There are two great mysteries in this world. First, how did the universe begin? Second, how does a book that attempts to answer that question -- a book about muons and gluons, about thermodynamic arrows and space-time singularities, about quantum gravity and superstrings, a book that argues convincingly against the existence of Einstein's cosmological constant -- become the No. 1 best seller for 20 weeks in a row? Having now twice read Stephen Hawking's "A Brief History of Time," a smash popularization of modern physics, I am preoccupied with the second question and no closer to an answer for the first than I was when I started.

True, we do have our annual, heavy-think best seller. First there was Allan Bloom's "The Closing of the American Mind." Then came Paul Kennedy's challenge to unreinforced coffee tables, "The Rise and Fall of the Great Powers." And now Hawking. But Bloom's book is difficult only in places. And Kennedy's is merely dense. The problem with Hawking's book is that it is utterly incomprehensible.

Incomprehensible in a very interesting way. Hawking's language is simple. The syntax is clear. The exposition is careful, at times even graceful. With the exception of E=mc , now a staple of subway walls, not a single equation appears in the book. (Hawking was persuaded of the well-known rule of thumb: every equation cuts your sales in half.)

If given enough attention, every sentence makes sense. But when you have registered all the sentences, you realize in the end that you understand nothing. It is not Hawking that is beyond comprehension, but modern physics.

For example: I understand, and if asked can readily repeat, the current notion of superstring theory that the universe has 10 (or 26) dimensions, all but four of which are curled up into tiny little balls. But what can that possibly mean?

I can also recite Hawking's solution to the age-old question: Did the universe have a beginning, or has it existed through an infinity of time? Hawking proposes a finesse: space-time is finite in extent but has no boundary or edge. Meaning: space-time is like the surface of the earth, which also is finite (197 million square miles) but round and enclosed, so that you can go around forever without reaching a beginning or an end. A universe of no beginning and no end, but no infinity. I understand. But what does it mean?

The Hawking book may be proof that physics has reached the limits of metaphor. Sir Arthur Eddington was once told by a journalist that only three people in the world understood Einstein's general theory of relativity. "I am trying to think who the third person is," replied Eddington. There are more than three now. Thousands of graduate students understand the equations whose meaning Hawking has set out to communicate. But physics is becoming the province of a small cadre of cognoscenti who occasionally send out emissaries like Hawking to speak to the rest of us in parables.

Inscrutable parables. Compare physics to biology, for example. Biology is very complicated, but in principle it is comprehensible. Give the man on the Clapham omnibus an hour, and he can gain a reasonable grasp of, say, immunology. Thirteen hours of Hawking have convinced me that you can no longer do that with physics. Physics has become a kind of fiction, an excursion into a mathematical universe so esoteric and so remote from ordinary experience as to be literally incredible.

Yet Hawking is an optimist. In 1928, excited by the recent discovery of the equation that governed the electron, Max Born said that "physics as we know it will be over" -- i.e., solved -- "in six months." Premature, admits Hawking, but then he adds: it should be over in our lifetime. Hawking believes that physics is on the threshold of a grand unification theory which will explain, well, everything. At which point ordinary people will begin to assimilate the principles of the new physics in the same way that people now have absorbed the rudiments of Newtonian mechanics (inertia, gravitational pull, equal and opposite forces).

I would be scared by this kind of scientific hubris if I didn't think it so deluded. Hawking knows better than I whether physics is about to abolish itself. But even if the improbable happens and he is right, none but the initiated will understand it then any better than they do now.

Which brings us back to the greater mystery: the wild success of Hawking's inscrutable book. The answer is that people don't read these books. They only want to own them. Not out of snobbery, I think, but out of a kind of reverence. Not many people read their Bibles either. But they like having them around. Even if the Truth will never make its way into your head, it is a comfort to have it at hand.