BOOK REVIEW : Assessing the Gravity of the Situation

An Old Man’s Toy: Gravity at Work and Play in Einstein’s Universe by A. Zee (Macmillan: $21.95; 272 pages)

Physics began in 1687 with the publication of Isaac Newton’s “Principia Mathematica,” which showed that the law of gravity governs falling apples, the moon and the planets. One law of physics rules everything in the heavens and on Earth. It was one of the greatest intellectual achievements of all time.

But in this century, Einstein showed that Newton didn’t have it quite right. Gravity is not merely a force that acts between two bodies. Rather, gravity is a symptom of the very essence of space and time. Gravity is deeper than Newton thought.

Nowadays, however, theoretical physicists don’t spend much time thinking about gravity. They are interested in quantum mechanics, subatomic particles, dark matter, superstrings and the like. This is a big mistake, says physicist A. Zee in “An Old Man’s Toy.” Gravity is still the name of the game, he says. It explains all we know about physics and cosmology, and it points to essential paradoxes that remain unresolved.

“Typically,” Zee writes, “graduate students are required to take two or even three years of quantum physics, while Einstein’s theory of gravity is brushed over in a half-year optional course. . . . But gravity is not to be denied. If it doesn’t get more stage time, it’s gonna call its agent! The audience hears ominous rumblings from the wings. In its petulance, gravity is threatening to disrupt the entire play.”

Zee’s book is a tour of modern physics from the point of view of gravity. There is no shortage of popular and semi-popular books that explain current theories of the Big Bang, the origin of matter, the formation of stars and galaxies, subatomic physics and superstring theory.

“An Old Man’s Toy” covers this ground from a different perspective, and it succeeds both in spinning out a new idea and in making it accessible. Zee’s writing is clear, straightforward and profound. He is a very good explainer.

“We spoke figuratively of gravity grumbling in the wings, waiting for its chance on center stage,” Zee writes. “In fact, gravity is the stage!”

Of course, reading about physics is never going to be like reading a romance novel. It requires attention. But that attention is handsomely repaid. As in so many areas of thought, in physics, the closer one examines the premises, the more elusive they become.

Zee is interested both in what is known and in what is not known. He is taken by mystery, and he notes that mysteries frequently spur progress in science.

The mystery that grabs him is the failure of physicists to reconcile the two great theories of this century. Besides Einstein’s theory of gravity, which deals with large bodies, there has been the development of quantum mechanics, which deals with very small ones. These two theories, each spectacularly successful in its own right, are not compatible.

“Much of what we do not understand of gravity can be traced to its frightful clash with the quantum,” Zee writes on the antepenultimate page of the book. “Were the world not quantum, gravity would have been happy. Einstein’s theory would be wonderful and consistent. But no, quantum fluctuation has to wreak its havoc.”

The inability of physicists to mesh quantum theory with gravity demonstrates to Zee that there is something fundamentally incomplete about our understanding of the physical world. “Physics began with gravity, but it may also end with gravity,” he says repeatedly. It is the theme of the book.

Along the way, Zee shows how gravity is essential to understanding the ideas of modern physics. “How wonderful gravity is!” he writes. “Without it, we would not be. The universe would be a thinning haze without much to admire in it.”

We know there is “dark matter” in the universe--stuff we cannot see or detect in any way--because of its gravitational effect on the matter that we can see. It might be that our theory of gravity is wrong. But there is so much experimental evidence for it that it cannot be junked.

“Scientists are characteristically conservative radicals,” Zee says. “When faced with a surprise, they tend to adopt the most conservative of the various radical options capable of explaining the observation. In this case, the overwhelming majority of physicists find it far easier to believe that something mysterious and invisible is out there than to jettison what we know about gravity.”

And yet. . . . We know so much, but there is something still missing. Zee explains what we know and what we don’t know. Physics doesn’t hang together. Either there is a mistake someplace or a deeper understanding waits to be discovered. So far, the best efforts by the smartest people have failed to find the mistake or the unifying theory.