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Guth, Alan (Harvey)

bang’ universe ‘big expansion

[gooth] (1947– ) US astrophysicist; made a major contribution to our understanding of the origin of the universe.

A student at MIT, Guth worked at Princeton, Columbia, Cornell and Stanford before taking posts in physics at MIT from 1980 and concurrently at the Harvard–Smithsonian Center for Astrophysics from 1984.

For some time the ‘Big Bang’ theory of the creation of the universe, proposed by in 1948, has been generally accepted as the best explanation. A key observation about the universe, the existence of a background microwave radiation, can be explained in no other way. There were, however, questions that were not adequately accounted for by the basic theory. The standard ‘Big Bang’ model required a very hot early universe; why? Why also is the present universe so uniform on a large scale when it might be expected to be more irregular? Above all, it requires extraordinarily precise values of some physical properties (to within one part in 100 000 million million) to give the rate of expansion that we see today without either a much greater rate of expansion or a gravitational collapse.

It was to try and resolve these problems that, in 1980, Guth proposed a refinement to the ‘Big Bang’ theory. He proposed that the universe underwent an exponential expansion (a 10 30 increase in radius) in the first microsecond of its existence– the so-called ‘inflation hypothesis’ of cosmology – as a result of a kind of ‘supercooling’, which in turn led to an antigravitational effect that enhanced the ‘Big Bang’ expansion. With subsequent refinements by , and the Russian scientist Andrei Linde and others, the inflation hypothesis accounts very well indeed for the problems found with the ‘basic’ ‘Big Bang’ model. Inflation is now thought to have begun with a period of exponential expansion lasting only 10 –32 s, and a temperature reaching 10 28 K–followed by the decelerating expansion of the standard Big Band model.

Evidence for the inflation hypothesis was found in 1992 by a team led by George F Smoot (1945– ) of the University of California at Berkeley. Using the Cosmic Background Explorer (COBE) satellite they observed very faint ripples in the background microwave radiation, which forms the ‘afterglow’ of the ‘Big Bang’ when the universe originated about 15 billion years ago. The ripples are related to the slight ‘clumpings’ of thinly dispersed matter, which later grow to form galaxies. This observation, which was subsequently confirmed by balloon-borne observations, is considered evidence for the ‘Big Bang’ theory with inflation, and was described by Hawking as ‘the discovery of the century, if not of all time’.

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