Interestingly enough, our civilization is contemplating the use of light sails for interstellar travel—on a much smaller scale. Stephen Hawking and Russian billionaire Yuri Milner think it’s a great idea, which is why they launched the $100 million Breakthrough Starshot project in 2016. And earlier this year, a research team from the Max Planck Institute explored the possibility of using a light sail-based system to explore the Alpha Centauri system—the closest star system to Earth.


As to why we see the FRB flashes here on Earth, that’s just leakage from the alien propulsion system. “The radio beam sweeps across the sky like a radar, because the source is changing its orientation relative to us,” explains Loeb. “This could be due to the spin of the host planet or the motion of the host star or galaxy.” Every once in a while, this beam just happens to point directly at Earth, confusing our astronomers in the process. The new study has been accepted for publication in the Astrophysical Journal Letters.


Assuming of course, that, the researchers are correct about the artificial nature of FRBs. More work clearly needs to be done, and more evidence gathered, but as Berkeley SETI Research Director Andrew Siemion explained to Gizmodo, FRBs are unlike like anything we’ve ever see before, and they’re forcing scientists to consider many different options. Siemion, who wasn’t involved in the study, lauds the Harvard astronomers for their work, even if it is a bit unconventional in its approach.

“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,” said Siemion. “The Lingam and Loeb paper presents an intriguing idea for a specific technology beyond traditional communication or radar systems that might produce intermittent radio bursts: directed energy propulsion systems. Although admittedly speculative, this is a wonderful example of the thoughtful and open-minded approach we must bring to all aspects of astronomy when searching for potential signals from extraterrestrial intelligence.”


Siemion’s comments notwithstanding, the new theory represents one possibility among many, so we need to be careful about jumping to conclusions. As evidenced by the recent excitement over a potential megastructure around a strange star called KIC 8462852, there’s a tendency, both among the public and the media, to gravitate towards theories involving aliens rather than something mundane like natural causes.

Loeb admits that his theory is a bit out there, but he says we can’t just dismiss his theory just because it sounds weird.


“The exciting aspect of doing science is that one rules out possibilities with better data,” he says. “The history of science shows that it would be unwise to rule out possibilities just based on prejudice. This often leads to stagnation rather than progress. Having worked out a set of parameters for the artificial origin of fast radio burst, I would have no problem accepting a different explanation, as soon as it is validated by future data. Science is a learning experience; we figure out the way nature by culling down possible explanations through observations and not prejudice.”

Update: We just heard from Anders Sandberg, a senior research fellow at Oxford’s Future of Humanity Institute, who had this to say about the study:

I think this is an extravagant explanation of what likely is a natural phenomenon. I like the out of the box thinking, but I would not bet any money on this explanation.

My main problem is that powering a solar sail using radio waves seems very inefficient. Beams spread out proportionally to their wavelength and inversely proportional to the diameter of the emitter, so radio requires a big emitter. Doing it using laser—which is what many designs such as the Breakthrough Starshot is aiming at—requires far smaller emitters (a million times smaller) and would waste less energy.

The radiobursts are also broadband. That is very different from efficient engineering design, which would make use of a rather tight frequency range which is both easy to generate and allows fine-tuning the reflectance of the sail to fit it. The authors suggest some ways out (recycling photons or cost efficiency), but they do not strike me as particularly strong arguments.

Of course advanced civilizations might be able to build planet-sized solar power stations to accelerate ships to relativistic speeds. But why would they all—remember, FRBs come from all directions in the universe—make use of an apparently inefficient radio model, merely using a planet-sized launcher instead of a full Dyson swarm or a tiny laser, and have accelerations and temperatures close to terrestrial values? It would not be too hard for a supercivilization to build a different launch system that produced a different kind of FRB, yet we see the same kind of bursts from all directions. Were the generating process or use close to physical limits or resource limits I might have believed they were all constrained to look alike, but the design in the paper can be varied a lot.

Could it be that a lot of what we see in astronomy is actually artifacts of really advanced civilizations? We can never rule it out, but we do understand things like pulsars (briefly thought of as possible messaging beacons), galaxies, dark matter halos, star formation, stellar evolution and planets well enough to say that it is much simpler to explain their properties by natural unplanned phenomena than some alien engineering. By Occam’s razor, alien engineering needs to be a simpler explanation than a natural explanation before it starts to seem plausible.

The universe is full of weird things. Intelligence almost by definition makes things that are even more unlikely than what naturally occurs. But unless we are really, really wrong about the world most odd things out there are natural odd things.


[Astrophysical Journal Letters (preprint available at arXiv)]