Imagine looking up into the night sky, knowing that someone could be looking back at you. It’s a really exciting and kind of creepy notion.How would we know? What if other alien civilizations could detect our presence? At no time has this question been more relevant than now, in our technology advancement journey.
For all these decades, we have been tuning in to the frequency of aliens, praying to pick up a whispered answer from civilisations light years away. But what if they are watching us? “We’re looking,” says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History. “That means other worlds might be looking too.”
Earth has been broadcasting its presence to the cosmos for over a century. From powerful radio transmissions that began in the early 20th century, through to relentless chatter from TV shows and satellite communications, we have been sending signals out into space, albeit not intentionally. As Howard Isaacson, an astronomer at the University of California, Berkeley, brings to our attention, “The early days’ radio transmissions were especially strong because our technology required the extra power back then.”.
Actually, some of our signals today are quite powerful. For example, it transmits big signals to communicate with Earth from NASA’s Voyager 1, which, conceivably, other civilizations could detect. Isaacson discovered that these signals have already begun to impinge upon nearby stars and will continue to do so into the foreseeable future, making ourselves a pretty loud presence in the cosmos. “The signal would definitely show up as artificial,” he says. By 2031, the nearest of these stars could have picked up our signals and actually could have replied.
But it’s not just radio waves that are giving us away. Advanced extraterrestrial astronomers might attempt to study our planet as it passes in front of the Sun. This way, they would be able to examine the light coming through our atmosphere, picking up signs of gases such as oxygen, nitrogen, and water vapor—detection signs for life. According to University of Cambridge astrochemist Paul Rimmer, these gases would “be an indication of a stable liquid ocean”—an indication of life.
So, too, do our industrial activities. Hector Socas-Navarro, an astrophysicist from the Institute of Astrophysics of the Canary Islands, points out that nitrogen dioxide from combustion processes could signal our presence. Even more intriguing, chlorofluorocarbons from aerosols and refrigerants are unique to technological civilizations. “We’re pretty sure they can only be produced by technology,” says Macy Huston, an astronomer at the University of California, Berkeley.
City lights, another type of technosignature, might also reveal our position. Back in 2021, astronomer Thomas Beatty calculated that advanced telescopes could detect the sodium issuing from urban lighting in our atmosphere. He said, “It has very sharp spectral features. You’d never get that through a natural process.” Although Earth is not so urbanized now to be readily detected this way, by 2150 our cities may glow enough to be distinguished.
So are we really running the risk of being discovered? “In films we’re always invaded,” says Beatty. But scientists such as Beth Biller of the University of Edinburgh are eager to advertise our existence. “I’m not really concerned about Independence Day scenarios,” she says.
The possibility of being detected by alien civilizations raises some serious questions about how we are managing our own technological advancement. The Sir Bernard Lovell chair of Astrophysics at the University of Manchester, Michael Garrett, has an interesting take: swift development of AI could be a significant obstacle for civilizations, thereby explaining why we have not observed any yet. He feels it might be that the rapid evolution of AI is actually the “great filter” which prevents civilizations from becoming interstellar.
It is this autonomous nature of AI that Garrett jumped at and voiced his warning: Civilizations, including ours, may not even survive long enough to explore the cosmos. “The potential for something to go badly wrong is enormous,” he observes. This puts the urgent need for robust regulations over the control of this development of AI to make sure it aligns with the long-term survival of our species. As Garrett states, “Our decisions now could decide whether we become an enduring interstellar civilization, or succumb to the challenges posed by our own creations.”
Not long before the debate really picks up on the question of whether to make ourselves known to any possible extraterrestrial observers, some, like Rimmer, urge proactive measures, suggesting that we broadcast our existence openly. “If it were just up to me, I’d be broadcasting our existence and hoping someone would answer,” he says. But this decision, he believes, should be made globally, reflecting the collective will of humanity.
For the moment, our signals are faint yet discernible. Seth Shostak, senior astronomer at the SETI Institute, points out, “They just need the technology we have, but on a larger scale.” Whether anyone is scanning our section of space and picking up those signals remains an open question, but as we reach out to learn more about the stars, we may discover we’re not quite so alone as we thought.
