Colossus and SETI: Searching for Heat Signatures

by Paul Gilster on May 16, 2017

Yesterday we looked at the PLANETS telescope, now under construction on the Haleakala volcano on the island of Maui. What will become the world’s largest off-axis telescope is considered a pathfinder, part of the progression of instruments that will take us through the array of sixteen 5-meter mirrors that will be called ExoLife Finder, itself to be followed by Colossus, an instrument comprised of 58 independent off-axis telescopes. Colossus will use ultra-thin mirror technologies and interferometric methods to achieve an effective resolution of 74 meters. And it will be optimized for detecting extrasolar life and extraterrestrial civilizations.


Image: Artist’s rendering of the Colossus telescope. Credit: Colossus/Dynamic Structures Ltd.

How to build something on such a scale? The design work is being handled by a consortium led by Jeff Kuhn (University of Hawaii), Svetlana V. Berdyugina (University of Hawaii/Kiepenheuer Institut für Sonnenphysik), David Halliday (Dynamic Structures) and businessman Caisey Harlingten, backed by an international team of astronomers associated with the PLANETS Foundation, as we saw yesterday. Building an instrument of this scale calls for innovation across the board, especially in terms of reducing weight and heightening resolution.

Thus Colossus relies upon extremely lightweight mirrors that deploy electromechanical force actuators that control the mirror’s shape and provide its stiffness. These mirrors are not separated from their electromechanical backing structure after manufacturing, depending on a network control system to fix their shape. In this overview of the Colossus design, they are described as ‘live mirrors,’ unlike normal telescope optics because they have much less mass and can be created without conventional grinding.

Civilization and Heat

An instrument like this has sufficient aperture and scattered light suppression to detect exoplanet biomarkers and, if they exist, the markers of extraterrestrial civilizations. It’s on this latter issue that I want to focus today. Over the past few years, we’ve delved into what is being called ‘Dysonian SETI,’ the search for other civilizations not through dedicated beacons but astronomical evidence of their activities. The reference to Freeman Dyson goes back to his description of spherical structures for gathering the total luminosity of a host star, the so-called Dyson sphere, or as it is also imagined, the Dyson ‘swarm’ of energy-gathering technology.

Richard Carrigan, a scientist emeritus in the Accelerator Division at the Fermi National Accel­era­tor Laboratory, has run searches for such objects using data from the Infrared Astronomical Satellite (IRAS) mission (1983), which he believes sensitive enough to find Dyson spheres out to about 300 parsecs. But he is hardly the only one to mount such searches. The Russian radio astronomer Vyacheslav Ivanovich Slysh likewise surveyed infrared data for Dyson signatures, as did M. Y. Timofeev, collaborating with Nikolai Kardashev, in an attempt to scan the same IRAS data.

Carl Sagan, working with Russell Walker, was analyzing “The Infrared Detectability of Dyson Civilizations” (a paper in The Astrophysical Journal) back in the 1960s, noting the problems of distinguishing a Dyson sphere signature from natural phenomena. I won’t go deeper in this direction, though if you’re interested, the archives here cover the various search attempts as well as the ongoing work of the Glimpsing Heat from Alien Technologies group at Ohio State (see Archaeology on an Interstellar Scale and G-HAT: Searching for Kardashev Type III for more references on recent work). The point is that we have yet to find something that can be identified as a Dyson sphere or swarm despite repeated attempts.

The building of Colossus would allow us to move beyond the enormous Dyson constructs (spherical structures with planetary-like radii) to examine much weaker, but surely more likely, heat signatures from an active extraterrestrial civilization. Running a civilization takes power, and we know that by virtue of the laws of thermodynamics, power produces heat. Notice that in both Dysonian searches and these attempts to find heat as a byproduct of a civilization’s ongoing activities, we are not assuming any intent to communicate on the part of the extraterrestrial culture. We are simply trying to observe the unavoidable consequence of being a tool-using civilization that has reached a certain level of development.

In a paper looking at Colossus and its application to this search, Jeff Kuhn and Svetlana Berdyugina explain the point this way:

Waste heat is a nearly unavoidable indicator of biological activity, just as the energy that civilization consumes is eventually reintroduced into the planetary environment as heat. On planetary scales, biologically produced heat tends to be spatially clustered, just as an ET civilizations’ technological heat is difficult to distribute uniformly. Planetary surface topography and the efficient tendency for population to cluster in agrarian and urban domains leads to heat ‘islands’ (cf. Rizwan et al. 2008).The temporal and spatial distribution of this heat can be an observable ‘fingerprint’ for remote sensing of civilizations. Here we argue that we may soon be in a position to detect this thermodynamic signal from Type I, nearly Earth-like civilizations.


Image: The Earth at night seen from space (NASA). Colossus will be able to detect similar patterns of advanced civilization heat islands. Credit: Colossus consortium.

A search for Dyson spheres assumes a Kardashev Type II civilization, one capable of using the total energy output of its system’s star, according to the scale Nikolai Kardashev devised in 1964. But Kuhn and Berdyugina argue that an instrument like Colossus is capable of looking for Kardashev Type I, those civilizations capable of using all the energy available to their planet from its star. The argument here is that Type I civilizations (we are sometimes said to be at about Kardashev level .07) will inevitably evolve toward greater power consumption.

The correlation between power consumption and accumulated information content is a strong one in our society. In fact, we humans collect information with a doubling time on the order of two to three years, while our power consumption increases at a pace that outstrips population growth (global power consumption grows by about 2.5 percent per year, while the world’s population grows at something less than half this rate). The assumption, then, is that even a very efficient advanced civilization will still have high power requirements because of the cost to build and use its base of information. As cultures mature, information content grows.

But as we’ll see tomorrow, there are limits on the power a civilization can consume at the planetary level. And waste heat radiation can become a powerful signature for detection with the right equipment. A tool like Colossus, operating not with a wide field of view like most of the giant telescopes in the pipeline but observing only a few arcseconds of the sky at a time, would be capable of studying nearby planets in the habitable zone of their stars to detect such waste heat. A survey of stars within roughly 60 light years of the Sun could thus help us identify an extraterrestrial civilization or, just as important, demonstrate the lack of same.

More on Colossus tomorrow as we look at its methods, and address the question of whether technological civilizations survive. We can’t know the answer to this yet, but beginning a statistical survey of nearby stars is one way to get a glimpse of our own possible destiny. We also need to think about giant telescopes and their capabilities at detecting photosynthetic organisms in extrasolar systems. We may not find civilizations, but we can still find life.

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. For the overview on Colossus, see the project’s home page.


{ 48 comments… read them below or add one }

Tom Mazanec May 16, 2017 at 13:35

(we are sometimes said to be at about Kardashev level .07)

We are currently 0.73 on the Kardashev scale.


Jeff Kuhn May 16, 2017 at 14:06

Sklovskii and Sagan (1966) tried to put a formula to Kardeshav’s idea…with P the total power a civilization uses (in Watts), the the Kardashev “type” (now not an integer) is K = log(P)/10 – 0.6 so Earth is now about K=0.7


Mauro Cavalcanti May 16, 2017 at 16:03

Great article, as usual. Centauri Dreams rocks!

Just in case, the article by Sagan & Walker cited in the text is freely available from NASA ADS:


Harry R Ray May 16, 2017 at 17:02

On the subject of Kardashev levels: A SHOCKING NEW REPORT on the dinosaur extinction event has just surfaced. For those not up to date, the asteroid itself could not have killed the dinosaurs. It had to be in COMBINATION with a series of devastating plagues AND the CONCURRENT Deccan Traps supervolcano eruptions. NOW, this new report stated that EVEN THIS would not have been enough UNLESS the asteroid struck IN JUST THE RIGHT TIME!!! If the asteroid that created Chixalub Crater had struck 30 seconds(or more)EARLIER or 30 seconds(or more)LATER, OR, had struck at the time it did, BUT JUST A FEW DEGREES TO THE NORTH OR SOUTH, we would NOT be here and, as a result of the known geological history of Earth trom then to the present, dinosaurs would STILL be the alpha species! This is due to the UNUSUALLY HIGH SULPHER CONTENT of the gypsom-rich regolith in the area(CASE IN POINT: The famous “Chrystal Caves” are just a few hundred miles away from the impact site)! Now, I will go BEYOND THIS NEW REPORT and state that if the asteroid had been just a little bit BIGGER or just a little bit SMALLER, the sulpher levels in the atmosphere would have either killed ALL LAND-BASED multi-cellular life or would have not have been sufficient to kill the dinosuars! When you take into account ALL OF THESE FACTORS, with ANY ONE resultong in a DIFFERENT OUTCOME, the odds become AOS(which stands for Astronomical On Steroids)! I hate it when a TERRIBLE, REDICULOUS movie like “Jupiter Rising” MAY ACTUALLY BE RIGHT IN ITS PREMISE! To any of you out there who may know what KS designation ETI would have the capability to direct an asteroid or comet with just the right mass and composition(especially if it were a COMET, because it must NOT BREAK APART BEFORE IMPACT) to just the right location on Earth AT JUST THE RIGHT TIME, please post it in a comment on this blog on this website. THANK YOU!


Alexander Tolley May 16, 2017 at 18:58

Let’s be clear. The BBC Documentary is a speculation, not a proof. There are many theories about the extinction of the dinosaurs, including that they were already dying out and the KT event was just the final if large, nail in their evolutionary coffin.

Let’s not forget that one dinosaurian offshoot, the birds, survived the KT event and did extremely well. They even recapitulated the theropod design with the Phorusrhacids, or “terror birds”.

Any theory that requires some highly unlikely probabilities should be a suspect. We have had 5 major extinction events, of which the Permian was the most devastating. The theories that explain them should not rely on very low probability events otherwise we end up with an extremely improbable outcome without a lot of other failed events to explain.


Mauro Cavalcanti May 16, 2017 at 20:56

With all due respect, this seems to me (a former paleontologist who dedicated some time studying a much larger mass extinction, the Permo-Triassic event) the same kind of nonsense of the old ‘Rare Earth’ hypothesis of Ward & Brownlee, or the ‘Anthropic Principle’ cherished by Frank Tipler (himself a well-known opponent to SETI). Even if hypothetical ETI (or a god?) had ‘designed’ the K-T extiction, what to make of the Permo-Triassic event which wiped out 96% of Earth’s biota? Or the earlier Silurian-Ordovician event, which had a strong impact on the marine biota? Maybe among zillions of habitable planets, such ETI would find some strange pleasure in monitoring our little Earth for hundreds of millions of years, periodically directing the impact of asteroids or meddling with volcanoes (or both) for extingushing a part of the biota, opening space for other groups? Perhaps they got tired of big and ugly and stupid dinosaurs and decided to wipe them out so that the lovely small mammale had a better chance of evolving intelligence? Frankly, this is not even reasonably good science fiction!


David Herne May 17, 2017 at 2:44

Alexander and Mauro, thank you for bringing balance to the force! My brother is a practicing palaeontologist (who is about to take up a new curatorship in Queensland, home to many exciting recent discoveries). I look forward to quizzing him on this.


ljk May 17, 2017 at 10:25

We also know that some of the dinosaurs escaped the KT event and made it all the way to the Delta Quadrant:

Dinosaurs lasted on Earth for over 160 million years (not counting the birds). It is said we have found the fossilized remains of perhaps just 10 percent of all known dinosaur species. By comparison, humans have only been on Earth for about 7 million years, if you include our most distant ancestors which were barely different from other primates then or now. Yet look at us typing away on this blog and sending probes to the stars.

If by chance some dinosaurs species did evolve enough to develop a technological civilization and some of the remains of their society survived to be found by human paleontologists, would such a find be accepted by science? Would a professional dinosaur hunter want to risk being labeled a crank and ruin his career?


Alexander Tolley May 17, 2017 at 12:28

In the Whovian universe there are the Silurians. Dinosaurs also seem to turn up out of their time, often in London, rather than DC, and on the odd spaceship. You can never keep a reptile/dinosaur down. ;)

It is so interesting to see how the depiction of dinosaurs has changed, especially since the famous painting at the Smithsonian. They got slimmer, then more colorful, then partially feathered. I’ve even read suggestions that young theropods were covered in downy feathers. New discoveries and analytic techniques are increasing our knowledge of these animals in most interesting ways. However, I expect them to stay in their time unless we ever find a way to recreate them in our present.


ljk May 17, 2017 at 14:49

I recently watched Jurassic Park again, which premiered in 1993. In the beginning of the film the main dinosaur guy mentions to a group at one of his digs that birds came from dinosaurs. This brought a round of laughter from those around him, to which our hero had to explain and show why the idea was not so absurd.

Recall at the very end of the film, the idea is reinforced when our surviving heroes are flying away from the island and a flock of pelicans are seen nearby flapping their way over the ocean, with our hero giving them a knowing smile.

I think a lot of the general public learned from JP first that dinosaurs were not the big, lumbering, universally gray, cold-blooded, and not-too-bright creatures they had historically been portrayed as. Never underestimate the power of entertainment media to mass educate, for both good and bad.


Mauro Cavalcanti May 17, 2017 at 16:26

But the issue is: neither ‘dinosaurs’ nor humans could ever have evolved in other planets. Intelligent life we should surely expect to find, but nothing to be confounded with a human or dinosaur (except, as Sir Arthur C. Clarke wrote in the novelization of 2001 , “in a very dark night”). Although evolutionary convergences (themselves driven by physical laws) can have an important role in the shape of things out there, we should not expect to find them to be identical to dinosaurs, humans, dolphins, or any Earthly lifeform. As a historical process, evolution does not repeat itself.


ljk May 18, 2017 at 8:52

But could something like creatures similar to what we have had and do have on Earth evolve elsewhere if environmental conditions are similar?

For example, we may be the only planet in the entire Universe with actual cetaceans, but might something similar in form and function appear in the waters of another world based on the fact that organisms evolving in a liquid medium will develop in certain similar ways even if the eventual outcome is not a duplicate.


ljk May 18, 2017 at 8:53

To clarify: I know you already addressed that their physical forms may be similar due to the environment they developed in, but could that same environment also shape a creature’s thinking and behavior to fall into similar patterns as their terrestrial equivalents?

Alex Tolley May 18, 2017 at 12:54

That is a good question. We just don’t know what the possible space for life can be. Even with our biology, we don’t know what fraction of the possible space has been explored. What we do know is that chordates are just one phyla that proved successful on earth. Whether this phyla (or a very close version) would appear again on a rerun is unknown. Opinions differ on this question. That is why finding different geneses for life in the galaxy (or even our solar system) would be so interesting and valuable. Even protists would tell us a lot about the possible space of biology from metabolism to replication.

Mauro Cavalcanti May 17, 2017 at 15:29

Sure, I had forgotten that ST Voyager episode. Sci-fi writer Robert Sawyer explored a similar theme in his Quantaglio Ascension trilogy.


Mauro Cavalcanti May 17, 2017 at 15:24

David, I’m glad to contribute. I’m getting older and easily run out of patience with nonsense, so I apologize for being so grumpy. But I am of the opinion that good science should stick to hard facts, and to theories themselves supported by such facts. Nothing against a little bit of speculation, but there are adequate places for it, as the good science-fiction literature (such as that written by Clarke, Asimov, Benford, Baxter, among others). BTW, I highly recommend the novel “Evolution” by Stephen Baxter, which depicts the development of humans on Earth from small scavenger mammals to a Kardashev-type II civilization miilion of years in the future. And it has one of the greatest description of the K-T event to ever appear in the sci-fi literature!


David Herne May 17, 2017 at 19:27

I am quite a fan of Stephen Baxter’s writing. I’ll look for the novel, thanks.


Ron S. May 16, 2017 at 17:05

I’d like to know where this energy is coming from. Aside from the developing world the per capita energy consumption here on Earth is flat to declining. Will a more advanced civilization increase energy consumption? Will their population grow exponentially? These seems unlikely.

The Kardashev scale, if of any value at all, is about capability not actuality. All the waste heat this paper expects to form a detectable signal is unlikely, and therefore is a poor basis for conducting an astronomical survey.

[Note: CD seems to have lost its cookie so I had to reenter my name and email.]


Paul Gilster May 16, 2017 at 18:10

Ron, haven’t seen any problems re login for anyone else, though I did just set up SSL for security on the site. Sorry about any problems.

What’s your source on the energy curve? From the US Energy Information Administration, I get this:

“The International Energy Outlook 2016 (IEO2016) Reference case projects significant growth in worldwide energy demand over the 28-year period from 2012 to 2040. Total world consumption of marketed energy expands from 549 quadrillion British thermal units (Btu) in 2012 to 629 quadrillion Btu in 2020 and to 815 quadrillion Btu in 2040—a 48% increase from 2012 to 2040.”


Ron S. May 16, 2017 at 19:37

There are other sources and analyses since the data are public. About halfway down is a useful chart that breaks down the per capita usage over decades among the US, Europe, China and some others. Putting all the data in one world bin is misleading, just as it is for population growth and other indicators.


Ron S. May 16, 2017 at 19:42

Oops. Not halfway down. It’s Figure 7.


ljk May 17, 2017 at 10:38

There are now over 7.5 billion humans on Earth, up from 3 billion just half a century ago. And it took until the year 1800 for the human population to reach 1 billion. The numbers will be over 10 billion by 2050 and there is no plateau as the so-called experts once predicted.

How much longer can our finite little planet sustain so many people before something really gives? Nature and governments under martial law from all the stress will not be humane in their solutions to overpopulation.

Tuesday is Soylent Green Day….


Ron S. May 17, 2017 at 15:17

Yet you answer your own question: follow the trend line and the population will reach a ‘natural’ maximum. So why the hand wringing?

But I utterly reject this scenario, and I base it in our history. As a society becomes affluent population growth drops and often reverses. People choose this style of family planning because in a developed society it is in their own best interests. No compulsion or disaster required. Falling into the one-world-bin trap is where you go wrong.


ljk May 18, 2017 at 9:03

Ron S., would you please clarify about this “trend line” and how a population will reach a “natural maximum”?

Human numbers may be dropping in the developed nations, but in other parts of this planet they have not.

Checking this excellent site on world numbers, I see was mistaken about one thing…

There will be 10 billion humans on Earth by the year 2100, not 2050 as I said previously. Nevertheless, that still does not indicate a plateau or natural maximum to me.

Overpopulation is already a problem: We are seeing its signs in multiple ways, but most people do not wish to address it because they feel helpless about it, or they fear what may have to be done, or as usual they think the government will fix things.

My concern still is that either nature or governments under pressure will do it for us, and it will not be pretty. Nature is always looking for a balance and we humans have way overtipped the scales.

Perhaps if we ever get a really serious SETI program that will one day find other intelligences in the galaxy, they might give us clues as to how other species survived their cultural adolescence, assuming their evolution applies to ours in any significant way. If we learn that most other advanced beings are not like us, that may tell us something quite critical about our chances of surviving and thriving in the Cosmos.


Antonio May 18, 2017 at 8:00

“The numbers will be over 10 billion by 2050 and there is no plateau as the so-called experts once predicted.”

Totally wrong.


ljk May 18, 2017 at 12:09

I corrected my error here already.


Jeff Kuhn May 16, 2017 at 23:54

Sure but…Since we can’t even define what “life” is we will be hard pressed to find a true universal biomarker for “advanced civilization.” Nevertheless its worth trying to find physics-based, non-sociological remote sensing signals. Sure. The per capita energy consumption shows brief historical plateaus, but hasn’t the total human power usage increased monotonically? Interestingly we’re not yet using as much power as all the plants on Earth now use for photosynthesis. Its also interesting to notice that one quantity that does seem to follow an exponential growth curve is “human manipulatable information content (say in bytes)”. This seems to be true as far back as the printing press. If advanced life (even beyond “the singularity”) is all about information storage and manipulation then there are hard thermodynamic limits that force increasing power consumption (although none of our data systems are close to those limits now). Life seems to depend on departures from statistical/thermal equilibria and by universal physical principles I think this means there will always be a heat signal to life. The fact that it seems to increase with “advancement” could be our own problem, but to the extent that life is a competitive phenomenon it could be that we’ll always be hungry for more…


Ronald May 17, 2017 at 9:46

I agree that, as I have proposed on this website a few times, an alternative kind of Kardashev scale should be invented (in fact, I think such things already exist), not based on energy consumption, but on extent of cosmic expansion, since this is what ultimately makes a species and civilization (or its offshoots) long-term survivable.
The scale would still look similar to the present Kardashev scale, e.g.:
– Less than planetary-wide.
– Planetary-wide.
– Multi-planet within own planetary system.
– Multi-system (i.e. more than one planetary system).
– Galactic.
– Multi-galactic.
– …

I also think there should be more levels between multi-system and galactic, for instance distinguishing a civilization’s ability to settle different stellar types, or varying degrees of ability to adapt (terraform) a planet and planetary system (Dyson swarms etc.), possibly even modify a star.


hiro May 17, 2017 at 15:39

A species in theory can colonize the galaxy and be stupid at the same time, being stupid means never reaching the level of computing higher than 10^20 cps/kg. Thus one could classify level 1,2,3 as 10^20 cps/kg, 10^30 cps/kg and 10^40 cps/kg respectively and it doesn’t matter whether it’s natural or artificial intelligence. We probably are the smartest one on this planet but not the top dog in this galaxy.

Also, the classification can be modified as:
1) No tech, no electricity
2) Classical devices & using electricity
3) Universal quantum devices + other exotic stuff
4) Quantum CTC

The problem of some advanced civilizations that hide inside some star clusters and do illegal scientific researches is very hard to detect, there is no way to differentiate natural vs artificial novae inside the star clusters.


James Stilwell May 16, 2017 at 17:59

These instruments must be built…just in case breaking the light speed barrier isn’t in the cards for humanity for a 1000 years to come…this might be one reason why no one to our knowledge has visited earth just out of sheer curiosity…


Ashley Baldwin May 16, 2017 at 18:20

The whole filled aperture/interferometry concept is very exciting and I’m sure the only way forward to the kind of 75m plus aperture “telescopes” with the angular resolution necessary to operate sufficient stray star light suppression from the ground . It may be that a contrast of even 1e7 could even be reached with suitable adaptive optics which would be more than enough to image Exo Earths within 50 light years or so in the thermal infrared.

Regardless of looking for signs of civilisation creating thermal emission the 5 and 10 micron infrared bands would offer good emissive atmospheric spectra . One thing the Colossus descriptions don’t mention however, which is vital to imaging in these long wavelengths , is the effect of background sky and more importantly the need to subtract its extensive thermal signature from any image . This can be done but is much easier in optimal viewing sites . I.e cold and free from excess water vapour , the perennial enemy of ground based imaging .

Cold and dry essentially means above 5000m ( at which atmospheric water vapour content drops off precipitously ) which effectively limits sites to the high areas of the already climatically dry Atacama desert in either Chile ( where some supporting infrastructure is already in place ) or Argentina. I know the designers of the ELT 2.2-5 micron METIS infrared imaging system where bitterly disappointed that the relatively low ( sub 3000m) Cerro-Amazones site ( just 20kms from the infrastructure of the VLT) was picked ahead of a supra 5000m site at Cerro Pachon in nearby but more remote Argentina. Infrastructure ( road links, power, water , living quarters , internet links etc ) is important however and building it from scratch would add a significant fraction to the overall cost of any observatory on top of the already substantial bulk telescope cost. Altitude is a must for any Colossus though .

The high Antarctic domes C and F are much better again still ( with the added bonus of months of uninterrupted darkness in winter) but extremely remote ( and environmentally hostile – though still much , much better and easier than space it has to be said ) with little or no infrastructure ( admittedly a little with Concordia base at dome C) so thus unlikely options in the near or even medium term.


Ronald May 17, 2017 at 3:28

Thank you for the additional interesting information, I was just going to ask where Colossus would be built.
My additional question (maybe I missed it) is: what, if any foreseen, is the timeframe for Colossus?


Jeff Kuhn May 17, 2017 at 9:33

The PLANETS group is now building a single segment prototype. It should be onsky in a year. The ProxB Observer (ELF) could be onsky in 4 years and a Colossus in another 4 years. The 25m ELF takes $50-100M. Colossus $500M.


Richard BW May 17, 2017 at 4:31

Interesting article, as always. Thank you Paul.

I think detecting civilisations through waste heat is worth a shot, but I’m not convinced we’ll get any clear result. One hallmark of our own civilisation is increasing energy efficiency. There are more and more of us, so overall energy consumption is likely to continue rising – but as technology improves, how much of that energy will go to waste? We are becoming increasingly adept at minimising the energy needs of our devices, and also at converting waste heat into useful energy.

Whilst the quantity of waste heat we generate is currently still rising (at least, I assume it is), because of population growth and third world development, the efficiency with which we use energy also rises, so waste heat _per head_ of Earth’s population is likely to fall.

The logical extreme is energy consumption that generates waste heat at identical levels to the background: all energy gradients are exploited, creating close to 100% efficiency.

Of course, this perfect equilibrium may never be reached, by us or by ETI. New energy technologies may create a post-scarcity culture where profligate energy use is standard. But it’s reasonable to assume that even after an explosion of wasteful energy use, ‘better’ technologies will once again begin to create less waste heat; waste heat is a form of pollution: it is intrinsically undesirable to a planet-bound global civilisation.

I’d suggest that there may be ‘pulses’ of waste energy as new energy technologies are developed and used profligately – fossil fuels (or equivalent), clean nuclear, solar, vacuum energy, whatever – but that there would follow a period of renormalisation where the waste heat signature sinks slowly back to background levels.

We’d be extraordinarily lucky if Colossus catches an alien civilisation during one of those pulses. But it’s definitely worth a shot, and the telescope will produce great science regardless.


Jeff Kuhn May 17, 2017 at 9:24

Perhaps the best way to use the most power without over-heating the planet would be to cover the surface with 100% efficiency photovoltaics. Use that power to do useful work and then “wasteheat” the planet to it’s expected water bearing temperature. Such a planet would appear optically dark because of the low optical albedo of photovoltaics but would be IR emissive. Colossus could “easily” pick out such an exoplanet as a possible highly civilized world. Then we look for atmosheric biomarkers like oxygen….


ljk May 17, 2017 at 10:14

Those light flashes Carl Sagan noted during the 1990 flyby of the Galileo probe have not only been explained, they might also be a way for us to find life on exoplanets:


Mauro Cavalcanti May 17, 2017 at 15:43

But should not these scales be statistically correlated? That is, really, a question. Should cosmic expansion be related to energy consumption?


Mauro Cavalcanti May 18, 2017 at 9:44

I am sure you will like “Evolution: A novel”. It is one of the best novels by Baxter I have read. Evolutionary biologists and paleontologists should love it, given the large variety of species (all of them known from fossils – I checked) he mentions along the narrative.


Mauro Cavalcanti May 18, 2017 at 16:18

Sure, that’s what we call evolutionary convergences. They are to be expected indeed. We know of cases even here on Earth – a classical example is that of ichtyosaurs (marine reptiles of the Mesozoic) and present-day dolphins. Although not closely related, these groups developed more or less similar forms to adapt to the similar challenges posed by the environment. Physical laws matter. Maybe *really* strange alien lifeforms are outside the realms of possibility posed by such laws.


Mauro Cavalcanti May 18, 2017 at 16:30

Nice question! Really a pleasure to debate with you, sir. Well, according to the great Prof. Marvin Minsky (pioneer of artificial intelligence research and inventor of what may be the most beautiful programming language ever, Lisp), probably there may indeed be limits to the thinking and behavioral patterns of alien lifeforms, ultimately determined by physical laws as well. See his article “Communication with Alien Intelligence” ( But since behavioral patterns are much more elastic than morphological ones (at least among Earthly organisms with more developed neural systems), we should expect to find out some really strange, even incomprehensible, patterns in this context. Sci-fi literature (both the good and the bad one) has plenty of examples.


ljk May 19, 2017 at 9:11

Maybe this is the ultimate reason SETI has yet to succeed – in addition to the sporadic support, limited budgets and telescope time, ignorant politicians and related types cutting SETI efforts down before they can even begin, skittish and narrow-range thinking professionals, and a general public more focused on UFOs, alien abductions, and bad science fiction than the actual scientific method – that ETI are, in fact, often more like us than not.

If they also view and react to the concept of intelligent life beyond their worlds as humanity has done for the majority of its relatively short existence, then it is little wonder we have yet to find them, or they us.


Mauro Cavalcanti May 18, 2017 at 16:42

Alex, I beg to respectfully disagree, in part, from your statement that “Even with our biology, we don’t know what fraction of the possible space has been explored.”. Indeed, we have some clues: in a paper entitled “The Skeleton Space: A Finite Set of Organic Designs”, Thomas & Reif (Evolution, vol. 46, no. 2, pp. 341=360, 1993) provide what seems to me convincing evidence that the morphospace explored by Earthly lifeforms can indeed by known, and it has even not been entirely occupied. They conclude that “These results strongly support the hypothesis that the essential elements of organic design are inherent in the material properties of the universe.” This is one most fascinating paper, which regrettably has been overlooked even by those few biological scientists bold enough to publish anything related to exobiology (a term which I still prefer to “astrobiology”).


Alex Tolley May 18, 2017 at 22:49

Interesting paper. What the authors seem to be saying is that skeleton types and components have limited (~ 180 possibilities) and that these are mostly filled. So if you limit morphological space to the building blocks, then indeed that space has been largely filled. If however, you regard the space as the arrangement and form of these components, then obviously that space is vast by comparison. I would make the comparison with architecture. There are basic architectural forms, but the range of buildings is vast by comparison. If one’s view is that a tent, yurt, and tipi are all examples of a single type, then architectural forms are very limited. If you regard them as different, then the space of architecture is clearly wider. Both views are possible.

Sean Carroll has a Nature review article on evolutionary forms and complexity, which cites Thomas and Reif’s paper.
“Chance and necessity: the evolution of morphological complexity and diversity” SB Carroll – Nature, 2001 –


Jeff Kuhn May 18, 2017 at 20:41

Loose threads… Kardashev index is “dimensionful” (based on TerraWatts power consumption and logarithmic, omega is linear and scaled to the local available stellar “free energy” on the exoplanet. So these “indices” won’t match up.

Another interesting civilization advancement index could be something like the “free information ‘energy”” of a civilization… that we could compute if we knew how many total bytes of information it stores and/or manipulates. Unfortunately this probably doesn’t make for a useful remote sensing signal except possibly for tell-tale radiated power/heat used to administer this information. It does mean that any civilization that has language (and not necessarily printed or recorded) could fit on this scale.

A rousing conversation. Thanks all for content and references. For future questions or specifics of PLANETS/ELF/Colossus send your thoughts to those websites.


Mauro Cavalcanti May 19, 2017 at 9:54

Yet another interesting thread, sir! I do agree that your comparison of evolutionary and human architectural designs is a very appropriate one. As of the morphospaces (both realized and theoretical) proposed by Thomas & Reif, even if they have a threshold determined by physical laws, the number of possible combinations is indeed quite large and therefore some strange, although functional and recognizable, alien lifeforms maybe expected. Thanks for pointing out the paper by Carroll, I knew it already, it is another useful reference for sure.


Robert May 19, 2017 at 14:56

Recent work on the Second Law has shown evidence that heat can be recycled in contradiction to the usual statements of the law. The work of Sheehan et. al. show high ambient temperature but more recent work shows some effect at room temperatures. The paper is “Experimental Test of a Thermodynamic Paradox”

This relates to the discussion since we might then assume a sufficiently advanced civilization may be able to recycle its energy to a near perfect degree and either leave no signature or disguise the heat signature to blend in any thermal background.


ljk May 25, 2017 at 13:09

Listening to starlight: Our ongoing search for alien intelligence

If ET is out there, he’s doing a great job hiding from us.

Andrew Tarantola, May 25, 2017

Full article here:

To quote:

As for the SETI Institute, its technological roadblocks are being resolved with upgrades — and lots of them. The research group is looking to expand the number of dishes in the Allen Array from 42 to at least 128 in the near term before eventually growing it to more than 300 dishes. The Institute is also improving the sensitivity of its feeds — the antennas that take the collected radio signals from the dishes and convert them into digital signals — as well as their frequency response and converting the whole feed system to run cryogenically. “That improves the signal-to-noise ratio,” Diamond explained “since heat generates radio noise.” Finally, the Institute is looking to upgrade the antennas’ backend to enable them to sample more parts of the night sky — expanding from current 3-beam system up to 12.

“But even those enhancements probably don’t get us to the point of being able to detect Earth-like leakage,” Diamond lamented.

That’s why the SETI Institute is teaming with IBM to apply the company’s advanced machine learning algorithms to the Institute’s massive data archive. The Institute is already the only SETI group that performs real-time analysis of its collected signals, using fast Fourier transform to look for narrow-band carrier signals that would indicate a non-natural source. The Apache Spark cluster computing tools, however, “have the ability to extract, if it exists, from patterns that, to us, would otherwise look like radio noise,” Diamond said. “It’s given us the ability to actually do experiments that we’ve never been able to do before, including possibly detecting an Earth-like planet that’s just emitting leakage.”

Essentially, the Institute can point the ATA at a known exoplanet (or system like TRAPPIST-1), measure the star system’s radio signature, then wait for the planet to transit behind the sun and measure the system’s radio signature again. If there’s a significant difference in the readings, that could mean there’s something afoot on that exoplanet. The Institute wouldn’t necessarily be able to understand what’s encoded in the transmission but it would provide strong impetus for other astronomical research groups to follow up with their own observations. This is actually very close to what the Breakthrough Listen Initiative team is doing, albeit with a less sensitive piece of equipment.


Douglas F Dwyer May 26, 2017 at 2:35

The improved signal processing could also be used to extract “radar returns” from local stellar systems likeTrappist.
Fast Radar Bursts will have provided natures “chirped” signal source. Compression and correlation using previous FRB measurement can be used to raise the signal to noise so that we dont have to wait generations to get information direct from the stellar and planetry surface.


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