Editing Electromagnetism (section)

==Classical electrodynamics==
{{Main|Classical electrodynamics}}

In 1600, [[William Gilbert (astronomer)|William Gilbert]] proposed, in his ''[[De Magnete]]'', that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects.<ref>{{Cite journal |last1=Malin |first1=Stuart |last2=Barraclough |first2=David |date=2000 |title=Gilbert's De Magnete: An early study of magnetism and electricity |url=http://doi.wiley.com/10.1029/00EO00163 |journal=Eos, Transactions American Geophysical Union |language=en |volume=81 |issue=21 |pages=233 |doi=10.1029/00EO00163 |bibcode=2000EOSTr..81..233M |issn=0096-3941 |access-date=2022-08-22 |archive-date=2024-10-03 |archive-url=https://web.archive.org/web/20241003193745/https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/00EO00163 |url-status=live }}</ref> Mariners had noticed that lightning strikes had the ability to disturb a compass needle. The link between lightning and electricity was not confirmed until [[Benjamin Franklin]]'s proposed experiments in 1752 were conducted on 10{{nbsp}}May 1752 by [[Thomas-François Dalibard]] of France using a {{convert|40|ft|m|adj=mid|-tall}} iron rod instead of a kite and he successfully extracted electrical sparks from a cloud.<ref>{{Cite web|url=http://www.mos.org/sln/toe/kite.html|title=Lightning! &#124; Museum of Science, Boston|access-date=2022-08-22|archive-date=2010-02-09|archive-url=https://web.archive.org/web/20100209131349/http://www.mos.org/sln/toe/kite.html|url-status=dead}}</ref><ref>{{Cite book |last=Tucker |first=Tom |url=https://www.worldcat.org/oclc/51763922 |title=Bolt of fate : Benjamin Franklin and his electric kite hoax |date=2003 |publisher=PublicAffairs |isbn=1-891620-70-3 |edition=1st |location=New York |oclc=51763922 |access-date=2022-08-22 |archive-date=2024-10-03 |archive-url=https://web.archive.org/web/20241003193844/https://search.worldcat.org/title/51763922 |url-status=live }}</ref>

One of the first to discover and publish a link between human-made electric current and magnetism was [[Romagnosi|Gian Romagnosi]], who in 1802 noticed that connecting a wire across a [[voltaic pile]] deflected a nearby [[compass]] needle. However, the effect did not become widely known until 1820, when Ørsted performed a similar experiment.<ref name="Stern-2001">{{cite web |url=http://www-istp.gsfc.nasa.gov/Education/whmfield.html |title=Magnetic Fields – History |access-date=2009-11-27 |last1=Stern |first1=Dr. David P. |first2=Mauricio |last2=Peredo |date=2001-11-25 |publisher=NASA Goddard Space Flight Center |archive-date=2015-11-16 |archive-url=https://web.archive.org/web/20151116034519/http://www-istp.gsfc.nasa.gov/Education/whmfield.html |url-status=live }}</ref> Ørsted's work influenced Ampère to conduct further experiments, which eventually gave rise to a new area of physics: electrodynamics. By determining a force law for the interaction between elements of electric current, Ampère placed the subject on a solid mathematical foundation.<ref>{{Cite web |date=2016-01-13 |title=Andre-Marie Ampère |url=https://ethw.org/Andre-Marie_Amp%C3%A8re |access-date=2022-08-22 |website=ETHW |language=en |archive-date=2022-08-22 |archive-url=https://web.archive.org/web/20220822112621/https://ethw.org/Andre-Marie_Amp%C3%A8re |url-status=live }}</ref>

A theory of electromagnetism, known as [[classical electromagnetism]], was developed by several physicists during the period between 1820 and 1873, when [[James Clerk Maxwell]]'s [[A Treatise on Electricity and Magnetism|treatise]] was published, which unified previous developments into a single theory, proposing that light was an electromagnetic wave propagating in the ''luminiferous ether''.<ref>Purcell, p. 436. Chapter 9.3, "Maxwell's description of the electromagnetic field was essentially complete."</ref> In classical electromagnetism, the behavior of the electromagnetic field is described by a set of equations known as [[Maxwell's equations]], and the electromagnetic force is given by the [[Lorentz force law]].<ref>Purcell: p. 278: Chapter 6.1, "Definition of the Magnetic Field." Lorentz force and force equation.</ref>

One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with [[classical mechanics]], but it is compatible with special relativity. According to Maxwell's equations, the [[speed of light]] in vacuum is a universal constant that is dependent only on the [[electrical permittivity]] and [[magnetic permeability]] of [[free space]]. This violates [[Galilean invariance]], a long-standing cornerstone of classical mechanics. One way to reconcile the two theories (electromagnetism and classical mechanics) is to assume the existence of a [[luminiferous aether]] through which the light propagates. However, subsequent experimental efforts failed to detect the presence of the aether. After important contributions of [[Hendrik Lorentz]] and [[Henri Poincaré]], in 1905, [[Albert Einstein]] solved the problem with the introduction of special relativity, which replaced classical kinematics with a new theory of kinematics compatible with classical electromagnetism. (For more information, see [[History of special relativity]].)

In addition, relativity theory implies that in moving frames of reference, a magnetic field transforms to a field with a nonzero electric component and conversely, a moving electric field transforms to a nonzero magnetic component, thus firmly showing that the phenomena are two sides of the same coin. Hence the term "electromagnetism". (For more information, see [[Classical electromagnetism and special relativity]] and [[Covariant formulation of classical electromagnetism]].)

Today few problems in electromagnetism remain unsolved. These include: the lack of [[magnetic monopoles]], [[Abraham–Minkowski controversy]], the location in space of the electromagnetic field energy,<ref>{{Cite book |last=Feynman |first=Richard P. |title=The Feynman lectures on physics. Volume 1: Mainly mechanics, radiation, and heat |date=2011 |publisher=Basic Books |isbn=978-0-465-04085-8 |edition=The new millennium edition, paperback first published |location=New York |chapter=27–4 The ambiguity of the field energy |chapter-url=https://www.feynmanlectures.caltech.edu/II_27.html |access-date=2024-09-05 |archive-date=2024-10-03 |archive-url=https://web.archive.org/web/20241003194754/https://www.feynmanlectures.caltech.edu/II_27.html |url-status=live }}</ref> and the mechanism by which some organisms can sense [[electroreception|electric]] and [[magnetoreception|magnetic]] fields.