The new wave of gravitational waves

Ripples in spacetime caused the collision of black holes were first detected in 2015. Now astrophysicists are looking for the waves created by the big bang itself

A bout 10 billion-trillion-trillionths of a second into the start of creation in the big bang, the universe is believed to have had a brief but absurdly fast growth spurt. This episode, called inflation, was so cataclysmic that the very fabric of space and time was set juddering with gravitational waves (GWs). By comparison, the GWs that were first detected six years ago to much fanfare were small-scale affairs caused by black holes colliding. But now scientists at the European Space Agency (Esa) are setting their sights on grander targets – and are hoping they might soon be able to detect the faint echoes of the universe’s inflationary birth throes, almost 14bn years after the event, using the largest instrument ever built. Hundreds of times bigger than the Earth, Esa’s planned gravitational wave detector will float in space and look for wobbles in spacetime caused by all manner of immense astrophysical convulsions.

The first GW was identified in 2015 by the Laser Interferometer Gravitational-Wave Observatory (Ligo), an international project whose success won the 2017 Nobel prize in physics for three of its key proponents. Ligo consists of two massive detectors in the American states of Washington and Louisiana. Each deploys two tunnels 2.5 miles (4km) long, intersecting at a right angle, along which a laser beam travels to a mirror at the far end and bounces back. The returning light waves interfere with one another where the arms cross. As a GW passes, it very slightly contracts or stretches spacetime. Because that effect will be different in each arm, it changes the synchrony of the light waves, and so alters the interference of the two beams.

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