Editorial on the GRG special issue on dark energy

Abstract

General Relativity and Gravitation has put together a special issue on “dark energy” in cosmology, because it is a major challenge to gravitational physics and actually to all of theoretical physics. We look at the observational side (the astrophysical data for dark energy and alternative explanations of that data), phenomenological models for dark energy and possible tests of these models, and the quantum gravity side (why do we expect a very large cosmological constant? what are the possible explanations of why it is small?). The idea is not to pursue one particular approach to this important problem, but rather to produce a survey of significant approaches that have been taken as regards each of its aspects. We consider this under three major headings: ASTRONOMICAL OBSERVATIONS, GRAVITATIONAL THEORY AND PHENOMENOLOGICAL MODELS, and QUANTUM ASPECTS Under ASTRONOMICAL OBSERVATIONS, we report on astronomical data for dark energy, which is of crucial importance: it is the first direct evidence for existence of physical fieldswith an effective negative gravitational energy. The crucial supernova data is surveyed by B. Leibundgut. This data is backed up by other astronomical data, surveyed by B. Nichol, and the overall observational case for dark energy is surveyed