Dark-Energy Dynamics Required to Solve the Cosmic Coincidence

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dc.creatorEgan, Chas A.
dc.creatorLineweaver, Charles H.
dc.date2007-12-19
dc.date2008-10-14
dc.date.accessioned2026-07-07T11:54:45Z
dc.date.available2026-07-07T11:54:45Z
dc.descriptionDynamic dark energy (DDE) models are often designed to solve the cosmic coincidence (why, just now, is the dark energy density $ρ_{de}$, the same order of magnitude as the matter density $ρ_m$?) by guaranteeing $ρ_{de} \sim ρ_m$ for significant fractions of the age of the universe. This typically entails ad-hoc tracking or oscillatory behaviour in the model. However, such behaviour is neither sufficient nor necessary to solve the coincidence problem. What must be shown is that a significant fraction of observers see $ρ_{de} \sim ρ_m$. Precisely when, and for how long, must a DDE model have $ρ_{de} \sim ρ_{m}$ 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 dark energy model fitting current observational constraints on $ρ_{de}$ and the equation of state parameters $w_0$ and $w_a$, does have $ρ_{de} \sim ρ_m$ for a large fraction of observers in the universe. This demotivates DDE models specifically designed to solve the coincidence using long or repeated periods of $ρ_{de} \sim ρ_m$.
dc.description16 pages, 8 figures, Submitted to Phys. Rev. D
dc.identifierhttps://arxiv.org/abs/0712.3099
dc.identifierhttp://arxiv.org/abs/0712.3099
dc.identifierPhys.Rev.D78:083528,2008
dc.identifierdoi:10.1103/PhysRevD.78.083528
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/205017
dc.subjectAstrophysics
dc.titleDark-Energy Dynamics Required to Solve the Cosmic Coincidence
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