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.

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'

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