Published in Physics World, 15 Feb 2012
For more than a decade, scientists have been aware that the theory used to explain how the lightest elements are created overestimates the overall amount of lithium-7 in the universe. Now, physicists in the US think the answer to this so-called lithium problem might lie in a hypothetical particle known as the axion – although many are not convinced.
The theory is called Big Bang nucleosynthesis and describes a stage early in the universe’s evolution when, at temperatures of thousands of degrees, protons and neutrons began to assemble into atomic nuclei and form the first light elements: deuterium, along with isotopes of helium and lithium. As temperatures dropped, nucleosynthesis drew to a close, and eventually electrons began to add themselves to the nuclei during a period called recombination. At this time, photons stopped scattering off charged particles and the universe became transparent. […]
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