A perfect black box defeated classical physics
Heated walls change color as their temperature rises. Experiments mapped the spectrum of an ideal absorber and emitter, but existing formulas worked only in parts of the curve.
In 1900 Heinrich Rubens brought Max Planck new long-wavelength measurements. Planck found a formula that matched the full spectrum, then asked what microscopic assumption could produce it.
Diagram description
Static physics diagram: planck_energy_quanta.
Energy in portions
Planck had to let oscillators exchange energy only in multiples of
High-frequency portions are larger, preventing the infinite high-frequency energy predicted by classical theory.
Planck did not celebrate discontinuity. He treated quantization as a desperate mathematical step and hoped for a more classical explanation. Five years later Einstein pushed the idea onto light itself.
Revolutions are not always begun by people seeking one. Sometimes careful data corners a conservative thinker into writing the first line of a new language.