What is the Big Bang?
The Big Bang Theory is the leading explanation of how the universe began. People believe that the Universe began in a Big Bang about 14 billion years ago; hence the theory name Big Bang.
It started 14 billion years ago. When the Universe was very small and very young, but it was hotter and denser than anything we can imagine. Particles were mixing with light and energy. In fact, the Big Bang was not an explosion; it was a rapid expansion of space over millions of years. As the universe expanded, everything took up more space and the universe began to cool down. The universe wasn’t expanding into anything, it was just expanding into itself because the universe is all there is. We don’t really know what happened during the Big Bang. Tools that we have break down, time and natural laws start to not make sense at all. There could have been a universe before us. This might not be the first and only universe…
We do know what happened after the Big Bang though. Tiny particles began to group together and over time, they formed atoms that grouped together to create stars and galaxies. Then stars created molecules that led to more stars being born. Galaxies were also grouping together. As this happened asteroids, comets, planets and black holes were formed.
Who came up with this idea/theory?
In 1927, an astronomer called Georges Lemaître had an idea. His idea was that millions of years ago, the entire universe started at just a single point. He also said the universe then expanded and stretched as big as we know it now, and it could keep on stretching.
Two years later, another astronomer called Edwin Hubble discovered that other galaxies were moving away from our galaxy, and the farthest ones were moving rapidly faster than the ones closest to us. This proved Lemaître’s idea right and that meant that everything was once close together.