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When the Atom Broke Down

Inward Bound: Of Matter and Forces in the Physical World

by Abraham Pais
Oxford University Press (Clarendon Press), 666 pp., $24.95

Inward Bound is a sweeping narrative of the history and present state of atomic physics. It is something of an official history, explaining what, in the opinion of the physics community, is known, and how it came to be known. Pais was a distinguished participant in a number of the events he describes, but he distances himself from them. His erudite chronology is written from a deep love of the subject, a desire to make it intelligible, and a zest for describing the actors in his story. You could use this book to learn physics in the order that the discoveries became established. According to one school of pedagogy, that is the best way to understand the problems and the prospects of the discipline.

So it is a wonderful book, but for whom? It is superb for apprentice or journeyman physicists who want to hear, from a master colleague, about the stages in the evolution of their craft, as seen from inside the trade. But what is in it for anyone else, for most readers of The New York Review, for example? Open it at random and you will find equations that look quite daunting.

Inward Bound is not quite as hard as it may look. For most of the book, the equations are more or less intelligible to someone who is not embarrassed by the applied mathematics now taught to sophomores at run-of-the-mill colleges (or, to put it differently, expected of entering freshmen at Caltech). But only halfway through Pais interrupts himself to say: “At this point the reader may like to have at hand a simple but good book on quantum mechanics (like the one by Schiff) where results merely stated here and in the rest of this section are derived in detail.” Schiff wrote in 1949 for graduate students in physics, even if by now his material is known to a Caltech undergraduate by the end of the first year. So why should the rest of us have to read this highly touted book that has an average of one mathematical formula per page?

Because, although demanding, it is the best book about the history of physics that is both sophisticated and accessible, and that tells what the world is made of, and how we are finding that out. Had you scratched a metaphysician of long ago and asked what the universe is, as likely as not you would have been told about space, time, causality, and substance. Those are also the most memorable topics of physics, but until Pais, most general writers told us only about the first three.

Everyone knows a little about all four because of the vast upheavals in their very definitions that have occurred in this century. Relativistic thinking put paid to stable ideas about space and time. Among the lesser effects of quantum theory are gaping holes in old ideas about causality. And substance, contrary to the old metaphysicians, is not stable. Atoms are no longer indestructible, and interactions in the nucleus can produce immense power.

Relativity and quantum mechanics were each well written up almost from the moment of inception. That was because there was a moment, call it 1905 for space and time, and 1926 for the new quantum mechanics. There are good stories to tell about those years. The number of heroes is small. The dramatic unities can be preserved (even if at the expense of sound history) by making everything seem to happen in a few weeks, if not a day. Substance, however, requires a different kind of telling. Pais calls his story an epic.

So it is. There is a cast of—how many? The names of more than five hundred physicists occur in the index, and Pais is not a writer to string along a lot of names to show off his knowledge. The present installment of the epic runs from 1895 to 1945 (I’ll explain the dates shortly). That covers two thirds of the book, which concludes with the next installment, in the form of a “memoir” from 1945 to the present. This second part spans Pais’s own career, but is in no way restricted to his own work. It is simply that period during which he was an active participant. The transformations since 1895 have been intense. Nuclear weapons and nuclear power have been the stuff of policy decisions for forty years, but there was not even an atomic nucleus on the books in 1910. Ernest Rutherford first speculated that the atom might have a nucleus the next year.

Although Pais quite properly has his own favorites—he loves Niels Bohr, for example—there is no one event or any handful of heroes around which to unfold the plot. The story of substance demands a treatment different from that of relativity or quantum mechanics. Moreover, I have spoken of installments. The year 1895 does not begin the entire story. The oldest and most permanent project in that kind of Western thinking we now call physics is to reveal the inner constitution of matter. Why on earth should matter have an inner constitution at all? Some of us seem always to have thought that it has. I happen to use a seventeenth-century phrase. I might better employ Locke’s typically more cumbersome but more precise term, “the real internal, but generally (in substances), unknown constitution of things.” The cronies of Democritus could have used similar terms when they postulated, against all reason, that the world is composed of indestructible atoms and emptiness. Such speculation has been going on by fits and starts since the dawn of our civilization. So too has the rival fantasy that we live in a plenum of fields of force and energy. Both models have appealed to many of the best minds. It was James Clerk Maxwell who (with others, of course) gave us both the kinetic theory of gases, marbles bouncing around in nothingness, and also the electromagnetic equations in which everything fills everything. This traditional feature of our entire culture is one reason that the facts recounted by Pais deserve to be widely known.

By and large, every success has taken us down and down, to smaller and smaller units of matter. Hence Inward Bound is a good title. In case you missed the pun, the book is also about the forces that bind the nucleus of the atom together. There is also the play on Outward Bound, the push-yourself-to-the-limit adventure movement founded in a British preparatory school. In order to assure you that the book is not all equations, I should say that there is a slight whiff of the stories from English schoolboy magazines published between 1918 and 1939. If you had read them, you would recognize some of the characters. There is the hearty sportsman (the bluff New Zealander who has come home to England) or the quiet fellow whose Swiss father, a Manchester schoolmaster, forces him to speak French at breakfast, driving him to shyness amounting to autism. Although Pais is evenhanded with his cast of hundreds, it is clear that, in addition to Niels Bohr, those two characters are among his favorite five. The hearty one is Ernest Rutherford, greatest experimenter of his day, the first to “split the atom,” albeit a trifle inadvertently. The introvert is P.A.M. Dirac, the superb theorist, who wrote down the best sentence in this book, an array of some fourteen symbols that says what the electron is.

Those two figure in the epic. From the memoir we get some subsequent dialogue, an exchange, in Pais’s presence, written down on the spot.

I am Feynman.”

I am Dirac.” (Silence.)

It must be wonderful to be the discoverer of that equation.”

That was a long time ago.” (Pause.)

What are you working on?”

Mesons.”

Are you trying to discover an equation for them?”

It is very hard.”

One must try.”

Incidentally, Pais’s personal admiration for Rutherford and Dirac reflects a great strength in the book to which I shall briefly return. This narrative is unusually sympathetic to both experiment and theory, and hence provides many real insights into the interplay between them. In the matter of theory/experiment, it is perhaps the most evenhanded general survey of physics ever written.

Now let’s turn to the dates. The division into two parts, epic and memoir, before and after 1945, is the result of a happy if whimsical chance. Pais was born in 1918, and was awarded a Dutch doctorate in 1941. He spent most of the war in hiding. Hence he grew up in prewar physics and began his career in postwar physics. After 1946 he seems always to have kept careful notes of what was going on around him, possibly a consequence of having spent his postdoctoral years in almost complete isolation. In two ways the book is a memoir. The choice of topics reflects the author’s taste, and the anecdotes come from his diary. He feels that events have been going on at such a pace since 1945 that it would be impossible, now, to write with the detachment and sound selection that were possible for the earlier epoch. But it is not just these accidents that make Pais’s division almost inevitable. Like a latter-day Rip van Winkle, he is also testifying to the tremendous transitions in physics effected while he was out of circulation. The era of big science and big funding had begun.

Precisely because of this institutional change—rather than any theoretical advance—1945 will appear as a fundamental date in many histories of physics until some iconoclast gets us to tear up that model.1 What about 1895? That year allows Pais his own whimsy, saying he is telling the story of physics “from X to Z.” In 1895 Roentgen stumbled across X-rays. In 1983 a group using the CERN collider in Geneva elicited a pair of particles called W and Z. These “weak neutral bosons” are latent in prewar ideas of Enrico Fermi. When efforts were made to create a unified theory of electromagnetism and gravitation, it turned out that in addition to these forces, there were also two “nuclear forces” as well. One of these, the “weak” nuclear force, which helps to hold atomic nuclei together, was found to be conveyed by W and Z. These particles were described in some detail in 1957 and 1958, but only in 1976 could anyone figure out how to produce the events that are their signature. The report of their discovery created much excitement in the community of physicists. They were theoretically important. They confirmed a particular longterm direction of theory. The actual experimentation had many elements of brilliance. It was a gamble that paid off; a collider experiment uses a great many available resources at a given time, and in fact Fermilab in Illinois was much slower in taking a similar gamble. All in all, then, 1983 was a good year to end the book with a Z. Let us not worry about Z, however, and ask about X.

  1. 1

    See, for example, Daniel Kevles, The Physicists (Random House, 1979), and the review of it by David Joravsky in The New York Review (June 28, 1979).

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