A Short History of Nearly Everything

by Bill Bryson

When we last met Edwin Hubble, he had determined that nearly all the galaxies in our field of view are flying away from us, and that the speed and distance of this retreat are neatly proportional: the further away the galaxy, the faster it is moving. Hubble realized that this could be expressed with a simple equation, Ho = v/d (where Ho is the constant, v is the recessional velocity of a flying galaxy and d its distance away from us). Ho has been known ever since as the Hubble constant and the whole as Hubble’s Law. Using his formula, Hubble calculated that the universe was about two billion years old31, which was a little awkward because even by the late 1920s it was increasingly evident that many things within the universe – including, probably, the Earth itself – were older than that. Refining this figure has been an ongoing preoccupation of cosmology.

Hubble's law - Hubble constant - age of universe