How the Big Bang Theory Works

According to the American Museum of Natural History, the idea first appeared in a 1931 paper written by Georges Lemaître.

According to the theory, the universe was extremely dense and hot. There was so much energy in the universe during those first few moments that matter as we know it couldn't form. But the universe expanded rapidly, which means it became less dense and cooled down. As it expanded, matter began to form and radiation began to lose energy. In only a few seconds, the universe formed out of a singularity that stretched across space.

The big bang is an attempt to explain how the universe developed from a very tiny, dense state into what it is today. It doesn't attempt to explain what initiated the creation of the universe, or what came before the big bang or even what lies outside the universe.

According to the big bang theory, there's no center of the universe. Every point in the universe is the same as every other point, with no centralized location.

At the earliest moments of the big bang, all of the matter, energy and space we could observe was compressed to an area of zero volume and infinite density. Cosmologists call this a singularity.