The Second Creation: Makers of the Revolution in 20th Century Physics, by Robert P. Crease and Charles C. Mann, New York: Elizabeth Sifton Books/Viking, 447 pages, $24.95
If physics can be said to have a Holy Grail, it is Unification. Physicists have always felt the impulse to knit up the world with a single, simple, elegant thread. In The Second Creation, one of the year's most widely acclaimed science books, Robert Crease and Charles Mann adroitly depict both the abstruse and the human side of modern particle physics, blending lucid description with gossipy verve.
Unification seeks a "theory of everything"—why matter has its present form and why the universe is as we find it. "Newton's recognition that the force that made apples fall was identical to the force that kept the earth in its orbit was a Unification, as was the approximately contemporaneous realization that lightning, static electricity, and St. Elmo's fire were all manifestations of one phenomenon: electricity." Later, James Clerk Maxwell showed that oscillating electrical and magnetic fields in wires radiate waves with precisely the speed of light. This unified circuitry with the light spectrum we see, two seemingly different phenomena.
Lofty aims do not rule out a warts-and-all attention to how physicists work. The book abounds in tales of intense rivalry, cutting criticism, and rueful failure. There were even cases of physicists announcing results first in the New York Times, only to have them disproved shortly afterward, before they were published in scientific journals. As science writer Freeman Dyson has said, "The ground of physics is littered with the corpses of unified theories." Einstein, for example, ruminated on a theory that would unite gravity with particle physics, following a blind alley during his final decades.
Crease and Mann are able to pick their way through the thicket of abstractions by perceptive, well-timed analogies and visual pictures. They report the many spectacular failures of the last century along with the triumphs, never neglecting the delicious gossip: "Heisenberg launched…a unified field theory that started as a collaboration with Pauli. When Pauli withdrew, Heisenberg claimed during a radio broadcast in February 1958 that a unified Heisenberg-Pauli theory was imminent, and only a few small technicalities remained to be worked out.…Pauli responded by mailing his friends a letter consisting of a blank rectangle, drawn in pencil, with the caption, 'This is to show the world that I can paint like Titian. Only technical details are missing.'"
Yet alongside the failures came great progress in the past 20 years. Electromagnetism was unified with the nuclear weak interaction, showing them to be two faces of the same coin. Now the quest pushes on to higher-energy particles, which means that the implications for cosmology reach further back in time, to when the universe was compact and far hotter. This is truly the final problem, though it deals with initial instants, when "matter and energy were one…at the dawn of time, in the ravening fire of the Big Bang. Thus the phenomena physicists now seek to describe existed only at unimaginable energies that can never be reproduced in the laboratory. Experiment consequently seems almost hopeless."
This does not, however, deter the particle physics community from pressing for a new, giant accelerator to push on to still higher energies. The Superconducting Collider would use superconducting magnets to ram beams of particles into each other. This accelerator would be 50 miles in circumference and cost about $4 billion—a huge fraction of today's science budget.
The physics community seems divided about the utility of this machine and whether it would in fact settle any truly fundamental issues. The major budget battle in the scientific community now looming is competition between a Superconducting Collider and funding for a space station. In a way, it is a contest between two different frontiers of discovery.
While space is an infinite frontier, the prospect of a final Unification may close the heroic era of particle physics. As long ago as the 1920s, theorists forecast "the end of physics as we know it within six months." Many hold that a complete theory would mean that science would continue, but "all of the fundamental questions that physics can pose would have been answered, and our knowledge of force and matter would henceforth change only in particulars and not in outline."
Such hubris will probably go untested, because there are serious doubts about whether we can ever do experiments at high enough energy, or observations of the large-scale universe in enough detail, to ever confirm or deny the candidate unified theories. Once the supreme empirical science, physics could then become mere "recreational mathematical theology," telling us in the end more about ourselves than it does about nature.
What is more, this book is shaped toward a special definition of what is fundamental. Basically, it holds that once we know the forces between particles, and find a mathematical expression that generates their properties from some general assumptions, the program of physics is over.
Yet many profound philosophical questions stem from the gritty particulars of the universe, not just the building blocks. (Is life an unavoidable outcome of complicated processes? How prevalent is it? Does intelligence inevitably arise?) It is as though a gourmet maintained that what matters in a meal is the raw ingredients, not how they are to be cooked and savored.
We have known the laws of mechanics and electromagnetism for a century but still cannot describe the deep dynamics of our own sun, whose conditions determine whether life is possible on planets like ours. Plasma physics, which seeks to understand the interaction of highly energetic matter such as the sun, is in its infancy. Some theorists have seriously proposed that life in the form of plasma beings may be possible. If so, this raises fundamental questions unrelated to Unification theories. The position of life itself in the universe depends on complex interactions, not just basic pieces.
Still, Unification asks questions as deep as one could like. Will matter itself last? (Are diamonds forever?) What happened on the far side of the Big Bang? One suspects the joy of asking may be more lasting and important than the problematic answers.
Gregory Benford is professor of physics at the University of California at Irvine and the author of Timescape.