussed different definitions of life in (Nielsen 2023), and I have formulated a common theoretical framework for discussing forms of life and intelligence not familiar to us in (Nielsen 2024b) and (Nielsen 2025a).
2. The discussion of empirically equivalent theories probably originates in (Van Fraassen 1980).
3. I am using “simple pendulum” here in the sense of an idealized mathematical model of a pendulum that assumes a frictionless fulcrum, a weightless string, a point mass weight bob, absence of air drag, short amplitude (small-angle approximation where sinθ≈θ), inelasticity of pendulum length, rigidity of the pendulum support, and a uniform field of gravity during operation of the pendulum. Actual pendulums can be made precise to an arbitrary degree, but they can never exhaustively converge on the properties of an ideal pendulum.
4. “Urable” planetary bodies are those that are, “conducive to the chemical reactions and molecular assembly processes required for the origin of life.” (Deamer, et al. 2022)
5. The degree of distribution of life from a single origins of life event, presumably a function of the particular form of life involved, the conditions of carriage (i.e., the mechanism of distribution), and the structure of the planetary system in question, would provide another metric relevant to assessing the ability of life to survive and reproduce on cosmological scales.
6. Brill has published fourteen volumes on idealization in the series Poznań Studies in the Philosophy of the Sciences and the Humanities.
References
Deamer, D., Cary, F., & Damer, B. (2022). Urability: A property of planetary bodies that can support an origin of life. Astrobiology, 22(7), 889-900.
Laudan, L. and Leplin, J. (1991). “Empirical Equivalence and Underdetermination.” Journal of Philosophy. 88: 449–472.
Lipton, Peter. (1991). Inference to the Best Explanation. Routledge.
Nielsen, J. N. (2023). “The Life and Death of Habitable Worlds.” Chapter in: Death And Anti-Death, Volume 21: One Year After James Lovelock (1919-2022). Edited by Charles Tandy. 2023. Ria University Press.
Nielsen, J. N. (2024a). Heroic virtues in space exploration: everydayness and supererogation on Earth and beyond,” Heroism Sci. doi:10.26736/hs.2024.01.12
Nielsen, J. N. (2024b). Peer Complexity in Big History. Journal of Big History, VIII(1); 83-98.
DOI | https://doi.org/10.22339/jbh.v8i1.8111 (An expanded version of this paper is to appear as “Humanity’s Place in the Universe: Peer Complexity, SETI, and the Fermi Paradox” in Complexity in Universal Evolution—A Big History Perspective.)
Nielsen, J.N. (2025a). An Approach to Constructing a Big History Complexity Ladder. In: LePoire, D.J., Grinin, L., Korotayev, A. (eds) Navigating Complexity in Big History. World-Systems Evolution and Global Futures. Springer, Cham. https://doi.org/10.1007/978-3-031-85410-1_12
Nielsen, J.N. (2025b). Human presence in extreme environments as a condition of knowledge: an Epistemological inquiry. Front. Virtual Real. 6:1653648. doi: 10.3389/frvir.2025.1653648
Poincaré, Henri. (1952). Science and Hypothesis. Dover.
Toomey, D. (2013). Weird life: The search for life that is very, very different from our own. WW Norton & Company.
Van Fraassen, B. C. (1980). The scientific image. Oxford University Press.
Ward, P. (2007). Life as we do not know it: the NASA search for (and synthesis of) alien life. Penguin.
“We might not feel much of a connection to the discovery of an exoplanet covered in a microbial mats, which couldn’t respond to us, much less communicate with us, but it would be evidence that there is other life in the universe, which suggests there may be other life yet to be found, which also would mean that, as life, we aren’t utterly alone in the universe.”
‘Microbial mats’, or something quite similar, is pretty much what ALL terrestrial life looked like on Earth for billions of years, in fact, for most of the history of this planet. We have no way of knowing if this type of life is common or not in the cosmos, but we know it developed here quite early in our history. Much, much later, more complex life arose here, but we really don’t know if that has arisen anywhere else either.
But what is life anyway? One definition is complex structures composed of chemical compounds and reactions that exhibit interesting properties such as reproduction, evolution, metabolism, mobility, growth, behavior and consciousness (whatever THAT is). It is capable of locally reversing entropy. We believe life CAN arise spontaneously where conditions are suitable, but we cannot say with any certainty it MUST do so.
That is the only kind of life we know of, although we suspect there may be others, For example, ecosystems, machines and even communities exhibit some of those properties. Are these artifacts and collectives alive as well?
I’ll leave that speculation to the philosophers.
Does the universe itself possess some inherent property that inevitably leads to other structures of similar increasing non-entropic complexity? Is there life composed of energy fields, space-time entities, hot plasmas, gravitational resonances…again, we don’t know. I’ll leave that speculation to the science-fiction writers.
Or perhaps life can be totally non-material, abstract, mathematical, existing only in our thought processes; look up Conway’s Game of Life and the whole idea of cellular automata. Conway’s critters are capable of at least some of the properties we have observed or imagined in microbial mats.
There may be other levels of ambiguity.
Extra-terrestrial life is like Santa Claus, we can only prove his existence if we meet him, but we can never disprove his existence, no matter how long we search without finding him.
Not that it matters. We have every reason to keep looking, a guarantee of success is not necessary.
I think it is in Dawkins’ book, “The God Delusion”, where he says I am technically agnostic because I can only think God doesn’t exist 99%, because I cannot prove this to make me 100% atheist.
Humans have believed in various gods for millennia. The monotheistic Abrahamic religions have been believing and praying to God for nearly 6000 years. Fundamentalists utterly believe Good is a living entity that touches their lives, and if you pray fervently and are “good,” He will look after you and take you to Paradise when you die. For those believing in the “End Times” and the Rapture, they are repeatedly disappointed when the promised day doesn’t arrive and gets delayed for one reason or another.
There are times when I think, rightly or wrongly, that we are in a similar mindset, hoping that SETI will succeed and ETI will be proven real. It seems that it is more rational than believing in a living God, but is it really? The logic seems sound. Abiogenesis seems unlikely to be unique to Earth; therefore, the universe must have other living worlds. As Dawkins notes, we can be sure that Darwinian evolution must apply to those living worlds. Therefore, organisms will evolve increasing intelligence, and ultimately result in a technological species, which leads to an advanced technological civilization. It should only be a matter of time before we discover ETI, even if we are the species that must go into the galaxy to meet ETI.
I think that Nielsen’s thought experiment is worth considering. It is an extreme version of my post on the Bayesian probability of life when all we have are null cases of evidence for life, let alone ETI. Even if we explore the whole accessible universe, simply because we would be limited to never being able to explore it completely, the Bayesian probability that life (and ETI) exists would be vanishingly close to zero, but not zero.
Would we really try to search that extensively, rather than giving up after a few galaxies were found to be completely sterile apart from Earth? I think I would “call it a day” and stop searching.
For some, it might even be proof that God exists and that we are his special creation. If so, I would wish we would take more care of this creation and look after it a lot better. My POV is that we should do our best to green the galaxy. But if Nielsen’s thought experiment showed that, despite our best efforts, we would fail, then we would be effectively trapped on Earth as biological beings. It would suggest to me that even living life support would fail too, preventing the development of O’Neill-type space habitats and cities. If we wanted to spread our ideas and civilization into space, it would have to be by our non-biological artefacts, i.e., intelligent machines. They would be our de facto descendants to populate space, assured that there could be no biological or artificial intelligences to counter their expansion. I would seem to be a rather sterile civilization from our biological POV. No diverse, living biospheres. Only machine “life” that would be able to settle in space and on other worlds. It may even be an incredibly diverse universe, in terms of artificial “species” and culture.
Suppose that such a machine culture spread throughout the universe, assuming they were alone, having been created by the biological race that spawned them., What would they think if they discovered us as the only biological planet in the universe apart from their original homeworld? We would be the only counterfactual to an assumed sterile universe beyond their homeworld. And if we were just on the cusp of sending our machine intelligences to explore the universe after finding all the worlds within a few thousand parsecs were sterile, and unable to terraform any other world?
Clarke thought that a universe devoid of ETI was a potentially frightening prospect. One where biological life was not only unique to Earth, but unable to spread further, might be even more unsettling, as the prospect of greening the universe would be denied us as a program to fill the future ages. All we could do would be to create artificial intelligence and hope we could spread our culture to the stars through our proxies. It would be very similar to the situation of our artificial beings spreading through the universe, albeit with our biological selves following in their footsteps as they terraformed the worlds for us, if we so desired. But if we were unable to follow, would we go extinct in despair?
Yes, I have long noticed the emotional/psychological parallels between religious belief and the phenomenon of SETI. But even as a devout ‘99% agnostic’ myself, it hasn’t stopped me from also becoming fascinated with extraterrestrial civilizations other than ours. Why not? You can give up on Santa Claus but still cling to the Deity, or you can give up on HIM and still be a space groupie. There is no contradiction and no silliness in that. We get to pick and choose. It is our alienable right.
Frankly, I find the absence of God much less terrifying than I do that of a universe where we humans are the only thinking conscious beings. But in either case, there is little I can do about it. It is conceivable that God deliberately hides from us (in order to test our faith?) and it is certainly possible that space-time is filled with other civilizations but they are so far apart that none is ever likely to stumble onto another. If I were forced to make a quantitative judgement on it, I would say the latter is more likely than the former.
Philosophically, we are all entitled to our beliefs and desires about reality, no matter how unlikely or ridiculous they may be. The only error is when we start believing in our fantasies so strongly that they prevent us from thinking
rationally and dealing with the universe as it is, not as it should be.
I suppose I am an Existentialist, in the formal philosophical definition of the term. We can’t know everything, we may not even know anything, but we have a right to decide what matters to us even if we recognize that banal biological or psychological forces influence much of what we think we know.
We can’t help being wrong sometimes, maybe even all the time. But we can certainly refuse to be stupid.
The Age of Disclosure = https://www.imdb.com/title/tt35520315/ 7.0
Too many academics want to play ignorant. Society is watching and knows enough. Isn’t it time to come down from the ivory tower and confront the issue like adults?
I have watched that “documentary,” and it is very far from being “adult.” If there are aliens out there, please could you give me the time back I spent watching that drivel?
Why documentary in quotes? Why is it drivel?
It is the ramblings of conspiracy theorists and cranks. The only “evidence” presented is the already well-publicized videos from naval aircraft. Everything else is at best hearsay.
One of the crazies is the infamous Harold Puthoff, a man who has dabbled in all sorts of nonsense, who, with a straight face, insisted that the aliens were “transdimensional beings” and that the spacecraft were using warp drives. There was no room for even one scientist or engineer to push back on these various claims.
The only disclosure I could see was that QAnon-like conspiracies were exposed.
A far better documentary is one by the BBC “What Are UFOs?”. This has scientists and engineers examining the evidence and demonstrating with experiments why the evidence, especially from the aircraft FLIR sensors, was misleading. They show how actual aircraft viewed in both visible light and IR show very different images, not unlike the naval aircraft videos. It doesn’t even attempt to “debunk” the nonsense claims, just shows how the claims, even of military pilots, have to be judged properly, not taken at face value. Remarkably, now that we know that Chinese balloons have been surveilling the USA, not one thought was given to the possible terrestrial origin of some of these sightings.
One of the pilots in Disclosure was also in the BBC documentary, when she was interviewed in her current teaching job, stating that she has no idea what these things she saw were, a very different impression from the Disclosure documentary.
That the US Congress has reps and senators taking this stuff seriously says more about their lack of sense than anything about UAP reality. Even a simple question such as “What about UAP sightings and crashes in other countries? Are their governments covering up the evidence and reverse-engineering the technology? If so, why is Russian technology so crappy? Are their scientists and engineers so useless that only the US has managed to extract some of the technology?” We truly live in a new age of conspiracy bubbles resistant to facts. It is a return to the pre-scientific era.
I have an alternative theory that I believe does much to explain the current UFO flap. It is a variant of one of the existing narratives, that governments are deeply pursuing UFO studies in order to reverse-engineer alien technologies but are ineptly pooh-poohing all efforts to reveal or explain these so-called conspiracies.
By deliberately “leaking” the idea that our military is investigating captured alien tech while simultaneously publicly and vigorously denying any such thing is going on, we can provoke our adversaries to expend intelligence assets and resources into trying to get to the truth. There is no shortage of crackpots, opportunists and cultists that will pick up on these supposed leaks and an impenetrable fog of conspiracies and
speculation will further confuse the issue. Meanwhile, the intelligence agencies of our rivals will waste talent and energy trying to sort out the mess. Those are resources that will not be available to potential enemies to penetrate our legitimate clandestine programs.
A variation of this theme will be that those leaks and whistleblowers are actually a means of generating a smokescreen to obscure and confuse similar but very real secret projects, like the development of exotic reconnaissance vehicles or electronic countermeasures.
I was in high school when President Kennedy was assassinated. Immediately. the nation was bombarded with breathless conjectures:
the KGB did it, the CIA did it, LBJ did it, the Mob did it, Fidel did it, the anti-Castro Cubans did it. Need I go on? I often wonder how future historians will ever sort it all out. I don’t know for sure who killed JFK, but I am sure anyone who claims to know is making it up.
UFO (I refuse to use the trendy new acronym) mythology has been in pretty much its current form since 1947, and it has historical antecedents that go back much further than that. (Victorian UFOs looked like balloons and Zeppelins). I am struck by the contradiction that highly advanced alien civilizations have been monitoring our planet without the ability to disguise themselves effectively, while simultaneously refusing to simply land and introduce themselves once and for all. Is that proof of anything? Of course not, but at least it makes sense.
I was born and raised in the Deep South. I can recognize religious fanaticism and apocalyptic fantasy when I see it.
@henry
I think there is a pretty clear association between UFO sightings and Area 51, which is used for testing new aeronautical technology. Whether the government made up a UFO cover story or not is debatable.
I don’t buy the idea that the UFO artifacts are a costly distraction for foreign intelligence. UFO sightings have occurred in many nations and have even spawned conspiracy theories of government cover-ups. I don’t think there is anything special about the USA in this regard.
Back in teh 1990s [?], there was a UFO flap over Denver. Supposedly, “everyone” saw a big, or several, huge triangular ships over the city. It made teh newspapers. A friend was convinced it was the real deal. I believe it was nothing more than 3 aircraft flying in formation. An example of mass delusion?
Most recently, we had the Chinese surveillance balloons. This caused a flurry of “sightings” over military bases. A local politician said he saw drones buzzing about over a base. Apparently, he couldn’t distinguish a star from a moving light in teh sky. So much for our “educated” elites.
Locally, where I live, someone posted a phone camera image of 3 lights that they said looked like the outline of a UFO. Both I and another commenter noted that the stars were Orion’s belt. This commenter showed that perfect correspondence of the photo and where Orion was in the night sky. So much for “country” folk being better observers than no-nothing “city slickers”.
Whenever I read or hear that the observers are rational professionals – policemen, pilots, etc., and should be believed, their descriptions are accurate, I think of the many experiments that demonstrate no such thing. We are subject to visual illusions, (e.g., the Moon is larger at the horizon, or that lights are moving in the night sky when they are fixed stars or planets). Multiple observers report different descriptions of teh same event. If allowed to compare experiences, often a group will coalesce around one explanation (like the Denver sighting).
And let’s not forget that the majority of Americans believe angels are real, and large minorities believe in paranormal phenomena Paranormal Phenomena Met With Skepticism in U.S..
The popularity of TV “documentaries” on ghosts, ancient aliens, strange creatures, etc., possibly reinforces such beliefs. I am told that many local Latinos believe in witches (Halloween decorations can freak them out), and we are well aware of the Christian fundamentalists who rail against the Harry Potter books and movies as they depict magic and therefore the works of Satan.
As Richard Feynman said, “The first principle is that you must not fool yourself and you are the easiest person to fool.” This applies to things well beyond science.
You still have a lot to learn, Alex, and I don’t see the point in trying to explain to someone who is close-minded on the subject.
The idea that Earth is being visited by extraterrestrial civilizations, and its variant, that our governments are aware of it and desperately trying to cover it up for sinister reasons, cannot be dismissed entirely. After all, it violates no accepted physical laws. But that does not mean it is necessarily true. The whole conjecture is very similar to speculations about Bigfoot, or the Loch Ness Monster: we can’t rule it out altogether, but we have no convincing reason to believe it.
What justifies my skepticism is the response from the True Believers (and I say that with Eric Hoffer firmly in mind) always justify their advocacy by declaring that it must be a sinister conspiracy, or the impenetrable hidebound careerism and conservatism of science, that works maliciously behind the scenes to deny us their version of the Truth.
My own experience with governments and scientists tells me that the former is dismally bad at keeping secrets, and the latter are highly motivated by their own ambitions to overthrow the current theory. That’s how you get rich and famous in science, you replace the accepted paradigm.
We may not have conclusive evidence yet, but when I hear words like ‘cover-up’ or “orthodoxy’, I instinctively reach for my wallet and make sure it’s still there; not because they don’t exist, but because they are calculated to discredit rather than persuade.
@henry
Or the inevitable “And Galileo was right.”
Notice that Avi Loeb named his monitoring the skies for UFOs, the Galileo project. “Coincidence, I think not!” (Quote from The Incredibles movie).
While I agree that governments keeping secrets is very difficult, I amazed me how much has been kept from the public by the British government even after the rules for disclosure have passed. Sometimes documents are discovered by researchers given access to the archives. It was recently revealed that the British officials in Kenya were doing the equivalent of Oliver North and the Iran-Contra documents, but just sinking boxes of incriminating documents in the Atlantic. Some boxes were kept and have now been discovered. It even appears that QEII was involved in agreeing to destroy the documents. The uncovering of slaveholding investments has been uncovered in both British and US universities. I believe an independent researcher was let go at Harvard [?] because he had discovered “too much”. And of course, interesting historical documents are constantly being unearthed in archives.
But the mother lode of all secrets is kept in the Vatican Archives. What historically important and revelatory secrets are there to be unearthed?
Maybe they found the body?
I found these articles today by Sindre Andre Zeiner-Gundersen;
https://www.researchgate.net/profile/Sindre-Zeiner-Gundersen
Energetic-Frame Dynamics (EFD) and the Dynamical Alfvén Reflection Engine.
(DARE): A Unified Field-Buoyancy Propulsion Framework.
Propellantless Propulsion via Dynamic Casimir Modulation.
Inducing Directed Solar Plasma Ejections for Interstellar Propulsion: A Theoretical Framework for Stellar-Scale Energy Harvesting.
Field Mediated Propulsion White Paper.
And many more like this, see on ResearchGate.net
Something a little more uplifting……………….
Sindre Andre Zeiner-Gundersen’s papers on “frontier science” are not peer-reviewed and are highly speculative. The subjects are controversial, and the ideas are not validated.
Just think how much of this stuff is polluting physics. Sabine Hossensfelder sometimes takes this sort of work to pieces with explanations on her YouTube channel. A few years ago, at a starship conference [IIRC], Lawrence Krauss made a simple remark about a presentation on a star drive just violating the law of conservation of energy. The presenter had no comeback or explanation for why Krauss might be wrong and was deflated. Was it a decade ago that an Irish [?] company made a big PR effort about solving cold fusion [?] (or some other extraordinary energy generation technology), but when it came to a public demonstration…it was a bust. And so it goes.
One can play all sorts of math games that can appear to demonstrate some conventional physics-violating effect. But either a demonstration fails to validate the maths, or the math cannot be demonstrated in an experiment. Sometimes the claim is made that a propulsion device demonstrates a violation of physics, but invariably, the experimenter is just fooling themselves. Marc Millis has done work showing that various claims of “propellantless propulsion” are false.
Remember the suggestion that the Pioneer 10 probe was not travelling at the expected velocity, which might indicate “new physics”? It turned out to be the effect of asymmetric heat radiation from the probe that was sufficient to explain the “anomaly”. Pioneer Anomaly.
As David Brin once said, if you have a propellantless drive, demonstrate that the effect is sufficiently large to be obvious, not relying on barely discernible movements that could be experimental errors or uncontrolled effects.
What I find interesting is that often the claims are made by people with sufficient qualifications that their claims are “supported” by their qualifications, even though this is the “argument from authority” fallacy. I put Dr. Puthoff in that category. Dr. Avi Loeb seems to be pushing in that direction, although he is being more circumspect and not making fantastic claims of “new physics”.
Back in the 1930s when movie theater short features might include episodes of Flash Gordon and his encounters with the inhabitants of planet Mongo, I suppose there was an element of apprehension in the audience. Now nearly a century later, would we prefer microbial mats or Ming the Merciless as an interplanetary neighbor? I suppose there are calculated risks with either, but from what we can gather so far the former is more likely than the latter.
But as to whether either are likely to exist within our radius of detection in the next few decades, the “mats” are more likely from our own experience based on the eons of their existence before we came along and then our own flash in the pan heritage.
However, moving back somewhat from bio accomplishments such as bio mats, there is still gathering evidence of widespread biochemistry. A recent illustration in the solar system (aside from Earth), is described in the summary report
“Bio-essential sugars in samples from asteroid Bennu”,
published 30 September 2025 in Nature -Geoscience Article
https://doi.org/10.1038/s41561-025-01838-6
There is also a similar report from the Japanese mission to asteroid Ryugu with some limitations placed on the return samples. But the take away is that around the time the Earth was formed – or even earlier, there were abundant biochemical precursors to life in the solar system. With these samples only scratching the surface, suggested earlier by the 1969 Allende meteorite, summarizing briefly as an object formed with the solar system but with pre-solar inclusion “grains”.
This is hardly enough to nail this proposition, but considering that stars seemed to hatch from clouds, such as those in the direction of Orion, and that their proximity to each other was likely much closer by magnitudes than say Alpha Centauri and the sun now, it is not so absurd to think that a lot of solar bio precursors were shared with similar newly formed stars in the vicinity. Not all G2V stars necessarily but close enough to share biochemistry precursors in material we now consider meteoritic or clumps from asteroids.
The big question, of course, is what do all these individual ( or even binary) stars do with this material. It could be that the Earth’s early state was even too hot for extremophiles, but precursors and even extremophiles might still have reached its surface. Or else the real start of life in the Solar System was further out and seeded Earth when it was less like a molten sphere. Too early to tell, but we still get a martian meteorite now and then. And then we have rovers gathering samples.
So, at the very least, I believe that there is a case for widespread “microbial mats”.
But what happens after they form is not necessarily set in stone. Here we might have an exceptional case; or maybe not. Earth might not have been the brightest
kid in the class. Sampling the neighborhood with exoplanet transits, we are getting about one out of a hundred systems. And were LGMs trying to do the same thing with Earth, its sampling rate would be 1 pass per year. The scientific community is obliged not to jump the gun, but if collectively they were as pessimistic as they let on, why would they exert themselves with Martian explorations in the first place? Professional obligation – since no one is dragging them to their laboratories and consoles in chains.
But had we had this discussion even half a century ago, the stellar astronomers in their majority would be skeptical about planets existing at all: “Close passage of stars might have caused the Solar System planets to form ( American astronomer Forest Ray Moulton was an advocate for one, the author of the Dover paperback “An Introduction to Celestial Mechanics, 2nd edition 1914). But who cares? We’ve got time on Kitt Peak or Mount Palomar.
A post script on the comment above. Pulling off the library shelf the paperback version of Moulton’s Introduction to Celestial Mechanics, it is noted that the cover illustration is the solar system from an old German print. Included are principal moons and asteroids and several comets.
It makes one wonder why a theory of solar system formation would be based on close passage of two stars… All these solid objects… Yet based on the information available at the time, it might not have been such an inconsistent conclusion.
Which might be a reason to examine it from our century later perspective and attempting to deductions of our own.
Perhaps this conclusion was related to the fact that as recently as a century ago it was thought that the primary constituent of the sun was iron – based on the prominence of iron absorption lines in its visible spectrum. In 1925 Cecelia Payne Gaposchkin at the Harvard observatory determined from optical spectra that the sun was mainly composed of hydrogen. The equation developed by Indian physicist Megnad Saha, the Saha equation. What exactly was being ionized in stellar atmospheres had to be sorted out and Saha’s equation indicated that hydrogen had to be the primary culprit for the given surface temperature, though iron absorption lines from ionization appeared all over the sun’s visible spectral range.
I was an astronomy-obsessed child in the 1950s, and the theory that the solar system was formed by a freak tidal interaction between the sun and another star was still being proposed. The alternative, that a rotating dust and gas cloud formed the planets when the sun condensed out, was much older, but was rejected. This may explain why the idea of many extrasolar planets had not caught on.
When viewed from the north, the sun, planets and their satellites rotate AND revolve in a counter-clockwise fashion in a flat plane (there are a few deviations and exceptions) so the nebular hypothesis seemed reasonable, but it had a serious objection: celestial mechanicians could not explain how the excess angular momentum had been dissipated. Today we know it occurred with the aid of magnetic fields.
Of course, back in that ancient time, we still believed we could see vegetation spreading towards the Martian equator from the poles in summer as the icecaps melted.
Hello, H.C..
When I wrote that entry, it was prior to the lengthy discussion about UFOs.
Consequently it does now seem like an off-topic outlier. But I think your remarks are worth remembering. For in a way this is another case of a “general consensus” being “stick to stellar astronomy” vs. attempting to search for exoplanets. The consensus on that one was partly analytical but wrong, but aslo an assumption that astronomical methods would never reach that state of the art.
Now, of course, we have another orthodoxy now, which might be right – or wrong. It could be that aliens are very remote and our best chances of detecting them is if they decide to become some sort of Kardeshev state visible from afar. That’s a rather showy path for people who are supposedly wiser than we are. We have hard enough time tending to our share of Earth resources. For aliens obsessed with funneling a whole star system’s or galaxy’s resources, “Good luck!” And it’s not natural anyway.
So that leaves us with an alternative hypothesis, at least. That aliens are more subtle in their tread on nature, but they have access to considerable means for transport and visitation.
And they might even stop by to visit us by means that are not yet provided self evident explanation.
Now whether one believes the explanations of UFO sightings after the witness accounts or not, some might be worth pondering or connecting with phenomena previously observed. And for my part I listen to the stories I encounter and file them away awaiting for further information.
By good fortune, I have heard a lot of them and interviewed many of the witnesses. A lot of them were flyers or pilots. And then some were institutional people that collect the information more methodically than I do, though i can’t vouch for which ones have institutional biases or not. Clearly some of them do. But we are all tempted to say now and then: “Just as I thought.”
At the very least though, I would say that many of the witnesses ( sometimes many at the same place or “on board”) had a darned good story to tell.
And that’s my hope. That if we keep our ears peeled and eyes open, the clutter might be filtered out and we might eventually discover something of note.
But if someone is making this stuff up, they should be warned that since astronauts do some spacefaring themselves, the standards for yarns are getting higher and higher.
So, if you hear a good UFO story from someone, make sure you write it down accurately for future reference. … My opinion of course. And I do not mean to suggest someone post it here. On the other hand, if nothing else, space could use a Conrad or Melville, observant of its remote islands and far ranging behemoths.
@wdk
Early Heinlein might have fit that role [Melville], had he lived in such a future. Perhaps we could do with something even Homeric in nature to tell of such adventures?
@wdk
I have a BA in astronomy, and have been an active amateur ever since I was a teenager. I have a lot of time looking up and I try to keep up with the literature. I have spent a lot of time as an informed observer and seen about a half dozen UFOs, one of them on a US Navy radar scope! By ‘Unidentified’, I mean something I could not explain away as an air or spacecraft, a meteorological or astronomical phenomenon, a hoax or hallucination, or some other conventional object or rare and unfamiliar natural phenomenon.
Does this mean I saw an alien spacecraft? Of course not. I witnessed some things that were probably (but not necessarily) ordinary events occurring under unusual circumstances, MAYBE they were visitors from another star system, but I don’t know that. I have no way of knowing that. If I had to make a statistical guess, something with a number attached to it, I would make it about < 5%, that is, the probability any of those sightings were of extraterrestrial artifice is small, but not zero. Five percent may seem like a big number to a skeptic, but I believe I am a highly trained and reliable observer. I have confidence in my own ability and reasoning.
I have also watched the reactions to UFOs of my companions who were NOT trained observers but which I regarded as honest, well-intentioned witnesses, and I find that they tended to exaggerate or misrepresent what they saw and clearly missed or ignored details I quickly picked up on. I feel this fact corroborates my conclusions. And yes, I have posted some of these sightings here.
When faced with insufficient data, and the requirement to continue research because even the extreme possibilities are so compelling, one must try to remain open-minded but also guard against fooling oneself, or succumbing to confirmation bias and other error.
Another example. I have intensely studied the 1977 WoW! signal, and I feel that the probability it is an artifact of an alien civilization is small, but cannot be ruled out as zero. If pressed for a number, I would have to say it is also about <5%. The available facts are consistent with an alien origin, but an ordinary cause cannot be ruled. My low probability guess is simply a recognition of Sagan's Law; "Extraordinary conclusions demand extraordinary evidence." Sagan is merely restating Occam's Razor, which is not a law of nature, but a wise strategy to follow nonetheless.
I believe in the possibility of extra terrestrial Life, and even of extra terrestrial intelligence in the cosmos. My subjective statistical assessment is rather small, and it has become even smaller as I have learned more. But I WANT to believe. I have been wrong before and I am aware of the pitfalls that beset the undisciplined speculator.
My legitimate role here is, and I believe the role of all of us should be, to remain cautiously optimistic and to restrict our activities to gathering additional information that will help to devise observational and experimental tests. This question may never be settled definitively one way or another, but we should never succumb to either intellectual arrogance or wishful thinking.
My takes it that there’s going to be a hell of a lot more algae mat planets than techaliens ones. \We have just got to keep looking, the galaxy is a very big place though.
@Michael
I techaliens are confined to their homeworld/system, then this seems almost obviously true, and certainly true using the Drake Equation. However, there have been numerous posts and journal articles about starfaring species and colonization of the galaxy. Indeed, this very blog is in support of humanity engaging in interstellar travel and probably colonization. Therefore, a species that does engage in such activity, with the goal of colonizing the galaxy, whether as a single culture civilization, or creating new species and cultures over millions of years, then, depending on the frequency of indigenous inhabited worlds, it may be that techaliens are the dominant form of [artificial] life.
I wouldn’t bet on that being the case, but it shouldn’t be ruled out. [I’m just playing the Avi Loeb gambit here. ;-) ]
If machines prove to be the agents exploring and exploiting the galaxy’s resources, rather than biological species, then, even if we prove to be the first technological civilization, our efforts may prove to fulfil the progenitors of such an expansion. Our descendants may accept that acquired knowledge of galactic life and the robotic exploration of the galaxy demonstrates that this is the case, albeit millennia, if not millions of years, from today.
Because we cannot logically prove a negative, henry’s assessment that anomalous observations may be:
techaliens < 5%,
should be more accurately defined as:
0% < Observation is techalien < 5%.
I am currently reading Judea Pearl's "The Book of Why" on causality. If I add path diagrams to the Drake Equation based on my comment to @Michael, I would modify the rather linear probability assessment to include the probabilities of life on any exoplanet as including panspermia of various types, which in turn influences the number of transmitting ETI, which also feeds back on the probability of life from directed panspermia, lack of planetary protection from probes and biological alien "garbage", and of course colonization by ETI. A far more complex situation than the simple Drake Equation suggests.
As regards the OP by Nielsen, I think we are on the cusp of demonstrating that sustainable ecosystems are possible off Earth. We know plants and animals can be kept in fully enclosed LLSs. We know that a plant survived in an enclosed bubble on the Moon's farside, carried on a Chinese rover.
I think we could demonstrate that a simple ecosystem could do the same using one of those commercialized bubble aquatic ecosystems of a shrimp, a water weed, and associated microorganisms. It could be put on a rover and kept lighted, warm, and protected from radiation almost anywhere in the solar system. This would go towards demonstrating that the extreme condition of life not existing anywhere in the universe, either indigenously or transplanted, is falsified. I hope that "Life finds a way" seems more likely than it cannot do so away from Earth. Perhaps this would have to be outside the solar system. Just any example of life beyond Earth would be a positive case that falsifies the hypothesis, and would end the need for further search to test the hypothesis and instead shift goals to catalog other biospheres.
There is one useful reason to search for biospheres, even if only bacterial mats. It can be shown that the possible sequences of proteins of average length vastly exceed the number of atoms in the universe (assuming the 20 terrestrial amino acids). IOW, the space of possible sequences already discovered on Earth is only an infinitesimal sample of protein sequence space. If a fraction of the exoplanets have life, there are billions of planets in our galaxy alone, with evolved prokaryotic life evolutionarily exploring the sequence space. If so, then we might get a better handle on what the functionally useful protein space is. Does it extend continuously, or is it restricted to a small subset of the possible sequence space, which would become clear once a set of inhabited exoplanets has been visited and the proteins cataloged? What might be the value of those ET proteins? (and not just the fictional Weyland-Yutani's wish for new bioweapons.)
“techaliens < 5%,
should be more accurately defined as:
0% < Observation is techalien < 5%."
What about the confidence interval? For the sake of argument let's say it's 95%, which is typical of polls. The probability range is 0% to 100%, with a 95% confidence that it is less than 5%. Except that in this case we have no reliable confidence interval. That makes the range meaningless.
"We know that a plant survived in an enclosed bubble on the Moon's farside, carried on a Chinese rover."
You can survive just about any environment, if the time interval is sufficiently short. You can survive being 500 meters from ground zero of a multi-megaton blast if you are there for only a fraction of a femtosecond. You can survive the vacuum of space for entire seconds.
This is a weak measure. What we want is to show survival sustained indefinitely, or as close to indefinitely as we can ensure and reliably extrapolate.
“You can survive just about any environment, if the time interval is sufficiently short. You can survive being 500 meters from ground zero of a multi-megaton blast if you are there for only a fraction of a femtosecond. You can survive the vacuum of space for entire seconds.”
Now those are words to remember!
@Ron S.
Does a probability need a confidence range? Throwing a pair of sixes with 2 dice doesn’t require any error bars for confidence, as we know the probability of that result. The probability of <5% is based on some bound of UFOs being possible alien technology vs the much larger number that have been identified as natural phenomena or terrestrial technology. [I would rule out "possibles" and require positive evidence.] You can add a Bayesian calculation based on personal observation and research, but I don't think that needs any confidence range.
What does "indefinitely" mean in this simple experiment context? While a biosphere can maintain itself over billions of years, it can also end, as it may have done on both Mars and Venus. Biomes last for shorter periods, subject to climate. Specific ecosystems last for quite short periods as they change due to succession through to their climax communities, e.g., forests, depending on climate, or climate change on an ecosystem – think of the Sahara grasslands that are now desert.
I don't know how long my proposed simple experiment would last, but certainly weeks and possibly several years. This redditor claims his is still going after 20 years! If so, that seems like a decently long time to prove a point, as it suggests a more complex ecosystem could be maintained for far longer.
I expect we will get our first low-ambiguity biosignature long before we have to explore the whole galaxy with robotic probes to find one [or not].
“Throwing a pair of sixes with 2 dice doesn’t require any error bars for confidence, as we know the probability of that result.”
Only because you have a fully characterized system. That is rare in cases of scientific discovery, and especially in the case being discussed. That 5% limit is based on assumptions, not data.
“What does “indefinitely” mean in this simple experiment context?”
Whatever you want it to be. A year, a decade, a millennium? Nothing is forever. But there must be an objective of interest. Leaving it undefined is unhelpful.
“I expect we will get our first low-ambiguity biosignature long before we have to explore the whole galaxy with robotic probes to find one [or not].”
Maybe. Unless the biomat says “hello” there will be ambiguity, no matter the signal’s nature or our theoretical model to explain it. There can be no absolute certainty otherwise. It just has to be strong enough evidence to convince us, and we’ve been wrong before when interpreting seemingly strong evidence for various phenomena.
@ Ron S.
Exploring the whole galaxy to sample exoplanets requires physical travel. Without FTL, we are talking at a minimum of 50,000 years just to traverse the galaxy, let alone check 100s of billions star systems. We don’t know when we will get lucky, but assuming life is detected at X ly, that requires at a minimum 2X years before we get an answer. That could be anywhere from 20 to 2000+ years if life is detected within 1000 ly, depending on propulsion and communication technology, if the first living planet with any recognizable life from bacteria/analogs upwards in complexity.
biosignatures don’t just have to be testing atmospheric gases ala Lovelock. Em radiation includes detecting anything that emits a wavelength that is detectable, including seeing discrete objects with a high-resolution optical telescope.
Remote observation only requires one lucky hit with a “super telescope” that could directly observe macroscopic complex life directly – trees and large animals, or structures such as cities, roads, fields from extant or extinct civilizations, or smart animals building dams or using fire, much as we can from Earth orbit. Are we really unlikely to achieve the latter before we have to explore the galaxy physically?
We can already detect phytoplankton from orbit, so it may even be possible to detect similar organisms on exoplanets in the future, too.
Your points about probability, I agree with, although I don’t think we must always add confidence limits.
Hi Paul
>What would it mean for humanity to be truly alone in the universe?
If we were certain to be the only form of life, it is quite possible that we would lose interest in the universe. What’s the point of doing it, since we now know that we are alone? The human species is curious; if there is nothing to find, nothing to gain, it will probably turn its head elsewhere to do something else. If I propose a treasure hunt by telling you *before* to start the game that there is nothing to find, will you play?
Of course there will still be researchers who will continue to look up there, but only to understand physical, “mechanical” phenomena since there is no life. (dark matter, various forces etc)
here raises a first question: are we looking for life in the universe to discover “mechanical” phenomena along the way or are we observing these phenomena hoping to find life? The priority seems important to me because it conditions our way of doing Science. Obviously the answer will be different depending on the specialties but from a global point of view, what is guiding our Science ?
There will also be some optimists who, through their beliefs; their cultures; their perception of the world, will refuse this idea of being alone to remain in a form of fatalism or religiosity because it is also in the human mind: the expectation of something above “superior to humans” allows to contradict a certainty but especially to keep hope. Here we live in the field of beliefs, an ancestral phenomenon to the human species (maybe just to accept its condition?)
What are cosmogonies used for? What would be hopeless astronomy?
In short, if we had the certainty of being the only form of life, there would surely be a vertiginous regression of Science perhaps to go through a moment of obscurantism (?) then for it to then reorient itself towards something else.
The most pessimistic earthlings would sink into despair because accepting to be alone is hard (especially when I see that I no longer have any beer in the fridge :) but it’s mainly accepting to be with his peers! In other words, the famous “are we alone in the universe?” leaves us with a “way out”, a scientific and philosophical “air bubble. It’s this question mark that is the most important because it opens all possibilities no matter what we are going to find… or not.
If it disappears and the sentence becomes negative, the notion anchored in every human being of “our beautiful blue planet” will immediately become the idea of a jail ; isolation is generally unbearable for human specie. The sociological impact of such a certainty would then surely have catastrophic repercussions on human societies and perhaps in particular on our societies now focused on technology and less on the spiritual. What would take over?
On the other hand, more optimistic, we can also assume that the [forced] acceptance of our interstellar isolation would refocus our Science no longer towards the outside but towards the inside, that is to say about ourselves, about earth and Life here. Our highly developed technological tools could be “reconverted” (we know how to do well) to multiply, for example, sub-miniature research; biology, quantum physics, etc. This could open up to other discoveries and another evolution of Science (panspermia; conservation of life for interstellar travel etc)
lest’s stop finally on the question of certainty: who will give it to us? what will give it to us? for how long? The answer will greatly influence our way of doing science and that of our descendants.
In the current state of Science and our knowledge, there is no certainty and that’s very good because a certainty can be a brick of Lego that will make us progress towards something else but it can also be an impasse, a final point and finally it is always up to us and to ourselves alone that the final decision lies.
(I need to fill the fridge :D )
Happy Christmas to all, Fred
A warning.
SETI researchers are handicapped by an inevitable bias: We have only one example of an intelligent technical civilization: our own.
Everything we know about ourselves serves as the template on which we can base speculations on potential extrasolar societies. We know it happened here so its possible it happened somewhere else. But we must also remember that it is possible it didn’t happen anywhere else, or that it happened differently, or that something totally different is happening ‘out there’. Still, we can always rely on using human history to justify our conjectures as reasonable. We have an example we can point to.
We must also realize we are talking about aliens and the very definition of the word tells us they will be different, they will be strangers to us, they will look different, think different, live different, their environment will be unlike ours and their behavior may be incomprehensible. We can qualify these doubts by adhering to some very reasonable assumptions such as they will be the result of a biological evolution whose effect on ourselves we have studied extensively. They will be affected by physical laws we know intimately and which we have every reason to believe are the same for them as they are for us. Their home star and planet may have had a different history than ours, but it couldn’t be too different. Even if they turn out to be machine intelligences created by now-extinct silicon creatures that breathed ammonia; F=ma in their home world works just like it does on ours.
There are some things we can say with confidence: ETI will have arisen on a world where conditions were stable enough for long enough that they were able to evolve and adapt just like we did. We know Earth’s environment has changed dramatically since Life first appeared here but it did not change so drastically, or so quickly, that Life was not able to adjust. We are pretty sure a species can escape devastating cosmic catastrophes once it has achieved space travel or some other extraordinary technology; but until that happens, it requires relative stability in its natural environment.
The evolution of biological life requires a long-lived star and planet that does not change too abruptly. The home star cannot go supernova or undergo any other rapid evolution, even a perfectly suitable home planet must escape radical orbital changes, destructive collisions, close encounters with other large objects in its system. A binary companion to the system must also be far enough or stable enough to not threaten Life on the home world during its own evolution. (Remember, MOST stars are members of binary systems and most binaries are composed of members with highly different masses and subsequently divergent histories.) We have already identified system characteristics that MAY be essential to Life, or intelligent Life, such as the presence of a nearby massive moon, plate tectonics, a strong magnetic field, oceans, I can go on. Some truly cosmic catastrophes may even make substantial portions of entire galaxies uninhabitable. No doubt there are many other potential obstacles to Life we haven’t even guessed at yet. But the Universe is so old and so big we can confidently hope that Life has arisen in other places and survived some local drama. After all, we made it. Why couldn’t they have gotten lucky too?
The SETI community is aware of these pitfalls and opportunities and is currently engaged in healthy debate as to which of them may be significant. There are biological bottlenecks, too; is the development of multicellular life inevitable or is it a lucky accident? We rely on the geologists and biologists to answer those questions but there are other assumptions which seem to have escaped criticism altogether.
The arising of highly complex life forms makes the appearance of intelligence possible but does that mean it is inevitable? Its late appearance and explosive development suggests it might be a fluke, a lucky accident. Does the appearance of intelligent and social creatures make science inevitable? Does the appearance of technology always lead to the type of engineering capable of interstellar travel and communication? What DOES an alternative form of engineering even look like? We may have only gotten lucky because of a fortunate but unlikely combination of biological, psychological, social and physical factors. Do upright bipedal savanna dwellers evolved from arboreal ancestors have a leg up on everybody else? We have no way of knowing any of this is possible, or even likely, for all intelligent reasoning organisms and societies. And finally, how do we know all civilizations who develop complex cultures choose to immediately found colonies on other worlds and start systematically exploring the Galaxy? I suggest even the spacefaring races that do exist will cool off their ambitions once they have ensured their security by populating multiple, separate worlds, or perhaps engage in relations (hostile or benevolent) with other species they encounter.
I continue hearing from SETI enthusiasts how ongoing and unstoppable interstellar diaspora is inevitable for any species that once managed to chip a projectile point from the local stone. This has never been persuasively demonstrated to me. Even if other civilizations have shown they are as aggressively expansive as we believe we are (remember, the SETI community selects for space and exploration enthusiasts), how many are there? What fraction? Even advanced terrestrial maritime societies (Portuguese, Spanish, English, Chinese, Polynesian, Viking) have sometimes suddenly decided to stop voyaging (for a variety of reasons). Even the USA, with its impressive nautical history, has pretty much given up building ships, except for men-of-war. Our excuse: “it is no longer economically feasible”.
All of these conjectures involve speculations on the motivations of extraterrestrials, or observations of our own history, both of which involve assumptions we can’t always justify. But there are further obstacles to the inevitability, or even potential, of a society to achieve a spacefaring technology, especially one that persists long enough to make the existence of such societies common. The question SETI asks is, “What is the likelihood we will ever encounter another intelligent species?” They may very well be out there, but they may be so far apart in space and time that we will never meet or communicate with them. Conversely, they should be so common that the fact we have not found any suggests we are alone. The universe is very big, and very old, but is it big enough AND old enough? And how long must these communities exist, on the average, for there to be a fighting chance for them to find one another?
We may assume that the technological development of our own civilization has been so rapid in the last few hundred years that it is reasonable to believe that this pattern must also be the case with many others. After all, there is no particular reason to think we are unique in this respect. But does this period of rapid growth continue indefinitely, or does it tend to quickly damp out as soon as all the ‘easy’ discoveries are made. The only reason the entire Galaxy is not teeming with multiple, expanding extrasolar cultures might be because there is some general process, characteristic, reality (a ‘filter’) that simply shuts down or eliminates cultures after some relatively short period of time. This could be some sort of recurring occasional cosmological catastrophe, or perhaps an inherent risk that advanced technologies destroy themselves through pollution, war, decadence, social collapse, etc.
But I suggest there may be another reason. Maybe interstellar travel and communication is just too hard; no technology exists, or can exist, to make it possible, or even likely. Perhaps the rapid advance in technology we have exhibited for the last few centuries is a phase many cultures experience, but natural limits eventually intervene for all societies that stop their scientific advance. We have assumed that that which is not forbidden must be mandatory, but that may simply not be the case.
We suspect that the speed of light is the maximum velocity possible in nature, but there might be other natural limits which cannot be overcome. Materials can be developed with higher melting points, but maybe there is a natural limit to the highest temperature solid matter can tolerate. Perhaps the energy sources available to us are limited and we will never be able to command enough to do everything we like. Direct matter-to-energy may exist in nature but perhaps we just can’t harness that with mere gadgets. We may already be approaching the actual limits of progress; what if we have gathered all the low-hanging fruit and we can’t reach the higher ones because nature will not allow it? Is it possible that we are close to achieving the limits of engineering? We have long assumed that there is no limit to our future progress; we’ve imagined an entire pantheon of Kardashevs and Matrioskas and other secular deities which may be just fantasies because nature may simply not allow them. For all we know, when (and if!) we reach our pinnacle of technological development, the universe may be populated with species that are more or less as scientifically capable as we are. That’s a long way from the commonplace assumption that ET will far outstrip us in scientific knowledge. The intelligent universe may be analogous to the Earth of a thousand years ago, many civilizations, some of them even aware of one another, but none with steam or electricity.
This is not an attractive prospect to those involved in SETI. We tend to be oriented to scientific progress and ever-increasing knowledge and capability but we cannot demonstrate that that future is achieved anywhere. Maybe Fermi was right and perhaps the reason they’re not here is not because they don’t exist, but because there is no way we can reach out to one another. A first contact may still be possible but it can only be with a contemporary who is not too far away, and it may not be for a long, long time.
Greetings—As a (now retired) historian of technology, I’ve been struck by how debates about the existence or non-existence of “tech aliens” (a term new to me until I read this essay) almost invariably pivot around discussions of high (advanced) technologies (technosignatures). It seems to be taken for granted that if an intelligent life form exists and has developed a civilization, then it will also develop communication technologies, computers, AI, and the capability, or at least the capacity, for interstellar travel and even galactic colonization. Yet in this debate, what is missing is an appreciation for how contingent technological development has been for our own species. Human civilizations have displayed marked diversity in their use or non-use of various technologies, owing to a host of variables. Take the case of simple tools, for example. Greek, Roman, and other Mediterranean civilizations developed and used the wheel, but Aztec and other Meso-American civilizations did not. Why? Among the most widely accepted explanations is that in Meso-America, there were few, if any, indigenous mammals capable of being domesticated and used for transport or hauling goods. On the other hand, Meso-American civilizations made greater strides, and showed greater innovativeness in, the development of screw-operated pumps used for irrigation. Going back even further, into human prehistory, the extent to which different human populations made, used, and innovated in the design of tools was constrained by the availability of rocks such as obsidian, which could be chipped without breaking.
It does not require belief in a “special creation” to acknowledge that humans’ technological history was fraught with circumstances, environmental conditions, or other factors that, at any point in time, could have led to markedly different outcomes. Imagine, for example, that Earth had no history of plate tectonics—a geological record that led to the mixing and re-mixing of mineralogical deposits that made possible the discovery and utilization of alloys. Or if Earth’s atmospheric level of oxygen had not fallen within the range (roughly 18 to 23 percent) necessary to support fire- and combustion-technologies that made possible the development of metallurgy?
It’s striking how often, in such debates, proponents cite Stephen Jay Gould’s famous metaphor of “rewinding the tape” to show how contingent human evolution was. It’s also rather ironic, since that metaphor itself tacitly depends upon the contingent development of technologies such as a tape with magnetizable properties; wheels and spools for taking up the tape; gearing to provide the means for turning the wheels and spools; the technology to convert magnetic traces into recognizable, coherent signals; and an external power source to drive the mechanism. Remove any one of those items from the mix, and the metaphor collapses.
The point is this: We may never really know if humans truly are the only “tech aliens” in the universe. But perhaps, and with an appropriate amount of humility, we can and should better understand the contingent history of our own species’ technological development, particularly at this moment in time where our technological future itself seems fraught.
Technology is contingent, but that can also be mitigated if it is a geographic constraint like the Meso-American lack of the wheel, with trade. We know that Pacific islanders traded goods, allowing those on limestone atolls to acquire flints, as the Vikings on Greenland acquired good metal tools from home.
Regarding metaphors, we use what we have. We talk of rewinding the tape because we had tape recorders . We didn’t have time machines. But if tapes were not yet invented, we could use other metaphors like cloths with histories woven into their length. If not that, a piece of rope, laid on the ground, and walking back to the beginning and retracing the events on the string. These are just analogies concerning the idea of time as another linear dimension.
Gould was not concerned with human history, but with biological evolution. Would the various phyla that emerged in the Cambrian reappear if evolution were restarted prior to that? What about the evolution of eukaryotes?
Evolution is very path-dependent. However, convergent evolution also occurs, where physics shapes form. Human culture uses nature to shape tools – e.g., spear points and arrow heads – mimicking canine teeth to penetrate flesh. This would likely not be created if nature had not been able to evolve strong, penetrating teeth if there was a shortage of calcium to combine with carbon dioxide and water to form the basis of such anatomical structures.
Despite all this, SciFi writers have dreamed up worlds where evolution has created very different cultures, from swarm intelligence in bacteria, to aliens with very different anatomies, to very different cultures and cultural technologies such as language.
Hi, John Rumm
My point exactly. But SETI “researchers” are tech enthusiasts, what I call “space groupies”. That is not a criticism, I happen to be one myself! They tend to believe that it is inevitable that all civilizations must turn out the way they wish we will eventually turn out. I am starting to rethink that assumption…
This thread is winding down, but others on this vein will follow. Join us!
A plug for a favorite of mine.
My 2026 edition of the Royal Astronomical Society of Canada Observer’s Handbook came in the mail today.
The RASC Handbook is published yearly and is a sort of almanac with ephemeral data useful to amateur astronomers,
but it is compiled with a detail and depth of value to professionals as well. Along with the ephemera (data which changes from year to year, like sunrise and sunset tables) it also contains many articles and listings of specific topics which are repeated yearly, but updated when new information is developed by ongoing research. Features on events of special interest are also included. There are tables of astronomical constants and observing tips. Even old editions are nice to keep around. There is plenty of material there to entertain you when you feel the need for reading material. I keep old copies in the bathroom, or give them to my friends. You don’t need to be an astronomer to treasure the Handbook, anyone with an interest in science will enjoy perusing it.
One of my favorite articles is “The Nearest Stars” by Todd J. Henry, which lists every known star within 5.0 parsecs (16.3 light-years). These are the closest known objects to the Sun, the ones we know the most about, and whose data has been determined to the highest precision. It is a detailed look at the solar neighborhood, and a useful sample of space in this corner of the galaxy. This a field of intense research and the list is updated frequently, and kept up to date.
The list contains 53 known systems comprised of 66 stars, 9 brown dwarfs and 13 known extrasolar planets. This catalog is constantly being updated by new observations, so I guess you could call this data “ephemeral”. Many of these guys are extremely faint, so new ones are turning up all the time. The brightest is Sirius (apparent magnitude -1.43). The faintest, Wise 1049-5319 B (apparent magnitude 24.07). They are also the intrinsically brightest and faintest, respectively. the nearest is Proxima Centauri (4.24 ly), the farthest, Omicron 2 Eridani (16.3 ly).
Forty eight of these stars are red dwarfs, spectral class M. Spectral classes O and B (the hottest) are totally missing from the list, and there is only 1 A and 1 F represented, the next lowest temperatures. Two share our Sun’s spectral class, G, while 8 are class K. (The spectral classes, from hottest to coolest are O,B,A,F,G,K,M.) The 5 white dwarfs, ancient, dying stars that have completed their evolution, are classed separately. The brown dwarfs are not stars at all, they glow from gravitational contraction only, they are not massive enough to ignite thermonuclear reactions in their cores.
These stars are listed in a table, with their names, positions, parallaxes (distances), proper motions (velocity across the line of sight) and radial velocity (velocity towards or away from us), their apparent magnitudes (how bright they appear) and their absolute magnitude (how bright they would appear at a standard distance of 10 pc). Also listed are their position angles (direction of proper motion) and their spectral classes. Some of these fields are left blank, this science is still rapidly expanding and there are still many questions.
This is what most of the Galaxy looks like, or at least the spiral arms and the disk. The brightest, hottest stars are also young, and the most short-lived, they can be seen at enormous distances, but they are extremely rare, even though they comprise much of the naked eye sky. The big red giants also are visible from afar, but they too are rare, and they are near death. The sample in this list is representative. It represents where we live.
The sky is like the sea, it contains whales and fishes, but most of the biomass is in the plankton.
Hello, H.C.
When you brought up the Canadian Observer’s Handbook and its features, it reminded me of a parameter that might ( or might not) be included explicitly in the tables. I suspect that there is raw doppler recession or approach velocity – and perhaps an angular rate ( declination and right ascension shift, e.g., per century).
But a significant consideration in the context of Centauri Dreams would be the tendency for stars to drift toward each other. Considering that technology such as ours falls short of reaching the nearest stars within many generations, then it is nearly as efficient to wait for a star to drift closer to our own. Technology for interstellar travel should at least advance above the threshold of random interstellar motions for this society, or perhaps another, to invest in such a measure seriously.
One qualification might be that life in an entire stellar system could be jeopardized by a stellar sized problem. Then it would be a survival question And that might launch life rafts in several directions. But we seldom take into consideration the
prospect of liviing entities similar to ourselves jumping from one star system to another because after millennia of civilization, as it were, “This is our chance!”
So, within a galaxy of billions of stars there would have to be some dependency on a civilization ( roughly speaking) stable enough to note the close approach of hospitable stars and planets and then taking the opportunity to make such a jump.
Alpha Centauri and neighbor looks pretty attractive from here, assuming it has planets, but we are living in an epoch when it would sure have helped if the system were less than a light year away. I don’t see any projections of passages for our system in the past or future ( 100,000 years) within that range. As for ten million years, well, possibly the proximity of some star would be even better than that.
This kind of conjecture assumes a lot of human psychology or features to a society that can sustain itself for millions of years, assuming they don’t use some other technological solution to go from one star to another – or have less wanderlust than we purport we have. But close passage of stars might have some impact on Drake equation speculations about the number of civilizations in the galaxy.
More likely in this way than stars actually colliding and knocking everybody out of the game.
@wdk
As you point out, there is little chance of another star approaching our system within 100,000 years. As we can already reach Proxima in less than 100,000 years with our chemically launched probes, why would we need to wait even that long? The other issue is, can we expect a civilization to last 100,000 years before collapse, perhaps permanently?
Over 4.5 by, there must have been many close approaches, but no technological species on Earth was able to take advantage of that.
Whether any civilization could make use of a close approach depends on the frequency of approach, the longevity of a civilization, and teh density of civilizations at any given moment. If civilizations are sparse over space and time, perhaps just a handful in the galaxy, then the probability of a technologically capable civilization having both the means and the timing of a close approach may be very low indeed. How dense would extant civilizations need to be in the galaxy to have a high probability of at least one being able to make use of the close approach?
Unless it turns out that there is some real [energy] barrier to travelling at several percent of c, then I would think that all interstellar travel will not benefit from close approaches. better to just leap into teh dark towards planets that look habitable, using whatever life extension cryosleep/generation/seed ship technology is available, depending on species’ biology [or machine intelligences].
As I have speculated in another thread, perhaps a more interesting question is whether natural panspermia might benefit from close approaches, especially if the outer icy_body/comet clouds intersect and exchange primaries. Life may then spread through teh galaxy irrespective of time or civilization longevity. On Earth, archaea and bacteria have been around for over 3.5 billion years. Eukaryotes have less time, but still billions of years. Wafted up into the upper atmosphere and transported by sunlight, or blasted into space on rocks, prokaryotes will potentially seed other planets and moons in the system, then icy bodies, as spores, able to survive millions of years as we now know, and therefore offering a potential reservoir of life to exchange stars and reach habitable planets in that neighboring system. To riff off Hoyle and Wickramasinghe [comet delivery of viruses], comets may be the delivery means to reach the inner, habitable zones, with their dusty tails and even broken up main body increasing the probability of a successful transfer of life.
Even with relatively few abiogenesis events, over time, the panspemia rate will increase as more stars become inhabited, until there is an exponential explosion of panspermia events dictated by the frequency of close encounters.
This is purely speculative, but I haven’t read of attempts to show the mathematics of such a process, with probabilities assigned to the various factors, much like the colonization models for star-faring species. I cannot be that difficult to model such a process. All I am aware of is the probability of panspermia from one system to another in a static galaxy, like bullets sprayed into the void, hitting a habitable target.
N.B. Unless Nielsen’s thought experiment on there being no habitable world anywhere else in the universe is a possible condition, then even Earth as the sole abiogenesis location may have seeded other stars since prokaryotes evolved that could survive various panspermia conditions.
Under the Anthropic Cosmological Principle, the physical constants of the Universe cannot hold values other than the values observed to a factor of 1 / 10**35 (one divided by 10 raised to the 35th power). Any deviation from their present values in excess of this number results in physical universes that are violently unstable and cannot host life.
Since the only stable universe that is physically possible also hosts life as a direct consequence of its most fundamental principles, is hugely implausible that earth hosts the only manifestation of that life. Such a statement shows an incomprehension of the timeless vastness and complexity of the universe we inhabit.
@imagtek
The logic is not correct.
This is usually stated as: “X is necessary for Y, but insufficient for Y.”
Concretely, “The constants as they are are necessary to allow life, but insufficient for the creation of life.”
We hope that there is nothing very special about Earth and our life, but we don’t know that for certain. A separate abiogenesis would support that hypothesis. But note that this is for abiogenesis. Life could be ubiquitous for another reason; [directed] panspermia. This will be hard to pick apart if we have examples of similar life from our system, and even with similar life we find on exoplanets elsewhere.
Comment *
Katie Mack evokes the ‘Planck wall’; Hubble’s constant or black energy and the effects of all that on our universe in his book.
what is fascinating is that we are in a balanced universe and indeed, a small constant more or less and we would not be…
https://www.astrokatie.com/book
We could find ourselves alone in the universe, and it is something to think about. Especially with how we are currently treating ourselves and the rest of the life on this planet. If life is extremely rare, then messing this planet up this badly would be beyond tragic.
But before we jump to the alone conclusion we really need more data. We’ve just started looking, and the fact that we aren’t receiving radio signals from other advanced civilizations within a hundred or so light years, just means there aren’t any at that level of technology in that range, trying to communicate with us, at this time. Just because ‘they’ haven’t colonized the entire galaxy/universe, and aren’t here on our planet (as far as we know), just means ‘they’ don’t exist, whoever we think those colonizers are. Neither of the above facts should lead us to think we are alone, neither one logically leads to the alone conclusion.
In the meantime, to get more data, we need boots on the ground on Mars for example, before concluding it is dead, and better instruments to examine the atmospheres of exoplanets before jumping to conclusions about life on the multitude of planets we are finding in the habitable zones of other stars. As soon as 2030 we should start getting some answers about some of the atmospheres, if they exist, on nearby planets. From this article:
https://www.universetoday.com/articles/the-telescope-that-will-study-our-nearest-exoplanet
“The RISTRETTO spectrograph, which will eventually be installed on the Very Large Telescope in Chile, represents a new approach to exoplanet observation. Rather than simply building bigger telescopes or better cameras, the team has developed sophisticated optical tricks to mask the star’s overwhelming brilliance and reveal the planets hiding in its glare.”
…
“With just 55 hours of observation time on the Very Large Telescope, the instrument should be able to detect Proxima b. With 85 hours, it could potentially identify signs of oxygen or water in the planet’s atmosphere.”
Let’s wait and see and be optimistic and hopeful about what could be found.
I remain an optimist and think that if the universe has a purpose, then life is it, and if it doesn’t have one, then life is still the result of all the processes and events that occur in it. Either way, I don’t think we are alone. It would sure be a waste if we somehow find out we are.