The particle's over

December 24, 1999

The cancellation of the Superconducting Super Collider project in the United States in 1993 closed a chapter in western scientific research during which physics achieved unparalleled primacy. Daniel Kevles tells the story of the rapid rise of particle physics during the 20th century, from the discoveries of X-rays and radioactivity to the manufacture of the atomic bomb and the cold war nuclear arms race.

In physics, the last century of the millennium began at the end of 1895, when Wilhelm Conrad Rontgen, a professor of physics at the University of Wurzburg in Germany, reported the discovery of the mysterious radiation that he called X-rays. In the next few years, Henri Becquerel announced to the French Academy of Sciences his discovery of what was soon dubbed "radioactivity"; at Cambridge University, J. J. Thomson isolated the electron, identifying it as a constituent of all matter; and in Berlin, in 1900, Max Planck proposed the quantum theory of radiation, the idea that radiators emit energy in discrete, indivisible units rather than, as physics had it, continously. As the 20th century began, physics was alive with new subjects for inquiry: X-rays, the mechanism of radioactivity, the structure of the electronic atom, the puzzles of quanta.

At the time, opportunities in physics for research, employment and advancement were also mushrooming. Since the late 19th century, the builders of the expanding electrical and communications industries had been drawing increasingly on academic physicists for their knowledge of electricity and magnetism. Corporations engaged professors as consultants and hired their students. The graduates brought their expertise to bear on the region between the pure physics of electromagnetism and the practical demands of developing power generators, lighting grids, electrical instruments and telephone networks. High-technology corporate managers, realising that scientific research would give them a competitive edge in national and international markets, began to establish their own research laboratories. In the United States, the leaders in the trend, General Electric and AT&T, hired physicists, who devised improved vacuum tubes, telephone equipment and circuits for the incipient marvel of the day - radio.

Academic physicists exploited the growing industrial interest in their work and their students. In Britain, William Thomson, a key contributor to the transatlantic telegraph, had used his physics laboratory in Glasgow to investigate industrially related phenomena in electrodynamics and thermodynamics, ploughing some of his patent income back into research. To train electrical specialists, physicists at several universities in Britain and the US obtained laboratory space and equipment that could also be used for research. For several decades, scientists in England and America had envied the emphasis that the German universities placed on research and had urged that their universities follow suit. By the early 20th century, university administrators, alive to the economic value of new knowledge, were responding to their pleas.

After the turn of the century, academic physicists in Germany, France, and England - the Great Powers in the discipline - commanded well-equipped laboratories, comfortable salaries, a burgeoning body of graduate students and growing support for research. US physicists were comparably well off, even though they often complained that they worked at a disadvantage compared with their European brethren.

Physicists everywhere pressed ahead with studies of X-rays, radioactivity and the structure of radiation and matter. In 1905, Albert Einstein, taking time out from his job as a patent examiner in Switzerland, concluded that light itself must consist of discrete energy quanta and also promulgated the theory of special relativity. A few years later Ernest Rutherford, working in Manchester, demonstrated that the positive charges in an atom were concentrated in a central core, the nucleus, and that they were surrounded at a distance by an equal number of negatively charged electrons.

In 1913, the Danish physicist Niels Bohr devised a quantum theory of spectra, holding that the electrons inRutherford's atom rotated around the nucleus in stationary orbits. He interpreted the spectral lines characteristic of an atom as the radiation emitted when an electron jumped from one of these orbits to another of lower energy. The energy lost in the transfer appeared as light whose frequency was exactly determined by Planck's quantum theory of radiation.

The triumphs raised more questions than they answered. How could light be both particles and waves? How could time itself vary? Bohr's theory explained why the elements gave off light at specific frequencies, but it also confounded common-sense understanding of electron motions around the nucleus, since the electrons were undefined in space and time while they quantum-jumped between orbits. Nevertheless, it worked, with the result, as a British physicist noted in 1914, that "the quantum hypothesis has spread like fire during a drought".

Western governments had provided physics with little direct support, but at the turn of the century economic nationalism was prompting a shift from such laissez-faire practice. The European powers competed commercially with each other, and in the US, entering the lists as a world power, considerations of international trade drew increasing attention. The economic significance of physics was clear in the US electrical and communications industries, where the value of manufactured goods rose from $19 million in 1889 to $335 million in 1914.

Commerce in the high technology of the day made uniform standards and instruments for measuring chemical and electrical quantities an imperative. In 1887, Germany established a handsomely equipped laboratory, the Physikalisch-Technische Reichsanstalt, to determine standard physical and chemical units. In Britain and the US, scientists, with support from industrialists urged the creation of comparable national laboratories in their own countries. In 1899, the British government authorised the creation of a National Physical Laboratory (NPL) and in 1901 the American government established the National Bureau of Standards (NBS).

After the turn of the century, physicists were increasingly employed in the technical branches of the armed services. Some at the NPL and the NBS assisted their respective armies and navies in assessing the new technologies of radio and flight. And in the first world war, more than a few demonstrated that physics was indeed useful to national defence.

The war cut off both the US and Britain from their accustomed imports of German dyes, scientific instruments and optical glass, forcing both their governments to foster scientific efforts aimed at making up the deficiencies. The conflict was rightly known as a chemist's war, but physicists were mobilised in the major belligerent nations. Working in industrial and governmental laboratories, they developed means for the detection of submarines and the location of enemy artillery; they also contributed to the solution of aeronautical problems and managed technical troops in the field. Along with chemists, they were in high demand, recognised as technical manpower worth conserving, especially after the death of the brilliant young X-ray spectroscopist Henry G. J. Moseley at Gallipoli, in 1915.

The war taught that science was essential not only to economic prowess but also to military security. The postwar retreat into isolationism and economising prevented a significant peacetime effort in defence research and development. Nevertheless, military agencies in the US and Britain invested growing sums in science. Reluctant to entrust defence research to civilian laboratories, they sponsored it in their own facilities, including the new Naval Research Laboratory in Washington, DC.

Analysts had held that a trade war was sure to follow the conflict of arms; French and Belgian scientists, alive to the point, insisted on excluding Central Powers scientists from international scientific organisations. In the 1920s, the British government gave Pounds 1 million to the war-born Department of Scientific and Industrial Research to assist industrial innovation so Britain could better compete with the great trusts and combines of Germany and America. It also inaugurated a programme of grants for research at universities that in 1920-21 already provided about a third of their budgets.

US attempts to establish a federal programme of support for university research failed, but high-tech corporate leaders acted on their conviction that, as an industrial physicist put it, "in commercial warfare ... research supplies the ammunition". During the 1920s, industrial research laboratories expanded and flourished, their reputations enhanced by the award of Nobel prizes, one to a scientist at General Electric, another to a physicist at the Bell Telephone Laboratories. Although industrial corporations contributed little directly to university physics in the US, industrial wealth made its way into academic science through philanthropic organisations, especially the Rockefeller philanthropies.

Meanwhile, the difficulties and contradictions of the quantised atom had become deeply vexing, prompting several physicists to contend that an entirely new mechanics - a quantum mechanics - was needed. Efforts in that direction were significantly facilitated by the Rockefeller Foundation, which, in the interest of restoring European science and international collaboration, granted subventions to a number of European scientific centres and established a system of international scientific fellowships that eventually benefited more than 500 budding researchers from 35 nations. The requisite mechanics was devised in the mid-1920s, the breakthrough accomplished with the invention by Werner Heisenberg of matrix mechanics, that of wave mechanics by Erwin Schrodinger, and through the union, elaboration and interpretation of the two approaches by a cadre of brilliant theorists - their efforts, as J. Robert Oppenheimer put it, guided by the "deep, creative and critical spirit of Niels Bohr". The quantum mechanical revolution was forged mainly in Europe, but by the opening of the 1930s, power in physics was moving westward. When, in 1932, it was announced that Albert Einstein would join the new Institute of Advanced Study in Princeton, New Jersey, a French physicist noted that the pope of physics had moved, and predicted that the US would now become "the centre of the natural sciences". From 1933, Adolf Hitler accelerated the trend, driving scores of talented physicists (and others) out of Germany into universities and laboratories elsewhere in Europe and the US. By the end of the century, German physics had not yet recovered its prowess.

During the 1930s, research in physics turned towards quantum mechanical understanding of radiation and energy and also, now that the structure of the atom had been mastered, towards explorations of its core, the nucleus.

Much of what was then known about the nucleus had come from the laboratory of Ernest Rutherford, at Cambridge University, where a productive group of physicists scattered alpha particles from radioactive sources off lighter nuclei, often achieving the disintegration of the nuclei under the bombardment. But the further progress of nuclear physics required a flow of bombarding particles far more energetic and plentiful than radioactive sources produced.

The need was filled in part by Ernest O. Lawrence, at the University of California, Berkeley, who devised the particle-accelerating cyclotron. This consisted of two hollow, semi-circular electrodes (two "dees"), with the straight edge of one facing that of the other but separated to form a gap across which an oscillating voltage was imposed. The machine operated by forcing the charged particles to spiral inside the dees, keeping their movement synchronised with the oscillating voltage so that each time they crossed the gap between the dees they were stepped up in energy, the accumulating increments totalling after numerous cycles to give a voltage far higher than that across the dees themselves. In January 1932, with the help of a graduate student, Lawrence obtained a sizeable flux of protons at an energy of more than one million volts, using an accelerating voltage of 4,000 volts.

Even before the million-volt cyclotron, which measured 11 inches in diameter, was completed, Lawrence was pressing ahead with plans for more energetic accelerators. He said the disintegration of nuclei under accelerator bombardment might eventually lead to the practical release of the energy contained in the atomic nucleus. Prominent physicists, including Rutherford, pooh-poohed the idea. Even so, with its intense beam the cyclotron could already produce radioactive isotopes and neutrons for use in medical research and cancer therapy.

Early on, Lawrence was far more occupied with barging ahead to higher energy machines than with using the machines to hand for physics research. As a result, his laboratory unwittingly ceded the first nuclear disintegration by particle accelerator to the team of John Cockroft and Ernest Walton, at the Cavendish Laboratory, who accomplished the feat, in 1932, with particles accelerated to only a few hundred thousand volts. But by 1939, Lawrence's laboratory commanded a hegemonic position in virtually all types of nuclear reactions, being credited for almost 50 per cent of those then known. Its staff large and diverse, it was a harbinger of the Big Science that would emerge from the flames of the worldwide conflagration that erupted in 1939.

The second world war, a physicist's war, indelibly identified physicists with national security. Allied physicists crafted numerous technical miracles, including rockets, proximity fuses and, long an unsung hero of the war, microwave radar. The radar - powered by a British invention, the cavity magnetron - was developed in numerous forms by Anglo-American teams. One version, able to detect surfaced submarines from aircraft, played a key role in the Battle of the Atlantic. Another, which permitted bombardiers to "see", through cloud cover, facilitated the strategic bombing of Germany. What obscured the story of wartime radar was the physicists' most dramatic accomplishment - the atomic bomb (which did not originate in a cyclotron laboratory but in the discovery of nuclear fission by two scientists doing table-top research in a small laboratory in Berlin).

The mushroom clouds over Hiroshima and Nagasaki, and then the cold war, convinced policy makers in the US and Britain to commit unprecedentedly large sums to scientific research and training. Both the US and Britain established atomic energy authorities that managed national laboratories devoted to basic research in physics, the development of nuclear reactors and innovations in nuclear weapons.

Although in Britain atomic and defence-related research was conducted primarily in government laboratories, in the US the military became a major patron of physics elsewhere, letting contracts to industrial firms for weapons development and to university laboratories for research unconstrained by practical requirements.

Throughout the cold war, physicists advised governments upon defence policy and assisted in developing new weapons. Some also fought to slow or end the arms race, contributing to the movements that led to the Nuclear Test Ban treaty and the Strategic Arms Limitation treaties, and energising opposition to President Ronald Reagan's Strategic Defense Initiative. Whatever their position on arms control and defence, physicists were recognised as essential to determining the shape and capabilities of western security.

They continued to play a significant role in the development of the high-tech economy. Their contributions - now made indirectly, through military spin-offs, and directly, through academic and industrial research - were essential in myriad fields, including transistors, computers, lasers, fibre optics, and the machineries of medical imaging such as MRI. Much basic research and training concerned the physics of condensed matter, a branch of physics that is related to such practical arenas as semiconductors and superconductivity and that has its own basic conundrums to be explained.

In the climate of the cold war, governmental enthusiasm for physics generated funds for giant accelerator laboratories in the US, Britain, the Soviet Union and Japan. In 1953, with the blessing of the US, several European states joined to establish the European Centre for Nuclear Research - Cern, from its French initials - in Geneva, Switzerland, to stem the brain drain to the US and prevent Europe from falling irreversibly behind the New World in particle physics. Particle physics left nuclear physics behind, moving into the high-energy region necessary to probe the elemental structure of matter and forces. The research programme required ever more powerful and expensive accelerators, and by the 1970s Britain ceased trying to develop its own machines and, like many nations across the Channel, resolved to rely entirely on Cern's.

In the early 1980s, high-energy physicists in the US, unwilling to cede leadership to Cern, urged the construction of a new, gargantuan accelerator - the Superconducting Super Collider (SSC). This would achieve an interaction energy of 40 trillion electron volts, a level characteristic of the early moments of the universe and necessary to probe beyond the limits of existing particle theory.

In the late 1980s, Congress authorised construction of the machine, which was then estimated to cost some $4 billion to build and several hundred million dollars a year to operate. But in 1993 the SSC, its estimated costs now at $11 billion, was killed in the House of Representatives, partly in response to angry opposition to it from condensed-matter physicists. But most important in this decision was the end of the cold war.

Senator Dave Durenberger, a Minnesota Republican, explained: "If we were engaged in a scientific competition with a global superpower like the former Soviet Union, and if this project would lead to an enhancement of our national security, then I would be willing to continue funding the project. But ... we face no such threat." The axeing of the SSC expressed more than a setback for high-energy physics: it symbolised the end of the privileged position that physics in the West had enjoyed since the second world war.

At the end of the century, particle physicists found themselves looking for new kinds of work, finding it in locations such as Wall Street, where their mathematical modelling skills were used in investment ventures. But if the blank-cheque era was over, physics remained indispensable to national defence, essential to competitiveness in the global economy and handsomely supported in esoteric pursuits that promised no payoff beyond the pleasure of knowing better the structure of the universe.l Daniel Kevles is Koepfli professor of humanities at California Institute of Technology and author of The Physicists: the History of a Scientific Community in Modern America.

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