This is a rather interesting article that some may find helpful to keep in mind when talking to atheists: New Support for the Cosmological Argument | Catholic Answers
I've frequently attempted to use the cosmological argument with my atheist friends, but talking with atheists is like punching at jello. When they see that the logic is irrefutable they simply find a proposition to deny without providing reason, simply because if they accept the propositions they must accept the conclusion. And the proposition that, "Whatever begins to exist has a cause," seems to be the proposition they simply reject. They claim they don't believe it is true, and they claim there is no evidence to support the proposition. In the case of my friends, most of the time they rely entirely on "science" what is provable, testable, fact is all that they will accept. But in this case, this one proposition, they refuse to acknowledge that the scientific evidence overwhelmingly supports the proposition. Everything science tests and explains and proposes in the history of science is wholly dependent on this being true. Light exists because energy is released. Chemical reactions occure because... If P1 is not true, then science does not exist. Because science is purely about explaining cause, understanding the specifics of how P1 plays out in the universe. The telling part is that once you start down this path, they quickly try to change the subject and if you won't change the subject the conversation quickly ends. No, I'll get back to you. No, acknowledgement that there is something here that requires deeper thought so they can figure out what they are missing that proves the argument for P1 wrong. No, they just whistle pass the graveyard as best they can...
I'm not sure that this approach would have better results, but it's certainly worth a try. What would be required to prove God's existence? Something that can not be explained by science, something happening has absolutely no natural cause. That can only be evidence for God if your presupposition is that everything that begins to exist, everything that happens, everything that changes must have a cause.
P1 is not be an argument that an atheist can deny, if they accept science. If you deny P1, you deny the possibilty of science, you deny the basic premise of science.
