Percy Williams Bridgman

Physicist

• Born: April 21, 1882
• Birthplace: Cambridge, Massachusetts
• Died: August 20, 1961
• Place of death: Randolph, New Hampshire

American physicist

Bridgman vastly extended the range of high-pressure physics. Through his development of the philosophical notion of operational analysis, he aided his colleagues in coping with the new ideas of twentieth-century physics. His work contributed significantly to the coming of age of physics as a field of science in the United States.

Born: April 21, 1882; Cambridge, Massachusetts

Died: August 20, 1961; Randolph, New Hampshire

Primary field: Physics

Specialties: Thermodynamics; condensed-matter (solid-state) physics

Early Life

Percy Williams Bridgman was the only son of Ann Maria (Williams) Bridgman and Raymond Landon Bridgman, a professional journalist who wrote on social and political matters. During his school years, the family lived in Newton, Massachusetts—a suburb of Boston—where Bridgman attended public schools.

Bridgman entered Harvard College (now Harvard University) in 1900 and graduated summa cum laude with a degree in physics in 1904. He continued at Harvard as a graduate student, receiving his master’s degree in 1905 and his doctorate in 1908. By that time he was already drawn to studying the behavior of materials when subjected to high pressure. His doctoral dissertation was titled “Mercury Resistance as a Pressure Gauge.” On completion of his doctoral studies, Bridgman was first named research fellow, then instructor in physics at Harvard. He subsequently rose through the professorial ranks, never leaving Harvard for more than brief periods of military research or sabbatical leaves.

Life’s Work

Bridgman devoted himself single-mindedly to exploring high-pressure physics. Others had worked in this area before him, but he was able to attain much higher pressures than had any previous investigator. Starting with pressures of about 6,500 atmospheres, he was able, over the years, to reach pressures of nearly 400,000 atmospheres. (One atmosphere equals about 15 pounds per square inch.) His success can be attributed to his own early invention of a leak-proof pressure seal for the vessel in which his samples were placed. His vessel was made from much stronger materials that had only become available in the twentieth century, allowing him to build better equipment for his experiments.

The improvements in Bridgman’s laboratory setup allowed him to measure the effect of increasingly high pressures on the physical properties of virtually every substance he could lay his hands on. He studied, for example, variations in melting points, electrical resistivity, compression, viscosity, fracture strength, and polymorphism. The results that he published proved to be of great value to theoreticians in solid-state physics. His findings also aided geophysicists interested in regions beneath the Earth’s surface that are subjected to very high pressure caused by the weight of the material above. His results had important industrial application as well.

Bridgman possessed great mechanical ability, which he enjoyed using in designing, building, and manipulating his equipment. He never collaborated with others in research. All of his papers were published under his sole authorship and often used the first-person singular, unlike most scientific papers, which are written very impersonally. He put in long hours in his laboratory, arriving on his bicycle about 8:00 a.m., even on Saturdays, during the academic year. His success has been ascribed to a rare combination of ingenuity, drive, and efficiency. In 1946 he was awarded the Nobel Prize in Physics.

Bridgman’s experience as a physics teacher transformed him into a critic of physical theory and a philosopher of science. When charged with the responsibility of teaching thermodynamics and electricity and magnetism to students, he scrutinized the ways in which basic concepts in those fields were defined and used. His discomfort in the definitions of basic physics impelled Bridgman to undertake a study of dimensional analysis of the basic equations of physics and caused him to inculcate in his students a deeply critical, searching attitude in all of their subsequent study. Bridgman believed that, unfortunately, the thinking of his predecessors and contemporaries was marred by metaphysics.

Spurred by the introduction of new ideas in physics, such as relativity and quantum theory, and by the widespread dilemmas facing the physics community in the early twentieth century, Bridgman began composing The Logic of Modern Physics (1927). He said that he wrote this book primarily for himself, to organize and clarify his own thinking, which was in the tradition of physicists Ernst Mach and Albert Einstein. Meaningful concepts, he believed, were those that can be defined as a set of operations, either physical or mental, hence the term operationalism, which became uniquely associated with Bridgman. In brief, he believed that a concept is defined by its corresponding set of operations.

Bridgman’s operationalism received wide attention not only from physicists and other scientists but also from psychologists, sociologists, and philosophers. It continued to permeate his later writings in physics as well as other fields. In all, he published some sixty papers and six books on the philosophy of science and its implications for other areas of human endeavor and thought.

In addition to his primary efforts in physics and philosophy, Bridgman was active in the scientific efforts for both world wars. During World War I he worked on the development of sound-detection systems for antisubmarine warfare. During World War II he investigated the plastic flow of steel under high pressure and studied the compressibility of uranium and plutonium for the Manhattan Project, which was responsible for developing the atomic bomb.

Bridgman continued as an active member of the Harvard physics department and attempted, with little or no success, to promote operational thinking in the social sciences. He believed that many of the difficulties experienced by individuals and societies arose from a lack of clear thinking.

Bridgman remained physically active until shortly before his death by his suicide on August 20, 1961, at the age of seventy-nine, after he developed a crippling form of bone cancer.

Impact

Bridgman’s outstanding high-pressure investigations attracted worldwide attention, resulting in invitations to international conferences and culminating in his being awarded the Nobel Prize in 1946. Highly respected at home and abroad, Bridgman contributed significantly to the maturing of the American physics profession.

His own research was entirely experimental, but he carefully followed the theoretical developments in relativity and quantum physics that were taking place. His experiments led directly to the creation of synthesized diamonds by General Electric (GE). His operational approach to all physics was espoused by many colleagues. Generations of physics students at Harvard were influenced by his philosophical outlook, many incorporating it into their own teaching. Thus Bridgman’s influence on physics in the United States extended far beyond the confines of Harvard University. Through his articles, lectures, and books on social and philosophical topics, he reached a wide audience outside physical science.

Bibliography

Bridgman, Percy W. The Logic of Modern Physics. 1927. New York: Arno, 1980. Print. Bridgman’s first full-length book dealing with the philosophical question of meaning in physics and setting forth his “operational analysis.”

---. Reflections of a Physicist. 1950. Whitefish: Kessinger, 2010. Print. A collection of Bridgman’s short, nontechnical essays addressing scientific and social questions. His manifesto is reproduced here.

---. A Sophisticate’s Primer of Relativity. 1962. Mineola: Dover, 2002. Print. Bridgman’s final work, published posthumously, analyzing his comprehension of relativity as developed over his lifetime.

Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. New York: Cambridge UP, 2004. Print. Chronicles major developments in physics since 1901, the year the first Nobel Prize in Physics was awarded. Includes information about the work of Bridgman.