Atheists: What proof do YOU have that heaven DOESNT exist?

You all seem so sure of yourselves, but have no proof. Show me PROOF that it DOESNT exist then. Just because the physical world is the only one we can investigate, doesnt mean its the only life out there. I believe the after life is real, but no one can say for sure either way. No ones proved it, but no ones disproved it either. So what proof do YOU have that it ISNT real?