Dark energy from vacuum fluctuations

by Djorgovski, G. (CALTECH)

Thursday 8 Jun 2006, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

The nature of dark energy is probably one of the most outstanding problems in physics today. Many published models postulate the existence of some as yet unknown scalar field or a similar entity, and a particular form of its temporal evolution, but so far none are compelling. An alternative approach is to consider gravity associated with the quantum fluctuations of the ground state of the physical vacuum, whose existence is inevitable in any finite measurement volume, e.g., as bounded by the horizon. For example, Gurzadyan & Xue derived a formula which reproduces the value of the vacuum energy density from the fluctuations alone, which is very close to the observed value. This result by itself is remarkable as it is based on the known physics only, and it also removes the need for the extreme fine-tuning which plagues many other models. These are very attractive features. There are, however, some fundamental uncertainties in the choices of the upper (~ horizon scale) and lower (~ Planck scale) bounds for the computation of fluctuations. The simplest version of this model is in conflict with the observed bounds on the evolution of the dark energy density, but a simple, phenomenologically motivated modification brings the model in agreement with all current observations, and makes testable predictions for the future measurements.