Max Planck

Major contributions

• Solved the blackbody radiation problem (1900) by proposing that energy is exchanged between matter and radiation only in discrete packets proportional to frequency, E = hf — the founding idea of quantum theory
• Introduced the Planck constant h, now recognised as one of the handful of truly fundamental constants of nature, exact by definition since the 2019 SI redefinition
• Derived Planck's law of blackbody radiation, correctly matching the observed spectrum across all wavelengths where earlier classical theories (the Rayleigh-Jeans law) failed catastrophically at short wavelengths — the so-called "ultraviolet catastrophe"
• Later became a key institutional supporter of Einstein and other quantum pioneers, and led the Kaiser Wilhelm Society (later renamed the Max Planck Society in his honour)

Named laws and equations

Law / Equation	Statement	Codex page
Planck-Einstein Relation	E = hf	View entry
Planck Constant	h = 6.62607015 × 10⁻³⁴ J·Hz⁻¹ (exact)	View entry

Career

Planck earned his doctorate at the University of Munich in 1879 and became a professor at the University of Berlin in 1889, where he worked for most of his career. His decisive 1900 breakthrough came from trying to find a mathematical formula that matched the experimentally measured spectrum of blackbody radiation across its entire range — something no existing classical theory could do. Planck found the correct formula essentially by mathematical trial and interpolation before he had a full physical justification for it, and only afterward derived it by assuming, as what he initially considered a mathematical convenience rather than a literal physical claim, that energy exchange between matter and the radiation field occurs in discrete quanta.

Planck remained in Germany through both World Wars; his son Erwin was executed by the Nazi regime in 1945 for involvement in the failed plot to assassinate Hitler, a personal tragedy that came at the end of a career during which Planck had also lost his eldest son in the First World War. Planck died in 1947, and the Kaiser Wilhelm Society, which he had led, was renamed the Max Planck Society in 1948 in recognition of his scientific and institutional legacy.

Key publications

• "Zur Theorie des Gesetzes der Energieverteilung im Normalspektrum" (1900) — the founding paper of quantum theory

Nobel Prize

Max Planck received the Nobel Prize in Physics for 1918 "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta."

Historical context

Planck was, by his own later account, a reluctant revolutionary — a physicist trained in and committed to classical thermodynamics, who treated the quantum hypothesis initially as a formal mathematical device to fix the blackbody spectrum rather than a literal claim about the physical world. It was Einstein's 1905 photoelectric effect paper that first treated quantisation as a real physical fact about light itself (not just a bookkeeping trick for energy exchange), a step considerably more radical than Planck himself was initially willing to take, and one Planck reportedly remained skeptical of for over a decade.

Planck's 1900 result is now recognised as the opening act of quantum theory, even though neither Planck nor his contemporaries fully grasped its implications at the time — the deeper reconceptualisation of matter and energy that quantum mechanics required only came together over the following 25 years, through the work of Einstein, Bohr, Heisenberg, Schrödinger, and others.