Dynamic dark energy (DDE) models are often designed to solve the cosmic
coincidence (why, just now, is the dark energy density ρde, the same
order of magnitude as the matter density ρm?) by guaranteeing ρde∼ρm 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 ρde∼ρm. Precisely when, and for how long, must a
DDE model have ρde∼ρm 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 ρde and
the equation of state parameters w0 and wa, does have ρde∼ρm 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 ρde∼ρm.Comment: 16 pages, 8 figures, Submitted to Phys. Rev.