Stephen Hawking, born in 1942, British theoretical physicist and mathematician whose main field of research has been the nature of space and time, including irregularities in space and time known as singularities. Hawking has also devoted much of his life to making his theories accessible to the public through lectures, books, and films.
Hawking was born in Oxford, England, and he showed exceptional talent in mathematics and physics from an early age. He entered Oxford University in 1958 and became especially interested in thermodynamics (the study of the interaction of matter and energy), relativity theory, and quantum mechanics (see Quantum Theory). In 1961 he attended a summer course at the Royal Observatory that encouraged these interests. He completed his undergraduate courses in 1962 and received a bachelor’s degree in physics. Hawking then enrolled as a research student in general relativity at the department of applied mathematics and theoretical physics at the University of Cambridge.
Hawking earned his Ph.D. degree from Trinity College at the University of Cambridge in 1966. He stayed at the University of Cambridge, doing post-doctoral research, until he became a professor of physics in 1977. He became one of the youngest fellows of the Royal Society in 1974. In 1979 he was appointed Lucasian Professor of Mathematics at Cambridge.
During his postgraduate program, Hawking was diagnosed as having Amyotrophic Lateral Sclerosis (ALS), a rare progressive disease that handicaps movement and speech. This disease makes it necessary for Hawking to carry out the long and complex mathematical calculations that his work requires in his head. He has been able to continue his studies and to embark upon a distinguished and productive scientific career despite his illness.
From its earliest stages, Hawking’s research has been concerned with the concept of singularities—breakdowns in space and time where the classic laws of physics no longer apply. The combination of time and three-dimensional space is called space-time. The most familiar example of a singularity is a black hole, the final form of a collapsed star. Much of what scientists believe about space-time comes from the theory of relativity, which was developed in the early 20th century by German American physicist Albert Einstein. During the late 1960s Hawking proved that if the general theory of relativity is correct, then a singularity must also have occurred at the big bang. The big bang is the explosion that marked the beginning of the universe and the birth of space-time itself.
In 1970 Hawking’s research turned to the examination of the properties of black holes. The boundary of a black hole 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 with time—this area could never decrease. This meant, for example, that if two black holes merge, the surface area of the new black hole would be larger than the sum of the surface areas of the two original black holes. He also noticed that there were certain parallels between the laws of thermodynamics and the properties of black holes. For instance, the second law of thermodynamics states that entropy, or disorder, must increase with time. The surface area of the event horizon of a black hole is therefore similar to the entropy of a thermodynamic system.
From 1970 to 1974, Hawking and his associates provided mathematical proof for the hypothesis formulated by American physicist John Wheeler known as the “No Hair Theorem.” This theorem states that the only properties that particles of matter keep once they enter a black hole are mass, angular momentum (or spin), and electric charge. Matter entering a black hole loses its shape, its chemical composition, and its distinction as matter or antimatter.
Since 1974 Hawking has studied the behavior of matter in the immediate vicinity of a black hole from a theoretical basis in quantum mechanics. Quantum mechanics is a theory that describes how subatomic particles behave and how matter and radiation interact. He found, to his initial surprise, that black holes—from which nothing was supposed to be able to escape—could emit thermal radiation, or heat. Several explanations for this phenomenon were proposed, including one involving the creation of virtual particles. A virtual particle differs from a real particle in that a virtual particle cannot be seen by means of a particle detector, but it can be observed through its indirect effects. Empty space is full of virtual particles fleetingly “created” out of nothing, forming a particle and antiparticle pair that immediately destroy each other. (This concept is a violation of the principle of conservation of mass and energy, which says that the combined amount of mass and energy in a system must stay the same. The concept is permitted—and predicted—by the uncertainty principle of German physicist Werner Heisenberg, which states that it is impossible to measure both the position and energy of a particle precisely. Hawking proposed that when a particle pair is created near a black hole, one half of the pair might disappear into the black hole, leaving the other half to radiate away from the black hole. To a distant observer, the radiation of the leftover particle would appear as thermal radiation.
Throughout the 1990s Hawking sought to produce a theory that could connect several theories used by scientists to explain the universe. This theory would combine quantum mechanics and relativity to form a quantum theory of gravity (see Unified Field Theory). Such a unified physical theory would incorporate all four basic types of interactions between matter and energy: strong nuclear interactions, weak nuclear interactions, electromagnetic interactions, and gravitational interactions.
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 all these areas. He has also made his work accessible to the public through several books, including A Brief History of Time (1988) and Black Holes and Baby Universes and Other Essays (1993), which are suitable for a general audience. In 1992 American filmmaker Errol Morris helped make A Brief History of Time into a film about Hawking’s life and work.