Big Bang Theory.

The Big Bang theory is an effort to explain what happened at the very beginning of our universe. According to the standard theory, our universe sprang into existence as "singularity" around 13.7 billion years ago.....

There is evidence for the Big Bang theory in the observed redshift of distant galaxies, which indicates that they are moving away from the Earth, in the existence of cosmic microwave background, and from other data. The Big Bang theory of the origin of the universe is accepted by most astronomers today.