Quantum Mechanics

Quantum mechanics deals with the interaction of matter and energy, with the assumption that energy is only released in discrete amounts, "quanta." It arose primarily to explain phenomenon that could not be explained by classical, or Newtonian physics. In this article, we will only cover quantum mechanics, not all of modern quantum theory, which extends the ideas of quantum mechanics into other areas of physics.

The first indications of quantum mechanics came in 1900, when physicists tried to explain the wavelength distribution of incandescent radiation. They were unable to find an answer in terms of classical theory, but Max Planck finally came up with the answer when he made the assumption that atoms may only emit of absorb energy equal to nhv, where n={1, 2, 3,...}, h is Planck's constant (6.626 x 10^-34 Joule-seconds), and v is the frequency of oscillation of the atom. This counterintuitive assumption seemed to have no basis, but faced with a formula that predicted results within a percent of experimental data, scientists accepted his assumption and searched for explanations, the result being modern quantum theory. (Planck's constant h determines the "graininess" of the universe. No energy can come in units smaller than hv, and this turns out to have implications for other properties too.)

While strange, quantum mechanics explains many phenomenon impossible to explain by classical physics. As stated above, the wavelength distribution of incandescent radiation was what led to quantum mechanics in the first place. Another phenomenon that tipped off scientists was the photoelectric effect, which led Einstein to propose that not only must atoms, but also light obeys quantum rules. (E=hv) Finally, another phenomenon discussed on this site caused by quantum effects is the electric discharge lamp, better known as neon light. Neon light comes only in certain wavelengths because it is produced when electrons release energy in quanta which determine the energy of the released photon. This is direct evidence for the quantum nature of radiation. (Why does incandescent light come in all wavelengths then? Incandescent light is produced by vibrating atoms, which are systems far more complex than a single electron. Thus they are able to emit many different energies because v can vary linearly, producing any E.)

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