From the big bang to the eureka moment

A Brief History of Time made Stephen Hawking famous, but he was already a world leader in cosmology. Peter Rodgers reports from the celebrations to mark Hawking's 60th birthday. Masters of the universe Stephen Hawking is the most famous physicist in the world. Indeed, the sales of Hawking's books and his appearances on The Simpsons and Star Trek have tended to overshadow his scientific achievements. But that was not the case in Cambridge last month when Hawking's contributions to physics and cosmology were celebrated at a week-long conference to mark his 60th birthday. 'We organized the meeting to look back on the immense contribution that Stephen has made to many areas of gravitational physics and cosmology,' said Gary Gibbons, one of Hawking's colleagues at Cambridge. 'We also wanted to look forward to what the future might hold for theoretical physics and cosmology, with special reference to the areas that Stephen has been most interested and most active in.' Hawking made his name with a series of papers in the 1960s on singularities in cosmology. Building on work by Roger Penrose, he showed that Einstein's general theory of relativity implied that space and time would have a beginning in the big bang and would end in a singularity. 'How unlike particle physics, where people were falling over themselves to latch onto the latest idea. They still are.' Hawking then switched his attention to black holes - regions of space where gravity is so strong that nothing can escape. He was also one of the first physicists to make progress in combining general relativity - the classical theory of gravity - and quantum mechanics. First he showed that when two black holes collide and merge, the area of the 'event horizon' around the resulting black hole is greater than the sum of the two original areas. This led Hawking and co-workers to link the area of the event horizon, A, with the entropy of a black hole, S. Hawking told the meeting that he wants this simple equation (S = Akc3/4h-bar G) to be on his tombstone. Hawking then went on to predict that black holes have a temperature and are not, therefore, completely black. In simple terms, what is now known as Hawking radiation is produced when quantum fluctuations give rise to pairs of short-lived virtual particles near the event horizon. The gravity of the black hole pulls one of the particles from each pair into the black hole, while the other escapes. From a distance it appears as if the black hole is radiating. This effect was symbolized by the conference mug, which changes from black to white to reveal the equation for the Hawking temperature when it is filled with hot tea or coffee. One speaker showed the meeting a list of Hawking's papers in the SPIRES database at the Stanford Linear Accelerator Center. Six of Hawking's papers have qualified for 'renowned' status, having been cited more than 500 times by other papers in the database. The paper on Hawking radiation had the most citations, followed by a paper with Jim Hartle on the initial wavefunction of the universe, and a paper on the inflationary theory of the early universe. The struggle to develop a quantum theory of gravity and to unify the four fundamental forces of nature was an overarching theme at the conference. Most theorists believe that the best approach is so-called M-theory, in which the fundamental particles are actually vibrations in tiny strings in a 11-dimensional space-time. So far theorists know that M-theory embraces a classical theory known as 11-dimensional supergravity and all five of the superstring theories that were previously candidates for a unified theory. However, they do not yet know how to apply M-theory to the real universe. (U.K.)