FOR the first time, detectors on Earth have put a meaningful limit on the strength of gravitational waves – the ripples in space-time – created during the first instants of the universe's existence.
According to Einstein's general relativity, gravitational waves should have been emitted during inflation, when the universe expanded exponentially moments after the big bang. "[Gravitational waves] can tell us how the laws of physics operated at that time," says Vuk Mandic of the University of Minnesota, Minneapolis. "This is very valuable because we cannot reproduce these high-energy conditions in the lab."
The latest measurement, made jointly by the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and VIRGO, its European counterpart, was sensitive to gravitational waves at frequencies around 100 hertz. But they found nothing. The null result, however, puts an upper limit on the energy density of gravitational waves in the infant universe, ...
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