Hubble's Law states that the velocity at which a galaxy recedes from an observer is directly proportional to its distance from the observer, implying that the universe is expanding. This relationship is fundamental to cosmology and provides evidence for the Big Bang theory, as it suggests that galaxies were once closer together in the past.
The universe expansion refers to the observation that galaxies are moving away from each other, suggesting that the universe has been expanding since the Big Bang. This expansion is driven by dark energy, which accelerates the rate at which the universe is growing over time.
The Cold Dark Matter (CDM) model is a theoretical framework that explains the structure formation of the universe, where dark matter is composed of slow-moving particles that clump together under the influence of gravity. It successfully accounts for the observed large-scale structure of the universe, such as galaxy clusters and cosmic microwave background anisotropies, while predicting the existence of unseen matter that interacts weakly with ordinary matter and radiation.