Wordorigins.org

The Big Bang theory is the idea that our universe began in a giant “explosion,” where a primeval singularity suddenly and rapidly began expanding, creating space, time, and matter/energy with it. This happened approximately 13 billion years ago. Throughout the history of the theory, there as been a playful streak exhibited by its proponents, silly names and puns associated with the Big Bang abound.

The name Big Bang was originally a derisive one, coined by astronomer Fred Hoyle who was one of the chief opponents of the theory. But the name caught on and was adopted by proponents, losing its derisive edge.