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Topic Name: UC researchers reveal how little we know about dark energy
Category: STAR (Space, Telecommunications & Radioscience)
Research persons: Saul Perlmutter, Eric Linder
Location: University of California, Berkeley, United States
Details
Three quarters of our universe is made up of some weird, gravitationally
repulsive substance that was only discovered ten years ago – dark energy. This
month in Physics World, Eric Linder and Saul Perlmutter, both at the University
of California at Berkeley, reveal how little we know about dark energy and
describe what advances in our knowledge of dark energy we can expect in the
coming decade from a series of planned space missions.
Perlmutter was the leader of one of the two separate teams of astrophysicists
who concluded, from watching distant supernovae, that the cosmic expansion was
accelerating and not slowing under the influence of gravity, as was previously
thought. The two teams' finding confirmed just how little we know about our
universe.
The two teams' discovery has led to the creation of the "concordance
model" of the universe, which states that 75 per cent of our universe is
made up of dark energy, 21 per cent of dark matter, another substance we know
little about, with only a remaining four per cent being made up of matter that
we do understand. The most conventional explanation is that dark energy is some
kind of "cosmological constant" that arises from empty space not being
empty, but having an energy as elementary particles pop in and out of existence.
Since the first evidence for the accelerating universe was made public in
early 1998, astrophysicists have provided further evidence to shore up the
findings and advances in the measurement methods bode well for increasing our
understanding in the future.
Galaxies and the cosmic background hold some significant clues. Equipment
that can make a more robust comparison between galaxy patterns across the sky
and investigate temperature fluctuations in the cosmic microwave background,
helping trace the pattern of galaxy formation, is being made available. Methods
for further observation of supernovae are expanding and improving too.
Eric Linder and Saul Perlmutter write, “The field of dark energy is very
young and we may have a long and exciting period of exploration ahead before it
matures.”
The December issue also includes reporting from Robert P Crease, historian at
the Brookhaven National Laboratory, US,
on the difficulty of deciding who should gain credit for the discovery of the
accelerating universe and comment from Lawrence M Krauss, director of the Center
for Education and Research in Cosmology and Astrophysics at Case Western Reserve
University, US, on the possibility that we may never be able to tell if dark
energy is a cosmological constant or something more exotic still.
Note for Dark energy
In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe.
Assuming the existence of dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for almost three-quarters of the total mass-energy of the universe.
Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space
homogeneously, and scalar fields such as quintessence or moduli, dynamic fields whose energy density can vary in time and space. In fact contributions from scalar fields which are constant in space are usually also included in the cosmological constant. The cosmological constant is thought to arise from the vacuum energy. Scalar fields which do change in space are hard to distinguish from a cosmological constant, because the change may be extremely slow.
High-precision measurements of the expansion of the universe are required to understand how the speed of the expansion changes over time. The rate of expansion is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.
Note for Galaxy formation
The formation of galaxies is still one of the most active research areas in astrophysics; and, to some extent, this is also true for galaxy evolution. Some ideas, however, have gained wide acceptance.
Galaxy formation is presently believed to proceed directly from structure formation theories, formed as a result of tiny quantum fluctuations in the wake of the Big Bang. N-body simulations have also been able to predict the types of structures, morphologies, and distribution of galaxies which we observe today both in our present universe, and - by examining distant galaxies - in the early universe.
About Researcher
Saul Perlmutter
Lawrence Berkeley Laboratory 50-232
University of California
Berkeley, CA 94720
Phone: (510) 486-5203
Fax: (510) 486-5401
Internet: saul@lbl.gov
Education:
Perlmutter graduated from Harvard magna cum laude in 1981 and received his PhD from the University of California, Berkeley in 1986. Perlmutter's PhD thesis was on searching for Nemesis candidates under Richard A. Muller.
Eric Linder
Co-Director, Institute for Nuclear and Particle Astrophysics, Lawrence Berkeley National Laboratory
INPA serves as a bridge between Divisions at Berkeley Lab, bringing together research groups in neutrino physics, astrophysics, particle physics, and cosmology. New initiatives include crossdisciplinary weekly discussions and the Computational Cosmology Center (C3) suite.
Director (LBL campus), Berkeley Center for Cosmological Physics
BCCP is a joint effort between UC Berkeley and LBL, directed by George Smoot, with research groups spanning the two institutions. Coordination of LBL activities includes joint seminars and design of a new Cosmology wing.
Full Research Physicist, University of California, Berkeley
For an overview of research activities, please see the descriptions below and the Science Resources link. Teaching activities include special "teach-ins" for scientists interested in cosmology, guest lectures, and education/outreach.
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