Between the filaments and sheets of supergalaxies lie enormous gulfs of space known as voids. Ranging in size between 40 million and 500 million light years, they are defined by a lack of clusters or superclusters, but are still home to a few scattered ‘field galaxies’. Along with superclusters, they were identified for the first time in the Harvard-Smithsonian Center for Astrophysics (CfA) Galaxy Redshift Survey, which attempted to map out the large-scale universe for the first time from 1977–82. Today, voids are thought to have arisen as a result of pressure waves called baryon acoustic oscillations (BAOs) that rippled through the fireball of the early universe and helped concentrate both dark and baryonic (luminous) matter in certain regions, while leaving others empty. The closest void to Earth – known as the Local Void – is around 200 million light years across, with the Local Sheet (including the Virgo Cluster and our own small Local Group of galaxies) defining one of its edges.