Scientists are some of the biggest fans of science fiction. But making claims of intelligent life in other parts of the universe? That’s a pretty big step to take for many researchers. So it’s somewhat surprising that two theorists, Avi Loeb and Manasvi Lingam from Harvard and the Harvard-Smithsonian Center for Astrophysics, recently submitted a paper suggesting that one of the many possibilities behind the enigmatic fast radio bursts emanating from space could be gigantic alien spacecraft.
The suggestion is not just some academic daydream. Fast radio bursts were first discovered in 2007, when West Virginia University astrophysicist Duncan Lorimer analyzed data from Australia’s Parkes Observatory. He noticed a weird phenomenon—a high-energy burst lasting just a few milliseconds with no ready explanation. It was an unique anomaly until 2012, when Puerto Rico’s Arecibo radio telescope also recorded an FRB. Earlier this year, researchers revealed they recorded nine FRBs coming from a puny, faint galaxy 3 billion light years away in the Auriga constellation.
FRBs are strange. In total, researchers have only recorded 18 of the bursts. Few of them repeat, but not on a regular schedule. There’s no known astrophysical explanation for the bursts, and Cornell astronomer Shami Chatterjee, who pinpointed the FRBs in Auriga, joked with Dennis Overbye at The New York Times that there are more theories about what FRBs may be than actual recorded FRBs.
In other words, no one really knows what these things are. One reason Loeb and Lingam went out on a limb to suggest alien technology is that fact that bursts are so energetic. According to George Dvorsky at Gizmodo, the bursts have a brightness temperature, a measure of intensity of microwave radiation, of 1037 degrees. “This means that a hot surface would need to have that temperature in order to radiate at the observed level,” Loeb tells Dvorsky. “There is no known astronomical object that generates radio bursts at such a high brightness, which is tens of billions of times brighter than the known population of pulsars, for example.”
The researchers also argue in their paper, which is accepted for publication in The Astrophysical Journal Letters, that FRBs are suspect because they repeat, but not in any regular pattern, and because they cluster around a frequency that is not consistent with natural phenomena like pulsars. “These clues are consistent with an artificial origin,” Loeb tells Dvorsky. In other words, they might be produced by alien technology.
What would a technology that could produce that much energy look like? According to a press release, the researchers suggest that the technology could be a transmitter powering a light-sail-based spacecraft. That transmitter would need twice the surface area of Earth to receive enough solar power to operate. While that seems absurdly huge to us, they note that it is physically possible to build.
The transmitter would then focus a beam of radio waves on a light sail in space. In this scenario, FRBs detected on Earth are the beam of radio waves sweeping across the sky, passing over our telescopes for just a millisecond as it pushes the sail-powered craft through space.
A craft of that size, 20 times the largest current terrestrial cruise ship, could transport about a million tons of cargo, the researchers estimate. “That’s big enough to carry living passengers across interstellar or even intergalactic distances,” Lingam says in the press release.
Just because they thought it up, though, doesn't mean Loeb and Lingam necessarily believe that FRBs are the engines of intergalactic cruise ships. The researchers says the work is just speculative. “Science isn’t a matter of belief, it’s a matter of evidence,” Loeb says in the press release. “Deciding what’s likely ahead of time limits the possibilities. It’s worth putting ideas out there and letting the data be the judge.”
Berkeley SETI Research Director Andrew Siemion tells Dvorsky that FRBs are so unusual that it’s hard to rule anything out at the current moment. “We cannot...exclude the possibility that anomalous signals like fast radio bursts are produced by an advanced extraterrestrial technology, and even though it is undoubtedly an unlikely possibility, it must remain a possibility until we can rule it out,” he says.
Chatterjee told Overbye earlier this year that there are still many natural possibilities for FRBs, including strange interactions between a neutron star and debris swirling around it or some unknown aspect of a supermassive black holes.
Anders Sandberg of Oxford’s Future of Humanity Institute says the alien spacecraft explanation seems a bit far-fetched. "I like the out of the box thinking, but I would not bet any money on this explanation,” he tells Dvorsky. He points out that a spacecraft powered by radio waves is unnecessarily large and complicated, and any advanced civilization would likely use lasers or a more efficient technology. “By Occam’s razor, alien engineering needs to be a simpler explanation than a natural explanation before it starts to seem plausible.”