By the end of the Particle Age, the universe was filled with a thin, spread-out gas. While it looked mostly the same everywhere, there were tiny patches that were slightly denser or more crowded than others. In these “crowded” spots, the gas began to clump together—pulled in by the gravity of dark matter. As these clouds of gas collapsed under their own weight, they eventually ignited to form the very first stars and galaxies. You can see this transformation in the simulation below.

The Millennium Simulation, pioneered in 2005 by Volker Springel and the Virgo Consortium, serves as a landmark computational model for visualizing the gravitational evolution of the universe. By tracking cold dark matter from a redshift of 20—when the cosmos was only 180 million years old—to the present day, the simulation reveals the emergence of a “cosmic web” across vast spatial scales. This timelapse created from the simulation shown above demonstrates how gravity relentlessly pulls matter into a complex network of sweeping filaments and ultra-dense nodes, providing a scaffolding to the visible distribution of galaxies.

Empirical observations from the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey confirm that the universe is organized into a non-random, sponge-like architecture rather than a chaotic scattering of matter. In this grand design, galaxies and clusters align along interconnected strings and two-dimensional sheets that wrap around enormous cosmic voids. These massive features, such as the Sloan Great Wall, can span hundreds of millions of ly, creating a structural resemblance to neural pathways or the interconnected lights of a global city seen from space.

This colossal scaffold is essentially a magnified fossil of the infant universe, where visible galaxies formed as gas condensed within the gravitational wells of dark matter halos. Modern cosmological models indicate that these macroscopic structures originated from microscopic quantum fluctuations present in the early moments of the Big Bang. During the epoch of inflation, these tiny density variations were stretched to astronomical proportions, setting the blueprint for the interconnected web of matter that defines our observable universe today.