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

TL;DR

This paper explores the near-unity dimensionless age of the universe, H_0*t_0, highlighting its consistency across cosmological models and astrophysical measurements, and discusses its implications as a potential cosmic coincidence.

Contribution

It demonstrates that H_0*t_0 is close to one across multiple data sets and models, revealing a possible cosmic coincidence and introducing the 'synchronicity problem.'

Findings

H_0*t_0 ≈ 0.96 ± 0.01 in LCDM model

Astrophysical measures also suggest H_0*t ≈ 1.0 ± 0.1

The universe's age appears to be a special time in cosmic evolution

Abstract

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_0t*_0 = 0.96 +/- 0.01 for the LCDM 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 comic 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 Omega_Matter and Omega_Lambda for which the usual coincidence problem holds but for which H_0*t_0 is not close to 1.