You're wondering about atheistic ontology or worldviews? Broadly speaking, the alternative is philosophical naturalism which begins with science. Science is methodologically naturalistic and thus atheistic. Scientists assume the best answers exclude miracles, so they search for natural explanations and exhaust them all before admitting that reason and experiment can't explain what's happening.

Atheistic ontology starts with scientific theories and explanations, and extends them with philosophical arguments and speculations. Some other relevant big words here would be "materialism," "physicalism," "property dualism," and "reductionistic explanation." Atheists would steer clear of substance dualism since that allows for miracles. That's why cosmologists are keen to explain what goes on inside a black hole in naturalistic terms that preserve scientific knowledge. There's also agnosticism, which says we can't know whether there's a God.

In terms of epistemology, there's skepticism, empiricism, rationalism, logic and critical thinking.

Theism is negated also by the mystical traditions of religions, which can amount to pantheism or to negative theology. God would be an abstract First Cause, Being itself or the ground of being, or the self-created universe as a whole, all of which might be consistent with atheism (with the denial that a literal perfect person created and intervenes in the universe).

The point of this article about the gall of imagining God's reality isn't to argue for theism, but to suggest that many so-called theists are only superficially and hypocritically interested in the possibility of a theistic God.