Imagine for just a moment that there is some other civilization out there in the universe, looking out at us radiantly, as we are. What would they perceive? All of our bustling metropolises glow from artificial lighting, or it’s the steady hum of radio waves, or even pollution that industrial activities spew into the atmosphere. It is precisely this tantalizing scenario formerly the realm of science fiction that is on the leading edge of scientific research into finding extraterrestrial intelligence.
For decades, though, the search for biological markers of life has taken a back seat to a search for “technosignatures”—markers of alien technology. It ranges from radio transmissions to huge structures that could be harnessing stellar energy. The technological traces might be more easily detectable across the vastness of space than biological markers.
The search for technosignatures really began in 1959 when astronomers Giuseppe Cocconi and Philip Morrison showed radio transmissions from Earth could be detected at interstellar distances. That same year Frank Drake launched the search for extraterrestrial intelligence Project Ozma, focusing a large radio telescope at two nearby stars to see whether any signals might come our way. They were searching for something akin to a cosmic “hello.” And with that, another branch of research was born: SETI, the Search for Extraterrestrial Intelligence. Today, it’s one of the pillars that prop up our quest for the search for intelligent life beyond Earth.
So far, we have the two most famous methods in existence on the search for extraterrestrial technosignatures: scanning for purposeful radio and laser signals. The concept is quite simple, yet not so in its realization. Early years’ efforts were devoted to capturing strong, directional signals that could have been directed toward our solar system. But the possibility is so small that another civilization is making an effort to contact us. That’s according to the “SETI Paradox,” whereby too many intelligent species may decide not to broadcast their presence the same way that humans rarely send targeted signals into space.
But even without intentional messages, we still have a shot at detecting technosignatures. Human technology everything from TV towers to space probes—leaks radio signals into space, and they are very faint. Still, they can be detected by very sensitive equipment like the Square Kilometer Array radio telescope, due for completion shortly, which will be 50 times more sensitive than the current arrays. Consider the following: an extraterrestrial civilization happens upon our Voyager 1 spacecraft’s signal hurtling through space. An obviously artificial signal like that might well prove to be the beacon that tips off others to our existence.
Freeman Dyson, in a 1960 theory, hypothesized that advanced civilizations will build large structures so-called Dyson spheres around stars, which would allow them to capture energy. A megastructure such as this could be detected by its infrared emissions or because it periodically suppresses light from its star.
Another interesting aspect could be the potential detection of pollution. As Macy Huston of the University of California, Berkeley, commented, chemicals like nitrogen dioxide and chlorofluorocarbons—both byproducts of human industry could become markers for technological activity. That would mean that, at some point in history, the James Webb Space Telescope, equipped for the study of exoplanet atmospheres, would detect such pollutants and realize there could be an industrialized civilization.
Artificial lights from cities might also serve as a technosignature. Thomas Beatty estimated in 2021 that in the atmosphere of a planet it would be possible to detect sodium coming from the streetlights of cities. Though he admitted that Earth is not enough urbanized to be detected on a rather large scale now, the future trends may well change everything. It’ll be gleaming like a beacon in 2150. Our planet’s gonna be beacon for distant astronomers.
It’s even a thought-provoking discovery that might let even our most mundane activities disclose our existence to the universe. Picture an alien astronomer equipped with a 100-meter telescope, which picks up the faint artificial glow of city lights on Earth or our TV broadcasts in radio waves. That would provide so much information to an observer about our civilization, ranging from determining the rotation and tilt of our planet to atmospheric composition.
Yet the issue always comes up: should we advertise our existence? For example, Paul Rimmer from Cambridge University is an advocate of active broadcasting. Others wonder about the dangers that entail. What if, as happens in far too many science fiction movies, the contact causes something unpleasant to ensue? So far the signals of humanity are more passive, but as technologies continue to enter the scene, purposeful efforts at contacting probable extraterrestrial neighbors could become doable.
Even though no technosignature has yet been confirmed, the search did not stop. AI and sophisticated algorithms are lending a hand to this task—in fact, shifting through reams of data for possible signals. According to Jason Wright from Penn State, “I think we have a real shot if something’s out there.”
But in the end, technosignature hunting is so much more than just E.T. searching. It’s our place among the stars, and an exploration of what might be out there, the glow of city lights from a far-off planet or the very faint hum of an alien broadcast.
