Final answer:
Galaxies are moving away from each other in terms of velocity and distance. The expansion of the universe can be described as space itself stretching. The Big Bang theory is a good model for explaining the expansion.
Step-by-step explanation:
According to Hubble's law, galaxies are moving away from each other in terms of velocity and distance. The more distant a galaxy, the faster it is receding from us. This relationship between distance and velocity allows us to establish how long ago the expansion of the universe began.
In terms of the expansion of the universe, it is more accurate to think of space itself stretching rather than galaxies moving through static space. The fact that galaxies are receding from us and that more distant galaxies are moving away more rapidly shows that the universe is expanding uniformly.
A good model for describing the expansion of the universe is the Big Bang theory. This model suggests that the universe began as a single point and has been expanding ever since. It explains the observations of galaxies moving away from each other and the relationship between distance and velocity.