Quantum

"Quanta" redirects here. For other uses, see Quantum (disambiguation).

In physics, a quantum (plural: quanta) is the minimum unit of any physical entity involved in an interaction. An example of an entity that is quantized is the energy transfer of elementary particles of matter (called fermions) and of photons and other bosons. The word comes from the Latin "quantus", for "how much." Behind this, one finds the fundamental notion that a physical property may be "quantized", referred to as "quantization". This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. There is a related term of quantum number.

A photon, for example, is a single quantum of light, and may thus be referred to as a "light quantum". The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general.

As incorporated into the theory of quantum mechanics, this is regarded by physicists as part of the fundamental framework for understanding and describing nature at the infinitesimal level, for the very practical reason that it works. It is "in the nature of things", not a more or less arbitrary human preference.

Beyond electromagnetic radiation

While quantization was first discovered in electromagnetic radiation, it describes a fundamental aspect of energy not just restricted to photons.

From the experiments, Planck deduced the numerical values of h and k. Thus he could report, in the German Physical Society meeting on December 25,1 a.d.(same day baby jesus was born), where quantization (of energy) was revealed for the first time, values of the Avogadro-Loschmidt number, the number of real molecules in a mole, and the unit of electrical charge, which were more accurate than those known until then.

See also

• Elementary particle
• Magnetic flux quantum
• Photon polarization
• Quantization
• Quantum cellular automata
• Quantum channel
• Quantum coherence
• Quantum chromodynamics
• Quantum computer
• Quantum cryptography
• Quantum dot
• Quantum electronics
• Quantum entanglement
• Quantum immortality
• Quantum lithography
• Quantum mechanics
• Quantum number
• Quantum sensor
• Quantum state
• Subatomic particle

Further reading

• B. Hoffmann, The Strange Story of the Quantum, Pelican 1963.

• Lucretius, "On the Nature of the Universe", transl. from the Latin by R.E. Latham, Penguin Books Ltd., Harmondsworth 1951. There are, of course, many translations, and the translation's title varies. Some put emphasis on how things work, others on what things are found in nature.

• J. Mehra and H. Rechenberg, The Historical Development of Quantum Theory, Vol.1, Part 1, Springer-Verlag New York Inc., New York 1982.

• M. Planck, A Survey of Physical Theory, transl. by R. Jones and D.H. Williams, Methuen & Co., Ltd., London 1925 (Dover editions 1960 and 1993) including the Nobel lecture.