a - Introduction

This is a story of a quest to understand nature at its deepest level. Its protagonists are the scientists who are laboring to extend our knowledge of the basic laws of physics. The period of time I will address — roughly since 1975 — is the span of my own professional career as a theoretical physicist. It may also be the strangest and most frustrating period in the history of physics since Kepler and Galileo began the practice of our craft four hundred years ago.

The story I will tell you could be read by some as a tragedy. To put it bluntly — and to give away the punch line — we have failed. We inherited a science, physics, that had been progressing so fast for so long that it was often taken as the model for how other kinds of science should be done. For more than two centuries, until the present period, our understanding of the laws of nature expanded rapidly. But today, despite our best efforts, what we know for certain about these laws is no more than we knew back in the 1970s.

How unusual is it for three decades to pass without major progress in fundamental physics? Even if we look back more than two hundred years, to a time were science was the concern mostly of wealthy amateurs, it is unprecedented. Since at least the late eighteenth century, significant progress has been made on crucial questions every quarter century.

By 1780, when Antoine Lavoisier's quantitative chemistry experiments were showing that matter is conserved, Isaac Newton's laws of motion and gravity had been in place for almost a hundred years. But while Newton gave us a framework for understanding all of nature, the frontier was still open. People were just beginning to learn the basic facts about matter, light, and heat, and mysterious phenomens like electricity and magnetism were being elucidated.

Over he next twenty-five years, major discoveries were made in each of these areas. We began to understand that light is a wave. We discovered the laws that governs the force between electrically charged particles. And we made huge leaps in our understanding of matter with John Dalton's atomic theory. The motion of energy was introduced and diffraction were explained in terms of the wave theory of light; electrical resistance and the relationship between electricity and magnetism were explored.

Several basic concepts underlying modern physics emerged in the next quarter century, from 1830 to 1855. Michael Faraday introduced the notion that forces are conveyed by fields, an idea he used to greatly advance our understanding of electricity and magnetism. During the same period, the conservation of energy was proposed, as was the second law of thermodynamics.

In the quarter century following that, Faraday's pioneering ideas about fields were developed by James Clerk Maxwell into our modern theory of electromagnetism. Maxwell not only unified electricity and magnetism, he explained the behavior of gases in terms of the atomic theory. During the same period, Rudolf Clausius introduced the notion of entropy.

The period from 1880 to 1905 saw the discoveries of electrons and X rays. The study of heat radiation was developed in several steps, leading to Max Planck's discovery, in 1900, of the right formula to describe the thermal properties of radiation — a formula that would spark the quantum revolution.

In 1905, Albert Einstein was twenty-six. He had failed to find an academic job in spite of the fact that his early work on the physics of heat radiation would come to be seen as a major contribution to science. But that was a warm-up. He soon zeroed in on the fundamental question of physics: First, how could the relativity of motion be reconciled with Maxwell's laws of electricity and magnetism? He told us this in his special theory of relativity. Should we think of the chemical elements as Newtonian atoms? Einstein proved we must. How can we reconcile the theories of light with the existence of atoms? einstein told us how, and in the process showed that light is both a wave and a particle. All in the year 1905, in time stolen from his work as a patent examiner.

The working out of Einstein's insight took the next quarter century. By 1930, we had his general theory of relativity, which makes the revolutionary claim that the geometry of space is not fixed but evolves in time. The wave-particle duality uncovered by einstein in 1905 had become a fully realized quantum theory, which gave us a detailed understanding of atoms, chemistry, matter, and radiation.

By 1930, we also knew that the universe contained huge numbers of galaxies like our own, and we knew they were moving away from one another. The Implications were not clear, but we knew we lived in an expanding universe.

With the understanding of quantum theory and general relativity as part of our understanding of the world, the first stage in the twentieth-century revolution in physics was over. Many physics professors, uncomfortable with revolutions in their areas of expertise, were relieved that we could go back to doing science the normal way, without having to question our basic assumptions at every turn. But their relief was premature.

Einstein died at the end of the next quarter century, in 1955. By then, we had learned how to consistently combine quantum theory with the special theory of relativity; this was the great accomplishment of the generation of Freeman Dyson and Richard Feynman. We had also discovered the neutron and the neutrino and hundreds of other apparently elementary particles. We had also understood that themyriad of phenomena in nature are governed by just four forces: electromagnetism, gravity, the strong nuclear force (which holds atomic nuclei together), and the weak nuclear force (responsible for radioacive decay).

Another quarter century brings us to 1980. By then we had constructed a theory explaining the rsults of all our experiments on the elementary particles and forces to date — a theory called the standard model of elementary-particle physics. For example, the standard model told us precisely how protons and neutrons are made up of quarks, which are held together by the gluons, the carriers of the strong nuclear force. For the first time in the history of fundamental physics, the theory had caught up with experiment. No one has since done an experiment that was not consistent with this model or with general relativity.

going from the very small to the very large, our knowledge of physics now extended to the new science of cosmology, where the Big Bang theory had become the consensus view. We realized that our universe not only contained stars and galxies but exotic objects such as neuron stars, quasars, supernovas, and black holes. @By 1980, Stephen Hawking had already made the fantastic prediction that black holes radiate. Astronomers also had evidence that the universe contains a lot of dark matter — that is, matter in a form that neither emits nor reflects light.

In 1981, the cosmologist Alan Guth proposed a scenario for the very early history of the universe called inflation. Roughly speaking, the theory asserts that the universe went through a spurt of enormous growth early in its life, andit explains why the universe looks pretty much the same in every direction. The theory of inflation made predictions that seemed dubious, until the evidence began to switch toward them a decade ago. As of this writing, a few puzzles remain, but the bulk of the evidence supports the predictions of inflation.