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Drake Equation: The Sustainability Filter

There are a lot of things that could prevent our species from expanding off-Earth and gradually spreading into the cosmos. Inertia is one of them. If enough people choose not to look past their own lifetimes as the basis for action, we’re that much less likely to think in terms of projects that will surely be multi-generational. That outcome doesn’t worry me overly much because it flies against the historical record. We have abundant evidence of long-term projects built by civilizations for their own purposes, and while we view pyramids or cathedrals differently than they did in their time, their artifacts show that humans are capable of this impulse. The Dutch dike system has been maintained for over 500 years, and precursor activity can be traced back as far as the 9th Century.

Nor am I concerned that most people won’t ever want to leave this planet. I have no ambition to leave it either, but in every era there have been small numbers of people who chose to leave what they knew to follow their impulses, whether they were explorers, exploiters or zealots. Given the opportunity, I’d say that spreading into the Solar System will happen as small outposts evolve into colonies, and colonies are gradually enlarged by the flow of the like-minded.

Or, at least, it will happen if we get past the L term in the famous Drake Equation, which on the level of technology describes the length of time a civilization can release detectable signals, and on a more profound level may describe the working lifetime of a technological society. It’s this factor that Adam Frank (University of Rochester) looks at in a recent New York Times essay. He’s studying the price we pay for developing a global industrial culture, wondering whether this ‘sustainability bottleneck’ may not account for the Fermi paradox; i.e., the lack of evidence for civilizations around nearby stars in an obviously fecund universe.


Image courtesy of University of Rochester.

Civilizations need energy to operate, and as Frank points out, waste (entropy) is an inevitable part of the process of energy generation. Humans harvest about 100 billion megawatt hours of energy every year, with the consequence that we put 36 billion tons of carbon dioxide into the biosphere. We can assume that other civilizations would face the same issues as they grew. We can also see the vast changes that both Mars and Venus have been through in our own Solar System as perhaps once habitable worlds were gradually transformed by natural processes. We’re beginning to piece together general rules that can help us understand what happens as biospheres change.

Some of this change happens without the mediation of living creatures, and some occurs because of them:

…any species climbing up the technological ladder by harvesting energy through combustion must alter the chemical makeup of its atmosphere to some degree. Combustion always produces chemical byproducts, and those byproducts can’t just disappear. As astronomers at Penn State recently discovered, if planetary conditions are right (like the size of a planet’s orbit), even relatively small changes in atmospheric chemistry can have significant climate effects. That means that for some civilization-building species, the sustainability crises can hit earlier rather than later.

Frank’s interest is in studying sustainability issues as a generic astrobiological problem. You’ll recall that we’ve looked at a paper of his on this idea before (see Astrobiology and Sustainability). Working with Woodruff Sullivan (University of Washington), Frank talks in reference to Species with Energy-Intensive Technology (SWEIT), and argues that we can profitably study not only other worlds but our own previous eras of climate alteration for insight. The research program that grows out of this models SWEIT evolution along with that of the planet on which it arises with a methodology based on dynamical systems theory.

Earth’s own past suggests how complex these interrelationships can be. There was a time about two billion years after the formation of the planet when anaerobic bacteria utterly changed the biosphere by driving up the oxygen content in the atmosphere, a form of what was then pollution eventually becoming an essential for life such as ours. Never mind technology — life itself can be a game-changer. With such principles in mind, Frank and Sullivan are interested in the ‘trajectories’ civilizations take as shaped by the choices they make, some of which could result in population collapse while others lead to long-lived technological societies.

It’s always possible, Frank speculates, that we have a Fermi paradox because no civilization makes it through its sustainability crisis. But there are models that indicate this doesn’t have to happen.

By studying sustainability as a generic astrobiological problem, we can understand if the challenge we face will be like threading a needle or crossing a wide valley. Answering this question demands a far deeper understanding of how planets respond to the kind of stresses energy-intensive species (like ours) place on them. It’s an approach no different from that of doctors using different kinds of animals, and their molecular biology, to discover cures for human disease.

So maybe we’re not the only ones to tackle these problems, which are the consequences of physical laws that govern the interactions between planets and the life they sustain. We don’t have enough knowledge to provide the answer, not yet, but the generic problem is one that advanced civilizations anywhere must at some time face. I leave it to specialists like Frank to discover whether the ‘needle’ or the ‘valley’ is the best metaphor. My own suspicion is that sustainability is a manageable matter, while civilizational collapse through inadvertence via war or accident is the more likely outcome. That’s the filter on L that keeps me up at night.

The Frank and Sullivan paper is “Sustainability and the astrobiological perspective: Framing human futures in a planetary context,” Anthropocene Vol. 5 (March 2014), pp. 32-41 (full text).


Comments on this entry are closed.

  • Alex Tolley January 21, 2015, 14:27

    It seems unlikely that no civilization made it through the bottleneck. As Diamond shows in “collapse”, some cultures managed their resources sustainability in the past. Despite the building AGW crisis, I think we will eventually get low to zero carbon energy solutions.

    To me the problem is a few centuries in the future if economic growth continues at even low rates. Heat pollution will be critical to planetary civilization sustainability. Unless we expand off planet, even with just machines, we will face a civilization that will become stagnant in regards to energy using technologies.

    In this situation, the only way out is to fake growth by retreating to virtual worlds where anything can happen by computational means. I find that unattractive, but that my change for a civilization in the future where physical restraints feel unacceptable, so that there restraints are removed in a virtual universe of infinite possibilities.

  • Harold Daughety January 21, 2015, 16:39

    It is possible that alien civilizations, if there are any, are not testosterone driven to overpopulation, wars, and buying a new car every two years. Maybe the human species resembles a virulent bacterial infection that multiplies to the point that massive die-offs kill almost everyone. We are the only species that kills its own kind because of ideology. If there is intelligent life in the universe, they may well quarantine humanity.
    Population pressure has fueled migrations into new lands: the discoverers were not pioneers. We cannot lift even one percent of humanity off the earth. Migration into space analogous of settling the New World is not going to happen.
    Establishing an outpost (a word that reflects a military paradigm) in the solar system, terraforming Mars, and space habitats are without evident rational purpose to human society as a whole. The pyramids were built with slave labor, as were the canals of the Fertile Crescent. Despotic kings with an eye to immortality ordered both. Again, I say that the old paradigms simply do not apply. Do not be concerned about outpost and colonies. Design a program ab initio that defines and establishes the paradigms of a space-exploring society. Those who leave, if leaving is even possible, will diverge from homo sapiens sapiens and become something different from the rest of humanity.

  • Alex Tolley January 21, 2015, 17:40

    @Harold – other species routinely breed to unsustainable population levels and then crash, e.g. The Canadian Lynx preying on the Snowshoe Hare. This is classic population dynamics.

    I tend to agree with you that relatively few will leave Earth unless technology and conditions change, ANC that they will reflect the new gene pool. But we shouldn’t assume conditions and technology won’t change. Baxter’s “Proxima” suggests 2 suggest currently magical technologies – “kernels” that are extremely energetic and can drive starships and some sort of transit gate that allows near light speed travel that appears instantaneous. Similarly, P K Dick often had his protagonists live in worlds that made off world colonization seem desirable. This second is the model that populated the Americas.
    England was far more comfortable and safe compared to the colonies, so it took a lot disaffection to want to leave, even as an indentured worker. In a stagnant civilization, I could see people wanting to make a go of colonizing other worlds in preference to staying home, whatever the hardships. I suspect advanced robots will be very helpful here – so it won’t be like pioneering the US.
    A key driver will be cost- and this has to be met or very little happens except tourism for the oligarchs.

  • Ole Burde January 21, 2015, 17:51

    Any intelectual effort that gets realy far away form comon sense , has to have an extreemely good reason to do so , as in string theory .
    When we talk about alien civilizations , that is not the case . The only thing we actualy know , is that none has been detected . There is no geat paradoks involved , which can only be explained by a mindbogling theory , because common sense is perfectly capable of explaining the evidence . It might be fashionable to predict doomsday-scenarioes caused be climatechange , but if that’s the point , we might as well claim all alien civilisations died out because of chain smoking , junk food or just plain bad taste .
    Common sense tells us that if a civilisation became capable of sucsesfully crossing the distance between stars , it would not take too long before it could be done again ,again and again , and that such a civilization would quickly populate all planets in the galaxy even remotely fitting for its needs. That leaves us with limited choices for high-probability scenarioes : either no civilzation developed the ablity , or there are as-yet unknown reasons why we cant hear any of the endless amount of comunications going on between endless millions of populated star systems …. as for low probability scenarioes there is ofcource an endless list , among them the most reasonable beeing the arbitrary chance that starflightcapability was achieved only a short time ago , and very far away from us .
    As for the heat polution thing , its very far down the list , exept if we are only talking about ourselves .

  • Ron S January 21, 2015, 17:52

    “explorers, exploiters or zealots”

    A nice and concise summary of leadership motivations. On the other hand, public projects (government led) tend to committees, meetings and project management, plus political drift. Painful but often necessary, and inimical to true leaders. It’ll be interesting to see which way we go, if we go at all.

  • James M Essig January 21, 2015, 18:10

    The number of stars, planets, and life-forms in the mere visible portion of our universe alone can completely delight us. In fact, that the number of stars as such is about equal to the number of grains of fine grained Morton brand table salt which would cover the entire United States land mass 10 meters deep. The number of planets as such is about equal to the number of grains of fine grained Morton brand table salt which would cover the entire United States land mass 100 meters deep. The number of moons as such is about equal to the number of grains of fine grained Morton brand table salt which would cover the entire United States land mass 1,000 meters deep. I explain relativistic methods for how we might access all these worlds in my book:

    Call Of The Cosmic Wild: Relativistic Rockets For The New Millennium. Expanded Edition.

  • Peter Popov January 21, 2015, 18:51

    Honestly, this explanation of Fermi’s paradox is hardly relevant. One can come up such explanations on a daily basis, given the current fads. For example a few years ago there was a genuine concern in the media that we were all going to die because the bees were disappearing hence no one to pollinate crops. Eventually the bees decided to not go into the fifth dimension and remained with us.
    It seems to me one should stick to the fundamentals in the Drake estimate. Of these, the obvious candidates are the frequency of arisal of technological civilizations, likely very low, and their lifetime, also likely to be low. Lifetime does not mean they die (because of the bees or whatever) but they change to a form which would be unrecognizable.

  • Astronist January 21, 2015, 19:08

    “in an obviously fecund universe” — if you want to believe that, then you’ll have endless fun debating the paradox thus created. But is this really science? Is it not more sensible to use lack of observations of extraterrestrial life to place constraints on that supposed fecundity?

    Stephen A.

  • DCM January 21, 2015, 19:41

    A problem in thinking about such things is the negative legacy of World War II and the Cold War, which supposes that some kind of suicidal action is almost inevitable in civilizations. Or that something is wrong with all of ours or us. We can’t make such a generalization with only one example of which we are part.
    Getting over this glitch is as necessary as getting over the seemingly obvious theories that the world is flat, then that everything revolves around the earth.

  • Moran January 21, 2015, 20:22

    Quite aside from any argument about how much we are effecting the climate ourselves it seems like a far to complexed question to answer without a better knowledge of planets other than our own. There might, for example, be a species who live on a planet subjected to great tidal forces, enough that it is almost completely volcanic, and thus can afford to use geothermal energy. If a civilisation developed around that it might well be fare more eco-friendly than our own, and the question of sustainability never become so urgent.
    As for an interstellar quarantine because of humanity’s destructive tendencies? It seems more likely that a preemptive strike with a relativistic bomb would be the solution, as any kind of ‘blockade’ of a solar system would be an almost impossible undertaking.


  • Kaps January 21, 2015, 21:12

    @Harold Daughety – You said:
    “We are the only species that kills its own kind because of ideology.”

    We are the only species we know of that HAS ideology. Plenty of species kill their own, they just lack the intellectual capability to do it the same way we do. If the principles of evolution are relatively universal, I doubt any species that didn’t have reproduction and control of resources as a key driver every became successful or reached an intelligent level.
    I think the question is, can we overcome our own biology and evolutionary instincts BECAUSE of our intelligence/ideologies and become something greater. We can’t answer that question yet, either based on our own species or any know intelligent species (since we don’t know of any others).


  • Macroscien January 21, 2015, 23:17

    What we already observed is the rule that live tend to concentrate around energy sources. On Earth it could be Sun energy or thermal/chemical vents in the ocean. Interesting will be to know what is the upper limit for external thermal and energy flow condition for life to exist. If we think about possible AI life (robots) form we already could see that our window of opportunity moved considerably in comparison to our benign Earth conditions. Possibly to the point that life could be energy flux by itself. I wonder if somebody did try to talk to our Sun seriously already, beside ancient magicians ?

  • Danangel January 21, 2015, 23:18

    @Moran Or a third possibility: Manipulating our genes over many millennia to change us slowly into an acceptable galactic species. Who knows?

  • Harold Daughety January 22, 2015, 2:06

    There was a story about a pragmatist and a theorist stranded on a sandy isle in the sea without even the ever-present three palm trees seen in cartoons. Then a battered crate of canned food washed ashore. The pragmatist pointed out that without a way to open the cans it was useless. The theorist was busy drawing in the sand and said, “I have a solution. First, we assume a can opener. . .”
    Colonizing other worlds might be impossible if life has established itself as microbes or if the elemental ratios were somewhat different from ol’ Mom Earth – assuming we could get there. I know of no serious theoretical basis for FTL flight, planet terraforming, or any of the trappings that make the sci-fi stories so interesting. I grew up with old paperbacks from the early age of science fiction and the speculations in Popular Science of Worlds of Tomorrow. I was eager to believe. . . .
    But now we live in a world that is dumping carbon that was laid down over eons in a matter of years. The breakdown of the oil market will result in a hemorrhage of CO2 in the developing countries. If all the arable land on the earth were covered in climax forest, it would not make a dent in the present CO2 accumulation. I have 3 young grandsons that I want to have a full and productive life. I fear they will not.
    I do believe there are civilizations on far distant worlds. I believe wherever conditions for CHON life are met, life arises. It is statistically almost certain that other beings are pondering the same questions as we are. But I believe the possibility of meeting them is a fantasy.
    I am not so old – but considering family history and my own health, I am overdue to depart. I hope someone can answer a few of these perplexing questions with hard numbers rather than assumptions.

  • Ronald January 22, 2015, 7:02

    This whole topic seems so fashionable to me that I even doubted whether to respond or not: now it is climate change for Fermi.
    Of course we humans can do significant damage to the planet and ourselves, but I strongly doubt that any of that could annihilate an entire technological civilization. We would eventually resurrect and adapt. Any manmade disaster that I can think of, and we would fully restore our civilization within a century, or a millennium at the most. A blink in galactic terms.
    Sorry, but Fermi will most probably require a better answer.

  • Mark Zambelli January 22, 2015, 11:52

    Yes Ronald I agree… but only if we’re not too stupid to learn from our mistakes, call it a near miss and move through it with more conviction to never allow something like that to threaten us again. If too stupid?… well here’s Fermi right on cue.

    I was intrigued by the suggestion that due to planetary/atmospheric conditions being so diverse, the sustainability bottleneck could happen at different stages in a civ’s development. As stated in the article, we have yet to start getting anything of a grip on classifying what type of atmosphere+artificial pollutants leads to changes in Drakes ‘L’ term, but it seems to me to be very important to do this sooner as it may well steer interest in certain exoplanets over others.

    Am I correct in thinking that, for example, if a civilization arises on a planet that I might take the liberty of categorizing as ‘hardy’ (can take a lot of abuse) then that civ should hit it’s bottleneck after it has become sufficiently advanced to rectify the problems? If so this should extend ‘L’ and give a greater chance of that civ still being with us (maybe conjouring-up Buck Rogers style city-domes with regulated micro-climates)?

    But what of the civ that arises on a ‘fragile’ world where their bottleneck occurs earlier (say on a level with our medieval period). Do they bite the dust before developing tech to combat the issues? Or do they have an easier time pulling through due to their low-tech level not being so damaging in the first place (ie before nukes, bio-research etc)? Their more friable environment may react quicker anyway and restore prior conditions sooner… the ‘hardy’ planets atmosphere may be very sluggish to change by comparison so they would endure harsher times for longer.

    Perhaps this cancels out. Civ A has been given more time to develop and is better equipped to deal with the bottleneck, but it’s harsher and longer lived… Civ B hits trouble earlier so is less equipped to handle stuff but it’s less severe and of shorter duration.

    If Ronald is right and any civilization stands a good chance of pulling through eventually regardless of initial conditions, then maybe civilizational-suicide doesn’t impact on ‘L’ at all (enter Fermi) and we need to be worried about natural causes shortening ‘L’. Afterall, with Mother-Nature having such an ever-present evil glint in her eye we shouldn’t be so oblivious to our actions as to appear willing to help her out sealing our fate. If we can mature to see the long-term then maybe we can help ourselves out by removing the man-made bottleneck entirely.

  • DCM January 22, 2015, 13:48

    Speculation is fun and useful, but now that we’re able to leave Earth our priority is our immediate neighborhood and making human (and other Earth life) use of such places as Mars while learning to design and build self-sustaining habitats in space.
    It simply isn’t possible to assume much about life elsewhere till we meet it, and not just one example but several.

  • Paul Gilster January 22, 2015, 13:56

    Harold Daughety writes:

    Design a program ab initio that defines and establishes the paradigms of a space-exploring society.

    Interesting. What would a program designed ab initio look like? And how would it differ from previous programs? Let’s hear your thoughts.

  • Ole Burde January 22, 2015, 16:05

    DCM : One thing more does not demand any asumptions about extraterrestial life , and that is the URGENCY with which we have to moove forward . For whatever reason , it becomes more and more probable that no other civilization has achieved starflight capability . If that is the case ,for whatever reason , starflight might be even more difficult than we have so far imagined .
    For me that can only be understood as a reason for urgency . It could take much longer than we have asumed , and so many unpleasant surprises could have time enough to happen … such as religious madnes acelerating the population explosion , total war in an era of nuclear proloferation , the depletion of critical raw materials , the arise of an airborne HIV-style virus , giant asteroid impact , cimate change disasters leading to uncontrolable massmigration ,or worst of all a deadly combination of several major factors . If we dont get mooving , we wil get to know why nobody else did .

  • Harold Daughety January 22, 2015, 16:40

    I think the first step is determining who, and why, among us would want to leave the earth forever. Not the corporate exec nor the romantic, the mystic – probably those who are prime candidate are off the radar, malcontents and asocial types. A multidisciplinary study seems in order.
    Second, what is the scope of the mission? We can’t sustain a colony on Mars and we can’t “terraform” Mars because it is too far different from Terra. Perhaps putting volunteers into an L5 biosphere with the sole objective to survive between unmanned resupply ships is enough, and maybe private finance , here and abroad, without publicity, would be a appropriate.
    Third, establish a permanent presence – no ticket home – somewhere as determined by the studies.

    Keep it small, keep it simple, keep it quiet.

  • DCM January 22, 2015, 19:52

    Yes, we do need to expand into our neighborhood. I don’t know why there don’t seem to be interstellar civilizations. Possibly, though it’s blasphemy to current thinking, we may become the first. Civilizations may be few and far between. We simply don’t know and have n basis for generalizing. But we do need to grow outward and expand for ourselves.

  • Rob Henry January 22, 2015, 20:38

    Once more an attempt at explaining “the great filter” using the one thing we feel sure of until we pause for a moment and think about it: that all ETI’s will be very similar to each other and different to humans.

    Here is the truth. Any ETI that expands to other stars faster that it self-destructs could fill our galaxy in < 100 million years, and the Milky Way is a hundred times older than that. Now if we give ourselves a 0.1% chance that we can learn the necessary lessons, we must give independently originated ETIs much much more than this (because we should expect MORE variety in the ways they might approach problems than we show – really!)

  • NS January 23, 2015, 3:06

    I think Harold Daughety is right about who’d want to leave and who’d want to stay:


  • DCM January 23, 2015, 5:19

    The recurrent problem here is the assumption that we, and everything alive, will “self-destruct”. That’s the belief dating from World War II and the Cold War I’m talking about.
    It isn’t the same thing as worry about asteroid collisions or invasion; it’s self-destructive.

  • Ole Burde January 25, 2015, 16:27

    We are not going to ”self -destruct” in any simple active meaning of the word , but on the other hand there could be endless passive possiblities for selfdestruction awaiting in the future . History has not ended , it is more logic to asume it has just started . The big question is , if we can harnes the endless reservoir of comitment and selfsacrifice that made former generations capable of overcomming impossible hardships and suffering .. if we can do that ,and combine it with scientific logic , there are NO limits to what human beings can achieve , even a relatively small number of them …..such as a hundred people surviving for 300 years in a tin can .

  • david lewis January 28, 2015, 19:15

    Quote: “Humans harvest about 100 billion megawatt hours of energy every year, with the consequence that we put 36 billion tons of carbon dioxide into the biosphere. We can assume that other civilizations would face the same issues as they grew.”

    I don’t see how we can assume that. An alien species might live on a very different planet than the one we call Earth. Fossils fuels might not be as abundant on their planet as on ours. Or perhaps it’s windier there, and wind turbines might be more feasible. Or perhaps they’re more intelligent than us, and moved onto nuclear fission when it became available. Or perhaps the ratio of land to ocean on their world is much smaller, so that the effects of industry might be more diluted than here. Or ….. *shrug* We don’t know.

    Suppose technological species are not uncommon. For our purposes assume not uncommon means there’s at least one per galaxy. Not a large number, but enough that if many of them made it past “the filter” then we would know it. As they spread out from their home world Dyson swarms would become common, altering the light from their galaxy enough for us to note that there’s something out of the ordinary there. We don’t see that. Since their planets would not be carbon copies of Earth, not every one of them would face climate change.

    No Assuming technological species are not uncommon, then the reason we don’t see them must be due to something more basic to all life than climate change, whether it be natural or due to industrial activity. And the one thing I can think of that would be common for all species, regardless of where, or on what type of planet they evolved is just that: evolution.

    From the time life starts it spreads, and eventually it runs out of room. I imagine that happens pretty quickly. What does it do then? It competes, and over eons evolution takes place. On our planet Earth every species is in competition. Each blade of grass we see sends out its roots, and seeks the water it needs even if it means its fellow blades of grass suffer. Each flower struggles to grabs the nutrients necessary for life, even if it means the doom of others of its kind. Trees strive to grow taller, needing sunlight to grow, and shades those around it. Even for the seemingly docile plants around us, the whole planet is a battle zone.

    We, and all life, would be the product of that evolution, and are not exempt from it. Designed to compete that is what we would do, even if it meant our demise. Climate change, and most resource depletion, would be symptoms of that, but not the cause for the silence that “appears” to reign in the universe.

    When did our space program soar? When we were competing. When that battle was won, we moved on to others, such as seeing who could build the most nuclear weapons. What rational reason could there be for that? None; it isn’t rational. A few hundred megaton yield nukes would be more than enough to deter a rational enemy, and if used would utterly destroy their way of life. There’s no excuse for building tens of thousands of them unless we’re so focused on competition that rather than admitting defeat we would rather destroy everything.

    Or take run-a-way capitalism. When people have enough to be more than comfortable, why strive for more and more at the expense of others? There were opponents to child labor laws who thought it okay to allow children to work in factories and other dangerous occupations. Why? Because their having more was of more importance to them than the lives of children. I’m sure many of them would’ve claimed to be Christian, though I’m unsure how being willing to throw away the lives of children for the sake of money fits in with Jesus’ warning not to harm a child. (I freely admit there’s a lot about us humans I don’t understand.)

    Take cigarette companies, and their willingness to lie and do whatever it took to sell a product that caused cancer. It would be one thing to tell the consumer that, “hey, this is dangerous,” and then let them decide to use it or not. That’s not what they did though. The call of money was too great, and they willingly sacrificed the lives of others for that gain.

    Competition is like fire. Too little, and you end up scavenging raw meat as a way of life; just the right amount and things get done; too much, and it ends in bloodshed. By evolution, it would seem we’re driven to the latter.

    I could see this ending two way:

    1. We kill each other off. Sure, we might survive a nuclear war, but would we learn anything from it? I doubt it. We would still fight and squabble, and then repeat it.

    2. We compete through upgrading our bodies until the old homo sapiens sapiens are no more. And then, to compete better, we keep upgrading. Eventually, to think faster, and be more productive, we move into a virtual world. This would deny us the potential to ever travel to the stars. When you’re a sentient program running at a trillion times normal speed the stars are no longer a few light years away, they’re trillions. Plus, at that speed of thinking, even travelling a centimeter would take the equivalent of a year. If you want adventure, you hop on the line to the next processor, and take a few years getting there where you would see how other “programs” have evolved. It would be a lot more exciting than spending an almost eternity getting to a place that’s almost guaranteed to be sterile. I would bet with a trillion years of divergent evolution, those programs on the next chip over would as different as true aliens would be.