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Seeing the Unseen

2.

Cathcart’s book ends with a discussion of the question why the tortoise beat the hares in the race to disintegrate nuclei with accelerators. He concludes that the main reason why Rutherford won was that he was not a machine builder. Van de Graaff and Lawrence were brilliant inventors, driven by passionate love for their machines. They were not so much concerned with what their machines could do when they were built. For Rutherford the machine was only a tool. He was not interested in the details of its design and trusted Cockcroft and Walton to get the details right. For him, what mattered was the science.

He had spent his life exploring the nuclei of atoms, and his driving passion was to dig deeper into the nucleus. That was why he made sure that the decisive experiment was carefully prepared and the lithium nuclei were ready and waiting to be disintegrated as soon as his machine was finished. The Americans had better machines, but Rutherford had a more single-minded concentration on the scientific goal. Two months after he won the race, Rutherford explained to a reporter from the Daily Herald why he had wanted so badly to disintegrate nuclei. “We are rather like children,” said Rutherford, “who must take a watch to pieces to see how it works.”

Alan Lightman’s book, A Sense of the Mysterious, tells a very different story. His book has no index, so I cannot be sure how many times Rutherford is mentioned. I believe he is mentioned only once, on page 133, in a list of names of famous people who were dead in the year 2002 when that page was written. I find it remarkable that we have two books designed to give nonexpert readers a feeling for the way research into the nature of the physical universe is done, and yet the central character of one book is barely mentioned in the other. How could two accounts of the same science be so different, in so many ways, in style and in substance?

Brian Cathcart is an Irish journalist with an amateur interest in science. Alan Lightman is an American, trained as a theoretical physicist, who made a mid-life change of career from scientific research to writing. Cathcart’s book is a straightforward historical narrative. Lightman’s book is a collection of essays, lectures, and book reviews, some of them published in this magazine, most of them describing individual scientists and their ideas. Cathcart is primarily interested in experiments, Lightman in theories. Cathcart sees progress in science mainly driven by new tools; Lightman sees progress driven by new concepts. Cathcart’s story is a simple drama with three heroes and no villains, a triumph of human pertinacity over technical and cultural obstacles. Lightman’s chapters are meditations on the human condition, illustrated by sketches of characters who are partly heroes and partly villains.

The main characters in Lightman’s stories are the theoretical physicists Albert Einstein, Edward Teller, and Richard Feynman, and the observational astronomer Vera Rubin. Not only is Rutherford absent, but almost all experimental scientists are absent too. The only experimenter who makes an appearance on Lightman’s stage is Joseph Weber, a brilliant and tragic figure whose experiments turned out to be wrong. The mainstream experimenters who explored the universe of particles and fields, continuing to play Rutherford’s game, taking the watch to pieces to see how it works, do not appear at all. Lightman’s title, A Sense of the Mysterious, and his subtitle, Science and the Human Spirit, do notexplain his neglect of experimenters. After all, Rutherford had as deep a sense of the mysteries of nature as Einstein. And the human spirit expresses itself as eloquently in the work of human hands as in the work of human minds. Rutherford was supreme as an experimenter and Einstein was supreme as a theorist, but each of them held the other in deep respect. Both of them understood that the human spirit is at its best when hands and minds are working together.

One theorist played an essential role in Rutherford’s thinking. George Gamow was a brilliant young Russian who came to Germany in 1928 and at the age of twenty-four started a revolution in nuclear physics. He was the first to understand how the quantum theory, which had been invented only three years earlier, could be applied to the nucleus. He used quantum theory to calculate how fast radioactive nuclei such as radium or uranium should decay, and found that the theory agreed pretty well with the observed rates of disintegration. He then made another decisive step, using quantum theory to calculate how easily a charged particle could come into a nucleus from outside. He understood that the same quantum rules apply in both directions. Easy out, easy in. If particles can escape from radioactive nuclei by quantum rules, then they can also penetrate into nuclei by quantum rules when fired at them from outside.

When Rutherford heard of Gamow’s idea, he saw at once that this dramatically improved the prospects for doing important science with the accelerator that he was planning to build. Rutherford did not pretend to understand quantum mechanics, but he understood that the Gamow formula would give his accelerator a crucial advantage. Even particles accelerated to much lower energies than the particles emitted naturally by radium would be able to penetrate into nuclei. Rutherford invited Gamow to Cambridge in January 1929. The fifty-eight-year-old experimenter and the twenty-four-year-old theorist became firm friends, and Gamow’s insight gave Rutherford the impetus to go full steam ahead with the building of his accelerator.

The same mutual admiration of experimenter and theorist was shown three years later when Einstein happened to be visiting Cambridge a few days after the triumph of Cockcroft and Walton. Einstein insisted on seeing the accelerator that had split the atom. Walton spent a morning showing him the apparatus and explaining the details of its operation. Einstein wrote a letter afterwards, expressing “astonishment and admiration” for what he had seen. “He seems a very nice sort of man,” wrote the imperturbable Walton to his fiancée in Ireland.

How is it that this mutual admiration and easy mixing of theory with experiment, which seemed natural and necessary in the 1930s, is absent from Lightman’s view of physics? Somehow it happened that the successors of Rutherford and Einstein drifted apart in the second half of the twentieth century. This was not the physicists’ fault. It resulted from the enormous growth of accelerators and the enormous proliferation of theories. Accelerators and the accompanying apparatus for detecting particles became so huge and complicated that each experiment was like a military operation. Hundreds of people with highly specialized skills were required to carry out a program planned many years in advance. Theorists became similarly specialized, some of them expert in accelerator design, some in particle interactions, some in general relativity, and some in string theory. It became difficult for theorists in different specialties to communicate with one another, let alone with experimenters. At the end of the century, accelerator physics was slowing down. Each experiment required about a decade to design and prepare. Alan Lightman, an imaginative theorist who liked to avoid narrow specialization, found such experiments unattractive. It was natural for him, following his sense of the beautiful, to move away from experimental physics and toward astronomy.

Astronomers have so far escaped the extreme specialization that has overtaken physicists. Telescopes are big, but they are not as complicated as accelerators. Observations with a big telescope can be carried out in hours rather than years. Astronomers can be skilled observers and also expert in the theory of what they are observing. That is why the astronomer Vera Rubin has a place of honor in Lightman’s book. She started her professional career as a student of George Gamow after Gamow moved to America. She spent the rest of her professional life observing galaxies and studying their dynamics. She found that the visible matter in galaxies is not heavy enough to explain the speed of their internal motions. She deduced from her observations that galaxies are pervaded by dark matter, invisible to our telescopes. Nobody knows what dark matter is. It is another deep mystery remaining to be explored. We know only that it is there, and that it weighs more than all the stuff that we can see.

Besides discovering and exploring dark matter, Rubin raised four children and crusaded publicly for the advancement of women in science. I was recently chairman of a committee that organized a scientific conference with a list of distinguished scientists as members. I received a blistering letter from Rubin, asking why we had no women on our list. She supplied me with another list of women who should have been invited. I wrote back to apologize and to thank her for her list, which I shall certainly use in the unlikely event that I ever become chairman of another such committee.

Lightman’s chapter on Edward Teller is a review of Teller’s memoirs, first published in these pages in 2002. Lightman considers Teller to be on the whole an evil character, in sharp contrast to his sympathetic portrayals of Einstein and Feynman. The title of the Teller chapter is “Megaton Man,” emphasizing the obsession with hydrogen bombs which made Teller famous. Lightman admits that there were two Tellers. He writes, “There is a warm, vulnerable, honestly conflicted, idealistic Teller, and there is a maniacal, dangerous, and devious Teller.” But his portrait of Teller shows us mostly the dark side.

Merle Tuve, the experimenter who was beaten to the punch by Rutherford in 1932, knew Teller well after Teller came to join George Gamow at George Washington University in 1935. In 1939 somebody at the University of Chicago asked Tuve for an appraisal of Teller. Tuve replied, “If you want a genius for your staff, don’t take Teller, get Gamow. But geniuses are a dime a dozen. Teller is something much better. He helps everybody. He works on everybody’s problem. He never gets into controversies or has trouble with anyone. He is by far your best choice.” That was the Teller I knew, when I worked with him every day for three months in 1956, designing a safe nuclear reactor. It was easy to disagree with him fiercely about politics, or about the details of the reactor, and remain friends. Those who had never been his friend did him a grave injustice when they tried to turn him into a demon.

Putting together the portrait of Rutherford in Cathcart’s book with my own recollections of Teller, I find striking similarities. Rutherford and Teller were both immigrants who became fiercely patriotic in defense of their adopted countries. Both often behaved like overgrown children, losing their tempers over trivialities and then regaining their equilibrium with a friendly smile. Both were father figures to their students, taking care of students’ personal problems as well as their professional education. Both were more interested in the strategy of science than in the tactics. Rutherford made the decision to explore nuclei with an accelerator, and then left the details of the accelerator to Cockcroft and Walton. Teller made the decision to build a hydrogen bomb or a safe reactor and then left the details to others. Both had a lifelong dedication to science, but spent more time helping younger people than doing research themselves. Teller published his version of the hydrogen bomb story under the title The Work of Many People. The names of Cockcroft and Walton appear on the letter to Nature announcing their discovery but Rutherford’s does not. My name appears on the patent for the safe reactor but Teller’s does not.

The most concise and original chapter in Lightman’s book is “Metaphor in Science,” an essay originally published in 1988 in The American Scholar. Illustrating his thesis with quotations from great physicists from Isaac Newton to Niels Bohr, Lightman traces the powerful influence of metaphors on their thinking. As science has become more abstract and remote from everyday experience, the role of metaphor in our descriptions of the world has become more central. The language that nature speaks, as Galileo long ago pointed out, is mathematics. The language that ordinary human beings speak, especially those of us who are not fluent in mathematics, is metaphor. Lightman ends his discussion with another metaphor: “We are blind men, imagining what we don’t see.” That is a good description of theoretical physics.

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