To be able to declare scientifically that I was an Atheist I would have to have the complete knowledge of all the universes and beyond. This is like saying that there is no black stone with purple dots anywhere.... how can I know that unless I had the capacity to see and examine every stone in existence. Only a fool would do this.
To declare there is no God is an act of faith.
I will even say it takes more faith to believe there is no God - with all the evidence of Intelligent Design that contradicts this - than to believe there is a God.