Drake Equation (1961).
hypothesisframeworkSETI & Technosignatures
Seven-factor formula estimating the number of currently-communicating galactic civilizations; a discussion road map, not a predictive number.
Frank Drake devised the equation in 1961 to structure the agenda of the first SETI meeting at Green Bank. N = R* × fp × ne × fl × fi × fc × L. Its value lies in organizing scientific inquiry and identifying what we must learn rather than producing a definitive count; it underpins astrobiology as a discipline. Many of its terms remain poorly constrained, so plausible answers span many orders of magnitude.