But one area of science held out: in the far reaches of space, there were believed to be phenomena that, alone in the universe, did not behave according to the principles of thermodynamics. Specifically, they appeared to defy the second law, namely that the entropy of a closed system such as our universe always increases. These objects, the most outlandish prediction of Einstein’s theory of general relativity, are black holes. Black holes are bizarre regions of space into which anything can fall but from which (almost) nothing can escape.
