23 April 1858, Kiel (Germany) - 4 October 1947, Göttingen (Germany)
Maximus Karl Ernst Ludwig Planck was a German physicist. Endowed with an extraordinary capacity for disciplines as disparate as the arts, sciences and letters, he finally opted for the pure sciences, and continued to study physics at the universities of Munich and Berlin; in this he had as teachers Helmholtz and Kirchhoff.
After obtaining his doctorate from the University of Munich with a thesis on the second law of thermodynamics (1879), he was successively professor at the universities of Munich, Kiel (1885), and Berlin (1889), in the latter of which he succeeded his former professor, Kirchhoff. He enunciated Wien's law (1896) and applied the second law of thermodynamics, formulating in turn the law of radiation that bears his name (Planck's law, 1900).
Throughout the year 1900 he managed to deduce said law from the fundamental principles of thermodynamics, for which he started from two assumptions: on the one hand, the theory of L. Boltzmann, according to which the second law of thermodynamics has a statistical character, and on the other hand, that the black body absorbs electromagnetic energy in elementary indivisible quantities, to which he gave the name of quanta (how many).
The value of these quanta had to be equal to the frequency of the waves multiplied by a universal constant, the so-called Planck constant. This discovery also allowed him to deduce the values of constants such as Boltzmann's and Avogadro's numbers.
Busy in the study of black body radiation, he tried to describe all its thermodynamic characteristics, and involved, in addition to energy, entropy. In accordance with L. Boltzmann's opinion that he would not be able to obtain a satisfactory solution for the equilibrium between matter and radiation if he did not assume a discontinuity in the absorption and emission processes, he succeeded in proposing the "Planck formula", which represents with accuracy the spectral distribution of energy for the radiation of the so-called black body. To arrive at this result he had to admit that the electrons could not describe arbitrary movements. Still, only specific privileged movements and, consequently, their radiant energies were emitted and absorbed in equal finite amounts, that is, they were quantized.
Planck's quantum hypothesis was a revolution in 20th-century physics, influencing both Albert Einstein (photoelectric effect) and Niels Bohr (Bohr model of the atom). The first concluded, in 1905, that the only valid explanation for the so-called photoelectric effect consists in supposing that in a radiation of a determined frequency, the energy is concentrated in corpuscles (quanta of light, currently known as photons) whose value is equal to the product of Planck's constant times that frequency. Despite this, both Planck and Einstein himself were reluctant to accept the probabilistic interpretation of quantum mechanics (Copenhagen school). His work was recognized in 1918 with the award of the Nobel Prize in Physics for the formulation of the quantum hypothesis and the radiation law.
He was secretary of the Prussian Academy of Sciences (1912-1938) and president of the Kaiser Wilhelm Gesellschaft of Sciences in Berlin (1930-1937) which, after World War II, adopted the name of the Max Planck Society. His private life was dominated by misfortune: he married twice, his four children died in tragic circumstances and his house was destroyed in 1944 during a bombing; Picked up by US troops, he was transferred to Göttingen, where he resided until his death.