The 2017 Nobel Prize in Physics was awarded for the first-ever detection of gravitational waves, confirming a 100-year-old prediction of Einstein’s. The discovery, announced in 2015, launched a new era of gravitational wave astronomy, but also raises challenging philosophical questions about the nature of space, time and gravity. What are gravitational waves and how are they being used to study the universe? And is there an inherent conflict between General Relativity and key metaphysical principles?