01 / The world before
Thermal radiation did not fit classical predictions.
02 / The discovery
Planck introduced discrete energy quanta.
03 / The people
Planck and later generations of physicists.
04 / The obstacles
The theory required decades of testing and refinement.
05 / The world after
Quantum mechanics provided new accounts of matter and light.
06 / Why it still matters
Semiconductors and lasers draw on quantum physics.