Cosmic queries answered —in a split second

Press, 23 September 1983, Page 18

Cosmic queries answered —in a split second

The Universe was bom with a Big Bang fifteen thousand million years ago, but the key to the way it is now structured probably lies in events that occurred in a minute fraction of that time. They lasted — scientists believe — less than a trillionth of a second, and they came at a moment when the universe was only a trillionth of a trillionth of a second old. Yet a theory now emerging about these events represents the most important development in cosmology for years.

“It is very exciting because it enables us to ask serious scientific questions about things we could only speculate about before,” says Professor Martin Rees, director of the Institute of Astronomy at Cambridge. Ever since that first cataclysmic explosion the universe has been expanding. But, says the new theory, in that crucial sliver of time it expanded at an ultra-rapid rate that has never been equalled before or since. Hence it is known as the “inflationary scenario.” When the high-speed burst ended, our universe, now some 30,000 million light years across, was still only the size of a cricket ball, but the scenario can explain many of its features that were previously inexplicable. The “scenario” has emerged from a marriage between scientists who study things on the largest possible scale — the cosmologists — and those who study the smallest — the particle physicists interested in the sub-atomic particles that are the basis of matter.

The cosmologists became increasingly interested in the crucial few minutes immediately after the Big Bang, when the universe was filled with energetic particles, so they turned to the particle physicists. The latter, for their part, began to see the Big Bang as a spectacular particle accelerator which was infinitely more powerful than any they could ever hope to build on earth, and turned to the cosmologists. Both parties have brought dowries to the marriage. The cosmologists’ contribution is the highly developed Big Bang theory of the origin of the universe (see the Three Echoes in the panel). The particle physicists’ contribution is a series of Grand Unification Theories (G.U.T.S) which attempt to explain in a single theoretical framework three of the Four Forces that exist in nature (again see panel). When put together, the Big Bang theory and G.U.T.S successfully explained some of the fundamental features of the universe which cosmologists previously had to take as god-given. They include the relative amounts of matter and energy in the universe, and why it contains no anti-matter in bulk. (Anti-matter is a kind of mirror

image of ordinary matter and there previously seemed no reason why nature should prefer one to the other.) A number of the puzzles — including five cosmic conundrums — remained. It was in the hope of explaining these that Alan Guth, now of the Massachusetts Institute of Technology, proposed the “inflationary scenario.” It has already undergone transformation at the hands of others, but Guth’s name remains the one most firmly associated with it. And it now provides answers to all five puzzles.

® Conundrum 1: Why is the universe so homogeneous on the largest scale — in such things as matter and temperature for instance? In the standard Big Bang model, the different parts are unable to “communicate” with one another, so there is no mechanism to achieve uniformity. During an “inflationary” phase there is.

® Conundrum 2: Why is the universe so delicately poised between a state in which it will continue to expand for ever, and one in which it will eventually begin to contract again because of the gravitational attraction of its parts for one another? The standard Big Bang has to assume this happened by chance, though it is incredibly unlikely. It is, however, a natural consequence of “inflation.”

• Conundrum 3: Where are the monopoles? These are extremely heavy particles whose production in vast numbers is predicted by the Big Bang theory and G.U.T.S. But they apparently do not exist. If they did — in the vast numbers predicted — the universe would

have started to contract under its own gravity long ago. “Inflation” avoids this problem because what is now our universe started as such an insignificant part of the whole that there were no monopoles in it. © Conundrum 4: Where are the “domain walls” and “vacuum strings”? These structures, which sound like the invention of a science fiction writer, are also predicted by the Big Bang and G.U.T.s. Vacuum strings are no thicker than an atomic nucleus, yet they are billions of light years long and weigh as much as millions of galaxies. Domain walls are walls of energy dividing the universe into zones. An encounter with one would lead to total destruction. Again, domain walls do not exist; vacuum strings might, but have not been detected. However, the absence of both can be explained by “inflation” along the same lines as the absence of monopoles. ® Conundrum 5: Why did matter clump into structures the size of galaxies? The standard theory simply assumes that conditions after the Big Bang were right for galaxy formation. “Inflation” makes it possible to calculate such conditions.

One alarming implication of the new ideas is that the universe may not yet have exhausted its capacity for the kind of change which produced “inflation.” If another did occur, anything could happen. Recently, Professor Rees and his colleagues did some calculations to see whether such a change could be triggered by particles produced in the latest ultra-powerful particle accelerators. Their conclusion, fortunately, was that it could not.

BRIAN SILCOCK,

“Sunday Times,” London