Crucially, the theory is compatible with Hubble-Lemaître law – the observation that the farther away galaxies are, the faster they are moving away from Earth. Extrapolating this cosmic expansion backwards in time using the known laws of physics, the theory describes a high density state preceded by a singularity in which space and time lose meaning. There is no evidence of any phenomena prior to the singularity. Detailed measurements of the expansion rate of the universe place the Big Bang at around 13.8 billion years ago, which is thus considered the age of the universe.