Max Planck's Quantum Hypothesis
Max Planck proposed that energy is radiated and absorbed in discrete "quanta" rather than in a continuous wave. This resolved the ultraviolet catastrophe in black-body radiation and marked the birth of quantum theory.
Einstein and the Photoelectric Effect
Albert Einstein built upon Planck's work to explain the photoelectric effect, proposing that light consists of individual particles, later named photons, which carry discrete amounts of energy.
Bohr Model of the Atom
Niels Bohr introduced a model of the hydrogen atom where electrons travel in quantized orbits around the nucleus. They emit or absorb a photon only when making a transition between these orbits.
De Broglie Hypothesis
Louis de Broglie proposed that just as light can exhibit particle-like properties, matter (like electrons) can exhibit wave-like properties, establishing wave-particle duality for matter.
Matrix and Wave Mechanics
Werner Heisenberg, Max Born, and Pascual Jordan formulated matrix mechanics. Shortly after, Erwin Schrödinger formulated wave mechanics and the Schrödinger equation. Both were later proven to be mathematically equivalent.
Heisenberg Uncertainty Principle
Werner Heisenberg introduced his uncertainty principle, stating that it is impossible to simultaneously know both the exact position and exact momentum of a particle.