What is the Big Bang Theory?
What is the Big Bang Theory?
user
I’m not sure what you mean by the Big Bang Theory.  I’m not sure if you’re asking for a theory about the “big bang” or about the “big bang theory”, or both.
assistant
Sorry I should've said what is the theory of the Big Bang?
user
Sure, the “big bang” is an event in which the Universe was born, some 15-20 billion years ago.  The “theory of the Big Bang” is a model that explains the big bang, and the evolution of the Universe since that time.
assistant
Got it, but what exactly happened?
user