Max Carl Ernst Planck Biography

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World of Scientific Discovery on Max Carl Ernst Planck

It is rare in science that one can point to the work of a single individual as being truly revolutionary, marking the turning point between two very different eras in science. Isaac Newton and Albert Einstein are two such individuals. Max Planck is yet another. In fact, scientists now tend to refer to the centuries before Planck's discovery of the quantum as classical physics and to the years since as modern, or quantum physics.

Planck was born in Kiel, Germany, on April 23, 1858, into a famous family that included scholars, lawyers, and public servants. He obtained his early education at the Maximilan Gymnasium in Munich, where his family had moved when Max was nine. He entered the University of Munich in 1874, but transferred to the University of Berlin three years later. At Berlin, he studied under Hermann von Helmholtz and Gustav Kirchhoff. He received his doctorate in physics from Berlin in 1879.

Planck's first teaching appointment was at Munich in 1880. Five years later, he moved to Kiel University and, in 1889, he succeeded Kirchoff in Berlin as professor of theoretical physics. He remained in that position until his retirement in 1928 when he was succeeded by Erwin Schrödinger. Planck's early research dealt with optics, electricity, and mechanics. It was his work on heat, however, that led to his most famous discoveries.

By the 1890s, scientists had become aware of a problem in describing the gain and loss of heat by a black body. A black body is defined as any object that absorbs all frequencies of electromagnetic radiation. Classical theory permitted calculations of the amount of energy a black body should radiate at various frequencies. The theory indicated that maximum intensity should be observed at the higher frequencies. This large excess of radiation at higher frequencies was referred to as the ultraviolet catastrophe.

But experiments showed no such results. Instead, the intensity of radiation emitted by a black body increases in the low frequency range and reaches a maximum there. As the frequency increases, the intensity begins to decrease. A graph of intensity versus frequency thus shows a sharp rise until it reaches a maximum, and then a slow decrease.

Various researchers had attempted to find an explanation for this unexpected behavior. Wien had developed a law that explained the graph reasonably well for high frequencies, but that did not work well at low frequencies. John William Strutt Lord Rayleigh) devised a law that worked for low frequencies, but not as well at high frequencies.

By 1900, Planck had found a solution to the problem that explained the frequency vs. intensity graph over its whole range. That explanation was based on an entirely new concept of energy. Planck assumed that energy did not exist as a continuous variable that could take on any value at all, but as a flow of discrete packages, to which he gave the name quanta. By a fairly simple mathematical manipulation, he showed that the energy of any one quantum was equal to some integer (n) multiplied by a proportionality constant () and the frequency of the energy (), or, E = n. Thus, quanta with values of , 2, 3, and so on can exist, but fractional quanta are not possible. The constant of proportionality in the preceding equation has the numerical value of 6.62 x 10^-34 joule second and has become known as Planck's constant.

This formulation readily explains the frequency vs. intensity curve. A black body can radiate low frequencies easily because is small and a single quantum contains a relatively small amount of energy. But quanta of high frequencies require higher energy and are, therefore, less probable.

Planck's explanation was not well received by most physicists. As might be expected, it was too revolutionary to be understandable or useful to the practicing physicist. However, the quantum concept was soon applied with quite remarkable success, first by Einstein in explaining the photoelectric effect, and then by Bohr, in his quantum model of the atom. Gradually it became apparent that Planck's anti-logical explanation of energy was enormously fruitful. By 1918, the quantum concept had become so widely adopted that Planck was awarded the Nobel prize for physics for its discovery.

Still, Planck was never entirely convinced that quantum theory was, itself, fundamental to physical thought. With Einstein and others, he hoped that quantum theory might someday be incorporated into classical theory rather than developed as an alternative to it.

Planck remained active and creative until he was almost 90. After retiring from Berlin, he became president of the Kaiser Wilhelm Society, which was then renamed the Max Planck Society. He stayed in Germany after the rise of Adolf Hitler, attempting to protect German science from the excesses of Nazism. He largely failed in that effort and was forced in 1937 to resign from the society that had been named after him.

Planck's later years were filled with tragedy. After losing one son in World War I and twin daughters at birth, Planck also saw a second son executed in 1944 for taking part in a plot to overthrow Hitler. His own home and library were destroyed in an air raid on Berlin and, at the end of the war, he himself was rescued from a nearby wood only when American soldiers discovered who he was. He lived out the last years of his life in Göttingen, where he died on October 3, 1947.