Place: United States of America
Subject: biography, astronomy
English cosmologist and astrophysicist, distinguished for his work on the evolution of stars, the development of the steady-state theory of the universe, and a new theory on gravitation.
Hoyle was born in Bingley, Yorkshire, on 24 June 1915. He attended the local grammar school and then went to Emmanuel College, Cambridge. In 1939 he was elected a fellow of St John's College, Cambridge, and in 1945 he became a lecturer in mathematics at the university. Three years later he developed the steady-state theory as a cosmological model to explain the structure and properties of the universe. In 1956 he left the UK for the USA to join the staff of the Mount Wilson and Mount Palomar observatories. He returned to the UK ten years later to become director of the Institute of Theoretical Astronomy at Cambridge 1967-73. Since 1972 he has been an honorary research professor at Manchester University. He became a fellow of the Royal Society in 1957 and was knighted in 1972.
According to Hoyle's new theory on gravitation, matter is not evenly distributed throughout space, but forms self-gravitating systems. These systems may range in diameter from a few kilometres to a million light years and they vary greatly in density. They include galaxy clusters, single galaxies, star clusters, stars, planets, and planetary satellites. Hoyle argues that this variety need not imply that the self-gravitating systems were formed in diverse ways, but rather that there is no significant intrinsic difference between one place in the universe and another or between one time and another.
To explain this structure of a universe composed of clusters of matter of different size and to explain its formation, Hoyle calculated the theoretical thermal conditions under which a large cloud of hydrogen gas would contract under the influence of its own gravitation. He found that a contracting cloud whose temperature is less than that required for it to exist in equilibrium will break up into self-gravitating fragments small enough to be at equilibrium in the new, increased density of the cloud fragments. Moreover, such fragmentation will continue until the formation of opaque fragments dense enough for gravitational contraction to offset radiation loss and to maintain the temperature at the necessary equilibrium.
To account for the origin of the elements in the universe, Hoyle, in collaboration with his colleague, William Fowler, proposed that all the elements may be synthesized from hydrogen in eight separate processes that occur in different stages of the continual process by which hydrogen is converted to helium by successive fusions of hydrogen with hydrogen. The second stage occurs when the supply of hydrogen is exhausted and the cloud of gas heats up to allow the helium-burning stage, in which helium nuclei interact, to proceed. The third stage is the alpha process, whereby the cloud contracts further to reach temperatures of 109K (10 billion°C/18 billion°F) until neon (20Ne) nuclei built up by the helium-burning stage can interact, releasing particles that in turn are used to build up nuclei of new elements, and so on, until only the element iron is left. Although alternative approaches continue to be explored, there is considerable evidence confirming such an account for the abundant distribution of the elements.
The steady-state theory was expounded, in collaboration with Thomas Gold and Hermann Bondi, as a model to explain the structure and properties of the universe. It postulated that the universe is expanding, but that its density remains constant at all times and places, because matter is being created at a rate fast enough to keep it so. According to this model the creation of matter and the expansion of the universe are interdependent. It calls for no new theory of space-time. Hoyle was able to propose a mathematical basis for his theory that could be reconciled with the theory of relativity.
New observations of distant galaxies have, however, led Hoyle to alter some of his initial conclusions. According to his theory, because no intrinsic feature of the universe depends on its distance from the observer, the distant parts of the universe are the same in nature as those parts that are near. But the detection of some radio galaxies indicates that in fact the universe is very different at different distances, evidence which directly contradicts the fundamental hypotheses of the steady-state theory.
Hoyle is a prolific writer of science fiction as well as popular books on science; these latter include Of Man and the Galaxies (1966), Astronomy Today (1975), Diseases from Space (1979), Space Travellers: the Bringers of Life (1981), and Our Place in the Cosmos (1993). His autobiography, Home is Where the Wind Blows, was published in 1993.
He has suggested that life originated in bacteria and viruses contained in the gas clouds of space, which were then delivered to the Earth by passing comets
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