Percy Williams Bridgman | Biography

Percy Williams Bridgman was an experimental physicist whose principal focus was on developing apparatus for producing high pressures and on measuring the effects of high pressures on materials. His work in high-pressure physics won him the Nobel Prize in 1946. His work on the electrical and thermal conductivity of metals became important to industrial metallurgists and had implications for such diverse fields as solid-state physics, geophysics, and cosmology.

Percy Bridgman was born on April 21, 1882, in Cambridge, Massachusetts. His father, Raymond Landon Bridgman, was a writer and journalist as well as a devout Protestant. His mother was Mary Ann Maria Williams. Both came from established New England families. Bridgman entered Harvard in 1900. He graduated in 1904 and remained at Harvard to earn his M.A. in 1905 and his Ph.D. in 1908. He joined the Harvard physics department as a research fellow in 1908 and became an instructor in 1910, a full professor in 1919, Hollis Professor in 1926, and Higgins Professor in 1950. He retired from Harvard in 1954. His students included John C. Slater and J. Robert Oppenheimer.

Bridgman entered his field of study, high-pressure physics, by accident. In the course of working on his doctorate at Harvard, he stumbled upon a form of packing that allowed him to construct an assembly capable of pressures higher than ever attained before. The pressures he could create were limited only by the strength of the metal parts of his equipment.

As Bridgman developed equipment capable of producing higher pressures, he needed gauges to measure them. Bridgman had worked with pressure gauges since his student days at Harvard, where they were the subject of his Ph.D. dissertation, "Mercury Resistance as a Pressure Gauge." From this dissertation Bridgman in 1909 wrote three papers, the second of which described the construction of a scale that correlated the electrical resistance of mercury with pressure.

In his early work, Bridgman attained pressures of up to 6,000 kg/cm², which was twice the limit set by nineteenth-century French experimenters. In 1909 he pushed his equipment to the point of collapse at 7,000 kg/cm², twice that attained by any other experimenter at the time.

In 1911 Bridgman developed another pressure gauge, using manganin, an alloy of copper, manganese, and nickel. This gauge could measure pressures up to 13,000 kg/cm² and was more accurate than the earlier mercury-based gauge because it had a more linear (direct) response between pressure and electrical resistance.

Through a combination of meticulous craftsmanship and innovative metallurgical techniques Bridgman soon was able to reach pressures of up to 20,000 kg/cm². In his 40 years of research in high-pressure physics, Bridgman eventually attained pressures of up to 500,000 kg/cm².

The refrigeration industry was intrigued when Bridgman's high-pressure experiments produced "hot ice," a form of water that was solid at 80 degrees centigrade. Hot ice turned out to be of no practical value, but other entrepreneurs speculated that a similar process might produce artificial diamonds. In 1955, much of Bridgman's work on high-pressure physics became the basis of the development of synthetic diamonds by General Electric.

In 1914 the death of a colleague at Harvard forced Bridgman to teach a course in advanced electrodynamics, a field that had just been revolutionized by Albert Einstein 's work. For Bridgman and most other physicists of his generation, Einstein's relativity rendered obsolete their Newtonian beliefs in absolutes like time and space. Bridgman was so troubled by this development that in 1927 he wrote The Logic of Modern Physics , in which he confessed his despair over the disarray in the foundations of physics that resulted from relativity. He struggled to reconcile the classical physics of his own training with the revolutionary physics that emerged during his career. In his A Sophisticate's Primer of Relativity Bridgman spelled out his criticisms of Einstein's theory. For example, he felt that light was no more than the illumination of things, not, as relativity said, something that traveled. Bridgman doubted the constancy of the speed of light, and he searched without success for ways to verify through experiments Einstein's notions about light. Many aspects of relativity would continue to bother Bridgman until his death.

Bridgman was able to regain some measure of equanimity when he extracted from Einstein's work a way for physicists to interpret the world by maintaining contact with experience and not by searching for ideals like absolute time. Bridgman called this approach to physics operationalism. It was a method that scientists could use to distinguish what is physically real from what is not. Operationalism required scientists to define things with respect to how their physical qualities are measured. For Bridgman, operationalism implied that knowledge was not possible without some human presence.

Bridgman was also tripped up by another revolutionary idea: quantum mechanics. Werner Heisenberg's uncertainty principle, which states that it is impossible to know both the exact position and the exact momentum of a particle, forced Bridgman to concede that beyond a certain point in nature science has no place. Operationalism did nothing to resolve this dilemma, but as it turned out, the discussions of quantum mechanics were indebted to operationalism for their vocabulary.

Bridgman was fiercely individualistic and objected to any show of authority, particularly religious authority. He believed that science could liberate people and protect their freedom because it is a practice based on intellectual integrity that can help humankind to ignore false gods and subdue base urges and emotions. Science can do this, Bridgman believed, because it rests not on authority but on fact. During World War I he refused to get caught up in the intense patriotism that emerged in the United States.

In the spring of 1961 Bridgman was diagnosed with cancer. He finished A Sophisticate's Primer of Relativity and submitted a book review for Science before taking his own life August 20, 1961 at his Randolph, New Hampshire home. His complete scientific papers were published by Harvard University Press in 1964.