Max Planck: The Father of Quantum Theory

Childhood in an Intellectual Family

Born on April 23, 1858 in Kiel, in the Duchy of Holstein (then under Danish rule), Max Karl Ernst Ludwig Planck (1858-1947) grew up in a family of intellectuals and jurists. His father, Julius Wilhelm Planck, was a professor of constitutional law, and his grandfather, Gottlieb Jakob Planck, was a theologian.

Educational journey:

• 1867-1874: Secondary studies at Maximiliansgymnasium in Munich
• 1874-1877: Physics studies at the University of Munich
• 1877-1878: Studies at the University of Berlin under Hermann von Helmholtz and Gustav Kirchhoff
• 1879: Defended his doctoral thesis on the second law of thermodynamics
• 1880: Obtained his habilitation with a thesis on equilibrium states of isotropic bodies

The Quantum Revolution (1900)

In December 1900, Planck presented his revolutionary theory of the quantum of action to the German Physical Society:

• Problem solved: the "ultraviolet catastrophe" in blackbody radiation
• Hypothesis: energy is not emitted continuously but in discrete packets (quanta)
• Planck's formula: \( E = h\nu \) where \( h \) is Planck's constant (\( 6.62607015 \times 10^{-34} \) J⋅s)
• Planck's law for blackbody radiation: $$ B_\nu(T) = \frac{2h\nu^3}{c^2} \frac{1}{e^{h\nu/kT} - 1} $$

This discovery marks the birth of quantum physics and earned him the Nobel Prize in Physics in 1918.

Major Contributions to Physics

1. Thermodynamics

Before his work on quanta, Planck made fundamental contributions to thermodynamics:

• 1879: Thesis on the second law of thermodynamics
• 1882: Concept of irreversibility in thermodynamic processes
• 1897: Work on entropy and its statistical interpretation
• Development of the notion of thermodynamic potential

2. Quantum Theory

After his 1900 discovery, Planck further developed quantum theory:

• 1906: Introduced the concept of quantum of action as a fundamental constant
• 1908: Formulated the hypothesis of light quanta (precursor to photons)
• 1911: First Solvay Conference on quantum theory
• 1913: Supported Niels Bohr's work on the hydrogen atom

3. Philosophy of Science

Planck was also interested in the philosophy of science:

• Reflections on the nature of physical reality
• Debates with Einstein on determinism and indeterminism
• Works on the relationship between science and religion
• Concept of "physical reality" independent of the observer

Academic Career and Engagements

Professional journey:

• 1885-1889: Privatdozent (lecturer) at the University of Munich
• 1889-1892: Associate professor at the University of Kiel
• 1892-1926: Professor of theoretical physics at the University of Berlin
• 1912-1938: Perpetual secretary of the Prussian Academy of Sciences
• 1930-1937: President of the Kaiser Wilhelm Society (precursor to the Max Planck Society)

Scientific and social engagements:

• Promotion of fundamental research in Germany
• Support for young physicists (including Einstein, Bohr, Heisenberg)
• Discreet resistance to the Nazi regime (protection of Jewish colleagues)
• Reconstruction of German science after World War II

Personal Life and Trials

Planck's life was marked by personal trials:

• 1909: Death of his first wife Marie Merck (died in childbirth)
• 1916: Death of his eldest son Karl in the Battle of Verdun
• 1917: Death of his twin daughters Emma and Grete from tuberculosis
• 1944: Destruction of his home in Allied bombings
• 1945: Death of his second son Erwin, executed for his involvement in the plot against Hitler

Despite these tragedies, Planck remained scientifically active until his death on October 4, 1947 in Göttingen.

Scientific Legacy

Planck's legacy is immense:

• Founder of quantum physics, basis of:
  • Quantum mechanics
  • Atomic and molecular physics
  • Solid state physics
  • Particle physics
• Posthumous honors:
  • The Planck constant \( h \) bears his name
  • The Max Planck Society for the advancement of sciences
  • The Max Planck Medal for theoretical physics
  • Asteroid (1069) Planckia
  • ESA's Planck satellite (2009-2013) for studying the cosmic microwave background

Einstein said about Planck: "He was a man to whom scientific truth was more precious than anything else, and whose personality could not be shaken by external difficulties."