What are the key principles of the Big Bang theory?

The Big Bang theory is the prevailing cosmological model for the observable universe from the earliest known periods through its subsequent large-scale evolution. The following are the key principles of the Big Bang theory:

• The universe began as an extremely hot, dense, and small point, known as a singularity, which expanded rapidly in a Big Bang event approximately 13.8 billion years ago.
• The universe is still expanding and cooling, which is evidenced by the cosmic microwave background radiation, which is the afterglow of the Big Bang.
• The abundance of light elements in the universe, such as hydrogen and helium, is a result of the Big Bang nucleosynthesis.
• The formation of large-scale structures in the universe, such as galaxies and galaxy clusters, is a result of the gravitational amplification of small perturbations in the density of matter in the early universe.