# Hawking, Stephen (William)

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(1942– ) British theoretical physicist: advanced understanding of space-time and space-time singularities.

Hawking graduated from Oxford in physics and, after a doctorate at Cambridge on relativity theory, remained there to become a Fellow of the Royal Society (1974) and Lucasian Professor of Mathematics (1979). He developed a highly disabling and progressive neuromotor disease while a student, limiting movement and speech. His mathematical work is carried out mentally and communicated when in a developed form. His life and work is an extraordinary conquest of severe physical disability.

Hawking began research on general relativity, recognizing that theory takes no account of the quantum mechanical nature of physics and is not adequately able to describe gravitational singularities such as ‘black holes’ or the ‘Big Bang’. In *The Large Scale Structure of Space-Time* (with G F R Ellis, 1973) he showed that a space-time singularity must have occurred at the beginning of the universe and space-time itself, and this was the ‘Big Bang’ (a point of indefinitely high density and space-time curvature). The universe has been expanding from this point ever since.

Hawking greatly advanced our knowledge of black holes–these are singularities in space-time caused by sufficient mass to curve space-time enough to prevent the escape of light waves (photons). The boundary within which light cannot escape is called the event horizon and is given by the radius. Hawking established that the event horizon can only increase or remain constant with time, so that if two black holes merge the new surface area is greater than the sum of that of the components. He showed that black hole mechanics has parallels with thermodynamic laws (in which entropy must increase with time). He also showed that black holes result not only from the collapse of stars but also from the collapse of other highly compressed regions of space.

During 1970–74 Hawking and his associates proved J Wheeler’s (1911– ) conjecture (known as the ‘no-hair theorem’) that only mass, angular momentum and electric charge is conserved once matter enters a black hole.

In 1974 Hawking deduced the extraordinary result that black holes can emit thermal radiation. For example if a particle–antiparticle pair are created close to an event horizon, and only one falls inside, then the black hole has effectively emitted thermal radiation. A finite temperature can there fore be associated with a black hole, and the analogy between black hole mechanics and thermodynamics is real. The indirect evidence for the actual existence of black holes at the centre of active galaxies is now compelling: and there is some evidence for a black hole at the centre of our own galaxy, the Milky Way.

More recently Hawking has sought to produce a consistent quantum mechanical theory of gravity, which would also link it with the other three basic types of force (weak nuclear, strong nuclear, and electromagnetic interaction). His non-technical book *A Brief History of Time* (1988) was an outstanding publishing success. He was admitted as a Companion of Honour by the Queen in 1989.

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