A Large Universe dominated by dark energy might be the most hospitable to harbouring complex life

Raúl Jiménez & Licia Verde – Insitut de Ciències del Cosmos Universitat de Barcelona (ICCUB)

Gamma-ray bursts (GRBs) are copious sources of gamma rays whose interaction with a planetary atmosphere can pose a threat to complex life. Using recent determinations of their rate and probability of causing massive extinction, we explored in a recent Physical Review Letters (PRL, 2016, 116, 1301) what types of universes are most likely to harbor advanced forms of life. Life survival to GRBs favors dark-energy-dominated universes. Within a cold dark matter model with a cosmological constant, the likelihood of life survival to GRBs is governed by the value of Λ and the age of the Universe. We find that we seem to live in a favorable point in this parameter space that minimizes the exposure to cosmic explosions, yet maximizes the number of main sequence (hydrogen-burning) stars around which advanced life forms can exist.

Reference

Piran T, Jimenez R, Cuesta AJ, Simpson F & Verde L 2016, ‘Cosmic Explosions, Life in the Universe, and the Cosmological Constant’, Physical Review Letters, 116, 8, 081301.

Number of isolated halos as a function of redshift that are protected from the damaging effect on life of GRBs; we show four cosmologies and two isolated radii of satellites: 20 kpc (upper panel) and 50 kpc (lower panel). The number of life-protected regions is significantly larger the dark-energy-dominated cosmologies. This is due to the effect of dark-energy at late times at clearing and smoothing virialised regions. Also remarkable is the fact that only below z ~ 1 the number of isolated halos grows significantly. This is about 7 Gyr ago, not too dissimilar from the age of Earth.