In
physics
Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which relates t ...
, a quantum (: quanta) is the minimum amount of any physical entity (
physical property) involved in an
interaction. The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of
quantization". This means that the
magnitude
Magnitude may refer to:
Mathematics
* Euclidean vector, a quantity defined by both its magnitude and its direction
* Magnitude (mathematics), the relative size of an object
* Norm (mathematics), a term for the size or length of a vector
* Order ...
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
Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres ...
of a specific
frequency
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, aud ...
(or of any other form of
electromagnetic radiation). Similarly, the energy of an
electron
The electron (, or in nuclear reactions) is a subatomic particle whose electric charge is negative one elementary charge. It is an elementary particle contained in the matter that makes up the universe.
All atoms are composed of electro ...
bound within an
atom
Atoms are the basic particles of the chemical elements and the fundamental building blocks of matter. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The che ...
is quantized and can exist only in certain discrete values. Atoms and matter in general are stable because electrons can exist only at discrete energy levels within an atom. Quantization is one of the foundations of the much broader physics of
quantum mechanics. Quantization of
energy
Energy () is the quantitative property that is transferred to a body or to a physical system, recognizable in the capacity to do work and in the form of heat and light. Energy is a conserved quantity—the law of conservation of energy ...
and its influence on how energy and matter interact (
quantum electrodynamics) is part of the fundamental framework for understanding and describing nature.
Origin
The modern concept of the quantum in physics originates from December 14, 1900, when
Max Planck reported his
findings to the
German Physical Society. He showed that modelling harmonic oscillators with discrete energy levels resolved a longstanding problem in the theory of
blackbody radiation.
In his report, Planck did not use the term ''quantum'' in the modern sense. Instead, he used the term to refer to the "quantum of electricity", now known as the
elementary charge. For the smallest unit of energy, he employed the term , "energy element", rather than calling it a ''quantum''.
Shortly afterwards, in a paper published in ''
Annalen der Physik'',
[. English translations:
*
* ] Planck introduced the constant ''h'', which he termed the "quantum of
action
Action may refer to:
* Action (philosophy), something which is done by a person
* Action principles the heart of fundamental physics
* Action (narrative), a literary mode
* Action fiction, a type of genre fiction
* Action game, a genre of vide ...
" () in 1906.
In this paper, Planck also reported more precise values for the elementary charge and the
Avogadro–Loschmidt number, the number of molecules in one
mole of substance. The constant ''h'' is now known as the
Planck constant. After his theory was validated, Planck was awarded the
Nobel Prize in Physics for his discovery in 1918.
In 1905
Albert Einstein suggested that
electromagnetic radiation exists in spatially localized packets which he called
"quanta of light" (''Lichtquanta'').
[. A partia]
English translation
is available from Wikisource.
Einstein was able to use this hypothesis to recast Planck's treatment of the blackbody problem in a form that also explained the voltages observed in
Philipp Lenard's experiments on the
photoelectric effect.
Shortly thereafter, the term "energy quantum" was introduced for the quantity
'.
Quantization
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 experiment, Max Planck postulated that electromagnetic energy is absorbed or emitted in discrete packets, or quanta.
[Modern Applied Physics-Tippens third edition; McGraw-Hill.]
See also
*
Introduction to quantum mechanics
*
History of quantum mechanics
*
Quantum geometry
References
Further reading
*
*
* M. Planck, ''A Survey of Physical Theory'', transl. by R. Jones and D.H. Williams, Methuen & Co., Limited., London 1925 (Dover edition 17 May 2003, ISBN 978-0486678672) including the Nobel lecture.
* Rodney, Brooks (14 December 2010) ''Fields of Color: The theory that escaped Einstein''. Allegra Print & Imaging. ISBN 979-8373308427
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Quantum mechanics