Humans May Only Have 41,000 Years to Catch Signs of Aliens Before They Fade

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2 days ago

Here's what you'll learn when you read this story:
Dyson swarms—theoretical arrangements of satellites orbiting a star to harness its energy—may seem like they could be eternal once constructed, but they are still at the mercy of gravity.
A new theoretical study argues that gravitational instabilities within an abandoned swarm could have satellites colliding and causing the whole thing to disintegrate in as little as a few tens of thousands of years.
If these things exist out in the universe, we better get cracking on searching for them.
So long as humans have wondered about other forms of intelligent life in the universe, we've hoped E.T. would phone home. But so far, no one has ever called. Even our most powerful antennas have only picked up false positives and radio silence. Could it be because any hypothetical civilizations made of beings with brains to rival our own have long since vanished, with even any advanced technosignatures they might have left behind turned to nothing more than space dust?
Breakthrough Listen is hoping to figure that out. It is the largest ever SETI (Search For Extraterrestrial Intelligence) initiative on Earth, and it not only surveys the million closest stars to our planet, but scans the entire galaxy and literally listens for messages from any beings out there who might be trying to communicate with us. Some of its spectroscopic instruments are hypersensitive enough to detect a laser with no more energy than a lightbulb from 25 trillion miles away.
If that little energy can show up at such a distance, it seems like it should be only a matter of time before a megastructure like a Dyson swarm—satellites arranged around a star to harvest its energy or send intergalactic messages—could be found. (That is, if they exist at all. The jury is still very much out on that one). The question is whether we have that time. If you ask one theorist, we might only have about 41,000 years to find a swarm large enough to surround a star the size of the Sun before it falls apart completely.
Theoretical astronomer Brian C. Lacki of Breakthrough Listen delves into such mind-bending topics as how intelligent aliens might be functioning, traveling, or making communication attempts—and now, he's looking into whether Dyson swarms could hang around long enough for us to find them. He thinks that we might have far less time to detect one of these megastructures than experts may have originally thought. If the civilization that created them vanishes, even behemoth technosignatures like these would ultimately be doomed without maintenance.
'Although long-lived megaswarms are extremely powerful technosignatures, they are liable to be subject to collisional cascades once guidance systems start failing,' Lacki said in a study recently published in The Astrophysical Journal. 'Structuring the swarm orbits does not prolong the initial collisional time as long as there is enough randomness to ensure collisions, although it can reduce collision velocities.'
Lacki argues that while Dyson swarms may seem like they should be indestructible (and would definitely be more resilient than the similarly hypothetical Dyson sphere, first dreamed up by physicist and mathematician Freeman Dyson in the early 1960s), they are prone to gravitational instabilities that would inevitably trigger collisions. These might be relatively minor at first—like fragments of space junk scraping against each other as they orbit Earth—but if the swarm were abandoned by the civilization that established it, just one collision could spell its ultimate destruction. Satellites already orbiting at high speeds would crash into each other just as fast.
Shards of destroyed satellites would scatter and strike other satellites, possibly causing further perturbations that lead to more collisions until every structure and scrap was reduced to dust. And even dust might not be around for long.
'The final result of a collisional cascade is to grind a swarm down into microscopic particles,' he said. 'These artificial grains are blown out into the general ISM if the host star is bright enough. Otherwise, the swarm is ultimately reduced into ionized gas.'
The only way to prevent this would be to somehow push planets in the star system out of the way, and that would give a civilization nowhere nearby to restart if their own planet fails them. Maybe any intelligent aliens out there have already figured that out, and decided to come up with an alternative method of capturing stellar energy. If they have, maybe we have more than a few ten thousand of years to find it.
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