What is the Big Bang?
The Big Bang is the scientific theory that the universe began about 13.8 billion years ago in an extremely hot, dense state and has been expanding and cooling ever since.
Despite the name, the Big Bang was not an explosion into empty space. Instead, space itself began expanding everywhere at once. In the first fractions of a second, the universe was far hotter than the center of any star. As it cooled, basic particles formed, then the first atoms of hydrogen and helium, and much later stars and galaxies.
The idea was first proposed in the 1920s by Belgian priest and physicist Georges Lemaître. In 1929, Edwin Hubble showed that distant galaxies are moving away from us, which supported an expanding universe. The term Big Bang was coined by astronomer Fred Hoyle in 1949, who actually preferred a rival theory.
The evidence
In 1965, Arno Penzias and Robert Wilson discovered the cosmic microwave background, a faint glow of radiation coming from every direction, which is left over from the early universe. Along with the expansion of space and the amounts of light elements in the cosmos, it is one of the strongest pieces of evidence for the Big Bang.
Did You Know?
A small part of the static on old analog television sets came from the cosmic microwave background, the leftover glow of the Big Bang.