I ran my own blog from November 2006 till October 2014. All posts are still online, but I don't have time to update it anymore. Please note that all images and media files have been removed when the backup was moved to a new host in early 2016. Enjoy!

Happy birthday, Max Planck!

22. april 2008

Max Planck was born 150 years ago on April 23, 1858 in Kiel, Holstein, Germany. He is considered to be the founder of quantum theory, and one of the most important physicists of the twentieth century.

When he was 9 years old his family moved to Munich. He enrolled in the Maximilians gymnasium school, where mathematician Hermann Müller taught him astronomy, mechanics and mathematics. He graduated early, at age 17. His physics professor advised Planck against going into physics, saying that everything important had already been discovered. Nevertheless he began his studies in 1874 at the University of Munich.

In April 1885 he became an associate professor of theoretical physics at the University of Kiel. Two years later he married Marie Merck, they had four children (Karl, Emma, Grete and Erwin). 1892 he finally became a full professor.

In 1894 Planck turned his attention to the problem of black-body radiation. It was still a mystery why the intensity of the electromagnetic radiation emitted by a black body depends on the frequency of the radiation and the temperature of the body. In 1900 he finally proposed his solution, claiming that electromagnetic energy could be emitted only in quantized form - the quantum theory was born.

Energy can only be a multiple of an elementary unit E = h ν, where h is Planck's constant and ν is the frequency of the radiation. The discovery of Planck's constant enabled him to define a new universal set of physical units (such as the Planck length and the Planck mass ), all based on fundamental physical constants.

In 1905 the completely unknown Albert Einstein publish the articles in a physics journal. Planck was among the few who immediately recognized the significance of the special theory of relativity. Thanks to his influence this theory was soon widely accepted in Germany.

In July 1909 Marie Planck died, two years later he married his second wife, Marga von Hoesslin. They had one child (Herrmann Planck). During the First World War Planck's oldest son, Karl, was killed in action at Verdun, and Erwin was taken prisoner by the French in 1914. Grete died in 1917 while giving birth to her first child.

Meanwhile Planck had been appointed dean of Berlin University, whereby it was possible for him to call Einstein to Berlin and establish a new professorship for him. Soon the two scientists became close friends and met frequently to play music together.

During the First World War Planck signed the infamous " Manifesto of the 93 intellectuals ", a polemic pamphlet of war propaganda, while Einstein retained a strictly pacifistic attitude which almost led to his imprisonment. In 1915 Planck revoked parts of the Manifesto, and in 1916 he signed a declaration against German annexationism.

In 1918 Max Planck was awarded the Nobel Prize in Physics for this discovery of the quantum theory, which should become the most successful physical theory of all times.

When the Nazis seized power in 1933, Planck was 74. He was critizised for continuing to teach the theories of Einstein and the Nazis started an investigation of Planck's ancestry. At the end of 1938 the Prussian Academy was taken over by Nazis, Planck protested by resigning his presidency. In January 1945 his second son, Erwin, was executed by the Gestapo because of his participation in the failed attempt to assassinate Hitler in July 1944.

Max Planck died shortly after the end of the war on October 4, 1947.