Why was the Big Bang not really a bang?

The Big Bang was not an explosion in space; it was the expansion of space itself. The theory says the universe expanded from an extremely hot, dense early state about 13.8 billion years ago. An explosion throws material outward into a surrounding emptiness, from a centre. The Big Bang has no surroundings and no centre: the expansion happens everywhere at once, which is why some have suggested calling it the "Everywhere Stretch".

So why the noisy name? It came from one of the theory's rivals. In March 1949 the astronomer Fred Hoyle, who believed in a "steady state" universe with no beginning, described the competing idea on BBC radio as "this big bang idea". People often say he meant it as an insult. Hoyle denied that, saying he just wanted a vivid image to contrast the two models, and the historian Helge Kragh finds the insult story unconvincing.

The idea itself came from Georges Lemaître, a Belgian physicist who was also a Catholic priest. In 1931 he proposed that, if you ran the expansion backward, everything would shrink into a "primeval atom". Evidence piled up on his side, especially the faint microwave glow found in 1964. In 1993 a magazine even held a contest to find a better name. None of the entries succeeded, so the bang stayed.