A Short Timeline of Quantum Mechanics, 1900-1962
1900 Johannes Rydberg refines the expression for observed hydrogen line wavelengths.
1900 Max Planck states his quantum hypothesis and blackbody radiation law1902 Philipp Lenard observes that maximum photoelectron energies are independent of illuminating intensity but depend on frequency.
1902 Theodor Svedberg suggests that fluctuations in molecular bombardment cause the Brownian motion.
1905 Albert Einstein explains the photoelectric effect.