Simon White (Max Planck Institute for Astrophysics)
© Georgine Treybal
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.
Dr. Hannelore Hämmerle
Max Planck Institute for Astrophysics, Garching
Tel. +49 89 30000-3980
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