A Question of Character

1.

The transformations in theoretical physics during the twentieth century have two main lines, each with a key term, “relativity” and “quantum theory.” Both sets of changes were responses to problems in the natural philosophy passed down from Isaac Newton to the scientists of the 1890s—the presuppositions underlying the body of theory we know, in retrospect, as “classical” physics. But the two sets of changes took place in very different ways.

The early history of relativity is dominated by a single creative thinker, Albert Einstein, and comes close to being his intellectual biography. Not that Einstein claimed to solve his own problems single-handed. He was aware of his debts to forerunners who had helped to clarify those problems, and to contemporaries who worked alongside him. But his imagination was so remarkable and the originality and power of his arguments carried such conviction that they did much to shape the general approach to solving these problems. By contrast, the early history of quantum physics has involved so large a cast of characters that even a cursory account must cover two dozen original physicists with different views and backgrounds: Max Planck, Niels Bohr, Paul Dirac, Louis de Broglie, Arnold Sommerfeld, Werner Heisenberg, and Erwin Schrödinger, as well as Albert Einstein himself, to list only the most eminent participants and to carry the story only up to 1939.

This difference, along with the difficulty of writing about quantum mechanics in colloquial language, explains why up to now few of the architects of quantum physics have been subjects of full biographies. There have been fine essays on Niels Bohr’s life and work; but the biography of Erwin Schrödinger (1887–1961) under review is one of the first full-scale attempts to evaluate the work of one such physicist and see him from a late-twentieth-century perspective. How did Schrödinger earn this place?

Nineteenth-century physics inherited two dichotomies from the new “mechanical philosophers” of the seventeenth century, notably René Descartes and Isaac Newton. One of them was external to physics. It set up a boundary dividing the realm of Matter, material objects and causal processes, from that of Mind, mental activities and rational thought: hence the epistemological “dualism” in which Newton fully shared. It is true that, from Hermann Helmholtz in the 1860s to Sigmund Freud, Ernst Mach, and Wilhelm Ostwald at the turn of the century, the “monists” looked for an epistemological approach that would show how physics and psychology could both be generated from a common starting point. But, even in 1900, there was still no way of putting this philosophical program on a strict scientific footing.

The other dichotomy was internal to physics. It separated physical processes of two kinds: mechanical interactions of tangible objects by contact or impact, and those phenomena—electrical, optical, magnetic, or gravitational—that were less tangible, and affected objects distant from one another. In classical physics it was taken as axiomatic that (as Newton put it) God in the Beginning made matter into “hard, massy, impenetrable, moveable particles” or “corpuscles”: all the less tangible phenomena were explained, first in terms of fields, light waves, and other invisible agencies, later by appeal to electromagnetic and other wavelike processes.

From the start, the “intangibles” were a source of perplexity and embarrassment. The founders of modern physics agreed that physical phenomena must ultimately be explained by forces exerted by one material object on another directly: that was what made theirs a “mechanical” philosophy. So they denied that any “action at a distance” could be what it seemed, and looked for mechanisms that supposedly underlay these intangible phenomena. Talking about “fields” was a façon de parler, which they might accept provisionally, but would be superseded once they had brought those deeper mechanisms to light.

That was easier said than done. The integration of electricity, magnetism, and optics by James Clerk Maxwell’s electromagnetic theory in the 1860s created a system of equations that was, in its own way, as elegant and comprehensive as Newton’s Principia. But all attempts to explain Maxwell’s results in mechanical terms—by invoking (say) a quasimaterial “luminiferous ether”—proved fruitless. In the world of electromagnetic waves, Maxwell conceded, the only clear function for the term “ether” was as the subject of the verb to undulate.

Between 1905 and 1930, this entire natural philosophy fell apart. In both relativity and quantum theory, the priority of electromagnetism and mechanics was reversed: instead of electromagnetic phenomena being explained in mechanical terms, matter and mechanism were now accounted for by electromagnetic theory. In itself, as Einstein found, this reversal circumvented those puzzles about Space and Time that had arisen when people tried to fit Maxwell’s results within the framework of Newton’s dynamics. At the same time, Matter itself was seen to consist of, for example, electrons, whose electric charge was at least as fundamental as their mass; while the “impenetrability” of material objects was, as Boscovich and Priestley claimed 150 years before, the effect of fields of force between the surface particles of the bodies concerned. So the internal dichotomy of modern physics came in doubt. Once light was shown to display some features of material particles (Einstein’s “photons,” 1905) the converse question soon arose: Does matter itself display some features of “fields” and “waves”?

This was one of the central questions addressed in the changeover from classical to quantum physics, and Erwin Schrödinger was the one who gave a truly stylish answer to it, with his novel theory of “wave mechanics.” The heart of this theory, worked out in a series of five papers written during a period of sustained creativity in the first half of 1926, is his “wave equation.” This equation replaces the older Newtonian equations, which represented the current state of a physical system by showing what, scientifically speaking, that physical system “really” consists of, and what is “really” going on in it, by reporting the positions and velocities of its constituent particles. In Schrödinger’s account, a physical system of electrons (say) was no longer seen as a collection of material corpuscles, free to take up an unlimited range of spatial configurations. Instead, it was compared to a vibrating string, or resonant fluid, whose present state limits the system to a fixed repertory of stable harmonics. The orbits of the single electron in a hydrogen atom, for example, were limited to a given set of quantum levels, corresponding to the fundamental and overtones of the resonant system described by Schrödinger’s wave equation.

What were the “waves” made of? What were they waves in? About that, there were initially three rival views. Schrödinger himself was inclined to believe that, like clouds or fogbanks, electrons and other particles have intrinsically fuzzy boundaries; Max Born argued that any such particle is, in itself, as sharply defined and located as in Newton’s theory, but humans can measure its location only approximately; while others again (like Werner Heisenberg) understood the new theory as a purely mathematical model, and ignored any question about “underlying substances.” Before long, Born’s interpretation was the most popular, and Schrödinger’s wave equations were read statistically, as measuring the “probability” of finding a particle at any chosen point.

For Descartes and Newton, the units of Nature were invisibly small pieces of Matter, each of which occupied a given part of Space to the exclusion of others: hence, Descartes’ maxim, “The essence of matter is extension.” Right up to the 1900s, physics treated the fundamental population of the world of nature in the way the Epicureans had done in antiquity, as solid chunks of material stuff. The new wave-mechanical description, which referred to “modes of vibration,” followed rather the Stoic model of seeing natural phenomena as alternate states of a continuous pneuma or “breath”: in principle, it provided a representation not just of single atoms, but of any system of energy whatever. Schrödinger’s theory was, in this respect, philosophically novel and of great general application.

The theory had intuitive elegance, was attractively presented, and struck a chord in many (but not all) of Erwin Schrödinger’s colleagues. Einstein wrote him flattering words of congratulation and he was catapulted into professional eminence. But the theory’s most charming features were also the subjects of strongest criticism from skeptics. Its admirers enjoyed the intuitive intelligibility of its “wavelike” aspects, though Schrödinger could not invoke a deeper, subquantum fluid to carry these waves representing matter, since that would at once revive all the old puzzles about the luminiferous ether. For many years, the standard (if gnomic) answer to the question, “What are Schrödinger’s waves waves in?” was “They are waves of probability.” (Solutions of the wave equation at any point, in practice, measured only the likelihood that the relevant particle was located at that point.)

As early as July 1925, Schrödinger’s critics pointed out, Werner Heisenberg had produced an alternative version of quantum mechanics known as “matrix mechanics,” which seemed to escape all the puzzles posed by a wave model of matter, just as Einstein had done with Maxwell’s ether. Heisenberg avoided prejudicing the results of future empirical studies by the use of either a particle or a wave model to make the descriptions of the state of physical systems intuitively intelligible: instead, he gave his “state descriptions” in formal, mathematical terms alone.

From the first days of quantum mechanics, then, physicists took sides between Heisenberg and Schrödinger. Niels Bohr and his Copenhagen colleagues shared Heisenberg’s discomfort with intuitive readings of the wave concept: they limited their “matrix” interpretation as if they were positivist philosophers, dismissed the intuitive appeal of wave mechanics as a sugar coating, and chose to take the mathematics of matrix mechanics neat. Schrödinger’s readiness to ignore the commitment of physicists to Newton’s “particle” view, and explore the implications of a wavelike, “noncorpuscular” account was, and still is, philosophically striking; while, regarded as an instrument of physical calculation, the wave equation had—and still has—an elegant utility independent of all interpretations. But, scientifically speaking, his achievement was less remarkable. Nothing he could explain in wave-mechanical terms was not explained just as well by Heisenberg’s more abstract theory. In the long run, many physicists found the “waves” of wave mechanics a distraction from the central issues of physics, in the same way that Maxwell’s “ether” had been fifty years before.

There followed the dispute in which Einstein, right up to his death, denied that the “state descriptions” of the physical world can be merely probabilistic: as in his famous remark, “God does not play with dice.” In this debate, Schrödinger consistently sided with Einstein; but his own contribution was limited to devising a single image describing what he called a “quite burlesque case”:

A cat is shut up in a steel chamber, together with the following diabolical apparatus (which one must keep out of the direct clutches of the cat): in a Geiger tube there is a tiny mass of radioactive substance, so little that in the course of an hour perhaps one atom of it disintegrates, but also with equal probability not even one; if it does happen, the counter responds and through a relay activates a hammer that shatters a little flask of prussic acid. If one has left this entire system to itself for an hour, then one will say to himself that the cat is still living, if in that time no atom has disintegrated. The first atomic disintegration would have poisoned it. The ¥-function [wave-function] of the entire system would express this situation by having the living and the dead cat mixed or smeared out (pardon the expression) in equal parts.

It is typical of such cases that an uncertainty originally restricted to the atomic domain has become transformed into a macroscopic uncertainty, which can then be resolved through direct observation. This inhibits us from accepting in a naive way a “blurred model” as an image of reality…. There is a difference between a shaky or not sharply focused photograph and a photograph of clouds and fogbanks.

How, Schrödinger asked himself, can one be happy with a theory that denies a physical meaning to the question, “On what conditions will [or will not] the cat be dead at the end of that hour?” Surely we cannot abandon the belief that the world of nature operates according to determinate processes, so that the cat’s fate is sealed in advance by factors that physicists should be able to discover.

This image, however, did not carry the argument further forward. Instead, some physicists argued, it gave a misleading tone of concreteness to a debate that belonged on an abstract, theoretical level. In the five papers of 1926, Schrödinger seems just about to have shot his bolt as a founder of quantum theory. Later, he was chiefly occupied less in expanding the explanatory power of quantum mechanics than in defending his “realistic” interpretation of wave mechanics against a growing body of critics. In the end, he and Einstein stood almost alone in arguing for unvarnished “realism” about the entities of quantum theory.

2.

Erwin Schrödinger was the only child of a Viennese businessman, a linoleum manufacturer with a private vocation as a painter or botanist. His mother, too, had frustrated ambitions as a violinist. At the Gymnasium, like his near contemporary Elias Canetti, Schrödinger was the bright student who stands apart from his classmates: a school photograph in 1900 shows an uncommonly elegant, self-satisfied-looking thirteen-year-old in a costume and pose that recall Octavian in Rosenkavalier. From 1906, at the University of Vienna, he again stood out from the crowd: younger physics students pointed to him with awe, calling him der Schrödinger. He gained his Ph.D. as quickly as he could, in May 1910.

There followed a year’s military service as a volunteer cadet in the Fortress Artillery—the uniform became him—and two years preparing for his Habilitation: this ended shortly before the 1914 war. Four years in the Austrian army, in Italy and in the meteorology service, still left time for physics: during this time, he published three short papers on relativity and quantum theory. But his central intellectual mission did not crystallize until his return to Vienna in late 1918. With the end of the war, the Allies blockaded the city. The Habsburg collapse, the 1919 influenza epidemic, and the resultant malnutrition led to a widespread mood of pessimism. In Schrödinger’s case, it was aggravated by three bereavements: in a couple of years he lost first his father, and later his mother and grandfather.

Even on active service, Schrödinger was strongly attracted by the works of Arthur Schopenhauer. Now, his reading of Schopenhauer and Lafcadio Hearn led him into Indian philosophy, and he was carried away by the Vedanta; he found intellectual support for the rest of his life in seeing his own “self” as part of a universal “mental reality.” At first, Walter Moore remarks, his Vedantic belief was “strangely dissociated” from his personal relations, and even more from his scientific work. Later, however, as his writing became concerned not only with physics, but with biology and epistemology, it was to play an increasing part in his thought.

Schrödinger’s early physics developed on more orthodox lines. His 1910 thesis had been “on the conduction of electricity on the surface of insulators in moist air”: an unadventurous, even pedestrian point of departure for a ground-breaking revolutionary. His originality was slow to make itself evident. He worked at established problems—the University of Vienna was never a major contributor to twentieth-century physics—and acquired his first reputation for work on color vision that followed in the footsteps of his teacher, Franz Exner. As a result, early in his career, a pattern emerges in his research that Walter Moore, who is himself a physical chemist at Cal Tech, Sydney, and Indiana, does not attempt to disguise.

Einstein started always from his own deep perplexities. Schrödinger had a knack for taking up half-worked-out problems from other people, finding comprehensive solutions for them, and presenting the results with great elegance. So his physics never had the overall coherence and continuity apparent in Einstein’s work. In this sense, both the major achievements for which we remember Schrödinger today dealt with “borrowed” problems. In his five papers on wave mechanics, he completed and generalized an explanation of the stability of quantum states that Louis de Broglie had already sketched. Likewise, in his book What is Life? (1944), which helped make the conception of a “molecular” biology plausible and interesting for younger physical scientists, he played impressive variations on themes that had been stated earlier by Max Delbrück, who was soon (with Francis Crick and James Watson) to develop them in fuller and more professional detail.

Anyone who writes about quantum theory for a general audience faces a difficult problem: its history is too closely linked to arguments about the technical standing of quantum mechanics to be summarized in nonmathematical language. Walter Moore tackles the problem in two ways. For a start, he chooses to present the main technical parts of his story at a high level of mathematical sophistication. In these parts, he gives a very fair assessment of Schrödinger’s work, but there are many passages of half a dozen pages or more that other readers will simply have to skip. In other places, he dilutes the technicalities by switching to Schrödinger’s personal life, and, in one respect above all, this personal narrative will catch the eye of the most untechnical readers.

Erwin Schrödinger’s sexual life was irregular and complex enough for any taste. He married in 1920, not long before his mother’s death, and the couple were happy for barely a year. They were childless, and did not divorce but stayed together on more distant terms: his wife was at his side when he died in 1961. Meanwhile, he was involved in a web of liaisons that makes Schnitzler look like a realist. This alone might have been nobody else’s business; but Schrödinger had an unhappy tendency to act irresponsibly toward the beautiful and intelligent young women who were overwhelmed by his charm and intellect. Promises of contraceptive care were frequently broken, and several of his lovers found themselves pregnant. His first teen-age lover had an abortion, but he took pride in the daughters born of later liaisons. Where possible, they were taken into the Schrödinger household, to be cared for by his long-suffering wife.

Some will wonder whether these “tales out of school” warrant as much concern as Walter Moore gives them. Schrödinger had no use for conventional morality, but it is not clear how this information helps us to understand his scientific career. There seem to be other reasons, too, why Moore pays so much attention to these episodes. They may shed some light on more general questions about Schrödinger’s motivation and character. No one who knew Schrödinger doubted his extreme charm; few of them, either, questioned the depth of his self-preoccupation.

In Moore’s biography this is seen in his professional career as well as in his political attitudes and philosophical positions. Schrödinger had throughout his life a flair for self-advancement. From 1920 on, he made his way up the academic ladders of three countries, from Vienna, Jena, Stuttgart, and Breslau to Zurich by late 1921, and in 1927, after his papers on wave mechanics, to the pinnacle, as Max Planck’s successor in Berlin. In this headlong career, he sometimes stayed only two or three months in a department before reacting to offers from an institution he saw as a higher rung. In the American academic world of the late 1950s and 1960s there were those who juggled institutions with similar skill, but Schrödinger knew how to play the appointments game consummately.

His later career had other troubling moments. In 1946, he wrote from Dublin to tell Einstein at Princeton about a new approach he had thought up to the problem of “unified field theory” which was to be the dominant interest of Einstein’s old age. Given only a bare outline of the approach, Einstein answered, twitting him—to his immense pleasure—by calling him ein raffinierter Gauner (“a clever rascal”). Soon after, Schrödinger lectured on the same subject at the Royal Irish Academy, and made sure that the Irish press reported it, the next day, as an “epoch making advance” going beyond anything done by either Arthur Eddington or Einstein himself. The science editor of The New York Times picked up this unprofessional piece of self-puffery, and reporters went to Einstein, who poured cold water on Schrödinger’s claims. Schrödinger’s friendship with Einstein then entered a long and chilly period. He wrote a vain placating letter, but soon found that he had made a public fool of himself. Yet there is no sign that he took the episode fully to heart, or understood how he had given colleagues offense: in his papers, there is only a folder of clippings and letters labeled Die Einstein Schweinerei—i.e., “the Einstein screw-up.”

What more nearly tripped Schrödinger up was his political naiveté. He had firm opinions about how particular people should best live, but no understanding of their social and political relations. His attitude to politics was uniformly dismissive: any ethics based on collective concerns he rejected as ersatz. When Hitler came to power in Germany in 1933, he was inconvenienced by the Nazis’ interference in academic life; but he never issued, or even joined, protests against their other activities. After a program was set up in Britain to support German academic refugees, however, he left Berlin for Oxford. He was not Jewish, and so under no real threat, but life in Berlin was becoming distasteful. The English were flattering, especially after his Nobel prize in the fall of 1933; and he happily accepted their support.

So little did he understand politics, however, that in 1936 he went back to Austria, to take a position at Graz, a university where Nazi partisans in the student body were unusually active. With the Anschluss in 1938, his lack of political enthusiasm soon led to his dismissal from this post and he had to return to Britain, this time as a genuine refugee. But he still did not register any disapproval of Hitler: rather, he tried to fend off the inevitable by writing for the university senate at Graz an open letter of “self-criticism” addressed to the Führer, which was quickly reprinted by the local newspaper.

The life of a charmer can be a charmed life. Schrödinger’s position seemed at last in real difficulty, when yet another lifeboat came in sight, from Dublin. Before becoming a political activist or the President of Eire, Eamon de Valera was a fine mathematician. In 1939, with the Second World War imminent, he saw the emigration of scholars from Central Europe as a chance to set up a new Institute for Advanced Studies, and invited Schrödinger to direct its School of Theoretical Physics: there he spent the entire war, and the first ten postwar years.

For so strongly apolitical a man, it was a convenient seat in the bleachers. Moore quotes a sardonic note in his diary for June 1941, on Hitler’s invasion of Russia:

The banner is turned around, the Proletariat of the world…now knows the reason for this war and will decide it. I don’t like it very much. They [the Proletariat] are a miserable people—but one must put up with them. Considered quite soberly, it is really a great joy to see the two wretches [Hitler and Stalin] in battle against each other.

Meanwhile, he continued with his existing research, built up a team of students and colleagues, and gratified his hosts by attempting to learn Erse. As a scientific center, however, Dublin was off the beaten track: and, after a war in which his colleagues elsewhere had entered into new friendships and collaborations, he was no longer at center stage. He took Irish citizenship in 1948, but in 1956 accepted a personal chair in Austria, where he divided his last five years between Vienna and the Tirol.

With Schrödinger more than with most other physicists, life and thought came together more clearly in philosophy than in physics proper. Moore uses four elements to define Schrödinger’s philosophical position:

His faith that the world is a universal consciousness, the idealistic elements in his view of science, his nostalgia for real waves as the ground of reality, and his growing estrangement from the advances in elementary-particle physics.

Speaking fifteen years after Schrödinger’s death, Paul Dirac recalled that they shared “a very strong appreciation of mathematical beauty. It was sort of an act of faith with us that any equations which describe the fundamental laws of Nature must have great mathematical beauty in them.”

A Pythagorean belief in the mathematical beauty of Nature has been quite common among modern theoretical physicists, but Schrödinger’s ideas about the mind were more idiosyncratic. His wave mechanics had broken down the internal dichotomy within classical physics, dividing matter and material particles from energy and fields; but his grasp of the external dichotomy, which separated matter and causal mechanism from mind and rational thought, was less certain. At this point, his belief from the Vedanta “that the underlying reality is a unity of Mind” helped to settle not merely his personal credo but also his views on the theory of knowledge.

His last epistemological manifesto (1960) began by declaring that we must “accept monism and reject dualism”; yet it at once went on, “Having opted for monism, we must choose between matter and mind.” As Ernst Mach had understood, you do not become a monist by choosing either matter or mind, and trying to explain the other away: a serious monism begins by questioning the meaning of the entire “mind/matter” distinction, and looks for a starting point that is neither “mental” nor “material” but neutral. Schrödinger left unquestioned the meaning of the entire “mind/matter” dichotomy. He was content to assert that our shared idea of the “real material world” is a product of human mental representation, and this in his eyes left its existence quite unclear. In a curious echo of Descartes, he concluded:

If we are to have only one realm, it must be the psychic since the psychic certainly exists (cogitat-est).

This entire argument, Schrödinger conceded, assumes a “hermetic separation of my sphere of consciousness from every other one.” This assumption he calls a psychic fact, which on his view is to be square with our common language and shared belief in a real external world by positing that, as individuals, “we are all different aspects of a [single mental] Unity.” Yet this is only one of the several epistemological conclusions available in the twentieth century: it stands at an opposite pole from the position of his Viennese contemporary, Ludwig Wittgenstein. For Wittgenstein, the fact that we can share a meaningful language and beliefs is a social fact: far from words being the personal property of isolated individuals, they draw their primary meanings from the public uses that they are given in collective situations. In this way, the public character of our epistemic criteria throws doubt on the image of individual human experience that Schrödinger regards as inescapable—that of being “hermetically separated consciousnesses.”

The weakness of Schrödinger’s epistemology lay in his inability to acknowledge anything but, on the one hand, the ideas of physics, and on the other, his own consciousness. Even the goal of his book What Is Life? was reductionist: not to broaden our grasp of biology by encompassing the historical and functional as well as the physical aspects of life, but to bring all the phenomena of (say) genetics within physical theory.

For him, the central problem in the theory of knowledge was, likewise, to explain the relation between the two distinct realms of physics and individual consciousness. As with the Irish atheist who is ready to argue that “There is no God, and the Virgin Mary is His Mother,” Schrödinger’s rejection of dualism accordingly left unquestioned the very belief that it claimed to escape.

Walter Moore’s life of Schrödinger is a portrait of a Viennese scientist who, lacking Einstein’s consistent concentration, executed some wonderful feats of theoretical imagination, but turned out to have too little grasp of larger (let alone political) realities. It will leave some readers with the feeling that, as a scientist and as a human being alike, there was less to Schrödinger than meets the eye. But the book has one special merit. In the material Moore has given us, we can find more for ourselves than the author decided to spell out. In choosing to write the book, Moore may not yet have been fully aware of his subject’s darker side but, despite reservations about Schrödinger’s personality, he projects a powerful picture of what it was like to be Erwin Schrödinger. It is a somewhat disturbing picture but, to his credit, he tells a full and candid story about an intellectual Narcissus who brought many of his personal and professional problems on his own head, and he recognizes many of the reasons why Erwin Schrödinger often found himself in personal difficulty.

Since Moore has raised questions about the “psychosexual histories” of Schrödinger and his wife, one last comment is in order. He writes of the strength of Schrödinger’s feelings for his father, but tells us little about his apparent coolness toward his mother: it is even unclear whether she was at his wedding. But in marriage, Erwin remained dependent on his wife Annemarie for “mothering” long after he had lost all sexual interest in her. One tantalizing item that Moore reports is Schrödinger’s bizarre suggestion that his own dislike of music—unusual in a theoretical physicist, and a Viennese—was a reaction to his mother’s death from breast cancer, which he thought was caused by mechanical trauma from her violin. More likely [Moore comments] he learned this distaste for music as a child, echoing his father’s lack of response to his mother’s talent.

This can hardly be the whole story. Nor can Moore’s suggestion that Schrödinger’s attitude to Vedanta was a purely intellectual one, a head trip, unconnected with the way he led his personal life and professional career. At the very least, Schrödinger’s view of human mental experience as “hermetically separated consciousness” leads one to raise again a longstanding question about the relations of solipsism in epistemology to narcissism in psychodynamics. Historians of ideas may wonder if it is a coincidence that two leading advocates of dualism, René Descartes and Isaac Newton, both lost their mothers before they were three, by death or by being put in foster care. We can at least ask if the belief that mental life necessarily goes on “behind closed doors” (Sartre’s Huis Clos)—i.e., the sense of being “locked up in” oneself and unable to participate effectively in collective human life—may not itself be a natural response to narcissistic injury.

Peter Medawar used to contrast the judgments different scientists make in deciding what fields of research to work in, asking themselves which questions are ripe for attack and show promise of being soluble in the next twenty years, and which questions (however intriguing) one should set aside as being out of reach. He likened this art to the art of choosing opponents in tennis or squash racquets. If you find people to play against who stretch your abilities but do not overwhelm you, you can improve your game quite rapidly; but if you always take on players who are much too good for you, you will be unable to learn from that experience. The scientists who are the most fascinating to study, as individuals, did not always succeed in telling the two sets of problems apart, and they did not, as scientists, achieve as much as they might have done, given only a better judged choice of subjects.

Both Albert Einstein and Erwin Schrödinger worked at the boundary between the scientifically soluble and the speculatively unattainable. The best measure of the difference between them is this. Even after Einstein’s initial annus mirabilis in 1905—when, in a single year, he launched the theory of relativity, explained the effect of light on the electrical properties of metals by the action of “particles” of light, or “photons,” and showed that the irregular motions of pollen grains in a test tube of water (observed by the botanist Robert Brown long before) result from single collisions between the grains and water molecules—he continued to produce important results in several branches of physics.

By contrast, Schrödinger never repeated his 1926 coup with the five papers on wave mechanics. Walter Moore does his best to make his subsequent work on physics appear as distinguished as that early triumph had been, but it is hard work. Certainly, he remained one of the major participants in the professional dialogue about quantum physics right up to 1940, and he deserved his reputation as one of the select few whose judgments had to be taken into account. But, increasingly, he was inclined to cross the line between problems that were soluble and questions whose answers were out of reach. The greatest merit of this biography may be that it shows us how easily this can happen, and how a scientist’s personality and nonscientific beliefs can help direct—or misdirect—his intellectual attention.