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'''Quantum mechanics''' ~~added to ~~is the branch of [[~~classical ~~physics]] ~~(in ~~that describes the ~~1920s) an understanding how particles behave inside ~~behavior of systems on very small length and energy scales, such as those found in [[atom]]~~s~~ic and subatomic interactions. ~~Quantum mechanics posits ~~It is essential for understanding certain concepts that ~~an ~~classical physics cannot explain, such as the discrete nature of small-scale interactions, [[~~electron]] (or any other [[sub~~wave-~~atomic ~~particleduality]]~~) behaves as both a ~~, the [[~~wave~~uncertainty principle]] , and ~~a ~~[[~~particle~~quantum entanglement]]. Quantum mechanics forms the basis for our understanding of many phenomena, including [[chemical ~~reactions~~reaction]]s and [[radioactive decay]], as well as all computers and electronic devices today.

==History==

While the roots of quantum mechanics can be traced to experiments performed in the 19th century, the theory began to emerge when [[Max Planck]] proposed a "quantum hypothesis" to explain the energy spectrum of [[black body]] radiation in 1900. In 1905, [[Albert Einstein]] suggested that light is composed of discrete packets (''quanta'') in order to explain the [[photoelectric effect]]. A decade later, [[Neils Bohr]] proposed a model of the atom in which [[angular momentum is quantized]]. Eventually, the mathematical formalism that became known as quantum mechanics was developed in the 1920s and 1930s, with [[Erwin Schrodinger]]'s discovery of wave mechanics and [[Werner Heisenberg]]'s discovery of matrix mechanics.

==The uncertainty principle==

As a result of the wave nature of the electron, the position of the electron can never be precisely known. Whenever it is attempted to be measured, knowledge of the electron's [[velocity]] is lost. Hence, there is an inherent uncertainty that prevents precisely measuring both the position and the momentum simultaneously. This is known as the [[Heisenberg Uncertainty Principle]].

==Applications==

An important aspect of Quantum Mechanics is the predictions it makes about the [[radioactive decay]] of [[isotopes]]. Radioactive decay processes, controlled by the wave equations, are random events. A radioactive atom has a certain probability of decaying per unit time. As a result, the decay results in an exponential decrease in the amount of isotope remaining in a given sample as a function of time. The characteristic time required for 1/2 of the original amount of isotope to decay is known as the "half-life" and can vary from quadrillionths of a second to quintillions of years.

==See~~:~~also=====Concepts in quantum mechanics===*~~[[Erwin Schrodinger]], ~~[[Schrodinger equation]]

*[[Heisenberg uncertainty principle]]

*[[Momentum (operator)]]===Important contributors to quantum mechanics===*[[Erwin Schrodinger]]*[[Werner Heisenberg]]*[[Neils Bohr]]*[[Albert Einstein]]*[[Max Planck]]

==External Links==

For an excellent discussion of quantum mechanics, see:

http://www.chemistry.ohio-state.edu/betha/qm/

[[Category:Quantum Mechanics]]

[[Category:Physics]]