Evidence for gravitational waves was picked up by the LIGO (Laser Interferometer Gravitational-Wave Observatory) in 2015, a hundred years after Einstein predicted their existence. As the book says 'a good case can be made that the discovery of gravitational waves is the most important development in astronomy since the invention of the telescope in 1608'. Why? And why does it matter for the understanding of physics and the universe? Well, Marcus Chown's new book will lead you gently through the background to this discovery and with a small amount of effort on your part you should grasp its relevance.