Quintessence, Cosmic Coincidence, and the Cosmological Constant
Abstract
Recent cosmological observations suggest that a large fraction of the energy density of the universe has negative pressure. One possibility is vacuum energy density or cosmological constant. Another possibility is quintessence, a slowly-varying, spatially inhomogeneous component, such as a scalar field evolving down a potential. These components and the matter density decrease at different rates as the universe expands. Hence, it seems to be pure coincidence that two of them are comparable today. In this paper, we introduce the notion of a ``tracker field,'' a form of quintessence, and show how it may explain the coincidence, adding new motivation for the quintessence scenario.Keywords
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