Difference between revisions of "Quantum mechanics"

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(needs much more, because it was {{vague}})
(Please explain what you think is inappropriate about the intro in talk. The M-M experiment does not have much direct bearing on QM.)
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'''Quantum mechanics''' is a branch of [[physics]] which was developed in the early 20th century as physicists adjusted their theories to the result of the [[Michelson-Morley experiment]]. According to quantum theory, energy comes in discrete amounts or packets (see [[quanta]]), rather than being infinitely divisible; this parallels the ancient concept of the [[atom]], viewed by the ancient Greeks as the smallest possible division of matter.
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'''Quantum mechanics''' is the branch of [[physics]] that describes the behavior of systems on very small length and energy scales, such as those found in [[atom]]ic and subatomic interactions.  It is essential for understanding certain concepts that [[classical physics]] cannot explain, such as the discrete nature of small-scale interactions, [[wave-particle duality]], the [[uncertainty principle]], and [[quantum entanglement]].  Quantum mechanics forms the basis for our understanding of many phenomena, including [[chemical reaction]]s and [[radioactive decay]], as well as all [[computer]]s and electronic devices today.
 
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Quantum mechanics describes the behavior of systems on very small length and energy scales, such as those found in [[atom]]ic and subatomic interactions.  It is essential for understanding certain concepts that [[classical physics]] cannot explain, such as the discrete nature of small-scale interactions, [[wave-particle duality]], the [[uncertainty principle]], and [[quantum entanglement]].  Quantum mechanics forms the basis for our understanding of many phenomena, including [[chemical reaction]]s and [[radioactive decay]], as well as all [[computer]]s and electronic devices today.
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==History==
 
==History==

Revision as of 08:39, 2 September 2008

Quantum mechanics is the branch of physics that describes the behavior of systems on very small length and energy scales, such as those found in atomic and subatomic interactions. It is essential for understanding certain concepts that classical physics cannot explain, such as the discrete nature of small-scale interactions, wave-particle duality, the uncertainty principle, and quantum entanglement. Quantum mechanics forms the basis for our understanding of many phenomena, including chemical reactions 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, Niels 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 by John von Neumann, Hermann Weyl, and others, after 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

Important contributors to quantum mechanics

External Links

For an excellent discussion of quantum mechanics, see: http://www.chemistry.ohio-state.edu/betha/qm/