The light from early galaxies had a dramatic impact on the gasses filling the universe. This video highlights the spatial structure of the light's effect, by comparing two simulations: one with a self-consistent radiation field (radiative), and one without (non-radiative), each with a very high dynamic range. Looking at the simulations side-by-side it's hard to see any difference. However, because the simulations have the same initial conditions, we can directly compare them, by looking at the relative difference of the density. The coral-like blobs are regions where light has radiated out, heating the gas, and raising the pressure. The red regions show where the density is much higher in the radiative simulation, while the yellow regions are where the non-radiative has more density, showing where gravity was able to pull the filaments into tighter cylinders, without having to work against pressure from stellar heating. This is the first known visualization of this process, known as Jeans smoothing.