https://www.centauri-dreams.org/2025/02/21/setis-hard-steps-and-how-to-resolve-them/ Centauri Dreams * Home * About * Administrative * Booklist * Contact Select Page [ ] SETI's Hard Steps (and How to Resolve Them) by Paul Gilster | Feb 21, 2025 | Astrobiology and SETI | 24 comments The idea of life achieving a series of plateaus, each of which is a long and perilous slog, has serious implications for SETI. It was Brandon Carter, now at the Laboratoire Univers et Theories in Meudon, France, who proposed the notion of such 'hard steps' back in the early 1980s. Follow-up work by a number of authors, especially Frank Tipler and John Barrow (The Anthropic Cosmological Principle) has refined the concept and added to the steps Carter conceived. Since then, the idea that life might take a substantial amount of the lifetime of a star to emerge has bedeviled those who want to see a universe filled with technological civilizations. Each 'hard step' is unlikely in itself, and our existence depends upon our planet's having achieved all of them. Carter was motivated by the timing of our emergence, which we can round off at 4.6 billion years after the formation of our planet. He reasoned that the upper limit for habitability at Earth's surface is on the order of 5.6 billion years after Earth's formation, a suspicious fact - why would human origins require a time that approximates the extinction of the biosphere that supports us? He deduced from this that the average time for intelligent beings to emerge on a planet exceeds the lifespan of its biosphere. We are, in other words, a lucky species that squeezed in our development early. [carter] Image: Two highly influential physicists. Brandon Carter (right) sitting with Roy Kerr, who discovered the Einsteinian solution for a rotating black hole. Carter's own early work on black holes is highly regarded, although these days he seems primarily known for the 'hard steps' hypothesis. Credit: University of Canterbury (NZ). Figuring a G-class star like the Sun having a lifetime on the order of 10 billion years, most such stars would spawn planetary systems that never saw the evolution of intelligence, and perhaps not any form of life. Because an obvious hard step is abiogenesis, and although the universe seems stuffed with ingredients, we have no evidence yet of life anywhere else. The fact that it did happen here tells us nothing more than that, and until we dig out evidence of a 'second genesis,' perhaps here in our own Solar System inside an icy moon, or on Mars, we can form no firm conclusions. There's a readable overview of the 'hard steps' notion on The Conversation, and I'll direct you both to that as well as to the paper just out from the authors of the overview, which runs in Science Advances (citation below). In both, Penn State's Jason Wright and Jennifer Macalady collaborate with Daniel Brady Mills (Ludwig Maximilian University of Munich) and the University of Rochester's Adam Frank to describe such 'steps' as the development of eurkarytic cells - i.e., cells with nuclei. We humans are eukaryotes, so this hard step had to happen for us to be reading this. We could keep adding to the list of hard steps as the discussion has spun out over the past few decades, but it seems agreed that photosynthesis is a big one. The so-called 'Cambrian explosion' might be considered a hard step, since it involves sudden complexity, refinements to body parts of all kinds and specialized organs, and it happens quickly. And what of the emergence of consciousness itself? That's a big one, especially since we are a long way from explaining just what consciousness actually is, and how and even where it develops. Robin Hanson has used the hard steps concept to discuss 'filters' that separate basic lifeforms from complex technological societies. Whichever steps we choose, the idea of a series of highly improbable events leveraging each other on the road to intelligence and technology seems to make the chances of civilizations elsewhere remote. But let's pause right there. Wright and colleagues take note of the work of evolutionary biologist Geerat Vermeij (UC-Davis), who argues that our view of innovation through evolution is inescapably affected by information loss. Here's a bit on this from the new paper: Vermeij concluded that information loss over geologic time could explain the apparent uniqueness of ancient evolutionary innovations when (i) small clades [a clade comprises a founding ancestor and all of its descendants] that independently evolved the innovation in question go extinct, leaving no living descendants, and (ii) an ancient innovation evolved independently in two closely related lineages, or within a short period of time, and the genetic differences between these two lineages become "saturated" to the point where the lineages become genetically indistinguishable. In other words, as we examine life on early Earth, we have to reckon with incompleteness in our fossil record (huge gaps possible there), with species we know nothing about going extinct despite having achieved a hard step. The authors point out that if this is the case, then we can't really describe proposed hard steps as 'hard.' Other possibilities exist, including that innovations do happen only once, but they may be so powerful that creatures with a new evolutionary trait quickly change their environment so that other lineages of evolution don't have time to develop. [sun] Image: Earth's habitability is compromised by a Sun that will, about 5.6 billion years after its formation, become too hot to allow life. Image credit: Wikimedia Commons. We're still left with the question of why it has taken so much of the lifetime of the Sun to produce ourselves, a question that bothered Carter sufficiently in 1983 that it drove him to the hard steps analysis. Here the authors offer something Carter did not, an analysis of Earth's habitability over time. It's one that can change the outcome. For each of the hard steps sets up its own evolutionary requirements, and these could be met only as Earth's environment changed. Consider, for example, that 50 percent of our planet's history elapsed before modern eukaryotic cells had enough oxygen to thrive. So maybe our planet had to pass certain environmental thresholds: ...we raise the possibility that there are no hard steps (despite the appearance of major evolutionary singularities in the universal tree of life) (51) and that the broad pace of evolution on Earth is set by global-environmental processes operating on geologic timescales (i.e., billions of years) (30). Put differently, humans originated so "late" in Earth's history because the window of human habitability has only opened relatively recently in Earth history. Suppose abiogenesis is not a hard step. Biosignatures, then, should be common in planetary atmospheres, at least on planets like Earth that are geologically active, in the habitable zone of their stars, and have atmospheres involving nitrogen, carbon dioxide and water. If oxygenic photosynthesis is a hard step, then we'll find atmospheres that are low in oxygen, rich in methane and carbon dioxide and other ingredients of the atmosphere of the early Earth. If no hard steps exist at all, then we should find the full range of atmospheric types from early Earth (Archean) to present day (Phanerozoic). Our study of atmospheres will help us make the call on the very existence of hard steps. Given a lack of hard steps, if this model is correct, then the evolution of a biosphere appears more predictable as habitats emerge and evolve. That would offer us a different way of assessing Earth's past, but also imply that the same trends have emerged on other worlds like Earth. Our existence in that sense would imply that intelligent beings in other stellar systems are more probable than Carter believed. The paper is Mills et al., "Reassessment of the "hard-steps" model for the evolution of intelligent life," Science Advances. Vol. 11, Issue 7 (14 February 2025). Full text. Brandon Carter's famous paper on the hard steps is "The Anthropic Principle and its Implications for Biological Evolution." Philosophical Transactions of the Royal Society of London A 310 (1983), 347-363. Abstract. [tzf_img_post] 24 Comments 1. Ron S. on February 21, 2025 at 16:14 A wonderful example of the dangers of selection bias and extrapolation from a single, poorly quantified data point. It's useful for hypothesis generation and little else. Question: Is life rare or common? Answer: We don't know, and we should not be ashamed to say so. Need. More. Data. Reply + Henry Cordova on February 21, 2025 at 18:26 It's not just about life, or its supposed obstacles or barriers or filters. The same process must play a role in the development of a technology capable of extraplanetary communication. Our development of physics depended highly on the fact our atmosphere is transparent to most electromagnetic radiation, and we have evolved senses capable of detecting it. Most living things on earth don't even have eyes. Would an aquatic species have developed fire or the use of tools and the limbs needed to manipulate them? What about a planet with no glass? Do we need telescopes, microscopes, test tubes, helmet faceplates and portholes to conquer the universe? Could we have skipped the vacuum tube altogether? We can imagine a society that never developed the prism or the diffraction grating. Could such a community ever have invented spectroscopy? How important are spectra in the exploration of the structure of matter. Are there any substitutes? Could a highly advanced civilization without electricity ever develop radio telescopes or computers or spacecraft? If not, what are the alternatives? What does a highly advanced technology not highly dependent on "our" physics even look like? It seems remarkable that all the technologies required to communicate across interstellar space seem to have been developed over the last few centuries, a tiny speck of time in the history of life on this planet. How easy it would be to have missed it! Would some other branch of knowledge currently unknown to us have substituted for steam, electricity, nuclear, genetic, chemical techs. Do intelligent species NEED to duplicate all the same steps we negotiated successfully, or could they have substituted some other skill we aren't even aware of? "The ring cannot be destroyed... by any craft that we here possess. -Lord Elrond Reply o fred on February 23, 2025 at 17:03 @Henri >It seems remarkable that all the technologies required to communicate across interstellar space seem to have been developed over the last few centuries, Technology does not develop on its own (although we arrive with AI?) it is the human mind that has the ability to conceptualize for example after observation, then experimentation and even without: Einstein by math. It is our brains through its senses that makes relationships between things, produces the Idea that will then allow humans to shape their world according to what they want to have, which creates technology (H. Arendt) Thus, we direct our own destiny. Currently, it is obvious to note that our societies are increasingly "techno-centric" but lose in sensitivity: Very few of us are able to track game in the forest and our senses have long since not perceived terrestrial magnetic fields like pigeons. This raises a question: if life exists elsewhere it may have tried to contact us but NOT through the technological channel in which we have locked ourselves. We live in a four-dimensional space, but what if "they" live in an X-dimensional space without technology? Yes our planet can indeed be transparent and we may have invented the prism but it is "of no use" if - no pun intended - "they" are not on the same wavelength. I'm teasing just to try to think WITHOUT the technology. Life on earth generated technology, but fortunately technology never generated life (except in the stories of Mary Shelley and it was more a failure :D What is amazing is not this small time window that can be explained by a sequence of causes and effects and a dose of chance, but well the development of the human mind but does it unfold in the right way ? Reply 2. Alex Tolley on February 21, 2025 at 20:29 Douglas Adams had a more humorous version: "This is rather as if you imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in -- an interesting hole I find myself in -- fits me rather neatly, doesn't it? In fact it fits me staggeringly well, must have been made to have me in it!' This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, frantically hanging on to the notion that everything's going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for." -- Douglas Adams, The Salmon of Doubt: Hitchhiking the Galaxy One Last Time I cannot improve on Ron S's comment above. IMO, it is spot on. Reply + Eniac on February 21, 2025 at 23:11 The observation that seemingly singular evolutionary developments may not in fact be singular, but rather due to the extinction of all but one of many clades, is a profound one. One example of this is early human evolution. There were a variety of hominid species. Is taking up tools a hard step, or an inevitable consequence of evolution that happened only once simply because the first to do so clubbed all the others into extinction? The same question may be asked of all of the other supposed hard steps, such as the rise of Eukaryotes. But one hard step stands out: Absence of life implies absence of evolution, so abiogenesis is the one hard step that cannot be an inevitable consequence of evolution. Abiogenesis is the simultaneous bootstrapping of both life and evolution. Like all bootstrapping, it is truly a hard step. Reply o Alex Tolley on February 22, 2025 at 14:40 Abiogenesis is the simultaneous bootstrapping of both life and evolution. Like all bootstrapping, it is truly a hard step. We don't know that. When it was thought that life was only evident 3.5bya, this was evidence of a hard step, even if the late heavy bombardment was the cause of the late start after Earth formed. If the phylogenetic tree estimates for LUCA are correct and LUCA was present just 200my after the formation of the Earth which means that earlier life forms were even earlier, then abiogenesis may not be a "hard step", at least on Earth. If panspermia is the source of life on Earth, then we have no idea how hard it was for life to start, just that it may seed habitable worlds when available. Was it random or directed? We have no information about abiogenesis, just hypotheses and the assumption that it occurred on the early Earth. I am prepared to keep an open mind on this, even if I expect progress to be made on the mechanisms of abiogenesis on Earth. Reply + Ron S. on February 22, 2025 at 11:34 "Douglas Adams" One of my favorite authors. He left us too soon. Reply 3. Michael Sloboda on February 22, 2025 at 10:32 I don't want to be pessimistic, yet the Sun might be near the upper limit of a star which can avoid frying a habitable planet before intelligence arises. Hydrogent fuel increases linearly with mass, not a hard equation. Luminosity increase with mass to the 3.5 power. That's what I guess from playing at the data. Don't ask me why. So the available time decreases to the minus 2.5 power. The sun might last 5.6 Gyr before life ceases on earth. (Could we use 100,000 asteroid flybys to increase our orbital radius? - another topic.) Yet after 5.0 Gyr, in another 450 Myr, global warming my make non-polar regions too hot for large land life. Suppose a star has M = l.04. Take it to the 2.5 power = 1.103. Invert and multiply by 5 = 4.533 GY, almost exactly the age of Planet Earth. OK for that slightly more massive G1 star. Take an F7 (?) star, M = 1.2 and do the math. 5 divided by 1.577441 = 3.17 Gyr, not long enough, unless bacteria can evolve to mammals and birds in record time. I wish the math looked more optimistic. Reply + wdk on February 22, 2025 at 22:48 M,S., On the stellar lifetime vs. time for biological entities to achieve the hard steps: It might be some consolation to consider stellar lifetimes and luminosity predictable as you described, but the odds or duration for transition, say, from prokaryotic to eukaryotic cells not necessarily as predictable. We might be on a rock where it was lucky and quick, - or it might have been retarded either by chance or environmental conditions specific to Earth. The textbook description of planet formation, unless specifically aimed Earth, does not include a planetary collision which produces a huge moon and a process producing a magnetic field. Maybe it it was essential for something to arise, but maybe not. Possibly a pathway to multi-cellular organisms could have been achieved faster with less tumult. Reply 4. wdk on February 22, 2025 at 12:48 Arguably the diagram of the life and times of the sun grabs one's attention as much or more than the premise of hard steps. 1.1 billion more years and for Earth all life is likely over. Here we are at 4.6 billion out from Earth's birth and it was only 0.4 billion ago that moss substantially raised the level of Earth's free oxygen. Finger-pointing somewhere, I guess, but wasn't that an awful long time for our ancestors to waste in cladistic exercises? The one's lacking free oxygen in particular. "Hard steps" seems akin to lighting a campfire on a windy cold night with a small pack of matches. These days their packaging seems to make it difficult to get a good strike - and that is even more to the point. But we do have a few other solid worlds in this solar system further out and a boundless number of exoplanets, whether inhabited, inhabitable as is or not. So the 1.1 billion year mark is not necessarily a cap on human future, but one that might loom among many more immediate ones. Should we make it to one of those worlds and dig in, this event would disrupt the statistical model. The authors certainly would not mind. But should I point out that perhaps this has been done before somewhere or maybe many times? As to regards to "hard steps", in some sort of ascendence, it is a little unclear what the engaged are striving for - or should be. They might have some choice in the succession of steps. And we might be more lucky or less in ascendance than some. In application it looks a little like a game show where the audience (us) is cheering on a prokaryotic cell to take on another and rise to the status of eukaryotic so it can pick up a flag and head to the next level toward being like "us". A bias we would like to deny, but at least admit that it is more fun that way. One could argue that "hard steps" occur or occurred in a random search. But even at those early development points there might be other branches where we never meet the same outcome out there. Not that it is necessarily unsuccessful but entirely different. Say perhaps all the benefits we bestow on ourselves were allocated to something like trees. Not entirely surprising to s/f readers, but worth a moment's reflection when awaiting an interstellar contact radio broadcast. Perhaps even cellular life is a cul-de-sac for many opportunities in the universe. A form of life that is "organized energy" that can inhabit silicon, germanium or some successor semi-conductor medium might transport from one world to another more readily - and look on things like ourselves as middlemen for their own objectives. As observed earlier, in the form that we arrived in physically and adapted to life on Earth's land masses at atmospheric pressure, warmth and hydration, we can identify a number of discoveries and environmental properties that placed our species, as it were, on the threshold of space travel and communication, backed by how we adapted the planet's resources. And I agree that living on an ocean world ( or maybe in the depths of Jupiter or Saturn) would make knowledge or exploration of space more difficult. But then again, what if some creatures could rise to the upper atmospheric layers to observe their planet's belts and bands or its moons and the sun or whatever star - and that they had millions of years to work on the access? Musings as much inspired by the solar timeline as the idea of cladistic thresholds. Reply + wdk on February 22, 2025 at 17:25 Having submitted a reflection earlier, on further reflection on this way of looking at biological development and mentioning trees as an evolutionary outgrowth of the process - perhaps elsewhere, I should note that we do in fact have "trees" here on Earth. My mention of them in context might have suggested they were a wrong path or unnecessary. But such paths of development are not necessarily isolated or irrelevant. Whether elements introduced before or after, part of what becomes an integrated picture. And that starting with eukaryotic cells, trees were the result of threshold events too. And whether trees were confronted with a hard step or not, they are part of what makes our current existence possible. For the intelligent life to exist, at least in the sense that we see ourselves as individuals - a background or a stage full of other interacting forms of life is necessary. Even in writing this self correction, it does seem as though there are other ways that this hard step model might need more explanation or expansion. For since we as a thinking species looking to communicate with others among the stars, our existence is dependent on other living entities as well. Reply 5. Alex Tolley on February 22, 2025 at 16:06 The Science article is interesting as it shows the various different "hard steps" by different authors. But note Figure 1 that shows life at less than 3.5 bya which is based on fossil, but not phylogenetic evidence. A more distant emergence would invalidate the Carter method that makes abiogenesis a "hard step". More generally concerning "hard steps" the authors state: However, if the singular nature of these candidates is questionable, or can be explained without resorting to improbability, then support for the hard-steps model would be undermined. I like that they propose looking at biosignatures as a test of the possible hard steps. Lastly, figure 4 assumes humans cannot control the biosphere. We can certainly create O2 directly as needed, but more likely we could technologically keep Earth habitable for all life, extending the habitability far longer than the increased solar luminosity without intervention would suggest. If we created large habitats in space, we could maintain life even farther into the future, especially if we can migrate to different star systems. Whether this requires H. Sapiens or our biological and/ or machine descendants is not knowable. Reply 6. Abelard Lindsey on February 22, 2025 at 17:54 I believe the biggest hard step is the endosymbiosis of the Eukaryote. https://nick-lane.net/publications/energetics-genome-complexity/ This is why I think we are alone. Reply + Alex Tolley on February 22, 2025 at 22:50 Since chloroplasts are also endosymbionts, that implies that endosymbiosis is not a unique event and therefore not a "hard step" according to the various authors' definition. Admittedly only plants took this 2nd step, but it shows that mitochondrial endosymbiosis may not have been that hard. While I accept that mitochondria are a very important evolutionary step, the single-cell eukarya were around a long time before true complex, multicellular organisms evolved. While O2 levels would be important to animals, this is not so true of photosynthesizing plants. So why the delay? Is the evolution of complex organisms the "hard step"? If so, life in the universe will be mostly single-cell, whether prokaryote or eukaryote. We need data to determine this. Addendum: If the universe proves full of machines or artificial life, what would this imply? Reply o Abelard Lindsey on February 24, 2025 at 11:20 I actually emailed Nick Lane about the chloroplasts. He said that the endosymbiosis (hydrogen hypothesis) that resulted in mitochondria enabled the subsequent one that resulted in chloroplasts, The second required the first to happen and that the first was indeed a singularly rare event. So, yes, I do consider it to be the hard step. You said, "..single-cell eukarya were around a long time before true complex, multicellular organisms evolved.", which is evidence itself of it being a hard step. You also point out: "Addendum: If the universe proves full of machines or artificial life, what would this imply?" Of course. But so far we have not seen any evidence of this. Everywhere we look, it appears to be a barren universe (but full of resources and possibilities). We actually do think the single-celled life is common. But eukaryotic (complex) life is very rare. This is not such a bad scenario, you know. If we do get that warp drive, there should be plenty of planets available for terraforming and the discovery of the "deep Oxygen" suggests there may well be lots of habitable planets. There is a difference between habitability and a planet full of life. Reply # Alex Tolley on February 24, 2025 at 15:27 Thank you for the clarification on the chloroplast. I was unaware that mitochondria were needed for that second endosymbiotic step to occur. You said, "..single-cell eukarya were around a long time before true complex, multicellular organisms evolved.", which is evidence itself of it being a hard step. If eukarya were a hard step to evolve complex organisms, then why the delay in the evolution of complex animals? Would it not imply that the evolution of complex organisms was a hard step itself, possibly even a harder step? I am aware that prokaryotes and eukaryotes do form colonies, from bacterial biofilms to colonial organisms like Volvox, and even yeast cells can be induced to form colonies, but that is not close to coordinated cell differentiation in complex animals. However, it is clear that the far greater genome sizes of eukarya compared to prokarya are a requirement to allow for complex life to evolve. Therefore, whether or not the evolution of eukarya is a hard step or not, their evolution is a prerequisite for complex life. The idea of hard steps in evolution seems like seeing patterns in random data. If Gould's theory of "punctuated equilibrium" was true, every jump would be considered a "difficult step" if there was a long equilibrium period after it. We see the same thing in computer simulations where a random collection of the right "genes" will allow the objective function to reach a new, higher, adjacent peak of "fitness". Is this "hard" or just a feature of randomness finding the better configuration of inherited and new features in the fitness landscape that is rather jagged rather than a smooth hillclimb? IOW, is throwing 10 heads in coins "hard" or just a low-probability event that can occur at any time? Reply @ Abelard Lindsey on February 24, 2025 at 22:31 You should email Nick Lane with your questions as he does respond to intelligent emails. He's responded to mine. You can find his contact on his website. Reply 7. Edwin on February 23, 2025 at 0:41 Hi Paul Very interesting to hear your thoughts on this one Cheers Edwin Reply 8. Harold Shaw on February 23, 2025 at 14:26 The nonpareil rarity of endosymbiosis is a persistent myth. There are scores of examples with two examples leading to kingdoms of life. Endosymbiosis looks like a general tool of biology. There are also scores of examples of multicellularity emerging, including examples of it being induced in lab experiments. Another general tool of biology. Multicellularity is likely a necessary step towards complexity and if the Ediacran biota includes complex life, we have an example of complex lifeforms with body plans not represented in modern lifeforms. A possible second emergence of complex life. Imho, abiogenesis and complexity are two hard steps. The two examples of complex biota both appear after planet wide glaciation events. Cold water has higher viscosity making feeding more difficult for single celled organisms. Resource scarcity leads to multicellularity, it is how it was induced in lab experiments. Perhaps complexity required a planet wide lab where the control mechanisms for multicellularity were selected for and hardened. How common is this? I don't think life's earlier appearance on Earth is evidence that abiogenesis is easy but rather early Earth was an ideal environment. The Moon would have been closer and faster, whipping water around the Earth. How common are inter-tidal zones and did the Moon turn the Earth into a giant mixing bowl? I think the fluke of chemistry, implicit probability, rna first model of life is woefully inadequate. The early Earth would have been teeming with auto-catalytic metabolisms. A metabolism first model doesn't necessarily make abiogenesis more common than a rna first model. Set the threshold for metabolic complexity high enough and it could be equally rare but more robust. Heck, biology may even be a state of matter, and a quantum one at that. https://pubs.acs.org/doi/10.1021/acs.jpcb.3c07936 A third hard step could the intersection of high general intelligence and tool use. Intelligence looks like a general tool of complex biology, tool use less so. The intersection of the two has happened several times and most of our ancestors used tools. Reply 9. fred on February 23, 2025 at 16:17 A provocative idea, but not much talked about (?) : suppose we are the only life form that is currently developed in the universe. Life can develop elsewhere but "it awaits us". we are beings of conscience which leads us to question ourselves about the universe and to seek to know if we have neighbours...why not ? But do we consider a moment from a universal and mechanistic point of view not as a "specificity" (I know it will be hard :) but as a simple trigger element in the great mechanics of the universe that will allow "something else" other forms of life rather than nothing. if we, animals's humain, were only one step ; the first step ? if our existence was only there to create these "small" instabilities that put the universe in motion; if we were only the pebbles in the pond that will trigger something else rather than nothing? And if we were finally only one element in the chain that will bring other forms of life in a distant future either by our biological development or because we have this irresistible need to touch everything? We are the pebbles in the pond but the waves have not yet reached the shore that will fly away the butterfly... here's something that would surprise me ;) Reply + Henry Cordova on February 24, 2025 at 13:38 I follow your reasoning, although I'm not sure I agree with its conclusions. If there is indeed some 'force' (I use the term in its metaphysical sense, NOT referring to the physical quantity normally measured in units of "Joules") that drives the universe to higher and higher levels of complexity; then the development of advanced technological communities may be only an intermediary step in the propagation of life, or intelligence or complexity. Presumably, the result of this speculative 'force' may be the development of advanced technological species which can then develop technologies such as space travel, panspermia, alternate biochemistries, genetic engineering, artificial intelligence, von Neumann probes and so on. If this is indeed the case, then technological species like us may be just an intermediate step in the introduction of further complex structures or even consciousness into the universe. For example, AI may require biological entities to be developed, but once established may be capable of spreading and even evolving without the encouragement of us lowly carbon units. Did humanity evolve because biology was seeded here by ETI, or God, or because of some spooky 'force'? I suppose this sort architecture may indeed be part of the universe's initial programming, it certainly cannot be ruled out, but neither is there even the slightest bit of evidence to suggest it. Things may happen for a reason, but that does not necessarily mean they happen for a purpose. I do not believe in God, or any other supernatural agency for that matter. I concede I may be mistaken, but at least up to now, I have no reason to believe so. Reply o Mike Serfas on February 24, 2025 at 19:42 There is a widespread assumption of past causality - a belief I would call "religious" although it is often taken as a given by religious and atheist people alike, and though it doesn't seem very inspiring. The notion is that the time is like a half-built tower, the past fixed and immutable, the future open to any possibility and somehow "changeable" in some way other than waiting for it to happen. The consequence of this belief is that people conclude that Physics, or God, or Something, cared very deeply about the random vibrations after the Big Bang, but what happens in our day and age is for the most part random, and so it can't possibly represent any deep purpose of the cosmos. I don't think there is any basis in the math to back this up. It is just as easy to use physical laws to calculate the past as the future. If anything in the universe was part of a plan, it may well be us, right now, whether arising out of the strong anthropic principle or some more traditional creation myth; or it could be some future event toward which we are inexorably drawn. Reply 10. Mike Serfas on February 24, 2025 at 20:11 I think Abelard is right that there was something special about the first endosymbiotic event. Bear in mind that Earth life is divided into two main types of prokaryotes - the Bacteria and the Archaea. Though they look similar, they have different membrane lipids and different properties. For example, many types of Bacteria will get you sick, but no Archaea have never been proved to be pathogenic. Our type of life, the eukaryotes, is derived from one single merger of these two basic prokaryotes through endosymbiosis. From that point onward, any further endosymbiosis has been tinged by the preadaptation of the host: we can't say it would never have happened, but we don't know it would. One notion I've had for how life could be so rare, is what if an initial abiogenetic origin of life doesn't actually produce just two very different lineages that then need to join up to survive? What if a planet that develops from a local abiogenesis - what I'll call a "protospermic" planet - develops thousands of lineages comparable to Bacteria and Archaea, so that no matter what biochemical niche becomes available for life to exploit, there is always some small, fast-breeding prokaryote that can exploit it? What if our Earth is "deuterospermic", receiving just a few (perhaps two) complex life forms scattered from a protospermic biosphere, then having to make do with what those can work out together? Then our slow, fragile, oversized eukaryotic cells would have the chance to explore the adaptive landscape, where otherwise they could never have survived the competitive struggle. Reply 11. wdk on February 25, 2025 at 14:51 Reviewing the source and discussion so far, one can see how the notion of "hard steps" evolves before one's eyes as initially "simple", but trickier and trickier the longer it's observed. The introduction mentions events or steps that lead to a "higher plateau". One could interpret that geographically imagining resources or some kind of dimensional space which has properties much different from river valleys and fruited plains. Of course, there are consequences of transition from the prokaryote to the eukaryote. But FWIW it would appear that space in the cosmos and spaces in analytical geometry constructions are getting fused in the exploration in behalf of what is titled "search for extra terrestrial intelligence" or SETI. It would seem that there is a threshold for such communication, should it be two- sided. And our biology does seem to indicate some mileposts toward that possibility on both ends. Assuming the other side would be similar. But it is easy to slip into a mind-set where we assume that the dimensional space of hard steps is designed for such a purpose. As in s/f an alien might land its spacecraft in a world capital and explain a different ultimate purpose for such a space, albeit that the alien had arrived. Backing off from the biological somewhat, I remember the brief stir in 1977 when Ilya Prigonine won the Nobel Prize in Chemistry "for his contributions to non-equilibrium thermodynamics, particularly the theory of dissipative structures". This was associated with treating "life" as a phenomenon that acted in the reverse of the law of entropy. But if has not already included in the difficult steps concept, an acceptance speech pdf is available at https://www.nobelprize.org/uploads/2018/06/prigogine-lecture.pdf And that it might give some sort of leverage in this discussion. Reply Submit a Comment Cancel reply Your email address will not be published. Required fields are marked * [ ] [ ] [ ] [ ] [ ] [ ] [ ] Comment * [ ] Name * [ ] Email * [ ] Website [ ] [ ] Save my name, email, and website in this browser for the next time I comment. [Submit Comment] [ ] [ ] [ ] [ ] [ ] [ ] [ ] D[ ] Search [ ]Search Charter In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi). Now Reading [kepler5] Recent Posts * Ernst Opik and the Interstellar Idea * SETI's Hard Steps (and How to Resolve Them) * Pandora: Exoplanet Atmospheres via Smallsat * A Three-Dimensional Look at an Exoplanet Atmosphere * What Would Surprise You? * Pondering Life in an Alien Ocean * Putting AI to Work on Technosignatures * Quantifying the Chances of a Technosignature On Comments If you'd like to submit a comment for possible publication on Centauri Dreams, I will be glad to consider it. The primary criterion is that comments contribute meaningfully to the debate. Among other criteria for selection: Comments must be on topic, directly related to the post in question, must use appropriate language, and must not be abusive to others. Civility counts. In addition, a valid email address is required for a comment to be considered. Centauri Dreams is emphatically not a soapbox for political or religious views submitted by individuals or organizations. A long form of the policy can be viewed on the Administrative page. The short form is this: If your comment is not on topic and respectful to others, I'm probably not going to run it. Follow with RSS or E-Mail RSS Follow by Email Follow by E-Mail Get new posts by email: [ ] [Subscribe] Advanced Propulsion Research Beginning and End Exoplanet Projects (Earth) * AFOE * Amateur Exoplanet Archive * Anglo-Australian Planet Search * APACHE Project * ASTEP: Antarctic Search for Transiting Extrasolar Planets * ASTRA * Astro Gregas * Atacama Large Millimetre Array * Automated Planet Finder * Berlin Exoplanet Search Telescope * California & Carnegie Planet Search * Carl Sagan Institute (Cornell) * CARMENES * Carnegie Astrometric Planet Search * CBA Belgium Observatory * CHIRON * CLEVER Planets * CODEX * Colossus * Coralie * DayNight * DEMONEX (DEdicated MONitor of EXotransits) * Dispersed Matter Planet Project * East Asian Planet Search Network * Elodie * ESO Coude Echelle Spectrometer * ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) * European Extremely Large Telescope * Evryscope * Exoplanet Tracker * Externally Dispersed Interferometry * Fabra-ROA * GAPS (Global Architecture of Planetary Systems) * Gemini Planet Imager * GEMSS: Global Exoplanet M-dwarf Search-Survey * Geneva Extrasolar Planet Search * Habitable Zone Planet Finder * HARPS North * HARPS-N * HATNet Exoplanet Survey * High Accuracy Radial velocity Planetary Search * Hobby-Eberly Telescope * Italian Search for Extraterrestrial Life * ITASEL * Keck Interferometer * Keck Planet Finder * KELT North * KELT South * KMTNet (Korea Microlensing Telescope Network) * KOBE: K-dwarfs Orbited By habitable Exoplanets * Large Binocular Telescope * Las Cumbres Global Telescope Network * Low Frequency Array * LYOT Project * MACHO * Magdalena Ridge Optical Interferometer * Magellan Telescope * MARVELS * MARVELS (Multi-object APO Radial Velocity Exoplanet Large-area Survey) * MASCARA * Maunakea Spectroscopic Explorer * McDonald Observatory * MEarth * METIS (Mid-Infrared E-ELT Imager and Spectrograph) * MicroFUN Microlensing Follow-Up Network * Microlensing Planet Search Project * MINERVA (MINiature Exoplanet Radial Velocity Array) * MOA * MONET * N2K * Nancay Decametric Search * NEAR * NEID Spectrograph * New Mexico Exoplanet Spectroscopic Survey Instrument * NGTS (Next-Generation Transit Survey) * NIRPS (Near Infrared Planet Searcher) * Okayama Planet Search Program * Optical Gravitational Lensing Experiment * OWL * PARAS (PRL Advanced Radial-velocity Allsky Search) * Permanent All Sky Survey * PHASES * PIRATE (Physics Innovations Robotic Astronomical Telescope Explorer) * PISCES (Planets in Stellar Clusters Extensive Search) * PLANET * PLANETS * PRIMA-DDL * Project 1640 * QES (Qatar Exoplanet Survey) * Radio Interferometric Planet Search * RoboNet (Microlensing) * SAINT-EX * Search for Trojan Extrasolar Planets * SEEDS (Subaru Strategic Exploration of Exoplanets and Disks) * SHINE * Solaris * Sophie * Spectrashift * SPECULOOS * SPHERE * SPOTS: (Search for Planets Orbiting Two Stars * Square Kilometer Array * STARE * STELLA * SuperWASP * Systemic * Tennessee Automatic Photoelectric Telescope * TEP * Thirty Meter Telescope * TransitSearch * Transitsearch * TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) * TrES: The Transatlantic Exoplanet Survey * TRESCA Project * United Kingdom Infrared Telescope * University of St. Andrews Planet Search * UNSWEPS Project * UVES * Very Large Telescope Interferometer * VIDA * WASP (Wide Angle Search for Planets) * WHAT * XO Project Exoplanet Projects (Space) * ACEsat * Aragoscope * ARIEL: (Atmospheric Remote-Sensing Infrared Exoplanet Large-survey) * ASTERIA * Astro-1 * ATLAST (Advanced Technology Large-Aperture Space Telescope) * CHEOPS - CHaracterising ExOPlanet Satellite * CoRoT * CubeSat * Darwin * Dual Use Exoplanet Telescope * ECHO (Exoplanet Characterization Observatory) * Eddington * EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) * Euclid * EXCEDE * ExoplanetSat CubeSat * FINESSE * Gaia * GEST * HabEx * HEK (Hunt for Exomoons with Kepler) * High Etendue Multiple Object Spectrographic Telescope (THE MOST) * High-Definition Space Telescope * HST Astrometry * James Webb Space Telescope * Kepler * Kilometer Space Telescope * Laser Interferometer Space Antenna * LISE Hypertelescope * LUVOIR * MOST (Microvariability and Oscillations of STars) * Nancy Grace Roman Space Telescope * NEAT * New Worlds Imager * Origins Billion Star Survey * Origins Space Telescope * Pegase * Planet Imaging Concept Testbed * Plato * PlaVi (PlanetVision) * Project Blue * SISTINE * Space Interferometry Mission * SPICES (Spectro-Polarimetric Imaging and Characterization of Exo-planetary Systems) * Spitzer Space Telescope * SUPER-SHARP * SWEEPS * Terrestrial Planet Finder * TESS (Transiting Exoplanet Survey Satellite) * TOLIMAN * Twinkle * UMBRAS Further Astronomical and Astronautical Resources * 100 Year Starship * Acta Astronautica * ADS Abstract Service * Alternative Earths Astrobiology Center * American Astronomical Society * American Geophysical Union * American Institute of Aeronautics and Astronautics * astro-ph preprint server * AstroArt of David A. Hardy * AstroBetter * Astrobiology Magazine * Astrobites * Astrometry.net * Astronautics Now * Astronomical Journal * Astronomy & Astrophysics * Astronomy Picture of the Day * Astrophysical Journal * Beyond NERVA * British Interplanetary Society * Bulletin of the American Astronomical Society * Cosmic Ancestry * Division for Planetary Sciences * European Federation of Biophysics * Event Horizon Telescope * Exoplanet Transit Database * Exploring the Universe with Andrew Fraknoi * Extrasolar Planets and Astrobiology * Extrasolar Planets Encyclopedia * Galaxy Forum * Galileo Project * Google Scholar * Icarus Interstellar * Institute for Interstellar Studies * Interstellar Journey * Interstellar Research Centre * Interstellar Studies Bibliography * James Benford * L'Institut de l'Information Scientifique et Technique * Lunar and Planetary Institute * Meteoritics and Planetary Science * NASA Technical Reports Server * Nature * Orbital Index * Orbital Index * Overview Institute * Physics * Planetary and Life Science Community Meetings Calendar * Planetary and Space Science * Principium (Journal of I4IS) * ResearchGATE * RocketSTEM * Science * Scitizen * SDSS SkyServer * SETI News * SFSU Exoplanet Group * SIMBAD Astronomical Database * Space Agenda * Space Sailing * Space Telescope Science Institute * Space Transport and Engineering Methods * spaceweather.com * The neighborhood * Trans-Neptunian Automated Occultation Survey * Troy Project Weblogs, Discussions, Commentaries * Adam Crowl (Crowlspace) * Airminded * Alien Life * Ancient Solar System * Antimatter * Apparent Brightness * AstroBlog * AstroEngine.com * Astrogator's Logs (Athena Andreadis) * Astronautical Evolution * Astronomist * Astronomy Blog * Astronomy.com Blog * astroPT * Astroquizzical * Asymptotia * Atlas of the Universe * B612 Foundation * Bad Astronomy * Beyond Earthly Skies * Beyond Impossible * Billion Year Plan * Buran Space Shuttle * Captain Interstellar (Paul Titze) * Celestial Matters * Cheap Astronomy * Cocktail Party Physics * collectSPACE * Colony Worlds * Comets & Asteroids: Small Bodies of the Solar System * Cosmic Diary * Cosmic Mirror * Cosmic Tusk * Cosmic Variance * Cosmic Visions * CosmoCoffee * Cumbrian Sky * Dad2059 * Deep Sky Blog * Dialogos of Eide * Dick's Rocket Dungeon * Dragon's Gaze * Dream of the Open Channel * Dreams of Space - Books and Ephemera * Dreams of Space: Books and Ephemera * Drew Ex Machina (Andrew LePage) * DSFP's Spaceflight History Blog * Dynamics of Cats * Eternos Aprendizes * Eureka * Eureka (Daniel Marin) * Ex Space * ExoClimes.com * Exoplanetology * Exoplanets Channel * Extrasolar Visions II * Final Frontier * Finding Pluto * Flank Speed * Fly Me to the Moon * Fraknoi's Universe * Future & Cosmos * Future Incredible * Future Planetary Exploration * Futurismic * Galactic Journey * Gregory Benford * Habitable Worlds * Habitable Zone * Hop's Blog * Il Tredicesimo Cavaliere * In the Dark (Peter Coles) * Innovation Watch * Innumerable Worlds * Invitation to ETI * Isaac Arthur (videos) * James Essig * James Randi Educational Foundation Forum * Jatan's Space * John Cleary Creations * Jon Lomberg * Kentucky Space * Know the Cosmos * Last Word on Nothing * Laurel's Pluto Blog * Leonard David's Inside Outer Space * Letters to Nature * Lifeboat Foundation * Lone Mind * Long Bets Foundation * Long Now Foundation * Lost in Transits * Magellan AO * Many Worlds (Marc Kaufman) * Martian Chronicles * Meridiani Journal * Music of the Spheres * Nano Age * NASA Watch * NASA-UC Eta-Earth Survey * New Papyrus * Next Big Future * NGTS (Next-Generation Transit Survey) * On the Path to Space * One-Minute Astronomer * OrbitalHub * Orion's Arm * Our Universe in 202 Notations * Out of the Cradle * Overcoming Bias (Robin Hanson) * Patrick McCray * peregrinus interstellar * PHASES (Palomar High-precision Astrometric Search for Exoplanet Systems) * Physics arXiv Blog * PI Club * Planet/Planet * PLANETPLANET (Sean Raymond) * Polymath (Robert Clark) * Posthuman Blues * Potentia Tenebras Repellendi * Profiles of Our Future in Space * Project Icarus Weblog * Project Rho (Winchell Chung) * Quasar9 * Real Science * Remote Central * Rick Costello Space Art * Riding with Robots * Robot Explorers * Robot Guy * Rymden i Dag * Science Meets Fiction * Science News * SciTech Journal * Scitizen * Simostronomy * Singularity Institute * Slacker Astronomy * SolStation * Sorting Out Science * Space Archaeology * Space Elevator Blog * Space FTW * Space Law Probe * Space Pragmatism * Space Review * Space Transport News * Space Travel Blog UT Tartu Observatory * Spaceflight History * Spacewriter's Ramblings * Stan Erickson's Alien Civilization Blog * Star Bright? * Star Stryder * Starts with a Bang * Strange Paths * Sufficiently Advanced * Supernova Condensate * This Is Rocket Science * This Week's Finds in Mathematical Physics * Tiny Mantras * Titan Exploration * Tom Barclay/Planet Hunter * Tomorrow Is Here * Trevor Paglen * Ultratech Memes * Universe Today * Unmanned Spaceflight * Velcro City Tourist Board * Visions 2200 * Visual Astronomy * Visualizing Science * Wanderingspace * Watered Down Physics * Where's The Flux (Tabby's Star) * Will Gater * Woodward Effect * Worlds of David Darling * Wow! Signal Podcast * Written Worlds Archives * 2025 (15) * 2024 (96) * 2023 (102) * 2022 (104) * 2021 (181) * 2020 (188) * 2019 (191) * 2018 (225) * 2017 (235) * 2016 (237) * 2015 (247) * 2014 (242) * 2013 (232) * 2012 (251) * 2011 (244) * 2010 (268) * 2009 (275) * 2008 (314) * 2007 (382) * 2006 (327) * 2005 (330) * 2004 (131) Copyright (c) 2023 Centauri Dreams. All Rights Reserved.