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Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale (at the atomic level). Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certainties. Classical physics can be derived as a good approximation to quantum physics, typically in circumstances with large numbers of particles. Thus quantum phenomena are particularly relevant in systems whose dimensions are close to the atomic scale, such as molecules, atoms, electrons, protons and other subatomic particles. Exceptions exist for certain systems which exhibit quantum mechanical effects on macroscopic scale; superfluidity is one well-known example. Quantum theory provides accurate descriptions for many previously unexplained phenomena such as black body radiation and stable electron orbits. It has also given insight into the workings of biological systems.

Contents [hide]
1 Overview
2 History
3 Relativity and quantum mechanics
4 Attempts at a unified theory
5 Quantum mechanics and classical physics
6 Theory
6.1 Mathematical formulation
6.2 Interactions with other scientific theories
7 Example
8 Applications
9 Philosophical consequences
10 See also
11 Notes
12 References
13 External links



[edit] Overview
The word quantum is Latin for "how great" or "how much." In quantum mechanics, it refers to a discrete unit that quantum theory assigns to certain physical quantities, such as the energy of an atom at rest (see Figure 1, at right). The discovery that waves have discrete energy packets (called quanta) that behave in a manner similar to particles led to the branch of physics that deals with atomic and subatomic systems which we...