That is not at all what I was trying to say. I was saying: Unless the OP meant something other than what every cosmologist means by the expression "Big Bang",

That is not at all what I was trying to say. I was saying: Unless the OP meant something other than what every cosmologist means by the expression "Big Bang", there is overwhelming evidence for it. I said this because contrary to what many people believe, the Big Bang Theory describes pretty much everything but the singularity at the beginning. The Big Bang Theory describes how the Universe evolved starting at some tiny fraction of a second after the "Big Bang". And this theory is confirmed without any reasonable doubt. You can literally see the expansion of the Universe right now, and you can see that remote regions of the Universe appear much younger than our region due to the finite speed of light. What happened precisely in the very first tiny fraction of a second is still very much up to debate, mostly because we don't have a working theory of quantum gravity, because both gravity and quantum mechanics become important at the same time, similar to some aspects of black holes. That's why I was phrasing it the way I did.