Moment
The black hole that was not black
Cambridge, 1974; Stephen Hawking brings quantum theory to the event horizon
Black holes were supposed to absorb everything and emit nothing. In 1974, Stephen Hawking calculated that quantum fields around an event horizon should produce thermal radiation. A black hole would therefore have a temperature, lose mass, and eventually evaporate. The result turned Bekenstein's proposed link between entropy and horizon area into a precise law.
- Paper
- Black hole explosions?
- Journal
- Nature
- Published
- 1974
The caveat
For a stellar black hole, Hawking's predicted temperature is vastly below the 2.7 kelvin cosmic microwave background, making direct detection extraordinarily difficult. The calculation is semiclassical: it uses quantum fields on curved spacetime, not a complete theory of quantum gravity.
The discovery joined quantum theory, general relativity, and thermodynamics. It also sharpened the black hole information problem: if the outgoing radiation is thermal, what happens to the information carried by everything that fell in? That question has become a central test for any theory of quantum gravity.
Jacob Bekenstein proposed in 1973 that black holes carry entropy proportional to horizon area. Hawking's calculation supplied the matching temperature and fixed the entropy formula.
How it connects
Hawking showed that even a black hole hides an immense number of microscopic states behind a simple exterior.
This moment appeared in The future has more ways to happen, the Involves connection for August 8, 2026, which asked: Why does an egg break but never put itself back together?
Check yourself
What did Hawking calculate about black holes in 1974?
Quantum fields around an event horizon should produce thermal radiation, giving a black hole a temperature.. Right. A black hole would therefore have a temperature, lose mass, and eventually evaporate, turning Bekenstein's area-entropy link into a precise law.
What the sources establish
In 1974 Hawking argued that black holes emit thermal radiation as if they had a temperature set by surface gravity, and would therefore lose mass over time.
Bekenstein proposed in 1973 that black-hole entropy is proportional to horizon area, measuring information inaccessible to an exterior observer.
For a solar-mass black hole, the predicted Hawking temperature is far below the cosmic microwave background, so the radiation is extraordinarily hard to detect directly.
Sources
Black hole explosions? (S. W. Hawking, 1974), Nature 248, 30–31: thermal emission, temperature, and finite lifetime
Black Holes and Entropy (Jacob D. Bekenstein, 1973), Phys. Rev. D 7, 2333–2346: entropy proportional to horizon area