How the Second Law Nearly Fell into a Black Hole

If black holes truly had no entropy, then any time an object fell into a black hole, its entropy would effectively be deleted, reducing the entropy of the universe and violating the second law of thermodynamics. The thermodynamic definition of temperature relates changes in energy to changes in entropy, so this revelation allowed Hawking to show that black holes actually do have entropy, consistent with the second law of thermodynamics. Once we know that black holes have entropy, we have a new form of the second law of thermodynamics that includes not only the universe outside the black hole, but also the universe within the event horizon: The total entropy, S = S + S , must never decrease.

Source: nautil.us