Recent data collected by the Hubble Space Telescope suggest that the universe may only be 8 billion years old. This contradicts the previous belief the universe was somewhere between 13 billion and 20 billion years old. The earlier figure was derived from the concept that the universe has been expanding at the same rate since its birth at the Big Bang. The rate of expansion is a ratio known as Hubble’s constant. It is calculated by dividing the speed at which the galaxy is moving away from Earth by its distance from Earth. By inverting Hubble’s Constant—that is, dividing the distance of a galaxy by its recessional speed—the age of the universe can be calculated. The estimates of both the velocity and distance of galaxies from Earth are subject to uncertainties, and not all scientists accept that the universe has always expanded at the same rate. Therefore, many still hold that the age of the universe is open to question.