Artwork entitled Bubble Universe", illustrating the foam or sponge-like structure of the universe. Galaxies are rarely found singly, but tend to clump together in groups called clusters, while clusters themselves also clump together forming massive superclusters. Recent surveys of the distribution in space of these superclusters have found that they tend to be organised in enormous sheets and filaments separated by large empty voids. In this image the galaxy superclusters form the surfaces of giant bubbles surrounding the empty voids."