You can't say state factually that God does not exist. In order to do so you must be able to see everything regarding distance/magnification (from the universe all at once all the way down to a pinpoint position and subatomic particles), you must also be able to see in every spectrum, detect all types of energy, and be all knowing to even know what to look for.

If you were able to do all of this then either you have some crazy tech from the future or you are in fact yourself a deity.

You are certainly entitled to believe that God does not exist however, but you don't know it for a fact.