Surfing spacetime with LISA

A new era of gravitational wave astronomy is on its way as the ambitious upcoming LISA space mission joins a host of huge detectors on Earth. Charlie Hoy explains

- Charlie Hoy

In September 2015, some of the most sensitive instruments ever built made a remarkable discovery: the first-ever detection of tiny ripples in space and time, known as gravitational waves. Created by a pair of black holes spiralling towards each other and crashing together, the observed wave travelled through space at the speed of light until it was detected by two separate observatories here on Earth.

Now scientists are setting their sights on grander goals, hoping to observe the entire Universe, looking back in time to its very origin, with gravitational waves. In January 2024, the European Space Agency (ESA) gave the green light for an international team of scientists to begin building the largest gravitational wave detector ever built - only this time it will be in space. Its name is LISA, the Laser Interferometer Space Antenna, and it will revolutionise our understanding of the Universe.

Gravitational waves are ripples in space and time, similar to those formed on the surface of water when a pebble is dropped from a height. Gravitational waves, however, are caused by some of the most violent astrophysical events in the Universe, such as black holes smashing together. They were predicted by Albert Einstein in his general theory of relativity more than a century ago. According to theory, gravitational waves expand and contract spacetime itself. Everything, including you and me, will stretch and squeeze as a gravitational wave passes by. Thankfully, although gravitational waves are thought to be like tsunamis at the source, by the time they reach us here on Earth their effects are minuscule; so small, in fact, that gravitational waves produced by some of the most energetic events in the Universe are thought to only stretch and squeeze the entire Earth by a fraction of the width of an atom.