Precision Cosmology and the Landscape

Abstract

After reviewing the cosmological constant problem - why is Lambda not huge? - I outline the two basic approaches that had emerged by the late 1980s, and note that each made a clear prediction. Precision cosmological experiments now indicate that the cosmological constant is nonzero. This result strongly favors the environmental approach, in which vacuum energy can vary discretely among widely separated regions in the universe. The need to explain this variation from first principles constitutes an observational constraint on fundamental theory. I review arguments that string theory satisfies this constraint, as it contains a dense discretuum of metastable vacua. The enormous landscape of vacua calls for novel, statistical methods of deriving predictions, and it prompts us to reexamine our description of spacetime on the largest scales. I discuss the effects of cosmological dynamics, and I speculate that weighting vacua by their entropy production may allow for prior-free predictions that do not resort to explicitly anthropic arguments.

39 pages, 6 figures. Based on a talk given at the conference in honor of the 90th birthday of Charles Townes (Berkeley, October 2005), and on a colloquium at Stanford University. v2, v3: references improved

References in corpus (30)

• Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
• Measurements of Omega and Lambda from 42 High-Redshift Supernovae
• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Cosmological parameters from SDSS and WMAP
• de Sitter Vacua in String Theory
• The Cosmological Constant
• Cosmological Constraints from the SDSS Luminous Red Galaxies
• The String Landscape, Black Holes and Gravity as the Weakest Force
• Quantization of Four-form Fluxes and Dynamical Neutralization of the Cosmological Constant
• On the Geometry of the String Landscape and the Swampland
• Quintessence and the Rest of the World
• The Stretched Horizon and Black Hole Complementarity
• A Covariant Entropy Conjecture
• The statistics of string/M theory vacua
• Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
• The Anthropic Landscape of String Theory
• Distributions of flux vacua
• From the Big Bang Theory to the Theory of a Stationary Universe
• The String Landscape and the Swampland
• Holography in General Space-times
• Report of the Dark Energy Task Force
• The Cosmological Constant and the String Landscape
• The landscape of intersecting brane models
• de Sitter Space in Non-Critical String Theory
• Present and future evidence for evolving dark energy
• Is Our Universe Likely to Decay within 20 Billion Years?
• Anthropic prediction for Lambda and the Q catastrophe
• The Cold Big-Bang Cosmology as a Counter-example to Several Anthropic Arguments
• A Review of Distributions on the String Landscape
• Cosmological Constant and Axions in String Theory

Cited by in corpus (1)

• Relativistic cosmology and large-scale structure