quantum mechanics: see quantum theory quantum theory, modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics.
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quantum mechanics

Branch of mathematical physics that deals with atomic and subatomic systems. It is concerned with phenomena that are so small-scale that they cannot be described in classical terms, and it is formulated entirely in terms of statistical probabilities. Considered one of the great ideas of the 20th century, quantum mechanics was developed mainly by Niels Bohr, Erwin Schrödinger, Werner Heisenberg, and Max Born and led to a drastic reappraisal of the concept of objective reality. It explained the structure of atoms, atomic nuclei (see nucleus), and molecules; the behaviour of subatomic particles; the nature of chemical bonds (see bonding); the properties of crystalline solids (see crystal); nuclear energy; and the forces that stabilize collapsed stars. It also led directly to the development of the laser, the electron microscope, and the transistor.

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 of devices we use every day.

Following are the important contributors to the foundation of quantum mechanics and the principles they uncovered.

   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