What is the Big Bang theory science: 

How did the universe start

The Big Bang Theory describes the initial expansion of the universe from a singularity about 13.8 billion years ago. It's not an event that occurs repeatedly; rather, it's a singular event that set the universe in motion. After the initial expansion, the universe has been evolving through various processes, but there hasn't been another Big Bang because it was a unique occurrence that initiated the universe's existence.

The Big Bang Theory is the prevailing cosmological model for the observable universe's earliest known periods. It suggests that the universe originated from a singularity, an extremely dense and hot state, approximately 13.8 billion years ago. This event marked the beginning of the universe's expansion, resulting in the formation of space, time, and all known matter and energy.

It's crucial to understand that the Big Bang wasn't an explosion in the conventional sense:

 Rather, it was a rapid expansion of space itself. As the universe expanded and cooled, fundamental particles formed, eventually leading to the creation of atoms, stars, galaxies, and the complex structures we observe today.

The reason why the Big Bang hasn't happened again is tied to the unique conditions that existed at the universe's inception:

According to current understanding, the Big Bang was a singular event that initiated the universe's existence. It's not a cyclical process that repeats over time. Once the universe began expanding, it continued to do so, undergoing various stages of development and evolution.

Additionally:

The conditions necessary for another Big Bang to occur are not present in the current state of the universe. The universe has undergone significant changes since its inception, including the formation of galaxies, stars, and planets, as well as the expansion of space itself. These changes have led to a different cosmic landscape compared to the initial conditions that gave rise to the Big Bang.

In summary:

The Big Bang Theory describes a unique event that marked the beginning of the universe's existence. It's not an ongoing or repeatable process, and the conditions necessary for another Big Bang are not present in the current state of the universe.