Diana Al - Hadid, Edge of Critical Density, 2009. (art21.org)
Independently, while puzzling out other astronomical mysteries, they arrived at the same tantalizing predication that the universe was exactly balanced at critical density, the knife's edge. (discovermagazine.com)
In the simplest cosmological model, critical density just means that the inward pull of gravity is exactly strong enough to halt the outward expansion of the universe.) (discovermagazine.com)