Mottled structure of the CMB, the
oldest light in the universe, is displayed in the high-latitude regions
of the map. The central band is the plane of our galaxy, the Milky Way.
(Courtesy of European Space Agency)
Eric Linder is a theoretical physicist with Berkeley Lab’s Physics
Division and member of the Supernova Cosmology Project. (Photo by Roy
Kaltschmidt)
Mystery fans know that the best way to solve a mystery is to revisit
the scene where it began and look for clues. To understand the mysteries
of our universe, scientists are trying to go back as far they can to
the Big Bang. A new analysis of cosmic microwave background (CMB)
radiation data by researchers with the Lawrence Berkeley National
Laboratory (Berkeley Lab) has taken the furthest look back through time
yet – 100 years to 300,000 years after the Big Bang – and provided
tantalizing new hints of clues as to what might have happened.
“We found that the standard picture of an early universe, in which
radiation domination was followed by matter domination, holds to the
level we can test it with the new data, but there are hints that
radiation didn’t give way to matter exactly as expected,” says Eric
Linder, a theoretical physicist with Berkeley Lab’s Physics Division and
member of the Supernova Cosmology Project. “There appears to be an
excess dash of radiation that is not due to CMB photons.”
Our knowledge of the Big Bang and the early formation of the universe
stems almost entirely from measurements of the CMB, primordial photons
set free when the universe cooled enough for particles of radiation and
particles of matter to separate. These measurements reveal the CMB’s
influence on the growth and development of the large-scale structure we
see in the universe today.
Linder, working with Alireza Hojjati and Johan Samsing, who were then
visiting scientists at Berkeley Lab, analyzed the latest satellite data
from the European Space Agency’s Planck mission and NASA’s Wilkinson
Microwave Anisotropy Probe (WMAP), which pushed CMB measurements to
higher resolution, lower noise, and more sky coverage than ever before.
“With the Planck and WMAP data we’re really pushing back the frontier
and looking further back in the history of the universe, to regions of
high energy physics we previously could not access,” Linder says. “While
our analysis shows the CMB photon relic afterglow of the Big Bang being
followed mainly by dark matter as expected, there was also a deviation
from the standard that hints at relativistic particles beyond CMB
light.”
Linder says the prime suspects behind these relativistic particles
are “wild” versions of neutrinos, the phantomlike subatomic particles
that are the second most populous residents (after photons) of today’s
universe. The term “wild” is used to distinguish these primordial
neutrinos from those expected within particle physics and being observed
today. Another suspect is dark energy, the anti-gravitational force
that accelerates our universe’s expansion. Again, however, this would be
from the dark energy we observe today.
“Early dark energy is a class of explanations for the origin of
cosmic acceleration that arises in some high energy physics models,”
Linder says. “While conventional dark energy, such as the cosmological
constant, are diluted to one part in a billion of total energy density
around the time of the CMB’s last scattering, early dark energy theories
can have 1-to-10 million times more energy density.”
Linder says early dark energy could have been the driver that seven
billion years later caused the present cosmic acceleration. Its actual
discovery would not only provide new insight into the origin of cosmic
acceleration, but perhaps also provide new evidence for string theory
and other concepts in high energy physics.
“New experiments for measuring CMB polarization that are already
underway, such as the POLARBEAR and SPTpol telescopes, will enable us to
further explore primeval physics, Linder says.
Linder, Hojjati and Samsing are the authors of a paper describing these results in the journal Physical Review Letters
titled “New Constraints on the Early Expansion History of the
Universe.” Hojjati is now with the Institute for the Early Universe in
South Korea, and Samsing is with the DARK Cosmology Centre in Denmark.
This research was primarily supported by the DOE Office of Science.
For more about the Supernova Cosmology Project go here
