It’s not quite “E.T. phone home,” but aliens in nearby star systems might be listening in on our cellphone calls, according to new research from the University of Manchester.
Scientists have long hypothesized that radio signals from Earth might be detectable as they spread out through the galaxy at the speed of light. In fact, SETI (the Search for Extraterrestrial Intelligence) turns that idea around, scanning the cosmos for radio waves that might be generated by aliens.
To date, SETI has produced no conclusive findings. The flip side was considered in a 1978 study that looked at radio signal leakage from TV broadcast towers. But in the decades since, the rise of cable and internet has reduced the strength of through-the-air TV signals, while cellphone towers have sprouted up like steel mushrooms across the planet.
Michael Garrett is the inaugural Sir Bernard Lovell chair of Astrophysics at the University of Manchester, and the director of the Jodrell Bank Centre for Astrophysics. His new study, published in the Monthly Notices of the Royal Astronomical Society, creates a model of radio leakage from cellphone towers, using crowd-sourced data and other publicly available information.
His research concludes that radio signal leakage from Earth’s cellphone networks is in the neighbourhood of 3.5 GW. A GigaWatt is a billion Watts, so picture the power output of 350 million LED bulbs, or about 1,000 industrial wind turbines.
Garrett notes that what cellphone towers lack in broadcast strength, they make up for in their ubiquity.
“I’ve heard many colleagues suggest that the Earth has become increasingly radio quiet in recent years — a claim that I always contested,” he said in a statement. “Although it’s true we have fewer powerful TV and radio transmitters today, the proliferation of mobile communication systems around the world is profound. While each system represents relatively low radio powers individually, the integrated spectrum of billions of these devices is substantial.”
Reached in a taxi — and of course on a cellphone — Garrett told the National Post that there exists a small but definite threat of discovery by a hostile alien race, but also that there isn’t much to be done to mitigate that risk.
“You might hope that they are sufficiently developed not only in technology but in ethics and morals that they wouldn’t represent a threat, but you never know,” he said. “We should try to appreciate what that means. There is a certain risk, although I think it’s probably a small risk.”
As to putting a damper on our signals: “You could stop using radio waves as a form of communication, and try to have everything going via fibre and underground cables,” he said. “But that’s not very useful.” The benefit of cellphone technology is “you can use it no matter where you are.”
While the study notes that even the next generation of radio telescopes on Earth are not quite sensitive enough to detect a signal of this strength, our own technology continues to improve – as does the strength of our radio signal leakage.
“Current estimates suggest we will have more than one hundred thousand satellites in low Earth orbit and beyond before the end of the decade,” it says. “The Earth is already anomalously bright in the radio part of the spectrum; if the trend continues, we could become readily detectable by any advanced civilization with the right technology.”
Garrett said his paper didn’t even begin to consider the influence of wifi. “You can get your wifi in your garden,” he noted, which means its signal is out of your house and into the cosmos. “And once we have these constellations of satellites providing wifi from low-Earth orbit, we’ll be surrounded, smothered by that radio leakage, or you could call it radio pollution.”
The research looked at the signal that might be picked up by an alien civilization around one of several nearby stars, including Alpha Centauri, HD95735, and Barnard’s Star, the latter of significance because it is known to have a potentially habitable planet.
Not only could a signal be detected from there, the report says. “We note that by analyzing the flux variation of our planet as a function of time, it should be possible for an extraterrestrial civilization to generate a simple model of our planet that reproduces regions that are dominated by land, vegetation, and oceans/ice.”
And, in a kind of cosmic coincidence, the paper notes that “mobile towers transmit at frequencies within or close to L-band, a major band for radio astronomy that includes the ‘water hole.’” This term was coined in 1971 by scientist Barney Oliver, who noted that certain radio frequencies are relatively quiet and thus might be used by extraterrestrials for communications.
SETI researchers already scan the water hole frequency for signals. Any aliens doing likewise, with sensitive enough detectors, are likely to pick up our own signals in that band. Whether they call back remains to be seen.
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