### Astronomy Bio...Stephen Hawking

#### Jay Bitterman

Stephen William Hawking was born on January 8, 1942 in Oxford, England. From an early age he showed exceptional talent in mathematics and physics. At Oxford University he became especially interested in thermodynamics, relativity theory and quantum mechanics while attending a summer course at the Royal Observatory in 1961. In 1962 he completed his undergraduate courses (receiving a First Class Honors degree in physics), he enrolled as a research student in general relativity at the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge.

During this postgraduate program, Hawking was diagnosed as suffering from an incurable and progressive neuromotor disease that affects various voluntary and involuntary brain functions, particularly the capacity for sequence of thought. Nevertheless he was able to continue his studies and became a distinguished and productive scientist. In 1974 he was elected Fellow of the Royal Society, and in 1980 he became Lucasian Professor of Mathematics at Cambridge University.

Hawking's earliest research was concerned with the concept of singularities breakdowns in the space-time continuum where the laws of physics may no longer apply. The principal example of a singularity is a black hole, the final form of a collapsed star. In the late 1960s, Hawking relied on various assumptions concerning the properties of matter. He developed a mathematical theory of causality in curved space-time that relied on Einstein's General Theory of Relativity. If correct, then a singularity must also have occurred at the Big Bang, the beginning of the Universe and the birth of space-time itself.

In 1970 his research centered on the properties of black holes. A black hole can be produced when a star expends its energy. The pressure produced by the remaining stellar nuclear reactions is inadequate to support the star against the force of its own gravity. It then collapses into a miniscule and extremely dense singularity having such strong a gravitational field that its escape velocity requires a speed greater than that of light. A black hole is a chasm in the fabric of space-time, and its boundary is called the event horizon. Hawking realized that the surface area of the event horizon around a black hole could only increase or remain constant. It could never decrease with time. He conceived, for example, that if two black holes merged, the surface area of the new black hole would be larger than the sum of the surface areas of the two original black holes.

For the next four years, Hawking, along with B. Carter, W. Israel and D. Robinson provided a mathematical proof for the "No Hair Theorem" hypothesis formulated by John Wheeler. The theorem states that the only properties of matter that were conserved, once it entered a black hole, were its mass, its angular momentum and its electric charge. Thus matter lost its shape, its "experience", its baryon number and its existence as matter or antimatter.

Since 1974 Hawking has studied the behavior of matter surrounding a black hole from a theoretical basis in quantum mechanics. To his initial surprise he found that black holes could emit thermal radiation although nothing was supposed to be able to escape. Several explanations for this phenomenon were proposed. One involves the creation of "virtual particles". A virtual particle differs from a "real" particle in that it cannot be seen by means of a particle detector. It can be observed through its indirect effects. Thus "empty" space can be full of virtual particles that are fleetingly "created" out of "nothing" and forming a particle and antiparticle pair which immediately destroy each other. (This is a violation of the principle of conservation of mass and energy, but is permitted and predicted by the "uncertainty principle" of Werner Heizenberg.) Hawking proposed that when a particle pair is created near a black hole one half of the pair might disappear into the black hole. The other half might radiate away from the black hole (rather than be drawn into it). This would be seen by a distant observer as thermal radiation.

Hawking's present objective is to produce an overall synthesis of quantum mechanics and relativity theory, to produce a full quantum theory of gravity. Such a unified physical theory would merge all four basic types of interaction, the strong nuclear, weak nuclear, electromagnetic and gravitational. The properties of space-time, the beginning of the Universe, and a unified theory of physics are all fundamental research areas of science. Hawking has made, and continues to make, major contributions to the modern understanding of them all.

Published in the January 2000 issue of the NightTimes