Accelerating Universe
Year of Discovery: 1998
What Is It? Our universe is not only expanding; the rate at which it expands is
speeding up, not slowing down as had been assumed.
Who Discovered It? Saul Perlmutter
Why Is This One of the 100 Greatest?
A great debate began after Edwin Hubble discovered that the universe is expanding: Is
that expansion slowing so that it will eventually stop and the universe will begin to collapse? Saul Perlmutter discovered that the expansion of the universe is actually accelerating, shattering all existing scientific models of the motion of the universe. The universe is
expanding faster now than it ever has before. It is tearing itself apart. Gravity is not slowing
the expansion as it is supposed to.
This discovery has created a monumental shift in how scientists view the universe, its
past, and its future. It has affected the calculations of the Big Bang and even scientists’ view
of what makes up the universe. The Journal of Science called this discovery the 1998
“Breakthrough of the Year.”
How Was It Discovered?
Edwin Hubble discovered that the universe was expanding in 1926. Scientists built
new models that assumed that the expansion was slowing down as gravity tugged on stars
and galaxies, pulling them back toward each other.
This model seemed logical. However, a few, highly technical problems existed with
the mathematics associated with this model. Einstein tried to explain these problems by creating something he called the “cosmological constant”—a force that opposed gravity. But
he then rejected the idea as his greatest scientific blunder.
After receiving a Ph.D. in physics in 1986, Saul Perlmutter worked at Lawrence
Berkeley National Laboratory and headed the Supernova Cosmology Project (SCP). This
group used the Hubble Space Telescope to find and study distant supernovae (exploding
stars). They chose supernovae because they are the brightest objects in the universe. Type Ia
supernovae produce a constant amount of light, and it is believed that all Ia supernovae
shine at about the same brightness. This made them ideal for Perlmutter’s study.
Over the 10-year period from 1987 to 1997, Perlmutter developed a technique to identify supernovae in distant galaxies and to analyze the light they produce. His team searched
tens of thousands of galaxies to find a half dozen type Ia supernovae.
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