Indifference principle and anthropic principle in cosmology

Abstract

The successes scored by the big bang model of cosmic evolution in the 1960’s led to an intensive application of quantum theory to the problem of how the expansion might have begun and what its likely first stages were. It seemed as though an incredibly precise setting of the initial conditions would have been needed in order that a long-lived galactic universe containing heavy elements might develop. One response was to suppose that the fine-tuning could somehow be explained by the presence of humans in the universe. This ran quite counter to the traditional supposition, according to which an initial chaos was sufficient. This essay outlines the history of the two principles, argues that the so-called weak anthropic principle is banal, distinguishes between two sorts of anthropic explanation, and assesses the prospects of the anthropic turn in cosmology.