Cold big-bang cosmology as a counterexample to several anthropic arguments

Phys. Rev. D 64, 083508 – Published 25 September 2001
Anthony Aguirre


A general Friedmann big-bang cosmology can be specified by fixing a half-dozen cosmological parameters such as the photon-to-baryon ratio ηγ, the cosmological constant Λ, the curvature scale R, and the amplitude Q of (assumed scale-invariant) primordial density fluctuations. There is currently no established theory as to why these parameters take the particular values we deduce from observations. This has led to proposed “anthropic” explanations for the observed value of each parameter as the only value capable of generating a universe that can host intelligent life. In this paper, I explicitly show that the requirement that the universe generates Sun-like stars with planets does not fix these parameters, by developing a class of cosmologies (based on the classical “cold big-bang” model) in which some or all of the cosmological parameters differ by orders of magnitude from the values they assume in the standard hot big-bang cosmology, without precluding in any obvious way the existence of intelligent life. I also give a careful discussion of the structure and context of anthropic arguments in cosmology, and point out some implications of the cold big-bang model’s existence for anthropic arguments concerning specific parameters.


  • Received 8 June 2001
  • Published 25 September 2001

© 2001 The American Physical Society

Authors & Affiliations

Anthony Aguirre

  • School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540

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