Where are the extraterrestrial civilizations?

If there is life out there and it is intelligent in the sense that it lives in an advanced and technological world, will we ever know? How? Big Hollywood productions tell us that we will find out that intelligent extraterrestrials exist when they arrive on our planet, with either good or bad intentions. We have a wide variety of situations in that regard: some aliens are lost, or even sick, and they arrive needing our help, like ET; others come looking for something they lack, like the lizards from V (and we make them sick), The War of the Worlds (they didn’t know biology), or the little ones in Independence Day (including Will Smith’s first slap); others simply seek fun in environments that are exotic to them, as with the predators. The problem with all these movies, at least based on our current scientific understanding, is that bridging the gaps between stars, let alone galaxies, seems impossible on a human time scale. Right now, accelerating at or beyond the speed of light and using wormholes is considered physically impossible.

So, do we have any remaining options for discovering advanced extraterrestrial civilizations in the near future? Moving beyond science fiction and staying within the realm of science, we can actually think of certain, more or less clear indications that there may be artifacts that some intelligent minds in the distant stars have created. Here, we will discuss some examples of technosignatures.

One might think of sending an electromagnetic signal as the first indication of the existence of an advanced extraterrestrial civilization; radio waves would be the most effective for this. But these no longer count as technosignatures. They’re too obvious. Even films like Contact have considered this indicator. Despite what the movie says, however, normally a radio emission launched in all directions is not sufficiently powerful or continuous for anyone to see it. It’s too much of a coincidence to be looking at Earth with a radio telescope just as the 1936 Berlin Olympics are being broadcast! Well actually, when the signal passes the planet, years after it is broadcast.

As they are understood today, technosignatures refer more to artifacts that have not been built expressly to communicate with other planetary systems. They would be gadgets for everyday use that could be detected at interstellar distances for long periods of time, even beyond the period during which the civilization that built them exists!

What might fit that definition? Normally, we would think about what worries us globally and what technology could be used to eliminate that concern (positively or negatively, which I will get to shortly). Based on that premise, it is worth thinking about how aliens who are more intelligent and/or advanced than us could have overcome those concerns.

One example could be energy, which has never been a more pressing concern than now. A technological world needs more and more energy. How to get it? We can think of producing large amounts of energy with nuclear fission reactors, which are not well regarded historically, or fusion reactors, which are much cleaner but more difficult to build. We can also think about blanketing roofs with solar panels, which we have done already. If we are already a more advanced civilization and the planet’s surface is not enough, we ought to think big and surround the sun with devices to collect energy. Consider that only one of every billion photons from the sun ever reaches a planet; the rest are lost in the universe forever! A megastructure that surrounds a star in 3 dimensions in order to extract as much energy as possible is called a Dyson sphere. This structure should be detectable because part of the star’s energy would be re-emitted in other areas of the spectrum, most likely in the infrared part because of the structure’s heating, or it would produce reflections with a subsequent change to the polarization of the light received.

Another example of a global issue that a highly advanced, intelligent civilization might consider is the problem of cosmic dangers, such as the impact of meteorites and comets or the explosion of nearby supernovae. Obviously, we have not reached that level of intelligence and progress. Here, that topic merely causes laughter in a movie that many interpret through another global problem, such as climate change, or in American-style action movies that have a meteorite explode just before it reaches Earth. When we become aware that this danger exists at the level of millennia or tens of millennia, we will find solutions (if we aren’t too late) that might involve moving stars away from their orbits (something that is already beginning to be explored), including the entire Sun along with its planetary system! One possibility could be to build sail-like megastructures that would use the star’s own light as “wind,” making it possible to avoid shock orbits. Here, we return to the topic at hand: detecting technosignatures. The interesting thing about this contraption—called a stellar engine—is that it must always maintain its relative position between the star and the celestial vault. It always points toward the same place, toward where you’d want to vary the stellar orbit; that is, the device would not orbit like a regular star. So, we could detect something built by a highly advanced civilization: an object with an unnatural orbit.

Perhaps our extraterrestrial cousins, the children of some sister star, are up to something else. Maybe their technology is much more advanced than ours and we can’t even imagine what goes through their heads—if they even have them—and what can be built. As Sir Arthur C. Clarke has said, “any sufficiently advanced technology is indistinguishable from magic.” If there really are extraterrestrial civilizations that are advanced enough to build gadgets like those mentioned above, or even some that we cannot (yet?) wrap our minds around, why wouldn’t they be clearly noticeable? There are three possible answers, some of which are more hopeless than others: 1) we do not yet have the technology to detect them; 2) they do not want to be found; or 3) such a technologically advanced civilization does not last long, because there are internal or external dangers that kill it. One only needs to consider that, on our “dear” Earth, it took less than 100 years for humanity to go from creating the first radio signal to creating weapons of planetary destruction. The so-called Drake equation includes that and more, but we will save that discussion for another day.

Pablo G. Pérez González is a researcher at the Astrobiology Center, part of the Spanish National Research Council and the National Institute for Aerospace Technology (CAB/CSIC-INTA).