According to Hubble's theory, as the distance between celestial bodies, such as galaxies, increases, they move away from each other at greater speeds. This phenomenon is observed through the redshift of light from distant galaxies, indicating that the universe is expanding.

The Big Bang theory supports this idea by suggesting that the universe began as a hot, dense point and has been expanding ever since. As the universe expands, the space between galaxies increases, causing them to move apart more quickly. This relationship, known as Hubble's Law, states that the farther away a galaxy is, the faster it appears to be receding from us.