The Big Bang Theory explains how the universe began. About 13.8 billion years ago, the universe started from an extremely small, hot, and dense point. This point, known as a singularity, exploded and began expanding, which is what we call the Big Bang.

In the beginning, the universe was full of energy and tiny particles. As it expanded and cooled, these particles started forming atoms, mainly hydrogen and helium. These atoms eventually came together to form stars and galaxies.

One of the strongest pieces of evidence for the Big Bang is the Cosmic Microwave Background Radiation (CMB). This is faint radiation left over from the early universe and is like a snapshot of the universe when it was just 380,000 years old. Scientists discovered this radiation in 1965, and it confirmed that the universe was once hot and dense before cooling down.

Another piece of evidence is redshift. When we look at galaxies far away, we notice that their light is stretched, or redshifted. This shows that those galaxies are moving away from us, and because of this, we know the universe is still expanding.

The universe has continued expanding ever since the Big Bang, leading to the stars, planets, and galaxies we see today. However, some questions still remain, like what happened in the very first moments of the Big Bang, and what caused it to happen in the first place?

The Big Bang Theory helps us understand how the universe came to be and continues to expand and change. It shows us that the universe isn’t static, but constantly growing.