The Cosmological Constant Problem, Dark Energy, and the Landscape of String Theory

Abstract

In this colloquium-level account, I describe the cosmological constant problem: why is the energy of empty space at least 60 orders of magnitude smaller than several known contributions to it from the Standard Model of particle physics? I explain why the "dark energy" responsible for the accelerated expansion of the universe is almost certainly vacuum energy. The second half of the paper explores a more speculative subject. The vacuum landscape of string theory leads to a multiverse in which many different three-dimensional vacua coexist, albeit in widely separated regions. This can explain both the smallness of the observed vacuum energy and the coincidence that its magnitude is comparable to the present matter density.

arXiv comment22 pages, 4 figures. To appear in the proceedings of "Subnuclear Physics: Past, Present and Future", Pontificial Academy of Sciences, Vatican (October 2011). v2: minor editing, typo in eq. (3.3) fixed

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
• Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• de Sitter Vacua in String Theory
• The Cosmological Constant
• The holographic principle
• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• Quintessence and the Rest of the World
• A Covariant Entropy Conjecture
• Cosmological Constraints from the Clustering of the Sloan Digital Sky Survey DR7 Luminous Red Galaxies
• Report of the Dark Energy Task Force
• Holographic probabilities in eternal inflation
• The Cosmological Constant and the String Landscape
• Predicting the Cosmological Constant from the Causal Entropic Principle
• de Sitter Space in Non-Critical String Theory
• First Observational Tests of Eternal Inflation
• First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results
• Determining the outcome of cosmic bubble collisions in full General Relativity
• Eternal Inflation, Bubble Collisions, and the Disintegration of the Persistence of Memory
• A geometric solution to the coincidence problem, and the size of the landscape as the origin of hierarchy
• Eternal inflation predicts that time will end
• Polarizing Bubble Collisions
• The Landscape "avant la lettre"
• Optimal filters for detecting cosmic bubble collisions
• Analyzing Cosmic Bubble Collisions
• Observing the Multiverse with Cosmic Wakes
• The Entropic Landscape
• Giant Leaps and Minimal Branes in Multi-Dimensional Flux Landscapes
• Saturating the holographic entropy bound

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• Gauge theory extension to include number scaling by boson field: Effects on some aspects of physics and geometry
• Making a Quantum Universe: Symmetry and Gravity
• Quantum gravity and the cosmological constant: lessons from two-dimensional dilaton gravity
• Seeking connections between wormholes, gravastars, and black holes via noncommutative geometry
• Classical, quantum, and phenomenological aspects of dark energy models
• Quantum state of fields in $SU(\infty )$ Quantum Gravity ($SU(\infty )$-QGR)
• The exoplanets analogy to the Multiverse