The dimensionless age of the Universe: a riddle for our time

We present the interesting coincidence of cosmology and astrophysics that points toward a dimensionless age of the Universe H (0) t (0) that is close to one. Despite cosmic deceleration for 9 Gyr and acceleration since then, we find H (0) t (0) = 0.96 ± 0.01 for the ΛCDM model that fits SN Ia data from Pan-STARRS, CMB power spectra, and baryon acoustic oscillations. Similarly, astrophysical measures of stellar ages and the Hubble constant derived from redshifts and distances point to H (0) t ∼ 1.0 ± 0.1. The wide range of possible values for H (0) t (0) realized during cosmic evolution means that we live at what appears to be a special time. This “synchronicity problem” is not precisely the same as the usual coincidence problem, because there are combinations of Ω(M) and Ω(Λ) for which the usual coincidence problem holds but for which H (0) t (0) is not close to 1.

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14 pages, 12 figures. Accepted for publication in the Astrophysical Journal (ApJ)

cosmological parameters
cosmology: miscellaneous
cosmology: theory

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