Cosmic voids, the largest component by volume of the cosmic web, are almost completely empty regions of space, containing very few galaxies and very low densities of dark matter.
By studying them and by studying the few galaxies which inhabit them we can learn about the nature of structure formation, and design experiments to test dark energy. We identified over two hundred of these voids in the VIPERS survey which are presented in a paper now available online http://arxiv.org/abs/1407.2969
