Estimates for the number of visible galaxy-spanning civilizations and the cosmological expansion of life

Abstract

If advanced civilizations appear in the universe with an ability and desire to expand, the entire universe can become saturated with life on a short timescale, even if such expanders appear rarely. Our presence in an apparently untouched Milky Way thus constrains the appearance rate of galaxy-spanning Kardashev type III (K3) civilizations, if it is assumed that some fraction of K3 civilizations will continue their expansion at intergalactic distances. We use this constraint to estimate the appearance rate of K3 civilizations for 81 cosmological scenarios by specifying the extent to which humanity is a statistical outlier. We find that in nearly all plausible scenarios, the distance to the nearest visible K3 is cosmological. In searches for K3 galaxies where the observable range is limited, we also find that the most likely detections tend to be expanding civilizations who have entered the observable range from farther away. An observation of K3 clusters is thus more likely than isolated K3 galaxies.

11 pages, 3 figures. In press, International Journal of Astrobiology. v2: Discussion added. Figures re-formated. Typos corrected. References added and updated

References in corpus (6)

• The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources in WISE
• The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. I. Background and Justification
• The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. II. Framework, Strategy, and First Result
• On the role of GRBs on life extinction in the Universe
• Extragalactic SETI: The Tully-Fisher relation as a probe of Dysonian astroengineering in disk galaxies
• Homogeneous cosmology with aggressively expanding civilizations

Cited by in corpus (7)

• SETI with Gaia: The observational signatures of nearly complete Dyson spheres
• Propulsion of Spacecrafts to Relativistic Speeds Using Natural Astrophysical Sources
• Project Hephaistos - II. Dyson sphere candidates from Gaia DR3, 2MASS, and WISE
• Project Hephaistos I. Upper limits on partial Dyson spheres in the Milky Way
• Interstellar communication network. I. Overview and assumptions
• If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare
• Qualitative classification of extraterrestrial civilizations