Cosmic expansion, also known as the expansion of the universe, is the scientific theory that suggests the universe is constantly growing and spreading out. This theory is supported by evidence such as the redshift of distant galaxies and the cosmic microwave background radiation. The concept of cosmic expansion is based on the idea that the universe began with the Big Bang, a massive explosion that created all matter and energy in the universe. As a result of this explosion, the universe has been expanding and stretching out ever since. Several key observations have supported the theory of cosmic expansion, such as the discovery of redshifted light from distant galaxies, which suggests that these galaxies are moving away from us at increasing speeds. Additionally, measurements of the cosmic microwave background radiation show a uniform distribution of radiation across the universe, providing further evidence of the universe's expansion. Cosmic expansion is a fundamental aspect of modern cosmology and has led to the development of theories such as the Big Bang theory and the concept of dark energy. The study of cosmic expansion helps scientists understand the origins and evolution of the universe, as well as its ultimate fate.