Editing Inertial frame of reference (section)

==Introduction==
The motion of a body can only be described relative to something else—other bodies, observers, or a set of spacetime coordinates. These are called [[frame of reference|frames of reference]]. According to the first postulate of [[special relativity]], all physical laws take their simplest form in an inertial frame, and there exist multiple inertial frames interrelated by uniform [[Translation (physics)|translation]]:{{anchor|principle}}<!--

REF
--><ref name="Einstein">{{Cite book|title=The Principle of Relativity: a collection of original memoirs on the special and general theory of relativity |last1=Einstein |first1=A. |author-link1=Albert Einstein |last2=Lorentz |first2=H. A. |author-link2=Hendrik Lorentz|last3=Minkowski |first3=H. |author-link3=Hermann Minkowski |last4=Weyl |first4=H. |author-link4=Hermann Weyl |page=111 |url=https://books.google.com/books?id=yECokhzsJYIC&q=postulate+%22Principle+of+Relativity%22&pg=PA111
|isbn=0-486-60081-5 |publisher=Courier Dover Publications |date=1952 }}</ref>{{blockquote|<i>Special principle of relativity: If a system of coordinates K is chosen so that, in relation to it, physical laws hold good in their simplest form, the same laws hold good in relation to any other system of coordinates K' moving in uniform translation relatively to K.</i>|Albert Einstein: ''The foundation of the general theory of relativity'', Section A, §1}}
This simplicity manifests itself in that inertial frames have self-contained physics without the need for external causes, while physics in '''non-inertial frames''' has external causes.<ref name="Ferraro">{{citation|title=Einstein's Space-Time: An Introduction to Special and General Relativity|first1=Rafael|last1=Ferraro|publisher=Springer Science & Business Media|date=2007|isbn=9780387699462|url=https://books.google.com/books?id=wa3CskhHaIgC&pg=PA209|pages=209–210|bibcode=2007esti.book.....F|access-date=2 November 2022|archive-date=7 March 2023|archive-url=https://web.archive.org/web/20230307110753/https://books.google.com/books?id=wa3CskhHaIgC&pg=PA209|url-status=live}}</ref> The principle of simplicity can be used within Newtonian physics as well as in special relativity:<ref name=Nagel>{{Cite book|title=The Structure of Science |author=Ernest Nagel |page=212 |url=https://books.google.com/books?id=u6EycHgRfkQC&q=inertial+%22Foucault%27s+pendulum%22&pg=PA212 |isbn=0-915144-71-9 |publisher=Hackett Publishing |date=1979 }}</ref><ref name="Blagojević">{{Cite book|title=Gravitation and Gauge Symmetries |author=Milutin Blagojević |page=4 |url=https://books.google.com/books?id=N8JDSi_eNbwC&q=inertial+frame+%22absolute+space%22&pg=PA5 |isbn=0-7503-0767-6 |publisher=CRC Press |date=2002}}</ref>

{{blockquote|<i>The laws of Newtonian mechanics do not always hold in their simplest form...If, for instance, an observer is placed on a disc rotating relative to the earth, he/she will sense a 'force' pushing him/her toward the periphery of the disc, which is not caused by any interaction with other bodies. Here, the acceleration is not the consequence of the usual force, but of the so-called inertial force. Newton's laws hold in their simplest form only in a family of reference frames, called inertial frames. This fact represents the essence of the Galilean principle of relativity:<br />&ensp;&ensp;&ensp;The laws of mechanics have the same form in all inertial frames.</i>|Milutin Blagojević: ''Gravitation and Gauge Symmetries'', p. 4}}

However, this definition of inertial frames is understood to apply in the [[Newtonian dynamics|Newtonian]] realm and ignores relativistic effects.

In practical terms, the equivalence of inertial reference frames means that scientists within a box moving with a constant absolute velocity cannot determine this velocity by any experiment. Otherwise, the differences would set up an absolute standard reference frame.<ref name="Einstein2">{{Cite book|title=Relativity: The Special and General Theory |author=Albert Einstein |page=[https://archive.org/details/relativityspeci00lawsgoog/page/n38 17] |date=1920 |publisher=H. Holt and Company |url=https://archive.org/details/relativityspeci00lawsgoog |quote=The Principle of Relativity. }}</ref><ref name="Feynman">{{Cite book |title=Six not-so-easy pieces: Einstein's relativity, symmetry, and space-time |author=Richard Phillips Feynman |page=73 |isbn=0-201-32842-9 |date=1998 |publisher=Basic Books |url=https://books.google.com/books?id=ipY8onVQWhcC&q=%22The+Principle+of+Relativity%22&pg=PA49 }}{{Dead link|date=January 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> According to this definition, supplemented with the constancy of the speed of light, inertial frames of reference transform among themselves according to the [[Poincaré group]] of symmetry transformations, of which the [[Lorentz transformation]]s are a subgroup.<ref name="Wachter">{{Cite book|title=Compendium of Theoretical Physics |author1=Armin Wachter |author2=Henning Hoeber |page=98 |url=https://books.google.com/books?id=j3IQpdkinxMC&q=%2210-parameter+proper+orthochronous+Poincare+group%22&pg=PA98 |isbn=0-387-25799-3 |publisher=Birkhäuser |date=2006 }}</ref> In Newtonian mechanics, inertial frames of reference are related by the [[Galilean group]] of symmetries.