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Resonance

May 2004
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In a remarkable paper published in Nature in 1975, James Gunn and Beatrice Tinsley argued that the expansion of our universe is not slowing down under the effects of its gravity, but that it is accelerating. They used simple ideas of how galaxies should evolve and interpreted the data on  brightnesses of galaxies at different distances (that is, at different epochs in the past) to come to this conclusion. After two decades, their result stands vindicated by new observations which do not suffer from uncertainties of galactic evolution, but which rely on the standard brightnesses of a certain kind of supernovae (explosions that destroy a star). New observations point toward the existence of a cosmological constant which endows space a repulsive force that accelerates the expansion of the universe, just as Tinsley describes below in this article she wrote in 1975.

From Big Bang to Eternity?

Beatrice Tinsley

From ancient times until only half a century ago, the prevailing cosmological belief was that the universe must be unchanging. Then came the fundamental astronomical discovery that the universe is expanding, followed shortly by theoretical indications that the expansion started billions of years ago from an explosive Big Bang. Recent research sheds new light on the key cosmological question about the distant future: Will the universe expand forever or will it eventually revert to a contraction that ends in an apocalyptic “big crunch?”

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