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Science 13 January 1995:
Vol. 267. no. 5195, pp. 192 - 199
DOI: 10.1126/science.7809624
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Articles

Science, Vol 267, Issue 5195, 192-199
Copyright © 1995 by American Association for the Advancement of Science

articles

Big-bang nucleosynthesis and the baryon density of the universe

CJ Copi, DN Schramm, and MS Turner

Department of Physics, University of Chicago, IL 60637-1433.

For almost 30 years, the predictions of big-bang nucleosynthesis have been used to test the big-bang model to within a fraction of a second of the bang. The agreement between the predicted and observed abundances of deuterium, helium-3, helium-4, and lithium-7 confirms the standard cosmology model and allows accurate determination of the baryon density, between 1.7 x 10(-31) and 4.1 x 10(-31) grams per cubic centimeter (corresponding to about 1 to 15 percent of the critical density). This measurement of the density of ordinary matter is pivotal to the establishment of two dark-matter problems: (i) most of the baryons are dark, and (ii) if the total mass density is greater than about 15 percent of the critical density, as many determinations indicate, the bulk of the dark matter must be "non-baryonic," composed of elementary particles left from the earliest moments.


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