They have not observed the big bang have they? But they believe it as fact, when indeed it isn't a proven fact. It is even taught as a fact to students today in many schools and that, to me, is a travesty. It needs to be taught as it really is, a theory!
Didn't we already explain in another thread a long time ago that a scientific theory is tantamount to a fact, because it is based on observable evidence and fact? You are thinking of the word "hypothesis," which is where someone just says, "I think this is how it is." A scientific theory is "this is how I observed things to be, and this is the simplest explanation." Like the earth rotating around the sun is a scientific theory (heliocentric theory) based on our observations. We observed how things move around in the sky, and sent satellites to space to verify observations, and the theory of "earth is rotating around the sun" is the simplest explanation we have for what we have seen. Keep in mind that we have never actually went to the sun and watched the earth rotate around from there just to be sure. We never needed to. Likewise with big bang, we can observe the universe expanding from a point, and can see background radiation far away in space that fits the simplest explanation of "everything came from one point." If you want to add your own evidence of a creator, you have to actually present the visible (or at least testable) evidence, not just something you think is true.