What does it mean to say that God is in the world?
There are many examples. A god who impregnates virgins, is in the world. A god who demonstrably answers prayers, is in the world. A god who smites cities because of their 'gay ways', is in the world. A god who communicates to mortals the word-of-god, is in the world. Indeed, any deed recorded in the Bible or Koran is a deed that allegedly occurred in the world. Right?
That is, unless the recorded deed is not meant to be a factual claim. Did Muhammad really split the moon? Did Jesus walk on water, feed 5,000 people with a few loaves and fishes, or heal the sick? Did Jesus really die and then rise from the dead? If these claims are not meant to be true in the sense that they actually happened, then science does not apply.
Similarly, the scientific approach is not applicable to Harry Potter or Mark Twain or tales of Hobbits because those tales are just stories. The incidents depicted never actually happened. There never really was a Hermione or a Huck or a Bilbo, even though it warms our hearts to think so.
But most believers want god to be real, as in, a part of this world (as opposed to an abstract or non-corporeal god) , so we'll move on to show how science proves a god-who-is-real does not exist.
If god is in the world, then science proves god does not exist. How so? Science proves that a god-of-this-world does not exist the same way it proves whether or not your car keys are in your pocket, that is, we look and see. To put it bluntly, the absence of evidence is overwhelming.
There is no more reason to believe that a god-of-this-world exists than there is to believe that Zeus exists, or that Santa Claus or the Tooth Fairy exist, or the Loch Ness monster or Big Foot. The list of things that obviously don't exist, is endless.