Edwin Hubble first observed this phenomenon in 1929, when he noticed that the light from distant galaxies shifted to the red end of the spectrum, as though it had been stretched as it traveled through space. By measuring the wavelengths of the light, Hubble observed that galaxies were expanding away from each other at a rate proportional to their distance from one another.
In the beginning, the universe was a single point. Where was that? It was, and still is, everywhere. Scientists even have proof: Light from the big bang, in the form of cosmic radiation, fills the sky in every direction.