Why is the night so completely dark in the environment of the book?

McCarthy never really tells us how the world has basically ended. THere is evidence to suggest something happened that ruined much of what we consider the atmosphere and natural elements. There are no city lights anymore making the "Nights dark beyond darkness and the days more grey..." The moon and stars seem to be gone or elude them, like God had decided to leave. What we are left with is utter blackness, "a blackness to hurt your ears with listening."