How quickly is the Universe expanding?
In 1929, Hubble published the outcome of his investigation – almost all galaxies are moving away from us and their speed increases in a linear relationship with their distance from us. According to today’s calculations, the ‘Hubble constant’ – the constant of proportionality between the distance of a galaxy and its speed – has a value of around 46 miles per second and per megaparsec. This means that a galaxy at a distance of one megaparsec would move away from us at a speed of 46 miles per second.
The galaxies are not racing away – space is simply expanding
It is rather improbable that the Earth is at the center of the Universe and all of the galaxies are thus moving away from us. More likely there is another cause for the frequent redshifts – the Universe is expanding. The Hubble constant thus indicates the speed at which the Universe is currently expanding. The observed redshifts are, therefore, less frequently caused by the Doppler effect than by the fact that space itself is being stretched in an expanding Universe and so too are the wavelengths of the electromagnetic radiation traveling through it.
Source: German Aerospace Center