Max Planck, at the University of Berlin, presented on December 14, 1900, before the German Physical Society, the solution to a problem that had resisted all classical explanation: black-body radiation. Classical physics models predicted that a hot object should emit infinite energy at very short wavelengths — the so-called "ultraviolet catastrophe" — an absurd prediction contradicting all experimental observation. Planck finds that the only way to make the mathematical formula match the experimental data is to assume that energy is not emitted continuously but in discrete packets — quanta — whose size is proportional to the frequency of the radiation, via a universal proportionality constant that would come to be known as Planck's constant (h). Planck himself initially regarded this quantization more as a convenient mathematical device than as a real physical property of light, and took years to accept its full implications. Albert Einstein would be the one who, five years later, took Planck's hypothesis seriously as a literal description of the nature of light in order to explain the photoelectric effect. Planck's quantum hypothesis is the founding act of all 20th-century quantum mechanics: without it there is no photoelectric effect, no Bohr atomic model, no solid-state electronics, no lasers, and none of the technologies that depend on quantum physics.