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Toward An Archaeology of Exo-Civilizations

Light of the Stars: Alien Worlds and the Fate of the Earth, by Adam Frank. W.W. Norton & Co. (2018), 272 pp.

Although he has published several previous books and is well represented in the technical literature, Adam Frank (University of Rochester) found himself suddenly thrust onto the public stage with an op-ed he wrote in the New York Times in 2016. Chosen by the paper’s editors, the title “Yes, There Have Been Aliens” injected a certainty Frank didn’t intend, but it brought up an intriguing point: We may not know whether other technological civilizations exist now, but the odds are exceedingly good that at some point, somewhere, they once did.

Frank and colleague Woody Sullivan had written the original idea up for Astrobiology, the result of their pondering how exoplanet data now streaming in could be used to refine the original Drake equation, which sets up the factors thought to determine the prevalence of technological societies in the universe. In his new book Light of the Stars, Frank explains by way of background that the duo realized they needed to change Drake’s focus by removing the question of the average lifetime of such a culture.

For the time being, then, the L factor that Drake used to cover the average lifetime of a technological civilization would be ignored (though it permeates the book in ways we’ll soon see). For now, let’s look at what our exoplanet data are telling us. For thanks to missions like Kepler and the effort going into other planet hunting methods from radial velocity to gravitational microlensing, we’re learning how to answer the astronomical terms in the Drake equation.

Ponder: We have a good read on the number of stars with planets, something Drake couldn’t have known in his early formulation (the value is now thought to be about 1, meaning just about every star we can see will have at least one planet). We can also begin to make estimates of the number of habitable zone planets around each star, another factor in the Drake equation, and Frank goes with the figure of one in five stars hosting a planet with a chance for life as we know it. That means planets with liquid water on their surface, the classic habitable zone definition.

Frank and Sullivan chose to re-write the Drake equation with the new values incorporated but without reference to L. They pursued the probability that humans might be the only civilization the universe has yet produced. Their answer: 10-22, which means one in ten billion trillion. The number identified what the author calls ‘the pessimism line.’ From the book:

To understand how to think about the pessimism line, imagine you were handed a very big bag of Goldilocks-zone planets. Our results say the only way human beings are unique as a civilization-building species would be if you pulled out ten billion trillion planets and not one of them had a civilization. That’s because Kepler has shown us that there must be ten billion trillion Goldilocks-zone planets in the universe. So the pessimism line is really telling us how bad the probability of a civilization forming would have to be in order for ours to be [the] only one that has ever existed.

Image: Astrophysicist and author Adam Frank. Credit: University of Rochester.

So while we can’t know how many civilizations exist right now, which was the Drake question (the relevance to SETI is obvious), we can get a sense for the odds that somewhere, somewhen, civilization has formed. As the author points out, your chance of being killed by lightning in any given year is about one in ten million. And that would be a thousand trillion times more likely than our species being the only civilization in the history of the cosmos.

You can see why this caught the attention of journalists and the public at large. We’ve looked at Frank’s work quite a few times on Centauri Dreams, as a look through the archives will show (the best place to start is probably Perspectives on Cosmic Archaeology). A criticism Frank addresses straightforwardly in the book is the obvious one: We have no information on the odds for abiogenesis itself, without which we can’t rule out the prospect that we are alone in the universe. Likewise we have no data on how likely intelligence is to develop once life has begun. We are dealing here solely in terms of probabilities, and probability is not proof.

Even so, these probabilities really are striking. The passages in Light of the Stars covering this work are among the most compelling in the book. Frank compares the one in ten billion trillion number to the pessimistic predictions of others who have addressed the probability of intelligent life arising. Ernst Mayr, for example, ruled it out because while he believed life could be common, only one of approximately 50 billion species that have existed on Earth had produced a civilization. But even given Mayr’s strictures, the sheer number of stars and planets implies at least 10 million high-tech civilizations have at some point developed somewhere.

The universe has had plenty of time and opportunity, in other words, to produce civilizations. Combine that with the fact that we have begun to understand, through our missions to other planets in our own Solar System, something about how planets grow and change over time. Thus the challenges we face in our own anthropocene era as we adapt our civilization to the planet around us and inescapably cause change to it — as all life has done — have likely been faced by many cultures, who have either found a way to make civilization an enduring process or have succumbed to planetary catastrophe driven by their growing demands for energy.

Life and Planetary Evolution

Life itself is a game-changer for planetary environments, operating on our world long before humans emerged. The single-celled organisms of the Archaean eon so early in the history of our planet would gradually have to cope with photosynthetic organisms. Eventually cyanobacteria began producing huge amounts of oxygen in what is known as the Great Oxidation Event. The sharp increase in atmospheric oxygen proved poisonous to pre-existing life but also allowed the evolution of creatures with far more interesting metabolisms.

So, what does the GOE, with all its power and reach, teach us about the Anthropocene? It demonstrates that life is not an afterthought in the planet’s evolution. It didn’t just show up on Earth and go along for the ride. The GOE makes it clear that, at an earlier point in Earth’s history, life fully and completely changed the course of planetary evolution. It shows us that what we are doing today in driving the Anthropocene is neither novel nor unprecedented. But it also tells us that changing the planet may not work out well for the specific forms of life that caused the change. The oxygen-producing (but non-oxygen-breathing) bacteria were forced off the Earth’s surface by their own activity in the GOE.

What Frank would like to arrive at is a ‘theoretical archaeology of exo-civilizations,’ a goal that seems philosophical at best, but one which can be interestingly modeled through computer simulations. The Second Law of Thermodynamics gives us insights into the feedbacks that energy use and the production of waste have on planetary systems. Frank would like to model young civilizations using combustion, wind and tidal power, geothermal methods, solar energy and nuclear in a huge variety of planetary environments to calculate the planetary impact.

A planet that lives close to the inner edge of its habitable zone might be so highly sensitive to runaway greenhouse warming that its civilization barely has time to progress before it faces its own version of the Anthropocene and collapses. Another world, farther out from its star, may be less sensitive to planetary change but have a civilization that refuses to recognize the change until the die-off has already begun. A different species on a different world could manage to build its project of civilization using only lower-impact forms of energy and make a gentle soft landing to a sustainable state that lasts thousands of millennia.

Now you can see how we circle back around to Drake’s final factor, L. It was useful for SETI because it helped to define the odds of discovering a currently existing civilization through our various methods of detection. But if we can develop simulated histories for hundreds of thousands of exoplanets in order to tweak the parameters of their civilizational responses to the changes they create on their home worlds, we can calculate an average civilization lifetime.

Frank sees this discussion as leading beyond this early research to increasingly realistic models fed by exoplanet studies, models that can be run for as many iterations as needed to simulate the possible trajectories of a vast number of worlds. These models can give us a sense for likelihoods that can have relevance to our own civilization’s future as we grapple with what must be universal issues of energy use and the inexorable scaffolding of thermodynamics. Don’t spend much time looking for a way around the Second Law of Thermodynamics, Frank advises. Most likely it’s simply ‘baked into the structure of the universe.’

Frank is thus calling for the development of a roadmap for civilizations to rise to Nikolai Kardashev’s Type 1 classification, meaning a society capable of capturing all the light energy reaching its planet from the host star, and perhaps, having survived this journey, able to rise even higher up the Kardashev scale. That scale, first presented at a famous meeting in Byurakan Observatory in Armenia, is another piece of the history of astrobiology that Frank examines in Light of the Stars, presenting a useful backgrounder for anyone hoping to discover how our views of the interactions between technology and our planet have been understood over time.

Drawing on the findings of the space program and exoplanetary research, Frank presents the Earth as one more example of a planet that needs to be understood as a tightly coupled system. Our civilization presents our world with only the latest of its challenges. The book is an eloquent call for harnessing our mathematical tools coupled with an exoplanet data influx to gain insight into our own transition to a stable pattern of growth. That pattern, if we assume ever increasing energy use, could well take a culture like ours off planet and into its local stellar system.


Comments on this entry are closed.

  • jonW August 7, 2018, 13:08

    There’s nothing more fun to daydream about (well, nothing G-rated, anyway) than what other forms life may take and how much of it is out there. Hey, isn’t Kardashev Type 1 a civilisation that makes use of all the energy reaching its planet? One that captures *all* the light energy of its parent star is Type II, no?

    • Paul Gilster August 7, 2018, 13:53

      Good catch. Sorry I misspoke re Type 1. Now fixed.

  • Gary Wilson August 7, 2018, 13:18

    We will never know whether other civilizations “currently” exist beyond a few hundred light years from earth unless we assume some faster than light signal is discovered emanating from them. Currently is a meaningless term for this kind of search. Even within a few hundred light years we won’t know if they have continued to survive.
    As for the “interaction” between our civilization and the earth and its ecosystems, it is rapidly becoming more of a head on collision. The latest report from the National Academy of Sciences points that out yet again. We are now at a very important decision point whether most humans know it or not. Decisions made now by all of earth’s governments will to a great extent determine whether we become one of the universe’s extinct civilizations.

    • Wojciech J August 8, 2018, 4:46

      Observations through telescopes using gravity lensing and other designs could allow us to detect other, further civilizations if they exist.
      As to global warming, it isn’t a threat to our civilization.Some areas will face disaster, but others will thrive.
      Most of developed world will see improved living conditions and agriculture.

    • Brad in Dallas August 8, 2018, 19:03

      Well, think of this discussion as a backgrounder for programmimg the artificial intelligences that will inherit the earth after we make it uninhabitable for organic life, and who will no doubt seek the answers to the Drake equation questions we posed in our dying decades.

  • Thomas R Mazanec August 7, 2018, 13:38

    Will the simulation cover the possibility that someone other than Stanislav Petrov is on duty 26 September 1983?
    From Wikipedia: in a 2013 interview, Petrov said at the time he was never sure that the alarm was erroneous. He felt that his civilian training helped him make the right decision. He said that his colleagues were all professional soldiers with purely military training and, following instructions, would have reported a missile strike if they had been on his shift.[2]

    • Wojciech J August 8, 2018, 4:37

      A nuclear exchange between Soviets and USA wouldn’t result in end of our civilization, but shift towards Southern Hemisphere and possibly stunted growth for century or two.
      It is even doubtful that USA and Soviets would cease to exist.

      • ljk August 17, 2018, 9:09

        “Mr. President, I’m not saying we wouldn’t get our hair mussed. But I do say no more than ten to twenty million killed, tops. Uh, depending on the breaks.”

        – General “Buck” Turgidson in Dr. Strangelove (1064). Based on real theoretical studies of how a nuclear conflict might still be “winnable” by its combatants.

  • Bob Steinke August 7, 2018, 13:43

    “We may not know whether other technological civilizations exist now, but the odds are exceedingly good that at some point, somewhere, they once did.”

    Nope, we don’t know anything of the kind.

    “That’s because Kepler has shown us that there must be ten billion trillion Goldilocks-zone planets in the universe.”

    Yes, we now have a good evidence-based estimate of this value.

    “A criticism Frank addresses straightforwardly in the book is the obvious one: We have no information on the odds for abiogenesis itself”

    Exactly. The odds against abiogenesis could be ten-billion-trillion-quadrillion-googleplex.

    “They pursued the probability that humans might be the only civilization the universe has yet produced. Their answer: 10^-22, which means one in ten billion trillion. The number identified what the author calls ‘the pessimism line.’”

    So this seems like a logical fallacy to me. What we can say is that IF the chances of a complex civilization arising on a habitable planet are better than 10^-22 THEN we are likely not the only civilization that has arisen. However, this is a different statement than “The chance we are not the only civilization that has arisen is 10^-22.”

    Someone may have an opinion on what the chances are of life arising on a habitable planet, but it’s just an opinion. We have no evidence-based estimate of this probability.

    I haven’t read the book so I don’t know if this fallacy occurred in the book or if it was a misinterpretation of the book’s intent by the author of this article.

    • Ron S. August 7, 2018, 15:59

      “The odds against abiogenesis could be ten-billion-trillion-quadrillion-googleplex.”

      That would be a difficult hypothesis to justify. When you combine the diversity of planets, stars, etc. with the probability of abiogenesis you ought to come up with a (statistical expected value) EV ~ 1, give or take an order or magnitude or two. After all, we are here. With such an EV it is indeed very probable that we are either not alone or we had (or will have) neighbors.

      You are arguing with your hypothetical probability for abiogenesis that EV ~ 0. That does a poor job of explaining our existence. Unless you’re arguing for the strong anthropic principle to avoid the statistical implausibility of your hypothesis. But that has its own difficulties and is not widely accepted.

      • Astronist August 7, 2018, 19:50

        “With such an EV it is indeed very probable that we are either not alone or we had (or will have) neighbors.” – But the statistical reasoning contains no information at all as to whether this particular civilisation here on Earth at present is the first to appear. In a universe of finite age there must by logical necessity be a first civilisation, and only observation can identify which it is.

        • Ron S. August 8, 2018, 9:59

          Well, yes, I never claimed that. We are dealing with probabilities based on a tiny data set. Therefore as of today the statistics can only tell us that the likelihood is good that there are, were or will be ETI. We can do better when/if we have more empirical data.

      • Bob Steinke August 8, 2018, 14:04

        I’m not really arguing that the odds against abiogenesis ARE ten-billion-trillion-quadrillion-googleplex. I’m just saying that we can’t rule out the possibility that something unlikely happened. The weak anthropic principle would explain why observers find themselves on the one planet that had the unlikely occurrence of developing observers.

        As far as the argument that the expected value of number of civilizations shouldn’t be too far below one or even our existence would have been unlikely, I’m not sure about that. I guess I don’t have the statistics background to know for sure, but I remember that with one data point you can’t make any estimate of standard deviation so if something unlikely could have happened, can you really put a bound on how unlikely it could have been with one data point?

        • Bob Steinke August 8, 2018, 14:10

          To put it another way, wouldn’t your confidence interval be plus or minus infinity?

        • Ron S. August 8, 2018, 21:49

          Not to worry, I didn’t take your number literally. However it is an important point. Another is that statistics is a tool for dealing with incomplete knowledge, that is, uncertainty, those values of probability in the open interval (0, 1).

          We exist. That’s a fact we can agree on. Another we should be able to agree on is the universality of physics: the same laws apply everywhere in the universe at all times (throughout our spacetime).

          The probability of ETI arising on a planet (I include us in the definition) is some function F of many variables, whatever those may be. There is a non-zero EV, which should be clear. That the EV is unlikely to be <<1 because otherwise the existing of even 1 ETI becomes unlikely. Since we are here the EV is, let's say, 0.001 on the low side and unknowable on the high side, but could be much larger than 1. Make it too high and Fermi starts rolling in his grave, but that's okay since his opinion is not data.

          The thing is, since F applies everywhere (and everywhen) and the EV is not uncomfortably tiny there is a pdf (probability distribution function) that peaks at EV that statistically predicts how many ETI did/do/will exist. It is not a delta function, which is what you'd need to state with confidence that we and only we did/do/will exist. (Sorry about the tenses, but we know that EV in every 'now' is a function of cosmological time.)

          Your point about confidence interval is correct. In fact for such a sparse data set the variance (square of standard deviation) is typically equal to the EV. You can therefore say the confidence interval is between 0 and 2.

          That is not terribly informative so I suggest it is more useful to think about that indefinite pdf not being a delta function, which tells us that since we exist the existence of one additional ETI has a probability of similar order to our existence.

          Again, these are probabilities, not data, and can only serve as a way to think about the problem in the face of little data. But the data we do have — our existence and physics — set constraints on ETI quantity range that are very, very real.

    • Ronald August 8, 2018, 7:36

      Well, that is not entirely right. Life arose remarkably quickly on Earth. While that does not offer a guarantee, it is valid to consider this telling and even use this ‘temporal indicator’ as a proxy for ‘chance for abiogenesis’, even on a cosmic scale. After all, we now know that small terrestrial planets are ubiquitous, as are solar type stars, water and all essential elements and physical conditions. The laws of nature as well as ‘matter as we know it’ are universal.
      So, it is indeed valid to state that at least primitive life is probably common.
      Technologically intelligent life is another matter, see below.

  • RobertL August 7, 2018, 14:00

    There are anthropocentric assumptions built in to the Drake equation and expressions like “technological civilisation” to the effect that all life aspires to scientific knowledge and the leveraging of that knowledge into transportation and power: calculate pi, build a spaceship, conquer space. Bower birds might think that all life aspires to better bower – building, and it isn’t as obvious as it is taken to be that we are right and they are wrong. Maths and physics are eternal and immutable, ok, so we are more likely to converge on the value of pi than on what constitutes a really classy bower. On the other hand what does knowing math and physics actually entail? We just have an imperfect grasp of some aspects of them and can produce crude models of some aspects of them, but that is not necessarily to say we have done anything more interesting and fundamental than a mynah bird that’s been taught to say e=mc^. As for travel and conquest, neither of those activities is fundamental to life either. They might just be ape things. People who think about the Drake equation are almost all scientists and definitely all apes, and their tacit assumption that their scientific ape concerns must necessarily be the omega points to which all life must ultimately aspire, must be tested for partiality.

    • Spaceman August 7, 2018, 15:05

      I vaguely remember the term ‘omega point’, but I cannot remember its meaning. What is the omega point, thanks?

      • RobertL August 7, 2018, 16:11

        In the mystical system of Teilhard de Chardin, it is the end result to which Christianity and evolution are intentionally tending – a divine unification of everything. I was using it loosely as an analogy for the apparent belief that technological excellence is a uniquely privileged endpoint of life and that its failure to arise, given the existence of alien life, would be a disturbing paradox, rather than just happenstance.

        • ljk August 17, 2018, 9:39

          Teilhard de Chardin was trying to reconcile his Roman Catholic faith with Twentieth Century science. He was also a Jesuit who did extensive paleontological field work on early human studies.

          de Chardin may be ultimately proven wrong, but the man was trying to work in two very different worlds that co-exist whether people like it or not. So many others just dismiss one side or the other and that can be just as fatal a mistake if not worse.

          And are we not working as a species towards some kind of technological utopia, whether we believe there is a God or not? The Singularity is still in fashion, is it not?

    • Geoffrey August 7, 2018, 20:26

      The equation was proposed to speculate about the likelihood of other communicative civilizations and should not be taken as a judgement statement on those species who don’t meet that description. The likelihood that a species is inclined to reach out in to the stars is just another factor that should be considered in the equation.

      “As for travel and conquest, neither of those activities is fundamental to life either.”
      It might be semantics but conquest seems like an odd word choice with negative connotations(but maybe that was unintentional?). Species naturally spread to neighboring environments that will sustain them.

      “They might just be ape things.”
      Anthropocentric assumptions?

      • RobertL August 9, 2018, 10:39

        Yes, absolutely anthropocentric assumptions – that is my point.

        You raise a really interesting question about “conquest” because the word means both going somewhere first, and military overthrow. It is perfectly natural English to say that Mallory conquered Everest.

        Aclot of science fiction (which I regard as the most accessible proxy for what the human race thinks about the rest of the universe) has the two meanings pretty much as twin themes; it’s largely about discovering new worlds and then fighting the Tharg imperial navy for possession of them. It is striking that the most successful scifi work of all time has two words in the title of which one is Star and the other is Wars.

        What I am suggesting is that the interest in knowledge and violence entailed by this universe view may be less universal, and more driven by our own evolution, than is sometimes thought.

    • Edward Wright August 8, 2018, 1:22

      The Drake Equation does not assume that all life aspires to such technology. In fact, that’s a variable built into the equation.

      • RobertL August 8, 2018, 13:42

        No, the variable is the number that actually make it, not the number that aspire to.

        • ljk August 17, 2018, 9:20

          The Drake Equation as originally envisioned in 1961 is about how many *technological* civilizations may be in the Milky Way galaxy. Part of this assumption are beings that have the means to communicate across interstellar distances.

          Its creators assumed that intelligent life would evolve along a path similar to what happened on Earth, even if the aliens are a bit “funny” looking. ETI that are smart but otherwise do not have or utilize technology as we do are not outright rejected by the Drake Equation, but neither are they the focus, either. Even their home worlds are expected to be much like Earth.

          I have mentioned this before throughout this blog, but I will bring it up again – You need to read this history of SETI, which thankfully is online in full here:


          SETI: A Critical History: Cover

          SETI’s Scope

          How the Search for Extraterrestrial Intelligence Became Disconnected from New Ideas About Extraterrestrials

  • Spaceman August 7, 2018, 14:07

    The astrophysical terms in the Drake equation are now part of established science; however, the biological terms– let alone the sociological variables– are anyone’s guess, right? For example, the transition from dead matter to living systems aka ‘abiogenesis’ may be so staggeringly small such that abiogenesis occurred only once in the observable Universe thus far and we are a product of that lone event.

  • Alex Tolley August 7, 2018, 17:08

    His pessimism value is for just 1 civ to have ever arisen in the whole universe. I would hope that it is pessimistic.

    Regarding abiogenesis. If it really is so rare that it occurred just once, on Earth, then conditions must be so unique, or luck played such an important role, that research into abiogenesis would seem like a fruitless quest. We might get lots of clues to what happened, but we could not start a new genesis. It might be as hopeless as alchemy. That is a depressing thought.

    I would hope that our models for planets in the HZ do provide good biosignatures and that they give us estimates for the probability of life arising on different types of worlds.

    If civilizations have arisen and then disappeared, or remain active, then we are back to the Fermi Question. Why are there no apparent signs of artifice? Does it mean that civs are unable to ever develop cosmic sized engineering capabilities, or that they pass through that stage quickly and transcend to something else? Whatever answers to the FQ is proposed that suggests that they are out there, but “invisible” to us, requires that all civs adhere to those precepts. None go “rogue”.

  • DCM August 7, 2018, 17:16

    Conclusions based on assumptions about things largely unknown. They could approach reality but it’s unlikely anyone now alive will find that out.
    It’s fun but the real task is us going to what worlds we can and building others from raw materials.

    • ljk August 17, 2018, 9:23

      We can at least ramp up laying down the groundwork for our descendants who will find out whether or not we are alone in the Universe one day. Few other questions in science and history are more important than this.

  • Astronist August 7, 2018, 19:46

    “we can get a sense for the odds that somewhere, somewhen, civilization has formed” – I do not agree. All works of this type leave out the fact that the universe began a finite time ago, and is still relatively young. Therefore at least one civilisation must observe that it is the first to appear (more than one, if some of the early ones at our stage collapse quickly). Now ask: is our civilisation that first one? Clearly, one can push speculations and probabilities around forever, but the only answer that should satisfy a scientist would be one that involves a lot of close-up surface observations of exoplanets in our galactic vicinity.

    • Ronald August 8, 2018, 8:03

      I agree, at least with regard to technological civilization. Primitive (bacterial, prokaryote) life is probably common. However, higher life and in particular ‘technological intelligence’ might be extremely rare.
      The only proxy to a guesstimate that we have is to use Earth as a ‘temporal proxy’, meaning: prokaryote life arose very quickly, within a few hundred million years and under rather harsh conditions. However, for the next 2 gy or so, there was only this. Eukaryotes seem to be a rare (unique?) symbiosis, possibly having occurred only once.
      Complex life is something of the last 500-600 my.
      Self-aware intelligence is even rarer, though encouragingly not restricted to one taxonomic group.

      I am even much more cautious with regard to chances of technological civilization.

      I strongly endorse the concept of analogical or convergent evolution: similar conditions will result in similar forms and functions. We see this over and over again in the history of life.

      However, although conditions on Earth have been suitable for higher intelligence and technology for a very long time, technological civilization is a totally unique and extremely recent phenomenon on Earth. This implies it could be a unique fluke.

      Another telltale sign that I sometimes mention in this context: our big neighbor, the Andromeda galaxy (M31), contains about 10^12 (a trillion) stars. Many of these are main sequence solar type. Recent spectroscopic analysis has revealed that the average age of the disc stellar population is about 7 gy, that is at least 2 gy older than our Sun.
      Despite this, there is no sign whatsoever, of a K3 civilization in M31.
      I.e., apparently even with this overwhelming abundance of suitable material and plenty of time, no single life form in M31 has ever made it to ‘galactic civilization’, or intergalactic explorer, or even a civilization able to leave clearly discernible beacons of its existence.

      • Alex Tolley August 8, 2018, 12:07

        However, although conditions on Earth have been suitable for higher intelligence and technology for a very long time, technological civilization is a totally unique and extremely recent phenomenon on Earth. This implies it could be a unique fluke.

        It is certainly arguable that the fluke that lead to technology is the invention of language. While there is some evidence of primitive language in other mamals, e.g. whales, and that apes can learn to crudely communicate using sign language, it may be a very hard to replicate genetic accident that led us on this path.
        For that reason, while life may well be abundant, technological (advanced) life may be exceedingly rare. Maybe SETI will eventually prove that supposition wrong.

        The most uninteresting case would be an abundance of worlds with prokaryotic life, all based on the same, or very similar basic chemistry. While the explored functional protein space might be very much larger than on Earth, the lack of multi-cellular eukaryotes would not provide much incentive to explore, while at the same time possibly making these worlds off limits to [post-] human colonization.

        Even if we are not the first technological civilization, if other civs have come and gone, we might only know of their existence when we have explored the galaxy/universe. Both are very far in the future.

        • Ronald August 9, 2018, 9:21

          “The most uninteresting case would be an abundance of worlds with prokaryotic life, all based on the same, or very similar basic chemistry. While the explored functional protein space might be very much larger than on Earth, the lack of multi-cellular eukaryotes would not provide much incentive to explore, while at the same time possibly making these worlds off limits to [post-] human colonization.”

          Though disappointing, this would in a way also be a fascinating idea, scientifically, philosophically and even ethically:

          Scientifically, because it would show that all life is based on the same chemistry and it would show the possible ranges and limits of that chemistry (e.g. amino acids, proteins).

          Scientifically and philosophically, because it would raise the question what particular extremely rare set of conditions lead to complex Eukaryote life.

          Philosophically and ethically, because indeed it would raise the issue of human colonization of ‘Prokaryotic planets’. I would then be inclined to say, why not, if these are indeed a dime a dozen AND these planets will in by far most cases never see higher life AND these planets are relatively suitable (i.e. earthlike) for human habitation AND higher life (i.e. our kind of life) is exceedingly rare and therefore precious and important to preserve.

          I think the best reason for declaring a planet off-limits for human colonization would be if the planet had complex life, which would, in the above-described scenario, be an extremely rare discovery.

          BTW, this view of abundance of simple prokaryotic life and (extreme) rarity of complex Eukaryotic life, is also shared by biologist Nick Lane, who wrote about this in Power, Sex and Suicide: https://en.wikipedia.org/wiki/Power,_Sex,_Suicide

          • Alex Tolley August 9, 2018, 15:06

            Prokaryotic planets may prove problematic to colonize as we cannot sterilize the world and there may be no way to determine whether our needed biosphere can colonize the planet without some problems arising without actual colonization as an experiment. That might be unethical. Of course future technology might invalidate both these statements.

            With sufficiently advanced technology, why not build artificial worlds (e.g. O’Neill’s) that are exactly tailored to the colonists and obviate the issue? Then rather than colonizing, we use the planet’s material to build the colony if desired.

            A third possibility, is that our technology is used to jumpstart eukaryotic and multicellular life on the planet. Our biology engineering should be easily up to the task at that point, making the engineers of the Alien movies reboot look like pikers. This might be akin to Clarke’s premise of star traveling ET seeding worlds and trying to increase intelligence as a goal.

            • Wojciech J August 9, 2018, 17:53

              Seeding intelligence might be a good strategy for long lived civilization that has found itself at the end of its potential for new ideas, both in culture and science.
              It might also one of the explanations behind Fermi Paradox-contacting us would spoil our unique development and potential to create something unique.

            • Ronald August 10, 2018, 4:01

              Your 3rd possibility is indeed what I had in mind: I have once coined the term ‘Terra-seeding’, logically following (or even coinciding with) terraforming.

              If it appears that Prokaryotic life is ubiquitous ánd very seldom leads to more ánd is largely based on the same chemistry, then it is both ethically ok and a feasible, even laudable, goal to seed those worlds with (where needed genetically adapted) earthly life.

  • Robin Datta August 7, 2018, 20:20

    There is only one here-now, that of the observer.

    And there is only one confirmed observer. All other observers (and implicitly, foci of consciousness) are based on unwitting or witting Turing tests. Infants and very small children will attribute sentience to their dolls and other toys.

    The further away one looks from the here, the further away one sees from the now – into the past. The future manifests here. The observer seems to be anchoring points even when space and time are stretched and squeezed, with new space constantly added.

    “Life” is a chemical process, organic chemistry being an extension of inorganic chemistry which had to be conceded when Friedrich Wöhler made urea by heating ammonium cyanate

    Biochemistry and molecular cell biology add further layers of complexity, but simple systems self organize into complex systems with energy streams. Even structures as complex as membranes identical to cell membranes and vesicles (the first fence of demarcation of the living from its non-living environment) have been produced through such manoeuvres.

    From the Miller-Urey experiment
    to gene and genome synthesis
    and even the creation of unnatural base pairs
    the issues confronted from either end have shown no evidence of intractability.

    “Abiogenesis” involves complexity and time not yet mastered in the lab, but does not invoke some mystic power, as might have been conjectured prior to Wöhler.

    Intelligence is found in unintelligent beings such as slime molds solving the travelling salesman problem, forest mycelia distributing nutrients among plants for better outcomes and termites building complex mounds from minimal pre-programming. Multifaceted intelligence requires multifaceted infrastructure: hence world-champion artificial intelligences lack “common sense”. Intelligence will manifest wherever and whenever an adequate infrastructure is available.

    Keeping in mind Forward’s Dragon’s Egg and Hoyle’s The Black Cloud, there may be more forms of “life” and “intelligence” than we categorize, spanning times accessible in our future to places now in our past.

  • Gary Wilson August 7, 2018, 21:12

    I greatly value Kim Stanley Robinson’s thoughts on the experiment we are currently conducting with our only home, i.e. this wonderful planet we call Earth. New York 2140 gives a depiction of a future earth which, sadly seems all too likely now. Perhaps 1,000 years from now (Earth time) beings on a planet circling a star 100 light years from here will wonder about a brief surge of electromagnetic radiation emanating from earth for several score years. The disappearance of the signal could mean a number of things. Which of those possibilities will it be?

    • Wojciech J August 8, 2018, 12:11

      KSR has gotten terribly radical with age, among other things he opposes interstellar exploration, his ideas on ecology and future of Earth are too tainted with ideological zeal to be taken seriously.
      While climate change does create challenged, it is by no means the end of our civilization.

      • Spaceman August 9, 2018, 8:18

        I do not know much about KSR, but to posit that modern civilization is immune to anthropogenic collapse is not at all ‘radical.’ In fact, the radical position would be assume the opposite and not take steps to reduce potentially catastrophic existential risks. We should not become complacent in our methodology.

  • Michael Fidler August 8, 2018, 2:52

    Do not forget about Chaos, the long history of it on our planet is well recognized in eastern philosophy. Western ideas seem so concrete and we all love that but concrete shoes leave us in deep water. The weather seemed so hard to predict until chaos theory came along and the dragons of yin and yang create and destroy…

  • Harold Shaw August 8, 2018, 18:54

    I am comfortable assuming Earthlings and tool making humans are part of a larger data set. Every other natural phenomenon is part of data set, so it is likelier that we are as well.

    Are there any steps in the genesis of Earthlings and humans that don’t present multiple examples of a set type? Symbiogenesis is believed to have happened often, creating a broad set of organelles including two organelles that specialize in generating ATP, another set. High productivity language may be the only example of a solitary set type example, though there are examples of possible low productivity language/high productivity communication.

    I wouldn’t propagate ETIs as a surety, but sure enough to take astrobiology, SETI and METI seriously.

    • RobertL August 9, 2018, 10:42

      It is the failure of terrestrial species to converge on intelligent tool making that worries me (I am aware of course that that failure is not without some very limited exceptions).

  • David H August 8, 2018, 23:06

    Civilizations may have limited lifespans, but advanced civilizations could easily leave behind something that endures long after the civilization dies. The most obvious such thing would be a multiplying fleet of Von Neuman probes. So why aren’t the probes here? Or, if you want to be slightly more creative than Von Neuman probes: How about plants that are engineered/bred to survive in space, to metabolize rocks and grow photovoltaic leaves, and to make seeds that sail on solar winds to systems unknown? Open space would as hospitable to such lifeforms as our biosphere is to weeds. So why aren’t there forests of them on Mercury or Ceres or the moon?

  • Dr. Eric W. Davis August 9, 2018, 5:06

    The Drake Equation is only a zeroth order approximation, thus it is strictly formulated on the basis of biased assumptions for a lack of ET evidence beyond the Earth. However, the statistical Drake Equation by Dr. Claudio Maccone [see: https://www.astrobio.net/alien-life/at-last-how-many-alien-civilizations-are-there/; references: https://www.sciencedirect.com/science/article/pii/S0094576510001499
    and https://link.springer.com/chapter/10.1007/978-3-642-27437-4_1%5D is a higher order approximation that has the fewest assumptions and no computational bias. The results are far more meaningful because the guesswork in estimating each term in the equation is largely removed, and statistics then gives you reasonable probabilities with error bars.

  • Hamilton1 August 9, 2018, 13:09

    “Ernst Mayr ruled out a multiplicity of intelligent civs because while he believed life could be common, only one of approximately 50 billion species that have existed on Earth had produced a civilization”.

    This is plainly wrong.

    Although 50 billion species have produced only 1 example of technology on this planet, that 50 billion could be just a subset of the total POSSIBLE number of species. Therefore each planet would have the same likelihood of producing an equal number of civs from its 50 billion quota as ours did… namely, one.

    • ljk August 9, 2018, 16:40

      Has anyone ever bothered to see if Mayr had a religious agenda regarding alien life, one that went with the traditional view that only Earth harbored life and only because of a divine being?

      Or did he also subscribe to the old solar system formation theory of a passing star pulling matter off our Sun, which coalesced into planets? Which was considered to be an extremely rare occurrence and therefore meant that life would also be deeply uncommon.

      These need to be factored in to why Mayr thought as he did.

      • NS August 10, 2018, 6:22

        An admittedly cursory review of Wikipedia and a couple of Mayr’s published articles shows no religious agenda, or belief in rarity of planets. His argument for the probable non-existence of extra-terrestrial intelligence was apparently based on the rarity of true intelligence on Earth (1 species out of ~50 billion) and a more general understanding of evolution as a chancy process that does not tend in any particular direction (e.g. intelligence).

        • ljk August 17, 2018, 9:31

          Perhaps being a 20th Century human male he did not take into account the intelligence of cetaceans, cephalopods, and certain other primates because they do not build and utilize tools as we do, which is NOT an indication that they are not smart.

          Any serious biographies on Mayr out there?

      • Michael T August 11, 2018, 16:36

        Agreed, but Mayr’s argument seems to be based on the rate of civilisations PER (say) million species GIVEN that life has actually arisen (admittedly based on just ONE planet).

        So that is independent of the rate of planetary formation (stellar encounters or whatever), abiogenesis, etc, and any ideas that Mayr might have had about them. Of course if he believed in the stellar encounter hypothesis of planetary formation exclusively, he might have made a very low estimate of the number of civilisations in the universe. And at that time no extrasolar planets were known.

        Michael T

  • ljk August 9, 2018, 16:41

    The search for life in Congress

    A Senate committee held a hearing last week about NASA’s efforts to search for life beyond Earth. Jeff Foust reports that the hearing covered a lot more ground than just the state of astrobiology research at the agency.

    Monday, August 6, 2018


  • Geoffrey Hillend August 9, 2018, 16:43

    We don’t have to change the laws of thermodynamics, but only make more clean, green, energy efficient and renewable energy technology which is in harmony with the biosphere, carbon cycle and water cycle. We clearly are not completely energy independent from greenhouse gas technology and we will have to be in the future so the laws of thermodynamics won’t be a problem.

  • hiro August 9, 2018, 23:05

    Do we have all the information/classification of G & K class stars’ properties (+ Earth-like planets orbiting around these stars) in the entire Virgo Supercluster? An important claim requires lots of data to back up the statement, but we have almost nil so this is more into philosophy than real sciences.

  • Exoplanet August 10, 2018, 11:08

    What really is puzzling . . . is this question . . . why is there only DNA/RNA based life? Why did that spark only happen once? Why don’t we see alternative forms of life evolving here . . like silicon based life? The elements are still here in the same concentrations as when earth was formed . . . we still have a soupy mix of all kinds of chemicals . . but nothing new in slightly less than 4 billion years. . . why? Perhaps life was brought here to seed our planet . . . and we are the end result. Maybe we cannot see evidence of other civilizations because we are looking at the galaxy and universe through the wrong lens.

    • Alex Tolley August 10, 2018, 21:59

      Silicon is very poor compared to carbon as the molecular backbone. Silicon bonds are weak and would not make the needed robust bonds that we see in our carbon based life on Earth. You may also recall the claimed discovery of life using arsenic instead of phosphorus despite the unlikelihood of this working. That was proven to be a mistaken claim.

      Because evolution favors the best replicators, even if there was a silicon based chemistry, it would have been out competed by the carbon chemistry on Earth.

  • George King August 12, 2018, 16:25

    “We may not know whether other technological civilizations exist now, but the odds are exceedingly good that at some point, somewhere, they once did.”

    According to Wikiquotes, the passage that Oppenheimer quoted from the Bhagavad Gita after the Trinity test also can be translated as:

    “Now I am become Time, the destroyer of worlds.”


    Very fitting for this topic.

    We are searching for needles in exceedingly large haystacks of both time and space.

  • stephen August 17, 2018, 18:40

    How recent is that estimate of 50 billion species having existed on our planet? Is there a more recent/more accurate estimate?

    What does everybody think of Peter Watts’ novel, Blindsight, and its sequels Echopraxia and Firefall? Firefall was published in 2014.

    I haven’t read them, but I’ve read about them. He suggests intelligence and complex technology can exist without self-awareness/sentience.

  • ljk October 30, 2018, 10:48

    Putting astrobiology at the heart of NASA science

    Astrobiology has gained increasing prominence in space science in the last 25 years thanks to better understanding about the potential habitability of worlds inside and outside our solar system. Jeff Foust discusses a recent report from the National Academies that examines how NASA should build upon its existing activities in astrobiology.

    Monday, October 29, 2018