How this calculator works
The Drake equation multiplies an assumed formation rate by planetary, biological and technological factors and a detectable lifetime. The alternative model starts with a Galactic star population, filters it by age, habitability and metallicity, then applies a lifetime-to-available-time occupancy fraction. All biological assumptions remain user inputs. A separate uniform-disk model gives a characteristic spacing and a Poisson search-area probability; it is an illustration, not an observational likelihood.
Formula
Drake: N = Rstar fp ne fl fi ft L. Population model: N = Nstar fmature fHZ fmetal L/tau. Disk spacing = sqrt(pi R²/N). Search mean lambda = N(r/R)²; P(at least one) = 1-exp(-lambda).
Worked example
With two stars formed per year, all fractions set to one, one habitable planet per system and a 100-year lifetime, the Drake result is 200. A filtered population of 50 eligible stars with lifetime 10 years in a 100-year interval gives an expectation of five.
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Frequently asked questions
Is a fractional civilization possible?
The number is an expectation over hypothetical populations, so a value below one is meaningful without describing part of an actual civilization.
Are these evidence that aliens exist?
No. Several factors are unknown and the outputs depend directly on your assumptions.
Are named strong and weak scenarios fixed laws?
No. Published scenarios impose particular age and metallicity choices. This tool exposes the factors for you to choose rather than treating one scenario as established fact.