The cosmological dust has begun to settle. A likely picture is a universe comprised (predominantly) of three components: ordinary baryons $({\Omega }_B\approx 0.05),$ nonbaryonic dark matter $({\Omega }_{\mathrm{dark}}\approx 0.22)$ and dark energy $({\Omega }_{\Lambda }\approx 0.7).$ We suggest that the observed similarity of the abundances of ordinary baryons and nonbaryonic dark matter $({\Omega }_B/{\Omega }_{\mathrm{dark}}\approx 0.20)$ hints at an underlying similarity between the fundamental properties of ordinary and dark matter particles. This is necessarily the case if dark matter is identified with mirror matter. We examine a specific mirror matter scenario where ${\Omega }_B/{\Omega }_{\mathrm{dark}}\approx 0.20$ is naturally obtained.

• Received 24 April 2003

DOI:https://doi.org/10.1103/PhysRevD.68.021304