title: Cosmic Explosions, Life in the Universe, and the Cosmological Constant.
abstract: 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 explore what types of universes are most likely to harbor advanced forms of life. We use cosmological N-body simulations to determine at what time and for what value of the cosmological constant (Λ) the chances of life being unaffected by cosmic explosions are maximized. Life survival to GRBs favors Lambda-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.
authors.affiliation: Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel.
authors.forename: Tsvi
authors.initials: T
authors.lastname: Piran
authors.affiliation: ICREA & ICC, University of Barcelona, Marti i Franques 1, Barcelona 08028, Spain.|Institute for Applied Computational Science, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Raul
authors.initials: R
authors.lastname: Jimenez
authors.affiliation: ICC, University of Barcelona, Marti i Franques 1, Barcelona 08028, Spain.
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: Cuesta
authors.affiliation: ICC, University of Barcelona, Marti i Franques 1, Barcelona 08028, Spain.
authors.forename: Fergus
authors.initials: F
authors.lastname: Simpson
authors.affiliation: ICREA & ICC, University of Barcelona, Marti i Franques 1, Barcelona 08028, Spain.|Institute of Theoretical Astrophysics, University of Oslo, Oslo 0315, Norway.
authors.forename: Licia
authors.initials: L
authors.lastname: Verde