Extraterrestrials in existential trouble might be easiest to find—and also the most informative

Credit: Caleb Scharf
written about in the past). The second aspect is that it’s possible that sentient, technological species experiencing change and trauma might be the ones most likely to give away their presence to the rest of the galaxy.

For example, the trigger for that trauma might be when species approaches a particular level of planetary dominance. With their civilization reaching a tipping point of scale that is far more likely to produce detectable technosignatures for distant astronomers—whether as infrared excesses from waste energy or a flood of peculiar atmospheric compounds from polluting industrial processes.

But it could also be that it is precisely at this point in its existence that a species begins to really look beyond its planetary confines. Is it a coincidence that human spaceflight and dreams of putting settlers on Mars are revving up today in a way that they haven’t for decades? Or a coincidence that there is a resurgence of scientific interest in the search for extraterrestrial intelligence? Or that there is an ongoing acceleration in machine learning and algorithms and devices that have the potential to grow exponentially and subvert aspects of our cognitive existence?

I think it’s an interesting idea to consider that civilizations (for want of a more general term) may only begin to make their presence known in the universe when things get really busy, and really bad, at home.

Apart from passive technosignatures, like rapid climate change, the launch of interplanetary or interstellar spacecraft could, if beamed-light propulsion is utilized, produce potent signals detectable elsewhere in the cosmos. Communications with a growing population of exploration vehicles and settlements within a planetary system, or with probes launched to other stars, could also create a noisy beacon for other species to detect. Even efforts to terraform other worlds (and of course this is stretching the realm of possibilities a little), would present a rather shocking event to advanced alien observers steadily tracking the properties of a system.

And perhaps the ultimate in last-ditch attempts to avert a slow-rolling planetary disaster is to send out a distress signal, looking for answers to existential challenges; because at that point why not?

There is a catch though, and it relates to the well-worn ideas of the Fermi paradox. By the time a species is compelled into doing any of these things, and even before its planetary environment is pushed to a Klaxon-like tipping point, perhaps it simply fails. There is no Hail Mary, there isn’t even a noticeable last gasp, instead it all just shuts down. In which case the apparent absence of any evidence for other intelligence in the universe is not just because of our limited searches to date, it is because of a great filter that—like an exhausted parent—just puts an end to any coherent change. There is no bang, and there isn’t even a whimper.

That is of course awfully depressing. But there is a ray of hope, and it’s in the fact that our quest to look for other technological life in the universe is very, very far from complete. We may yet find ourselves detecting the shrieks of civilizations across our galaxy. Even if they’re experiencing their own apocalypse, we would learn critical things about the properties of a great filter; that there might be time yet to slither past it, and that at least we still have a way to go.



Caleb A. Scharf

Caleb A. Scharf is director of astrobiology at Columbia University. He is author and co-author of more than 100 scientific research articles in astronomy and astrophysics. His work has been featured in publications such as New Scientist, Scientific American, Science News, Cosmos Magazine, Physics Today and National Geographic. For many years he wrote the Life, Unbounded blog for Scientific American.

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