- Press Release
- Mar 22, 2023
South Pole experiment supports inflation theory of universe’s origin, measures density of ordinary and dark matter in universe
The leading theory regarding the origin of the universe has just passed
another major test, one posed by University of Chicago astronomers and
their colleagues working at a National Science Foundation observatory at
the South Pole.
The theory, called cosmic inflation, proposes that the universe underwent
a gigantic growth spurt in a fraction of a second just moments after the
big bang. According to inflation, the largest structures in the universe
trace their origins to the fundamental fuzziness of the subatomic world.
Inflation created tiny lumps in the distribution of matter and tiny
variations in the temperature of the cosmic microwave background, the
afterglow of the big bang, sowing the seeds that stretched the fuzziness
of the subatomic world to cosmic scales.
“With these new data, inflation looks very strong,” said John Carlstrom,
the S. Chandrasekhar Distinguished Service Professor in Astronomy &
Astrophysics at the University of Chicago. “It’s always been theoretically
compelling. Now it’s on very solid experimental ground.”
Carlstrom leads a team of astrophysicists working with the $3 million
Degree Angular Scale Interferometer (DASI) at the NSF’s Center for
Astrophysical Research in Antarctica. The team, which consists of the
University of Chicago’s Nils Halverson, Clem Pryke, Erik Leitch, and
John Kovac, and colleagues at the California Institute of Technology,
University of California, Berkeley, and Caltech’s Jet Propulsion
Laboratory, will present its first results from DASI Sunday, April 29,
at the American Physical Society meeting in Washington, D.C.
“The thing I find exciting about this field is that you have theoretical
models of the entire universe becoming testable,” said Pryke, a Chicago
Research Scientist. “You can do an experiment and match up the results
against these models.” Twenty years ago, by contrast, experimental
technology limited cosmological theories like inflation strictly to the
When introduced in the early 1980s, inflation predicted that astronomers
should see a pattern of temperature differences in the cosmic microwave
background radiation, which pervades the sky. DASI, a highly sensitive
interferometer, can measure these subtle temperature variations at an
angular resolution of one-tenth of a degree across the sky, about a
fifth of the moon’s angular size.
DASI detects these temperature differences at a time when the universe,
now approximately 14 billion years old, was only 400,000 years old.
These temperature differences show up in DASI’s data as a ripple pattern
that displays as many as three progressively fainter peaks in the blast
waves emanating from the big bang.
The inflation model predicts this series of peaks. Two previous
experiments have already detected the large first peak, which indicates
that the geometry of the universe is flat. This means that light travels
in straight lines rather than on curved trajectories.
“DASI sees the first two peaks and strongly suggests a third peak,”
Carlstrom said. “If no peaks had shown up, inflation would have
difficulties. We’d be back to the drawing board.”
The ratio of the intensity between the first and second peaks tells
scientists how much ordinary matter exists in the universe. The DASI
data indicate that ordinary matter, the stuff of which humans, stars and
galaxies are made, accounts for only 4.5 percent of the universe’s total
mass and energy. Astrophysicists know that eight times as much dark
matter exists in the universe. “The DASI result strengthens the case
that most of the mysterious dark matter is comprised of some new form of
matter,” said Michael Turner, the Bruce and Diana Rauner Distinguished
Service Professor at the University of Chicago. “We may be made of star
stuff, but we are not made of the stuff of the cosmos.”
The 4.5 percent figure agrees with the estimate of ordinary matter that
Turner and David Schramm published in 1998 using a completely different
method based on the amount of deuterium produced in the big bang.
The University of Chicago’s Schramm, who died in 1997, was among the
first to realize that deuterium was a sensitive indicator of the density
of ordinary matter in the universe, Turner said. “The agreement between
measures of the amount of ordinary matter is simply stunning,” Turner
said. “The underlying physics is completely different. The big bang
framework and Einstein’s general relativity have passed a major new
Even though astrophysicists have nearly nailed down the validity of
inflation, more work remains.
“This is just the beginning,” Turner said. Further data will come from
DASI and its sister instrument, the California Institute of Technology’s
Cosmic Background Imager, as well as the University of Chicago’s TopHat
experiment and NASA’s Microwave Anisotropy Probe.
“Not only will we be able to test inflation, but we will be able to learn
about its underlying physical cause,” he said.
Peter West, (703) 292-8070, [email protected]
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