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A new analysis from astronomer Michael Garrett at the University of Manchester suggests intelligent civilizations across the galaxy may only emit detectable signals for a short period between 100 and 1,000 years before becoming effectively invisible.
The finding could help explain why decades of SETI (Search for Extraterrestrial Intelligence) surveys have yet to detect alien broadcasts, despite the vast number of potentially habitable planets in the Milky Way.
Garrett’s research focuses on how fast technology evolves once a species gains the ability to communicate wirelessly. His models show that once a civilization masters radio or laser communication, it quickly moves toward more efficient, secure, and low-energy systems. That means their detectable “loud” phase when they leak or beam out radio signals may be brief compared to the billions of years that stars and planets exist.
“We may be missing them by timing alone,” Garrett said in a University of Manchester release. “Civilizations likely go silent quickly, not because they vanish, but because they stop using technologies we can detect.”
The idea offers a fresh take on the Fermi Paradox, the question first posed by physicist Enrico Fermi in 1950: if life is common, why haven’t we found it? Garrett’s calculations imply that many civilizations could exist, but only a tiny fraction would overlap with our brief listening window.
On Earth, radio broadcasts began just over a century ago, with satellite and digital networks reducing our own signal leakage since the 1990s. In another few centuries, Garrett predicts, our outward radio footprint could disappear completely as fiber optics and quantum networks replace open transmissions. From another planet’s point of view, humanity might already be fading from the galactic map.
The study also considers the problem of energy growth. Rapid advances in computing and communication efficiency mirror trends similar to Moore’s Law. As societies expand technologically, they risk overheating their worlds if energy use grows unchecked.
A 2024 paper from the University of Rochester estimated that continued exponential energy use could raise planetary temperatures to uninhabitable levels within a thousand years. To survive, civilizations must shift toward compact, low-emission technologies, which would also make them harder to detect.
Garrett argues that SETI strategies should adapt to this reality. Instead of focusing mainly on radio signals, he suggests searching for indirect evidence: infrared emissions from large-scale solar collectors, starlight dimming from partial Dyson spheres, or even unusual neutrino bursts from advanced communications. Such signs would point to mature societies that still exist but no longer radiate traditional signals.
Astronomers are already expanding the search in this direction. NASA’s Technosignature Program and projects like Breakthrough Listen are using machine learning to scan vast datasets for subtle anomalies. Instruments such as the Australian Square Kilometre Array Pathfinder (ASKAP) in Western Australia and the upcoming SKA Observatory are expected to play key roles in identifying potential technosignatures that might otherwise go unnoticed.
Garrett’s model also encourages researchers to examine Earth’s own future as a guide. Studies at NASA’s Goddard Space Flight Center simulate how our planet might appear to distant observers 1,000 years from now, showing declining radio output but a growing technosphere of satellites, solar arrays, and artificial light. Understanding how our signal fades could help scientists recognize similar transitions elsewhere.
While the findings narrow the odds of intercepting a message, they also reshape expectations. The universe may not be silent; it could be full of civilizations operating in communication modes we have yet to understand. For scientists, the next step is widening the search beyond traditional radio frequencies to the full spectrum of possible technologies.
“If intelligence survives long enough, it becomes quieter,” Garrett said. “The challenge for us is to learn how to listen differently.”
