"The Big Bang theory is just that- a theory. That's not science, simply conjecture. "
Oh, lord -- more misuse of the word "theory". A scientific theory is *not* a conjecture. There is a scientific word for a conjecture and it's... conjecture. They are different concepts.
Theories in science are coherent explanations for natural phenomena that are backed up by experimental evidence. They also make predictions for what future experiments will observe that can than be tested, and the theory therefore further supported, or modified, according to those results. They are certainly not wishy-washy explanations that may or may not be true according to your fancy, nor are they down to the whim of scientific opinion.
In maths, a theorem is something that has been proven to be true. In Science, nothing is ever proven, but theories still have the same essential status: a theory, in science, is about as close to truth as it's possible to get.