A quick note on atheism before I move on to other things:
It's true of course that the existance or non-existance of a God, or gods can not be proved. That's a given.
The mistake alot of atheists make is to think that being an atheist is to be free of religon. They are not. The conviction that there is no god is a religious belief.
What do I mean by that? Just that it's an unprovable assumption, based on the small evidence that a person can see from limited perspective of a human life span on a teeeny speck of a planet in a dwarfish galaxy in a crazy huge universe. Just like a christian's assumption that Jesus is real, or a hindu's assumption that reincarnation happens.
An agnostic- one who "reserves judgement" - now that I can understand. But to think that you can somehow "know" that there is no God is ... rather closeminded. There might be one or two you know...
And either way, a person is not defined by their opinions and guess work as to how the universe is or is not structured. A person is defined by their actions.
Pure religon is the path a person walks. It's the way you chose to live and interact with everyone else. Cosmology has little to do with it.