The branch of physics developed in the first part of the 20th century that was highly successful in explaining the behavior of atoms, molecules and nuclei. Developed between 1900 and 1930 and combined with the general and special theory of relativity, it revolutionized the field of physics. The new concepts, which were the particle properties of radiation, the wave properties of matter, quantization of physical properties and the idea that one can no longer know exactly where a single particle such as an electron is at any one instance were necessary to explain all of the new experimental evidence that was available at the time. For example, quantum mechanics explains the behavior of semiconductors which are used to make the myriad devices we use every day. See wave-particle duality.

   Year  Researcher    Quantum Mechanics Concept
   1901  Planck        Blackbody radiation
   1905  Einstein      Photoelectric effect
   1913  Bohr          Quantum theory of spectra
   1922  Compton       Scattering of photons
                        off electrons
   1924  Pauli         Exclusion principle
   1925  de Broglie    Matter waves
   1926  Schroedinger  Wave equation
   1927  Heisenberg    Uncertainty principle
   1927  Davison and
          Germer       Wave properties of electrons
   1927  Born          Interpretation of the
                        wavefunction