No offence, it is not Ji lametor, it is Georges Lemaitre, he was Priest and Cosmologist, His complete name Georges Henri Joseph Édouard Lemaître. Now talking about Scientific theories, they stand on the base of scientific evidence and mathematical equations and these theories take decades before being sent out to be considered by the rest of the world. Big Bang Theory was proved by the exitance of CMB. Thereafter there has been no solid pieces of evidence to prove Big Bang Theory invalid.