Chinese scientists' claims that their "Sky Eye" telescope could have picked up signals from intelligent aliens have been met with skepticism by an American colleague.
Dan Werthimer, a Search For Extraterrestrial Intelligence (SETI) researcher at the University of Berkeley, California and a coauthor on the research project (opens in new tab) which first spotted the signals, told Live Science that the narrow-band radio signals he and his fellow researchers found "are from [human] radio interference, and not from extraterrestrials."
Natural sources don't typically produce narrow-band radio signals. Scientists picked up three of these signals, seemingly from space, in 2019 and 2022 using the largest radio telescope in the world — the Five-hundred-meter Aperture Spherical radio Telescope (FAST), nicknamed "Sky Eye," which was performing a preliminary scan of exoplanets in preparation for an upcoming five-year-long sky survey.
The news of the signals' possible alien origins first appeared in a report published Tuesday (opens in new tab) (June 14) in the official newspaper of China's Ministry of Science and Technology, which contained a claim that the team had discovered "several cases of possible technological traces and extraterrestrial civilizations from outside the Earth."
One FAST official who was not directly involved in the research also said that an extraterrestrial origin for the signals was "likely."
The claims quickly went viral, spreading across Chinese state media and the Chinese social media platform Weibo before being reported by the international press and Live Science. But Werthimer says that, while the signals are certainly artificial, they're almost definitely from humans and not aliens.
"The big problem, and the problem in this particular case, is that we're looking for signals from extraterrestrials, but what we find is a zillion signals from terrestrials," Werthimer told Live Science. "They're very weak signals, but the cryogenic receivers on the telescopes are super sensitive and can pick up signals from cell phones, television, radar and satellites — and there are more and more satellites in the sky every day. If you're kind of new in the game, and you don't know all these different ways that interference can get into your data and corrupt it, it's pretty easy to get excited."
In spite of this excitement, Werthimer's Chinese collaborators were nonetheless cautious to hedge the more sensational remarks, emphasizing the ultimate likelihood that the signals originated on Earth.
"These are several narrow-band electromagnetic signals different from the past, and the team is currently working on further investigation," Zhang Tongjie, head scientist at the China Extraterrestrial Civilization Research Group at Beijing Normal University, said in the report. "The possibility that the suspicious signal is some kind of radio interference is also very high, and it needs to be further confirmed and ruled out. This may be a long process."
The recent false alarm is one of several instances in which alien-hunting scientists have been misled by noise from human activity. In 2019, astronomers spotted a signal beamed to Earth from Proxima Centauri — the nearest star system to our sun (sitting roughly 4.2 light-years away) and home to at least one potentially habitable planet. The signal was a narrow-band radio wave typically associated with human-made objects, which led scientists to entertain the thrilling possibility that it came from alien technology. Studies released two years later, however, suggested that the signal was most likely produced by malfunctioning human equipment, Live Science previously reported. Similarly, another famous set of signals once supposed to have come from aliens, detected between 2011 and 2014, turned out to have actually been made by scientists microwaving their lunches.
"A lot of very sophisticated astronomers looked at that and we couldn't figure out what it was for a long time," Werthimer said, referring to the microwave lunch incidents. "Finally, somebody figured out (opens in new tab) they were happening at lunchtime."
Radio interference is a big problem for a telescope like FAST precisely because of its scale and sensitivity. The 1,600-foot-diameter (500 meters) dish is powerful enough to detect radio devices like those on Earth operating many light-years away, and the data it captures contains just under 40 billion observations per second. In this setup, picking up a false positive is a lot like flipping a coin to get twenty heads in a row, Werthimer told the publication Futurism (opens in new tab) — it may seem like a remarkable outcome on its own, but not when the coin has been flipped trillions of times or more.
And the less history a given research team has with a particular radio telescope, the more likely it is that they won't spot a subtle interference effect. According to Werthimer, the FAST telescope's receiver can look at 19 different places in the sky at once. Scientists are used to ruling out interference if it shows up in all 19, but if the interference only appears in one (as it did with all three of the supposedly "alien" signatures detected in this case) even experienced researchers can be led astray.
With the ever-increasing numbers of satellites orbiting above our heads, Werhimer says this problem will only get worse.
"100 years ago, we didn't really know how to do SETI. 100 years from now, I don't think we'll be able to do it from the ground," Werthimer said. "This may be a unique window in our history as Earthlings where we can do pretty good SETI searches, where not all of the possible radio bands are corrupted by our own signals."
The possibility also remains that if aliens are sending us, or unintentionally leaking, signals across the vast expanse of the cosmos, they may not be encoded in radio waves, but in ways that we haven't yet developed the technology to understand.
"It wouldn't surprise me if we were on the wrong track. If you look at the history of SETI, the original ideas proposed around 200 years ago were things like 'let's build some big fires on Earth'; 'let's have some big mirrors that reflect sunlight to the Martians' or 'let's build some mile-long right-angled triangles to show aliens we know about Pythagorean Theorem,' and now we look back and say those guys were idiots," Werthimer said. "So, what's to say that 200 years from now people won't look back at us and ask why we didn't use tachyons or subspace communication? But you've got to do what you know how to do."
Despite the dispiriting likelihood that these signals have an Earthbound source, SETI astronomers are still fairly confident that we're not alone in the universe. And that one day, we may dig up something real amid all of our own backchatter.
"I think it'd be very strange if we're the only ones. If you look at the numbers, there's a trillion planets in the galaxy — five times more planets than there are stars. A lot of them are little dinky planets like Earth. Many of them have liquid water, so intelligent life, while not as common as bacterial life, could still be fairly common," Werthimer said. "Maybe they don't want to interfere with primitive civilizations like us that are still killing each other. Maybe they have us in a big zoo to look at. Or maybe they got a little tired of technology and growth and they're more interested in music and poetry."
Live Science reached out to Zhang Tongjie for comment but had not heard back at the time of publication.
Originally published on Live Science.