Atheists attest to the fact that their spirit (their God-conscious part) is dead. They know God exists intellectually—because of their conscience and creation—but they are not aware of His omnipresence because they are dead spiritually. They are like a fish in the ocean that is not aware of the ocean.
“We are born dead in trespasses and sins, alienated, cut off, detached from the life of God. The day that man believed the devil’s lie (which is sin), he forfeited the life that distinguished him from the animal kingdom—the life of God. When sin came in, the life went out.” Ian Thomas
Ephesians 4:18 having their understanding darkened, being alienated from the life of God, because of the ignorance that is in them, because of the blindness of their heart;