across). These could have been produced in the early stages of the Big Bang and are consequently known as 'primordial black holes'.Stephen Hawking is one of the pioneers of the theory of quantum gravity and of modern cosmology. Having graduated from Oxford University, he moved to Cambridge University where he obtained his PhD and where, in 1979, he was appointed to the Lucasian Chair of Mathematics, a post once occupied by Sir Isaac Newton.
Working with Roger Penrose, Hawking's first important contributions to theoretical physics concerned the theory of black holes. Between 1965 and 1970, they demonstrated that, according to the general theory of relativity, within every black hole there must be a singularity, of infinite curvature and density, where the laws of physics break down. The results showing the conditions under which such singularities will arise in general relativity are known as the singularity theorems.
Turning his attention to quantum mechanics, Hawking was the first to apply this theory successfully to describe black holes. In the early 1970s, he used quantum ideas to demonstrate on purely theoretical grounds the unexpected result that black holes emit energy as if they were black bodies. Hawking has also speculated on the existence of 'mini-black holes' that each weigh about a billion tonnes but are no bigger than a proton (about across). These could have been produced in the early stages of the Big Bang and are consequently known as 'primordial black holes'.
Hawking has done a good deal of other important 
and mathematically extremely difficult work in which he has innovatively applied quantum theory to the early universe. Notable among his works is the conceptually demanding theory that incorporates imaginary time and that has no singularities. In this theory space-time would be finite but closed, with no boundaries and neither a beginning nor an end. Many of these ideas are outlined in his extraordinarily successful book A Brief History of Time, which has sold millions since it was published in 1988. Hawking's achievements are all the more remarkable because he developed in the 1960s a motor neurone disease that has, for the past twenty years, confined him to a wheelchair. Moreover, most of his communication is through a speech synthesizer. Hawking has remarked that 'I was fortunate in that I chose theoretical physics, because that is all in the mind'.
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