What does the Big Bang Theory say?

According to the theory, the observable universe is not eternal or self-existent because it had a beginning.

Empirical evidence suggests that everything that has a beginning also has an end. It also suggests that the universe is an open system.

The Big Bang theory, open nature of the universe, and the idea that matter and energy are not eternal lead to the philosophical conclusion that there must be something other than matter and energy.

Supported by evidence such as the cosmic microwave background radiation, the observed redshift of galaxies, and the abundance of light elements, the Big Bang Theory postulates that the universe started as a hot, dense state about 13.8 billion years ago and has been expanding ever since. It suggests that all matter and energy in the universe were initially concentrated in a singularity, which then rapidly expanded and continues to expand today.