Quantum mechanics
From Pharmpedia
Quantum mechanics is a fundamental physical theory that extends, corrects and unifies Newtonian mechanics and Maxwellian electromagnetism, at the atomic and subatomic levels. It is the underlying framework of many fields of physics and chemistry, including condensed matter physics, quantum chemistry, and particle physics. The term quantum (Latin, "how much") refers to the discrete units that the theory assigns to certain physical quantities, such as the energy of an atom at rest (see Figure 1, at right).
Quantum mechanics is a theory of mechanics, a branch of physics that deals with the motion of bodies and associated physical quantities such as energy and momentum. It is a more fundamental theory than Newtonian mechanics, in the sense that it provides accurate and precise descriptions for many phenomena where Newtonian mechanics drastically fails. Such phenomena include the behavior of systems at atomic length scales and below (in fact, Newtonian mechanics is unable to account for the existence of stable atoms), as well as special macroscopic systems such as superconductors and superfluids. The predictions of quantum mechanics have never been disproven after a century's worth of experiments. Quantum mechanics incorporates at least three classes of phenomena that classical physics cannot account for: (i) the quantization (discretization) of certain physical quantities, (ii) wave-particle duality, and (iii) quantum entanglement. However, in certain situations, the laws of classical mechanics approximate the laws of quantum mechanics to a high degree of precision; this is often expressed by saying that quantum mechanics are "reduced" to classical mechanics, and is known as the correspondence principle.
Quantum mechanics can be formulated in either a relativistic or non-relativistic manner. Relativistic quantum mechanics (quantum field theory) provides the framework for some of the most accurate physical theories known, though non-relativistic quantum mechanics is also frequently used for reasons of convenience. We will use the term "quantum mechanics" to refer to both relativistic and non-relativistic quantum mechanics; the terms quantum physics and quantum theory are synonymous. It should be noted, however, that certain authors refer to "quantum mechanics" in the more restricted sense of non-relativistic quantum mechanics.
Most physicists believe that quantum mechanics provides a correct description for the physical world under almost all circumstances. It seems likely that quantum mechanics fails in the vicinity of black holes, or when considering the observable Universe as a whole. In these regimes, quantum mechanics conflicts with the predictions of general relativity, the dominant theory of gravity. The question of compatibility between quantum mechanics and general relativity remains an area of active research.
The foundations of quantum mechanics were established during the first half of the 20th century by Max Planck, Albert Einstein, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, Max Born, John von Neumann, Paul Dirac, Wolfgang Pauli and others. Some fundamental aspects of the theory are still actively studied.
Reference
http://en.wikipedia.org/wiki/Quantum_mechanics
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