Annotated: Hawking's 'Black Hole Explosions?' (1974)

In 1974, Stephen Hawking published a short paper in the journal Nature with a startling title: "Black hole explosions?" In barely two pages, it overturned the settled belief that nothing can ever escape a black hole. This page walks through what that paper actually argued, in plain English, and why it remains his single most important contribution. The full citation is Nature 248 (1974) 30, and the rigorous follow-up was "Particle Creation by Black Holes," Communications in Mathematical Physics 43 (1975) 199.

The setting: black holes were supposed to be one-way

Before 1974, the consensus was simple: a black hole only ever grows. Anything crossing its event horizon is lost forever, and the area theorem Hawking himself had proved in 1971 said the horizon can never shrink. Black holes were the ultimate trap.

The surprising claim

Hawking's paper claimed the opposite of what everyone expected: black holes are not entirely black. They emit a steady stream of particles, glow with a real temperature, slowly lose mass, and, given enough time, can disappear entirely in a final burst, hence "explosions." This is now called Hawking radiation.

The argument, step by step

The reasoning combined two pillars of physics that rarely meet: Einstein's gravity and quantum mechanics.

First, quantum mechanics says that empty space is not truly empty. Pairs of "virtual" particles constantly appear and vanish everywhere, borrowing energy for a fleeting instant. See virtual particles.

Second, Hawking asked what happens when such a pair appears right at the edge of a black hole. Occasionally, one particle of the pair falls in while the other escapes. The escaping particle carries away energy, and to balance the books, the black hole must lose a tiny amount of mass. To a distant observer, the black hole appears to be glowing.

Third, he calculated the spectrum of this radiation and found, remarkably, that it is exactly the glow of a hot body at a specific temperature, now the Hawking temperature. This tied black holes directly to thermodynamics.

Why it was so important

The result was profound because it united three areas of physics that had seemed separate: gravity, quantum theory and thermodynamics. It confirmed that the earlier "analogy" between black hole mechanics and thermodynamics was real, giving genuine physical meaning to the idea of black hole entropy. And it raised a disturbing question, what happens to the information in everything the black hole swallowed once it evaporates, that became the information paradox and occupied physics for decades.

The sting in the tail

There is a reason this discovery never won Hawking a Nobel Prize. For any real black hole, the radiation is unimaginably faint, far too cold to detect against the noise of the universe. The prediction is almost universally accepted by physicists, yet it has never been directly observed. That story is told in why Hawking never won a Nobel Prize.

Read it yourself

The original papers are technical but the 1974 Nature paper is strikingly short. For the accessible version of the same ideas, Hawking's own A Brief History of Time explains them for general readers, and our Hawking radiation page gives the plain-English account. For his other landmark works, see his key scientific papers and the full bibliography.

References

The primary sources for this page are Hawking's own papers and the official record of his publications.

1. Hawking, S. W. "Black hole explosions?" Nature 248, 30 to 31 (1 March 1974). DOI: 10.1038/248030a0.
2. Hawking, S. W. "Particle Creation by Black Holes." Communications in Mathematical Physics 43, 199 to 220 (1975). DOI: 10.1007/BF02345020.
3. Bardeen, J. M., Carter, B. and Hawking, S. W. "The Four Laws of Black Hole Mechanics." Communications in Mathematical Physics 31, 161 to 170 (1973). DOI: 10.1007/BF01645742.
4. Bekenstein, J. D. "Black Holes and Entropy." Physical Review D 7, 2333 (1973). DOI: 10.1103/PhysRevD.7.2333.
5. The Stephen Hawking Estate, official publications list: hawking.org.uk/in-print.

This page is an explanatory summary for general readers and is not a substitute for the original papers, which are linked above for those who wish to read them in full.