When you take your last breath here on earth, you'll believe in God for sure ...
Your assertion is based on what? Have you died and came back? Has anyone died, say for a week and came back to tell us that God exist? Post a link, I'd love to send my fellow atheists to investigate.
... If you can not define what exactly God is, then how can you say that God does not exist?
Why would I want to define something that has no evidence in reality. I'm not in the business of writing Harry Potter's novels.
If you believe in God,
you define it and provide evidence of its existence. I can guarantee you'll win a Nobel Price and will be rich beyond your dreams if you provide a testable, scientific proof that supernatural beings exist. Anything, ghosts, angels, devil, god, tooth fairies etc...
It just does not make sense to prove that something does not exist if that something does not exist.
It does not exist because there is no proof of it's existence. What else is there to prove?
It is childish. It is like asking someone to prove that Santa Claus does not exist. It is a made up story like all religions. Grow up people.
As we explore the world and discover how it actually works, the space for religion and superstition gets smaller and smaller...
Can you prove that he doesn't exist? What is at the center of every galaxy? When did we discover this? How much do we actually know about black holes? Time is relative, but how? So, the universe with it's immense order and perfection was created by chance? There will never be physical proof that god exists until the savior comes again or until you die. Then you will be able to see with your own eyes how things really are. If physical proof exists of God then there is no need to believe or have faith in Him, hence the lack of physical proof.