All stars are suns. Our Galaxy, the Milky Way, is a spiral galaxy containing several hundred billion stars. The universe contains over a billion galaxies, or, in all, more stars than there are grains of sand on all the beaches of Earth. Out of the findings of the sciences that have converged to give us our present picture of cosmic evolution we draw certain conclusions that are the premises of a plausibility argument for the prevalence of technologically advanced extraterrestrial life.
Planetary systems are the rule rather than the exception.
Our understanding of the process of star formation leads us to expect planetary systems around most stars, and to expect a favorably situated planet in most systems. The origin and early evolution of life on Earth is apparently explicable in terms of the basic laws of physics and chemistry operating in the primitive terrestrial environment. The laws of physics and chemistry apply throughout the universe. Moreover, the composition of the primordial material, from which life on Earth arose in accordance with these laws, is commonly repeated elsewhere. The factors causing natural selection, which led to the evolution of more complex species and ultimately to intelligent life on Earth, may reasonably be expected to be present on any planet on which life originated.