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Science breakthrough of the year: proof of our exploding universe 
http://www.guardian.co.uk/spacedocumentary/story/0,2763,1110244,00.html

Tim Radford, science editor
Friday December 19, 2003
The Guardian 

Welcome to the dark side. Around 73% of the universe is made
not of matter or radiation but of a mysterious force called dark
energy, a kind of gravity in reverse. Dark energy is listed as the
breakthrough of the year in the US journal Science today. 

The discovery - in fact a systematic confirmation of a puzzling
observation first made five years ago - paints an even more
puzzling picture of an already mysterious universe. Around
200bn galaxies, each containing 200bn stars, are detectable by
telescopes. But these add up to only 4% of the whole cosmos. 

Now, on the evidence of a recent space-based probe and a
meticulous survey of a million galaxies, astronomers have filled
in at least some of the picture. 

Around 23% of the universe is made up of another substance,
called "dark matter". Nobody knows what this undetected stuff
could be, but it massively outweighs all the atoms in all the
stars in all the galaxies across the whole detectable range of
space. The remaining 73% is the new discovery: dark energy.
This bizarre force seems to be pushing the universe apart at an
accelerating rate, when gravitational pull should be making it
slow down or contract. 

"The implications for these discoveries about the universe are
truly stunning," said Don Kennedy, the editor of Science.
"Cosmologists have been trying for years to confirm the
hypothesis of a dark universe." 

Sir Martin Rees, Britain's astronomer royal, called it a "discovery
of the first magnitude". 

The findings were made by an orbiting observatory called the
Wilkinson Microwave Anisotropy Probe (WMAP). This measured
tiny fluctuations in the cosmic microwave background, in effect
the dying echoes of the Big Bang that launched time, space and
matter in a tiny universal fireball. 

These painstaking measurements were then backed up by the
telescopes of the Sloan Digital Sky Survey, which mapped a
million galaxies to see how they clumped together or spread
out. Both confirmed that dark energy must exist. 

The findings settle a number of arguments about the universe,
its age, its expansion rate, and its composition, all at once.
Thanks to the two studies, astronomers now believe the age of
the universe is 13.7bn years, plus or minus a few hundred
thousand. And its rate of expansion is a bewildering 71km per
second per megaparsec. One megaparsec is an astronomical
measure, totting up to 3.26m light years. Something latent in
space itself is acting as a form of antigravity, exerting a push on
the universe, rather than a pull. 

Dark matter was proposed more than 20 years ago when it
became clear that all the galaxies behaved as if they were far
more massive than they seemed to be. All sorts of explanations
- black holes, brown dwarfs and undetectable particles that are
very different from atoms - have been suggested. None has been
confirmed. 

But dark matter exists, all the same. The dark energy story
began in 1998 when astronomers reported that the most distant
galaxies seemed to be receding far faster than calculations
predicted. A study of a certain kind of supernova confirmed that
they had not been misled: the universe was indeed expanding
ever faster, rather than decelerating. 

The discovery that some unexpected and undetectable force
was pushing the fabric of space apart seemed to confirm a
famous observation decades ago by the British scientist JBS
Haldane: "The universe is not only queerer than we suppose. It
is queerer than we can suppose." It once again raised profound
questions about the nature of the universe: about space, and
time, and energy, and matter. And it set the theorists on the
hunt first for an explanation, and then for an experiment that
would confirm their hypothesis. 

So they turned once again to the original evidence for the Big
Bang, the cosmic microwave background radiation. This is the
original blaze of creation, cooled to minus 270 C - just about 3 C
above absolute zero. Several lines of research, including
experiments in the Antarctic and from high-flying balloons,
began to provide a clearer picture: the universe simply had to
consist of something more than just atoms and so-called dark
matter. 

"But WMAP, with superbly precise data beamed back from a
little spacecraft a million miles away, has made the evidence
more precise," said Sir Martin, of the Institute of Astronomy at
Cambridge. 

"The dark energy is spread uniformly through the universe, latent
in empty space. Its nature is a mystery. Whereas there's a real
chance of learning what the dark matter is within the next five to
10 years, I'd hold out less hope of understanding the dark
energy unless or until there's a unified theory that takes us
closer to the 'bedrock' of space and time." 

http://www.guardian.co.uk/spacedocumentary/story/0,2763,1110244,00.html