In physics, a quantum (plural: quanta) is the minimum amount of any
physical entity involved in an interaction. The fundamental notion
that a physical property may be "quantized" is referred to as "the
hypothesis of quantization". This means that the magnitude of the
physical property can take on only discrete values consisting of
integer multiples of one quantum.
For example, a photon is a single quantum of light (or of any other
form of electromagnetic radiation), and can be referred to as a "light
quantum". Similarly, the energy of an electron bound within an atom is
also quantized, and thus can only exist in certain discrete values.
Atoms and matter in general are stable because electrons can only
exist at discrete energy levels in an atom. Quantization is one of the
foundations of the much broader physics of quantum mechanics.
Quantization of the energy and its influence on how energy and matter
interact (quantum electrodynamics) is part of the fundamental
framework for understanding and describing nature.
1 Etymology and discovery
2 Beyond electromagnetic radiation
3 See also
5 Further reading
Etymology and discovery
The word quantum comes from the
Latin quantus, meaning "how great".
"Quanta", short for "quanta of electricity" (electrons), was used in a
1902 article on the photoelectric effect by Philipp Lenard, who
Hermann von Helmholtz
Hermann von Helmholtz for using the word in the area of
electricity. However, the word quantum in general was well known
before 1900. It was often used by physicians, such as in the term
quantum satis. Both Helmholtz and
Julius von Mayer
Julius von Mayer were physicians as
well as physicists. Helmholtz used quantum with reference to heat in
his article on Mayer's work, and the word quantum can be found in
the formulation of the first law of thermodynamics by Mayer in his
letter dated July 24, 1841.
Max Planck used quanta to mean "quanta
of matter and electricity", gas, and heat. In 1905, in response
to Planck's work and the experimental work of Lenard (who explained
his results by using the term quanta of electricity), Albert Einstein
suggested that radiation existed in spatially localized packets which
he called "quanta of light" ("Lichtquanta").
The concept of quantization of radiation was discovered in 1900 by Max
Planck, who had been trying to understand the emission of radiation
from heated objects, known as black-body radiation. By assuming that
energy can only be absorbed or released in tiny, differential,
discrete packets he called "bundles" or "energy elements", Planck
accounted for certain objects changing colour when heated. On
December 14, 1900, Planck reported his findings to the German Physical
Society, and introduced the idea of quantization for the first time as
a part of his research on black-body radiation. As a result of his
experiments, Planck deduced the numerical value of h, known as the
Planck constant, and could also report a more precise value for the
Avogadro–Loschmidt number, the number of real molecules in a mole
and the unit of electrical charge, to the German Physical Society.
After his theory was validated, Planck was awarded the Nobel Prize in
Physics for his discovery in 1918.
Beyond electromagnetic radiation
While quantization was first discovered in electromagnetic radiation,
it describes a fundamental aspect of energy not just restricted to
photons. In the attempt to bring theory into agreement with
Max Planck postulated that electromagnetic energy is
absorbed or emitted in discrete packets, or quanta.
Introduction to quantum mechanics
Magnetic flux quantum
Quantum cellular automata
Quantum Field Theory
^ Wiener, N. (1966). Differential Space,
Quantum Systems, and
Prediction. Cambridge: The Massachusetts Institute of Technology Press
^ E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
^ E. Helmholtz, Robert Mayer's Priorität (in German)
^ Herrmann, Armin (1991). "Heimatseite von Robert J. Mayer" (in
German). Weltreich der Physik, GNT-Verlag. Archived from the original
on 1998-02-09. CS1 maint: BOT: original-url status unknown (link)
^ Planck, M. (1901). "Ueber die Elementarquanta der Materie und der
Annalen der Physik (in German). 309 (3): 564–566.
^ Planck, Max (1883). "Ueber das thermodynamische Gleichgewicht von
Annalen der Physik (in German). 255 (6): 358.
^ Einstein, A. (1905). "Über einen die Erzeugung und Verwandlung des
Lichtes betreffenden heuristischen Gesichtspunkt" (PDF). Annalen der
Physik (in German). 17 (6): 132–148. Bibcode:1905AnP...322..132E.
doi:10.1002/andp.19053220607. . A partial English translation is
available from Wikisource.
Max Planck (1901). "Ueber das Gesetz der Energieverteilung im
Normalspectrum (On the Law of Distribution of Energy in the Normal
Spectrum)". Annalen der Physik. 309 (3): 553.
Bibcode:1901AnP...309..553P. doi:10.1002/andp.19013090310. Archived
from the original on 2008-04-18.
^ Brown, T., LeMay, H., Bursten, B. (2008). Chemistry: The Central
Science Upper Saddle River, NJ: Pearson Education
^ Klein, Martin J. (1961). "
Max Planck and the beginnings of the
quantum theory". Archive for History of Exact Sciences. 1 (5): 459.
^ Melville, K. (2005, February 11). Real-World
^ Modern Applied Physics-Tippens third edition; McGraw-Hill.
B. Hoffmann, The Strange Story of the Quantum, Pelican 1963.
Lucretius, On the Nature of the Universe, transl. from the
R.E. Latham, Penguin Books Ltd., Harmondsworth 1951.
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.
Rodney, Brooks (2011) Fields of Color: The theory that escaped
Einstein. Allegra Print & Imaging.