This cosmological thread led him to the study of black holes and his suggestion that following the big bang primordial, or mini, black holes—objects of immense mass occupying only the space of an elementary particle—were formed. He also showed that the surface area of a black hole can increase but never decrease, that there is a limit on the radiation emitted when black holes collide, and that a single black hole cannot cleave into two black holes. In 1974 Hawking calculated that black holes thermally create and emit subatomic particles until they exhaust their energy and explode. This so-called Hawking radiation linked gravity, quantum mechanics, and thermodynamics mathematically for the first time. Hawking proposed in 1981 that although the universe has no boundary, it is finite in space-time; he collaborated with James Hartle to formulate this mathematically in 1983.
Hawking wrote an explanation of his work that became a popular bestseller, A Brief History of Time: From the Big Bang to Black Holes (1988). He has also published Superspace and Supergravity (1981), The Very Early Universe (1983), Black Holes and Baby Universes and Other Essays (1993), and The Nature of Space and Time (1995).
See M. White, Stephen Hawking: A Life in Science (1992); D. Wilkenson, God, the Big Bang, and Stephen Hawking (1993); M. McDaniel, Stephen Hawking: Revolutionary Physicist (1994).