Primordial ripples confirm Big Bang

FOR the first time ever humans have grabbed a peep-hole into the birth of the universe about 15 billion years ago. Since the Big Bang theory was first mooted in 1964, scientists have found it difficult to explain how the universe acquired its lumpy character, that is, its stars, planets and galaxies. As one scientist puts it: "the Big Bang would have spread matter like thin gruel evenly throughout the universe. The problem was to work out how the lumps (stars and galaxies) got into the porridge."

The recent recordings (a total of 300 million observations) made in space by the Cosmic Background Explorer (COBE) satellite which has been orbiting 800 km above the earth since 1989, show, in the words of George Smoot of the Lawrence Berkeley Laboratory who heads the COBE team, "wispy clouds of matter.... stretching as long as 59 billion trillion miles and dating to almost 15 billion years ago," when the universe was just 300,000 years old.

Over the last two years COBE has been scanning the sky, piling up data on the intensity of the background radiation from different directions. The aim is to see just how uniform sky brightness is. It has now detected almost imperceptible variations in the temperature of the radiation, which are as small as six parts in a million.

In 1964, scientists had detected microwave radiation coming uniformly from all parts of the sky, which they believe is the faint after-glow left over from the Big Bang itself. Since then, powerful optical telescopes have helped probe the history of the universe through beams from quasars and galaxies so far away that "their light set out when the universe was less than a tenth of its present age", according to Martin Rees, professor of astronomy and director of the Institute of Astronomy at Cambridge University.

But the Big Bang theory raises several questions. How could everything become so evenly mixed in the instant following the Big Bang? And how could this evenly distributed matter then clump together?

The COBE map shows the universe as a vast ellipse. The temperature gradients exhibited by the incoming radiation define the way our universe finally took shape. The temperature gradients which COBE has mapped reveal "tiny ripples in the fabric of space-time, put there by the primeval explosion process. Over billions of years, the smaller of these ripples have grown into galaxies and the great voids of space," says George Smoot.

The COBE observations, even while they lend additional evidence to support the Big Bang theory, have raised a further question for astrophysicists. Where does the gravitational force that has pulled all the matter together to make galaxies and planets come from? Scientists who have tried to calculate the - weight of our galaxy 2 have found that the total mass of all the stars does not account for even a tenth of the gravitational foice needed to hold all the stars and gas in place. Some scientists have argued that probably up to 90 per cent of the universe is made up of invisible and unfathomable matter,', termed aptly, Dark Matter.

Edward Wright, a COBE scientist from the University of California, says this "must be a new kind of matter, not yet detected. We ne'ed such invisible matter to explain how galaxies formed in the early universe and gathered themselves together into huge clusters. There is 10 times more matter in the universe than we see in the stars.

Some particle physicists think that the Dark Matter could be in the form of large objects such as dead stars and black holes. Others have proposed a list of exotic particles left over from the Big Bang. The Dark Matter theory predicts fluctuations in the background radiation of exactly the size COBE has observed. Because these had not been seen earlier, theoreticians were beginning to get worried that they had got it wrong. "If COBE had found no ripples," says Michael Rowan-Robinson, a leading British cosmologist, "the theoreticians would have been in disarray, their best shot at understanding how galaxies were formed would have been disproved."