Method of estimating the number of intelligent, technologically advanced species (i.e., able to communicate with other species) in existence in our Concentration of 106 to 1012 stars, dust and gas, that are gravitationally bound. Our galaxy contains ~2 × 1011 stars. There are four main types of galaxies: • Elliptical
N is the number of species (life) at any given moment in our Galaxy. The parameters are as follows: R = rate of Self-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars. formation in our Galaxy (in stars per year); fp = fraction of stars which have planets; ne = number of habitable planets per Definable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with with planets; fl = fraction of habitable planets upon which life arises; fi = fraction of these planets upon which life develops intelligence; ft = fraction of these planets where the intelligence develops into a technological civilization capable of communication; and L = mean lifetime of such a technological civilization. Only R and fp are known with any reliability with values of ~10 stars per year and ~1, respectively. The others are almost entirely pure speculation at this point. Calculations of N made by respectable astronomers differ by ~10 orders of magnitude. Further information on this fascinating subject may be found on the SETI website.
Some or all content above used with permission from J. H. Wittke.