In the dark
By Alexandra Witze s Illustration by Nicolle Rager Fuller
In ancient times, listing the ingre- dients of the universe was simple: earth, air, fire and water. Today,
scientists know that naming all of that,
plus everything else familiar in everyday life, leaves out 95 percent of the
cosmos’s contents.
From the atoms that make up an
astronomer, to the glass and steel of a
telescope, to the hot plasma of the stars
above — all ordinary stuff accounts for
less than 5 percent of the mass and
energy in the universe. “All the visible
world that we see around us is just the tip
of the iceberg,” says Joshua Frieman, an
astrophysicist at the University of Chi-
cago and the Fermi National Accelerator
Laboratory in Batavia, Ill.
A different matter
Dark matter made its debut in 1933,
when Swiss astronomer Fritz Zwicky
measured the velocities of galaxies in a
group known as the Coma cluster and
found them moving at different rates
than expected. Some unseen and large
