Evolution of energy densities and expansion rate in the ΛCDM concordance model. Top panel: evolution of the energy densities, determined by Eq. (4). Bottom panel: evolution of the expansion rate H in natural units, determined by the total of the energy densities given by Eq. (5). The vertical lines in blue bracket the epoch of big bang nucleosynthesis, between neutron-proton freeze-out at a_n/p ∼ 1.3 × 10⁻¹⁰ and nuclei production a_nuc ∼ 3.3 × 10⁻⁹, while the vertical lines in red (at larger scale factor) indicate the time of matter-radiation equality a_eq, followed by recombination a_rec, in terms of the scale factor a.