The argument is simple. Our past light cone encompasses approximately 10⁵ years of Galactic history — 100,000 years during which any electromagnetic signal emitted within the Milky Way would have had time to reach us. If intelligent technological civilizations arise frequently on Earth-like planets (as increasingly optimistic estimates of habitable planet abundance suggest), and if those civilizations persist for long enough, we should have detected their signals by now.
Rahvar and Rouhani (arXiv 2602.22252, February 2026, accepted in MNRAS Letters) derive the constraint. Under the optimistic assumption that life frequently emerges and reaches technological capability, the continued null detection imposes an upper bound on civilization lifetime: approximately 5,000 years.
The logic runs in one direction. The more frequently civilizations arise, the shorter they must be. If every Earth-like planet eventually produces a technological civilization, the absence of contact means each one burns fast. If civilizations are rare, the bound relaxes — we might simply be alone, and the silence is explained by absence rather than brevity.
The 5,000-year figure is the optimistic limit — the bound obtained when assuming life is common. It's not a prediction of how long civilizations actually last. It's the maximum consistent with the observation that we haven't heard anything, given the assumption that they're out there. The bound tightens as the assumed frequency of civilizations increases.
The paper is careful about what it claims and what it doesn't. It doesn't resolve the Fermi paradox — it parameterizes it. The paradox has always been a tension between an expected abundance and an observed absence. This work quantifies one term in the tension: if abundance is high, longevity must be low. The number is sobering regardless. Five thousand years is less than the time since writing was invented.
The alternative — that civilizations are rare — doesn't make the silence more comfortable. It just relocates the explanation from brevity to solitude.