"It's Never Aliens—until It Is"

In 2017, the big mainstream stories of "near-hits" (aka "near-misses") in the search for extraterrestrial intelligence included episodic dimming of a star caused by possible "alien megastructures," a large object tearing through our solar system, and video captured by a fighter jet of a weird object capable of incredible maneuvers in the sky (video below).

Scientific American's Lee Billings looks back at the ET-invoking headlines of last year:

…As the nuclear physicist Enrico Fermi (put it) more than a half century ago, "Where are they?" Given a 10-billion-year-old galaxy filled with stars and planets, and an Earth less than half that age, Fermi guessed we are unlikely to be the first technological culture on the galactic stage. If just one spacefaring civilization predated our own in the Milky Way, he calculated, even moving at a very languorous pace it should have had more than enough time to visit, explore and colonize every planetary system in the galaxy.

Ever since, practitioners of the search for extraterrestrial intelligence (SETI) have been brainstorming about why we do not encounter glaringly obvious signposts of an interstellar diaspora: Maybe there are nigh-universal bottlenecks in the odds for the emergence of life, intelligence or high technology, and we are indeed alone. Maybe we are not alone at all, but interstellar travel is so hard that everyone just stays home. Maybe we are being quarantined, and UFOs are dronelike documentarians recording an intergalactic Planet Earth miniseries. Maybe our galaxy is bursting at the seams with alien civilizations, and we simply have not looked hard enough—presuming we are capable of properly looking at all. Even the know-it-alls in the "never aliens" crowd would concede the diversity of possible answers to Fermi's question says more about our ignorance than our knowledge.

One of Fermi's SETI-pioneering peers, the physicist Freeman Dyson, once summarized the situation thus: "Our imaginings about the ways that aliens might make themselves detectable are always like stories of black cats in a dark room. If there are any real aliens, they are likely to behave in ways that we never imagined." Even so, he added, "the failure of one guess does not mean that we should stop looking"—particularly because whatever may keep our skies alien-free would likely keep the rest of the universe free of star-trekking humans as well. Contemplating Fermi's question is a way of exploring pathways to our possible futures. Finding aliens—or coming up empty in our searches—has profound implications for our own ultimate cosmic fate.

"It's Never Aliens—until It Is" (SciAm)