The Anthropic Landscape of String Theory

TL;DR

This work argues that string theory does not yield a unique vacuum but a vast landscape of vacua (the landscape) with varying cosmological constants, supported by moduli and 4-form fluxes; the small observed $\lambda$ is natural only if a huge number of vacua exist. It discusses the nontrivial physics of de Sitter space, showing that eternal de Sitter is problematic and de Sitter vacua are metastable. The paper proposes bubble cosmology and eternal inflation as mechanisms to realize anthropically favorable vacua, and reframes de Sitter states as resonances in a generalized S-matrix, rather than ordinary eigenstates. It connects to holography and complementarity as essential concepts to resolve horizon-related issues and to define quantum descriptions across cosmological horizons.

Abstract

In this lecture I make some educated guesses, about the landscape of string theory vacua. Based on the recent work of a number of authors, it seems plausible that the lanscape is unimaginably large and diverse. Whether we like it or not, this is the kind of behavior that gives credence to the Anthropic Principle. I discuss the theoretical and conceptual issues that arise in developing a cosmology based on the diversity of environments implicit in string theory.

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