PERFECT SYMMETRY; The Search for the Beginning of Time. By Heinz R. Pagels. Simon and Schuster. 390 pp. $18.95.

IN THE BEGINNING, people described the physical world in whatever appropriate terms the human mind could imagine. The ancient Egyptians, for example, described the natural world mostly in terms of fanciful beasts possessing remarkable and unearthly powers. But then the ancient Greeks defined rationality and the Occidental world view became scientific. Greek mythologies, logical and to a degree verifiable, involved mostly gods who were scrutable and whose only powers were those that could be observed in the natural world, such as Zeus' power to create lightning and thunder.

In Perfect Symmetry, theoretical physicist Heinz Pagels attempts to explain and impress us with just how far we rationally-minded Westerners have come. As a result of "the intellectual synthesis of two scientific disciplines," he writes, "for the first time the problem of the origin of the universe is being discussed in rational, mathematical terms." The two disciplines are quantum physics, whose main interest is the atom, and astrophysics, whose main interest is the universe at large.

The unlikely collaboration began in the 1970s, after astrophysicists found evidence that the universe came into being some 10 billion years ago in one gigantic explosion -- the Big Bang, whose aftermath appears to be manifest today in the rapid movement away from us of galaxies. Considering the extraordinary energy that would naturally accompany such an event, atoms simply could not have held themselves together. This raised a problem for astrophysicists essaying to understand the early universe that quantum physicists are expert at handling.

With the assistance of powerful atom smashers, quantum physicists have discovered over he past four decades that the typical atom, once thought to be indivisible, is a motley aggregation of quantum particles, of which there are more than 300 known species. "The observed properties of the quantum particles can be described in the language of mathematics," Pagels explains, "and within that language the notion of symmetry has come to play an increasingly important role."

In part, this is because for every way in which nature is symmetrical, there is a law to which it conforms. For instance, the law that the universe has no north pole, that all of its directions are indistinguishable, is a consequence of its being spatially symmetric. The collection of such laws represents nature's rational order, so that if it were somehow perfectly rational, scientists would refer to it as being perfectly symmetric.

WORKING ALONE, astrophysicists have long since determined that our universe is far from being perfectly symmetric. But with the recent infusion of ideas from quantum physics, they are now realizing the possibility that it was born perfect and only subsequently corrupted by the events of the Big Bang. Pagels' thesis in Perfect Symmetry is that we are at the threshold of being able to settle this possibility one way or the other.

Pagels, who is executive director of the New York Academy of Sciences and author of The Cosmic Code: Quantum Physics as the Language of Nature, defends his thesis with authority, skillfully explicating such complex topics as relativistic field theory and thermodynamics. The result is a welcome primer on the way today's scientists (rationally) imagine just how a perfectly symmetric universe of quantum particles can erupt out of nothing, and how those particles can subsequently combine to make atoms and how they in turn can evolve to "make stars, planets, molecules and life."

At least as impressive as the thoroughness and expertise with which Pagels details these contemporary scientific ideas is the importance he imputes to them. For him, they are the beginning of the end of myth and mystery. "I believe that physicists will someday soon understand the basic laws of the quantum creation of the universe," he predicts, and when that happens, "the universe will hold no more mystery for those who choose to understand it than the existence of the sun." In the meantime, he writes: "As our knowledge of our universe matures, that ancient awestruck feeling of wonder at its size and duration seems inappropriate, a sensibility left over from an earlier age."

Pagels' enthusiastic appraisal of the state and stature of today's scientific cosmology strikes me as similarly inappropriate, though understandable, considering that his own worthy research has contributed to the subject. Quantum physics, a discipline which is scarcely 60 years old, has created nearly as many compelling mysteries as it has resolved.

One of these is a quantum particle called the quark, whose existence is as primary an element in the ideas Pagels discusses as Zeus was in the mythologies of the past. Like Zeus, it has never been observed and, most contemporary theories hold, never can be. We may never be able to prove the existence of the quark, but merely be able to infer it from circumstantial evidence.

As long as we rely on concepts as enigmatic and elusive as this, however mathematically rational they may be, it is difficult to see how they can really emancipate us from our "ancient awestruck feeling of wonder" for the universe. For all its technical sophistication, our best rational effort at explaining the origins and machinations of the natural world remains, like the ancient Greek mythologies, but logical and to a degree verifiable.