I Anthropic Lower Limit on Cosmological Constant

[bcrowell]

Piran et al., "Cosmic explosions, life in the Universe and the Cosmological Constant," http://arxiv.org/abs/1508.01034

Gamma-Ray Bursts (GRBs) are copious sources of gamma-rays whose interaction with a plane- tary atmosphere can pose a threat to complex life. Using recent determinations of their rate and probability of causing massive extinction, we explore what type of universes are most likely to har- bour advanced forms of life. We use cosmological N-body simulations to determine at what time and for what value of the cosmological constant () the chances of life being unaffected by cosmic explosions are maximised. Life survival to GRBs favours -dominated universes. Within a CDM cosmology, the likelihood of life survival to GRBs is governed by the value of and the age of the Universe. We find that we seem to live in a favorable point in this parameter space that minimises the exposure to cosmic explosions, yet maximises the number of main sequence (hydrogen-burning) stars around which advanced life forms can exist.

I thought this was interesting. If I'm understanding correctly, the idea is that satellite galaxies such as the Magellanic Clouds have low metallicity, which causes them to host a lot of gamma-ray bursts. These GRBs are deadly to life in the main galaxy. Having a larger cosmological constant reduces the number of satellite galaxies that form, and therefore puts an anthropic lower limit on the cosmological principle.

Of course this is all very speculative.