The
ugly truth about the universe
Recent astronomical findings
are bad news for Einstein and his dream of a simple, beautiful
explanation for the universe, says Graham Farmelo
Could it be that the universe is fundamentally
ugly? For 90 years, most astronomers believed that the simplest,
most beautiful version of Einstein's theory of gravity describes
how the universe evolves.
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The universe as a
baby: the detailed sky-map prepared by the Wilkinson Microwave
Anisotropy Probe (MAP) shows that 73 per cent of the universe
is mysterious 'dark energy'
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Four years ago, however, a group
of astronomers astonished the world by showing that, according
to new data, nature does not adopt the most beautiful version
of the theory but prefers an ugly variant and last week NASA announced
stunning new observations that lent strong support to the notion
that the universe is not beautiful in the way Einstein supposed.
Soon, other astronomers will contribute new evidence on the way
the universe is built. Will beauty prevail?
It was Einstein himself who first pointed out that
it was logically possible to make an unsightly addition to his
gorgeous 1915 theory of gravity. He even used this flexibility
to tinker with his theory by introducing something he called the
cosmological constant. Always uneasy about the presence of this
constant in his theory, he hoped that its value would be zero.
Einstein wrote in 1947 to the Belgian cleric and Big Bang pioneer
Georges-Henri Lemaître: "I am unable to believe that such
an ugly thing should be realised in nature."
For once, it appears that Einstein's intuition
was wrong. The unwanted constant really does seem to be needed
if Einstein's theory is to describe nature. The first experimental
demonstration that the cosmological constant is not zero was announced
four years ago by a team of astronomers led by Brian Schmidt and
his former research supervisor the ebullient Robert Kirshner,
of the Harvard-Smithsonian Centre for Astrophysics. In 1998, Science
magazine in the US cited this discovery as the "Science breakthrough
of the Year".
The data, however, had large uncertainties and
many fellow astronomers were sceptical. "At first, I thought this
must be wrong," Kirshner admits. "After all, Einstein thought
the cosmological constant was his greatest blunder, and he was
pretty smart. But now, five years later, I'd bet my bull terrier!"
Confidence in the results was boosted when a similar
result was reported by another team led by Saul Perlmutter of
the Lawrence Berkeley Laboratory in California. Both groups were
studying supernovae, exploding stars that disgorge their matter
into outer space, simultaneously giving off light that astronomers
measure when it arrives on Earth after travelling for several
billion years. These supernovae are the torrid cauldrons that
cook up the universe's supply of heavy chemical elements. For
example, the iron in your blood and in soil was originally manufactured
billions of years ago in those stellar convulsions.
Kirshner and his colleagues were hunting for supernovae
whose emitted light has taken more than seven billion years to
reach the Earth - that's a long way away even for astronomers.
The supernovae that the experimenters were studying each have
a very similar brightness, so the astronomers were puzzled when
they found that the distant supernovae were rather dimmer than
they expected.
They eventually came to the remarkable conclusion
that the disparity in the brightnesses was an artefact of the
way the universe is evolving. It turned out that this could most
simply be explained if the universe is expanding at a gradually
increasing rate. We appear to be living in a universe that's accelerating
towards oblivion.
One explanation is that the acceleration is due
to mysterious force fields known as "quintessence". Another, less
adventurous but more popular, theory is that the apparent cosmic
acceleration is due to the cosmological constant not being zero
after all. If Einstein had been buried, he would have been turning
in his grave.
His rotations would have resumed last week when
spectacular evidence for the accelerating universe theory and
the non-zero cosmological constant was announced in the US. This
evidence did not come from astronomers studying supernovae but
from a satellite, located on the other side of the Moon. This
satellite, MAP, has been taking data that examine the microwave
radiation that pervades the universe like light from the dying
embers of the fireball of its distant past.
By studying the temperature of this background
radiation, the group found that the universe is, in the jargon
of Einstein's theory, "flat". This means that parallel lines will
never meet, even over cosmically large distances. This flatness
makes it relatively easy to account for the different types of
matter in the universe.
By comparing this satellite data with other astronomical
observations, it is now possible to pin down the relative amounts
of the different types of matter in the universe. It turns out
that about 23 per cent of the universe is made of mysterious particles
of "dark matter", stuff that doesn't shine or reflect light, but
whose existence is evident from the forces it exerts on distant
galaxies (a bit like the waving of a distant flag tells us that
it's in a wind).
Only about four per cent of the universe is made
of the common-or-garden atoms that make up you, me and all the
matter on our planet. So a whopping 73 per cent of the universe
should be made of a mysterious material (unhelpfully dubbed "dark
energy") that somehow provides a negative pressure that drives
the expansion of the universe.
Astronomer David Spergel of Princeton University
says: "Remarkably, all the evidence from different cosmological
sources now fits together, giving a simple description of the
universe from its origins in the Big Bang 13.7 billion years ago."
But could this widely accepted picture be built on sand and the
cosmological constant be zero after all, as Einstein hoped? Several
experiments are now under way to check this, once and for all.
The satellite has another three years' worth of
data to collect and it will be fascinating to see what new insights
are in store. In the field of supernova research, Robert Kirshner's
former research student Adam Reiss is leading a team that is using
a new camera on the Hubble Space Telescope to take repeated images
of a typical spot in the sky every 40 days. By subtracting one
picture from another, the hope is to find more distant supernovae
than can be detected from telescopes on the ground. If the current
picture for cosmic acceleration is correct, these supernovae should
be so distant that they will show the effects of cosmic slowing
down, before the dark energy gained the upper hand.
Kirshner says: "It's like a tug-of-war. First we
expect the weight of dark matter to slow the universe, but as
the universe expands, the dark energy gets the upper hand, so
we expect acceleration to take over at later times. If we see
that change, from slowing down to acceleration, it will clinch
the case.''
If later observations don't wreck the current consensus,
the aesthetes will have to come to terms with their disappointment.
This is a classic case of what the biologist T H Huxley described
130 years ago as "the great tragedy of science - the slaying of
a beautiful hypothesis by an ugly fact".
Einstein's simplest version of his theory of gravity
would be dead, but at least Kirshner's dog would be spared. Could
it be that the version of Einstein's theory with a cosmological
constant is but part of a yet-to-be-conceived more encompassing,
even more beautiful theory of the universe? My bet is that
Einstein will have the last laugh and that beauty
will prevail.
Graham Farmelo edited the collection
of essays It Must be Beautiful: Great Equations of Modern Science
(Granta), which is available for £9.99 plus £1.99
p&p. To order please call Telegraph Books Direct on 0870 155
7222.
21 feb
2003


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