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MAX LUDWIG HENNING DELBRÃCK 70 So this relatively affluent residential suburb after the war became almost a ghost town" (1). World War II also brought tragedy to the Delbrück family. Two Bonhoeffer brothers, Klaus (Max's brother-in-law) and Pastor Dietrich, two Bonhoeffer sons-in-law, and two von Harnack cousins, Ernst and Arvid, together with the latter's American wife, were executed by the Nazis as leading members of the Resistance. Max's brother Justus was imprisoned by the Nazis, and liberated after the fall of Berlin but ten days later was arrested by the Russians and died in a diphtheria epidemic in a Russian camp. The husbands of two of Max's sisters also were killed by marauding soldiers in the last days of the war. EARLY INTEREST IN SCIENCE Of all the many children in the Delbrück, Harnack and Bonhoeffer families, Max was the youngest. Moreover, none of his intimates, save one, had any knowledge of, or interest in, science. The exception was Karl Friedrich Bonhoeffer, 8 years his senior, who became a distinguished physical chemist and Max's mentor and lifelong friend. Max's main boyhood interests were astronomy and mathematics. In retrospect, some 40 years later, he considered that he chose astronomy as a means of finding and establishing his own identity in an intimate society of so many able and strong personalities, all of them older than himself; but only he was an astronomer, and proclaimed himself one during his last 2-3 years at the Grunewald Gymnasium. He read popular books on the subject, was the enthusiastic possessor of a 2-inch telescope, and sometimes woke the whole household with the loudest of alarm clocks in the small hours of the morning when he had an appointment with the stars! (1) Despite Max's nuisance value, his parents proved tolerant and even helpful, while his
MAX LUDWIG HENNING DELBRÃCK 71 knowledge of astronomy blossomed under the tutelage and friendship of Karl Friedrich Bonhoeffer. It thus became Max's intention to study astronomy at the university. In 1924, at the age of 171/2, he went first to Tübingen where Hans Rosenberg offered an introduction to astrophysics which was then in its infancy; he also took courses in mathematics and physics, but chemistry failed to attract him and he never learned this subject as a student. He spent only one semester at Tübingen and then moved for a semester to Berlin where he had free tuition because of his father's professorship there, and thence to Bonn and back to Berlin again until, in the summer of 1926, he finally settled at Göttingen for 3 years until he obtained his degree. Although Göttingen was at that time the center of excitement in theoretical physics, following Heisenberg's discovery of quantum mechanics in 1925, Max continued to be interested in astronomy and mathematics until his attempt to write a Ph.D. thesis on novae failed because, he admitted, the mathematics of astrophysical theory of the interior of stars was beyond him, while the relevant literature was in English which he did not know at the time. But in the effort he had had to learn a good deal of quantum mechanics which brought him into contact with some of the theoretical physicists, among them Max Born, Pasqual Jordan, Eugene Wigner and Walter Heitler. At this time he wrote a short paper (1929) providing formal mathematical proofs for a theorem that Wigner had used in the application of group theory to theoretical physics. Born, who was Professor of Theoretical Physics, thereupon offered Max a Teaching Assistantship, and Heitler suggested that he extend to lithium the quantum mechanical theory of the homopolar bond that had just been developed for
