Max Planck

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Max Planck
This article is about Planck, the German physicist. For the proposed European Space Agency artificial satellite, see "Planck (satellite)".

Max Karl Ernst Ludwig Planck (April 23, 1858October 4, 1947) was a German physicist who is considered to be the inventor of quantum theory.

Born in Kiel, Planck started his physics studies at Munich University in 1874, graduating in 1879 in Berlin. He returned to Munich in 1880 to teach at the university, and moved to Kiel in 1885. There he married Marie Merck in 1886. In 1889, he moved to Berlin, where from 1892 on he held the chair of theoretical physics.

In 1899, he discovered a new fundamental constant, which is named Planck's constant, and is, for example, used to calculate the energy of a photon. Also that year, he described his own set of units of measurement (such as the Planck length and the Planck mass) based on fundamental physical constants. One year later, he discovered the law of heat radiation, which is named Planck's law of black body radiation. This law became the basis of quantum theory, which emerged ten years later in cooperation with Albert Einstein and Niels Bohr.

From 1905 to 1909, Planck acted as the head of the Deutsche Physikalische Gesellschaft (German Physical Society). His wife died in 1909, and one year later he married Marga von Hoesslin. In 1913, he became head of Berlin University. For the foundation of quantum physics, he was awarded the 1918 Nobel Prize in Physics. From 1930 to 1937, Planck was head of the Kaiser-Wilhelm-Gesellschaft zur Frderung der Wissenschaften (KWG, Emperor-Wilhelm-Society for the advancement of science).

During World War II, Planck tried to convince Hitler to spare Jewish scientists. Planck's son Erwin was executed in January, 1945, for treason in connection with an attempted assassination of Hitler. Right after the end of World War II, Max Planck served once more as president of KWG from July 1945 to April 1946. After his death on October 4, 1947 in Gttingen, a successor organization of KWG was founded on February 28, [1948]] under the name Max-Planck-Gesellschaft zur Frderung der Wissenschaften (MPG, Max Planck Society for the advancement of science).


Life and work

Origin and youth

Planck came from a traditional, intellectual family. His paternal great-grandfather and grandfather were both theology professors in Gttingen, his father was a law professor in Kiel and Munich, and his paternal uncle was a judge.

Max Planck was born in Kiel on April 23, 1858 to Johann Julius Wilhelm Planck and his second wife, Emma Patzig. He had four siblings, two of whom were from his father's first marriage. In 1867 the family moved to Munich, where Planck attended high school, graduating early at age 16.


Planck was musically gifted: he played piano, organ and cello in addition to taking voice lessons and composing songs and operas. However, instead of music he chose to study physics.

The Munich physics professor Philipp von Jolly advised him against going into physics, saying, "in this field, almost everything is already discovered, and all that remains is to fill a few holes." Planck replied that he didn't wish to discover new things, only to understand the known fundamentals of the field and began his studies in 1874 in Munich. With Jolly Planck performed the only experiment of his entire intellectual career (studying the diffusion of hydrogen through heated platinum), but soon transferred to theoretical physics.

In 1877 he went to Berlin for a year of study with the famous physicists Hermann von Helmholtz and Gustav Kirchhoff and also the mathematician Karl Weierstrass. He wrote that Helmholtz was never quite prepared, spoke slowly, miscalculated endlessly, and bored his listeners, while Kirchhoff spoke in carefully prepared lectures, which were, however, dry and monotonous. Despite this he soon became close friends with Helmholtz. While there he mostly undertook a program of self-study of Clausius's writings, which led him to choose heat theory as his field.

In October 1878 Planck passed his qualifying exams and in February of 1879 defended his dissertation, "ber den zweiten Hauptsatz der mechanischen Wrmetheorie" (On the second fundamental theorem of the mechanical heat theory). In June 1880 he presented his habilitation thesis, "Gleichgewichtszustnde isotroper Krper in verschiedenen Temperaturen" (Equilibrium states of isotropic bodies at different temperatures).

Academic career

With the completion of his habilitation thesis, Planck became an unpaid private lecturer in Munich, waiting until he would be offered an academic position. Although he was initially ignored by the academic community, he furthered his work on the field of heat theory and discovered one after the other the same thermodynamical formalism as Gibbs without realizing it. Clausius's ideas on entropy occupied a central role in his work.

In April 1885 the University of Kiel appointed Planck an associate professor of theoretical physics. Further work on entropy and its treatment, especially as applied in physical chemistry, followed. He proposed a thermodynamic basis for Arrhenius's theory of electrolytic dissociation.

Within four years he was named the successor to Kirchhoff's position in Berlin - thanks to Helmholtz's intercession - and by 1892 became a full professor. In 1907 Planck was appointed to Boltzmann's position in Vienna, but turned it down to stay in Berlin. He retired on January 10, 1926, and the successor to his position was Erwin Schrdinger.

Black-body radiation

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Max Planck and Albert Einstein

In 1894 Planck turned his attention to the problem of black-body radiation, a problem that Kirchhoff formulated in 1859: How does the intensity of the electromagnetic radiation emitted by a black-body (a perfect absorber, also known as a cavity radiator) depend on the frequency of the radiation and the temperature of the body? The question had been explored experimentally, but the Rayleigh-Jeans law, derived from classical physics, failed to explain the observed behavior at high frequencies. Wilhelm Wien proposed Wien's law, which correctly predicted the behavior at high frequencies, but failed at low frequencies.

Planck interpolated between both laws using an assumption about the entropy, which led to the famous Planck black-body radiation law. This law describes the experimentally observed black-body spectrum very well; it was first proposed on October 19, 1900.

By December 14, 1900 he was ready to present a theoretical derivation of the law, using ideas from statistical mechanics, as introduced by Boltzmann. In order to solve the problem, he made the supposition that the energy could be treated as quantized: in other words, the energy radiated at a frequency could only be a multiple of <math>E = h \nu<math>, where h is Planck's constant (introduced already in 1899) and ν is the frequency of the radiation. At the time he described this assumption as a purely technical one, which he didn't actually think much of. Today this assumption, which goes against classical physics, is considered the birth of quantum mechanics and the greatest intellectual accomplishment of Planck's life.

Subsequently, Planck tried to grasp the meaning of the energy quantization. Other physicists like Rayleigh, Jeans, and Lorentz set Planck's constant to zero in order to align with classical physics, but Planck knew well that the constant had a precise nonzero value.

(to be continued)

External links and references


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