Atheists ???

Okay, question: Why do you believe there is no "higher power"? How could the earth, let me change that, the Universe could be created out of nothingness. I myself being Christian also believes that there are holes in every religion , but let me refer to the big bang theory ... How could those several particles have created the Universe if nothing was to create them ...? I do believe that the theory of evolution is probable, because of coarse life will evolve when exposed to new environments. But science is not my religion, so please explain why you are not at least agnostic when you can't prove that there is not a god?