A significant number of researchers are convinced that extraterrestrial life is highly probable. At the very least, this is suggested by probability theory. However, why aren’t our intelligent counterparts sending us messages? Or perhaps the question should be framed differently: are they sending them, but we are failing to decode them, and is successful decryption achievable in the near future?
Claudio Grimaldi, representing the École Polytechnique Fédérale de Lausanne (EPFL), has calculated the quantity of alien signals that must have passed by our planet for humanity to be capable of intercepting them right now. This research was published in the journal AstroJournal.
The initial SETI experiment commenced in 1960. Since then, astronomers have been scanning the Milky Way in pursuit of technosignatures—measurable evidence of advanced technologies originating beyond Earth. These could manifest as radio transmissions, laser beacons, or thermal traces left by enormous engineering projects.
For us to detect a signal, two conditions must be met: it must arrive at Earth, and our instruments must possess sufficient sensitivity and be aimed in the correct direction to register it. A signal might go unnoticed either because it is too weak or too brief, or because it gets drowned out by background noise.
In his model, Grimaldi treated technosignatures as emanations from potential technological civilizations situated within the Galaxy. These signals travel at the speed of light and can persist anywhere from a few days to millennia.
The expert employed a Bayesian statistical approach, linking three parameters: the number of past “contacts,” the average duration of a signal, and the distance at which current instruments are capable of detection.
The calculations revealed that for a high probability of detection within a range of a few hundred or a thousand light-years, immense torrents of signals would have had to traverse Earth by now. In several scenarios, the sheer volume of these signals became so enormous that it surpassed the number of potentially habitable planets in that particular sector of the Galaxy. These particular outcomes were deemed highly improbable.
A more plausible scenario emerges only when searching at distances spanning several thousand light-years or more, and even then, only under the presupposition that technosignatures are long-lived and widely dispersed throughout the Galaxy. Yet, even under this “optimistic” projection, only isolated signals could be detected at any given moment.
The scientist emphasizes: acknowledging that signals might have passed by undetected does not imply that a discovery is imminent. It simply underscores the need for sustained effort: the search is not a matter of luck but a long-term strategic endeavor.
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