What is dark energy? Physicist Tessa Baker at the University of Portsmouth, UK, is at the forefront of the search for elusive dark matter, using some of cosmology’s most powerful tools, including the Laser Interferometer Gravitational-Wave Observatory (LIGO). By studying ripples in space-time sent out by the most extreme events in the cosmos, such as black hole mergers, experimentalists like Baker are beginning to test radical ideas: that dark energy might stem from hidden dimensions, elusive fi