Dark energy -- 10 years on
Date: Saturday, December 01, 2007 @ 20:09:47 MST
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
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.
Source: Institute of Physics