The Dark Ages began in the 6th century and extended well into the 13th century. In fact, Europe did so poorly in the 8th century that they had to repeat it, and the other continents made fun of them. This made Europe feel really insecure, and led Europe tp seek some serious psychoanalysis as soon as Sigmund Freud invented it in the 19th century.
This was a time of ignorance and superstition, when people reverted to primitive beliefs. For example, many people in the Dark Ages did not use statistical mechanics to derive the fact that electromagnetic radiation is discreet and not continuous. Who does that? Oh, foolish Dark Agers!
At the same time in the Middle East, the Arabs were inventing zero, writing amazing literature and just generally kicking Europe’s puny, Dark Ages ass.