The twentieth century was the age of physics. The origins of today's most visible artifacts — radios, telephones, television sets, lasers, computers, space ships, and the atomic bomb — lie in the discoveries of the twentieth-century physicists. And these are only the visible side-effects.

At times during this century, the pace at which nature's secrets were being revealed seemed so great that physics appeared ready to swallow the other sciences whole: first chemistry, then biology. But physics does not exploit nature; that is left to engineering and politics. Physics does not even try to explain, but only to describe.

The universe that physicists have painstakingly assembled during this century is their greatest triumph. It is a universe in which galaxies exist — an unknown fact until well into the century — where stars are born and die, and where black holes gobble up their remains. It is a universe of curved space, antimatter, and supergravity, in which everything is comprised of mysterious stuff called quarks, found in three families of two quarks each.

The universe can be seen either as a swarm of particles, or as an ocean of waves with equal clarity. It is a universe born in an unfathomable primal explosion that may someday cease to exist. It is a universe that, in J. B. S. Haldane's words. is not only a queerer place than we imagined, but perhaps a queerer place than we can imagine.

The first Nobel Prize in Physics went to the German physicist Wilhelm Röntgen in 1901. The selection and timing were right. At the end of the nineteenth century, virtually every scientist believed that the universe according to Isaac Newton and James Clerk Maxwell — what is now called classical physics — was a complete, accurate, and unassailable description of the fundamental laws of nature. Alexander Pope's famous couplet:

Nature and Nature's laws lay hid in the night:
God said, Let Newton be! and all was light.

had achieved the status of scientific dogma.

Yet cracks were already beginning to show in the grand edifice of Newtonian physics, and what is now called the second scientific revolution was ready to be launched. "It seems probable," said the American physicist Albert Michelson; "that most of the grand underlying principles have been firmly established . . . the future truths of physics are to be looked for in the sixth place of decimals." Michelson's premature announcement of the end of physics was made to a conference of scientists in 1894.

The following year Röntgen discovered X-rays. The year after that, the year of Alfred Nobel's death, the French physicist Antoine Henri Becquerel discovered spontaneous radiation; in 1897, the British physicist Joseph John Thomson deduced the existence of electrons, which he called "corpuscles"; in 1898, Marie Curie, the discoverer of radium and polonium, coined the term "radioactivity". By the turn of the century the atomic age had begun, and from it came what textbooks now refer to as twentieth-century, or "modern", physics. In 1903 Becquerel shared the Nobel Prize with Marie Curie and her husband Pierre; Thomson became a laureate in 1906.

As for Michelson, he lived to regret his statement, and received a Nobel Prize in 1907 for his experiments in optics. Today, he is best remembered for an experiment he conducted with chemist Edward Morley in 1887, perhaps the most important failure in the history of science. Michelson set out to prove the existence of the so-called ether which at the time was thought (wrongly) to pervade space. His failure to prove its existence was to become the cornerstone of Albert Einstein's theory of relativity.

Einstein received his Prize in 1921, but not for relativity. That theory generally is acknowledged to be his most important work, along with quantum theory, one of the two great triumphs of modern physics. Instead, Einstein's Prize was for his work on the photoelectric effect, one of the foundations of quantum theory, a theory that Einstein himself never could accept.

The roster of Physics laureates since and including Röntgen is a remarkably representative list of the giants of twentieth-century physics. "The Nobel has had a very good record," said American physicist Leon Lederman not long after he won the Physics Prize in 1988. Lederman is the former director of Fermilab, the high-energy physics center in Illinois that was named after the 1938 Physics laureate Enrico Fermi. Lederman's ambition is to reduce physics to a single equation. "... the biggest mistake was Fermi," Lederman said. "They gave him the prize for discovering transuranic elements when he really had discovered fission. But that's the kind of mistake you like to make. There have been very few mistakes, but some curious choices, like the man who got the prize for inventing some kind of reflector for lighthouses." (Lederman was referring to Swedish physicist Nils Dalen, who received his prize in 1912 "for his invention of automatic regulators in conjunction with gas accumulators for illuminating lighthouses and buoys.")

There have been unaccountable delays and strange omissions, of course: Einstein waited seventeen years after the publication of his work to receive his award, and Lederman himself waited almost three decades. He used to tell his children the delay was because the Nobel Committee "couldn't make up its mind which of my accomplishments to recognize." And every physicist can name favourite theorists or experimenters who should have won the Prize but did not.

The most celebrated also-ran undoubtedly is the great New Zealand-born physicist Ernest Rutherford, the first to uncover the structure of atoms. Rutherford, who at age twenty-four went to England to work with J. J. Thomson in 1895, was the consummate experimentalist: a gruff, purposeful man one colleague described as graced with an unparalleled gift for getting experiments to work by cursing at them. Over his long career, Rutherford trained no fewer than eleven Nobel laureates, and strongly believed he deserved a Physics Prize of his own. In 1908 he did receive a Prize, but it was in Chemistry. It distressed and bewildered him for the rest of his life. He was, after all, the man who once declared "all science is either physics or stamp—collecting."

Looking back over the careers of the more than 100 men and,women who have won Nobel Prizes in Physics, the mix of experimentalists and theorists is somewhat weighted toward the theorists; getting nature to yield her secrets to experiment has become increasingly difficult and expensive. Nevertheless, as 1923 Physics laureate Robert Millikan put it, "science walks forward on two feet, namely theory and experiment. Sometimes it is one foot which is put forward, sometimes the other, but continuous progress is made only by the use of both." Röntgen, on the other hand, made the case for the experimentalists. When asked what he thought about while he was discovering X—rays, Röntgen responded: "I didn't think. I experimented." Einstein, who became the personification of theoretical physics, much preferred "thought experiments" to those conducted in a laboratory, but he realized the importance of both.

As the outstanding theoretical physicist Steven Weinberg stated in his acceptance speech for the 1979 Prize he shared with Sheldon Glashow and Abdus Salam: "Our job in physics is to see things simply, to understand a great many complicated phenomena in a unified way, in terms of a few simple principles. At times, our efforts are illuminated by a brilliant experiment . . . but even in the dark times between experimental breakthroughs, there always continues a steady evolution of theoretical ideas, leading almost imperceptibly to changes in previous beliefs."

What is most surprising about the roster of Physics laureates is how few of these men and women — among them some of the most brilliant minds of this century — achieved wide public recognition outside the realm of science. Even before he received his Nobel Prize, Einstein was a worldwide celebrity, but, with the possible exception of the Curies and Marconi, it is difficult to think of a Physics laureate who is as well known as even a minor rock star.

The relative obscurity of the majority of Nobel Prizewinning physicists is due both to the language of physics — mathematics, a language that translates poorly — and the mind-boggling universe it describes. The great British astronomer Arthur Stanley Eddington clarified the problem when he was interviewed shortly after the publication of the theory of relativity, an idea that physicists say is a stroll in the woods compared to the thorny jungle of quantum theory. When asked if it was true that only three people in the world understood Einstein's theory, Eddington quipped, "Who is the third?"

In the world of science, however, the roster of Nobel Physics laureates could double as an honour roll of the most famous names of the century. A brief list of eponyms makes the case: Planck's constant (after Max Planck, who received the Prize in 1919); the Compton effect (Arthur Compton, 1927); De Broglie waves (Prince Louis—Victor de Broglie, 1929); the Heisenberg uncertainty principle (Werner Heisenberg, 1933); Cerenkov radiation (Paver Cerenkov, 1958); Josephson junctions (Brian Josephson, 1973); and Feynman diagrams (Richard Feynman, 1965) — to name only a few. A number of Physics laureates have been awarded the singular honour of having their names given to units of measurement— the rontgen, the curie, and the fermi come to mind. Einstein had an element of nature named after him: einsteinium, the ninety-ninth element, discovered shortly after his death; the 102nd element, first isolated in Sweden in 1958, was named nobelium after Alfred Nobel.

Outside the world of science, there is a popular if distorted picture of the physicist as a down-to-earth scientist whose discoveries immediately and irrevocably change the way we live. In some ways, Röntgen fits that description: barely a month after the discovery of X-rays, Eddie McCarthy of Cartmouth, New Hampshire became one of the first to have his broken arm set by a physician using X-ray images.

Marconi's wireless had a similar impact on everyday life, as did the discovery of colour photography by French physicist Gabriel Lippman (1908 laureate); the development of laser theory by American physicist Charles H. Townes (1964); and the invention of the transistor by American physicists William Shockley, Walter Brattain, and John Bardeen (1956 laureates). To date, Bardeen is the only laureate to win two Physics Prizes. He was honoured again in 1972 along with Leon Cooper and Robert Schrieffer for work in developing a theory of superconductivity, which may change the way we live in the not-too-distant future.

Of course, the most visible and ominous invention of twentieth-century physics was the atomic bomb, the result of work by a long list of Nobel laureates, Einstein among them. The bomb itself was the by-product of an effort to solve the most intriguing problem of modern science, namely, what is the structure of the atom and how do its parts behave? "The constitution of the atom is, of course, the great problem that lies at the base of all physics and chemistry," said Lord Rutherford early in the century, "and if we knew the construction of atoms we ought to be able to predict everything that is happening in the universe." Today's physicists no longer accept Rutherford's promise of prediction — not since 1933 when laureate Werner Heisenberg abolished the notion of absolute certainty in science — but the central question remains the same.

Over the course of the century, the majority of Physics laureates have devoted their lives to understanding the workings of the atom and its parts. Because of the nature and complexity of this effort, the results and breakthroughs more often than not are beyond the grasp of the general public. Nobel's Physics Prize, in a sense, makes up for this lack of general recognition, and there is no doubt that it is cherished as much for its prestige in the community of physicists as for its monetary reward.

Consider the case of Nils Bohr, the Danish physicist who won the Prize in 1922 for "his services in the investigation of the structure of atoms and of the radiation emanating from them". The torch-bearer of the quantum revolution, Bohr donated his Nobel medal to Finnish war relief at the beginning of the Second World War. Soon after the War began he was entrusted with the medals of the German physicists Max von Laue (1914 laureate) and James Franck (1926). Before he escaped from occupied Denmark in 1943, Bohr, a meticulous man who was known to write drafts of postcards, dissolved the medals in acid in order to get them safely out of the country. After the War, he precipitated the gold from the acid, and had the medals re-cast.

As this century comes to a close, the picture of the universe provided by modern physics appears fairly complete. It describes a universe that operates according to the laws of quantum mechanics and relativity, and is governed by four basic forces — gravity, electromagnetism, weak nuclear, and strong nuclear. The forces themselves are mysteries; nobody can explain them. Physicists call them explanatory principles which themselves cannot be explained, but they nevertheless govern the behaviour of everything from electrons to elephants.

As the new century approaches, the dream of physicists is to combine these four mysteries into one, to successfully marry quantum mechanics and relativity and produce a single set of simple, elegant equations that perfectly describe the first moment of time and everything since then: a theory of everything.

Some physicists, among them the British physicist Stephen Hawking, predict that such a theory is close to hand. Others point to Michelson's announcement of the death of physics in 1894, and Max Born's prediction in the late 1920s that "Physics as we know it will be over in six months." The answer to the question of physics' ultimate demise will probably not be settled until the next century. But then in physics, answers have never been as important or interesting as the questions.

It is the questions, not the answers, that are the triumphs of twentieth-century physics. How did the universe begin? How will it end? Will time someday reverse itself? What goes on inside the atom? If space is primarily empty, why does the ground hold us up? Why is the sky dark at night? In posing these questions in a unique, precise way, physics in this century has extended the sphere of human knowledge, illuminating regions previously explored only by philosophers and children.

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