The Last Cry of an Alien Civilization ⚡ экспресс
In astronomy, many significant discoveries began with the detection of extreme objects whose signals stand out sharply from the background. The authors propose the "Eschatian hypothesis": first contact with an extraterrestrial technological civilization will most likely occur through the registration of an anomalously powerful technosignature (artificially generated radiation). Using a simplified model, they show: for such a "loud" civilization to dominate detections, it must emit at least $${\gtrsim}1\%$$ of all available energy during a brief period of activity (e.g., just $$10^{-6}$$ of its lifespan). This is akin to a situation where in a nighttime forest, a bright camera flash is much easier to notice than a dim campfire glow.
The galaxy is like a city at night: most windows shine steadily, but sometimes a skyscraper lights up all its lights and then goes dark. Just like that, according to a new hypothesis about planets around alien stars (exoplanet), we might first notice another civilization — by a short but blinding flash that could mark its demise. Astronomers have long known: the most noticeable objects are the ones that behave extremely. For example, an exploding star (supernova) is visible across half the universe. Likewise, a civilization becomes 'loud' when it spends colossal energy — building megastructures or burning resources. Calculations show that in that phase it must radiate at least 1% of its total historical energy.
This brief flash is likely what we'll take as first contact. So we should search not for familiar signals, but for any anomalies: sudden excess heat, a strange chemical fingerprint in light (studied by spectroscopy). If such a civilization is on the other side of the Galaxy, its last 'cry' will travel for thousands of years — we'll see the flash of a world long gone.
🎯 An example of a 'loud' technology might be a Dyson sphere — a giant shell around a star that an advanced civilization could build to harvest all its energy. Such a structure would completely enclose the star, but would itself glow in infrared, giving away its creators.