The time required for the Universe to expand to its present size, assuming that the Hubble constant has remained unchanged since the Big Bang. It is defined as the reciprocal of the Hubble constant, 1/H₀. For a Hubble constant of 70 km/s/Mpc, as given by current measurements, the Hubble time is around 14 billion years. In practice, the actual age of the Universe is slightly less than the Hubble time because the expansion rate was faster in the early Universe, although it is now believed to be accelerating again.