All objects, from stars and planets to passing spaceships, can fall into a black hole, adding to its mass. As this happens, its pull on the flow of the space around it increases. Therefore, the speed of the “space flow” reaches light speed at a greater distance from the center of a black hole as its mass goes up. The radius of the event horizon grows. But nothing can fall out of a black hole and reduce its mass. Therefore the radius of its event horizon cannot shrink. Hawking spotted an uncanny similarity between this behavior and the behavior of entropy. Both event horizons and entropy never
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