View source for Physics:Quantum

In [[HandWiki:Physics|physics]], a '''quantum''' ({{plural form}}: '''quanta''') is the minimum amount of any physical entity ([[Physics:Physical property|physical property]]) involved in an [[Physics:Fundamental interaction|interaction]].  The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of [[Physics:Quantization|quantization]]".<ref>Wiener, N. (1966). ''Differential Space, Quantum Systems, and Prediction''. Cambridge, Massachusetts: The Massachusetts Institute of Technology Press</ref> This means that the [[Magnitude (mathematics)|magnitude]] of the physical property can take on only discrete values consisting of [[Multiple (mathematics)|integer multiples]] of one quantum. For example, a [[Physics:Photon|photon]] is a single quantum of [[Company:Light|light]] of a specific [[Physics:Frequency|frequency]] (or of any other form of [[Physics:Electromagnetic radiation|electromagnetic radiation]]). Similarly, the energy of an [[Physics:Electron|electron]] bound within an [[Atom|atom]] is quantized and can exist only in certain discrete values.<ref>{{Cite book |last=Rovelli |first=Carlo |title=Reality is not what it seems: the elementary structure of things |date=January 2017 |publisher=Riverhead Books |isbn=978-0-7352-1392-0 |edition=1st American |location=New York, New York |pages=109–130 |translator-last=Carnell |translator-first=Simon |translator-last2=Segre |translator-first2=Erica}}</ref> 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 [[Physics:Quantum mechanics|quantum mechanics]]. Quantization of [[Physics:Energy|energy]] and its influence on how energy and matter interact ([[Physics:Quantum electrodynamics|quantum electrodynamics]]) is part of the fundamental framework for understanding and describing nature.

==Origin==
[[File:Max Planck (1858-1947).jpg|thumb|upright=1|German [[physicist]] and 1918 Nobel Prize for Physics recipient [[Biography:Max Planck|Max Planck]] (1858–1947)]]
The modern concept of the quantum in physics originates from December 14, 1900, when [[Biography:Max Planck|Max Planck]] reported his [[Physics:Planck's law|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.<ref name="Baggott-2013">{{Cite book |last=Baggott |first=J. E. |title=The quantum story: a history in 40 moments |date=2013 |publisher=Oxford University Press |isbn=978-0-19-965597-7 |edition=Pbk |location=Oxford [England]}}</ref>{{rp|15}}<ref name="Planck1901">{{cite journal |last = Planck |first = M. |year = 1901 |title = Ueber die Elementarquanta der Materie und der Elektricität |journal = [[Physics:Annalen der Physik|Annalen der Physik]] |volume = 309 |pages = 564–566 |doi = 10.1002/andp.19013090311 |bibcode = 1901AnP...309..564P |issue = 3 |language = de |url = https://zenodo.org/record/1423997 |via=Zenodo |access-date = 2019-09-16 |archive-date = 2023-06-24 |archive-url = https://web.archive.org/web/20230624230014/https://zenodo.org/record/1423997 |url-status = live }}</ref> In his report, Planck did not use the term ''quantum'' in the modern sense. Instead, he used the term {{Lang|de|Elementarquantum}} to refer to the "quantum of electricity", now known as the [[Physics:Elementary charge|elementary charge]]. For the smallest unit of energy, he employed the term {{Lang|de|Energieelement}}, "energy element", rather than calling it a ''quantum''.<ref name=":0">{{Oed|term=Quantum|id=1164299139|access-date=6 May 2025|date=2007}}</ref>

Shortly afterwards, in a paper published in ''[[Physics:Annalen der Physik|Annalen der Physik]]'',<ref name="Planck01">{{citation |last=Planck |first=Max |title=Ueber das Gesetz der Energieverteilung im Normalspectrum |journal=[[Physics:Annalen der Physik|Annalen der Physik]] |volume=309 |issue=3 |pages=553–63 |year=1901 |url=http://www.physik.uni-augsburg.de/annalen/history/historic-papers/1901_309_553-563.pdf |access-date=2008-12-15 |archive-url=https://web.archive.org/web/20120610124128/http://www.physik.uni-augsburg.de/annalen/history/historic-papers/1901_309_553-563.pdf |archive-date=2012-06-10 |url-status=live |language=de |bibcode=1901AnP...309..553P |doi=10.1002/andp.19013090310 |doi-access=free}}. English translations:

* {{Cite web |title=On the Law of Distribution of Energy in the Normal Spectrum |url=http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Planck-1901/Planck-1901.html |url-status=dead |archive-url=https://web.archive.org/web/20080418002757/http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Planck-1901/Planck-1901.html |archive-date=2008-04-18}}
* {{cite web |title=On the Law of Distribution of Energy in the Normal Spectrum |url=http://theochem.kuchem.kyoto-u.ac.jp/Ando/planck1901.pdf |url-status=dead |archive-url=https://web.archive.org/web/20111006162543/http://theochem.kuchem.kyoto-u.ac.jp/Ando/planck1901.pdf |archive-date=2011-10-06 |access-date=2011-10-13}}</ref> Planck introduced the constant ''h'', which he termed the "quantum of [[Action|action]]" ({{Lang|de|elementares Wirkungsquantum}}) in 1906.<ref name=":0" /> In this paper, Planck also reported more precise values for the elementary charge and the [[Physics:Avogadro constant|Avogadro&ndash;Loschmidt number]], the number of molecules in one [[Mole (unit)|mole]] of substance.<ref>{{cite journal |last1=Klein |first1=Martin J. |year=1961 |title=Max Planck and the beginnings of the quantum theory |journal=Archive for History of Exact Sciences |volume=1 |issue=5 |pages=459–479 |doi=10.1007/BF00327765 |s2cid=121189755}}</ref> 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.<ref>{{Cite web |title=Max Planck Nobel Lecture |url=https://www.nobelprize.org/prizes/physics/1918/planck/lecture/ |url-status=live |archive-url=https://web.archive.org/web/20230714164215/https://www.nobelprize.org/prizes/physics/1918/planck/lecture/ |archive-date=2023-07-14 |access-date=2023-07-14}}</ref>

In 1905 [[Biography:Albert Einstein|Albert Einstein]] suggested that [[Physics:Electromagnetic radiation|electromagnetic radiation]] exists in spatially localized packets which he called [[Physics:Photons|"quanta of light"]] (''Lichtquanta'').<ref name=":0" /><ref name="Einstein1905">{{cite journal |last = Einstein |first = A. |year = 1905 |title = Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt |url = http://www.physik.uni-augsburg.de/annalen/history/einstein-papers/1905_17_132-148.pdf |journal = [[Physics:Annalen der Physik|Annalen der Physik]] |volume = 17 |pages = 132–148 |doi = 10.1002/andp.19053220607 |bibcode = 1905AnP...322..132E |issue = 6 |language = de |doi-access = free |access-date = 2010-08-26 |archive-date = 2015-09-24 |archive-url = https://web.archive.org/web/20150924072915/http://www.physik.uni-augsburg.de/annalen/history/einstein-papers/1905_17_132-148.pdf |url-status = live }}. A partial [https://en.wikisource.org/?curid=59468 English translation] {{Webarchive |url=https://web.archive.org/web/20210121022128/https://en.wikisource.org/?curid=59468 |date=2021-01-21 }} is available from [[Wikisource]].</ref>
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 [[Biography:Philipp Lenard|Philipp Lenard]]'s experiments on the [[Physics:Photoelectric effect|photoelectric effect]].<ref name="Baggott-2013" />{{rp|23}} Shortly thereafter, the term "energy quantum" was introduced for the quantity [[Planck relation|''{{mvar|hν}}'']].<ref>{{Cite book |last=Kuhn |first=Thomas S. |url=https://archive.org/details/blackbodytheoryq0000kuhn/mode/1up |title=Black-body theory and the quantum discontinuity, 1894-1912 |date=1978 |publisher=Clarendon Press |isbn=978-0-19-502383-1 |location=Oxford |pages=201}}</ref>

==Quantization==
While quantization was first discovered in [[Physics:Electromagnetic radiation|electromagnetic radiation]], it describes a fundamental aspect of energy not just restricted to photons.<ref>{{Cite web |last=Parker |first=Will |date=2005-02-11 |title=Real-World Quantum Effects Demonstrated |url=http://www.scienceagogo.com/news/20050110221715data_trunc_sys.shtml |access-date=2023-08-20 |website=ScienceAGoGo |language=en-US}}</ref>
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.<ref>Modern Applied Physics-Tippens third edition; McGraw-Hill.</ref><!-- This source is vague -->

==See also==
* [[Physics:Introduction to quantum mechanics|Introduction to quantum mechanics]]
* [[Physics:History of quantum mechanics|History of quantum mechanics]]
* Quantum geometry

==References==
{{Reflist}}

==Further reading==
* {{Cite book |last=Hoffmann |first=Banesh |title=The Strange story of the quantum: An account for the general reader of the growth of the ideas underlying our present atomic knowledge |date=1959 |publisher=Dover |isbn=978-0-486-20518-2 |edition=2 |location=New York}}
* {{Cite book |last1=Mehra |first1=Jagdish |title=The historical development of quantum theory. 4: Pt.1, the fundamental equations of quantum mechanics, 1925-1926 |last2=Rechenberg |first2=Helmut |author-link2=Helmut Rechenberg |last3=Mehra |first3=Jagdish |last4=Rechenberg |first4=Helmut |date=2001 |publisher=Springer |isbn=978-0-387-95178-2 |edition=1. softcover print |location=New York Heidelberg}}
* 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

{{Quantum mechanics topics}}

[[Category:Quantum mechanics]]

{{Sourceattribution|Quantum}}