Abstract
Dynamic dark-energy (DDE) models are often designed to solve the cosmic coincidence (why, just now, is the dark-energy density the same order of magnitude as the matter density ?) by guaranteeing for significant fractions of the age of the Universe. However, such behavior is neither sufficient nor necessary to solve the coincidence problem. Cosmological processes constrain the epochs during which observers can exist. Therefore, what must be shown is that a significant fraction of observers see . Precisely when, and for how long, must a DDE model have in order to solve the coincidence? We explore the coincidence problem in dynamic dark-energy models using the temporal distribution of terrestrial-planet-bound observers. We find that any realistic DDE model which can be parametrized as over a few e-folds has for a significant fraction of observers in the Universe. This demotivates DDE models specifically designed to solve the coincidence using long or repeated periods of .
1 More- Received 26 December 2007
DOI:https://doi.org/10.1103/PhysRevD.78.083528
©2008 American Physical Society