Quantim Mechanics is abranch of mathematical physics that deals with the emission and absorption of energy by matter and with the motion of material particles. Because it holds that energy and matter exist in tiny, discrete amounts, quantum mechanics is particularly applicable to Elamentry Pprticlesand the interactions between them. According to the older theories of classical physics, energy is treated solely as a continuous phenomenon and matter is assumed to occupy a very specific region of space and to move in a continuous manner. According to the quantum theory, energy is emitted and absorbed in a small packet, called a quantum (pl. quanta), which in some situations behaves as particles of matter do; particles exhibit certain wavelike properties when in motion and are no longer viewed as localized in a given region but as spread out to some degree. The quantum theory thus proposes a dual nature for both waves and particles, with one aspect predominating in some situations and the other predominating in other situations. Quantum mechanics is needed to explain many properties of matter, such as the temperature dependence of the specific heat of solids, as well as when very small quantities of matter or energy are involved, as in the interaction of elementary particles and fields, but the theory of Relativity assumes importance in the special situation where very large speeds are involved. Together they form the theoretical basis of modern physics. (The results of classical physics approximate those of quantum mechanics for large scale events and those of relativity when ordinary speeds are involved.) Quantum theory was developed principally over a period of thirty years. The first contribution was the explanation of blackbody radiation in 1900 by Max Planck, who proposed that the energies of any harmonic oscillator, such as the atoms of a blackbody radiator, are restricted to certain values, each of which is an integral (whole nu
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