One (I'm sure not the only one) difference between science and religion is that religion is based on belief, including (in most cases) a god or gods with specified powers. In many cases, all things are claimed to be explained by the religion.

Science (specifically scientists) recognizes that it doesn't know everything. It tries to find out things by observing and constructing theories which fit these observations. To cite a well known example, what happened after the a small fraction of a second after the big bang can be described fairly well by known physics. However, the onset is still just guesswork. The inflation model is a good attempt to resolve certain problems, but it could be replaced by another explanation sometime in the future. Peeble's article (Jan. 2001 Scientific American) gives a good summary of the state of knowledge of the subject. In particular he grades different aspects of the theory in terms of how certain the science is.