In 1981, Davis led the Harvard-Smithsonian Center for Astrophysics (CfA) survey of 2400 galaxies at various distances, extraordinary census of how the heavens look on the largest scales. This hinted at what today is called “the cosmic web”, galaxies grouped into lengthy filaments, or superclusters, separated by vast voids. Two competing theories tried to explain how matter could have coalesced in such a manner; both theories including “dark matter”. In the “hot dark matter” theory, the particles would travel at velocities approaching the speed of light at early times, leaving the normal matter behind. In contrast to this, in the “cold dark matter” theory, the slowly moving particles would fall together to build galaxy halos, dragging the regular matter along for the ride.

To test these theories, the astronomers needed to model the evolution of the universe over billions of years. Adapting a numerical method from another field of physics, Efstathiou succeed in creating a code for cosmology and Davis, Frenk, and White then used that code to demonstrate that a simulated universe based on the hot dark matter theory did not remotely match the CfA observations. Then, in a series of five landmark papers from 1985 to 1988, Davis, Efstathiou, Frenk, and White showed that observations of galaxies, clusters, filaments, and voids were consistent with a simulated universe that had evolved under the influence of cold dark matter.

Cold dark matter (or CDM) is today one of the two key components of the standard cosmological model. The other is the acceleration of the expansion of the universe, a discovery observers made in the late 1990s that simulations of the four astronomers had anticipated. Today the match between observation and theory indicates that the universe is composed of 4.6 percent “ordinary” matter, 23.3 percent dark matter, and 72.1 percent dark energy, which is responsible for the accelerated expansion. Numerical simulations of the kind pioneered by Davis, Efstathiou, Frenk, and White show that a universe with this astonishingly precise yet remarkably strange composition does indeed develop structures which are a close match to those we see around us.

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