A team of UK and Australian astronomers has discovered new, independent
evidence that the expansion of the universe is accelerating. Their findings
have just appeared in the Monthly Notices of the Royal Astronomical Society.

Three years ago, two teams of astronomers rocked the scientific world by
finding evidence that the expansion of the universe is accelerating rather
than slowing down as had generally been expected because of the
gravitational attraction between the matter within it. According to these
groups, the brightnesses of supernovae (massive exploding stars) they
observed in remote galaxies require a universe filled with a strange kind of
dark energy that causes it to accelerate increasingly faster into the
infinite future.

The concept of dark energy was first postulated by Einstein (who called it
‘the cosmological constant’). But Einstein later referred to this idea as
his greater scientific blunder since it spoilt the simplicity and elegance
of his General Theory of Relativity. Since then, the cosmological constant
has had a controversial history. The great Cambridge astronomer Sir Arthur
Stanley Eddington was convinced of its existence, arguing that the
cosmological constant distinguished between the vast size of the observable
universe and the tiny scales of subatomic particles. But to most theoretical
physicists the cosmological constant has seemed utterly mysterious and7Now, a team of 27 astronomers led by Professor George Efstathiou of the
University of Cambridge has published strong evidence for the existence of
dark energy using an entirely different technique. They used the clustering
pattern of 250,000 galaxies in a large volume of the universe surveyed with
the Anglo-Australian Telescope at Siding Spring in New South Wales,
Australia. By comparing the structure in the universe now, some 15 billion
years after the Big Bang, with structure observed in the cosmic microwave
background radiation, which preserved information about what the universe
was like when it was only 300,000 years old, the Anglo-Australian team could
apply a simple geometrical test to elucidate the composition of the
universe.

Their results show that the universe is full of dark energy, completely
consistent with the earlier supernovae results. “It seems that Einstein did
not made a blunder after all — dark energy appears to exist and to dominate
over more conventional types of matter” says Professor Efstathiou. “An
explanation of the dark energy may involve String Theory, extra dimensions
or even what happened before the Big Bang. At present nobody knows. The ball
is now firmly in the theorists court.”

NOTES

1. The paper reported here is published in the Monthly Notices of the Royal
Astronomical Society, Volume 330, No. 2, 21 February 2002.

2. The galaxy data used in this analysis was from the 2dF (2-degree field)
Galaxy Redshift Survey (2dFGRS). More information about the 2dFGRS is
available at
http://www.mso.anu.edu.au/2dFGRS/