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Hawking radiation

a surprising discovery on the path to a new theory of quantum gravity East Anglia,

Hand drawn diagram illustrating Hawking radiation.
Section of Hawking’s diagram of the radiation mechanism. Courtesy of Stephen Hawking.

One long-standing goal of physicists has been to blend the theory of the very big (general relativity) with the very small (quantum theory) to produce an overarching theory known as quantum gravity. 

General relativity can, for example, describe a black hole. This is an extremely dense concentration of mass with a gravitational field so powerful that, within a boundary known as the event horizon, nothing escapes - not even light. 

However in 1974 Stephen Hawking (born 1942) of the University of Cambridge challenged this. He suggested that black holes might not be so black after all, and could emit what we now call ‘Hawking radiation’. According to quantum theory, empty space is not really empty - pairs of particles are constantly popping into and out of existence. If a pair appears right on a black hole’s event horizon, one particle could be sucked in, with the other zooming free as Hawking radiation. 

The same mathematics can also be applied to the residual warmth left over from the Big Bang, and to the way in which a soup of ultra-hot matter ‘crystallised’ to form the universe. In 1982, Hawking made a bold proposal: that variations in the cosmic background radiation - the echoes of that initial explosion 13.7 billion years ago - could be traced back to Hawking radiation as the tiny seeds around which the structure of the universe coalesced. However, experimental evidence of this has yet to be found.

Science Museum

East Anglia
University of Cambridge
Key Individuals
Stephen Hawking,