A ‘Census’ for Civilizations

by Paul Gilster on May 17, 2017

We’ve been talking about the Colossus project, and the possibility that this huge (though remarkably lightweight) instrument could detect the waste heat of extraterrestrial civilizations. But what are the chances of this, if we work out the numbers based on the calculations the Colossus team is working with? After all, Frank Drake put together his famous equation as a way of making back-of-the-envelope estimates of SETI’s chances for success, working the numbers even though most of them at that time had to be no more than guesses.

Bear in mind as we talk about this that we’d like to arrive at a figure for the survival of a civilization, a useful calculation because we have no idea whether technology-driven cultures survive or destroy themselves. Civilizations may live forever, or they may die out relatively quickly, perhaps on a scale of thousands of years. Here Colossus can give us useful information.

The intention, as discussed in a paper by Jeff Kuhn and Svetlana Berdyugina that we looked at yesterday (citation below), is to look out about 60 light years, a sphere within which we have numerous bright stars that a large instrument like Colossus can investigate for such detections. We’re making the assumption, by looking for waste heat, that civilizations living around such stars could be detected whether or not they intend to communicate.

Screenshot from 2017-05-17 08-41-14

Image: Figure 1 from Kuhn & Berdyugina, “Global Warming as a Detectable Thermodynamic Marker of Earth-like Extrasolar Civilizations: The case for a Telescope like Colossus.” Caption: Man-made visible light on the Earth in 2011. From DMPS/NASA. The brightest pixels in this 0.5 × 0.5 degree resolution map have a radiance of about 0.05 × 10−6 W/cm2/sr/micron. Credit: Jeff Kuhn/Svetlana Berdyugina.

Let’s take the fraction of stars with planets as 0.5, and the fraction of those with planets in the habitable zone as 0.5, numbers that have the benefit of Kepler data as some justification, unlike Drake’s pre-exoplanet era calculations. Kuhn and Berdyugina have to make some Drake-like guesses as they run their own exercise, so let’s get really imaginative: Let’s put the fraction of those planets that develop civilizations at the same 0.5, and the fraction of those that are more advanced than our own likewise at 0.5. These numbers operate under the assumption that our own civilization is not inherently special but just one of many.

Work all this out and we can come up with a figure for the fraction of civilizations that might be out there. But how many of them have survived their technological infancy?

Let me cut straight to the paper on the outcome of the kind of survey contemplated for Colossus, which is designed to include “a quantifiably complete neighborhood cosmic survey for [Kardashev] Type I civilizations” within about 20 light years of the Sun, but one that extends out to 60 light years. In the section below, Ω stands for the ratio of power production by an extraterrestrial civilization to the amount of stellar power it receives (more on this in a moment).

From the paper:

…current planet statistics suggest that out of 650 stars within 20 pc at least one quarter would have HZEs [Habitable Zone Earths]. Assuming that one quarter of those will develop Ω ≥ 0.01 civilizations, we arrive at the number of detectable civilizations in the Solar neighbourhood ND = 40fs, where fs is the fraction of survived civilizations (i.e., civilizations that form and survive). Hence, even if only one in 20 advanced civilizations survive (including us at the time of survey), we should get a detection. Taking into account the thermodynamic nature of our biomarker, this detection is largely independent of the sociology of detectable ETCs.

Independent because we are not relying on any intent to communicate with us, and are looking for civilizations that may in fact be advanced not far beyond our own level, as well as their more advanced counterparts, should they exist.

Suppose we detect not a single extraterrestrial civilization. Within the parameters of the original assumptions, we could conclude that if a civilization does reach a certain level of technology, its probability of survival is low. That would be a null result of some consequence, because it would place the survival of our own civilization in context. We would, in other words, face old questions anew: What can we do to prevent catastrophe as a result of technology? We might also consider that our assumptions may have been too optimistic — perhaps the fraction of habitable zone planets developing civilizations is well below 0.5.

But back to that interesting figure Ω. The discussion depends upon the idea that the marker of civilization using energy is infrared heat radiation. Take Earth’s current global power production to be some 15 terawatts. It turns out that this figure is some 0.04 percent of the total solar power Earth receives. In this Astronomy article from 2013, Kuhn and Berdyugina, along with Colossus backers David Halliday and Caisey Harlingten, point out that in Roman times, the figure for Ω was about 1/1000th of what it is today. Again, Ω stands for the ratio of power production by a civilization to the amount of solar power it receives.

The authors see global planetary warming as setting a limit on the power a civilization can consume, because both sunlight from the parent star as well as a civilization’s own power production determine the global temperature. To produce maximum energy, a civilization would surely want to absorb the power of all the sunlight available, increasing Ω toward 1. Now we have a culture that is producing more and more waste heat radiation on its own world. And we could use an instrument like Colossus to locate civilizations that are on this course.

In fact, we can do better than that, because within the 60 light year parameters being discussed, we can study the heat from such civilizations as the home planet rotates in and out of view of the Earth. Kuhn and Berdyugina liken the method to studying changes of brightness on a star. In this case, we are looking at time-varying brightness signals that can identify sources of heat on the planet, perhaps clustered into the extraterrestrial analog of cities. A large enough infrared telescope could observe civilizations that use as little as 1 percent of the total solar power they intercept by combining visible and infrared observations. A low value of Ω indeed.

Screenshot from 2017-05-17 08-41-55

Image: Figure 3 from the Kuhn/Berdyugina paper “Global Warming as a Detectable Thermodynamic Marker of Earth-like Extrasolar Civilizations: The case for a Telescope like Colossus.” Caption: Fig. 3. Expanded view of a representative North American region illustrating temperature perturbation due to cities (left, heated cities are seen in red) and corresponding surface albedo (right). From NEO/NASA.

You can see what a challenge this kind of observation presents. It demands, if the telescope is on the ground, adaptive optics that can cancel out atmospheric distortion. It also demands coronagraph technology that can distinguish the glow of a working civilization from a star that could be many millions of times brighter. And because we are after the highest possible resolution, we need the largest possible collecting area. The contrast sensitivity at visible and infrared wavelengths of the instrument are likewise crucial factors.

I’ll refer you to “New strategies for an extremely large telescope dedicated to extremely high contrast: The Colossus Project” (citation below) for the ways in which the Colossus team hopes to address all these issues. But I want to back out to the larger view: As a civilization, we are now capable of building technologies that can identify extraterrestrial cultures at work, and indeed, instruments like Colossus could be working for us within a decade if we fund them.

We can add such capabilities to the detection of non-technological life as well, through the search for biomarkers that such large instruments can enable. More on that tomorrow, when I’ll wrap up this set on Colossus with a look at photosynthesis signatures on exoplanets. Because for all we know, life itself may be common to habitable zone planets, while technological civilization could be a rarity in the galaxy. Learning about our place in the universe is all about finding the answers to questions like these, answers now beginning to come into range.

The Colossus description paper is Kuhn et al., “Looking Beyond 30m-class Telescopes: The Colossus Project,” SPIE Astronomical Telescopes and Instrumentation (2014). Full text. The paper on Colossus and waste heat is Kuhn & Berdyugina, “Global warming as a detectable thermodynamic marker of Earth-like extrasolar civilizations: the case for a telescope like Colossus,” International Journal of Astrobiology 14 (3): 401-410 (2015). Full text.


{ 35 comments… read them below or add one }

ole burde May 17, 2017 at 14:47

”We’re making the assumption, by looking for waste heat, that civilizations living around such stars could be detected whether or not they intend to communicate.” …that would seem to be a very problematic assumtion . Waste heat can only be distinguished form other heat sources if you know exactly what the these other sources are, and how they interact with each other .


Larry Kennedy May 17, 2017 at 15:11

Well they’re certainly in good company. Carl Sagan likewise set many factors in the Drake equation unrealistically high and then neutralized it in the last term.
Kuhn and Berdyugina are setting the early terms unrealistically high and then stating that it justifies a pessimistic last term assuming a negative search.


Jeff Kuhn May 17, 2017 at 23:20

Unrealistically large?
When we think back 25 years to earlier days of the Drake “equation” we should note that there is only one term that we’ve qualitatively learned *much* more about, today — its the f_p – fraction of stars with planets, term. In the old days, before exoplanets took over astronomy, we speculated that this number might be “optimistically” 0.001 (or even less). But we now know that f_p is actually much much bigger — more than two orders of magnitude larger. As a grad student in the late ’70s I remember one of the astronomy greats, Lyman Spitzer, once commenting in his graduate course that he thought “planet formation is likely to be exceedingly rare”. Of course we didn’t have better information back then, but we know now that a kind of cosmo-exo-principle, that “we’re not special” really does seem to bear fruit every time we reach sensitivity levels that are good enough to explore habitable zone exoplanets. So, while none of us can logically say how to apportion our uncertainties against these unknown ‘Drake’ terms, we do have defensible arguments for our rather minimal assumptions.


Larry Kennedy May 18, 2017 at 11:15

I’ve been around long enough to read these arguments since the Drake equation itself. I feel very safe saying that for all who would’ve believed .001 many more would’ve believed .5 or higher. Of course both were only guessing since we had little real data. I would’ve found the .001 arguments about as compelling as the overly optimistic estimates now.


Spaceman May 19, 2017 at 9:07


My interest in astronomy began when I was about 6 years old in the mid 1980s. At that time, I remember reading then that we did not know if there are “other solar systems” and that it might still be many years before telescopes would be capable of detecting them or ruling out their existence. Fast forward 3 decades and I think we do pretty much have the value for Fp and it is close to 1. I think with space-based microlensing and additional transiting survey data post-Kepler, we will know Fp to an even higher degree of accuracy. What are your thoughts on the subsequent terms in the Drake equation? The Fne seems like it could be around 1 since there are moons in our solar system with liquid water, an energy source, and organic molecules. However, I personally think the Fl value will turn out to be very small because abiogenesis here may have been a fluke event such that even simple life, let alone anything more complex, may arise only once per 1000 large galaxies.


hiro May 17, 2017 at 15:51

Using “creative estimate” shows that if one fails to detect any artificial signature in the radius of 2000 light-years during a period of 500,000 years then the rare-Earth hypothesis might apply to this (only) galaxy. There is no way to know anything (positive or negative) in the Virgo, Coma, and the Shapley super-group etc…


spaceman May 19, 2017 at 18:31


You make an interesting point; however, what leads you to think that the Rare Earth hypothesis would apply to some galaxies more than others?


hiro May 20, 2017 at 17:53

A comparison between galaxy superclusters such as the Virgo supercluster (we’re in the backyard corner I think) vs Horologium or Shapley Concentration show to big different amount of the richness of material. Then there are the Sloan Great Wall and other Great Wall around or more than 7 billion light-years from here; of course the probability of life appearing in these regions is much higher than the probability of some galaxies which are close to the boundary of Great Voids. Therefore, it’s reasonable to give an “educated guess” that if there is one habitable planet in the Virgo supercluster then there should be at least one or more in somewhere else such as the Horologium & Shapley super-group. The rare Earth hypothesis can’t be generalized to the rest of the visible Universe.

I also have an hypothesis, it’s very simple: if we are alone in this entire Universe then we’re living inside some high qubit (> 300 qubits) universal quantum computer’s simulation. Otherwise, there are ETs out there.


Spaceman May 21, 2017 at 21:49


Interesting hypothesis about simulations, would you care to explain it in more detail? :)


hiro May 22, 2017 at 16:27

AI’s fancy empire game? The idea that we have the entire universe to conquer is just too good to be true.


james stilwell May 17, 2017 at 18:01

When we look at a star system 500 light years away we are seeing the system 500 years ago…Humanity has come a long way these past 500 years…Astronomers on such a system seeing us today would be seeing earth 500 years ago…Hopefully someone will crack the FTL barrier and like Arthur C. Clarke suggested, we may go to the stars aboard spacecraft designed by an alien race…Tsiolkovsky hinted at this in his interesting book, The Will of the Universe…


ljk May 22, 2017 at 9:33

And why would ETI who can do FTL travel just hand over this technology to us or beings like us?


hiro May 22, 2017 at 16:25

Hehehehe, so that we can wipe them out to extinction and then colonize the galaxy & universe right?


Joe May 17, 2017 at 19:30

“We have no idea whether technology-driven cultures survive or destroy themselves.” A third possibility is that a technology driven culture might rise and decline as part of a historical cycle where the level of technology never quite reaches the level required for interstellar travel. It’s not hard to envision a future here on Earth where insurmountable problems limit advances in space exploration, and where the human race survives at a lower level of technology. An extreme example of this idea is the SF novel “1632” where aliens, via time travel, force the residents of a small town in West Virginia to use use failing 20th century technology to replicate sustainable 19th century technology. It’s not pleasant, but they survive.


Robert May 19, 2017 at 15:13

Even a 19th century civilization should leave significant thermal signals as the heat island effect of cities would still be in effect. Also, 19th century technology if explored, refined and advanced as far as applications goes, could do much that it never had the chance to do as it was replaced by more modern technologies. I mean by that certain new devices and applications would be inherently 19th century in character while doing things never envisioned in the 19th century. An example might be long range steam cars, great airships running regular routes between cities or an hyper refined telegraph system linking private users to send messages instantly like the internet but without the modern electronics. In fact, they had transatlantic telegraphy, telephony and even electricity. No need it be uncomfortable at all.


ljk May 22, 2017 at 9:32

It makes one really wish they had gone ahead with that plan to dig huge geometric symbols in the Sahara Desert, fill them with oil, then light them on fire to be seen by others worlds (hint Mars) so their inhabitants would know there are creatures on Earth who can at least do some math.




Robert May 22, 2017 at 14:17

But then they would have laughed at us for not figuring out how to do it without burning half the planets oil reserves. The earthwork art of Robert Smithson comes to mind.



ljk May 23, 2017 at 10:10

You assume they would understand petroleum or care that we would use it in such a manner. If anything I consider that much of what we do with so much gasoline on a daily basis in regular life to be the real laughable and wasteful effort.


Robert May 25, 2017 at 12:35

We use it because we have a choice between living in an advanced technological civilization or not. The alternatives are not ready to fully take over but I’m waiting for the era of Hydrino power myself.


Spaceman May 17, 2017 at 21:33

Fascinating project. The more diverse our methods of looking for intelligent life, the better our chances of detecting it there will be. This assertion, however, is somewhat dependent on how common intelligent life is in our galaxy. I personally tend to lean in the direction of the Rare Earth hypothesis, and so I will not be surprised if these searches come up dry. I suspect that there may only be 1 to 10 planets with complex life in our galaxy. Even though ET life is probably rare, we should still look for it!


ljk May 23, 2017 at 10:16

We neither know enough nor have we done enough when it comes to searching for alien life to make any real assertions about its existence or lack thereof in this galaxy.

For starters SETI needs to really start breaking out of its decades old paradigm (radio looking at Sol-type star systems) and start making real efforts beyond the largely token ones I have seen so far.

Here is a primer on the possibilities for SETI (and METI). That it is from 1992 and so many concepts are still waiting to be done properly says a lot about human efforts to search for alien life, not much of it good:



Alex Tolley May 17, 2017 at 21:49

I take issue with the authors’ statement:

Such a program could tell us just how fragile advanced
life is, i.e., statistically, how likely it is for an Earth-like
civilization to survive.

If they see no signal, that could mean that civilizations have a 0% survival, or that no civilizations ever developed. I do not see how they can separate these two cases. Along the same lines, even if they detect an unambiguous civ heat signature, that still won’t tell us much about survival, although such a detection would be very exciting.

Whether they can indeed unambiguously detect a civilizational hear signature is something to be determined. It seems to me natural phenomena might easily mimic the signatures they have calculated. Using a spectrographic scope of a probe in the outer solar system pointed at Earth might well be a reasonable test of their approach that could be done quite soon.

Let’s also speculate that such a heat signature was found, but there was no detectable biosignature. Would that imply a false positive, or that perhaps a machine civilization was present? If the latter, then why restrict exoplanets withing teh HZ, as presumably machines could colonize any suitable body, or none?


Joe May 18, 2017 at 13:10

I would also suggest that there could be lots of technological civilizations in the galaxy that exist in a pre-industrial state and therefore don’t give off excess heat. Human civilization up until the 19th century fit this category.


Alex Tolley May 18, 2017 at 14:15

Agreed. Even Ancient Roman or Chinese levels of civilization might not have produced the heat signatures needed for detection, although fires for heating in winter just might be enough of a contrast for a city heat island. But generally, I think you are correct.


J. Jason Wentworth May 21, 2017 at 0:34

Yes–these three sentences (“Suppose we detect not a single extraterrestrial civilization. Within the parameters of the original assumptions, we could conclude that if a civilization does reach a certain level of technology, its probability of survival is low. That would be a null result of some consequence, because it would place the survival of our own civilization in context.”) don’t make sense, even if plant and animal life were found to exist on any the planets in question. If no life is found on those exoplanets, the more likely reason is that it never *was* there, rather than that civilizations once existed there but then died out or destroyed themselves, and:

If any of those worlds do have life, intelligent life may not have arisen, and even if it did, that’s no guarantee that technological civilizations would ever appear on such worlds. Life is not a necessity, even on planets where everything is set up “just right” to be in its favor. Chemically and energetically speaking, life is a needlessly complicated thing that doesn’t have to arise (nor does intelligence, even if life arises on any given world); in a sense, life is a solution in search of a problem. There are plenty of far simpler compounds that–on a planet with a promising organic “soup,” water, and plentiful energy sources–will satisfy the valence requirements and bring all of the various chemical compounds to their most stable, “reacted” states. Also:

I’m not saying that we are alone in the Milky Way, or in the universe, but that it *could* easily be the case–but so could the state of affairs that we hope for (other civilizations, whether many or few), or something in between (that life could be rare or even fairly common, while ^intelligent^ life could be exceedingly rare, or even unique to Earth). Since we don’t know, we should keep looking, while being prepared for the “lonely” possibility to be the correct one (if we are alone, we can change that outcome by gradually colonizing and engaging in robotic panspermia missions [there would be no ethical problems with either one if there’s no life out there]).


ijv May 18, 2017 at 2:14

How does an omega of 0.04% square with estimates of Earth as a Kardashev 0.7 civilization? Shouldn’t the two be equivalent?


Ronald May 18, 2017 at 4:31

“Let’s put the fraction of those planets that develop civilizations at the same 0.5, and the fraction of those that are more advanced than our own likewise at 0.5.”.
“We might also consider that our assumptions may have been too optimistic — perhaps the fraction of habitable zone planets developing civilizations is well below 0.5.”.

There is the crux: I think that Kuhn & Berdyugina are ridiculously optimistic about the chances of advanced intelligence, and in particular technological civilization. Anyone can come up with an adapted Drake formula with arbitrary fractions. However, it is the realism of these numbers, and the actual testing of them in practice, in which the real value is.

It seems as if some people want to make an unrealistic giant leap. I would say, one step at a time and prioritize: let’s first get a good picture of the occurrence of terrestrial planets in the HZ, in particular of solar type stars, then let’s try to get bio-signatures, to find out how (un)common life is.

Martin Fogg, the terraforming expert, classified terrestrial planets in 3 categories: habitable, biocompatible, (easily) terraformable.
I think that a prioritization reflecting something like this would make a lot of sense.


Albert A Jackson May 18, 2017 at 9:39

As in all these papers one would hope someday someone would list all the possible uncertainties in a more rigorous quantitative manner than even done here. It’s had to draw conclusions if there is not enough definitive fuzz surrounding a Fermi-Question topic. I am left unconvinced that has been done in this study.


DCM May 18, 2017 at 11:59

If we do locate what appears to be a civilization we should avoid going there.
Possibly we can send a probe programmed to orbit the area at a certain distance, close enough to examine the place optically and otherwise. But of course it will take a long time to get there even with a superfast ion drive and a long time to get information back to us. Still, that would be the safest thing.

I’m not optimistic, though. We just don’t have enough information and won’t for thousands of years to be able to make solid generalizations. Here, patience and systematic terraforming and world building are in order.


Jeff Kuhn May 18, 2017 at 21:00

Some loose threads…
Yes, there are oh so many ways to miss a civilization by looking just for heat. Clearly the challenge is to devise a “remote sensing” signal that does better… Mean temperature, and temperature gradients across an exoplanet surface *will* be measured, and on a statistically interesting number of exoplanets. Corresponding atmospheric molecular biomarkers are almost as easy as temperature when we get to Colossus-size telescopes. Interesting (i.e. “non-natural”) mean surface albedo variations (think “canals”) might end up being our most glaring clue for exocivilizations that terraform or most efficiently use stellar energy to manage planetary-scale natural resources, (as ELF/Colossus will measure). As to the question of geothermal confusion and false positives we have other hooks…for example the temperature or surface distribution of geothermal sources might be an important discriminant. Of course, we’ll probably never learn much about advanced life on a Venus-like planet or an Enceladus moon with these tools. Nevertheless, we humans *are* rather clever, and we *do* live in an optimistic universe of infinite possibility.

Thanks all. A rousing discussion. Future questions or thoughts are welcome by email to the PLANETS/ELF/Colossus participants (or join this merry band!).


hiro May 20, 2017 at 18:03

This might be off topic, if some advanced civilizations had capabilities to produce power from nuclear fusion cheaply (the cost of building 1 TW fusion power plant is quite low) then would they still use solar panels to collect solar energy? The concept of Dyson swarm/shell/sphere exists only if it’s used to power something that requires huge amount of energy such that normal fusion power plants can’t reach.


ljk May 22, 2017 at 9:39

Or a weapon:


Rockets didn’t get serious support and funding until the authorities realized they would make really great and devastating weapons. There is a reason the DoD has an annual budget of $670 billion and NASA has only $19 billion. Those reasons may extend across the Universe.


Andrew Palfreyman May 22, 2017 at 10:03

“Take Earth’s current global power production to be some 15 terawatts. It turns out that this figure is some 0.04 percent of the total solar power Earth receives.”

I don’t think so. Total insolation is 173 PW, yielding 0.0086%.


ljk May 25, 2017 at 13:04

What will humanity be like in one billion years?


This piece is terribly conservative and lacks imagination, but it has a video and we may be able to glean something from it.


ljk May 25, 2017 at 22:11

‘Aliens’ asks scientists to consider – seriously – extraterrestrial life

The main purpose of ‘Aliens’ isn’t to argue for or against the proposition that we are not alone, but to discuss the conditions necessary for life and the possibility that such conditions exist.

By Rayyan al-Shawaf

MAY 17, 2017

Full article here:


To quote:

If at least a portion of any putative extraterrestrial life qualifies as intelligent, the chances of contact increase, as the aliens themselves may be trying to find the likes of us. However, as Martin Rees notes, there remains a distinct possibility that, should such aliens have been around longer than humans, they will have begun a transition to inorganic forms. After all, intelligent life – at least here on Earth – seems to crave yet more intelligence. In Rees’s view, “This suggests that if we were to detect ET, it would be far more likely to be inorganic: we would be most unlikely to ‘catch’ alien intelligence in the brief sliver of time when it was still in organic form.”


Perhaps the most mind-boggling aspect of this book (and that’s saying something, given that it’s about extraterrestrial life) concerns just who at our end would make contact with aliens, should they turn out to exist. Remember Rees’s point about prospective aliens having evolved into something inorganic by the time we find them? Well, it works both ways. Indeed, Rees’s chapter is titled “Aliens and Us: Could Post-humans Spread through the Galaxy?” Both Rees and Seth Shostak (“What Next? The Future of the Search for Extraterrestrial Intelligence”) argue that by the time Earthlings and aliens locate each other, let alone meet, “we” – or some of us, at any rate – will essentially have ceased to be human. Not only that, but our (artificially engineered) evolution toward cyborgs or something silicon-based is precisely what will enable physical contact, as opposed to mere electronic communication. “Interstellar travel will only be a realistic possibility for post-humans,” asserts Rees.

It sounds far-fetched, but if Rees and Shostak are correct, their view has at least one serious implication for the here and now. Actually, it’s equal parts serious implication and major bummer. For those of you taking succor in the belief that, even if you fail to arrange that much-desired powwow bringing together humans and aliens, your progeny will manage the feat, think again. Far from being your grandkids or great grandkids, any Earthlings who eventually rendezvous with aliens may well constitute replacements for the human race. Shostak muses that “it’s at least possible that once GAI [General Artificial Intelligence] establishes a presence on Earth, it may so dominate the planet’s resources – material, energetic and geographic – that Homo sapiens will be marginalised in the way that great apes are.”


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