Editing Inertia (section)

===Relativity===
[[Albert Einstein]]'s theory of [[special relativity]], as proposed in his 1905 paper entitled "[[On the Electrodynamics of Moving Bodies]]", was built on the understanding of [[inertial reference frames]] developed by Galileo, [[Christiaan Huygens|Huygens]] and Newton. While this revolutionary theory did significantly change the meaning of many Newtonian concepts such as [[mass]], [[energy]], and [[distance]], Einstein's concept of inertia remained at first unchanged from Newton's original meaning. However, this resulted in a limitation inherent in special relativity: the [[principle of relativity]] could only apply to inertial reference frames. To address this limitation, Einstein developed his [[general theory of relativity]] ("The Foundation of the General Theory of Relativity", 1916), which provided a theory including ''noninertial'' (accelerated) reference frames.<ref>Alfred Engel English Translation:{{Citation| last = Einstein| first = Albert| title = The Foundation of the General Theory of Relativity| publisher = Princeton University Press| year = 1997| location = New Jersey| url = http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_GRelativity_1916.pdf| access-date = 30 May 2014| archive-date = 15 November 2015| archive-url = https://web.archive.org/web/20151115215202/http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_GRelativity_1916.pdf| url-status = dead}}</ref>

In general relativity, the concept of inertial motion got a broader meaning. Taking into account general relativity, inertial motion is any movement of a body that is not affected by forces of electrical, magnetic, or other origin, but that is only under the influence of gravitational masses.<ref name=Born>{{cite book|title=Einstein's Theory of Relativity|author1=Max Born |author2=Günther Leibfried |url=https://archive.org/details/einsteinstheory000born|url-access=registration|quote=inertial motion.|isbn=0-486-60769-0|publisher=Courier Dover Publications|location=New York|year=1962|page=[https://archive.org/details/einsteinstheory000born/page/315 315]}}</ref><ref>{{cite web|url=https://archive.org/details/einsteinstheoryo00born/page/252/mode/2up?view=theater|title=Einstein's Theory of Relativity - inertial motion, p. 252|author=Max Born|year=1922 |publisher=New York, E. P. Dutton and company, publishers }}</ref> Physically speaking, this happens to be exactly what a properly functioning [[accelerometer|three-axis accelerometer]] is indicating when it does not detect any [[proper acceleration]].