Near a black hole, gravity does more than pull objects inward — time itself runs more slowly, meaning two observers could experience different amounts of time simply because one ventured closer to the darkness.

Near a black hole, gravity does more than pull objects inward — time itself runs more slowly, meaning two observers could experience different amounts of time simply because one ventured closer to the darkness.

Picture two astronauts saying goodbye near a black hole. One stays behind on a ship, parked at a safe distance. The other flies in closer, loops around near the edge of the black hole’s pull, and comes back. From the traveler’s own perspective, the whole trip might take a few hours. When they dock back at the ship, though, their friend has aged years. Neither astronaut’s clock was broken. Both were telling time correctly. Time itself, near that …