Nuclear Forces

The Making of the Physicist Hans Bethe

Silvan S. Schweber

• Publisher: Harvard University Press
• Year: 2012
• ISBN:
  9780674070127
• Topic: Tecnologia e ingegneria
• Subtopic: Biografie in ambito scientifico e tecnologico

On the fiftieth anniversary of Hiroshima, Nobel-winning physicist Hans Bethe called on his fellow scientists to stop working on weapons of mass destruction. What drove Bethe, the head of Theoretical Physics at Los Alamos during the Manhattan Project, to renounce the weaponry he had once worked so tirelessly to create? That is one of the questions answered by Nuclear Forces, a riveting biography of Bethe's early life and development as both a scientist and a man of principle.As Silvan Schweber follows Bethe from his childhood in Germany, to laboratories in Italy and England, and on to Cornell University, he shows how these differing environments were reflected in the kind of physics Bethe produced. Many of the young quantum physicists in the 1930s, including Bethe, had Jewish roots, and Schweber considers how Liberal Judaism in Germany helps explain their remarkable contributions. A portrait emerges of a man whose strategy for staying on top of a deeply hierarchical field was to tackle only those problems he knew he could solve.Bethe's emotional maturation was shaped by his father and by two women of Jewish background: his overly possessive mother and his wife, who would later serve as an ethical touchstone during the turbulent years he spent designing nuclear bombs. Situating Bethe in the context of the various communities where he worked, Schweber provides a full picture of prewar developments in physics that changed the modern world, and of a scientist shaped by the unprecedented moral dilemmas those developments in turn created.

1

Growing Up

What we achieve inwardly will change outer reality.

Plutarch

If you were not to find satisfaction in the search for knowledge, you would despairingly put your hands in your lap and say: It is too difficult for us humans.

Albrecht Bethe, 1899

This chapter recounts Hans Bethe’s childhood, until he entered university. It tells of his parents, of his home, of his Gymnasium experiences, and of his bout of tuberculosis. I have devoted a great deal of attention to the role played by his father, Albrecht Bethe, for a number of reasons. Albrecht was deeply committed to Darwin’s theory of evolution, and Hans grew up in an environment where describing how things came to be was a natural form of explanation and understanding. His first exposure to doing science was through an introduction to the extraordinary variety and complexity of living entities, entities that according to his ethologist father could only be understood in relation to their environment.

It is interesting to note that after he had won the Nobel Prize the mature Bethe had a second career as an astrophysicist. Astronomical observations have revealed an astounding variety of objects and phenomena populating the universe, many of which are yet to be analyzed and explained. Astrophysics has been described as “the realm of the many-body problem,” in which “individual behavior can never be considered in itself and is always seen through interactions with many particles.”¹ It may well be that Bethe’s interest in astrophysics and stellar evolution has its origin in Albrecht’s evolutionism. It is also the case that Bethe proved himself to be an outstanding astrophysicist.

Strassburg, Kiel, Frankfurt

Hans Bethe was born in Strassburg on July 2, 1906, and was christened in an Evangelical Lutheran church shortly thereafter. Strassburg, now Strasbourg, the capital of Alsace, was then part of Germany. Alsace and Lorraine had been ceded to Germany after France’s defeat in 1871. Hans’s father, Albrecht, was a physiologist who, at the time of Hans’s birth, held an appointment at the University of Strassburg as Assistent to J. Richard Ewald, a distinguished physiologist,² under whom he had obtained his Habilitation.³ Already Albrecht Bethe was recognized as an outstanding scientist then charting new directions in neurobiology.⁴

Albrecht Bethe was a tall, handsome, and quite remarkable man. He was born in 1872 in Stettin, the capital of Pomerania, the city where the Bethe family had lived since the sixteenth century. The Bethes who originally settled in Pomerania were Scottish Protestants who had migrated when Scotland was still Catholic. Albrecht was the youngest of the five children in the family.⁵ His father was a very successful doctor, a passionate beetle collector, but also a very strict disciplinarian. As a young boy Albrecht was sent to a humanistic Gymnasium and thus forced to learn Latin and Greek, subjects in which he had no interest and came to hate. At age fifteen he ran away from home and joined a circus. But juggling was not his forte, and so after six weeks he returned home to the deafening silence of his father, who didn’t speak to him for a month. Already as a teenager in Gymnasium he was a liberal in his political views, and he told Hans that “he and his friends went sometimes to political meetings, speaking against anti-Semites.”⁶ Failures in Latin and Greek kept him from being promoted to the next grade on four occasions. Thus he was twenty when he graduated from the Gymnasium. His love of animals led him to study zoology, first in Freiburg and then in Munich. His studies there made it clear to him that he was really interested in physiology, and in particular, in the neural mechanisms that determine and regulate animal behavior. He went to Berlin to study neuroanatomy with Wilhelm von Waldeyer and then returned to Munich, where he earned his doctorate in 1895 working with Richard Hertwig,⁷ carrying out extensive histological work on the central nervous system of the crab Carcinus maenas. He thereafter spent some time at the Naples Zoological Station.

The Naples experience was very important. The Stazione Zoologica had been founded in 1872 by the German zoologist Anton Dohrn, who had been a student of Ernst Haeckel. Haeckel was the remarkable and inspiring biologist who had disseminated Charles Darwin’s work in Germany.⁸ Dohrn became “an unwavering defender of evolutionary theory” and made the Naples station a mecca for evolutionists, the hub of a worldwide network of research facilities for studies in marine biology and an international model for laboratory research in morphology and physiology.⁹

During his stay in Naples Albrecht became a committed evolutionist. Understanding something meant being able to account for how that something came to be. Dohrn influenced Albrecht in another important way. He believed that the science of biology could not be confined to the laboratory or the museum but must include the study of organisms in their natural environments. He stressed the importance of the study of the habits and conditions of the lives of animals (Lebensweise der Tiere). This became Albrecht’s perspective, and he implemented this vision of biology when he became the editor of Pflügers Archiv.

After his stay in Naples and one in Heidelberg, Albrecht accepted the position of Richard Ewald’s Assistent in Strassburg.¹⁰ He there continued making anatomical and physiological investigations of the nervous system of invertebrates. Albrecht had an enormous capacity for work and was very productive in his histological research. He earned a medical degree (Dr. med.) in 1898 and one year later submitted his Habilitationsschrift (dissertation), becoming a Privatdozent. This gave him the right to teach physiology at a university.¹¹

Joseph Fruton in his book on research groups in the chemical and biochemical sciences in Germany at the end of the nineteenth century noted that although Albrecht could not be considered a biochemist, nonetheless his influence on that community was deep “because of his leading role in bringing together the younger members of various departments in the Strassburg medical faculty in a journal club that met frequently.”¹²

Hans’s mother, Anna, was born in Strassburg in 1876. She was the daughter of Abraham Kuhn, a professor of medicine at the Strassburg University Hospital. His specialty was diseases of the ears, nose, and throat. Neither of Anna’s parents was Alsatian. Abraham was born in Worms, Germany, where his quite well-off family owned vineyards and his father was a wine merchant. Abraham was the first member of the family to attend university. He went to Paris to study medicine, wrote a book in French on diseases of the ear, and thereafter settled in Alsatian-speaking Strasbourg, staying there after its annexation by Germany in 1871.¹³ He clearly was an unusually able and well-informed physician, for it was very difficult for a Jew to be appointed to a professorial position in a German university. Anna’s mother, Amalie Seligmann, was born in Karlsruhe into a very prosperous Jewish family of cloth merchants and bankers. The Kuhns were well on the road to total assimilation. Thus in 1893 they allowed Anna’s older sister, Bertha, to marry Carl Fitting, a German artillery officer. To do so she had to convert to Protestantism. At the conversion ceremony Anna also converted.¹⁴

As a child Anna was considered frail, so her parents decided not to send her to public school. Instead she was instructed with a half-dozen other girls by a private teacher, who taught them reading, writing, arithmetic, and some French. In her teens she went to the Strassburg Conservatory to study violin and singing and “became quite good at both.” As a young woman she began writing little sketches for the Strassburger Post that were well received by its readership. As she was quite pretty, very lively, and witty, she was courted by many of the young lieutenants stationed in the town. Her deportment concealed a highly intelligent, very talented, strong-willed and very capable woman.

Hans’s parents met at a social gathering of the faculty of medicine sometime after Albrecht had come to Strassburg. They married in October 1900 on the heels of a tragedy that had befallen Anna’s family: a month earlier, on September 14, Anna’s father had died of scarlet fever, and a week later her sister Bertha succumbed to the same illness. It was a traumatic experience for Anna.¹⁵ The first ten years of Albrecht and Anna’s marriage were seemingly happy. They had more than adequate financial resources, a modest part of which came from Albrecht’s salary as Assistent and from the students’ fee in the courses he taught as a Privatdozent.¹⁶ The major part of their income derived from Anna’s considerable dowry of 200,000 marks, which had been invested in bonds that paid regular interest until the end of World War I and the subsequent inflation.¹⁷

Hans recalled that “Mama loved music, sang and played the violin many evenings. She also began writing fairy tales for children. Papa was not musical but liked to hear music.” Albrecht excelled in the use of his hands—a necessary requirement to be a good neuroanatomist—and was quite gifted as a wood carver. He would often spend the evening carving pieces of furniture while listening to Anna sing or play the violin. He was physically active, and passionate about mountain climbing. But the foremost and central passion of his life was science—his laboratory and his scientific research.

In 1911 Albrecht had an operation to repair a hernia, which resulted in a blood clot in his leg. Medical practice at the time required patients with a thrombosis to stay in bed for an extended period; in Albrecht’s case this turned out to be over five months in a hospital. Hans marveled at his father’s patience, but also remembered that his father became somewhat religious during the episode. It took a long time to get the leg to function normally again. Only in the summer of 1915 after the family had moved to Frankfurt could Albrecht go for long walks in the nearby Taunus Mountains. But by the early 1920s he was again climbing moderate mountains.

A measure of Albrecht’s professional accomplishments is indicated by the fact that by 1900 Albrecht had published a monograph on the nervous system of the crab Carcinus maenas, subtitled “An anatomical-physiological experiment”;¹⁸ written a long review that presented a comparative study of the functions of the nervous system of arthropods; investigated the role of certain chemicals in ant colonies and bee hives that gave these insects the ability to find their way back to their homes;¹⁹ and written a very important, lengthy paper on whether one should attribute psychological qualities to ants and bees.²⁰ The work on arthropods had been carried out at the Naples Marine Biological Station. While there in the mid-1890s he had met Hans Driesch and had been introduced to his views on the plasticity of organisms. He also got to know Theodor Beer and Jakob von Uexküll there.²¹ The three of them wrote an influential paper—an elaboration of Albrecht’s paper on the inappropriate attribution of psychological traits to ants and bees—that recommended the use of a new, “objective” terminology in the sensory physiology of lower animals to replace anthropomorphic descriptions, and thus not prejudge the mental capabilities of the animals in question. They urged replacing “seeing” with “photoreception,” “hearing” with “audioreception,” “smelling” with “stibireception,” and more generally replacing “sense organs” with “reception organs” and “receptors.” Their paper played an important role in the history of behaviorism. Many psychologists were influenced by the paper and considered it “fundamental” in the development of “objective” psychological research in the period from 1900 to 1925.²² Albrecht’s professional standing can be gauged by the fact that already in 1901 he was identified in Baldwin’s Dictionary of Philosophy and Psychology as one of the eight authors of “important recent books on comparative psychology.”²³ The publication in 1903 of his General Anatomy and Physiology of the Nervous System made him an internationally known, widely respected physiologist, and its publication led to an invitation to be on the editorial board of the Journal of Comparative Neurology. Soon thereafter he was asked to join the editorial board of Pflügers Archiv für die gesamte Physiologie des Menschen und der Tiere, then the most prestigious and widely read physiology journal. In 1918, Albrecht became its co-editor and discharged that responsibility until his death in 1954.

Albrecht and Anna stayed in Strassburg until 1912 and had an apartment in Anna’s mother’s house. It had an enormous garden in which Hans remembered playing very happily. The house was located at Ruprechthauer Allee 59, off a boulevard a few blocks away from the Orangerie. The Orangerie is a beautiful park in the western part of the city, to which Hans was taken almost daily by his mother.

Hans was an only child. A bout of syphilis Albrecht had contracted before he and Anna were married affected their sexual relations, and Hans was only born six years after they were married.²⁴ Anna thereafter was very concerned about Hans’s health, and she remained very apprehensive as he grew up. She became overprotective and allowed him but few contacts with the outside world. Hans wore dresses until he was old enough to go to the toilet by himself. Anna also kept his hair long and curled until he was three and a half years old. Albrecht then decided “that he has to look like a boy” and took him to a barber. Anna shed bitter tears that day.²⁵

On the surface, relations between the parents were amiable, but Hans’s father would later tell him that there had been difficulties from the beginning of the marriage. Albrecht sublimated his marital relations in his work, and his professional successes must have made him content. After Hans was born, Hans’s obvious precocity and mathematical abilities gave Albrecht great joy. But, in part due to Albrecht’s wartime duties, it was only when Hans became a teenager that Albrecht began spending time with him, nurturing his potentialities. Anna, on the other hand, must have felt isolated and frustrated. Though she could sublimate her desires somewhat in her music and in her writing, she became deeply attached to Hans, and he became the focus and the center of her life.

One of Bethe’s earliest memories was being interested in numbers and playing with numbers. His numerical and mathematical abilities manifested themselves very early. Richard Ewald, the professor of physiology in whose laboratory Hans’s father was working, became a close friend of the family and Hans’s godfather.²⁶ Ewald took great interest in the little Hans and was fascinated by his love of numbers. One day, when Hans was four, Ewald asked him, “What is 0.5 divided by 2?” Hans’s answer, believing that Ewald needed the information, was “Dear Uncle Ewald, that I do not know myself!” A few days later, upon seeing Ewald, Hans ran to him across the wide boulevard through the thick of traffic and informed him triumphantly, “0.25!” Hans’s father told of Hans at age five sitting on the stoop of their house, a piece of chalk in each hand, taking square roots of numbers.²⁷ By the age of five Hans fully understood fractions and could add, subtract, multiply, and divide any two of them. In an early (undated) letter to his mother (probably when he was five years old and had just learned how to write in Gothic letters) Hans wrote:

Dear Mama,

. . . Today I have figured out—it took me about a half an hour—how many seconds there are in a year! There are 300015000 . . . I told Clara [their cook] She always forgets about the calendar, and for every day that she has not torn it off she has to pay me 10 Pfennig, and she already owes me 80 Pfennig . . .

100 000 000 greetings and

1 000 000 000 kisses

By the age of nine Hans was finding ever larger prime numbers and had made a table of the powers of two and three up to 2²⁰ and 3¹⁰ and had memorized them. When he was ten, he was introduced to algebra and later in life commented: “I became fascinated with algebra as I learned about it. I never was much interested in geometry.”²⁸

Hans started reading at the age of four and began writing in capital letters at about that same age. He developed a distinct mode of writing: he was left-h...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Contents
• Introduction
• 1: Growing Up
• 2: Maturing
• 3: Becoming Bethe
• 4: Beyond the Doctorate: 1928–1933
• 5: England, 1933–1935
• 6: Hilde Levi
• 7: Cornell University
• 8: The Happy Thirties
• 9: Rose Ewald Bethe
• Conclusion: Past and Future
• Appendixes
• A. The Bethe Family Genealogy
• B. Courses Taken at Frankfurt University
• C. A Brief History of the Genesis of Quantum Mechanics
• D. Courses Taken at Munich University
• E. Bethe’s Doctoral Thesis
• F. The Habilitationsschrift Defense
• Notes
• References
• Acknowledgments
• Index