In 2007, a team of astronomers at the Parkes radio telescope in Australia discovered the first "fast radio burst," a millisecond-long flash of radio waves that has so far defied a natural explanation. To date, fewer than two dozen fast radio bursts (FRBs) have been discovered and many seem to originate from galaxies that are billions of light years away. And when you can't pin something on a natural explanation in science, you might as well pin it on aliens.
"Fast radio bursts are exceedingly bright given their short duration and origin at great distances, and we haven't identified a possible natural source with any confidence," said Avi Loeb, a theorist at the Harvard-Smithsonian Center for Astrophysics. "An artificial origin is worth contemplating."
As detailed in a paper recently accepted for publication in the Astrophysical Journal Letters, Loeb and his colleague Manasvi Lingam wanted to figure out whether or not it would even be physically possible to create a radio transmitter that was able to send such strong signals that were detectable over such huge distances.
Based on their calculations, they found that if such a transmitter were solar powered, it would require the amount of energy roughly equal to that of all the sunlight falling on a planet twice the size of Earth. The next question was if an artificial structure would even be able to withstand that much concentrated energy, or whether it would simply melt. According to Loeb and Lingam, it's possible if the massive device is water-cooled. While such a construction project is way beyond the capabilities of Earthlings, it is at least physically possible.
So what interest would an extraterrestrial civilization have in building such a massive, powerful device? Loeb and Lingam theorize that it might be used as a way to propel gigantic light sails across interstellar distances. Indeed, according to their calculations, the amount of power generated by this device would be strong enough to push a craft weighing about 1 million tons, or about 20 times heavier than the largest cruise ship on Earth.
This ship would require a radio beam to be focused on it continuously in order to move, but here on Earth we'd only see short, bright flashes of this radio signal. Since both the ship and the source of the radio beam would be moving relative to us, the beam would only be visible as it momentarily sweeps across our field of view.
The idea is pretty far out, but not inconceivable. In fact, we're working on our own light sails here on Earth, albeit on a far smaller scale.
NASA launched the first of these light sails, weighing only 8 pounds, into low Earth orbit in 2011 as a proof of concept. The Planetary Society has plans to send a second light sail into orbit later this year to test the viability of using photon pressure from solar radiation as a means of propulsion. At the same time, the Breakthrough Initiative is flirting with the idea of sending a nanocraft just a few centimeters in size through interstellar space to our nearest neighbor, the Alpha Centauri star system. To make this four-light-year journey feasible on human timescales, researchers want to accelerate the craft to about one-fifth the speed of light, using giant arrays of lasers for propulsion.
As to whether or not any of this—be it a giant extraterrestrial spacecraft, or our own nanocraft bound for Alpha Centauri—is likely, Loeb said it best.
"Science isn't a matter of belief, it's a matter of evidence," Loeb said in a statement. "Deciding what's likely ahead of time limits the possibilities. It's worth putting ideas out there and letting the data be the judge."
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