BOOK REVIEW / SCIENCE : Taking the Time to Prove Common Sense Wrong--Again : ABOUT TIME: Einstein’s Unfinished Revolution <i> by Paul Davies</i> , Simon & Schuster, $24, 294 pages

My good friend Prentiss Willson Jr. is a distinguished tax lawyer and a very smart guy. He is a supreme rationalist with more than a passing interest in science, and he keeps up with the latest developments.

There is one area, however, in which he says modern physics cannot be right: How can time expand and contract? For the life of him, he says, he cannot believe that if you get into a rocket ship and travel very fast (almost the speed of light), time will slow down and you will not age as fast as your twin back on Earth. When you get home, the people on Earth will say that 20 years have passed. But for you, only 12 years have passed.

That’s what the textbooks say, but to my friend Prentiss, it is simply impossible, incomprehensible and unbelievable.

Paul Davies, a professor of mathematical physics at the University of Adelaide, has written a book for Prentiss and for all other skeptics on this subject. “About Time” is elegantly written and comprehensible, full of wonder and lucid explanations.

Davies recognizes that most people can’t believe the theory, and he spends some time addressing their concerns. He reports on mail he has received and continues to receive from people who want to prove to him that it’s all wrong. His message to them is simple: Forget it. And in this book, he lays out the case.

To the Western mind, nothing seems more obvious than the immutable and regular passage of time. As you read these words, the clock ticks, and the unknowable future becomes the constant present and instantaneously vanishes into the unreachable past. Common sense tells us that’s the way it has always been and always will be. We don’t make it up, and we cannot alter it.

But at the beginning of this century, Albert Einstein made one of the great discoveries in the history of knowledge: Time is relative. As Davies writes, “Time and space are not, as Newton had proclaimed, simply there , fixed once and for all in an absolute and universal way for all observers to share. Instead, they are in some sense malleable , able to stretch and shrink according to the observer’s motion.”

Elsewhere he says, “There is no universal time, no master clock that monitors the heartbeat of the cosmos.”

This discovery shocked physics to its core and led to many mind-boggling implications, including time warps and black holes. There is increasing evidence that such things exist. They were predicted by Einstein’s theory, and evidence is accumulating to verify those predictions. Davies explains all of this with great clarity.

There have also been experimental verifications of the mutability of time. Extremely sensitive atomic clocks have been flown around the world on jet airplanes, whose speed is insignificant compared to the speed of light. Nonetheless, they have come back a tiny bit slow. Their time was stretched by their motion, just as Einstein’s theory predicts.

The relativity of time is also bound up in the ultimate questions about the origin of the universe and the Big Bang that set matter on its way, leading eventually to thee and me. What was there before the Big Bang? Answer: There was nothing before the Big Bang. Time itself was created in that monumental blast.

(These are not new questions. Recall that St. Augustine was asked what God was doing before he created the universe. According to one account, he replied, “He was creating hell for people who ask such questions.”)

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If it violates common sense to think that time is mutable, recall that much of modern science has required disproving common sense. It was not until the 16th Century that Galileo demonstrated that heavy objects fall at the same rate as light ones do. Until then, everyone knew by common sense that heavy objects fall faster.

And common sense had also told everyone that the Earth is motionless and the sun moves, just as we observe. The Earth moves? How can that be? We feel no motion.

The Copernican revolution--the Earth goes around the sun, not vice versa--had a profound effect on people’s understanding of nearly everything. It challenged both their fundamental beliefs and their ideas about how things are known.

The Einsteinian revolution, while perhaps harder to grasp, will ultimately have a similar effect. The full implications of what Einstein did are still not completely understood--not even by theoretical physicists.

It remains unclear, for example, whether time travel is possible. It doesn’t look likely, but it has not been ruled out as a theoretical possibility.

For that matter, it seems that our division of time into past, present and future is inaccurate. Since there is no universal “now”--because time is affected by motion and, it turns out, by gravity--”events and moments have to exist ‘all at once’ across a span of time,” Davies writes.

Einstein himself wrote, “The distinction between past, present and future is only an illusion, even if a stubborn one.” Think about that and your head spins.

Davies makes clear that what Einstein did to time is every bit as profound as what Copernicus did to the solar system. Most people still don’t believe it.