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Nature 415, 27-29 (3 January 2002) | doi:10.1038/415027a

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Cosmology: A baryometer is back

Corinne Charbonnel

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The usefulness of helium-3 as a probe of the early Universe has been in doubt. A rethink of stellar theory and new observational data put those doubts to rest.

Do we live in an open Universe that will expand forever, or in a closed Universe whose expansion will eventually reverse? Part of the answer can be found by accurately estimating the amount of ordinary — baryonic — matter in the Universe.