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Mistakes in the Drake Equation

Juggling all the factors impacting the emergence of extraterrestrial civilizations is no easy task, which is why the Drake equation has become such a handy tool. But are there assumptions locked inside it that need examination? Robert Zubrin thinks so, and in the essay that follows, he explains why, with a particular nod to the possibility that life can move among the stars. Although he is well known for his work at The Mars Society and authorship of The Case for Mars, Zubrin became a factor in my work when I discovered his book Entering Space: Creating a Spacefaring Civilization back in 2000, which led me to his scientific papers, including key work on the Bussard ramjet concept and magsail braking. Today’s look at Frank Drake’s equation reaches wide-ranging conclusions, particularly when we begin to tweak the parameters affecting both the lifetime of civilizations and the length of time it takes them to emerge and spread into the cosmos.

by Robert Zubrin

There are 400 billion other solar systems in our galaxy, and it’s been around for 10 billion years. Clearly it stands to reason that there must be extraterrestrial civilizations. We know this, because the laws of nature that led to the development of life and intelligence on Earth must be the same as those prevailing elsewhere in the universe.

Hence, they are out there. The question is: how many?

In 1961, radio astronomer Frank Drake developed a pedagogy for analyzing the question of the frequency of extraterrestrial civilizations. According to Drake, in steady state the rate at which new civilizations form should equal the rate at which they pass away, and therefore we can write:

Equation (1) is therefore known as the “Drake Equation.” Herein, N is the number of technological civilizations is our galaxy, and L is the average lifetime of a technological civilization. The left-hand side term, N/L, is the rate at which such civilizations are disappearing from the galaxy. On the right-hand side, we have R∗, the rate of star formation in our galaxy; fp, the fraction of these stars that have planetary systems; ne, is the mean number of planets in each system that have environments favorable to life; fl the fraction of these that actually developed life; fi the fraction of these that evolved intelligent species; and fc the fraction of intelligent species that developed sufficient technology for interstellar communication. (In other words, the Drake equation defines a “civilization” as a species possessing radiotelescopes. By this definition, civilization did not appear on Earth until the 1930s.)

By plugging in numbers, we can use the Drake equation to compute N. For example, if we estimate L=50,000 years (ten times recorded history), R∗ = 10 stars per year, fp = 0.5, and each of the other four factors ne, fl, fi, and fc equal to 0.2, we calculate the total number of technological civilizations in our galaxy, N, equals 400.

Four-hundred civilizations in our galaxy may seem like a lot, but scattered among the Milky Way’s 400 billion stars, they would represent a very tiny fraction: just one in a billion to be precise. In our own region of the galaxy, (known) stars occur with a density of about one in every 320 cubic light years. If the calculation in the previous paragraph were correct, it would therefore indicate that the nearest extraterrestrial civilization is likely to be about 4,300 light years away.

But, classic as it may be, the Drake equation is patently incorrect. For example, the equation assumes that life, intelligence, and civilization can only evolve in a given solar system once. This is manifestly untrue. Stars evolve on time scales of billions of years, species over millions of years, and civilizations take mere thousands of years.

Current human civilization could knock itself out with a thermonuclear war, but unless humanity drove itself into complete extinction, there is little doubt that 1,000 years later global civilization would be fully reestablished. An asteroidal impact on the scale of the K-T event that eliminated the dinosaurs might well wipe out humanity completely. But 5 million years after the K-T impact the biosphere had fully recovered and was sporting the early Cenozoic’s promising array of novel mammals, birds, and reptiles. Similarly, 5 million years after a K-T class event drove humanity and most of the other land species to extinction, the world would be repopulated with new species, including probably many types of advanced mammals descended from current nocturnal or aquatic varieties.

Human ancestors 30 million years ago were no more intelligent than otters. It is unlikely that the biosphere would require significantly longer than that to recreate our capabilities in a new species. This is much faster than the 4 billion years required by nature to produce a brand-new biosphere in a new solar system. Furthermore, the Drake equation also ignores the possibility that both life and civilization can propagate across interstellar space.

So, let’s reconsider the question.

Estimating the Galactic Population

There are 400 billion stars in our galaxy, and about 10 percent of them are good G and K type stars which are not part of multiple stellar systems. Almost all of these probably have planets, and it’s a fair guess that 10 percent of these planetary systems feature a world with an active biosphere, probably half of which have been living and evolving for as long as the Earth. That leaves us with two billion active, well-developed biospheres filled with complex plants and animals, capable of generating technological species on time scales of somewhere between 10 and 40 million years. As a middle value, let’s choose 20 million years as the “regeneration time” tr. Then we have:

where N and L are defined as in the Drake equation, and ns is the number of stars in the galaxy (400 billion), fg is the fraction of them that are “good” (single G and K) type stars (about 0.1), fb is the fraction of those with planets with active biospheres (we estimate 0.1), fm is the fraction of those biospheres that are “mature” (estimate 0.5), and nb, the product of these last four factors, is the number of active mature biospheres in the galaxy.

If we stick with our previous estimate that the lifetime, L, of an average technological civilization is 50,000 years, and plug in the rest of the above numbers, equation (2) says that there are probably 5 million technological civilizations active in the galaxy right now. That’s a lot more than suggested by the Drake equation. Indeed, it indicates that one out of every 80,000 stars warms the home world of a technological society. Given the local density of stars in our own region of the galaxy, this implies that the nearest center of extraterrestrial civilization could be expected at a distance of about 185 light years.

Technological civilizations, if they last any time at all, will become starfaring. In our own case (and our own case is the only basis we have for most of these estimations), the gap between development of radiotelescopes and the achievement of interstellar flight is unlikely to span more than a couple of centuries, which is insignificant when measured against L=50,000 years. This suggests that once a civilization gets started, it’s likely to spread. Propulsion systems capable of generating spacecraft velocities on the order of 5 percent the speed of light appear possible. However, interstellar colonists will probably target nearby stars, with further colonization efforts originating in the frontier stellar systems once civilization becomes sufficiently well-established there to launch such expeditions.

In our own region of the galaxy, the typical distance between stars is five or six light years. So, if we guess that it might take 1,000 years to consolidate and develop a new solar system to the point where it is ready to launch missions of its own, this would suggest the speed at which a settlement wave spreads through the galaxy might be on the order of 0.5 percent the speed of light. However, the period of expansion of a civilization is not necessarily the same as the lifetime of the civilization; it can’t be more, and it could be considerably less. If we assume that the expansion period might be half the lifetime, then the average rate of expansion, V, would be half the speed of the settlement wave, or 0.25 percent the speed of light.

As a civilization expands, its zone of settlement encompasses more and more stars. The density, d, of stars in our region of the galaxy is about 0.003 stars per cubic light year, of which a fraction, fg, of about 10 percent are likely to be viable potential homes for life and technological civilizations. Combining these considerations with equation 2, we can create a new equation to estimate C, the number of civilized solar systems in our galaxy, by multiplying the number of civilizations N, by, nu, the average number of useful stars available to each.

For example, we have assumed that the average lifespan, L, of a technological species is 50,000 years, and if that is true, then the average age of one is half of this, or 25,000 years. If a typical civilization has been spreading out at the above estimated rate for this amount of time, the radius, R, of its settlement zone would be 62.5 light years (R = VL/2 = 62.5 ly), and its domain would include about 3,000 stars. If we multiply this domain size by the number of expected civilizations calculated above, we find that about 15 billion stars, or 3.75 percent of the galactic population, would be expected to lie within somebody’s sphere of influence. If 10 percent of these stars are actually settled, this implies there are about 1.5 billion civilized stellar systems within our galaxy. Furthermore, we find that the nearest outpost of extraterrestrial civilization could be expected to be found at a distance of 185-62.5 = 122.5 light years.

The above calculation represents my best guess as to the shape of things, but there’s obviously a lot of uncertainty in the calculation. The biggest uncertainty revolves around the value of L; we have very little data to estimate this number and the value we pick for it strongly influences the results of the calculation. The value of V is also rather uncertain, although less so than L, as engineering knowledge can provide some guide. In Table 1 we show how the answers might change if we take alternative values for L and V, while keeping the other assumptions we have adopted constant.

Table 1 The Number and Distribution of Galactic Civilizations

V=0.005 cV=0.0025 cV=0.001 c
L=10,000 years
N (# civilizations)1 million1 million1 million
C (# civilized stars)19.5 million2.4 million1 million
R (radius of domain)25 ly12.5 ly5 ly
S (Separation between civilizations)316 ly316 ly316 ly
D (distance to nearest outpost)291 ly304 ly311 ly
F (fraction of stars within domains)0.048%0.006%0.0025%
L=50,000 years
N (# civilizations)5 million5 million5 million
C (# civilized stars)12 billion1.5 billion98 million
R (radius of domain)125 ly62.5 ly25 ly
S (Separation between civilizations)185 ly185 ly185 ly
D (distance to nearest outpost)60 ly122.5 ly160 ly
F (fraction of stars within domains)30%3.75%0.245%
L=200,000 years
N (# civilizations)20 million20 million20 million
C (# civilized stars)40 billion40 billion18 billion
R (radius of domain)500 ly250 ly100 ly
S (Separation between civilizations)131 ly131 ly131 ly
D (distance to nearest outpost)0 ly0 ly31 ly
F (fraction of stars within domains)100%100%44%

In Table 1, N is the number of technological civilizations in the galaxy (5 million in the previous calculation) , C is the number of stellar systems that some civilization has settled (1.5 billion, above), R is the radius of a typical domain (62.5 ly above), S is the separation distance between the centers of civilization (185 ly above), D is the probable distance to the nearest extraterrestrial outpost (122.5 ly, above), and F is the fraction of the stars in the galaxy that are within someone’s sphere of influence (3.75% above).

Examining the numbers in Table 1, we can see how the value of L completely dominates our picture of the galaxy. If L is “short” (10,000 years or less), then interstellar civilizations are few and far between, and direct contact would almost never occur. If L is “medium” (~50,000 years), then the radius of domains is likely to be smaller than the distance between civilizations, but not much smaller, and so contact could be expected to happen occasionally (remember, L, V, and S are averages; particular civilizations in various localities could vary in their values for these quantities). If L is a long time (> 200,000 years), then civilizations are closely packed, and contact should occur frequently. (These relationships between L and the density of civilizations apply in our region of the galaxy. In the core, stars are packed tighter, so smaller values of L are needed to produce the same “packing fraction,” but the same general trends apply.)

Any way you slice it, one thing seems rather certain: There’s plenty of them out there.

What are these civilizations like? What have they achieved?

It would be good to know.


Comments on this entry are closed.

  • Alex Tolley February 16, 2018, 14:14

    This analysis runs smack into the Fermi Question. Unless all these civs have transcended physical form and have left their systems in what look like natural states, the evidence of their presence should be abundant and perhaps obvious even to us.

    • iwan February 17, 2018, 22:10

      if you consider that some of the cases of unidentified aerial phenomena are real and are not of terrestrial origins and if you furthermore consider the possibility that such visitors are not interested in closer contact with us (may it be because we are to primitive to them or because they dont want to interfere with our civilisation to protect us) then there is no fermi paradox at all!!!

      • Zanstel February 19, 2018, 4:37

        An interesting solution. We are not interesting, so we are not visited, first because they could watch us from the distance, and second because we are terrible common, so no new here.
        Perhaps the galaxy is so full of civilizations that nobody has special interest on us.
        And nobody make “noise” because noise is inefficiente. Simply we are not enough advanced to see a developed civilization and our noisy style is only typical of a “teenager civilization”, when it begins to dominate technology but it hasn’t dominate efficiency enough to avoid unnecesary emissions.
        The same could work for out dreams of “fill everything” on the galaxy. Perhaps older civilizations surrounding us has seen that fill everything with repetitions of the same is boring and more diverse nature filled planets are prettier.

        Atmosphere of exoplanets will respond this answers on the future.

  • David H February 16, 2018, 14:22

    This is all very sensible and I agree with each amendment. But the common thread of all these changes is that the original Drake equation is too pessimistic about the likelihood of alien life. So, more than ever, we need to ask: Where are they? Why aren’t they everywhere by now?

  • David H February 16, 2018, 15:17

    The Drake equation should be complemented by a related but different equation that shares many of its parameters: The Alien Technology Detectability equation. It will have some extra terms, including some about the distance from us. Of course not every advanced alien civilization will be detectable. But conversely, many alien civilizations will be detectable long after they ceased to exist. Much will depend on the likelihood of one such civilization setting off a wave of interstellar expansion with either lifeforms or AI.

    Crucially, the weights we set in this equation should be calculated by the same means we use in the Drake equation. We should simply do our best to estimate various conditional probabilities based on our (very incomplete) understanding of how civilizations develop. For example, this will need a quantitative account of “screamers” – individuals in a civilization that will choose to broadcast or otherwise reveal the civilization’s existence. We have no choice but to model these probabilities on dynamics of potential human screamers, and take into account the probability of permanently repressing all individual screamers. Should we expect it to be a nearly universal norm of advanced life that screamers should be repressed? And if it is, how should we value the probability that a civilization has enough coordination to successfully repress all screamers, and to do so over cosmic timescales?

    Remember that successful screamers could build beacons or monoliths that outlive them by billions of years. The most obvious way of doing so would be to launch Von Neumann probes. Once they’re loose, there is no reigning them in.

    Ultimately, much in the Alien Technology Detectability equation will depend on our estimate of the likelihood that we will at some point succeed in building Von Neumann probes. I put that at 20%. But if their expected lifetime of detectability is longer than the expected lifetime of our civilization by a factor of 5 – which it surely is – then we should get the result that there ought to be more currently-detectable alien technological civilizations in the Milky Way than there are living civilizations in the Milky Way.

    Any way you calculate, our best science predicts that thousands of Milky Way civilizations should have been discovered by us given the searches we have performed by now. I’m not even talking about SETI. I’m just talking about ordinary walking around and looking and not finding any sign of alien technology on our planet or elsewhere in our solar system. And please don’t respond to this by saying something like “Aliens forbid themselves from doing such things” – as if that’s an answer. Which forbidden acts on Earth actually never happen? Can you imagine how repressive a human government would need to be in order to gaplessly enforce one single ban for even a century? Even North Korea has escapees, and anyway, we shouldn’t pretend that North Korea is the universal model of advanced civilization. We may be a zoo for aliens, but despite the fact that human zoos forbid feeding the bears, visitors feed the bears.

    So let’s sack up and rigorously try to build a literature on the Alien Technology Detectability equation. I think the debate will fill the worst gap in the current debate about extraterrestrial life.

  • John Donaldson February 16, 2018, 15:18

    If the Defense Department is correct, they’re here and they’re observing us. Also, they apparently have space/time metric engineering to propel their ships. But observations contrary to the popular scientific paradigm are commonly maligned.

    • Paul Gilster February 16, 2018, 21:14

      We need to keep on topic here. Whether or not unidentified things in the sky are interstellar craft is not our subject, though there are many places on the Net where this can be discussed. Let’s stay on the question of the Drake Equation as Zubrin analyzes it and what it may imply.

  • jim February 16, 2018, 15:47

    This is ridiculous, by your own definition our civilization is less than 100 years old and it doesn’t look like it will last another 100 years. The reason, our technological civilization depends on non renewable resources and we are destroying our own ecological life support system.

    • jordan Bassior February 17, 2018, 0:29

      We already know how to substitute longer-lasting resources for the ones you’re thinking of, and as we continue to develop we will be able to obtain resources from places other than the Earth.

    • Antonio February 17, 2018, 6:20

      Huh??? If we are destroying our life support system, why are we better nourished than ever??? https://ourworldindata.org/food-per-person And no, our civilization doesn’t depend on non-renewable resources, it can easily switch to renewable resources if needed, like nuclear power. http://large.stanford.edu/publications/coal/references/docs/pad11983cohen.pdf

      • spaceman February 17, 2018, 11:53

        There is something to be said for the sustainability solution to the Fermi question even though I think the probable solution is that life is generally rare to begin with. We are shortsighted because our lifetimes are small compared to geological timescales. Furthermore, the dominant economic systems is based on infinite growth on a finite planet and is focused on the end with little concern for the means by which we reach the end. The end is accumulation of more stuff, more money, and the continuous conversion of resources with not as much concern for the conservation of resources, etc. I think we have been able to nourish ourselves due to the green revolution, but technological fixes will be sufficient until they aren’t. It is erroneous to think that technological fixes, without changes in values, will ALWAYS be sufficient to keep things afloat. Even Eric Weinstein says that we cannot keep the current system in place for another 300 years for if we do much of the biosphere upon which civilization depends will be destroyed. Instead of more techno-wizardry, we need a change of philosophy combined with technological solutions. Many serious thinkers see the need to transition to a steady-state ecological economics based on reuse, efficiency, and well-being whereas those who think we can continue business as usual are delusional– sure, they may not see the collapse in their lifetime, but human lifetimes are short! As for being more nourished, yes, that is true but it also true that there could be a short interval between the current nourishment and famine and collapse of unsustainable socioeconomic model.

        • Antonio February 17, 2018, 12:18

          A lot of extraordinary claims but no data nor arguments to support them. I provided data for the opposite.

          • spaceman February 17, 2018, 17:37


            Actually, none of the claims I made are extraordinary, but the glib blandishments of “infinite planet thinkers” are not just extraordinary– they are downright bizarre. What I discussed above is very much based on well-established science and the fact that you cannot sustain infinite growth on a finite planet. You can try, but you will fail miserably. Perhaps Jim is exaggerating that we only have a 100 years left, but if he’s got the right idea whereas those who maintain the opposite are clearly engaging in magical thinking. The current economic system runs into an irreducible barrier called entropy. Despite the grandiose social naturalism espoused by neoliberal economists, the the Second Law of Thermodynamics strikes a stake in the heart of the idea that one can have infinite growth, extraction of resources, and concomitant waste production on a finite planet. Pernicious, arrogant neoliberal ideology declares its natural status as an economic system even though it is greatly at odds with one of the most well-established laws of nature. Perhaps read Georgescu-Roegen’s “The Entropy Law and Economic Process.” The fact is that no country on earth is currently sustainably meeting its needs according to a Nature study (a pretty reliable publication).


            https://arxiv.org/abs/0906.0568 The Sustainability Solution to the Fermi Paradox

            https://www.nature.com/articles/s41893-018-0021-4 A good life for all within planetary boundaries

            Georgescu-Roegen, N. (1999). The entropy law and economic process. Cambridge MA: Harvard university Press.

            • spaceman February 17, 2018, 18:10

              I am not saying that “we are for sure doomed”, but we also do not want to become complacent in our methodology and ignore planetary ecological boundaries. Also, technological fixes are only PART (an important part) of the solution, but social changes and behavioral changes will also be part of the equation if we hope to become an interstellar civilization. The following quote by Sagan sums up my thinking on the matter:

              “The simple passage of so many generations will have changed us. Necessity will have changed us. We’re an adaptable species. It will not be we who reach Alpha Centauri and the other nearby stars. It will be a species very much like us. But with more of our strengths and fewer of our weaknesses.”

            • Antonio February 18, 2018, 7:37

              “Actually, none of the claims I made are extraordinary, but the glib blandishments of “infinite planet thinkers” are not just extraordinary– they are downright bizarre.”

              Huh??? It’s you who talked about infinite things, not me. You said “the dominant economic systems is based on infinite growth”. I never said anything like that nor talked about infinite anything.

              The rest of your comment is simply elaborating around that strawman.

              You don’t know what your extraordinary claims are? OK, let’s quote some of them:

              “life is generally rare”

              Life on Earth started almost immediately after the Earth became cold enough.

              “the dominant economic systems is based on infinite growth”

              “the dominant economic systems [have] little concern for the means by which we reach the end”

              How that can be true when in large parts of the world is so difficult to make busssiness with tobacco, nuclear power, GMO, opioids, arms, cryonics, etc.?

              “there could be a short interval between the current nourishment and famine and collapse of unsustainable socioeconomic mode”

              • spaceman February 18, 2018, 14:09


                Actually, talking about a straw man: you truncated my statement thereby doing away with the qualifier “probable.” I could very well be wrong and the galaxy may be brimming with life, but I think there are valid reasons to be skeptical of this view– that’s all. I tend to think, unlike Zubrin or Sagan who I both respect enormously, that there are PROBABLY not millions of civilizations and/or planets with complex life in our galaxy.

                Here is a paper that you might find interesting by Speigel et al (2011) that addresses your following statement head-on:

                “Life on Earth started almost immediately after the Earth became cold enough.”

                https://arxiv.org/abs/1107.3835 Bayesian analysis of the astrobiological implications of life’s early emergence on Earth

                Though you did not specifically mention the infinite, my mentioning it was in defense of Jim who made the important point that our current civilization is precarious and probably has a shelf-life if changes are not made. Many who contend that there is a shelf-life get jumped on as “doomsayers” and the common argument used against them is that there will always be a technological fix. I think from your dismissive reaction (its content and tone) to his statement, it could be reasonably inferred that you are a strong believer in technological fixes which, again, I never said I was against only that I think social changes and behavioral changes might also be part of the equation. We need to take care of earth better than what we have and reduce existential risks so that we can become a space-faring civilization.

                Yes, the dominant economic system is based on endless growth, resource extraction, and concomitant waste production. The end is accumulation of more and more: even if the form that takes changes, the basic underlying logic stays the same and is at odds with the Second Law of Thermodynamics.

                Lastly, I did not say you were the one making glib blandishments, but there are many defenders of the status quo who do despite the evidence that change will be necessary to propel us into a better (possibly interstellar) future. I was mostly critiquing your dismissal of Jim even though I actually happen to agree with many of the other points you have made in this thread.

                You seem to know a fair amount about energy. How close do you think we are to achieving nuclear fusion for energy generation and/or space propulsion? I ask this because I think nuclear fusion could help us on earth and in space…

                • Antonio February 19, 2018, 7:31

                  Thanks for the Bayesian paper, I’ll take a more detailed look at it later. It says:

                  “Although terrestrial life’s early emergence provides evidence that life might be common in the Universe if early-Earth-like conditions are”

                  Maybe that was not clear in 2011 when the paper was written, but it’s more and more clear now that such conditions aren’t rare.

                  “Finding a single case of life arising independently of our lineage (on Earth, elsewhere in the Solar System, or on an extrasolar planet) would provide much stronger evidence that abiogenesis is not extremely rare in the Universe.”

                  Of course, nobody denies that. I was not saying that the early emergence of life on Earth guarantees that life is everywhere in the Universe. I was only replying to the people that say that life is probably rare in the Universe. I was simply pointing out that all the (limited) evidence we have points the other way, not in the rare life direction but in the common life direction. I think Mars is a good place to find more strong evidence for either possibility, as Zubrin usually says on his talks.

                  Now, about the ecological doomsday / overpopulation debate and all that… I will clarify my position. I certainly don’t believe that our socioeconomical system is based on infinite progress/growth. I don’t think either that we need infinite progress to sustain our civilization. What I think, and it’s clear from the data, is that we never had an overpopulation problem and, when we had a growth in the population in the last two centuries, we always solved it easily with technology, never with politics.

                  Look, China passed from more than 6 children per woman to less than 3 children per woman in only 11 years, from 1967 to 1978, BEFORE the one-child policy. Iran did it in only 10 years (1986-1996) without any major political changes. The world total fertility rate has been decreasing from at least 1950, when we started to have accurate global data about it. We are now facing an underpopulation problem, not an overpopulation problem, and it’s part of a process that has been happening for the centuries. Malthusians have been arguing for centuries against the facts.




                  “Yes, the dominant economic system is based on endless growth, resource extraction, and concomitant waste production. The end is accumulation of more and more”

                  Repeating it doesn’t make it true.

                  “How close do you think we are to achieving nuclear fusion for energy generation and/or space propulsion?”

                  It depends mostly on politics. A couple of years ago the politicians changed the ITER schedule, from first fusion around 2030 to a 2-phase program: first plasma in 2025, then open the tokamak, upgrade it, and first fusion in 2035. It was not a technical decision, it was political, they simply wanted to spend less money per year. Thus, the only solution was to make the program longer (and more expensive in the end, but not per year), not going for fusion right away but doing it in two steps. So… if they don’t change their minds again, and no member leaves (like Canada in 2003), etc. I think ITER will achieve its goals around 2037, we will see some Asian prototypes producing electricity around 2045 and the first commercial plants around 2050. It can be faster if there is some breakthrough in superconductors in the meantime (current high-temperature superconductors are fragile and expensive to manufacture).

                  If I were Musk, I would put my dollars on the flow z-pinch concept (no need for magnets nor superconductivity, and can be used for propulsion) but sadly I’m not him :P

                  • Spaceman February 19, 2018, 10:30

                    I am not a Mathusian, I just think technological fixes, though undoubtably important, are part of the solution to the problems facing humanity.

                    ITER is great, but like you said it has been underfunded. Do you think any of the smaller fusion start-ups or Lockheed Martin will overtake ITER?

                    • Antonio February 19, 2018, 17:01

                      No, I don’t think so. The LM design is based on concepts that were tried in the 60s and 70s and discarded by most labs. Also, it’s suspicious that LM has never released any data about the performance of their machine, like pressure or temperature.

                • Antonio February 19, 2018, 7:37

                  And of course the extinction of species, reduction of biodiversity, etc. is happening and is horrible, but we are talking about humanity’s survival here, that’s a different thing. I’m all in favour of protecting the Amazon, reducing CO2 emissions, etc. but we are not facing our extinction nor will do any time soon.

        • Wojciech J February 18, 2018, 13:35

          ” Even Eric Weinstein says that we cannot keep the current system in place for another 300 years for if we do much of the biosphere upon which civilization depends will be destroyed.”
          You can move industrial and even agricultural production to off planet habitats(orbitals, not other planets). Jeff Bezos is keen on the idea, although he does point out it is centuries in the future.

          • spaceman February 18, 2018, 14:12

            Sounds great! I hope this happens sooner rather than later.

  • John walker February 16, 2018, 16:31

    Its hard to know where to start. This article makes broad assumptions that are simply not reflected in observation.

    “..it’s a fair guess that 10 percent of these planetary systems feature a world with an active biosphere, probably half of which have been living and evolving for as long as the Earth. That leaves us with two billion active, well-developed biospheres filled with complex plants and animals, capable of generating technological species on time scales of somewhere between 10 and 40 million years”

    This is wrong on so many levels.

    Let’s not constantly draw emotional conclusions and call them rational. With all respect for your belief in a vibrant galactic society, the calculations made in this article don’t reflect an objective view of existing science. It is mathematically highly unsound.

    • Bill Bennett February 18, 2018, 15:27

      You are spot on. This is what bothers me about posts like this one, they are, for want of a better term, faith based rather than rational.

      It’s only natural that people who want there to be aliens start finding ways to prove they must be out there. 18th century theologians did much the same thing with their religious beliefs.

  • Alex Tolley February 16, 2018, 16:38

    For a different take on how the equation should be handled, I recommend
    Dissolving the Fermi Paradox – Anders Sandberg, Eric Drexler & Toby Ord

    Their summary:

    * The Fermi question is not a paradox: it just looks like one if one is overconfident in how well we know the Drake equation parameters.
    • Doing a distribution model shows that even existing literature allows for a substantial probability of very little life, and a more cautious prior gives a significant probability for rare life.
    • The Fermi observation makes the most uncertain priors move strongly, reinforcing the rare life guess and an early great filter.
    • Getting even a little bit more information can update our belief state a lot!

  • Robin Datta February 16, 2018, 16:45

    How about the percentage of civilizations able to rise above their biological imperatives and thereby enhance both their longevity and spread? An existential consideration for Homo sapiens at this moment

    • Antonio February 17, 2018, 15:19

      What do (a) to rise above their biological imperatives, (b) enhance their longevity and (c) spread have to do with each other??

      • Michael February 17, 2018, 16:29


  • Iain Roberts February 16, 2018, 16:53

    A marvellous leap of faith here:

    Technological civilizations, if they last any time at all, will become starfaring … the gap between development of radiotelescopes and the achievement of interstellar flight is unlikely to span more than a couple of centuries

    A sample size of one is bad enough, but this is a sample size of zero. We have no data on starfaring species. Ours has not been back to the moon in almost 50 years, so a little caution is in order before asserting we will launch (manned?) interstellar expeditions by 2130.

    • Frank February 16, 2018, 18:33

      I agree! I think the ‘ease’ of achieving interstellar travel capacity is wildly overestimated. It represents the simplest resolution of the Fermi paradox: interstellar travel might be technologically incredibly difficult. It is not just a matter of technology though but also of sociology and psychology. See the difficulties we experience in even reaching the nearest planet:Mars.

      • Antonio February 17, 2018, 6:33

        I totally disagree with the “technologically incredibly difficult”. One only needs to master fusion, and we are near that. I highly doubt we can’t develop a decent fusion rocket in less than 100 years, something along the lines of the flow z-pinch concept: https://www.aa.washington.edu/research/ZaP/research/plasmaOverview

        Yes, politics can be a problem, and has been a problem for the last half century, but, as a technology matures and becomes cheaper and cheaper, politics is less and less a factor. And we are seeing that, at least two private companies developing the means to colonize Mars.

      • Rob Flores February 17, 2018, 6:45

        My POV, is that tech civs are rare, mostly because it is a lottery type odds due what are some harsh filtering events, (even things we have not thought of) . The earth had human civilization (of sorts) for 200,000 yrs. yet advanced technology only arose in the last 10,000yrs. (the conditions required to get a technological civ, do not align often, which i think is often ignored in these discussions.

        We also ignore that it is very costly to launch a viable colonization effort, and the failure rate of colonization maybe very high. how many times would it be tried at great cost?. this would explain why even with a score of cotemporaneus tech civs their expansion would be so slow that the mother civilization collapses before the expansion reaches a few ly,

        NOTE if it turns out that it is impossible to create practical modest mass/size fusion devices this would also tend to explain the fermi paradox. (as anti matter based power is a very expensive proposion}

        • Antonio February 17, 2018, 12:52

          “The earth had human civilization (of sorts) for 200,000 yrs. yet advanced technology only arose in the last 10,000yrs. (the conditions required to get a technological civ, do not align often, which i think is often ignored in these discussions.”

          I think you ignore the archeological evidence. What the archeological record shows is not a sudden, random appearance of advanced technology 10,000 years ago, but a increasingly faster (maybe exponential) technological progress in the last couple million years.

          “We also ignore that it is very costly to launch a viable colonization effort, and the failure rate of colonization maybe very high.”

          Why would it be very costly and failure-prone?? I can’t see it at all. The civilization that will colonize other stars will not be ours, but the humanity of the future, one that has already colonized the Solar System, terraformed planets, developed large scale space habitats, etc. For them it will not be so costly nor difficult but a natural step in their progress.

          “NOTE if it turns out that it is impossible to create practical modest mass/size fusion devices”

          That is simply contrary to factual evidence.


          • Spaceman February 17, 2018, 23:10

            Interesting graphic. It almost looks like there’s been a Moore’s law-like progression for experimental fusion reactors. Interestingly, I think Zubrin had a similar graphic in his book ‘Entering Space’ related to fusion power generation. Why might you suppose this positive trend rarely gets mentioned in discussions on fusion energy?

            • Antonio February 18, 2018, 18:08

              Well… I don’t think it’s rare. People that are in favour of fusion usually know it. People against fusion, OTOH, always repeat the fusion-is-always-30-years-in-the-future mantra and don’t know or deliverately ignore the graph.

              PS: Zubrin has a PhD in nuclear engineering.

              • Bill Osberg February 18, 2018, 19:56

                I notice that this graphic ends at 2005. I don’t think it will look so good if the last 13 years of results are added to it. For example, ITER is still a pretty long ways off.

                • Antonio February 19, 2018, 8:10

                  That gap is mostly due to two reasons:

                  1) The global fusion community has focused on ITER. So, for example, the European JET tokamak, that achieved Q=0.65 with D-T fuel (Q=energy produced/energy consumed), was shutdown shortly after that and started a long upgrade program to become more ITER-like to support ITER research. The japanese JT-60U, wich achieved Q=1.25 conditions but without tritium, only deuterium (so no fusion was produced) was totally dissasembled to be upgraded (new name, JT-60SA) and become… you guess… more ITER-like.

                  JT-60SA will be completed and resume operations in 2020, but will never use fusion fuel (they want the possibility to open the tokamak and do fast changes). JET upgrade was completed a couple of years ago but it’s operating without fusion fuels. Anyway, it will do a brief fusion experimental campaign again in 2019, and most probably reach break-even (Q=1) and beyond with fusion fuel and actual fusion happening inside it.

                  2) The ITER members delayed development of ITER, not putting the neccesary money. That delay generated cost overruns, that generated more delays, etc. Also, one member resigned (Canada). There were also problems with international cooperation (if a member was delayed, nobody helped it; there was poor communication and coordination, etc.). Finally in 2015-2016 they agreed in a much more detailed schedule, gave more power to the ITER organization (instead of the member countries), and are complying with the new schedule, for a first fusion in 2035.

                  • Bill Osberg February 19, 2018, 12:30

                    Well, the current ITER timeline is first plasma in 2035, and the plan is to run it for several decades after that. If that program is successful, only then does work begin on a prototype fusion power station. I haven’ t even mentioned the economics. On the ITER schedule, practical fusion power is more than 30 years away. I think other approaches should be getting much more funding.

                    • Spaceman February 19, 2018, 13:56

                      But why assume that the ITER, for all its glory, is the only game in town? There are a number of private sector start ups working on the problem.

                    • Antonio February 19, 2018, 17:22

                      “Well, the current ITER timeline is first plasma in 2035”

                      No, it’s first plasma in 2025: https://www.iter.org/newsline/-/2482

                      “If that program is successful, only then does work begin on a prototype fusion power station.”

                      That’s not very clear yet. At first, they intended to start building that prototype (DEMO) a few years after starting building ITER. Unsurprisingly, the country members changed their minds because that would imply more funding per year, preferring to start building DEMO when ITER was completed or almost completed. Some years later, they changed their minds again and it seems that the most probable scenario is not an international DEMO but several national DEMOs, each built by a single member, probably only China, Korea and Europe, and probably the first of them by China.

                      “I think other approaches should be getting much more funding.”

                      Maybe, but funding for fusion has always been decreasing, even for tokamaks, and other approaches are all more immature than ITER (including stellerators) and would probably take longer than ITER, even the conceptually better approaches. I favour the flow z-pinch approach, but I still think it would take longer. The good point is that it can be used for fusion rockets.

                    • Antonio February 19, 2018, 17:28

                      And ITER is not only the tokamak, they also do materials research, trough the IFMIF project. The first phase, IFMIF/EVEDA, in Japan, is almost done, and the second phase, IFMIF/DONES, will soon start, probably in Spain.


    • Bill Bennett February 18, 2018, 15:30

      Yes. And we haven’t even canvassed the idea that manned interstellar travel is not possible.

  • Geoffrey Hillend February 16, 2018, 16:58

    Quote by Robert Zubrin: “Current human civilization could knock itself out with a thermonuclear war, but unless humanity drove itself into complete extinction, there is little doubt that 1,000 years later global civilization would be fully reestablished.” A thermonuclear war would cause all human life to become extinct if it included the weapons of the major super powers. We would never recover. This can be used in the drake equation if we make the assumption that all intelligent civilizations survive since they have to learn to get along and a nuclear war would end human life on a planet. The result is more ET civilization should be out there if we assume the only extinctions are by low probability natural causes like large meteor impacts, supernovas, gamma ray bursts from kilonova explosions or Wolf Rayet star explosions, etc.

    • Antonio February 17, 2018, 6:58

      “A thermonuclear war would cause all human life to become extinct if it included the weapons of the major super powers.”

      Nope, it would be mostly restricted to the North Hemisphere: http://climate.envsci.rutgers.edu/pdf/RobockNW2006JD008235.pdf

      And even if it wouldn’t, you still have people of both sexes and highly qualified in science and technology that can certainly survive to that war and rebuild the human species: people in nuclear submarines, Antartic stations, etc.

      • NS February 17, 2018, 18:59

        Those people are very unlikely to have the knowledge required to rebuild civilization from scratch. Most of their knowledge is likely to be useless because the resources and infrastructure that used to be available to implement it are gone. I agree that even a major nuclear war probably wouldn’t destroy human life entirely, but the survivors are likely to be knocked back to a subsistence level for a very long time, possibly forever.

        • Antonio February 18, 2018, 7:53

          “Most of their knowledge is likely to be useless because the resources and infrastructure that used to be available to implement it are gone.”

          That’s totally non-sense. All nuclear weapons in the world CAN’T destroy a significant part of humanity’s infraestructure at all. It will never come close, by and large. At most, they can change the climate for some years or decades, that’s all. They can’t destroy all power plants, libraries, factories, roads, buildings, ships, … in the world even in the wildest scenario.

  • Anton M. February 16, 2018, 17:44

    This line of thought what I call “draketurbation” might seem entertaining but what does it add, really? We have not the slightest idea about the basic terms of the formula like the life probability. Until we have the theory of abiogenesis, we have no idea if one should expect some life under each rock in the Goldilocks zone, or we are lucky to have _us_ in this observable volume of the Universe.

    • Spaceman February 17, 2018, 22:20

      Well said, Antonio. Abiogenesis could be incredibly rare. But “draketurbation” can be fun! ;)

      • Antonio February 18, 2018, 18:17

        He is not me, I’m Antonio and he is Anton :P

        Nevertheless, I, like him, am not a big fan of draketurbation. I’m much more in favour of developing interstellar travel as soon as possible and go out there and see by ourselves, rather than speculating with the Fermi paradox or doing SETI/METI. Go to the stars and you don’t need all that! Moreover, you can find answers much faster!

  • hiro February 16, 2018, 18:00

    There are 3 types of civilization:
    1) Those don’t have AI
    2)Those were/will (be) destroyed by AI
    3)Those fuse with AI

    The 1st type can’t colonize the entire galaxy because they would make mistakes that lead to their own collapses.
    The 3rd type would always use cold logics to make complicated decisions, they don’t have idiots going around to feed bears in the zoo.
    We are too early to know which type we belong to but the current situations don’t seem bright from my personal biased point of view.

    • Michael C. Fidler February 16, 2018, 22:03

      AI is just a passing trend in the study of ETC, like the proverbial canals on Mars when everybody was building canals on Earth! With all the guns and weapons on earth do you think robots are going to take over? Now there even talking about ET messages having dangerous viruses in them, this just sounds so much like a child that cannot relate to the rest of the universe. We need better perspective on the case for ETC just as the Europeans finding the Americas (They did not Discover them!) brought a major change in perspective that ushered in a new age for civilization.

      • Antonio February 17, 2018, 13:07

        Yeah, I mostly agree. My own guess about AGI (Artificial General Intelligence) is that we’ll never develop it. Before that we will start introducing artificial neurons in our brains (and other nanomachines in the rest of our bodies) so we’ll not need AGI. As for AI, it depends on definition. For some definitions, we have already developed it.

        • Alex Tolley February 17, 2018, 14:49

          There are roles for pure machines with AGI, primarily in environments inimical to biology.

        • hiro February 18, 2018, 15:52

          We don’t need AGI =/= AGI is impossible. The development of synthetic neurons is cool but quite creepy.

      • usmcsaluki February 17, 2018, 14:26

        I think it’s more than a fad; I think “first contact” would surely entail meeting AI than actual lifeforms due to the distance between stars (assuming FTL isn’t possible).

      • hiro February 18, 2018, 15:49

        Fighting with guns and bombs is so old school. Putting drugs like Opiroid in the water over a long period is much more efficient. AI think in very long term similar to the way AlphaGo(-0) played Go, it only needed to win the game with 0.5 point and there is no need for overkill.

      • hiro February 18, 2018, 16:28

        By the way, we don’t have any flapping airplane; brain researches if stay too close to the natural model will probably go no where, one should know how to adjust the balance between natural and artificial processes in order to create objects that function like human brain with higher computational limit.

        • Michael C. Fidler February 19, 2018, 6:23

          Yea But It Ain’t Got No Soul!

          • hiro February 19, 2018, 19:26

            Well, I got a -F in the Soul Study class, can’t expect too much from me.

  • Adam Crowl February 16, 2018, 18:46

    I think the idea of multiple intelligences arising on a planet or even multiple industrial civilization reboots is highly unlikely. There have been a billion species and 1 technological civilization in 4.567 Gyr of Earth history. I suspect that means the odds against tech civs arising is about 1/3 over the age of the Cosmos per planet. Which drastically changes the priors on a Fermi analysis. More optimistic than the “We’re probably alone” analysis by Sandberg et al, but less so than Zubrin’s uber-hopeful guesstimate.

    But it’s a fun estimate to play with. I just don’t like the “50,000” year lifespan… feels like a use-by-date. He might be right – an ultra-virulent memetic contagion could spread through a star empire at lightspeed – but I hope he’s wrong.

    • Antonio February 17, 2018, 13:12

      “Zubrin’s uber-hopeful guesstimate”

      I think just the opposite. It’s a rather conservative approach, only considering exoplanets around G and K stars, not considering other star types, rogue planets, etc., and assuming that the colonies collapse and become extinct when the metropoly does the same.

    • Gerhard Wesp February 18, 2018, 2:29

      See, I’ve always been wondering about that: How can we be so sure that we’ve been the only tech civilisation on Earth so far? Granted, we’re probably the only one right now and, according to historic records, we can almost certainly rule out anything up to 10 ky back.

      But historic data points decay exponentially with time, and the fossile record doesn’t necessarily contain much info about technology, or does it? What about 1 My back? 10 My, 100 My?

      If we assume, just for the sake of argument, that a tech civilisation would eventually become smart enough to clean up their sh*t after themselves, that would by definition mean that they leave no traces, right?

      Put in another way, what would remain of our civilisation in 10 My? In 100 My? What if we learned at some point to properly dispose of our trash (i.e., burn or recycle it) and decommission and recycle buildings and infrastructure?

      This is a genuine question to solicit input, preferably with references. I don’t pretend to know the answer.

      • Alex Tolley February 18, 2018, 14:11

        “If we assume, just for the sake of argument, that a tech civilisation would eventually become smart enough to clean up their sh*t after themselves, that would by definition mean that they leave no traces, right?”

        Wrong. There would be signs in ice cores, the rocks, etc. One cannot recycle everything perfectly. Even where you do, there will be signs of changes. Even if we had no fossil evidence, there are plenty of geological signs of biology from the deep past.

        Even if they ground up every concrete building and ensured it was self-dismantling, there would be signs of civilization in ocean sediments. Our Anthropocene will leave a layer of concrete in geological layers, and certainly in the fossil record of the 6th extinction, as well as possibly obvious signs of genetic engineering that will show up as unnatural.

        So I doubt very much there were some ancient terrestrial civilizations or even alien ones on our planet at any time in the past we have looked at.

      • Joe H. February 19, 2018, 14:29

        A better question is why has human civilization only arisen in the last 10,000 years, given that homo sapiens has been around for 200,000 years? I guess the ice age was a factor, but still there were large parts of Earth that were temperate even during the ice age. And yet, no agricultural revolution, no discovery of metal. Just hunter gatherers for 190,000 years! This implies it takes more than just intelligence and the right environment to spark civilizations. Maybe just plain luck is a factor.

        • Brett Bellmore February 20, 2018, 19:09

          Just speculation, but until agriculture was invented, there likely wasn’t enough surplus above the survival level to advance. So it all had to wait on the invention of agriculture.

          You can wonder why agriculture took so long to be invented, of course; You’d think it could have been invented at any time. Possibly it’s not stable against hunter gatherer societies unless you manage to implement it in an isolated area; Otherwise you give it a try on a small scale and somebody else wanders by and gathers the product of your hard work.

          You have to get it going, and on a large enough scale that you can use the surplus to defend your fields against theft. That might take isolation, just the way speciation does.

      • NS February 19, 2018, 15:13

        One line of evidence against the existence of an ancient industrial civilization is that near-surface deposits of coal, iron, oil etc. were still readily available when our own industrial civilization developed. An earlier industrial civilization would have used them up.

    • Michael C. Fidler February 18, 2018, 9:20

      Multiple intelligences: Dolphins, Whales, Elephants, and Primates (Plus my Cat) probably think we are pretty dumb. If and when we destroy ourselves these groups would probably develop some form of higher civilization most likely closer to natures ideals. We have deserted nature and that will be our downfall, why do we live in square structures? We see nature as our adversary and unless someone has the sense to lead civilization into a golden age based on Taoist Philosophy we will shortly see our demise. When we find or they contact us this will be the most likely course that a ETC will take to be able to survive for millions or billions of years. Tao expresses the path human beings must take to join with the unity of the universe and work with nature.

      • Antonio February 18, 2018, 18:28

        Nature has no ideals nor can be deserted. We simply form part of it like ants or willow trees. The difference is that we are the only ones that can expand life to all the Solar System and beyond (bacteria probably can, at some extent, in suitable planets, but things like terraforming Mars or Venus are totally out of their powers; and even more so for Taoist philosophers).

      • Mephane February 19, 2018, 5:08

        Your comment is a good example of an “appeal to nature”: https://en.wikipedia.org/wiki/Appeal_to_nature

        The problem with that type of thinking is that there is nothing inherently good in nature out of its sheer “naturalness”, which is a very fuzzy concept to begin with. A fungus producing penicillin is natural, alright. Is it natural to cultivate the fungus and extract the penicillin, then used it as an antibiotic? Or let’s go even further: it is technically unnatural to treat any infection with antibiotics.

        Most people that use any appeal to nature argument are actually just cherry-picking useful things in nature versus bad things in technology, while there are just as many bad things in nature and useful things in technology. Also, many of the bad things in technology used in the argument are merely neutral, and only claimed to be bad without any objective reason (e.g. your point about living in “square structures”).

    • Robert Reeder February 19, 2018, 2:47

      This is critical I think to understanding the Fermi paradox. On earth, the only model we have right now, of some five billion species only one has ever developed technology more sophisticated than a broken rock or a digging stick.

      Life may be ubiquitous, intelligence may be commonplace, and still technology may be vanishingly rare.

      • Michael C. Fidler February 19, 2018, 9:51

        Fermi Paradox?
        From Wikipedia:

        “In 1950, while working at Los Alamos National Laboratory, Fermi had a casual conversation while walking to lunch with colleagues Emil Konopinski, Edward Teller and Herbert York.[21] The men discussed a recent spate of UFO reports and an Alan Dunn cartoon[22] facetiously blaming the disappearance of municipal trashcans on marauding aliens. The conversation shifted to other subjects, until during lunch Fermi suddenly exclaimed, “Where are they?” (alternatively, “Where is everybody?”). Teller remembers, “The result of his question was general laughter because of the strange fact that in spite of Fermi’s question coming from the clear blue, everybody around the table seemed to understand at once that he was talking about extraterrestrial life.”[23] Herbert York recalls that Fermi followed up on his comment with a series of calculations on the probability of Earth-like planets, the probability of life, the likely rise and duration of high technology, etc., and concluded that we ought to have been visited long ago and many times over.”

        Well this explains the problem, three old men talking about garbage! :-(

    • Project Studio February 20, 2018, 4:48

      Artefacts of past civilisation could lie beneath the Antarctic ice or the sands of the Gobi desert, not to mention below the oceans. To a large extent, the glaciation of repeated ice ages could do quite a lot to clean up the mess of past civilisations. We can not rule in, or rule out, what appear to be plausible possibilities until an exhaustive search, currently impossible for our current civilisation, has been completed.
      People migrated to Australia in small boats, dated to over 50,000 years ago, the record of which is clearly depicted in our rock art — long before the last ice age. Evidence has also been uncovered that Homo Sapiens ‘out-of-Africa’ migration may have occurred as much as 200,000 years ago, and other advanced fire and tool-using hominids occupied northwestern Europe nearly a million years ago. There may well have been an earlier pre-ice age human civilisation that disappeared without a trace up to now.
      To relate this to the Drake Equation and its variants, we have good evidence that a sentient species lifetime can be more than 100,00o years. So, as for the lifetime of a technological civilisation, this same value (100 k) would appear to be a reasonable first approximation .

      • torque_xtr February 23, 2018, 5:17

        If you look at the industrial layer in the sediments closely, you will find many unnatural things simultaneously. All the weird particulates from the plants, that cannot be simulated even remotely by any natural process. CFC inclusions, technogenic isotope ratios, pieces of ground microprocessors… A civilization can mask itself from less advanced observation, and clean up all crude traces in it’s environment (which is one of the possible answers to the Paradox), but absolutely cannot erase all the evidence to more advanced investigation, and that is governed by the Second Law. There may have been fire- and primitive wooden tool users in the Carboniferous, not noticed by us and even by expected near-future tools (if it wasn’t against our understanding of evolution), but I guess, we would have discovered and recognized evidence of XXI-cen-equivalent industrial civilization even in the Archaean by now, if it was the case. (or at least, firmly recognized that something very, very flaky was taking place then)

  • Brad in Dallas February 16, 2018, 18:55

    Why be planet-centric? If as he states habitable planets are uncommon, technologically advanced spacefaring species would overcome that by living in Island 3’s, which would be the only way to move civilizations between stars anyway. But saying so would obviate the need for Zubrin’s favorite project, Mars colonization.

    • Antonio February 17, 2018, 13:17

      “But saying so would obviate the need for Zubrin’s favorite project, Mars colonization.”

      Huh? Why?

      • Brad in Dallas February 17, 2018, 23:35

        Because by admitting that living in habs would be more flexible, and wouldn’t suffer Mars’ drawback of spending your life in 1/3g, with its health consequences, nobody would want to buy the Mars future Zubrin is selling.

        • Michael February 18, 2018, 12:47

          Centrifugal stations can also be built on Mars to simulate 1g if needed. It is just Mars like any other planet has a gravity well which is expensive to get out of.

          • Wojciech J February 18, 2018, 13:45

            “Centrifugal stations can also be built on Mars to simulate 1g if needed.”
            That’s immensely impractical. But for anyone studying this long enough it becomes clear that orbital habitats are simply the obvious and better option for colonization(perhaps located near planetoids like Ceres).

            • Michael February 19, 2018, 8:51

              I agree space has much to offer but if we need g habs on Mars it would not be that impractical, a circular tunnel with tracks and a long train would work.

          • Alex Tolley February 18, 2018, 14:00

            Building centrifuges for human habitation may be feasible, but what about the everything else – for forests, farms, livestock? Large space habitats provide a better approach for such tailored habitats. On Mars, you would be constantly transitioning from one centrifuge to the next, and “outside” would remain at 1/3 g.

            Zubrin wants Mars [now]. With no distractions.

            • Antonio February 18, 2018, 18:40

              “Building centrifuges for human habitation may be feasible, but what about the everything else – for forests, farms, livestock? Large space habitats provide a better approach for such tailored habitats.”

              On the contrary, large space habitats are much worse for that. You need much much much infraestructure and technology to do that in space that in Mars. On the latter, you have all the soil you need, with adequate amounts of the elements needed for life, with sunlight readily available, with plenty water, with radiation protection, with plenty CO2 and O2, with only lightweight greenhouses and houses needed, etc.

              • Alex Tolley February 19, 2018, 13:29

                On the latter, you have all the soil you need, with adequate amounts of the elements needed for life, with sunlight readily available, with plenty water, with radiation protection, with plenty CO2 and O2, with only lightweight greenhouses and houses needed, etc.

                Those conditions would require a terraformed Mars. Colonizing now requires pressure domes, radiation protection etc. We’ve discussed this all before regarding what is needed to colonize Mars and set up farms.

                Space habitats offer all the advantages of open living in an Earthlike environment. The sheer land area and volumes possible by using asteroidal material, let alone planetary bodies, to construct such habitats dwarfs the limited surface area of Mars. At best Mars offers a smaller Earth without oceans, whilst space habitats could house literally trillions of people in a vast variety of environments and cultures. Such habitats offer a far more open-ended solution to expand and grow, building a very wealthy system-wide economy to launch starships for interstellar expansion. The logic of this approach (effectively a Dyson swarm) was behind the excitement of the light signal from Tabby’s star.

                Space habitats might seem difficult to build (although robotic construction will be helpful) but they offer far more benefits for colonization and when applied to other star systems, solve the problem of disrupting native biospheres and the time delay for terraforming dead worlds.

                • Antonio February 19, 2018, 17:40

                  “Those conditions would require a terraformed Mars. Colonizing now requires pressure domes, radiation protection etc.”

                  Nope. While humans do need pressure domes in Mars, plants don’t. They only need the greenhouses for the heat and humidity they provide. They can live at Mars pressures and within and atmosphere that’s mostly CO2. And Mars atmosphere provides enough radiation protection for plants. That is all known.

                  • Alex Tolley February 19, 2018, 23:12

                    Evidence please.

                    • Antonio February 20, 2018, 10:57

                      You claimed first that they need pressure domes, so provide you the evidence.

                    • Michael February 20, 2018, 15:06

                      Antonio, plants need around 7-8 kPa to survive, that is ten times what Mars has at the moment.


                    • Antonio February 21, 2018, 5:11

                      Michael: I must correct a little my previous statement. I recalled the data incorrectly. As your paper states, it has been shown that plants can live in a ~50 mbar terrestrian atmosphere. That means less than 1 mbar of carbon dioxide partial pressure. Martian atmosphere is around 6-8 mbar, mostly carbon dioxide. So I assumed that a 6-8 mbar mostly carbon dioxide atmosphere would suffice. It seems that that has not been tested. Anyway, for a 50 mbar air pressure, you only need a 0.2 mm thick plastic greenhouse, much different from the several cm thick strong plastic or glass that would be needed in the Moon or an asteroid (and, as the paper correctly says, that would significantly reduce sunlight). Now, in Mars, if you don’t want farmers to wear space suits but only an oxygen mask, you can have a greenhouse with ~350 mbar pressure, that humans can tolerate. That would requiere a 1 mm thick greenhouse, still much more affordable than a lunar greenhouse or an O’Neil cylinder.

                    • Alex Tolley February 21, 2018, 18:16

                      Plants and animals will rapidly desiccate in a few bars of any gas.

                      It doesn’t matter what the pressure is, if it is contained, it is in a pressure vessel. You can argue all you like about mass, costs, etc, but you have to build them. If they are thin to contain 250mbr, then a space habitat could be built equally thin.

                      Both on Mars and with the habitat, you would need radiation protection as well as meteoroid/meteor protection. The advantage of the space habitat is that the structure does not need to withstand 1/3 g, so it can be much larger and concomitantly safer from punctures.

            • Michael February 19, 2018, 8:38

              ‘Building centrifuges for human habitation may be feasible, but what about the everything else – for forests, farms, livestock?…On Mars, you would be constantly transitioning from one centrifuge to the next, and “outside” would remain at 1/3 g.

              Plants and livestock would benefit from low ‘g’ I would think. Movement between ‘g habs’ would not be such a big issue if a network of pressurised tunnels are connected to the hubs of each centrifuge habitat.

              • Alex Tolley February 19, 2018, 13:17

                If humans need centrifuges, why would low g not also be a problem for our mammalian livestock?

                Of course one could build cities of connected centrifuges (Karl Schroder’s “Virga Cluster” novels have centrifuge cities in a bubble in space) but residents don’t get the large vistas that that we need on Earth. It would be like living indoors all the time with views piped into screens. A space habitat like an O’Neill Island 3 would offer a far more earthlike existence, IMO.

                • Michael February 19, 2018, 16:21

                  There is plenty of materials in the form of two moons in orbit about mars for a huge number of colonies. The moon to can be used to make and also launch these rotating colonies, if we have a large laser system on the moon it could use the photomultiplying principle to good effect.

        • Antonio February 18, 2018, 18:34

          That’s a false dichotomy, you can have habitats on Mars and in O’Neill cylinders. But the fact is that Mars is much more easily colonizable than void space, so it will predate space colonies by some centuries. By space colonies I don’t mean the ISS or a small mining expedition, but a real civilization, and only Mars can offer that with our current technology.

        • Alex Tolley February 19, 2018, 13:38

          suffer Mars’ drawback of spending your life in 1/3g, with its health consequences, nobody would want to buy the Mars future Zubrin is selling.

          Apparently, quite a few people would. We don’t know the consequences of partial g because the various space agencies have not studied it. There was a nice idea to test various g levels with a tethered arrangement, which maybe will be looked at seriously by a private entity if NewSpace companies can deliver on low-cost access to space.

          While Arthur C Clarke suggested in his stories that lunar g might offer extended lives (less stress on the anatomy, etc) the reverse might well be the case. We are adapted to 1 g and significantly changing that may well have health consequences as you suggest. If so, and widely known, that might well dampen the enthusiasm of prospective Martian colonists. I think just the issue of lung damage from inevitable exposure to Martian dust might deter some people. Red lung disease?

          • Antonio February 19, 2018, 17:51

            While we don’t know exactly what a 38% g will do to the human body, we do know what the much worse 0% g can do the human body and it’s not worrying for accomplishing the mission. Valeri Polyakov, after 438 days in the Mir space station and landing on Earth, could leave his capsule alone and walk with no help from others. Since the Mars Direct stay time on Mars is around 500 days, there is no need to worry about Mars gravity. It’s not mission critical at all.

            • Alex Tolley February 19, 2018, 23:10

              The issue isn’t about a mission, but about colonization. That implies generations being born and dying on Mars or the Moon.

              • Antonio February 20, 2018, 10:54

                That simply implies that we need to study the effect of Martian gravity in the first astronauts (and some pregnant animals). That’s much much much easier than constructing and maintaining an O’Neil cylinder.

                • Michael February 21, 2018, 16:21

                  The beauty of toroidal colonies is that they can be built up in modules, imagine these colonies in orbit about Mars, the views would be out of this world to pardon a pun. As for bone and muscle loss due to low g they should try powerlifting techniques as they build up bone density and muscles for small expenditures of time. They could also use ‘mass’ suits to offset muscle and bone losses.

  • Spaceman February 16, 2018, 19:31

    Interesting article on the Drake equation. Didn’t Carl Sagan also think that the L term was the most uncertain variable in the Drake equation? In contrast, Paul Davies asserts that Fl (the fraction of planets that give rise to life) is by far the most uncertain term because abiogenesis, the transformation of dead matter into living matter, may rely on a profoundly improbable series of events.

  • Ural Bas February 16, 2018, 20:31

    As stated in other sites, we all simply fail to see what’s in front of us. We all suffer this issue due to our biased assumptions on our perception of the universe.

    We are trying to find other civilizations in space when we are unable to detect one on Earth? Besides humans, there is another species that has covered most of Earth. How many of you knew this fact? No, it’s not rodents, these creatures have a global society.


    Linepithema humile, covers al continents. Some see it as a super colony, others as a family. Regardless, the fact is: There are two species on Earth that have colonized the planet with organized societies.

    The question then becomes, even with a sample of one environment with life, what are the implications of the assumptions within the Drake equation?

    If humans didn’t exists, crows have shown they the intelligence to learn and teach other generations on: dangers and tools. Let’s not talk about chimps, dolphins, canines, felines, etc.

    My point, if Nature on Earth is able to create at least a few species capable of generating societies, one that has created civilisation and technology. These terms alone can provide a more positive outcome with Drake’s assumptions. The assumptions he made were conservative at best, so it’s very likely, as humans evolve, and hopefully if they survive mutual destruction or an external event, we will see a more positive scenario than the accepted assumptions at present. This is can be consider an valid assumption due to: confirmation that planets are more abundant than was previously assumed and that water is present through our galaxy. These facts can’t be ignored, even by the most sceptical scientist.

    • Alex Tolley February 17, 2018, 14:47

      I am not clear why you think social insect societies are relevant to this discussion unless you imagine that there are intelligent insect civilizations out there that have almost no technology yet have some sort of highly developed civilization. Ant societies are not civilizations.

      While science is demonstrating the reasoning powers and tool use of other species, this is a far cry from civilization as we understand it.

      H.s.s has only started flowering with the cultural explosion some tens of thousands of years ago. Other hominid species failed completely despite millions of years of evolution. The great apes that separated from us millions of years ago have not created any civilizations. If they vanished, they would leave no trace except fossil bones. If we vanish, the Anthropocene will be detectable in the rocks by distant future observers.

  • Thomas Hair February 17, 2018, 0:01

    Thank you Robert Zubrin for eloquently exposing the hype the media gives to the Drake Equation and doing it in a mathematically rigorous way, and I say that with no disrespect for Frank Drake. He formulated his famous equation in a sea of unknowns, but to his enduring credit he has us talking about ETI in an intellectually rigorous way as well.

    My academic research is in this area, but I must add that the 800 lb gorilla in the room is the problem of Abiogenesis. We don’t have a good handle on the probability of life arising from chemical reactions. We have been doing Miller-Urey type experiments since before we were born, but the academic literature is not at a stage that we cannot say that the formation of life is not very very rare.

    • Alex Tolley February 17, 2018, 14:32

      Which is why the great interest in exoplanet biosignatures. We will probably have some idea of whether life is common or not within a decade or 2. This bypasses the lab experiments on abiogenesis mechanisms to answer that question with emprical data.

    • Simon Farmer February 20, 2018, 16:14

      I’m a big fan of yours. “Temporal Dispersion of the Emergence of Intelligence: an Inter-arrival Time Analysis” is core to my thinking on this subject. Two questions: Have you updated the simulated time range of 2-222 million years? Also, regarding Abiogenesis, as the evidence for earlier and earlier life (now up to 4.2+ billion years ago) mounts, isn’t that gorilla losing a little weight?

  • Thomas Hair February 17, 2018, 0:09

    It is distinctly possible that we are alone in the Milky Way galaxy, although if I had to bet, then I would genuflect to Sagan, Drake, others and your sound argument.

  • Harold Daughety February 17, 2018, 1:21

    It is obvious that we have only ourselves as an example, and we are biologically driven to wanderlust. Maybe E.T. is quite content to limit his numbers and never dream of space travel. Another thought: What if one nation on earth decides that one child per couple is quite sufficient world wide, and all nations must be persuaded by force of arms to achieve that? Other than our biological imperatives (which are not necessarily found elsewhere) what reason is there for space exploration?

    • Antonio February 17, 2018, 12:57

      Really?? Do you really can’t image any reason to visit the 99.999999999999999999999% of the Universe apart from the need of having children??

  • DCM February 17, 2018, 4:09

    Interesting, but of course we simply don’t yet know enough even to have a valid idea of how close to reality this is.
    We need to keep developing our area and be thankful there’s no nearby life we’d have to avoid contaminating.
    As always, such speculations bring out negativity and self-hate. We’re going to destroy ourselves in a couple of centuries, etc.

  • Michael February 17, 2018, 5:40

    There is plenty of life out there, just no proof yet, at one time we thought there were no planets! It is just they may not have the ability or inclination to develop technology. Technology is not a requirement for the survival of a species and so there may be many species out there that well just sit on the their home world going about there business thinking is there any other life out there.

    As for the Drake equation I find the civilisation demises factor a bit of a problem, there have been many ‘great’ civilisations that have fallen only for even greater ones to appear later, it is just a matter of time.

    • DCM February 17, 2018, 13:24

      The civilization thing is a problem but we’re inclined to negativity because the Western Empire collapsed and reemerged in a somewhat different form. Chinese civilization seems to have been continuous since at least the neolithic despite setbacks; even the earliest writing is apparently legible to modern scholars and they’ve been good about keeping historical records.
      India seems to have undergone a drastic collapse once, and so on.
      I don’t think we can assume technologically advanced civilizations will inevitable destroy themselves. That’s a negative idea spawned by World War II and the Cold War. I find the assumption irritating and admit I get pissed when I hear it or anything claiming inevitable catastrophe is built into civilizations like death into most biological Earth organisms.

      But I shy away from making more than hypothetical claims about life elsewhere simply because we don’t know anything definite about it.

    • Alex Tolley February 18, 2018, 13:55

      “There is plenty of life out there

      That is an assumption. I hope it is true, even if mostly microbial. But we just don’t know. Hopefully, we will have a much better idea within our lifetimes.

      • Michael February 19, 2018, 8:48

        Space is just so large that it would statistically going to zero that there would be no life other than our own…and my money is on Ceres.

  • Thomas Finch February 17, 2018, 5:47

    The entire exercise is ridiculous. Both the Drake equation and it’s rebuttal, or modification are nothing but lists of assumptions. Assumptions built on assumption built on assumptions. Any error in the equationn will have a multiplicating effect of error on all other factors in the equation, But the killer to the exercise is, There are no known, certain factors in the equation every factor is a shot in the dark to begin with There are no known accepted factors in the equation to begin with. One thing is certain If every factor is unknown, the chances of coming up with a correct answer are infinitely small

  • Infinite123Lifer February 17, 2018, 6:00

    I was even a little struck by the presumptions in the article, most of them already mentioned in the comments. I can only assume the writer was extrapolating our Solar System into … the beyond.

    I have been thinking a lot about The Great Filters for some reason lately, I literally fall asleep with it on my mind 5 nights a week. For the past 30 years, I thought for sure, no doubt there must be Alien Intelligence out there like a Class III. Something 2 weeks ago made me change my mind, it wasn’t anything I read or saw to my knowledge at least, I just felt like I truly understood the ramifications of billion year timescales, I understood that in that amount of time … a lot can happen (that could not have been understated any more than it was). I now … simply believe … if there is Alien Intelligence there might only be1 Class 3 Civilization and maybe that’s it, in the entire observable universe. No numbers, just an assumption, not even a guess really, more like a feeling and honestly I say 1 because I want to be optimistic. I know that’s extremely muddy but forgive me, I only have my imagination to work with within this realm. I mean, it’s survival in the jungle, survival of the fittest right? Adaptability? However, you cannot “beat” the jungle. It’s survival of the fittest within the jungle, the jungle will always win. The universe is the ultimate jungle, it’s out to kill everything! Violently, largely, quickly, from up close to far away it’s emanating death to life as we try to understand it and to life as we know it. In the end, it will win, after billions of years, if not billions of cycles how can we hope or hope that anything can outlive the very thing that gave it existence or life. You might be the strongest within a system, but those within cannot exist outside. Sure, humans moved from the jungle to cities, and maybe to other worlds but these are all just jungles within jungles within jungles. Of course, in my eyes, since technically stuff in the universe gave rise to life in the universe so it’s kind of self defeating for the universe to destroy everything unless of course it gave/gives rise to something with the means to transcend it but it gets a little ridiculous out here in fantasy land so enough.

    Perhaps vast swaths of the universe just belch out of existence, I mean there has to be dangers out there that not even Artificial Intelligence could calculate .

    In order for a species such as ourselves to outlast all the dangers (let alone just getting to where we are today) but to outlast the death of our Sun, to outlast the dangers that come into a Solar System once every billion, 5 billion, 20 billion years or so, black holes, gamma ray burst, planetary collisions or disruptions, to outlast that which the universe can throw at you, not to mention that which we create for ourselves … I mean you might make it pretty far but sooner or later, disease, war, black hole, supernova, really bad Artifical Intelligence … all sorts of threats even ones we can’t think of will come, eventually if you live long enough your gonna get some mean problems, and I don’t imply average, I literally mean mean :) For any species to make it through this stuff to attain a galaxy wide civilization, I mean it takes billions of years just to evolve who knows how long it will take us to create starships and over that time things are gonna happen, things that are not good for life, things already have happened and it’s probably a miracle we made it through. I just don’t see in my mind how it is very plausible… it just does not seem prudent to me anymore that any advanced civilization could stay alive long enough to colonize a galaxy. I mean, the Universe is so brutal man, you cant breath out there and pretty much everything wants to kill you or crush your atoms or use them for fusion or break your molecules apart or radiate you into oblivion and this is just stuff we know of. I think the true Great Filter lies ahead of us not beyond us, and we probably are still in the intermediate stages of filters when trying to attain galactic empires. Obviously, many filters already lie behind us but the one that keeps civilizations from flourishing on a galaxy wide scale, the filters once passed that would allow civs to communicate with one another must surely be ahead of us. In which case you know our time is limited. It’s just so gut wrenching to think about the way we treat each other and that we ain’t all on the same page to take this run as far as it can go. Such a fruitful but empty place our planet seems at times.

    I was pondering the Artificial Intelligence ideas too. Bet your just dieing to know what I was thinking about that lol, I was thinking that, like some of you that we cannot possibly survive long without it, at some point we won’t be able to calculate that which needs to be done for our survival. I think the only way our deep future takes place is with an Artificial Intelligence that “needs, almost wants” to keep the biologic alive. And I sincerely think that not even the most advance Artificial Intelligence could colonize a galaxy on the first try so to speak.

    I suppose it depends on where the limit of understanding is. I mean like Absolute Zero, there must be a point where nothing can learn anymore. At that point what tools do you possess?

    Where are they? I wish I knew my friends. I really wish I knew. I really want to believe. In fact I always have. Anything is possible, which by definition almost rules out other realities. Whichever reality it is, or has been or could be, is at this point anybody’s guess, educated or not.

  • Paul Juranek February 17, 2018, 13:37

    There is some interesting research being done on the potential for random molecules to build self organizing structures. The research looks at thermodynamics and how external energy sources (stars), create non-equilibrium conditions that favor the dissipation of energy consistent with the fact that entropy increases in a system. Here is a link to the article discussing Jeremy England’s research at MIT. The embedded video is also interesting.

  • ole burde February 17, 2018, 14:26

    Well , if we examine the factors of the Drake equation from a common sense point of view , it might make sense to evaluate them separately and see where it goes : N, L, Fl, Fi and Fc is to all purposes unknown , while R , Fp and Ne are more-or-less known …..so anybodys guess about N and L can be as good as any other …on the other hand there is a good chance that fl could become known in the short future ,at least in the range of 500LY and there are some scenaria where this would make it possibble to infer limitations on the equation ….if Fl is 0 , then the equation is probabaly history , and if Fl is relatively big we can point all the radiotelescopes at the known lifebearing planets , and have a better chance at learning something about Fi …..exept ofcourse for the unpleasant possiblity that no radio-noise is heard for the same reason the birds in certain forests can be VERY quit because any noise could atract a squirrel who would happily eat their eggs

  • Costas February 17, 2018, 16:15

    The dark forest hypothesis that was presented in the “The Three Body Problem” trilogy gives the best solution to the Fermi Paradox. Long story short, aliens avoid contact of fear of extermination. And we should probably be wise enough to do the same.

    • Antonio February 18, 2018, 8:02

      I have never seen a rational argument presented for the dark forest hypothesis, only gut feelings. And there are rational arguments against it, the most compelling of them being that our forest isn’t dark at all! Even a primitive civilization like our own could detect signs of life or civilization tens or hundreds of light years away by spectroscopy.

      • ole burde February 18, 2018, 16:27

        Antonio : In the short future it wil be relatively easy to detect life in general by spectroscopy , but MUCH more difficult , (and perhaps impossible if camuoflage was used ) to detect a mature civilisation that doesnt want to be found

        • Antonio February 18, 2018, 19:46

          Wouldn’t that be a very unintelligent strategy? If you are affraid of possible aggresive spacefaring neighbours, would you show that your planet is able to sustain life but not defended by anybody? Isn’t that like putting a huge “invaders welcome” sign on it?

          The whole dark forest hypotesis makes no sense at all to me.

          • Spaceman February 20, 2018, 10:57


            What is your favorite solution to the Fermi paradox?

            • Antonio February 21, 2018, 5:23

              Mostly the zoo hypothesis, but also the hypotheses in the line of “they don’t care about us nor our resources, and our search is very incomplete or primitive to have found such advanced, indifferent ETI”.

  • Geoffrey Hillend February 17, 2018, 17:25

    Antonio the paper: “Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences,” is not very scientific. It only mentions the dust raised by a nuclear exchange or nuclear winter which is the least of the problems. The radiation is the real problem which would affect the biosphere of our entire Earth. The radiation would not leave right away due to the half lives of radioisotopes and the fact that radiation is not simply a contaminant but the result of changes in the atomic and molecular structure of the elements or matter itself so that it is unstable and radioactive.

    Also the nitrogen in our atmosphere would be burned by the black body x ray and gamma radiation from so many thermonuclear explosions and be turned into nitrous oxide which would destroy the ozone layer and that would also affect our crops and life. Check out the story about the Bikini Atolls, islands which were nuclear tests sites in the 1940’s and 1950’s which are still radioactive. The natives were forced leave due to the radioactive fallout and were moved to another island far away. The radiation remains harmful for 100,000 years or more.

    • Antonio February 18, 2018, 9:27

      “It only mentions the dust raised by a nuclear exchange or nuclear winter which is the least of the problems. The radiation is the real problem which would affect the biosphere of our entire Earth.”

      OK… let’s try a quick rebuttal…

      Quoting from the study of survivors of Hiroshima and Nagasaki bombs and their children: http://www.rerf.jp/general/qa_e/index.html

      How many cancers in atomic-bomb survivors are attributable to radiation? From the 49,204 survivors studied, 204 died of leukemia, and 94 of those deaths were due to the bombs. From the 49,204 survivors, 7,851 had solid cancers sometime in their life, and 848 of those cancers were due the bomb.

      Are radiation-induced cancers still occurring among atomic-bomb survivors? The excess risk of leukemia, seen especially among those exposed as children, was highest during the first ten years after exposure, but has decreased over time and has now virtually disappeared. In contrast, excess risk for cancers other than leukemia (solid cancers) has stayed constant and seems likely to persist throughout the lifetime of the survivors.

      What health effects have been seen among the children born to atomic-bomb survivors? Efforts to detect genetic effects began in the late 1940s and continue. Thus far, no evidence of increased genetic effects has been found. Monitoring of deaths and cancer incidence in the children of survivors continues, and a clinical health survey was undertaken for the first time during 2002 to 2006 to evaluate potential effects of parental radiation exposure on late-onset lifestyle diseases. To date, there is no radiation-related excess of disease in adulthood, but it will require several more decades to fully determine this, as this population is still relatively young.

      What percentage of the original atomic-bomb survivor study population is still alive? As of 2007, about 40% of the RERF study population was still living, and more than 90% of the survivors exposed under the age of 10 were still living. As of 2007, the average age of the RERF study participants was 74 years.

      • Alex Tolley February 18, 2018, 13:53

        It has been 72 years since the 2 A-bomb attacks on Japan. I find it remarkable that 40% of their populations are still living, given Japan’s demographics. The populations of Hiroshima and Nagasaki must have been very young. What happened to the older population that was not in the military?

        We may or may not be over-fearful of fission products and radiation, but the Japanese are spending an awful lot of money and resources to try to restrict the Fukushima reactors from spreading their fissile material into the surrounding areas. Perhaps they shouldn’t bother?

        • Antonio February 18, 2018, 19:09

          “What happened to the older population that was not in the military?”

          Most of the population were not military.

          “Perhaps they shouldn’t bother?”

          What they are doing is solely by political reasons, not for a real danger. They should simply make a concrete enclosure, don’t care about the melting of the core, wait some decades until the core solidifies and then open the concrete, cut the mess into pieces and put it in some medium-level deposit. See for example this:



          Or this for Chernobyl, that was much worse:


          “The radiation exposures to the populations most affected by the Chernobyl accident (emergency workers and people continuing to live in contaminated areas) results in an average additional mortality risk no greater than that caused by (relatively common) elevated exposures to natural background radiation either at home or through occupation.”

          “The increased mortality rate of the populations most affected by the Chernobyl accident may be comparable to (and possibly lower than) risks from elevated exposure to air pollution or environmental tobacco smoke. It is probably surprising to many (not least the affected populations themselves) that people still living unofficially in the abandoned lands around Chernobyl may actually have a lower health risk from radiation than they would have if they were exposed to the air pollution health risk in a large city such as nearby Kiev.”

          “Increased mortality due to:

          Living in Central London compared to Inverness: 2.8%

          Passive smoking (risk to non-smoker at home if spouse smokes): 1.7%

          Chernobyl emergency workers in the 30-km zone, 1986–87, 100 mSv: 0.4%

          Chernobyl emergency workers in the 30-km zone, 1986–87, 250 mSv: 1.0%”

  • Astronist February 17, 2018, 18:45

    “Clearly it stands to reason that there must be extraterrestrial civilizations. We know this, because the laws of nature that led to the development of life and intelligence on Earth must be the same as those prevailing elsewhere in the universe. Hence, they are out there. The question is: how many?” – Incorrect, because this argument does not take account of time. The time required for life to evolve from non-life is currently unknown. The universe is not infinitely old. Therefore it is not yet possible to say whether life has only appeared once, or many times (as Paul Davies also makes clear in his 2010 book “The Eerie Silence”.

    • Antonio February 18, 2018, 9:28

      “The time required for life to evolve from non-life is currently unknown.”

      In Earth it took no more than ~200 million years.

      • Alex Tolley February 18, 2018, 13:43

        But Earth also required the universe to create heavy elements from earlier star populations. Therefore a chunk of cosmic time may have been lifeless until stars had created heavier elements for the next generations of stars.

        Life may have started quickly on Earth (we don’t know), but we do know that it took a long time for eukaryotes to appear, and even longer for multi-cellular like. What we do know, from our single example, is that it took at least 3.5 bn years for terrestrial life to develop a technological civilization, which is about 1/4 of the age of the universe. During that time, there is no evidence that any species on Earth created such a technological civilization.

        • Hamilton1 February 19, 2018, 17:17

          Stars that generate heavy elements pass through their lives very quickly – no more than 10 million years for a supergiant. So not much time lost at all before heavy elements proliferate.

  • Night Owl February 17, 2018, 20:14

    Just to reiterate a few points that stood out for me:

    If L is less than 100 years for the only technological species we know about, and we already have thermonuclear weapons and other deadly WMD’s on the horizon, isn’t it wildly optimistic to think that L is 10000?

    “Technological civilizations, if they last any time at all, will become starfaring … (within) a couple of centuries”. This seems wildly optimistic. We have no idea if this is true for our own civilization, let along anyone else. It may turn out that starflight, as a practical matter, taking into account economics, social factors, etc. is extremely difficult or impossible.

    Is it really true that many technological civilizations will arise to replace ours after it falls?
    In “Of Men and Galaxies”, Fred Hoyle wrote:

    “It has often been said that, if the human species fails to make a go of it here on the Earth, some other species will take over the running. In the sense of developing intelligence this is not correct. We have or soon will have, exhausted the necessary physical prerequisites so far as this planet is concerned. With coal gone, oil gone, high-grade metallic ores gone, no species however competent can make the long climb from primitive conditions to high-level technology. This is a one-shot affair. If we fail, this planetary system fails so far as intelligence is concerned.”

    If this is true, then Zubrin is again way too optimistic. Maybe many of us, who have lived through this exceptional period of technological change in our planet’s history, and have read a lot of science fiction, lack objectivity on these matters? It seems to me that the Great Silence is strong evidence that something is wrong with our assumptions, and good reason for more humility and possibly pessimism on this question.

    • Brett Bellmore February 18, 2018, 10:21

      But we haven’t exhausted those resources yet.

      Take copper for an example. We used to mine native copper, which was handy, because you could just pick a lump of it up and hammer or melt it into something useful. But as industry increased in scale, we switched to sulfide copper ores that could be open pit mined, even though their ease of primitive use was less.

      Result? You can still walk around in parts of Northern Michigan, and pick up lumps of copper off the ground.

      We’re discontinuing use of coal before it’s exhausted, and both wood and peat are renewable. Bog iron was used before the ores we use now, and could be used again. Clay is still around for ceramics.

      If civilization collapsed, and had to rise again, it would face certain obstacles, but I doubt they’d be insurmountable.

      None the less, we might emulate the Moties, and place very comprehensive, durable libraries in out of the way places. That might be a smart backup plan.

      • torque_xtr February 23, 2018, 5:41

        The accessibility of resources is linked to thermodynamics. The less concentrated resources are used, the more energy has to be used to achieve low entropy again. If ve have no concentrated energy sources, we need more time. A 100.000 year-long climb from wood-powered steam engine to information age may seem long to us, but it is still an eyeblink in geological scales. More, when concentrated resources and fuels are totally used up in “pervious attempts”, the waste itself becomes the next “concentrated resource”. When we put those 100-yr-ish numbers in the equation, we forget how patient a civilisation is allowed to be :-)

  • Robin Datta February 17, 2018, 21:36

    Hemoglobin in quantities to transport enough oxygen for a large brain would make the blood viscous if it were free hemoglobin: it happens to be in erythrocytes. Adequate oxygen exchange with the environment requires a gas exchange mechanism – the lungs, rather than a liquid exchanger.

    Brachiation (swinging from one overhead branch to another) demanded three axes of movement at the shoulders and stereoscopic vision, both of which help in manipulating and shaping small objects into tools; the opposable thumb and bipedal gait (freeing the forelimbs) also helped. The vocal apparatus and speech were also essential.

    Current great apes do not have speech, opposable thumbs or bipedal gait. And in extinct hominins only the last of these is obvious. That’s a lot of factors to make us human. Almost a Drake-like equation for our lineage in the DNA-based animal kingdom.

    • Alex Tolley February 18, 2018, 13:35

      How very anthropocentric. That is a Kiplinesque “Just So” story. There will be other routes to technological civilization, and no doubt some of those species will make similar arguments about their particular physical form.

      • Robin Datta February 18, 2018, 15:50

        Not even standard DNA need be evoked by xenobiology or systems so far removed as to be beyond the accepted norms of “biology”. And similar arguments about their particular physical form may be ensconced in their equivalent of biology.

    • Mephane February 19, 2018, 5:55

      > Current great apes do not have speech, opposable thumbs or bipedal gait.

      Current greats apes definitely do have opposable thumbs, and are able to walk in a bipedal mode to a limited extent. And while they do not have speech, they can for example learn simple sign language.

      • Robin Datta February 19, 2018, 14:45

        Current great apes have a thumb too short for a forceful pinch. Their upper airways do not form effective vocal tracts. Visual transmission of speech signals has quite different implications from the auditory mode. Pelvic, pedal, proximal femoral, knee, lumbar & cervical spine and craniofacial modifications permitting a default bipedal gait in humans are absent.

        All of these and brain size will need substantial modification to produce another human equivalent.

        • Antonio February 19, 2018, 18:02

          Human bipedalism appeared very fast. Brain enlargement took much longer.

  • iwan February 17, 2018, 21:59

    i welcome this new equation.
    also i think there should be another thing added!
    what is about the possibility of a civilisation developing artificial intelligence? this civilisation could profit from this invention in many ways, like in developing of new spacetravel technology, solving of physical problems or energy production and such and therefore could get an extension in time span of existence. also an artificial intelligence, if self-sufficient (or maybe some sort of cyborg-ish), would not be limited in the duration of spacetravel due to mortality or maybe also not have problems with things like g-force as biological intelligent beings would have. also an artificial intelligence would be quicker in developing new outposts on new planets and then spread from there again. this would affect the possibility of contact between zivilisations. so i think it would be important to find a way to determine if and how fast a biological civilisation is able to create artificial intelligence.
    furthermore it would be interesting (specially regarding AI) how high the possibility of a galaxywide interstellar civilisation would be. :)
    thank you for your attention!

  • Brollen February 17, 2018, 23:00

    Very interesting and compelling. But two things occur to me that are not even modeled in the equations:

    1. The number of planets in habital zones having moons that might be capable of harboring life and supporting the same evolutionary runway as modeled for planets. This would likely bolster the ET count.

    2. To my way of thinking, I believe possibly the f’i but especially the f’c value is grossly overestimated. I have no doubt that life is common amongst the stars in the universe but I wonder how likely the emergence of intelligent and radio transmitting life really is. Scientifically we really do not understand or cannot identify when or what lead to Homo sapiens. The emergence of life seems to be a scientific certainty based on the presence of certain environmental factors but regarding the emergence of radio wielding intelligence … do we really know?

  • Andras Kaptás February 18, 2018, 3:03

    Pls see beyond the a technological singularity.
    From this point of view theres no any barrier what divide us from interstellar travels.
    For an artificial lifeform time does not matter. They can use almost any kind of resource to live, reproduce, and spread. Asteroids, comets, unhabitable planets, interstellar gas and any derbies…
    In this picture we can see the whole galaxy as a living space, and for it, we can use or population dinamyc models on interstellar scale.

  • Spencer Grow February 18, 2018, 6:51

    It’s pretty mind-blowing how inevitable galactic civilizations seem to be. We have measurements and models to suggest inevitability. My thoughts: prokaryotic and eukaryotic cells can naturally disperse — especially within stellar nurseries. Other habitable biospheres are found within our own system, and with water in proto-planetary disks, would simply be in every star system on Mars- and Europa-type bodies. Earthlike…Earthlike could be tricky. A eukaryotic cell might need a full accompaniment of very complex metabolic pathways and a near-perfect environment as on Earth. There’s always the informing and haunting spekter our eclipse affords. But much of this has inevitability, mechanism, and observation.

  • Roger February 18, 2018, 8:02

    An issue rarely talked about is the ability to permanently colonise a new world. If humans need very specific environmental ranges, then long term terraforming will be needed before we can gain any foothold on new worlds. Not only is a terraforming effort very costly and uncertain, it is also done a long way from home so logistically very difficult. Maybe it’s so hard that technological civilisations rarely spread to other systems, even if they can travel there.
    AI systems can do some exploration, but won’t leave much of a trace for other civilisations to see.
    We need some experiments with reduced gravity to see if humans can survive and reproduce successfully. Gateway Foundation has a proposal for doing this in low earth orbit.
    If humans can survive and reproduce in a large range of enironmental ranges you still have the issue that incompatible low level microbes in candidate planets may prevent colonisation. Humans evolved to deal with microbes from earth, but it could be automatically deadly to live on anything but life empty worlds with life imported from earth.
    And if we can’t develop colonies off planet, we may remain relatively small and undetectable to other civilisations.

    • Alex Tolley February 18, 2018, 13:31

      Space habitats obviate the need to terraform planets. They offer far more room with fewer resources, can be tailored to any species’ needs, and offer excellent quarantine capabilities to prevent contagion.

      While I would hope colonies are not set up on living worlds, it is entirely possible that the colonists’ biology is so different that they would represent a separate biosphere. George Church has suggested that we regig the human genetic code so that viruses are prevented from replicating in humans, providing complete immunity.

      If however, species do want to live on suitable planets, rather than just habitats, they may want to terraform dead worlds in advance of colonization. Humans could attempt that feat so that in a million years or so, the galaxy could be full of living worlds with terrestrial biology, suitable for occupation by future terrestrial [biological] civilizations.

      Having said that, my guess is that this is obviated by machine species that will develop well before that, allowing worlds of any type to be “colonized”. Such artificial species could interact with living worlds without any issue of contamination in either direction, although metal and plastic eating bugs might just prove dangerous enough to be avoided.

    • Rob Flores February 18, 2018, 13:59

      Too many unknowns about interstellar travel that is the rub. Fast travel implies smaller colony higher risk of failure. Large colony. Slow travel Introduces fatal social risks, break down of critical systems.

  • Wojciech J February 18, 2018, 12:40

    There are so many assumptions in the article that I can’t consider it seriously.
    Just at a glance, one example;
    ”Technological civilizations, if they last any time at all, will become starfaring. In our own case (and our own case is the only basis we have for most of these estimations), the gap between development of radiotelescopes and the achievement of interstellar flight is unlikely to span more than a couple of centuries, which is insignificant when measured against L=50,000 years. This suggests that once a civilization gets started, it’s likely to spread”
    *will become starfaring
    *civilization is likely to spread
    *the gap between development of radiotelescopes and the achievement of interstellar flight is unlikely to span more than a couple of centuries

    All of the above are assumptions that can’t be really proven in one way or another, and serious counter-arguments can be made against them.

    At the moment making these assumptions is just throwing your darts in the dark, hopefully next generation telescopes will bring us closer to answers.

  • Wojciech J February 18, 2018, 12:55

    A civilization capable of starflight to colonize other planets no longer has the need to do so.
    It already has technology to sustain life-support systems and closed environment capable of preserving life and providing it with energy and resources needed for survival.
    Therefore rather than waste hundreds if not thousands of years on terraforming barren planets or ruining biospheres(which are far more valuable in themselves) it can create artificial habitats for settlement.
    That or it reaches post-biological status that makes the need for living space unnecessary.

    I really don’t see civilizations constantly expanding and settling more and more worlds. It is safe to assume that the need for living space isn’t that big, and after all, even our solar system could support trillions of humans for billions of years without much effort .

    Therefore I would guess that alien civilizations, if they exist, don’t really need to colonize that much.

    Also the numbers seem very exaggerated. Our rise to technological civilization was very lucky and based on numerous unique conditions. It is very questionable if other species would have the same luck.

    • Alex Tolley February 18, 2018, 13:21

      The expansion could be driven by the need for more energy, more physical resources, and the acceptance that isolated populations offer more opportunities to survive catastrophes. Cultural speciation may be as important to civilization as it is to biology.

    • Mephane February 19, 2018, 6:26

      > A civilization capable of starflight to colonize other planets no longer has the need to do so.
      It already has technology to sustain life-support systems and closed environment capable of preserving life and providing it with energy and resources needed for survival.

      This is is true for certain forms of interstellar travel (e.g. generation ships), but not all of them, and certainly not for interplanetary travel. A colony ship to Mars, for example, would only need to bring supplies for half a year to a year, which is a far cry from creating an actual self-sustaining artificial environment. And creating the latter on a planet is an order of magnitude easier due to the access to the planet’s resources.

  • Spencer Grow February 18, 2018, 13:42

    It’s pretty mind-blowing how inevitable galactic civilizations seem to be. We have measurements and models to suggest inevitability. My thoughts: prokaryotic and eukaryotic cells can naturally disperse, especially within stellar nurseries. Other habitable biospheres are found within our own system, and with water in proto-planetary disks would simply be in every star system on Mars- and Europa-type bodies. Earth-like…Earth-like could be tricky. A eukaryotic cell might need a full accompaniment of very complex metabolic pathways and a near-perfect environment as on Earth. There’s always the informing and haunting specter our eclipse affords. But much of this has inevitability, mechanism and observation.

  • Robert L February 18, 2018, 13:47

    “Human ancestors 30 million years ago were no more intelligent than otters. It is unlikely that the biosphere would require significantly longer than that to recreate our capabilities in a new species.”
    This is a massive begging of the question. There is also rather good experimental evidence against it, in the failure of the hominid-free Americas to produce a rival species with “our capabilities.”

  • SelfAwarePatterns February 18, 2018, 14:01

    I question the modification to fi. In truth, I think Drake was already far too optimistic with this value. Yes, if nuclear war wiped out our civilization, we might recover in a few centuries. And yes, the biosphere would likely recover in a few million years from an extinction level event, and there would no doubt be many (relatively) intelligent species along the lines of dolphins, elephants, etc.

    But, civilization requires more than intelligence. It also requires a species that can manipulate its environment with dexterity. It’s why, of all the intelligent species out there, only a branch of primates actually ever developed to the point of having symbolic thought and producing a civilization. This required, first, trees, so a species could develop a body plan to navigate their branches, second, a drying climate pushing some of the species to come down from the trees, and third, grasslands, so after the species came down from the trees, it had a reason to stand up, freeing up its hands for other things.

    It is possible that if enough primate species survived human extinction, that another civilization might eventually arise sometime in the next 50-100 million years, but it seems far from certain. And if the primates were wiped out, then the probability starts to look remote to me that anything would develop before the sun heated the earth up too much for it.

    It’s also worth noting that we don’t have a lot of reason to suspect that complex life (animals, plants, etc) are all that common. It took 85% of Earth’s history to date for it to develop. There were many low probability events (prokaryotes, sexual reproduction, oxygenation, etc) that, if they hadn’t happened, complex life may never have developed. It may be that most of the alien biospheres are populated primarily with microscopic life.

    And, as others on this thread have already pointed out, there’s the Fermi paradox. If alien civilizations are so pervasive, where are they? Why hasn’t Earth been colonized many times over?

  • Steven Torry Rappolee February 18, 2018, 15:21

    It took 4 Billion years for metazoans to evolve on Earth is this a common outcome or are we an outlier?
    The center of galaxies can be very dangerous places with radiation effects on evolution
    I would like to see a Zubrin VS rare Earth hypothesis debate

    • Antonio February 18, 2018, 19:24

      “The center of galaxies can be very dangerous places with radiation effects on evolution”

      That’s the same than saying that planets with free oxygen can’t harbor life, because it’s highly corrosive and toxic, and it was a poison for all life on Earth during most of its history.

  • J. Jason Wentworth February 19, 2018, 0:25

    I find it interesting how hypotheses so rapidly become assumptions. We really have little that is hard and factual to go on. AI, Artilects, Machine civilizations, Mind uploading, Space Colonies (and slow starships made from them), and Von Neumann machines (and starprobes of this type, including berserkers), are only hypothetical ideas, any of which might–or might *not*–prove to be workable in practice, and:

    All we know is that our kind of life and intelligence came into being here, on this Earth. While this suggests that similar life and intelligence might have arisen elsewhere (or might do so in the future) in places with similar environments, it does not necessarily follow that is has (or will). The alternative hypothesis–that “life as we *don’t* know it” (non-carbon-based, non-DNA-based, etc.) may be possible–could also be true, but it might not be true. Also:

    With such a small stock of certain knowledge, we aren’t yet in a position to theorize about the existence–or non-existence–of extra-terrestrial life, intelligent or otherwise. Theories (as opposed to hypotheses) make predictions that can be checked by experiment or observation, which can falsify or support them. We are simply not knowledgeable enough–at this time–to theorize in either direction. In addition:

    While it is frustrating, right now we can’t determine whether the Earth is home to the only life in the galaxy (or perhaps the entire universe), the only complex and/or intelligent life, or just one of a few (or many) other technological civilizations. *Any* of these possibilities (the hopeful as well as the depressing ones), and variations on them (comet- or space-based life or civilizations, conscious stars [as Dr. Gregory Matloff and some other scientists hypothesize], and/or perhaps other possibilities we have yet to conceive of) might be correct. With so little certain information to go on, there are only two courses of action that we should take:

    [1] Keep looking, via all possible methods (spectroscopic observations for life signatures on exoplanets, gravity focus imaging of exoplanets, radio and optical SETI, gravity wave and/or neutrino SETI [when/if they become possible], SETA probe and off-Earth artifact searches, etc.), and–when we can do it–launching our own Bracewell probes for close-up exoplanet examination and listening for any local civilizations, and;

    [2] Conducting ourselves as if our Earth *is* the only home of life in this universe, because it might be! Even if the Earth isn’t the only inhabited planet, and even if intelligent life is common in the Milky Way, nowhere else–in this reality–are we *ever* likely to find another planet populated by human beings and the plants and animals we know.

  • david lewis February 19, 2018, 11:56

    People, we need not worry – the galaxy is teeming with life. It was 4.134 billion years ago they first visited the solar system to make a new home for themselves. Yet they saw that the beginnings of life had appeared on the planet Earth and they pondered what to do. Greed drove them to desire the wealth of the solar system, yet they were buddists and knew not to harm other living creatures, no matter how small of insignificant.

    So they uploaded the beginnings of life that had appeared on the planet, giving it a nice, new home utilizing science that’s a billion years beyond ours. Then the tored the planet Earth apart to make space habitats, along with the rest of the planets. Then they went to work mining the Sun. All that is left of that solar system is a swarm of trillions upon trillion upon trillions of habitats with massive stockpiles of hydrogen.

    For 10^100 years they will dwell there, living and thriving.

    But what of us? We will dwell forever within the 0.74kg sphere that is now our universe. And we will learn that there is no escape, for those beings with all their intellect and power, not imagining that such crude chemistry could aspire to true life, left us no way to access the outer universe. And, of course, neither did they want the competition.

    To keep us safe they tossed that sphere into space. Travelling at a measely 1/1000th the speed of light, there is nothing around us for four million light years even if we did find a way to escape our cozy, eternal prison. Here we will grow; here we will expand; here we will learn the truth; here we will die.

    Okay, so the above is a bit far fetched, but it’s based on fewer assumptions than those mentioned in the article. Nor are those assumptions any less plausible.

    We each have our beliefs, and desires, yet the only way to learn the truth is to learn. Missions to Mars to look for life, to Europa and Titan. To build telescapes that can pear through space to sample the atmospheres of alien worlds.

    I just hope we aren’t trapped within a 0.74kg probe that’s four million light years from anything. But if we are, we can still explore the simulated universe we have. Within a near eternity who knows what will happen? In few trillion, trillion, trillion years we might even encounter another species that will free us.

  • LocalFluff February 19, 2018, 17:45

    The only possible conclusion given your numbers, is that there exist ONE and only one space faring civilization in the Milky Way. Because the first one would immediately have colonized all of it before anyone else had a chance the keep up with it. Not that it would be able to keep up any coherent empire given that light travel time is enormous relative to technological and cultural development time scales.

    All interstellar communication with colonies would be archaeology. Like egyptologists studying cave and tomb paintings. Ancient irrelevant messages that no one really cares about. (That’s a solution to the Fermi paradox, the lag is too bad to make multi player gaming fun).

    As we know from biology, all life on Earth had one and the same origin at least four billion years ago. So that still leaves the Fermi paradox unanswered. Why haven’t those who seeded Earth with life returned? Why did they seed us only once? Haven’t they come up with anything better than our slow random evolution, since 4 000 000 000 years? If “they” have some kind of space policy, how come they can stay to it a billion times longer than NASA can?

  • Geoffrey Hillend February 19, 2018, 18:19

    My point was that it may be that the idea that an ET civilization dies from a nuclear war is rare or non existent so we can throw that idea out of the Drake Equation since we all have to learn to get along and I predict we eventually will and so did all ET civilizations. The assumption is that a civilization has the power to destroy itself with nuclear weapons. If one does not believe that it does not matter since that variable of the drake equation would thought to not apply anyway which was my opinion.

  • David Brin February 19, 2018, 20:29

    Arguments rage on and on about the so-called “Fermi Paradox” or “The Great Silence”… the puzzling fact that we see no signs of advanced civilizations among the stars. Nor evidence that Earth was ever even visited, during the two billion years that it has been prime real estate, with an oxygen-rich atmosphere.  (That blank period says much more than the failure to detect SETI radio messages.) Many theories have been offered fervently by very smart people, each of them convinced that he or she has the aha-answer!  But way back in 1983 I published what is still – to this day – the only major review article about alien contact, surveying almost a hundred different hypotheses and ranking them according to plausibility. Surprisingly, there have been almost no new ideas since then, though plenty of heated opinion!

    Bob’s revision of the Drake Equation, to take into account likely colonizations/expansion rates, is somewhat simpler than the one I presented in my 1983 “Great Silence” paper in QJRAS.* There I also included factors for “Approach-Avoidance” or detectability. e.g. a civilization that likes to dwell inside comets might not be easily spotted, even if they spread widely. (A simple “N” number density predicts no observable.)

    Alas, the biggest problem with Bob’s analysis is the series of blithe assumptions. For example, he deems it likely that even a human extinction event might easily be followed with another Earth species taking our place, within a few million years. But it took three billion years for Earth to create metazoan life (and any alien toilet-flush into our seas would have changed that.) And another billion for metazoans to make advanced, brainy creatures like dinosaurs and us.

    Are there other “clever” species on Earth? Yes! Otters, dolphins, apes, crows, parrots, elephants, sea lions… and no reason to think velociraptors weren’t very smart at the same level. And that is harsh, because nature apparently makes it VERY hard to get above that glass ceiling. I’ve been cataloguing hypotheses for the Great Silence for 30+ years, and the most plausible of 100 that I’ve seen is that human sapience is very, very anomalous.

    Bob also assums that colonization is easy. But even a high tech race might have troubles adapting to existing ecosystems… or else get sick of endless-dreary terraforming.

    I have no time to get into Bob’s other factors, but many others are taken as “given” or reasonable that seem quite problematic. Moreover, if the factors are all so friendly on the left side of the D.E., then that only gives weight to the arguments of the Existential Risk guys – like Nick Bostrom – who claim that our “Fermi Filter” lies ahead of us.

    Given current insane politics in humanity’s supposed-leading and supposedly most progress-oriented culture, I am leaning toward giving that notion greater credence. A species in which supposedly smart fellows give loyalty and support to a War on Science may not reach the stars.

    Here’s a whole compilation of my articles and speculations about the Search for Extraterrestrial Intelligence (SETI) & related matters, some of them published on Centauri Dreams. http://www.scoop.it/t/seti-the-search-for-extraterrestrial-intelligence

    — David Brin, PhD

    * Quarterly Journal of  Royal Astronomical Society, fall1983, v.24, pp283-309 http://adsabs.harvard.edu/abs/1983QJRAS..24..283B http://articles.adsabs.harvard.edu//full/1983QJRAS..24..283B/0000283.000.html

    • Alex Tolley February 19, 2018, 23:16

      Given your pessimism about sapience, why your concern over METI? The jungle is quiet because it is likely empty of smart predators.

    • J. Jason Wentworth February 20, 2018, 4:20

      You had me, and then you lost me; the administration’s financial support of scientific research is about the same, overall, as last year’s figures (as “Scientific American” reports: http://www.scientificamerican.com/article/trump-budget-gives-last-minute-reprieve-to-science-funding/ ). There are also budget allocation increases in some areas, such as the National Science Foundation and NASA budgets, while the U.S. Geological Survey’s budget has been reduced by 21%. That is hardly a “war on science,” particularly given our national debt. Nazi Germany’s denouncement of “Jewish physics” and persecution of such people, and the Soviet purges of scientists who disagreed with Trofim Lysenko’s biology theories (some of them just disappeared), constituted true attacks on science. Regarding the eerie silence:

      It could simply be that life has never arisen elsewhere, because it doesn’t have to. Life is entirely optional, a chemical extravagance, a *far*-more-complex-than-necessary way for elements and compounds to combine in order to reach lower, more stable energy states. There are many such compounds, and they don’t have to be self-replicating, as living ones are, in order to achieve those states (some, such as salts, which have ionic bonds, do “self-replicate”–after a fashion–but they aren’t alive). But we should keep looking for other life, because it may exist (even if only as algae-like organisms or foliage detectable by spectroscope), and at the very least, we’ll gain new astronomical knowledge from every exoplanetary system we examine.

  • Geoffrey Hillend February 19, 2018, 21:33

    What if the ET’s don’t leave behind any evidence which is something that is simple to do with an civilization with the advanced spacecraft technology of interstellar travel which does not mean there never were here. There is again that non interference prime directive. I predict evidence will come in the future and I don’t think we will stop looking.

    • J. Jason Wentworth February 21, 2018, 5:36

      In our current state of ignorance (in which we could be alone, or could be one of a number of galactic civilizations), it is entirely possible that the Earth has had extrasolar visitors–even multiple times–in the distant past, whose visit traces were eroded, oxidized, subducted into the crust, and/or buried by the Earth’s natural processes. (If not for the discovery of the Antikythera wreck in 1900, we would never have known that the ancient Greeks built sophisticated mechanical astronomical computers.) We might also find such evidence of past visitation on the other planets, moons, or small bodies of our solar system, perhaps even on our own moon, or orbiting between the planets, and:

      Sunward of the Earth, our star’s glare makes it very difficult to even discover if there are–or are not–Vulcanoids (small asteroids orbiting in a stable region inside Mercury’s orbit, named for the hypothetical planet [not Mr. Spock’s home world] that was once thought to orbit there and cause the peculiar advance of Mercury’s perihelion via gravitational perturbations [it was later found that Relativistic effects are why this happens]). There could be any number of natural objects (below certain size limits) or artificial ones (interstellar probes, deliberately-left-behind instrument packages, etc.) orbiting near the Sun, which we could not detect if they are there. While I wouldn’t wager in favor of there being any alien equipment in our solar system, I wouldn’t bet against it either.

  • Brian February 20, 2018, 4:11

    This essay pretty much ignores the concept of a filter. That advanced technology only emerged once in the history of complex life on Earth is telling.

    Can we assume that an industrial revolution-equivalent civilization would have left behind subtle clues to its existence even hundreds of millions of years later? Anomalies in the abundance of compounds in the geologic record, or a dearth of fossil fuels and minerals in the Earth’s crust compared to what we would expect to find?

    In that case it’s safe to say we are the first such civilization on Earth. So while primitive life, or even complex life might be common in the universe, I think that advanced technology probably isn’t. It takes a lot of factors coming together to get machinery rather than just the kind of intelligence we associate with dolphins or chimps. Language and tactile dexterity. Sociability. Long life span. Probably many more.

    I wouldn’t be surprised to find alien raptors or whales or crows out there, but I believe space faring civilization is probably incredibly rare.

    • J. Jason Wentworth February 21, 2018, 6:22

      Brian, this astonishing article (see: http://cosmosmagazine.com/biology/australian-raptors-start-fires-to-flush-out-prey ) is about Australian birds of prey who have learned to use fire to flush out prey, including by placing twigs where they will be ignited by brush fires, then carried by them to their desired hunting sites. I do doubt, though, that they will one day become sentient and star-faring, as did an avian race in Alan Dean Foster’s story “With Friends Like These” (the genius and poet horse Pericles in “Dream Done Green,” also in that anthology [which bears the name of the first story] is more plausible, having been–like other animals–“uplifted” by humans, but I’d rather be a unicorn), and:

      In his book “The Eerie Silence,” Paul Davies posited something that is haunting to contemplate, because of its ramifications for the abundance–or the possible lack thereof–of extraterrestrial technological civilizations:

      Science arose only once in human society, a fortunate confluence of Greek philosophy (experimentation–which was considered manual labor–wasn’t considered a worthy pursuit by most Greek philosophers, however, as pure reason was considered the path to knowledge) and Jewish–and later, Christian–philosophy (which hold that history has a definite direction [it isn’t just cyclical, although certain cycles do occur within it], that manual labor *is* a worthy pursuit, and that the universe operates according to laws that human beings can at least partly discover and understand). Also:

      Other cultures had experimentation without reason (hypotheses and theories), and/or philosophical speculation without experimentation (sometimes within the same societies, but among different people or social strata), but only Greco-Judaic-Christian thought led to science, in which devices are built and observations are made due to combined observation, experiment, and theorization, often regarding phenomena that human senses cannot perceive (atoms, molecules, magnetic fields, radiation, radio, X-rays, etc.). Without this, Davies pointed out, no radio telescopes would ever have been built (it isn’t the sort of thing that pure “tinkering” would lead to, without the theory behind its operating principles, which would also predict that stars emit the unseen radio waves which can be “heard”). Now:

      If we lucked out–like a Powerball Lottery winner, whose chances of winning are almost vanishingly tiny–in stumbling across the scientific method, how likely is it that intelligent beings elsewhere (who are likely quite rare, as Davies fears [but hopes otherwise, of course]) would also be as fortunate?

      • Mark Zambelli February 27, 2018, 12:10

        “Marooned in RealTime” is a sci-fy book by Vernor Vinge that I loved growing-up and in it, several million yrs hence, he describes a bird that builds large nests from stones and dry sticks that it then throws flint into to actually start fires from the resulting sparks. Always loved that idea, a bird that cooks it’s own food.