PADERBORN, July 5 -- Fifty-two years elapsed between Stephen Hawking's 1974 prediction that black holes slowly radiate energy away and lose mass, and the first experiment to confirm not just the radiation itself but the feedback mechanism that makes the mass loss happen. That confirmation came this week from a fiber-optic physics laboratory at Paderborn University in Germany, in a study published in Nature.

The gap is not a failure of science. Real Hawking radiation from an actual black hole is, by current estimates, undetectably faint against the cosmic microwave background. A black hole with the mass of the Sun would require longer than the age of the universe to radiate measurably. No telescope, however sensitive, will observe the pro...