Simulating the characteristics of extra-terrestrial civilizations that encounter Earth

Abstract It is generally believed that it is unlikely that our civilization is alone in this galaxy. This belief is central to the premise of the Search for Extraterrestrial Intelligence (SETI), which has focused mainly on searching for radio signals originating from extraterrestrial communications, since it is believed that extraterrestrial craft visiting Earth would be an extremely unlikely event. However, the fact that we ourselves are currently working on developing probes to send to the Alpha Centauri system by 2069, strongly suggests that other civilizations may make similar, or more ambitious, efforts. Therefore, it is reasonable to inform our expectations by considering what characteristics and capabilities would be required for an interstellar civilization to find and visit Earth. In this paper, a physics-based analytic model of expanding interstellar civilizations is developed. A million civilizations that encounter Earth are simulated and their statistics are studied to determine their characteristics.