Gravitational waves were predicted by Albert Einstein in 1916 as a consequence of the field equations of his general theory of relativity. These ripples in space–time cause space to stretch in one direction perpendicular to the line of travel while simultaneously compressing it in the other. In this video from our 100 Second Science series, Nergis Mavalvala of the Massachusetts Institute of Technology describes how interferometry is used to search for the effect of gravitational waves here on Earth.

Almost a century after gravitational waves were predicted, the hunt to detect them directly is hotting up. In a feature article in the September issue of Physics World, science writer David Appell explains how a major upgrade to the Laser Interferometry Gravitational-wave Observatory (LIGO) may soon bring this hunt to a successful close.

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