Why We Need to Study Nothing

Beginning in the 1970s cosmologists started to uncover the structure of the universe writ large. They already knew that galaxies occasionally clump together into clusters, but over even larger distances, spanning 100 million light-years and more, they found superclusters. And in between those superclusters they saw something even more unexpected: vast regions devoid of galaxies, great and immense dark hollows. The first of these cosmic voids that cosmologists discovered was 65 million light-years across. No theoretical work had predicted their existence, and for years cosmologists thought they were creating patterns with their imaginations.

We now realize that the largest structures in the universe are not superclusters or any other agglomeration of matter. They are the voids: the negative spaces, the intergalactic Saharas.

I was introduced to voids by my mentor Ben Wandelt while I was in grad school. He was fascinated by them; they appeared too empty to be explained by standard cosmology. My graduate advisor, Paul Ricker, and I worked with Wandelt on this problem for a while. But like most cosmologists, even though I knew about the voids, I didn’t think much of them. I favored galaxies and clusters. Voids were nothing, after all.

You could stretch 25 Milky Ways side-by-side in the gap between us and the nearest galaxy.

But after I got my Ph.D. I moved to Paris to join Wandelt for a postdoc position. Voids