The Dilemmas of an Upright Man

Max Planck and the Fortunes of German Science, With a New Afterword

J. L. Heilbron

• Publisher: Harvard University Press
• Year: 2000
• ISBN:
  9780674238046
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

In this moving and eloquent portrait, John Heilbron describes how the founder of quantum theory rose to the pinnacle of German science. With great understanding, he shows how Max Planck suffered morally and intellectually as his lifelong habit of service to his country and to physics was confronted by the realities of World War I and the brutalities of the Third Reich.In an afterword written for this edition, Heilbron weighs the recurring questions among historians and scientists about the costs to others, and to Planck himself, of the painful choices he faced in attempting to build an "ark" to carry science and scientists through the storms of Nazism.

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ESTABLISHING THE WORLD PICTURE

Max Planck, exemplar of the classical physicist, came from a line of pastors, scholars, and jurists. To go back no further than three generations, his great-grandfather Gottlieb Jakob Planck (1751-1833), a student of immediate disciples of Leibniz, was professor of theology for almost fifty years at the University of Gottingen. His Enlightenment ideals of rationalism and tolerance, reexpressed in late-nineteenth-century terms with God, not Christ, at the center of belief, grounded his great-grandson’s firm, liberal, ecumenical religion.

Gottlieb Planck’s example descended through his son, likewise a Gottingen theologian, and his grandson, Wilhelm Johann Julius Planck, who reversed the emphasis in the family’s fascination with church law and became a professor of jurisprudence. Wilhelm Planck taught until 1867 at Kiel, and then in Munich, where he died in 1900. His sixth child, Max, was born in 1858. Wilhelm’s second wife, Max Planck’s mother, came from a family of pastors. She is said to have been a lively, even passionate, woman. Planck remained attached to her until her death, at the age of ninety-three, in August 1914.¹

Planck’s strong ties to his family extended to his aunts and cousins, with whom as a boy he shared the subdued amusements of the children of Wilhelmian professors, lawyers, clerics, and high government officials. A few glimpses of this life can be caught through letters: summers at the Baltic resort of Eldena, which he remembered as the paradise of his childhood; croquet on the lawn; evening readings from the novels of Sir Walter Scott; skeet shooting; plays; musicales.² We see Planck as an earnest young man exchanging impressions of life with equally earnest friends, who wrote out their thoughts for two weeks in turn in a large book that has not survived. There were trips to Austria and Italy, a courtship that won a banker’s daughter, Marie Merk, and excursions to an uncle’s hunting lodge in East Prussia.³

In 1885, on one of these excursions, Planck met a man six years his junior, a student of physics whose experimental and theoretical work was to be the starting point of his own most important contribution to science. The young man was Wilhelm Wien, son of a Prussian landholder, who became and remained a friend and collaborator of Planck’s for over forty years. Their long friendship and shared professional interests did not extend to political alliance. The Plancks, although conservative on an ordinary scale, may appear almost liberal in comparison with the reactionary and chauvinistic Wiens, who thought the firing of Bismarck the greatest disaster in German history and regretted that the emperor lacked the power to destroy his grandmother Victoria’s nation of shopkeepers. Planck’s father did not approve Bismarck’s policy of annexation, and neither father nor son would have countenanced a preventive war against England.⁴ And Planck regarded himself as more liberal politically and socially than most of his family.⁵ But he was no more a social than a scientific revolutionary. A conservative in the root meaning, his particular effectiveness lay in his ability to adapt to, and even direct, current realities while saving, and acting on, traditional values.

Planck was not a genius. His teachers at the Maximilians-Gymnasium in Munich ranked him near, but never at, the top of his class: fourth of twenty-eight in 1868-69, then fifth of thirty-seven, eighth of twenty-three, third of twenty-one, fourth of nineteen. He did well in everything—languages, mathematics, history, music—and was extremely diligent and dutiful, but his teachers noted no special brilliance or aptitude, except in his personal qualities. They esteemed the quiet force of his personality, his shy strength of character, and they judged him to be, “deservedly, the favorite of his teachers and classmates.”⁶

Planck’s success in physics, for which he always thought he had no particular gift,⁷ and in his many other intellectual and administrative activities came from a long absorption in the material and a slow maturing of ideas. He did not run after novelties (“for by nature I am peaceful and disinclined to questionable adventures”) or respond to them spontaneously (“for unfortunately I have not been given the capacity to react quickly to intellectual stimulation”).⁸ He expressed astonishment at the ability of others to pursue several research lines simultaneously; as he wrote Arnold Sommerfeld, a contemporary theoretical physicist and long-time friend, he found it very difficult “to leave a subject quickly after I’ve worked my way into it and to take it up [again] quickly at a favorable opportunity.”⁹ “Quickly” was not his speed. But once Planck had mastered something, he understood it with that force and clarity of intellect that, according to Descartes, are our best guarantee of the truth of our opinions.

Planck’s confidence in himself and his ideas increased in step with Prussia’s triumphs on the battlefield and with the new Reich’s rise to dominance among the European nations. Although personally the most modest of men, Planck identified his own development so fully with Germany’s that the preservation of its cultural capital was inseparable from the preservation of his personal values and professional life. Over all these values stood the ideal of unity, which in the political sphere inspired the creation of the Wilhelmian empire and in the cultural sphere inspired belief in the interconnectedness of all respectable branches of learning. Planck’s pride in imperial Germany and his commitment to the academic ideal of the unity of knowledge were the pillars on which he raised his science policy.

Respect for law, trust in established institutions, observance of duty, and absolute honesty—indeed sometimes an excess of scruples—were the hallmarks of Planck’s character. His modesty in the face of his virtues, his renown, and his authority were frequently remarked; his contemporaries respected the man as much as they admired the scientist. To take but one example, when his longtime colleagues at the Berlin Academy observed the fiftieth anniversary of his doctorate in 1929, they praised not only his science but also, what is less common among academics, “the spotless purity of his conscience.”¹⁰ Planck valued a clear conscience as the greatest blessing a human being can enjoy.

The inner grace of clarity of conscience may appear to the outside world as a great impediment to change of mind. One of Planck’s students, Walther Meissner, had the impression that Planck never was “swayed by the opinions of others, not only in science but also in human relations.” His clear conscience was the only compass he needed. Planck once described to his student and successor, Max von Laue, his way of fixing his direction: “My maxim is always this: consider every step carefully in advance, but then, if you believe you can take responsibility for it, let nothing stop you.”¹¹ Planck of course did change his opinions, and on important matters, but he did not change them easily.

It was not his stubbornness or his probity that made Planck the chief spokesman for German science between the world wars, although he needed both, and much patience too, in his dealings with colleagues and bureaucrats. Planck’s domestic power derived from his reputation as a German natural philosopher who had changed the course of international science.

Planck’s Formula

Planck’s upsetting of physics, which dates from the turn of the century, resulted from a compromise on his part, and even a capitulation. It followed the uncomfortable realization that he could not solve a problem on which he had worked for several years in the terms in which he had conceived it. The problem might seem scarcely worth the attention, much less the discomfort, of a grown man. Planck had set himself the task of calculating from first principles the relative intensity of each color in the radiation emerging from a small hole in a special electric oven or cavity. Very loosely put, he wanted to be able to compute the tints (“red hot,” “white hot,” etc.) of the inside of a furnace for any assigned temperature.

There were two dissimilar reasons for desiring to know the color intensities, or energy distribution, of the cavity radiation. Fundamental and plausible arguments showed that at equilibrium the distribution does not depend on the size or shape of the cavity or on the material of its walls. A formula for the distribution would provide, for a unit volume of the cavity, a specification of the energy carried by the light waves of each color. The formula would consequently contain only the temperature, the length of the waves (a measure of color), and one or more “universal constants,” the same for all cavities, colors, and distributions. For Planck, finding the formula meant discovering a relationship of very general theoretical interest, something “independent of special bodies and substances, which will necessarily retain its importance for all times and cultures, even for nonterrestrial and nonhuman ones.”¹²

A second reason for concern with cavity radiation was entirely practical. The equilibrium distribution maximizes the amount of heat (longer wavelengths) for a given amount of light (shorter wavelengths). Hence the formula Planck sought described the worst possible source of illumination, and so could serve as a zero-point standard for rating new electric lamps. Accordingly, the Physikalisch-Technische Reichsanstalt, the imperial bureau of standards, took an interest in measuring the equilibrium distribution of cavity radiation. In 1896 Wilhelm Wien and others in the Reichsanstalt’s physics department put together an expensive empty cylinder of porcelain and platinum and recorded the color distribution of radiation allowed to escape from a hole in one of its ends. They worked primarily with shorter wavelengths, from the near infrared into the violet. At the Berlin Technische Hochschule, another of Planck’s close associates, Heinrich Rubens, operated another oven and pursued the measurements into the deep infrared. A good many empirical formulas were concocted, which more or less fit the facts. For a time a semitheoretical formula proposed by Wien in 1896 seemed the best.¹³ Planck set out to derive Wien’s formula from the basic laws of electro- and thermodynamics.

Because the equilibrium distribution does not depend upon the nature of the walls, Planck was free to model them in the most convenient manner. He represented cavity walls as a collection of “resonators” and each resonator as a massless spring with an electric charge at its end. The springs come in all possible stiffnesses and therefore can oscillate at all possible frequencies. Heating the walls puts the springs in motion; the accelerating charges radiate energy into the cavity in accordance with Maxwell’s electrodynamics and also absorb colors with whose waves they resonate; equilibrium eventually sets up, in which all the resonators of a given frequency absorb as much energy from the cavity radiation as they put into it.

Maxwell’s equations tell, or rather then told, everything about the emission, absorption, and propagation of radiation from the resonators, but they said nothing about the energy distribution at the ultimate equilibrium. Planck thought that by making a special assumption relating the average energy of the resonators to their entropy he could obtain Wien’s formula. (The physical significance of entropy, a favorite concept of Planck’s, will occupy us presently.) His optimism was rudely shattered by criticism from the world’s authority on such problems, Ludwig Boltzmann, who had studied in detail the equilibrium and the approach to equilibrium of gases. Although Planck had not approved Boltzmann’s gas theory, he admired its author;¹⁴ he accepted the criticism Boltzmann drew from his theory, found another special assumption about entropy and energy, and rederived Wien’s formula. That was in 1899. Since the formula still fit the facts, the j...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Preface
• Abbreviations
• 1 Establishing The World Picture
• 2 Defending The World Picture
• 3 Doctor of Science
• 4 In Shipwreck
• Afterword
• Bibliography
• Index