An illustration of the evolution of the observable universe

    Features:

    1. In Image 1, the 2-dimensional cosmic time slices represent 3-dimensional space at each era.

      The slices exhibit exponential growth from the beginning to the end of hypothetical inflation era. After that, the slices grow more slowly with Friedmann equation evolution as given by the Λ-CDM model which consistent so far with the observed expansion of the universe.

      The growth illustrated in the Image 1 is not-to-scale.

    2. The expansion of the universe means the growth of space itself. How this is possible is explained by the theory of general relativity of Albert Einstein (1879--1955).

      The growth of space is just a scaling up of space in the Λ-CDM model and in Friedmann-equation (FE) models in general. These cosmological models are solutions of the Friedmann equation which is derived from general relativity plus extra cosmological assumptions: the main ones being cosmological principle (i.e., the assumption that the observable universe is homogeneous and isotropic in average properties on a large enough scale) and that actual mass-energy contents of the observable universe can be approximated by a perfect fluid.

    3. The expansion of the universe is actually only the growth of space between bound systems.

      You and yours truly, the planets (and smaller astro-bodies), the stars, the galaxies, galaxy groups and galaxy clusters are NOT expanding.

    4. Before stars, galaxies, and the large scale structure of the observable universe formed, the expansion of the universe just caused a decrease the in the cosmic density, and thus a decrease in the cosmic density of the primoridal light elements (hydrogen (H-1), deuterium (D, H-2) helium-3 (He-3), Helium-4 (He-4), and lithium-7 (Li-7)), cosmic background radiation (CBR) (which evolved to the present-day cosmic microwave background (CMB)), cosmic neutrino background, and dark matter (whatever that is).