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If Alien Signals Have Already Reached Earth, Why Haven't We Seen Them?

A new EPFL study uses Bayesian statistics to ask how many alien technosignatures must have crossed Earth since 1960 for today’s instruments to have a realistic chance of detection. The analysis shows that achieving a high detection probability within a few hundred or thousand light‑years would require an implausibly large number of past signals, far exceeding the count of habitable planets in that region. Detection becomes more plausible only for long‑lived signals originating several thousand light‑years away, where only a handful would be observable at any time. The findings push SETI toward broader, deeper surveys rather than expecting nearby beacons.