Taking the Drake Equation forward or modifying it, researchers have attempted to find out — estimate — the total number of intelligent civilizations that have ever existed in the visible universe since the Big Bang. In their words; Abstract: In this paper we address the cosmic frequency of technological species. Recent advances in exoplanet studies provide strong constraints on all astrophysical terms in the Drake Equation. Using these and modifying the form and intent of the Drake equation we show that we can set a firm lower bound on the probability that one or more additional technological species have evolved anywhere and at any time in the history of the observable Universe. We find that as long as the probability that a habitable zone planet develops a technological species is larger than ~10-24, then humanity is not the only time technological intelligence has evolved. This constraint has important scientific and philosophical consequences. The paper . ...
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