Planck Quantizes Energy: Birth of Quantum Physics

Max Planck did not set out to revolutionize physics. He was trying to fix an equation. On December 14, 1900, the German physicist presented his theoretical derivation of the black-body radiation law to the German Physical Society in Berlin, introducing the concept of energy quanta that would overturn two centuries of classical physics and launch the quantum revolution. The problem was stubborn. Classical physics predicted that a heated object should radiate infinite energy at short wavelengths, a result so absurd it was called the "ultraviolet catastrophe." Experimental measurements showed radiation from hot bodies followed a specific curve that classical theory could not reproduce. Planck had been working on it for years, and by October 1900 he found an empirical formula matching the data perfectly. But he needed theoretical justification. His solution required a radical assumption: energy was not emitted continuously, as every physicist assumed, but in discrete packets he called "quanta." The energy of each quantum was proportional to the frequency of radiation, related by a new fundamental constant denoted h. The value, approximately 6.626 times ten to the negative thirty-fourth joule-seconds, became one of the most important numbers in physics. Planck himself was deeply uncomfortable with his discovery. He spent years trying to reconcile quantization with classical physics, viewing it as a mathematical trick rather than physical reality. Albert Einstein took the idea further in 1905, proposing that light itself was quantized into photons. Niels Bohr applied quantization to atomic structure in 1913, and by the 1920s Heisenberg and Schrodinger had built full quantum mechanical theories. Planck received the Nobel Prize in Physics in 1918. The constant bearing his name remains the foundation of quantum mechanics, governing everything from semiconductors to black holes.