Light from distant quasars, the ultra-bright cores of galaxies, pushes through a ghostly forest of hydrogen clouds. Each atom leaves a dark line in the spectrum, like a personal autograph. By collecting hundreds of these signatures, astronomers reconstruct a map of invisible gas.

Still, it's unclear whether dark matter interacts with the almost intangible neutrinos. The growth of entire galaxies depended on this. To find out, scientists created forty-eight universes inside a computer, numerical simulations, and used neural networks to compare them with actual observations. Redshift, the stretching of light by the expanding Universe, let them peer billions of years into the past.

Dark matter remains remarkably lonely. This strengthens our picture of the cosmos, where galaxies evolve just as we observe them. Astonishingly, over the entire age of the Universe, a dark matter particle may never have collided with a neutrino, so indifferent are they to each other.