Erwin began his career in physics during the last peaceful years of the Danube monarchy. Old Franz Josef still retained the respect and affection of the lower and upper classes among his subjects, but his control over the bourgeois politicians and their nationalistic tendencies began to falter. The Hungarian leaders consistently placed the privileges of the great Magyar landowners above all else, and extorted special concessions as the price of loyalty to the throne. The annexation of Bosnia-Herzegovina in 1908 created a large population of disaffected Slavs and Muslims in the southern borderlands. The K & K structure was becoming more unstable, and as for a radioactive atom, the question was not if but when it would disintegrate.

Before the war

The chief of the general staff, Franz Conrad, was a persistent warmonger, urging the emperor to embark upon ‘preventive war’, one year against Serbia, the next against Italy. At the end of 1911, he was dismissed, not so much for meddling in foreign policy as for his affair with a married woman, Gina Reininghaus, which offended the religious sensibilities of the old emperor. After a year in disfavor, he was called back, but soon thereafter Franz Ferdinand, heir to the throne, was appointed General Inspector of all the Armed Forces. In May, 1913, the war machine was shaken by the revelation that Colonel Alfred Redl, one of the chiefs of military intelligence, was a Russian spy and a member of a homosexual coterie among the army officers. Since he had sold the Russians all the plans for a prospective eastern theater of war, a hasty revision of K & K strategy was required. Meanwhile, the two Balkan wars of 1912—1913 had left Serbia as a much stronger military force in the region. Even Conrad realized that it was now too late for preventive war.

President Gordon had hoped that Schrödinger would arrive in Oxford by October 21, so that he could matriculate and receive the M.A. degree that had been arranged for him (a requirement for the fellowship), but the VIIth Solvay Conference was to be held in Brussels, October 22 to 29, and he was obliged to attend this. The Schrödingers stayed at the elegant Hotel Gallia et Brittanique, and as usual Erwin arrived looking more like a Tirolean mountaineer than a distinguished scientist. Hilde March joined them there, and she wrote to Lindemann that she would be coming to Oxford with the Schrödingers, while her husband would be delayed. He replied that they were looking forward to seeing her and he hoped that she would ‘persuade Professor March to come over as soon as possible’.

Seventh Solvay Conference

The VIIth Council of Physics of the Solvay Institute, devoted to ‘Structure and Properties of Atomic Nuclei’, was opened by its President, Paul Langevin, on October 23 at the Université Libre de Bruxelles. Thirty-five of the most eminent workers in the field comprised the members of the scientific committee and the invited members of conference. Six members were from Cambridge. The German universities were represented by Walter Bothe (Heidelberg), Werner Heisenberg, Pieter Debye (Leipzig), and Lise Meitner who was still holding out at the Hahn Institute in Berlin. Marie Curie and Frederic Joliot, and both Maurice and Louis de Broglie came from Paris. The only American member was Ernest Lawrence from Berkeley. This was the first conference devoted to nuclear structure and nuclear reactions; with the discoveries of the neutron and positron, dramatic progress had been achieved in this field during the past few years and the results presented at the conference were important and exciting.

The discussions after the formal papers were extensive and lively, but Schrödinger took little part in them.

Heredity or environment, nature or nurture, there is no general solution to the problem of how much each contributes to the structure of a personality or the achievements of a person. It has been said that any medical student can become an adequate surgeon provided he or she is willing to work long hours, follow the hospital rules, and placate the nursing staff. In other words, this particular skill is not significantly determined by genetic factors. No such prescription can be applied to mathematical physics; original work in this field requires a special kind of native aptitude, the genes must be right. This is a necessary but not a sufficient condition. A potential Schrödinger may be lost to physics if he happens to be born in a Bengali village rather than a university town.

Many theoretical physicists have come from academic families, which, at least in Germanic countries, are considered to be upper middle class on the social scale. The fathers of Max Planck, Niels Bohr, Max Born, Wolfgang Pauli and Werner Heisenberg were all university professors, of Law, Biology, Anatomy, Colloid Chemistry and Byzantine Studies, respectively. Paul Dirac's father taught French at a Bristol grammar school, in the English context, a respected but lower-middle-class profession; Paul originally aspired only to be an engineer, but turned to pure theory after his ineptness in practical work became evident. Albert Einstein's lower-middle-class background was exceptional among German scientists. The Einsteins lived in an industrial suburb of Munich, and the early stages of Albert's scientific career were unusually precarious.

Thus the ancestry and family history of Erwin Schrödinger are relevant to the story of his life, even if the relative contributions of genetics and economics cannot be clearly separated. Fortunately his Aunt Rhoda compiled a history of his mother's side of the family; less is known about the Schrödinger side.

After five years of World War II, the end of the conflict and the defeat of Germany and Japan could be foreshadowed, so that the Irish ‘Emergency’ was becoming less anxious, although shortages of supplies and restrictions on travel were scarcely improved. Schrödinger no longer confined his intellectual work to unified field theory and he began to take an interest in a variety of other problems, including some of a more philosophical nature. Physically, as he neared the age of sixty, he enjoyed good health, despite annual attacks of respiratory illness, aggravated by the dismal Irish climate and excessive smoking. When springtime came, Dublin broke out with great masses of yellow daffodils for sale at almost every corner and as he strolled down O'Connell Street Erwin exclaimed in joy at the sight of all the pretty girls who had emerged from winter coats to warm themselves in the occasional midday sunshine.

Statistics again

From January to March, 1944, Schrödinger had returned to one of his first loves in science in a course of lectures on Statistical Thermodynamics at D.I. A. S. They were published in a small hectographed edition and later (1946) by the Cambridge University Press. In less than one hundred pages he covered the fundamentals of the subject with an insight and clarity that have never been equaled. The book is a distillation of his many years of creative work in the field, and one hears echoes of the passionate discussions of the twenties with Planck, Ehrenfest, and Einstein. He was pleased to learn that Max Born liked the little book on statistics, and wrote to him: ‘For I have no higher aim than to work out the beauty of science. I put beauty before science. Nitimur in vetitum [Ovid: we strive for that which is forbidden]. We are always longing for our neighbour's housewife and for the perfection we are least likely to achieve.’

Niels Bohr was fond of quoting ‘an old Danish proverb’ to the effect that ‘prediction is always difficult, especially of the future’. Schrödinger later described his decision to return to Austria in 1936 as a miscalculation of the political situation that was ‘an unprecedented stupidity’, but it would not have seemed so at the time. He was not satisfied with the quality of life in either Britain or America, and old friends like Fritz Kohlrausch in Graz and Hans Thirring in Vienna were urging him to return to his native land. Hans even offered to relinquish his Vienna post if Erwin preferred that one.

Nevertheless, Erwin knew that in going to Graz, he was stepping into a cesspool of Nazi activity. The university was a center for the Styrian Nazi party, whose leader was Armand Dadieu, professor of physical chemistry. More than half the students were active Nazis and they dominated the campus. The principal Graz newspaper, Der Tagespost, followed the Nazi line and the provincial Heimwehr was controlled by the party.

The Austrian situation

During the fifteen years that Schrödinger had lived abroad, the history of Austria had been marked by political strife between two major forces, the Christian Socialists or ‘blacks’ and the Social Democrats or ‘reds’. Antisemitism in Austria, with its Catholic culture, was more prevalent but less extreme than in Germany. The clerical party was traditionally antisemitic; for example, in 1933, its chairman, with the good German name of Czermak, announced that ‘the religious German must decisively reject baptism as an “entrance ticket” for Jews’. There were about 190 000 Jews in Austria, with 176 000 in Vienna (9% of population of city) where they were prominent in learned professions, the press, music and the arts. As in Germany, the universities were citadels of antisemitism and it was difficult for even distinguished Jewish scholars to obtain professorships.

In 1932, the clericals selected Engelbert Dollfuss as chancellor.

Soon after the end of the war, Schrödinger's friends in Austria began to explore various avenues for his return to his native land, but it was to prove a long and tedious process. As early as February, 1946, he agreed to accept a professorship at Vienna, provided he could find a suitable successor for his position at D. I. A. S. In April, the Austrian authorities advised that he should apply for a restoration of his professorship at Graz, and then they would arrange a transfer to Vienna, but he was not willing to do this without a more definite understanding.

The main problem was the continuing occupation of Austria by the four allied powers. In January, 1947, General Kurasov told General Mark Clark: ‘I expect there will be an Austrian treaty. We have done enough for Austria and it is time we got out.’ The winter of 1947 was unusually harsh and there were food riots in Vienna recalling those of 1919. An attempted communist coup in May did not succeed, and in June, Austria was included in the Marshall plan, receiving more dollars per capita during its first year than any other country. In February, 1948, communists took over control of Czechoslovakia, and Stalin showed no willingness to conclude an Austrian peace treaty.

Thus, although Schrödinger told his friends that he wished to return to Austria, he also made it clear that he had no intention of doing so while the threat of a Russian takeover remained. As the peace negotiations dragged on, they became increasingly acrimonious. In October, 1950, there was a second attempt at a communist putsch. Karl Renner, the socialist president, who in 1938 had advised his followers to vote for Hitler, protested to the British government: ‘You sacrificed the Austro-Hungarian Empire in 1919, and in 1938 you abandoned Austria for Czechoslovakia, which you then abandoned also. These are bad precedents.’

The situation at the Vienna Physics Institute was rather surprising.

The establishment of the Dublin Institute for Advanced Studies was due almost entirely to the efforts of one man, Eamon de Valera, the Taoiseach [prime minister] of Ireland. Dev, as he was called by friend and foe, was born in New York City in 1882, so that he was five years older than Schrödinger. His mother, Kate Coll, was an Irish servant girl, and his father, Vivion de Valera, a delicate Spanish artist. Eddie, their only child, was three years old when the father died, and he was brought to Ireland to be raised by his grandmother in a cottage at Bruree, County Limerick. As a schoolboy, mathematics was his best subject and he never lost his love for it.

Dev was always a devout Catholic, in fact, a daily communicant. At that time it was not easy for a Catholic to get a university degree in Ireland, since Trinity College Dublin (T.C.D.) was almost exclusively Protestant and the Royal University of Ireland gave examinations but no courses. In 1904, however, Dev received the B.A. degree from the Royal University, and the following year had his first opportunity to attend some good lectures in mathematics, given by Arthur Conway at the newly established University College Dublin (U.C.D.). From 1906 to 1908 he followed a course in mathematical physics by Edmund Whittaker, who was professor of astronomy at T.C.D. and Royal Astronomer at the Dunsink Observatory. In 1908, Dev joined the Gaelic League and began an intensive study of the Irish language, which became an intellectual love second only to mathematics. In 1910, he married his Gaelic teacher, Sinead Flanagan, and they had seven children.

In 1913 Dev became convinced that Ireland would never obtain any measure of self government without a show of force. He joined the Irish Volunteers, an underground military organization, quickly rising to commandant of one of the Dublin battalions.

In this book I have tried to tell something of the life of Erwin Schrödinger in such a way that even those who are not scientists may be able to understand the greatness of his work, the range of his ideas, and the kind of person he was. Montaigne wrote that ‘our life is divided betwixt folly and prudence: whoever will write of it only what is reverend and canonical will leave about the one-half behind’. In order to come closer to the whole of Schrödinger, I have included some account of his personal life. It is not thirty years since his death and thus many personal memories and sensitivities have not yet receded into history, a situation that is both a help and a hindrance for a biographer. It is possible to interview former friends and colleagues, but some important collections of letters and memoirs remain closed to research.

My book was made possible by the generosity with which Schrödinger's eldest daughter, Mrs Ruth Braunizer, made available many of the archives concerning her father's life.

Special thanks are due to Professor Ludvik Bass of the University of Queensland, Schrödinger's last postdoctoral student, who reviewed the entire manuscript; his scientific and historical comments have been invaluable.

Dr Linda Wessels of Indiana University provided many helpful suggestions. Professor James McConnell of the Dublin Institute for Advanced Studies never failed to answer my seemingly endless questions about Schrödinger's Dublin years. Dr Anthony Bracken reviewed several theoretical sections; Professor David MacAdam clarified some of the difficulties of color theory. My friend and neighbor, Robert Halporn, assisted in the decipherment of Gothic script and in explaining life in Vienna and the Austrian educational system. Dr John Fletcher helped with the study of Schrödinger's poetry. Professor Sture Nordholm provided translations of the Nobel Archives, and Dr Kirsten Streib translated some of Niels Bohr's letters from the Danish.

When Schrödinger returned from his summer holidays for the winter semester of the academic year 1925/26, he would have been quite unaware that he was on the verge of an outburst of creative activity that would change forever the world of physics. He had just reviewed and codified his personal world view and it was unlikely that his philosophical outlook would change in any revolutionary way. He had set down his belief in Vedanta and thus in Schopenhauer, through whom the Kantian a priori categories of space and time had been refurbished. During five carefree years in Switzerland, he had been insulated from both the hypocrisy of Vienna and the brutality of German politics. It would not be surprising if Swiss society, with its deep roots in economic security, had made him more conservative in other ways. His more unconventional beliefs, he kept to himself, and neither his inaugural lecture nor My World View was published at this time.

Hermann Weyl once said that Schrödinger ‘did his great work during a late erotic outburst in his life’. His marriage with Anny was at a high point of disagreement and tension, with constant talk of breakup and divorce. Their Zürich circle provided ample opportunities for amorous adventures, and if Erwin cared to venture outside the usual academic liaisons, both Weyl and Debye were available as competent guides to the uninhibited night life of the city.

Before the breakthrough

The semester began on October 15, and Schrödinger had his usual heavy teaching schedule, five hours a week on Theory of Electricity, two hours on Theory of Spectra, a weekly seminar for the electricity course, and the joint seminar with E.T.H., which met for two hours every fortnight. Pieter Debye suggested that Erwin should give a seminar talk on the de Broglie thesis, which had just been published in Annales de Physique.

Schrödinger had accepted an invitation from the University of Wisconsin to give a course of lectures early in 1927; they would pay $2500, which included an allowance for travel costs. He sent a paper to Physical Review which was published in the December, 1926, issue, so that the American physicists would have an excellent summary of his work on wave mechanics, and he would not need to review all the fundamentals when he lectured at American universities. Shortly before he left for America, he heard that he was a leading candidate for the succession to Max Planck at the University of Berlin.

American voyage

On December 16, Erwin and Anny attended a Christmas and Farewell Party held in the Physics Institute of the University. Edgar Meyer was master of ceremonies, and he recited one of the long doggerel poems for which he was famous. It included the verses:

Since Edgar Meyer always had some basis for his verses, it is likely that considerable urging was necessary to get Erwin to leave Zurich and thereby sacrifice his Christmas vacation.

They set out on December 18 for the new world, by train to Basel and Paris, and then the boat train to Le Havre where they boarded the French liner de Grasse for a ten-day voyage to New York. Erwin grumbled from the beginning. He found his fellow passengers distinctly unattractive ‘examples of the modern “society” that I usually manage to keep at arm's distance.’ At dinner he was seated between two painted and powdered ladies ‘beyond the canonical age’ and he found the ‘hard, ruthless expressions’ of their consorts equally repulsive.

In the midst of all the postwar turmoil and suffering, Erwin took no respite from his intensive research at the Physics Institute. He also filled notebook after notebook with commentaries based upon his reading of European and Eastern philosophers. It was in these dying days of the Danube Empire that he formed the foundations of his philosophy, which was to remain remarkably constant all his life. His interest in philosophy at this time was so intense that he even considered the possibility of devoting his intellectual life to that field. It would have been an inopportune decision, since philosophers now began to consider their subject as a self-contained discipline pursued by specialists for academic ends. Wittgenstein's Tractatus Logico-Philosophicus became the bible of the Vienna School of logical positivism. ‘What is history to me?’, he wrote, ‘Mine is the first and only world’. The task of trying to repair the wreckage of European civilisation may, however, have been hopeless even if help from the philosophers had been forthcoming.

Schopenhauer

Erwin read everything written by Schopenhauer. The luminous words of the philosopher of pessimism were perfectly suited to the world of 1919, and in that context may even have had a consoling effect, making some sense of Europe's four years of self destruction.

Arthur Schopenhauer (1788-1860) was born in Danzig, the son of Heinrich, a rich Hanseatic merchant, and Johanna, a romantic novelist. As a youth, he traveled widely, becoming fluent in English and French, so that his prose style acquired a lightness and clarity quite unlike the murky philosophic German of his times. His first education was that of a man of the world, only later did he obtain the usual academic credentials. He became a friend of Goethe, and in 1816 wrote a small book on color theory inspired by the ideas of the older man.

Between 1927 and 1936 no one had a greater influence on Bohr's thinking than Einstein. It was Einstein's unremitting criticism which provided the severest test of Bohr's interpretation of quantum physics, and which forced him to clarify and refine his arguments. The debate between Bohr and Einstein concerning the interpretation of quantum physics is generally recognised as one of the great intellectual disputes in the history of science. What was the nature of the disagreement between them, and what were the arguments with which each defended his position?

The fifth Solvay Conference, 1927

Einstein was not present at the Volta Centennial Conference at Como in September 1927, where Bohr first presented his theory of complementarity; Einstein first learned of Bohr's interpretation of quantum mechanics at the fifth Solvay Conference of Physics at Brussels in October 1927. In the discussion following Bohr's paper Einstein examined an imaginary experiment in which an electron passes through a slit in a diaphragm and impinges at a point on a hemispherical screen. This experiment, Einstein suggested, could be interpreted in either of two ways: the de Broglie–Schrödinger waves represent either (a) an ensemble of electrons spread out in space (but not an individual electron), or (b) a wave-packet corresponding to an individual electron. There is, he noted, a difficulty with the latter interpretation.

Now that Bohr's philosophy of quantum physics has been surveyed in detail, it is time to provide a general description of his philosophy that illuminates the details. The question which I wish to address, then is: what is the general philosophy, or philosophical point of view, that underlies Bohr's philosophy of physics? Can his philosophy be neatly categorised in terms of any well known philosophical position? Apropos his philosophy of physics in particular, the question of primary interest is: to what extent, if any, is Bohr's philosophy of physics realist? No simple answer to this question can be given: indeed, certain realist and non-realist components are subtly interwoven in his philosophy, and to unravel them we shall need a fairly refined conception of what constitutes a realist interpretation of physics.

Realism in the interpretation of physics

The basis of realism is the view that statements of a certain class predicate properties of real objects, the truth-values of these statements being determined by reality as it is independently of how it appears to us to be. This notion is captured in the following characterisation of what constitutes the adoption of a realist interpretation of a physical theory.