Editing Length contraction (section)

==History==
{{Main|History of special relativity}}
Length contraction was postulated by [[George Francis FitzGerald|George FitzGerald]] (1889) and [[Hendrik Antoon Lorentz]] (1892) to explain the negative outcome of the [[Michelson–Morley experiment]] and to rescue the hypothesis of the stationary aether ([[Lorentz ether theory#Length contraction|Lorentz–FitzGerald contraction hypothesis]]).<ref>{{Citation|author=FitzGerald, George Francis|year=1889|title=The Ether and the Earth's Atmosphere|journal=Science|volume=13|pages=390|doi=10.1126/science.ns-13.328.390|pmid=17819387|issue=328|bibcode = 1889Sci....13..390F |title-link=s:The Ether and the Earth's Atmosphere|s2cid=43610293}}</ref><ref>{{Citation|last=Lorentz|first=Hendrik Antoon|year=1892|title=The Relative Motion of the Earth and the Aether|journal=Zittingsverlag Akad. V. Wet.|volume=1|pages=74–79|title-link=s:Translation:The Relative Motion of the Earth and the Aether}}</ref>
Although both FitzGerald and Lorentz alluded to the fact that electrostatic fields in motion were deformed ("Heaviside-Ellipsoid" after [[Oliver Heaviside]], who derived this deformation from electromagnetic theory in 1888), it was considered an [[ad hoc hypothesis]], because at this time there was no sufficient reason to assume that intermolecular forces behave the same way as electromagnetic ones. In 1897 [[Joseph Larmor]] developed a model in which all forces are considered to be of electromagnetic origin, and length contraction appeared to be a direct consequence of this model. Yet it was shown by [[Henri Poincaré]] (1905) that electromagnetic forces alone cannot explain the electron's stability. So he had to introduce another ad hoc hypothesis: non-electric binding forces ([[Electromagnetic mass#Poincaré stresses and the 4/3 problem|Poincaré stresses]]) that ensure the electron's stability, give a dynamical explanation for length contraction, and thus hide the motion of the stationary aether.<ref name=pais>{{Citation
|author=Pais, Abraham
|author-link=Abraham Pais
|year=1982
|title= [[Subtle is the Lord: The Science and the Life of Albert Einstein]]
|location= New York
|publisher=Oxford University Press
|isbn=0-19-520438-7}}</ref>

Lorentz believed that length contraction represented a ''physical contraction'' of the atoms making up an object. He envisioned no fundamental change in the nature of space and time.<ref name="Miller1998">{{cite book |last1=Miller |first1=Arthur I. |title=Albert Einstein's Special Theory of Relativity: Emergence (1905) and Early Interpretation (1905–1911) |date=1998 |publisher=Springer-Verlag |location=New York |isbn=978-0-387-94870-6}}</ref>{{rp|62–68}}
Lorentz expected that length contraction would result in compressive strains in an object that should result in measurable effects. Such effects would include optical effects in transparent media, such as optical rotation<ref name="LorentzPolarization">{{cite journal |last1=Lorentz |first1=H.A. |title=The rotation of the plane of polarization in moving media |journal=Huygens Institute – Royal Netherlands Academy of Arts and Sciences |date=1902 |volume=4 |pages=669–678 |url=http://www.dwc.knaw.nl/DL/publications/PU00014324.pdf |access-date=15 November 2018| bibcode=1901KNAB....4..669L }}</ref> and induction of double refraction,<ref name="LorentzElectromagnetic">{{cite journal |last1=Lorentz |first1=H. A. |title=Electromagnetic phenomena in a system moving with any velocity smaller than that of light |journal=Huygens Institute – Royal Netherlands Academy of Arts and Sciences |date=1904 |volume=6 |pages=809–831 |url=http://www.dwc.knaw.nl/DL/publications/PU00014148.pdf |access-date=15 November 2018|bibcode=1903KNAB....6..809L }}</ref> and the induction of torques on charged condensers moving at an angle with respect to the aether.

Lorentz was perplexed by experiments such as the [[Trouton–Noble experiment]] and the [[experiments of Rayleigh and Brace]], which failed to validate his theoretical expectations.<ref name="Miller1998"/>

For mathematical consistency, Lorentz proposed a new time variable, the "local time", called that because it depended on the position of a moving body, following the relation {{nowrap|1={{prime|''t''}} = ''t'' − ''vx''/''c''<sup>2</sup>}}.<ref name="Lorentz1895">{{cite book |last1=Lorentz |first1=Hendrik |title=Attempt at a Theory of Electrical and Optical Phenomena in Moving Bodies (Versuch einer Theorie der electrischen und optischen Erscheinungen in bewegten Körpern) |date=1895 |chapter=Investigation of oscillations excited by oscillating ions |chapter-url=https://en.wikisource.org/wiki/Translation:Attempt_of_a_Theory_of_Electrical_and_Optical_Phenomena_in_Moving_Bodies/Section_III |at=(subsection § 31) |publisher=E. J. Brill |location=Leiden |url=https://en.wikisource.org/wiki/Translation:Attempt_of_a_Theory_of_Electrical_and_Optical_Phenomena_in_Moving_Bodies}}</ref> Lorentz considered local time not to be "real"; rather, it represented an ad hoc change of variable.<ref name="Bernstein2006">{{cite book |last1=Bernstein |first1=Jeremy |title=Secrets of the Old One: Einstein, 1905 |date=2006 |publisher=Copernicus Books (imprint of Springer Science + Business Media) |isbn=978-0387-26005-1}}</ref>{{rp|51,80}}

Impressed by Lorentz's "most ingenious idea", Poincaré saw more in local time than a mere mathematical trick. It represented the actual time that would be shown on a moving observer's clocks. On the other hand, Poincaré did not consider this measured time to be the "true time" that would be exhibited by clocks at rest in the aether. Poincaré made no attempt to redefine the concepts of space and time. To Poincaré, Lorentz transformation described the ''apparent'' states of the field for a moving observer. ''True states'' remained those defined with respect to the ether.<ref name="Darrigol2005">{{cite journal |last1=Darrigol |first1=Olivier |title=The Genesis of the Theory of Relativity |journal=Séminaire Poincaré |date=2005 |volume=1 |pages=1–22 |url=http://www.bourbaphy.fr/darrigol2.pdf |access-date=15 November 2018 |bibcode=2006eins.book....1D }}</ref>

[[Albert Einstein]] removed the ad hoc character from the contraction hypothesis<ref name=pais /> declared the aether to be "superfluous" along with the concept of any absolutely stationary space, discussed length contraction effects in his 1905 paper on his theory of special relativity.<ref>{{Citation
|doi=10.1002/andp.19053221004
|author=Einstein, Albert
|year=1905a
|title=Zur Elektrodynamik bewegter Körper
|journal=Annalen der Physik
|volume=322
|issue=10
|pages=891–921|bibcode = 1905AnP...322..891E
|url=http://www.physik.uni-augsburg.de/annalen/history/einstein-papers/1905_17_891-921.pdf|doi-access=free
}}. See also: [http://www.fourmilab.ch/etexts/einstein/specrel/ English translation].</ref> Einstein proposed that Lorentz's transformation apply to both electromagnetism and mechanics.<ref name=Weinberg-1972>{{cite book |last=Weinberg |first=Steven |url=https://archive.org/details/gravitationcosmo00stev_0 |title=Gravitation and cosmology |date=1972 |publisher=John Wiley & Sons |isbn=9780471925675 |author-link=Steven Weinberg |url-access=registration}}.</ref>{{rp|17}}
[[Hermann Minkowski]] gave the geometrical interpretation of all relativistic effects by introducing his concept of four-dimensional [[spacetime]].<ref>{{Citation|author=Minkowski, Hermann|year=1909|title=Raum und Zeit|journal=Physikalische Zeitschrift|volume=10|pages=75–88|title-link=s:de:Raum und Zeit (Minkowski)}}
:*Various English translations on Wikisource: [[s:Space and Time|Space and Time]]</ref>

The numerous and confusing visual effects of combination of length contraction and the finite speed of light were poorly understood at first. Lorentz erroneously claimed in 1922 that they could be photographed. Even the famous [[George Gamow]] showed bicycles as only foreshortened in his illustrations for [[Mr Tompkins in Wonderland]]. Even though a paper with the correct appearance of a moving rod was published in 1924, it was not widely read. Only in 1959 when [[James Terrell (physicist)|James Terrell]] and [[Roger Penrose]] wrote about the visual effect now called [[Terrell rotation]] were the difficulties clear.<ref name="m884">{{cite journal | last=Appell | first=David | title=The invisibility of length contraction | journal=Physics World | publisher=IOP Publishing | volume=32 | issue=8 | date=2019-08-01 | issn=0953-8585 | doi=10.1088/2058-7058/32/8/35 | pages=41–45}}</ref> Terrell's paper named "Invisibility of the Lorentz Contraction" said a meter stick would appear to be rotated and the contraction itself could measure from photographs without corrections for the finite velocity of light.