The German physicist Max Karl Ernst Ludwig Planck, b. Apr. 23, 1858, d. Oct. 3, 1947, developed the concept of the quantum, or fundamental increment of energy, basic to quantum mechanics, and a cornerstone of modern physics. After receiving his Ph.D. from the University of Munich in 1879, Planck taught at the University of Kiel (1885-89) and the University of Berlin (1889-1926). His appointment at the latter institution included the directorship of the Institute of Theoretical Physics that was newly founded for him.

Planck began studying black body radiation in 1897 and discovered that at very short wavelengths it did not obey the distribution laws given by Wilhelm Wien. In trying to understand this spectrum using Wien’s laws, Planek ran smack into an "ultraviolet catastrophe". A black body would give off an infinite amount of energy at the ultraviolet end of the spectrum. That was impossible.

After working on this problem unsuccessfully for several years. he took a fateful step in late 1900 that he eventually called "an act of desperation." Planck cautiously proposed that, contrary to classical wave theory, matter emits and absorbs radiation in tiny discrete packets or bundles called "quanta" — not continuously, as everyone had assumed.

Initially Planck was not comfortable with this explanation and fully expected the idea to be disproved by further research. Instead quantum theory, which gained Planck the Nobel Prize for physics in 1918, was used by Albert Einstein to explain (1905) the photoelectric effect and by Niels Bohr to propose (1913) a model of the atom with quantified electronic states; the theory was later developed into quantum mechanics. Understanding the implications of quantum mechanics lead directly to the development of atomic energy and the semiconductor industry.

Planck mastered every aspect of physics from thermodynamics and electrodynamics to relativity and also wrote extensively on the philosophy of science.