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and showed that the arbitrary function <math>\ell\left(\varepsilon\right)</math> must be unity for all <math>\varepsilon</math> (Lorentz had set <math>\ell = 1</math> by a different argument) to make the transformations form a group. In an enlarged version of the paper that appeared in 1906 Poincaré pointed out that the combination <math>x^2+ y^2+ z^2- c^2t^2</math> is invariant. He noted that a Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing <math>ct\sqrt{-1}</math> as a fourth imaginary coordinate, and he used an early form of four-vectors. Poincaré expressed a lack of interest in a four-dimensional reformulation of his new mechanics in 1907, because in his opinion the translation of physics into the language of four-dimensional geometry would entail too much effort for limited profit. So it was Hermann Minkowski who worked out the consequences of this notion in 1907.

and showed that the arbitrary function <math>\ell\left(\varepsilon\right)</math> must be unity for all <math>\varepsilon</math> (Lorentz had set <math>\ell = 1</math> by a different argument) to make the transformations form a group. In an enlarged version of the paper that appeared in 1906 Poincaré pointed out that the combination <math>x^2+ y^2+ z^2- c^2t^2</math> is invariant. He noted that a Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing <math>ct\sqrt{-1}</math> as a fourth imaginary coordinate, and he used an early form of four-vectors. Poincaré expressed a lack of interest in a four-dimensional reformulation of his new mechanics in 1907, because in his opinion the translation of physics into the language of four-dimensional geometry would entail too much effort for limited profit. So it was Hermann Minkowski who worked out the consequences of this notion in 1907.

并证明了任意函数<math>\ell\left(\varepsilon\right)</math>对于所有<math>\varepsilon</math>必须是统一的（Lorentz通过一个不同的参数设置<math>\ell = 1</math>），以使变换形成一个组。在1906年发表的论文的放大版中，庞加莱指出组合<math>x^2+ y^2+ z^2- c^2t^2</math>是不变的。他通过引入<math>ct\sqrt{-1}</math>作为第四个虚坐标，指出Lorentz变换仅仅是四维空间中绕原点的旋转，他使用了四个向量的早期形式。庞加莱在1907年表示对他的新力学的四维重新表述不感兴趣，因为在他看来，将物理学翻译成四维几何的语言需要付出太多的努力才能获得有限的益处。1907年，由赫尔曼·明科夫斯基（Hermann Minkowski）提出了这个概念的后果。

并证明了任意函数<math>\ell\left(\varepsilon\right)</math>对于所有<math>\varepsilon</math>必须是统一的（Lorentz通过一个不同的参数设置<math>\ell = 1</math>），以使变换形成一个组。在1906年发表的论文的放大版中，庞加莱指出组合<math>x^2+ y^2+ z^2- c^2t^2</math>是不变的。他通过引入<math>ct\sqrt{-1}</math>作为第四个虚坐标，指出Lorentz变换仅仅是四维空间中绕原点的旋转，他使用了四个向量的早期形式。庞加莱在1907年表示对他的新力学的四维重新表述不感兴趣，因为在他看来，将物理学翻译成四维几何的语言需要付出太多的努力才能获得有限的益处。1907年，由赫尔曼·明科夫斯基（Hermann Minkowski）得出了这个概念的后果。

In a second letter to Lorentz, Poincaré gave his own reason why Lorentz's time dilation factor was indeed correct after all—it was necessary to make the Lorentz transformation form a group—and he gave what is now known as the relativistic velocity-addition law.<ref name="univ-nantes2">{{Citation | author=Poincaré, H. | year=2007 | editor=Walter, S. A. | contribution= 38.4, Poincaré to H. A. Lorentz, May 1905 | title=La correspondance entre Henri Poincaré et les physiciens, chimistes, et ingénieurs |pages=257–258 |place=Basel | publisher=Birkhäuser|contribution-url=http://henripoincarepapers.univ-nantes.fr/chp/text/lorentz4.html}}</ref>

In a second letter to Lorentz, Poincaré gave his own reason why Lorentz's time dilation factor was indeed correct after all—it was necessary to make the Lorentz transformation form a group—and he gave what is now known as the relativistic velocity-addition law.<ref name="univ-nantes2">{{Citation | author=Poincaré, H. | year=2007 | editor=Walter, S. A. | contribution= 38.4, Poincaré to H. A. Lorentz, May 1905 | title=La correspondance entre Henri Poincaré et les physiciens, chimistes, et ingénieurs |pages=257–258 |place=Basel | publisher=Birkhäuser|contribution-url=http://henripoincarepapers.univ-nantes.fr/chp/text/lorentz4.html}}</ref>

在给洛伦兹的第二封信中，庞加莱给出了他自己的理由，为什么洛伦兹的时间膨胀因子确实是正确的，毕竟要使洛伦兹变换形成一个群，他还给出了现在所知的<font color="#ff8000">相对论速度加法定律</font>。<ref name="univ-nantes2">{{Citation | author=Poincaré, H. | year=2007 | editor=Walter, S. A. | contribution= 38.4, Poincaré to H. A. Lorentz, May 1905 | title=La correspondance entre Henri Poincaré et les physiciens, chimistes, et ingénieurs |pages=257–258 |place=Basel | publisher=Birkhäuser|contribution-url=http://henripoincarepapers.univ-nantes.fr/chp/text/lorentz4.html}}</ref>

在给洛伦兹的第二封信中，庞加莱给出了他自己的理由，为什么洛伦兹的时间膨胀因子确实是正确的，毕竟要使洛伦兹变换形成一个群，他还给出了现在所知的<font color="#ff8000">相对论速度加法定律</font>。<ref name="univ-nantes2">{{Citation | author=Poincaré, H. | year=2007 | editor=Walter, S. A. | contribution= 38.4, Poincaré to H. A. Lorentz, May 1905 | title=La correspondance entre Henri Poincaré et les physiciens, chimistes, et ingénieurs |pages=257–258 |place=Basel | publisher=Birkhäuser|contribution-url=http://henripoincarepapers.univ-nantes.fr/chp/text/lorentz4.html}}</ref>

Poincaré later delivered a paper at the meeting of the Academy of Sciences in Paris on 5 June 1905 in which these issues were addressed. In the published version of that he wrote:<ref name="1905 paper">[http://www.academie-sciences.fr/pdf/dossiers/Poincare/Poincare_pdf/Poincare_CR1905.pdf] (PDF) Membres de l'Académie des sciences depuis sa création : Henri Poincare. Sur la dynamique de l' electron. Note de H. Poincaré. C.R. T.140 (1905) 1504–1508.</ref>

Poincaré later delivered a paper at the meeting of the Academy of Sciences in Paris on 5 June 1905 in which these issues were addressed. In the published version of that he wrote:<ref name="1905 paper">[http://www.academie-sciences.fr/pdf/dossiers/Poincare/Poincare_pdf/Poincare_CR1905.pdf] (PDF) Membres de l'Académie des sciences depuis sa création : Henri Poincare. Sur la dynamique de l' electron. Note de H. Poincaré. C.R. T.140 (1905) 1504–1508.</ref>

and showed that the arbitrary function <math>\ell\left(\varepsilon\right)</math> must be unity for all <math>\varepsilon</math> (Lorentz had set <math>\ell = 1</math> by a different argument) to make the transformations form a group. In an enlarged version of the paper that appeared in 1906 Poincaré pointed out that the combination <math>x^2+ y^2+ z^2- c^2t^2</math> is [[Invariant (mathematics)|invariant]]. He noted that a Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing <math>ct\sqrt{-1}</math> as a fourth imaginary coordinate, and he used an early form of [[four-vector]]s.<ref name=long>{{Citation

and showed that the arbitrary function <math>\ell\left(\varepsilon\right)</math> must be unity for all <math>\varepsilon</math> (Lorentz had set <math>\ell = 1</math> by a different argument) to make the transformations form a group. In an enlarged version of the paper that appeared in 1906 Poincaré pointed out that the combination <math>x^2+ y^2+ z^2- c^2t^2</math> is [[Invariant (mathematics)|invariant]]. He noted that a Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing <math>ct\sqrt{-1}</math> as a fourth imaginary coordinate, and he used an early form of [[four-vector]]s.<ref name=long>{{Citation

并证明了任意函数<math>\ell\left（\varepsilon\right）</math>对于所有<math>\varepsilon</math>必须是统一的（Lorentz通过一个不同的参数设置<math>\ell=1</math>），以使变换形成一个组。在1906年发表的论文的放大版中，庞加莱指出组合<math>x^2+y^2+z^2-c^2t^2</math>是[[不变量（数学）|不变量]]。他指出，通过引入<math>ct\sqrt{-1}</math>作为第四个虚坐标，Lorentz变换仅仅是四维空间中绕原点的旋转，他使用了[[four vector]]s的早期形式。<ref name=long>{{Citation

并证明了任意函数<math>\ell\left（\varepsilon\right）</math>对于所有<math>\varepsilon</math>必须是统一的（Lorentz通过一个不同的参数设置<math>\ell=1</math>），以使变换形成一个组。在1906年发表的论文的放大版中，庞加莱指出组合<math>x^2+y^2+z^2-c^2t^2</math>是[[不变量（数学）|不变量]]。他指出，通过引入<math>ct\sqrt{-1}</math>作为第四个虚坐标，Lorentz变换仅仅是四维空间中绕原点的旋转，他使用了[[四向量]]s的早期形式。<ref name=long>{{Citation

| author=Poincaré, H. | year=1906 | title=Sur la dynamique de l'électron (On the Dynamics of the Electron) | journal=Rendiconti del Circolo Matematico Rendiconti del Circolo di Palermo | volume =21 | pages =129–176

| author=Poincaré, H. | year=1906 | title=Sur la dynamique de l'électron (On the Dynamics of the Electron) | journal=Rendiconti del Circolo Matematico Rendiconti del Circolo di Palermo | volume =21 | pages =129–176