The universe is expanding

Hubble's law is 'explained' by the statement, 'The Universe is expanding'. That implies a subtle distinction between the galaxies moving away from us because they are moving through space, or because they are being carried along by space itself, as it grows. The central position of the earth in the description of the galaxies moving away from us is illusory. The same Hubble's Law would be discovered by an astronomer in any other galaxy.

The fact that the universe is expanding is the central idea to be explained by cosmology, which is the study of the universe on the largest scale known.