Anthropic reasoning in multiverse cosmology and string theory

Abstract

Anthropic arguments in multiverse cosmology and string theory rely on the weak anthropic principle (WAP). We show that the principle, though ultimately a tautology, is nevertheless ambiguous. It can be reformulated in one of two unambiguous ways, which we refer to as WAP_1 and WAP_2. We show that WAP_2, the version most commonly used in anthropic reasoning, makes no physical predictions unless supplemented by a further assumption of "typicality", and we argue that this assumption is both misguided and unjustified. WAP_1, however, requires no such supplementation; it directly implies that any theory that assigns a non-zero probability to our universe predicts that we will observe our universe with probability one. We argue, therefore, that WAP_1 is preferable, and note that it has the benefit of avoiding the inductive overreach characteristic of much anthropic reasoning.

7 pages. Expanded discussion of selection effects and some minor clarifications, as published

References in corpus (5)

• Quantization of Four-form Fluxes and Dynamical Neutralization of the Cosmological Constant
• Towards Inflation in String Theory
• Observational Consequences of a Landscape
• Multiple universes, cosmic coincidences, and other dark matters
• Anthropic Reasoning and Quantum Cosmology

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• Role of initial conditions in the Universe formation
• Spectra of conditionalization and typicality in the multiverse
• Resolving the observer reference class problem in cosmology
• Does Cosmological Evolution Select for Technology?