The chronology of the universe describes the history and future of the universe according to Big Bang cosmology, the prevailing scientific model of how the universe developed over time from the Planck epoch, using the cosmological time parameter of comoving coordinates. The metric expansion of space is estimated to have begun 13.8 billion years ago.[1] The time since the Big Bang is also known as cosmic time. For the purposes of this summary, it is convenient to divide the chronology of the universe into four parts