Where are all the galactic empires?

Two newly discovered galaxies with suspicious infrared signatures could potentially be playing host to Kardashev type III civilisations, which have spread to every star in their galaxy and surrounded them with swarms of solar-energy collectors. Yet does the fact that out of many thousands of galaxies surveyed, only two are candidates, tell us that our assumptions about what technologically advanced life might get up to are amiss?

Could there exist galaxies, out in the distant firmament, that have been completely overrun by a technologically advanced civilisation? If such a civilisation were interested in energy, and followed the Kardashev Scale for levels of energy consumption, we might expect that such a galaxy-spanning species might surround every star in their galaxy with energy collectors, gathering all the sunlight of hundreds of billions of stars. 

Such a species would have at their disposal some 4 x 1037 watts, compared to our current energy consumption on Earth, which is about 1013 watts. They would have at their metaphorical fingertips (assuming they even had fingers) immense power. We can barely guess at what they might do with it.

Nikolai Kardashev’s famous scale, which the Soviet astronomer devised in 1964, have become woven into the fabric of both the Search for Extraterrestrial Intelligence (SETI) and the futurology of the human species. They’re almost considered fait accompli, the inevitable progression of a technological species.

The first rung on Kardashev’s scale is type I, signifying a species that can harness all the energy available to it on its planet. Earth could, at maximum, offer us 1017 watts, in terms of energy from not only fossil fuels, but geothermal, tidal, wind power, nuclear and solar, but we humans have not yet even reached Type I status yet. 

Things go up a notch for a type II civilisation, which as at its disposal the entire energy output of a star. While the total amount of energy would vary depending upon the mass, luminosity and age of the star, in the present-day Sun’s case it amounts to 4 x 1026 watts, and would involve us constructing an enormous swarm of solar-energy collectors around the Sun, in the spirit of a Dyson sphere, which is a mega-engineering concept first proposed by Freeman Dyson in 1960.

The thing about solar-energy collectors is that, as they absorb radiation from the star around which they orbit, they will grow hot. To avoid melting they would have to re-radiate some of that excess heat away into space. Hence while a Dyson swarm may absorb most of a star’s light, the swarm itself will produce its own thermal mid-infrared emission. Fermilab’s Richard Carrigan did much of the foundational work in calculating the observational signature of a Dyson sphere, and found that they’d radiate at infrared wavelengths equivalent to temperatures between 100 and 600 kelvin (–173 degrees Celsius to 326 degrees Celsius). In other words, a star surrounded by a Dyson swarm should be very faint in visible light, but bright at thermal infrared wavelengths.

The difference between a Kardashev type II civilisation and a type III civilisation is that type II is just a single star, whereas type III is an entire galaxy’s worth of stars. That entire galaxy should then radiate strongly in thermal infrared from hundreds of billions of Dyson swarms.

An artistic representation of a Dyson sphere, made from rings. Image: Kevin Gill (CC BY 2.0).

Searching for galactic empires

In 2014, Jason Wright of Penn State University and Director of the Penn State Extraterrestrial Intelligence Center, led a search for type III civilisations called G-HAT (or Ĝ), which is short for ‘Glimpsing Heat from Alien Technologies’. It analysed the infrared output of about a million galaxies observed by NASA’s Wide-field Infrared Survey Explorer (WISE) space telescope. Ultimately, the search came to naught.

Part of the problem is that many galaxies, particularly those with large amounts of ongoing star-formation, naturally radiate with excess mid-infrared emissions. Cold dust produced through the rapid life cycle of stars is a copious radiator of infrared, while that same dust can obscure starlight, so we get a similar effect to what we’d expect to see from a type III civilisation. So when astronomers see a galaxy that has a particularly low ratio of visible to infrared light (that is, a relatively small amount of visible starlight compared to the amount of infrared), the first assumption has to be that it is a galaxy experiencing a high degree of star formation, possibly with an active black hole as its beating heart. There would have to be something very different about such a galaxy to give us a reason to think it might not be natural.

The radio connection

One big clue could be a galaxy’s infrared to radio correlation (known as its ‘IRC’, for short), which is a property that has come under scrutiny in a new paper from Hong-Ying Chen of the Chinese Academy of Sciences and Michael Garrett of Leiden University and Jodrell Bank Observatory.

The correlation arises primarily from the presence of star formation in a galaxy – hot young stars heat the surrounding interstellar dust, causing the dust to re-radiate in infrared light. The hottest, most massive young stars do not have long lives – they explode after a few million years while stars are still being born around them. When they go supernova, they blast cosmic rays into space that spiral around magnetic field lines, releasing radio waves known as synchrotron radiation. Hence there is a tight correlation between the infrared emission from the stellar nurseries, and the radio emission from the stellar deaths. While there are some occasions this relation does not hold – for example, a galaxy with an active supermassive black hole at its centre produces huge amounts of synchrotron radiation – for most galaxies, the correlation is pretty definitive.

If astronomers found a galaxy with a strong infrared excess but without the corresponding radio emission, it could be a big clue that the infrared is not a product of star formation. This opens the door to the possibility, at least, that a type III civilisation could be involved.

Chen and Garrett assessed 16,367 galaxies from the LoTSS-DR1 catalogue. LoTSS is the LOFAR Two-metre Sky Survey, LOFAR being the Low Frequency Array, which has 20,000 radio antennas distributed across nine European countries. DR1 is the first data release from the survey. Each of the 16,367 galaxies selected for this study also have had their infrared emission measured by WISE.

Almost all of those galaxies maintained the IRC. Only four did not. One of these four is a known Seyfert galaxy, which is a galaxy with a modestly active supermassive black hole at its centre. Another of the quartet is what is known as an emission-line galaxy, which is a galaxy that emits very strongly at a particular wavelength, in this case that of hydrogen-alpha, which tells us that hot young stars recently formed are heating hydrogen gas clouds. The infrared emission in that galaxy can therefore be attributed to star formation.

Two of the four, however, are mysterious. Designated as ILT J134649.72+542621.7 and ILT J145757.90+565323.8 (the long strong of numbers are their right ascension and declination coordinates on the sky, so other astronomers can find them) respectively, there’s no prior record of them being listed as interesting by any other survey. In all likelihood they too have natural explanations for their deviation from the IRC, but with all the cards still on the table, Chen and Garrett suggest that they are at least worthy of being followed up on as candidate hosts of type III civilisations.

An artist’s impression of a luminous infrared galaxy, swathed in dust. Image: NASA/JPL–Caltech.

Was Kardashev wrong?

One thing that this study, and the G-HAT study before it, tells us is that Kardashev type III civilisations would apparently seem to be extremely rare. For if intelligent life exists in all those other galaxies, should we not seen evidence for it? What conclusions we might draw from this will depend upon our own biases. 

A pessimistic, glass-half-empty outlook is to say that this means technologically intelligent life must be rare in the Universe, or that it goes extinct before it can reach type III status. The latter point harkens back to the Great Filter, which is postulated to be some common event that stops life in its tracks, as a way of explaining the Fermi Paradox. Life is more vulnerable when stuck on one planet. All it takes is one catastrophe and you’re wiped out. As the old analogy goes, it’s safer not to keep all your eggs in one basket. Once you begin spreading to other planets, it becomes much harder for nature, or even self-inflicted catastrophe, to extinguish you. You might lose one planet here and there, but other settlements will be able to continue. So, if the lack of type III civilisations is down to life going extinct before it can achieve it, then the Great Filter must lie at some point in a species’ evolution before they achieve interstellar travel. That’s pretty bleak, as it would mean the Great Filter would be in our relatively near future. 

But hey, I’m more optimistic than that. Maybe life, and technological life, is common, and that it’s the assumptions of Kardashev scale that are wrong.

Kardashev based his scale around levels of energy consumption, which was perhaps a natural thing to do in 1964, but in the 21st century when energy consumption is a vast problem in terms of climate change, perhaps it’s not seen as the best choice for a civilisation. A Dyson swarm is going to create cosmic climate change, of course not, but perhaps civilisations are able to move away from the trait of ever-growing energy consumption and materialistic, consumer-based societies before it causes them irrevocable damage on their home planet. Or maybe not all alien species have these traits in the first place, and have been able to develop and evolve in more harmony with their environment than we have. Milan Ćirković, for example, has suggested that technologically advanced species may be more driven towards optimisation rather than unbounded consumption.

That’s not to say that they would be luddites, or that we should become luddites, but just that they might step aside from excessive energy consumption. If that’s the case, maybe they’re not really thinking about the need for Dyson swarms. 

Even if they are, building a Dyson swarm would not be easy, never mind building hundreds of billions of them all across a galaxy. To build a Dyson swarm in our Solar System (and it would have to be a swarm of solar collectors, since a single rigid sphere encapsulating the Sun would be too unstable, and would eventually collide with the Sun) would require dismantling Jupiter, or taking apart the rocky inner planets to use as raw materials, both of which which would be impressive feats of engineering but not necessarily desirable, especially if we’d have to lose worlds like Earth and Mars to do so.

Then there’s all the interstellar space travel involved, to spread to every star in the galaxy (although I’ve written a forthcoming article for Supercluster.com about one way this may be made a little more feasible). So another explanation for the lack of type III species is that climbing up the Kardashev ladder may ultimately prove too difficult, and therefore nobody gets very far up it.

The galaxy NGC 1015. A type III civilisation would have settled around every star in a galaxy like this, and built Dyson swarms around each of them. Image: ESA/Hubble & NASA, A. Riess (STScl/JHU).

What would Dyson warms be used for?

Another question we should ask is, what would alien species do with all this energy? And would they all want to do the same thing? Increasing rungs on the Kardashev scale do imply increasingly greater homogeneity in the motivations of a species as they climb higher up it. To create a type III species, you’d need the aliens who have settled in a galaxy’s spiral arm over here to want to do the same thing as those that live in the spiral arm over there. Remember, unless they’ve discovered some fantastic faster-than-light communication that only exists here in science fiction, they are separated by vast spans of time and space. You’d expect them to go down their paths rather than continue to share a common path, even if that was the intention when the originally set out. The aliens in the spiral arm over here might want to build Dyson swarms, but if the aliens in the spiral arm over there don’t want to, then you’re not going to achieve type III status.

This brings us back to motivation, and what all that energy could be used for. This is where our imagination may ultimately fail us, but there have been some ideas out forward. For example, a sufficiently technologically advanced species may be interested in information and data processing. Maybe they want to know all that is knowable (maybe they’re related to the aliens that send back V’ger), or perhaps they plan to generate an incredibly realistic virtual reality of the entire Universe that plan to go and live in – subjective time in their virtual Universe could be slowed such that they would live forever. It’s even been suggested that they may even use all that processing power to generate digital copies of ourselves, bringing the dead back to life (kinda).

Certainly, data processing would requires energy, and one flavour of a Dyson swarm suited to this task would be a Matrioshka brain. Proposed by Robert Bradbury, the idea is that several layers of Dyson swarms nested inside one another (like a Russian Matryoshka doll) would make the energy collection more efficient, enough to power an immensely powerful computer.

A recent argument suggested that building Dyson swarms now would not be the best option. Anders Sandberg (who runs an informative website about Dyson spheres; I’ll forgive him for the shade he throws on the Star Trek: The Next Generation’s Dyson sphere episode, Relics), Milan Ćirković and Stuart Armstrong proposed that aliens interested in information processing might go into hibernation, or otherwise remain dormant, for tens of billions of years until the Universe has cooled to just a fraction of a degree above absolute zero, since the colder the environment is, the more efficiently calculations can be conducted. However, this theory has been debated and disagreed with by Charles Bennett, Robin Hanson and C. Jess Riedel, who point out that it’s possible to dump the excess heat required for efficient computation now without waiting for an even lower background temperature. (For comparison, the background temperature of the Universe is currently 2.73 degrees Celsius above absolute zero, which is the temperature of the cosmic microwave background radiation.)

Black holes, rather than stars, could also attract technological intelligence as sources of energy and data processing, far outstripping that which could be attained from surrounding all the stars with Dyson swarms.

So we shouldn’t be disheartened by the lack of type III civilisations. Their apparent absence may not be because life is rare, but just that life might take a different path. And there’s always the possibility that the two galaxies discovered by Chen and Garrett could turn out to be playing host to type III civilisations. If they are, then the discovery would change everything, but if they are not, then we should also listen to what that is telling us too. 

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