Conservative Revolutionary

The Dilemmas of an Upright Man: Max Planck as Spokesman for German Science

by J.L. Heilbron
University of California Press, 238 pp., $16.95

Max Planck
Max Planck; drawing by David Levine

The title of John Heilbron’s biography of the physicist Max Planck, The Dilemmas of an Upright Man, is well chosen. The chief characteristics of Planck were his integrity, his feeling for tradition, and his sense of duty. Yet throughout his adult life he faced conflicts, some of which involved reversing a stand he had taken on matters of principle; in other cases he pursued a futile struggle against inevitable disasters. Heilbron gives a very readable, and very balanced, account of the successes and disasters of this great physicist, without attempting to pass judgment. But the character of the man comes clearly through the narrative.

Planck’s work was the starting point of the quantum theory, one of the two great revolutions in twentieth-century physics. Yet he was a most unlikely revolutionary. Descended from a long line of professors of theology and law, he was deeply religious, but without belief in a personal god. He was patriotic, but never chauvinistic, and he deeply regretted one lapse in the war fever of 1914. In his science he was driven by an urge for order and unity; he regarded the edifice of physics as it then was with awe, and with the wish to complete, and not to rebuild it. Once he had formed an opinion he was slow to change it. In his many administrative functions he would prefer to act through quiet diplomacy, never through public stands or angry confrontation. He had an iron self-discipline and sense of duty, which enabled him to cope with enormous administrative burdens, and to carry on in times of the most appalling personal tragedies.

The discovery that had such revolutionary consequence was the “Planck law of radiation,” which described heat radiation. By the end of the nineteenth century it was known from observations that the color and intensity of the radiation filling a cavity in a hot body did not depend on the nature of the walls of the cavity, but only on the temperature. It was a challenge to physicists to find and explain the law determining this dependence.

Planck succeeded in finding a formula that fitted the observations accurately. Now the problem was to derive this formula from the general laws of physics. He had previously worked on thermodynamics, the science of heat, and had clarified the important concept of entropy, a measure of disorder. The concept of entropy is vital to understanding the difference between a body falling under gravity, and heat passing from a hot to a cold body. The first is reversible; if the body is elastic, like a tennis ball, it will bounce back to where it came from, whereas heat will never flow back from the cold to the hot body. This is expressed by saying that the entropy increases as the heat spreads, and that it can never decrease.

Planck now had to find how to express the entropy…

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