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On 17 March, astronomer John Kovac of the Harvard-Smithsonian Center for Astrophysics presented long-awaited evidence of gravitational waves — ripples in the fabric of space — that originated from the Big Bang during a period of dramatic expansion known as inflation.

By the time the Sun set that day in Cambridge, Massachusetts, the first paper detailing some of the discovery’s consequences had already been posted online1, by cosmologist David Marsh of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, and his colleagues.

The authors wrote that the measurements made by Kovac's team using the BICEP2 telescope at the South Pole all but ruled out a class of models that attempted to explain both inflation and another cosmic mystery — the nature of dark matter — based on a hypothetical elementary particle called the axion. The researchers did not rule out all axion models, however, only that “this particular class of axions make up only a tiny fraction of the dark matter”, says Marsh.

Cosmologist Marc Kamionkowski of Johns Hopkins University in Baltimore, Maryland, agrees that some axion models no longer work, “because they require inflation to operate at a lower energy scale than the one indicated by BICEP2”.

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