Hawking radiation
/ HAW-king /
We are told nothing escapes a black hole — yet Stephen Hawking showed in 1974 that, if you take quantum physics seriously, black holes are not perfectly black after all. They glow, ever so faintly, with a feeble whisper of radiation, and over unimaginable stretches of time they slowly leak away their mass and shrink. This is Hawking radiation: the astonishing idea that black holes evaporate, and the closest thing we have to a bridge between gravity and quantum theory.
How can anything come out? The trick is that empty space is not truly empty — quantum theory says pairs of particles constantly flicker into and out of existence everywhere. Right at the event horizon, one member of a pair can fall in while the other escapes, carrying away a tiny bit of energy. To balance the books, the black hole loses an equal sliver of mass. The radiation is colder the bigger the black hole: a stellar-mass black hole's Hawking glow is far colder than empty space, utterly undetectable. Smaller black holes would be hotter and evaporate faster, ending in a final burst.
The consequences are staggering in scale. A black hole the mass of the Sun would take some 10^67 years to evaporate — vastly longer than the current age of the universe — so in practice astrophysical black holes are growing, not shrinking, today. Hawking radiation has never been directly observed and likely never will be for a real black hole; it remains a theoretical prediction. Yet it is deeply important, because it ties together gravity, quantum mechanics, and thermodynamics, and it sharpens the unresolved puzzle of whether information that falls in is truly lost forever.
A black hole as massive as the Sun has a Hawking temperature of about 60 billionths of a kelvin — far colder than the 2.7-kelvin glow of empty space itself. It would take roughly 10^67 years to evaporate, so the universe is far too young for any star-born black hole to have noticeably shrunk.
A Sun-mass black hole's glow is colder than empty space; evaporation takes 10^67 years.
Hawking radiation is a theoretical prediction, never observed, and is laughably feeble for real black holes — colder than the cosmos around them. It matters for theory, not as something we can detect today.