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In [[physics]], Lorentz transformations became known at the beginning of the 20th century, when it was discovered that they exhibit the symmetry of [[Maxwell's equations]]. Subsequently, they became fundamental to all of physics, because they formed the basis of [[special relativity]] in which they exhibit the symmetry of [[Minkowski spacetime]], making the [[speed of light]] invariant between different inertial frames. They relate the spacetime coordinates of two arbitrary [[inertial frame of reference|inertial frames of reference]] with constant relative speed ''v''. In one frame, the position of an event is given by ''x,y,z'' and time ''t'', while in the other frame the same event has coordinates ''x′,y′,z′'' and ''t′''.
In [[physics]], Lorentz transformations became known at the beginning of the 20th century, when it was discovered that they exhibit the symmetry of [[Maxwell's equations]]. Subsequently, they became fundamental to all of physics, because they formed the basis of [[special relativity]] in which they exhibit the symmetry of [[Minkowski spacetime]], making the [[speed of light]] invariant between different inertial frames. They relate the spacetime coordinates of two arbitrary [[inertial frame of reference|inertial frames of reference]] with constant relative speed ''v''. In one frame, the position of an event is given by ''x,y,z'' and time ''t'', while in the other frame the same event has coordinates ''x′,y′,z′'' and ''t′''.


==Mathematical prehistory==
== {{anchor|Lorgen}}Most general Lorentz transformations ==
The general [[quadratic form]] ''q(x)'' with coefficients of a [[symmetric matrix]] '''A''', the associated [[bilinear form]] ''b(x,y)'', and the [[linear transformation]]s of ''q(x)'' and ''b(x,y)'' into ''q(x′)'' and ''b(x′,y′)'' using the [[transformation matrix]] '''g''', can be written as<ref>Bôcher (1907), chapter X</ref>
Using the coefficients of a [[symmetric matrix]] '''A''', the associated [[bilinear form]], and a [[linear transformation]]s in terms of [[transformation matrix]] '''g''', the Lorentz transformation is given if the following conditions are satisfied:


{{NumBlk|:|<math>\begin{matrix}\begin{align}\begin{align}q=\sum_{0}^{n}A_{ij}x_{i}x_{j}=\mathbf{x}^{\mathrm{T}}\cdot\mathbf{A}\cdot\mathbf{x}\end{align}
:<math>\begin{matrix}\begin{align}-x_{0}^{2}+\cdots+x_{n}^{2} & =-x_{0}^{\prime2}+\dots+x_{n}^{\prime2}\\
& =q'=\mathbf{x}^{\mathrm{\prime T}}\cdot\mathbf{A}'\cdot\mathbf{x}'\\
b=\sum_{0}^{n}A_{ij}x_{i}y_{j}=\mathbf{x}^{\mathrm{T}}\cdot\mathbf{A}\cdot\mathbf{y} & =b'=\mathbf{x}^{\mathrm{\prime T}}\cdot\mathbf{A}'\cdot\mathbf{y}'
\end{align}
\quad\left(A_{ij}=A_{ji}\right)\\
\hline \left.\begin{align}x_{i}^{\prime} & =\sum_{j=0}^{n}g_{ij}x_{j}=\mathbf{g}\cdot\mathbf{x}\\
x_{i} & =\sum_{j=0}^{n}g_{ij}^{(-1)}x_{j}^{\prime}=\mathbf{g}^{-1}\cdot\mathbf{x}'
\end{align}
\right|\mathbf{g}^{{\rm T}}\cdot\mathbf{A}\cdot\mathbf{g}=\mathbf{A}'
\end{matrix}</math>|{{equationRef|Q1}}}}

in which case ''n=1'' is the [[binary quadratic form]], ''n=2'' is the ternary quadratic form, ''n=3'' is the quaternary quadratic form.

<p style="border:1px solid black">{{Wikiversity-inline|list=
The binary quadratic form was introduced by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Gauss|Lagrange (1773) and Gauss (1798/1801)]], and the ternary quadratic form by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Gauss2|Gauss (1798/1801)]].}}</p>

The general Lorentz transformation follows from ({{equationNote|Q1}}) by setting '''A'''='''A′'''=diag(-1,1,...,1) and det '''g'''=±1. It forms an [[indefinite orthogonal group]] called the [[Lorentz group]] O(1,n), while the case det '''g'''=+1 forms the restricted [[Lorentz group]] SO(1,n). The quadratic form ''q(x)'' becomes the [[Lorentz interval]] in terms of an [[indefinite quadratic form]] of [[Minkowski space]] (being a special case of [[pseudo-Euclidean space]]), and the associated bilinear form ''b(x)'' becomes the [[Minkowski inner product]]:<ref name=ratcliffe>Ratcliffe (1994), 3.1 and Theorem 3.1.4 and Exercise 3.1</ref><ref>Naimark (1964), 2 in four dimensions</ref>

{{NumBlk|:|<math>\begin{matrix}\begin{align}-x_{0}^{2}+\cdots+x_{n}^{2} & =-x_{0}^{\prime2}+\dots+x_{n}^{\prime2}\\
-x_{0}y_{0}+\cdots+x_{n}y_{n} & =-x_{0}^{\prime}y_{0}^{\prime}+\cdots+x_{n}^{\prime}y_{n}^{\prime}
-x_{0}y_{0}+\cdots+x_{n}y_{n} & =-x_{0}^{\prime}y_{0}^{\prime}+\cdots+x_{n}^{\prime}y_{n}^{\prime}
\end{align}
\end{align}
\\
\\
\hline \left.\begin{matrix}\mathbf{x}'=\mathbf{g}\cdot\mathbf{x}\\
\hline \begin{matrix}\mathbf{x}'=\mathbf{g}\cdot\mathbf{x}\\
\mathbf{x}=\mathbf{g}^{-1}\cdot\mathbf{x}'
\downarrow\\
\end{matrix}\\
\begin{align}x_{0}^{\prime} & =x_{0}g_{00}+x_{1}g_{01}+\dots+x_{n}g_{0n}\\
\hline \begin{matrix}\begin{align}\mathbf{A}\cdot\mathbf{g}^{\mathrm{T}}\cdot\mathbf{A} & =\mathbf{g}^{-1}\\
x_{1}^{\prime} & =x_{0}g_{10}+x_{1}g_{11}+\dots+x_{n}g_{1n}\\
& \dots\\
x_{n}^{\prime} & =x_{0}g_{n0}+x_{1}g_{n1}+\dots+x_{n}g_{nn}
\end{align}
\\
\\
\mathbf{x}=\mathbf{g}^{-1}\cdot\mathbf{x}'\\
\downarrow\\
\begin{align}x_{0} & =x_{0}^{\prime}g_{00}-x_{1}^{\prime}g_{10}-\dots-x_{n}^{\prime}g_{n0}\\
x_{1} & =-x_{0}^{\prime}g_{01}+x_{1}^{\prime}g_{11}+\dots+x_{n}^{\prime}g_{n1}\\
& \dots\\
x_{n} & =-x_{0}^{\prime}g_{0n}+x_{1}^{\prime}g_{1n}+\dots+x_{n}^{\prime}g_{nn}
\end{align}
\end{matrix}\right|\begin{matrix}\begin{align}\mathbf{A}\cdot\mathbf{g}^{\mathrm{T}}\cdot\mathbf{A} & =\mathbf{g}^{-1}\\
\mathbf{g}^{{\rm T}}\cdot\mathbf{A}\cdot\mathbf{g} & =\mathbf{A}\\
\mathbf{g}^{{\rm T}}\cdot\mathbf{A}\cdot\mathbf{g} & =\mathbf{A}\\
\mathbf{g}\cdot\mathbf{A}\cdot\mathbf{g}^{\mathrm{T}} & =\mathbf{A}\\
\mathbf{g}\cdot\mathbf{A}\cdot\mathbf{g}^{\mathrm{T}} & =\mathbf{A}
\\
\end{align}
\end{align}
\\
\begin{align}\sum_{i=1}^{n}g_{ij}g_{ik}-g_{0j}g_{0k} & =\left\{ \begin{align}-1\quad & (j=k=0)\\
1\quad & (j=k>0)\\
0\quad & (j\ne k)
\end{align}
\right.\\
\sum_{j=1}^{n}g_{ij}g_{kj}-g_{i0}g_{k0} & =\left\{ \begin{align}-1\quad & (i=k=0)\\
1\quad & (i=k>0)\\
0\quad & (i\ne k)
\end{align}
\right.
\end{align}
\end{matrix}
\end{matrix}</math>|{{equationRef|1a}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
Such general Lorentz transformations ({{equationNote|1a}}) for various dimensions were used by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Gauss4|Gauss (1818)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Jacobi|Jacobi (1827, 1833)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Lebesgue|Lebesgue (1837)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Bour|Bour (1856)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Somov|Somov (1863)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Hill|Hill (1882)]] in order to simplify computations of [[elliptic function]]s and integrals.<ref>Musen (1970) pointed out the intimate connection of Hill's scalar development and Minkowski's pseudo-Euclidean 3D space.</ref><ref>Touma et al. (2009) showed the analogy between Gauss and Hill's equations and Lorentz transformations, see eq. 22-29.</ref> They were also used by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Poincare|Poincaré (1881)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Cox|Cox (1881/82)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Picard|Picard (1882, 1884)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Killing|Killing (1885, 1893)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Gerard|Gérard (1892)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Hausdorff|Hausdorff (1899)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Woods2|Woods (1901, 1903)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Liebmann|Liebmann (1904/05)]] to describe [[hyperbolic motion]]s (i.e. rigid motions in the [[hyperbolic plane]] or [[hyperbolic space]]), which were expressed in terms of Weierstrass coordinates of the [[hyperboloid model]] satisfying the relation <math>-x_{0}^{2}+\cdots+x_{n}^{2}=-1</math> or in terms of the [[Cayley–Klein metric]] of [[projective geometry]] using the "absolute" form <math>-x_{0}^{2}+\cdots+x_{n}^{2}=0</math>.<ref>Müller (1910), p. 661, in particular footnote 247.</ref><ref>Sommerville (1911), p. 286, section K6.</ref> In addition, [[infinitesimal transformation]]s related to the [[Lie algebra]] of the group of hyperbolic motions were given in terms of Weierstrass coordinates <math>-x_{0}^{2}+\cdots+x_{n}^{2}=-1</math> by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Killing3|Killing (1888-1897)]].}}</p>

If <math>x_{i},\ x_{i}^{\prime}</math> in ({{equationNote|1a}}) are interpreted as [[homogeneous coordinates]], then the corresponding inhomogenous coordinates <math>u_{s},\ u_{s}^{\prime}</math> follow by

:<math>\left[\frac{x_{0}}{x_{0}},\ \frac{x_{s}}{x_{0}}\right]=\left[1,\ u_{s}\right],\ \left[\frac{x_{0}^{\prime}}{x_{0}^{\prime}},\ \frac{x_{s}^{\prime}}{x_{0}^{\prime}}\right]=\left[1,\ u_{s}^{\prime}\right],\ (s=1,2\dots n)</math>

so that the Lorentz transformation becomes a [[homography]] leaving invariant the equation of the [[unit sphere]], which [[John Lighton Synge]] called "the most general formula for the composition of velocities" in terms of special relativity (the transformation matrix '''g''' stays the same as in ({{equationNote|1a}})):<ref>Synge (1955), p. 129 for ''n''=3</ref>

{{NumBlk|:|<math>\begin{matrix}\begin{matrix}-x_{0}^{2}+\cdots+x_{n}^{2}=-x_{0}^{\prime2}+\dots+x_{n}^{\prime2} & \rightarrow & \begin{align}-1+u_{1}^{2}+\cdots+u_{n}^{2} & ={\scriptstyle \frac{-1+u_{1}^{\prime2}+\cdots+u_{n}^{\prime2}}{\left(g_{00}+g_{01}u_{1}^{\prime}+\dots+g_{0n}u_{n}^{\prime}\right)^{2}}}\\
{\scriptstyle \frac{-1+u_{1}^{2}+\cdots+u_{n}^{2}}{\left(g_{00}-g_{10}u_{1}-\dots-g_{n0}u_{n}\right)^{2}}} & =-1+u_{1}^{\prime2}+\cdots+u_{n}^{\prime2}
\end{align}
\\
\hline -x_{0}^{2}+\cdots+x_{n}^{2}=-x_{0}^{\prime2}+\dots+x_{n}^{\prime2}=0 & \rightarrow & -1+u_{1}^{2}+\cdots+u_{n}^{2}=-1+u_{1}^{\prime2}+\cdots+u_{n}^{\prime2}=0
\end{matrix}\\
\end{matrix}\\
\hline \mathbf{A}={\rm diag}(-1,1,\dots,1)\\
\hline \begin{align}u_{s}^{\prime} & =\frac{g_{s0}+g_{s1}u_{1}+\dots+g_{sn}u_{n}}{g_{00}+g_{01}u_{1}+\dots+g_{0n}u_{n}}\\
\det \mathbf{g}=\pm1
\\
u_{s} & =\frac{-g_{0s}+g_{1s}u_{1}^{\prime}+\dots+g_{ns}u_{n}^{\prime}}{g_{00}-g_{10}u_{1}^{\prime}-\dots-g_{n0}u_{n}^{\prime}}
\end{align}
\left|\begin{align}\sum_{i=1}^{n}g_{ij}g_{ik}-g_{0j}g_{0k} & =\left\{ \begin{align}-1\quad & (j=k=0)\\
1\quad & (j=k>0)\\
0\quad & (j\ne k)
\end{align}
\right.\\
\sum_{j=1}^{n}g_{ij}g_{kj}-g_{i0}g_{k0} & =\left\{ \begin{align}-1\quad & (i=k=0)\\
1\quad & (i=k>0)\\
0\quad & (i\ne k)
\end{align}
\right.
\end{align}
\right.
\end{matrix}</math>|{{equationRef|1b}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
Such Lorentz transformations for various dimensions were used by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Gauss4|Gauss (1818)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Jacobi|Jacobi (1827–1833)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Lebesgue|Lebesgue (1837)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Bour|Bour (1856)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Somov|Somov (1863)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Hill|Hill (1882)]], [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Callandreau|Callandreau (1885)]] in order to simplify computations of elliptic functions and integrals, by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Picard|Picard (1882-1884)]] in relation to [[Hermitian form|Hermitian quadratic form]]s, or by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Woods2|Woods (1901, 1903)]] in terms of the [[Beltrami–Klein model]] of hyperbolic geometry. In addition, infinitesimal transformations in terms of the [[Lie algebra]] of the group of hyperbolic motions leaving invariant the unit sphere <math>-1+u_{1}^{\prime2}+\cdots+u_{n}^{\prime2}=0</math> were given by [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Lie3|Lie (1885-1893) and Werner (1889)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (general)#Killing3|Killing (1888-1897)]].}}</p>

== {{anchor|Lorimag}}Lorentz transformation via imaginary orthogonal transformation ==
By using the [[Imaginary unit|imaginary]] quantities <math>[\mathfrak{x}_{0},\ \mathfrak{x}'_{0}]=\left[ix_{0},\ ix_{0}^{\prime}\right]</math> in '''x''' as well as <math>[\mathfrak{g}_{0s},\ \mathfrak{g}_{s0}]=\left[ig_{0s},\ ig_{s0}\right]</math> ''(s=1,2...n)'' in '''g''', the Lorentz transformation ({{equationNote|1a}}) assumes the form of an [[orthogonal transformation]] of [[Euclidean space]] forming the [[orthogonal group]] O(n) if det '''g'''=±1 or the special orthogonal group SO(n) if det '''g'''=+1, the Lorentz interval becomes the [[Euclidean norm]], and the Minkowski inner product becomes the [[dot product]]:<ref>Laue (1921), pp. 79–80 for n=3</ref>

{{NumBlk|:|<math>\begin{matrix}\begin{align}\mathfrak{x}_{0}^{2}+x_{1}^{2}+\cdots+x_{n}^{2} & =\mathfrak{x}_{0}^{\prime2}+x_{1}^{\prime2}+\dots+x_{n}^{\prime2}\\
\mathfrak{x}_{0}\mathfrak{y}_{0}+x_{1}y_{1}+\cdots+x_{n}y_{n} & =\mathfrak{x}_{0}^{\prime}\mathfrak{y}_{0}^{\prime}+x_{1}^{\prime}y_{1}^{\prime}+\cdots+x_{n}^{\prime}y_{n}^{\prime}
\end{align}
\\
\hline \begin{matrix}\mathbf{x}'=\mathbf{g}\cdot\mathbf{x}\\
\mathbf{x}=\mathbf{\mathbf{g}^{-1}}\cdot\mathbf{x}'
\end{matrix}\left|\begin{align}\sum_{i=0}^{n}g_{ij}g_{ik} & =\left\{ \begin{align}1\quad & (j=k)\\
0\quad & (j\ne k)
\end{align}
\right.\\
\sum_{j=0}^{n}g_{ij}g_{kj} & =\left\{ \begin{align}1\quad & (i=k)\\
0\quad & (i\ne k)
\end{align}
\right.
\end{align}
\right.
\end{matrix}</math>|{{equationRef|2a}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The cases ''n=1,2,3,4'' of orthogonal transformations in terms of real coordinates were discussed by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Euler|Euler (1771)]] and in ''n'' dimensions by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Cauchy|Cauchy (1829)]]. The case in which one of these coordinates is imaginary and the other ones remain real was alluded to by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Lie|Lie (1871)]] in terms of spheres with imaginary radius, while the interpretation of the imaginary coordinate as being related to the dimension of time as well as the explicit formulation of Lorentz transformations with ''n=3'' was given by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Minkowski|Minkowski (1907)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Sommerfeld|Sommerfeld (1909)]].}}</p>

A well known example of this orthogonal transformation is spatial [[rotation]] in terms of [[trigonometric function]]s, which become Lorentz transformations by using an imaginary angle <math>\phi=i\eta</math>, so that trigonometric functions become equivalent to [[hyperbolic function]]s:

{{NumBlk|:|<math>\begin{array}{c|c|cc}
\mathfrak{x}_{0}^{2}+x_{1}^{2}+x_{2}^{2}=\mathfrak{x}_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2} & \left(ix_{0}\right){}^{2}+x_{1}^{2}+x_{2}^{2}=\left(ix_{0}^{\prime}\right)^{2}+x_{1}^{\prime2}+x_{2}^{\prime2} & & -x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline (1)\begin{align}\mathfrak{x}_{0}^{\prime} & =\mathfrak{x}_{0}\cos\phi-x_{1}\sin\phi\\
x_{1}^{\prime} & =\mathfrak{x}_{0}\sin\phi+x_{1}\cos\phi\\
x_{2}^{\prime} & =x_{2}\\
\\
\mathfrak{x}_{0} & =\mathfrak{x}_{0}^{\prime}\cos\phi+x_{1}^{\prime}\sin\phi\\
x_{1} & =-\mathfrak{x}_{0}^{\prime}\sin\phi+x_{1}^{\prime}\cos\phi\\
x_{2} & =x_{2}^{\prime}
\end{align}
& (2)\begin{align}ix_{0}^{\prime} & =ix_{0}\cos i\eta-x_{1}\sin i\eta\\
x_{1}^{\prime} & =ix_{0}\sin i\eta+x_{1}\cos i\eta\\
x_{2}^{\prime} & =x_{2}\\
\\
ix_{0} & =ix_{0}^{\prime}\cos i\eta+x_{1}^{\prime}\sin i\eta\\
x_{1} & =-ix_{0}^{\prime}\sin i\eta+x_{1}^{\prime}\cos i\eta\\
x_{2} & =x_{2}^{\prime}
\end{align}
& \rightarrow & \begin{align}x_{0}^{\prime} & =x_{0}\cosh\eta-x_{1}\sinh\eta\\
x_{1}^{\prime} & =-x_{0}\sinh\eta+x_{1}\cosh\eta\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{0} & =x_{0}^{\prime}\cosh\eta+x_{1}^{\prime}\sinh\eta\\
x_{1} & =x_{0}^{\prime}\sinh\eta+x_{1}^{\prime}\cosh\eta\\
x_{2} & =x_{2}^{\prime}
\end{align}
\end{array}</math>|{{equationRef|2b}}}}

or in exponential form using [[Euler's formula]] <math>e^{i\phi}=\cos\phi+i\sin\phi</math>:

{{NumBlk|:|<math>\begin{array}{c|c|cc}
\mathfrak{x}_{0}^{2}+x_{1}^{2}+x_{2}^{2}=\mathfrak{x}_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2} & \left(ix_{0}\right){}^{2}+x_{1}^{2}+x_{2}^{2}=\left(ix_{0}^{\prime}\right)^{2}+x_{1}^{\prime2}+x_{2}^{\prime2} & & -x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline (1)\begin{align}x_{1}^{\prime}+i\mathfrak{x}_{0}^{\prime} & =e^{-i\phi}\left(x_{1}+i\mathfrak{x}_{0}\right)\\
x_{1}^{\prime}-i\mathfrak{x}_{0}^{\prime} & =e^{i\phi}\left(x_{1}-i\mathfrak{x}_{0}\right)\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{1}+i\mathfrak{x}_{0} & =e^{i\phi}\left(x_{1}^{\prime}+i\mathfrak{x}_{0}^{\prime}\right)\\
x_{1}-i\mathfrak{x}_{0} & =e^{-i\phi}\left(x_{1}^{\prime}-i\mathfrak{x}_{0}^{\prime}\right)\\
x_{2} & =x_{2}^{\prime}
\end{align}
& (2)\begin{align}x_{1}^{\prime}+i\left(ix_{0}^{\prime}\right) & =e^{-i(i\eta)}\left(x_{1}+i\left(ix_{0}\right)\right)\\
x_{1}^{\prime}-i\left(ix_{0}^{\prime}\right) & =e^{i(i\eta)}\left(x_{1}-i\left(ix_{0}\right)\right)\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{1}+i\left(ix_{0}\right) & =e^{i(i\eta)}\left(x_{1}^{\prime}+i\left(ix_{0}^{\prime}\right)\right)\\
x_{1}-i\left(ix_{0}\right) & =e^{-i(i\eta)}\left(x_{1}^{\prime}-i\left(ix_{0}^{\prime}\right)\right)\\
x_{2} & =x_{2}^{\prime}
\end{align}
& \rightarrow & \begin{align}x_{1}^{\prime}-x_{0}^{\prime} & =e^{\eta}\left(x_{1}-x_{0}\right)\\
x_{1}^{\prime}+x_{0}^{\prime} & =e^{-\eta}\left(x_{1}+x_{0}\right)\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{1}-x_{0} & =e^{-\eta}\left(x_{1}^{\prime}-x_{0}^{\prime}\right)\\
x_{1}+x_{0} & =e^{\eta}\left(x_{1}^{\prime}+x_{0}^{\prime}\right)\\
x_{2} & =x_{2}^{\prime}
\end{align}
\end{array}</math>|{{equationRef|2c}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
Defining <math>[\mathfrak{x}_{0},\ \mathfrak{x}'_{0},\ \phi]</math> as real, spatial rotation in the form ({{equationNote|2b}}-1) was introduced by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Euler2|Euler (1771)]] and in the form ({{equationNote|2c}}-1) by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Euler3|Wessel (1799)]]. The interpretation of ({{equationNote|2b}}) as Lorentz boost (i.e. Lorentz transformation ''without'' spatial rotation) in which <math>[\mathfrak{x}_{0},\ \mathfrak{x}'_{0},\ \phi]</math> correspond to the imaginary quantities <math>[ix_{0},\ ix'_{0},\ i\eta]</math> was given by [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Minkowski|Minkowski (1907)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)#Sommerfeld|Sommerfeld (1909)]]. As shown in the next section using hyperbolic functions, ({{equationNote|2b}}) becomes ({{equationNote|3b}}) while ({{equationNote|2c}}) becomes ({{equationNote|3d}}).}}</p>

== {{anchor|Lorhyp}}Lorentz transformation via hyperbolic functions ==

The case of a Lorentz transformation without spatial rotation is called a [[Lorentz boost]]. The simplest case can be given, for instance, by setting ''n=1'' in ({{equationNote|1a}}):

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
\hline \begin{align}x_{0}^{\prime} & =x_{0}g_{00}+x_{1}g_{01}\\
x_{1}^{\prime} & =x_{0}g_{10}+x_{1}g_{11}\\
\\
x_{0} & =x_{0}^{\prime}g_{00}-x_{1}^{\prime}g_{10}\\
x_{1} & =-x_{0}^{\prime}g_{01}+x_{1}^{\prime}g_{11}
\end{align}
\left|\begin{align}g_{01}^{2}-g_{00}^{2} & =-1\\
g_{11}^{2}-g_{10}^{2} & =1\\
g_{01}g_{11}-g_{00}g_{10} & =0\\
g_{10}^{2}-g_{00}^{2} & =-1\\
g_{11}^{2}-g_{01}^{2} & =1\\
g_{10}g_{11}-g_{00}g_{01} & =0
\end{align}
\rightarrow\begin{align}g_{00}^{2} & =g_{11}^{2}\\
g_{01}^{2} & =g_{10}^{2}
\end{align}
\right.
\end{matrix}</math>
\end{matrix}</math>


It forms an [[indefinite orthogonal group]] called the [[Lorentz group]] O(1,n), while the case det '''g'''=+1 forms the restricted [[Lorentz group]] SO(1,n). The quadratic form becomes the [[Lorentz interval]] in terms of an [[indefinite quadratic form]] of [[Minkowski space]] (being a special case of [[pseudo-Euclidean space]]), and the associated bilinear form becomes the [[Minkowski inner product]].<ref name=ratcliffe>Ratcliffe (1994), 3.1 and Theorem 3.1.4 and Exercise 3.1</ref><ref>Naimark (1964), 2 in four dimensions</ref> Long before the advent of special relativity it was used in topics such as the [[Cayley–Klein metric]], [[hyperboloid model]] and other models of [[hyperbolic geometry]], computations of [[elliptic function]]s and integrals, transformation of [[indefinite quadratic form]]s, [[squeeze mapping]]s of the hyperbola, [[group theory]], [[Möbius transformation]]s, [[spherical wave transformation]], transformation of the [[Sine-Gordon equation]], [[Biquaternion]] algebra, [[split-complex numbers]], [[Clifford algebra]], and others.
or in matrix notation


<div style="border:1px solid black">{{Wikiversity inline|list=
<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
*{{anchor|Lorgen}}''The [[v:History of Topics in Special Relativity/Lorentz transformation (general)|Wikiversity: History of most general Lorentz transformations]]''
\hline \left.\begin{align}\mathbf{x}' & =\begin{bmatrix}g_{00} & g_{01}\\
::includes contributions of [[Carl Friedrich Gauss]] (1818), [[Carl Gustav Jacob Jacobi]] (1827, 1833/34), [[Michel Chasles]] (1829), [[Victor-Amédée Lebesgue]] (1837), [[Thomas Weddle]] (1847), [[Edmond Bour]] (1856), [[Osip Ivanovich Somov]] (1863), [[Wilhelm Killing]] (1878–1893), [[Henri Poincaré]] (1881), [[Homersham Cox (mathematician)|Homersham Cox]] (1881–1883), [[George William Hill]] (1882), [[Émile Picard]] (1882-1884), [[Octave Callandreau]] (1885), [[Sophus Lie]] (1885-1890), [[Louis Gérard]] (1892), [[Felix Hausdorff]] (1899), [[Frederick S. Woods]] (1901-05), [[Heinrich Liebmann]] (1904/05).
g_{10} & g_{11}
*{{anchor|Lorimag}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (imaginary)|Wikiversity: History of Lorentz transformations via imaginary orthogonal transformation]]''
\end{bmatrix}\cdot\mathbf{x}\\
::includes contributions of [[Sophus Lie]] (1871), [[Hermann Minkowski]] (1907–1908), [[Arnold Sommerfeld]] (1909).
\mathbf{x} & =\begin{bmatrix}g_{00} & -g_{10}\\
*{{anchor|Lorhyp}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)|Wikiversity: History of Lorentz transformations via hyperbolic functions]]''
-g_{01} & g_{11}
::includes contributions of [[Vincenzo Riccati]] (1757), [[Johann Heinrich Lambert]] (1768–1770), [[Franz Taurinus]] (1826), [[Eugenio Beltrami]] (1868), [[Charles-Ange Laisant]] (1874), [[Gustav von Escherich]] (1874), [[James Whitbread Lee Glaisher]] (1878), [[Siegmund Günther]] (1880/81), [[Homersham Cox (mathematician)|Homersham Cox]] (1881/82), [[Rudolf Lipschitz]] (1885/86), [[Friedrich Schur]] (1885-1902), [[Ferdinand von Lindemann]] (1890–91), [[Louis Gérard]] (1892), [[Wilhelm Killing]] (1893-97), [[Alfred North Whitehead]] (1897/98), [[Edwin Bailey Elliott]] (1903), [[Frederick S. Woods]] (1903), [[Heinrich Liebmann]] (1904/05), [[Philipp Frank]] (1909), [[Gustav Herglotz]] (1909/10), [[Vladimir Varićak]] (1910).
\end{bmatrix}\cdot\mathbf{x}'
*{{anchor|Lorconf}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (conformal)|Wikiversity: History of Lorentz transformations via sphere transformation]]''
\end{align}
::includes contributions of [[Pierre Ossian Bonnet]] (1856), [[Albert Ribaucour]] (1870), [[Sophus Lie]] (1871a), [[Gaston Darboux]] (1873-87), [[Edmond Laguerre]] (1880), [[Cyparissos Stephanos]] (1883), [[Georg Scheffers]] (1899), [[Percey F. Smith]] (1900), [[Harry Bateman]] and [[Ebenezer Cunningham]] (1909–1910).
\right|\det\begin{bmatrix}g_{00} & g_{01}\\
*{{anchor|Lorcay}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)|Wikiversity: History of Lorentz transformations via Cayley–Hermite transformation]]''
g_{10} & g_{11}
::was used by [[Arthur Cayley]] (1846–1855), [[Charles Hermite]] (1853, 1854), [[Paul Gustav Heinrich Bachmann]] (1869), [[Edmond Laguerre]] (1882), [[Gaston Darboux]] (1887), [[Percey F. Smith]] (1900), [[Émile Borel]] (1913).
\end{bmatrix}=1
*{{anchor|Lormoeb}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)|Wikiversity: History of Lorentz transformations via Cayley–Klein parameters, Möbius and spin transformations]]''
\end{matrix}</math>|{{equationRef|3a}}}}
::includes contributions of [[Carl Friedrich Gauss]] (1801/63), [[Felix Klein]] (1871–97), [[Eduard Selling]] (1873–74), [[Henri Poincaré]] (1881), [[Luigi Bianchi]] (1888-93), [[Robert Fricke]] (1891–97), [[Frederick S. Woods]] (1895), [[Gustav Herglotz]] (1909/10).
*{{anchor|Lorqua}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)|Wikiversity: History of Lorentz transformations via quaternions and hyperbolic numbers]]''
::includes contributions of [[James Cockle]] (1848), [[Homersham Cox (mathematician)|Homersham Cox]] (1882/83), [[Cyparissos Stephanos]] (1883), [[Arthur Buchheim]] (1884), [[Rudolf Lipschitz]] (1885/86), [[Theodor Vahlen]] (1901/02), [[Fritz Noether]] (1910), [[Felix Klein]] (1910), [[Arthur W. Conway]] (1911), [[Ludwik Silberstein]] (1911).
*{{anchor|Lortrig}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)|Wikiversity: Lorentz transformation via trigonometric functions]]''
::includes contributions of [[Luigi Bianchi]] (1886), [[Gaston Darboux]] (1891/94), [[Georg Scheffers]] (1899), [[Luther Pfahler Eisenhart]] (1905), [[Vladimir Varićak]] (1910), [[Henry Crozier Keating Plummer]] (1910), [[Paul Gruner]] (1921).
*{{anchor|Lorsqu}}The ''[[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)|Wikiversity: History of Lorentz transformations via squeeze mappings]]''
::includes contributions of [[Antoine André Louis Reynaud]] (1819), [[Felix Klein]] (1871), [[Charles-Ange Laisant]] (1874), [[Sophus Lie]] (1879-84), [[Siegmund Günther]] (1880/81), [[Edmond Laguerre]] (1882), [[Gaston Darboux]] (1883–1891), [[Rudolf Lipschitz]] (1885/86), [[Luigi Bianchi]] (1886–1894), [[Ferdinand von Lindemann]] (1890/91), [[Mellen W. Haskell]] (1895), [[Percey F. Smith]] (1900), [[Edwin Bailey Elliott]] (1903), [[Luther Pfahler Eisenhart]] (1905).}}</div>


==Electrodynamics and special relativity==
which resembles precisely the relations of [[hyperbolic function]]s in terms of [[hyperbolic angle]] <math>\eta</math>. Thus by adding an unchanged <math>x_{2}</math>-axis, a Lorentz boost or [[hyperbolic rotation]] for ''n=2'' (being the same as a rotation around an imaginary angle <math>i\eta=\phi</math> in ({{equationNote|2b}}) or a [[Translation (geometry)|translation]] in the hyperbolic plane in terms of the hyperboloid model) is given by
===Overview===

In the [[special relativity]], Lorentz transformations exhibit the symmetry of [[Minkowski spacetime]] by using a constant ''c'' as the [[speed of light]], and a parameter ''v'' as the relative [[velocity]] between two [[inertial reference frames]]. Using the above conditions, the Lorentz transformation in 3+1 dimensions assume the form:
{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline g_{00}=g_{11}=\cosh\eta,\ g_{01}=g_{10}=-\sinh\eta\\
\hline \left.\begin{align}x_{0}^{\prime} & =x_{0}\cosh\eta-x_{1}\sinh\eta\\
x_{1}^{\prime} & =-x_{0}\sinh\eta+x_{1}\cosh\eta\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{0} & =x_{0}^{\prime}\cosh\eta+x_{1}^{\prime}\sinh\eta\\
x_{1} & =x_{0}^{\prime}\sinh\eta+x_{1}^{\prime}\cosh\eta\\
x_{2} & =x_{2}^{\prime}
\end{align}
\right|{\scriptstyle \begin{align}\sinh^{2}\eta-\cosh^{2}\eta & =-1 & (a)\\
\cosh^{2}\eta-\sinh^{2}\eta & =1 & (b)\\
\frac{\sinh\eta}{\cosh\eta} & =\tanh\eta & (c)\\
\frac{1}{\sqrt{1-\tanh^{2}\eta}} & =\cosh\eta & (d)\\
\frac{\tanh\eta}{\sqrt{1-\tanh^{2}\eta}} & =\sinh\eta & (e)\\
\frac{\tanh q\pm\tanh\eta}{1\pm\tanh q\tanh\eta} & =\tanh\left(q\pm\eta\right) & (f)
\end{align}
}
\end{matrix}</math>

or in matrix notation

<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
\hline \left.\begin{align}\mathbf{x}' & =\begin{bmatrix}\cosh\eta & -\sinh\eta\\
-\sinh\eta & \cosh\eta
\end{bmatrix}\cdot\mathbf{x}\\
\mathbf{x} & =\begin{bmatrix}\cosh\eta & \sinh\eta\\
\sinh\eta & \cosh\eta
\end{bmatrix}\cdot\mathbf{x}'
\end{align}
\right|\det\begin{bmatrix}\cosh\eta & -\sinh\eta\\
-\sinh\eta & \cosh\eta
\end{bmatrix}=1
\end{matrix}</math>|{{equationRef|3b}}}}

in which the rapidity can be composed of arbitrary many rapidities <math>\eta_{1},\eta_{2}\dots</math> as per the [[Hyperbolic functions#Sums of arguments|angle sum laws of hyperbolic sines and cosines]], so that one hyperbolic rotation can represent the sum of many other hyperbolic rotations, analogous to the relation between [[List of trigonometric identities#Angle sum and difference identities|angle sum laws of circular trigonometry]] and spatial rotations. Alternatively, the hyperbolic angle sum laws ''themselves'' can be interpreted as Lorentz boosts, as demonstrated by using the parameterization of the [[unit hyperbola]]:

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}=1\\
\hline \left[\eta=\eta_{2}-\eta_{1}\right]\\
\begin{align}x_{0}^{\prime} & =\sinh\eta_{1} & & =\sinh\left(\eta_{2}-\eta\right) & & =\sinh\eta_{2}\cosh\eta-\cosh\eta_{2}\sinh\eta & & =x_{0}\cosh\eta-x_{1}\sinh\eta\\
x_{1}^{\prime} & =\cosh\eta_{1} & & =\cosh\left(\eta_{2}-\eta\right) & & =-\sinh\eta_{2}\sinh\eta+\cosh\eta_{2}\cosh\eta & & =-x_{0}\sinh\eta+x_{1}\cosh\eta\\
\\
x_{0} & =\sinh\eta_{2} & & =\sinh\left(\eta_{1}+\eta\right) & & =\sinh\eta_{1}\cosh\eta+\cosh\eta_{1}\sinh\eta & & =x_{0}^{\prime}\cosh\eta+x_{1}^{\prime}\sinh\eta\\
x_{1} & =\cosh\eta_{2} & & =\cosh\left(\eta_{1}+\eta\right) & & =\sinh\eta_{1}\sinh\eta+\cosh\eta_{1}\cosh\eta & & =x_{0}^{\prime}\sinh\eta+x_{1}^{\prime}\cosh\eta
\end{align}
\end{matrix}</math>

or in matrix notation

<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}=1\\
\hline \begin{align} & \begin{bmatrix}x_{0}^{\prime}\\
x_{1}^{\prime}
\end{bmatrix}=\begin{bmatrix}\sinh\eta_{1}\\
\cosh\eta_{1}
\end{bmatrix}=\begin{bmatrix}\sinh\left(\eta_{2}-\eta\right)\\
\cosh\left(\eta_{2}-\eta\right)
\end{bmatrix}=\begin{bmatrix}\cosh\eta & -\sinh\eta\\
-\sinh\eta & \cosh\eta
\end{bmatrix}\cdot\begin{bmatrix}\sinh\eta_{2}\\
\cosh\eta_{2}
\end{bmatrix} & & =\begin{bmatrix}\cosh\eta & -\sinh\eta\\
-\sinh\eta & \cosh\eta
\end{bmatrix}\cdot\begin{bmatrix}x_{0}\\
x_{1}
\end{bmatrix}\\
& \begin{bmatrix}x_{0}\\
x_{1}
\end{bmatrix}=\begin{bmatrix}\sinh\eta_{2}\\
\cosh\eta_{2}
\end{bmatrix}=\begin{bmatrix}\sinh\left(\eta_{1}+\eta\right)\\
\cosh\left(\eta_{1}+\eta\right)
\end{bmatrix}=\begin{bmatrix}\cosh\eta & \sinh\eta\\
\sinh\eta & \cosh\eta
\end{bmatrix}\cdot\begin{bmatrix}\sinh\eta_{1}\\
\cosh\eta_{1}
\end{bmatrix} & & =\begin{bmatrix}\cosh\eta & \sinh\eta\\
\sinh\eta & \cosh\eta
\end{bmatrix}\cdot\begin{bmatrix}x_{0}^{\prime}\\
x_{1}^{\prime}
\end{bmatrix}
\end{align}
\end{matrix}</math>|{{equationRef|3c}}}}

Finally, Lorentz boost ({{equationNote|3b}}) assumes a simple form by using [[squeeze mapping]]s in analogy to Euler's formula in ({{equationNote|2c}}):<ref name=rind>Rindler (1969), p. 45</ref>

{{NumBlk|:|<math>(1)\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \begin{align}x_{1}^{\prime}-x_{0}^{\prime} & =e^{\eta}\left(x_{1}-x_{0}\right)\\
x_{1}^{\prime}+x_{0}^{\prime} & =e^{-\eta}\left(x_{1}+x_{0}\right)\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{1}-x_{0} & =e^{-\eta}\left(x_{1}^{\prime}-x_{0}^{\prime}\right)\\
x_{1}+x_{0} & =e^{\eta}\left(x_{1}^{\prime}+x_{0}^{\prime}\right)\\
x_{2} & =x_{2}^{\prime}
\end{align}
\end{matrix}\left|{\scriptstyle \begin{align}X_{1} & =x_{1}+x_{0}\\
X_{2} & =x_{2}\\
X_{3} & =x_{1}-x_{0}\\
\\
a_{1} & =e^{-\eta}\\
a_{2} & =1\\
a_{3} & =e^{\eta}=a_{1}^{-1}
\end{align}
}(2)\begin{matrix}X_{2}^{\prime2}-X_{1}^{\prime}X_{3}^{\prime}=X_{2}^{2}-X_{1}X_{3}\\
\hline \begin{align}X_{1}^{\prime} & =a_{1}X_{1}\\
X_{2}^{\prime} & =a_{2}X_{2}\\
X_{3}^{\prime} & =a_{3}X_{3}\\
\\
X_{1} & =a_{3}X_{1}^{\prime}\\
X_{2} & =a_{2}X_{2}^{\prime}\\
X_{3} & =a_{1}X_{3}^{\prime}
\end{align}
\\
\left(a_{1}a_{3}-a_{2}^{2}=0\right)
\end{matrix}\right.</math>|{{equationRef|3d}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
Hyperbolic relations (a,b) on the right of ({{equationNote|3b}}) were given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Riccati|Riccati (1757)]], relations (a,b,c,d,e,f) by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Lambert|Lambert (1768–1770)]]. Lorentz transformations ({{equationNote|3b}}) were given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Laisant|Laisant (1874)]], [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Cox|Cox (1882)]], [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Lindemann|Lindemann (1890/91)]], [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Gerard|Gérard (1892)]], [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Killing2|Killing (1893, 1897/98)]], [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Whitehead|Whitehead (1897/98)]], [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Woods2|Woods (1903/05)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Liebmann|Liebmann (1904/05)]] in terms of Weierstrass coordinates of the [[hyperboloid model]]. Hyperbolic angle sum laws equivalent to Lorentz boost ({{equationNote|3c}}) were given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Riccati|Riccati (1757)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Lambert|Lambert (1768–1770)]], while the matrix representation was given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Glaisher|Glaisher (1878)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Gunther2|Günther (1880/81)]]. Lorentz transformations ({{equationNote|3d}}-1) were given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Lindemann|Lindemann (1890/91)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Herglotz1|Herglotz (1909)]], while formulas equivalent to ({{equationNote|3d}}-2) by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Klein|Klein (1871)]].}}</p>

In line with equation ({{equationNote|1b}}) one can use coordinates <math>[u_{1},\ u_{2},\ 1]=\left[\tfrac{x_{1}}{x_{0}},\ \tfrac{x_{2}}{x_{0}},\ \tfrac{x_{0}}{x_{0}}\right]</math> inside the [[unit circle]] <math>u_{1}^{2}+u_{2}^{2}=1</math>, thus the corresponding Lorentz transformations ({{equationNote|3b}}) obtain the form:

{{NumBlk|:|<math>\begin{matrix}\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2} & \rightarrow & \begin{align}-1+u_{1}^{2}+u_{2}^{2} & =\frac{-1+u_{1}^{\prime2}+u_{2}^{\prime2}}{\left(\cosh\eta+u_{1}^{\prime}\sinh\eta\right)^{2}}\\
\frac{-1+u_{1}^{2}+u_{2}^{2}}{\left(\cosh\eta-u_{1}\sinh\eta\right)^{2}} & =-1+u_{1}^{\prime2}+u_{2}^{\prime2}
\end{align}
\\
\hline -x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}=0 & \rightarrow & -1+u_{x}^{2}+u_{y}^{2}=-1+u_{x}^{\prime2}+u_{y}^{\prime2}=0
\end{matrix}\\
\hline {\scriptstyle \begin{align}\frac{\sinh\eta}{\cosh\eta} & =\tanh\eta=v\\
\cosh\eta & =\frac{1}{\sqrt{1-\tanh^{2}\eta}}
\end{align}
}\left|\begin{align} & (a) & & (b) & & (c)\\
u_{1}^{\prime} & =\frac{-\sinh\eta+u_{1}\cosh\eta}{\cosh\eta-u_{1}\sinh\eta} & & =\frac{u_{1}-\tanh\eta}{1-u_{1}\tanh\eta} & & =\frac{u_{1}-v}{1-u_{1}v}\\
u_{2}^{\prime} & =\frac{u_{2}}{\cosh\eta-u_{1}\sinh\eta} & & =\frac{u_{2}\sqrt{1-\tanh^{2}\eta}}{1-u_{1}\tanh\eta} & & =\frac{u_{2}\sqrt{1-v^{2}}}{1-u_{1}v}\\
\\
u_{1} & =\frac{\sinh\eta+u_{1}^{\prime}\cosh\eta}{\cosh\eta+u_{1}^{\prime}\sinh\eta} & & =\frac{u_{1}^{\prime}+\tanh\eta}{1+u_{1}^{\prime}\tanh\eta} & & =\frac{u_{1}^{\prime}+v}{1+u_{1}^{\prime}v}\\
u_{2} & =\frac{u_{2}^{\prime}}{\cosh\eta+u_{1}^{\prime}\sinh\eta} & & =\frac{u_{2}^{\prime}\sqrt{1-\tanh^{2}\eta}}{1+u_{1}^{\prime}\tanh\eta} & & =\frac{u_{2}^{\prime}\sqrt{1-v^{2}}}{1+u_{1}^{\prime}v}
\end{align}
\right.
\end{matrix}</math>|{{equationRef|3e}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
These Lorentz transformations were given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Escherich|Escherich (1874)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Killing2|Killing (1898)]] (on the left), as well as [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Beltrami|Beltrami (1868)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Schur|Schur (1885/86, 1900/02)]] (on the right) in terms of [[Beltrami–Klein model|Beltrami coordinates]]<ref>Rosenfeld (1988), p. 231</ref> of hyperbolic geometry.}}</p>

By using the scalar product of <math>\left[u_{1},u_{2}\right]</math>, the resulting Lorentz transformation can be seen as equivalent to the [[hyperbolic law of cosines]]:<ref name=pau>Pauli (1921), p. 561</ref><ref group=R name=var>Varićak (1912), p. 108</ref><ref name=barr>Barrett (2006), chapter 4, section 2</ref>

{{NumBlk|:|<math>\begin{matrix} & \begin{matrix}u^{2}=u_{1}^{2}+u_{2}^{2}\\
u'^{2}=u_{1}^{\prime2}+u_{2}^{\prime2}
\end{matrix}\left|\begin{matrix}u_{1}=u\cos\alpha\\
u_{2}=u\sin\alpha\\
\\
u_{1}^{\prime}=u'\cos\alpha'\\
u_{2}^{\prime}=u'\sin\alpha'
\end{matrix}\right|\begin{align}u\cos\alpha & =\frac{u'\cos\alpha'+v}{1+vu'\cos\alpha'}, & u'\cos\alpha' & =\frac{u\cos\alpha-v}{1-vu\cos\alpha}\\
u\sin\alpha & =\frac{u'\sin\alpha'\sqrt{1-v^{2}}}{1+vu'\cos\alpha'}, & u'\sin\alpha' & =\frac{u\sin\alpha\sqrt{1-v^{2}}}{1-vu\cos\alpha}\\
\tan\alpha & =\frac{u'\sin\alpha'\sqrt{1-v^{2}}}{u'\cos\alpha'+v}, & \tan\alpha' & =\frac{u\sin\alpha\sqrt{1-v^{2}}}{u\cos\alpha-v}
\end{align}
\\
\Rightarrow & u=\frac{\sqrt{v^{2}+u^{\prime2}+2vu'\cos\alpha'-\left(vu'\sin\alpha'\right){}^{2}}}{1+vu'\cos\alpha'},\quad u'=\frac{\sqrt{-v^{2}-u^{2}+2vu\cos\alpha+\left(vu\sin\alpha\right){}^{2}}}{1-vu\cos\alpha}\\
\Rightarrow & \frac{1}{\sqrt{1-u^{\prime2}}}=\frac{1}{\sqrt{1-v^{2}}}\frac{1}{\sqrt{1-u^{2}}}-\frac{v}{\sqrt{1-v^{2}}}\frac{u}{\sqrt{1-u^{2}}}\cos\alpha & (b)\\
\Rightarrow & \frac{1}{\sqrt{1-\tanh^{2}\xi}}=\frac{1}{\sqrt{1-\tanh^{2}\eta}}\frac{1}{\sqrt{1-\tanh^{2}\zeta}}-\frac{\tanh\eta}{\sqrt{1-\tanh^{2}\eta}}\frac{\tanh\zeta}{\sqrt{1-\tanh^{2}\zeta}}\cos\alpha\\
\Rightarrow & \cosh\xi=\cosh\eta\cosh\zeta-\sinh\eta\sinh\zeta\cos\alpha & (a)
\end{matrix}</math>|{{equationRef|3f}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The hyperbolic law of cosines (a) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Taurinus|Taurinus (1826) and Lobachevsky (1829/30)]] and others, while variant (b) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (hyperbolic)#Schur|Schur (1900/02)]].}}</p>

== {{anchor|Lorvel}}Lorentz transformation via velocity ==
In the [[theory of relativity]], Lorentz transformations exhibit the symmetry of [[Minkowski spacetime]] by using a constant ''c'' as the [[speed of light]], and a parameter ''v'' as the relative [[velocity]] between two [[inertial reference frames]]. In particular, the hyperbolic angle <math>\eta</math> in ({{equationNote|3b}}) can be interpreted as the velocity related [[rapidity]] <math>\tanh\eta=\beta=v/c</math>, so that <math>\gamma=\cosh\eta</math> is the [[Lorentz factor]], <math>\beta\gamma=\sinh\eta</math> the [[proper velocity]], <math>u'=c\tanh q</math> the velocity of another object, <math>u=c\tanh(q+\eta)</math> the [[velocity-addition formula]], thus ({{equationNote|3b}}) becomes:

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \begin{align}x_{0}^{\prime} & =x_{0}\gamma-x_{1}\beta\gamma\\
x_{1}^{\prime} & =-x_{0}\beta\gamma+x_{1}\gamma\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{0} & =x_{0}^{\prime}\gamma+x_{1}^{\prime}\beta\gamma\\
x_{1} & =x_{0}^{\prime}\beta\gamma+x_{1}^{\prime}\gamma\\
x_{2} & =x_{2}^{\prime}
\end{align}
\left|{\scriptstyle \begin{align}\beta^{2}\gamma^{2}-\gamma^{2} & =-1 & (a)\\
\gamma^{2}-\beta^{2}\gamma^{2} & =1 & (b)\\
\frac{\beta\gamma}{\gamma} & =\beta & (c)\\
\frac{1}{\sqrt{1-\beta^{2}}} & =\gamma & (d)\\
\frac{\beta}{\sqrt{1-\beta^{2}}} & =\beta\gamma & (e)\\
\frac{u'+v}{1+\frac{u'v}{c^{2}}} & =u & (f)
\end{align}
}\right.
\end{matrix}</math>|{{equationRef|4a}}}}

Or in four dimensions and by setting <math>x_{0}=ct,\ x_{1}=x,\ x_{2}=y</math> and adding an unchanged ''z'' the familiar form follows, using <math>\sqrt{\tfrac{c+v}{c-v}}</math> as Doppler factor:


{{NumBlk|:|<math>\begin{matrix}-c^{2}t^{2}+x^{2}+y^{2}+z^{2}=-c^{2}t^{\prime2}+x^{\prime2}+y^{\prime2}+z^{\prime2}\\
:<math>\begin{matrix}-c^{2}t^{2}+x^{2}+y^{2}+z^{2}=-c^{2}t^{\prime2}+x^{\prime2}+y^{\prime2}+z^{\prime2}\\
\hline \left.\begin{align}t' & =\gamma\left(t-x\frac{v}{c^{2}}\right)\\
\hline \left.\begin{align}t' & =\gamma\left(t-x\frac{v}{c^{2}}\right)\\
x' & =\gamma(x-vt)\\
x' & =\gamma(x-vt)\\
Line 432: Line 63:
\end{matrix}\Rightarrow\begin{align}(ct'+x') & =(ct+x)\sqrt{\frac{c+v}{c-v}}\\
\end{matrix}\Rightarrow\begin{align}(ct'+x') & =(ct+x)\sqrt{\frac{c+v}{c-v}}\\
(ct'-x') & =(ct-x)\sqrt{\frac{c-v}{c+v}}
(ct'-x') & =(ct-x)\sqrt{\frac{c-v}{c+v}}
\end{align}
</math>|{{equationRef|4b}}}}

In physics, analogous transformations have been introduced by [[#Voigt|Voigt (1887)]] and by [[#Lorentz1|Lorentz (1892, 1895)]] who analyzed [[Maxwell's equations]], they were completed by [[#Larmor|Larmor (1897, 1900)]] and [[#Lorentz2|Lorentz (1899, 1904)]], and brought into their modern form by [[#Poincare3|Poincaré (1905)]] who gave the transformation the name of Lorentz.<ref>Miller (1981), chapter 1</ref> Eventually, [[#Einstein|Einstein (1905)]] showed in his development of [[special relativity]] that the transformations follow from the [[principle of relativity]] and constant light speed alone by modifying the traditional concepts of space and time, without requiring a [[Lorentz ether theory|mechanical aether]] in contradistinction to Lorentz and Poincaré.<ref>Miller (1981), chapter 4–7</ref> [[#Minkowski|Minkowski (1907–1908)]] used them to argue that space and time are inseparably connected as [[spacetime]]. [[#Minkowski|Minkowski (1907–1908)]] and [[#Varicak|Varićak (1910)]] showed the relation to imaginary and hyperbolic functions. Important contributions to the mathematical understanding of the Lorentz transformation were also made by other authors such as [[#Herglotz1|Herglotz (1909–10)]], [[#Ignatowski|Ignatowski (1910)]], [[#Noether|Noether (1910) and Klein (1910)]], [[#Borel|Borel (1913–14)]].
<p style="border:1px solid black">{{Wikiversity-inline|list=
In pure mathematics, similar transformations have been used by [[v:History of Topics in Special Relativity/Lorentz transformation (velocity)#Lipschitz1|Lipschitz (1885/86)]].}}</p>

Also Lorentz boosts for arbitrary directions in line with ({{equationNote|1a}}) can be given as:<ref>Møller (1952/55), Chapter II, § 18</ref>

:<math>\mathbf{x}'=\begin{bmatrix}\gamma & -\gamma\beta n_{x} & -\gamma\beta n_{y} & -\gamma\beta n_{z}\\
-\gamma\beta n_{x} & 1+(\gamma-1)n_{x}^{2} & (\gamma-1)n_{x}n_{y} & (\gamma-1)n_{x}n_{z}\\
-\gamma\beta n_{y} & (\gamma-1)n_{y}n_{x} & 1+(\gamma-1)n_{y}^{2} & (\gamma-1)n_{y}n_{z}\\
-\gamma\beta n_{z} & (\gamma-1)n_{z}n_{x} & (\gamma-1)n_{z}n_{y} & 1+(\gamma-1)n_{z}^{2}
\end{bmatrix}\cdot\mathbf{x},\quad\left[\mathbf{n}=\frac{\mathbf{v}}{v}\right]</math>

or in vector notation

{{NumBlk|:|<math>\begin{align}t' & =\gamma\left(t-\frac{v\mathbf{n}\cdot\mathbf{r}}{c^{2}}\right)\\
\mathbf{r}' & =\mathbf{r}+(\gamma-1)(\mathbf{r}\cdot\mathbf{n})\mathbf{n}-\gamma tv\mathbf{n}
\end{align}
</math>|{{equationRef|4c}}}}

Such transformations were formulated by [[#Herglotz2|Herglotz (1911) and Silberstein (1911)]] and others.

In line with equation ({{equationNote|1b}}), one can substitute <math>\left[\tfrac{u_{x}}{c},\ \tfrac{u_{y}}{c},\ 1\right]=\left[\tfrac{x}{ct},\ \tfrac{y}{ct},\ \tfrac{ct}{ct}\right]</math> in ({{equationNote|3b}}) or ({{equationNote|4a}}), producing the Lorentz transformation of velocities (or [[velocity addition formula]]) in analogy to Beltrami coordinates of ({{equationNote|3e}}):

{{NumBlk|:|<math>\begin{matrix}\begin{matrix}-c^{2}t^{2}+x^{2}+y^{2}=-c^{2}t^{\prime2}+x^{\prime2}+y^{\prime2} & \rightarrow & \begin{align}-c^{2}+u_{x}^{2}+u_{y}^{2} & =\frac{-c^{2}+u_{x}^{\prime2}+u_{y}^{\prime2}}{\gamma^{2}\left(1+\frac{v}{c^{2}}u_{x}^{\prime}\right)^{2}}\\
\frac{-c^{2}+u_{x}^{2}+u_{y}^{2}}{\gamma^{2}\left(1-\frac{v}{c^{2}}u_{x}\right)^{2}} & =-c^{2}+u_{x}^{\prime2}+u_{y}^{\prime2}
\end{align}
\\
\hline -c^{2}t^{2}+x^{2}+y^{2}=-c^{2}t^{\prime2}+x^{\prime2}+y^{\prime2}=0 & \rightarrow & -c^{2}+u_{x}^{2}+u_{y}^{2}=-c^{2}+u_{x}^{\prime2}+u_{y}^{\prime2}=0
\end{matrix}\\
\hline {\scriptstyle \begin{align}\frac{\sinh\eta}{\cosh\eta} & =\tanh\eta=\frac{v}{c}\\
\cosh\eta & =\frac{1}{\sqrt{1-\tanh^{2}\eta}}
\end{align}
}\left|\begin{align}u_{x}^{\prime} & =\frac{-c^{2}\sinh\eta+u_{x}c\cosh\eta}{c\cosh\eta-u_{x}\sinh\eta} & & =\frac{u_{x}-c\tanh\eta}{1-\frac{u_{x}}{c}\tanh\eta} & & =\frac{u_{x}-v}{1-\frac{v}{c^{2}}u{}_{x}}\\
u_{y}^{\prime} & =\frac{cu_{y}}{c\cosh\eta-u_{x}\sinh\eta} & & =\frac{u_{y}\sqrt{1-\tanh^{2}\eta}}{1-\frac{u_{x}}{c}\tanh\eta} & & =\frac{u_{y}\sqrt{1-\frac{v^{2}}{c^{2}}}}{1-\frac{v}{c^{2}}u{}_{x}}\\
\\
u_{x} & =\frac{c^{2}\sinh\eta+u_{x}^{\prime}c\cosh\eta}{c\cosh\eta+u_{x}^{\prime}\sinh\eta} & & =\frac{u_{x}^{\prime}+c\tanh\eta}{1+\frac{u_{x}^{\prime}}{c}\tanh\eta} & & =\frac{u_{x}^{\prime}+v}{1+\frac{v}{c^{2}}u_{x}^{\prime}}\\
u_{y} & =\frac{cy'}{c\cosh\eta+u_{x}^{\prime}\sinh\eta} & & =\frac{u_{y}^{\prime}\sqrt{1-\tanh^{2}\eta}}{1+\frac{u_{x}^{\prime}}{c}\tanh\eta} & & =\frac{u_{y}^{\prime}\sqrt{1-\frac{v^{2}}{c^{2}}}}{1+\frac{v}{c^{2}}u_{x}^{\prime}}
\end{align}
\right.
\end{matrix}</math>|{{equationRef|4d}}}}

or using trigonometric and hyperbolic identities it becomes the hyperbolic law of cosines in terms of ({{equationNote|3f}}):<ref name=pau /><ref group=R name=var /><ref name=barr />

{{NumBlk|:|<math>\begin{matrix} & \begin{matrix}u^{2}=u_{x}^{2}+u_{y}^{2}\\
u'^{2}=u_{x}^{\prime2}+u_{y}^{\prime2}
\end{matrix}\left|\begin{matrix}u_{x}=u\cos\alpha\\
u_{y}=u\sin\alpha\\
\\
u_{x}^{\prime}=u'\cos\alpha'\\
u_{y}^{\prime}=u'\sin\alpha'
\end{matrix}\right|\begin{align}u\cos\alpha & =\frac{u'\cos\alpha'+v}{1+\frac{v}{c^{2}}u'\cos\alpha'}, & u'\cos\alpha' & =\frac{u\cos\alpha-v}{1-\frac{v}{c^{2}}u\cos\alpha}\\
u\sin\alpha & =\frac{u'\sin\alpha'\sqrt{1-\frac{v^{2}}{c^{2}}}}{1+\frac{v}{c^{2}}u'\cos\alpha'}, & u'\sin\alpha' & =\frac{u\sin\alpha\sqrt{1-\frac{v^{2}}{c^{2}}}}{1-\frac{v}{c^{2}}u\cos\alpha}\\
\tan\alpha & =\frac{u'\sin\alpha'\sqrt{1-\frac{v^{2}}{c^{2}}}}{u'\cos\alpha'+v}, & \tan\alpha' & =\frac{u\sin\alpha\sqrt{1-\frac{v^{2}}{c^{2}}}}{u\cos\alpha-v}
\end{align}
\\
\Rightarrow & u=\frac{\sqrt{v^{2}+u^{\prime2}+2vu'\cos\alpha'-\left(\frac{vu'\sin\alpha'}{c}\right){}^{2}}}{1+\frac{v}{c^{2}}u'\cos\alpha'},\quad u'=\frac{\sqrt{-v^{2}-u^{2}+2vu\cos\alpha+\left(\frac{vu\sin\alpha}{c}\right){}^{2}}}{1-\frac{v}{c^{2}}u\cos\alpha}\\
\Rightarrow & \frac{1}{\sqrt{1-\frac{u^{\prime2}}{c^{2}}}}=\frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}\frac{1}{\sqrt{1-\frac{u^{2}}{c^{2}}}}-\frac{v/c}{\sqrt{1-\frac{v^{2}}{c^{2}}}}\frac{u/c}{\sqrt{1-\frac{u^{2}}{c^{2}}}}\cos\alpha\\
\Rightarrow & \frac{1}{\sqrt{1-\tanh^{2}\xi}}=\frac{1}{\sqrt{1-\tanh^{2}\eta}}\frac{1}{\sqrt{1-\tanh^{2}\zeta}}-\frac{\tanh\eta}{\sqrt{1-\tanh^{2}\eta}}\frac{\tanh\zeta}{\sqrt{1-\tanh^{2}\zeta}}\cos\alpha\\
\Rightarrow & \cosh\xi=\cosh\eta\cosh\zeta-\sinh\eta\sinh\zeta\cos\alpha
\end{matrix}</math>|{{equationRef|4e}}}}

and by further setting ''u=u′=c'' the relativistic [[aberration of light]] follows:<ref>Pauli (1921), pp. 562; 565–566</ref>

{{NumBlk|:|<math>\begin{matrix}\cos\alpha=\frac{\cos\alpha'+\frac{v}{c}}{1+\frac{v}{c}\cos\alpha'},\ \sin\alpha=\frac{\sin\alpha'\sqrt{1-\frac{v^{2}}{c^{2}}}}{1+\frac{v}{c}\cos\alpha'},\ \tan\alpha=\frac{\sin\alpha'\sqrt{1-\frac{v^{2}}{c^{2}}}}{\cos\alpha'+\frac{v}{c}},\ \tan\frac{\alpha}{2}=\sqrt{\frac{c-v}{c+v}}\tan\frac{\alpha'}{2}\\
\cos\alpha'=\frac{\cos\alpha-\frac{v}{c}}{1-\frac{v}{c}\cos\alpha},\ \sin\alpha'=\frac{\sin\alpha\sqrt{1-\frac{v^{2}}{c^{2}}}}{1-\frac{v}{c}\cos\alpha},\ \tan\alpha'=\frac{\sin\alpha\sqrt{1-\frac{v^{2}}{c^{2}}}}{\cos\alpha-\frac{v}{c}},\ \tan\frac{\alpha'}{2}=\sqrt{\frac{c+v}{c-v}}\tan\frac{\alpha}{2}
\end{matrix}</math>|{{equationRef|4f}}}}

The velocity addition formulas were given by [[#Einstein|Einstein (1905)]] and [[#Poincare3|Poincaré (1905–06)]], the aberration formula for cos(α) by [[#Einstein|Einstein (1905)]], while the relations to the spherical and hyperbolic law of cosines were given by [[#Sommerfeld|Sommerfeld (1909)]] and [[#Varicak|Varićak (1910)]].
<p style="border:1px solid black">{{Wikiversity-inline|list=
These formulas resemble the equations of an [[ellipse]] of [[Orbital eccentricity|eccentricity]] ''v/c'', [[eccentric anomaly]] α' and [[true anomaly]] α, first geometrically formulated by [[v:History of Topics in Special Relativity/Lorentz transformation (velocity)#Euler|Kepler (1609)]] and explicitly written down by [[v:History of Topics in Special Relativity/Lorentz transformation (velocity)#Euler|Euler (1735, 1748), Lagrange (1770)]] and many others in relation to planetary motions.<ref name=plum>Plummer (1910), pp. 258-259: After deriving the relativistic expressions for the aberration angles φ' and φ, Plummer remarked on p. 259: ''Another geometrical representation is obtained by assimilating φ' to the eccentric and φ to the true anomaly in an ellipse whose eccentricity is v/U = sin β.''</ref><ref name=robin>Robinson (1990), chapter 3-4, analyzed the relation between "Kepler's formula" and the "physical velocity addition formula" in special relativity.</ref>}}</p>

== {{anchor|Lorconf}}Lorentz transformation via conformal, spherical wave, and Laguerre transformation ==

{{Main|Spherical wave transformation|Lie sphere geometry}}

If one only requires the invariance of the light cone represented by the differential equation <math>-dx_{0}^{2}+\dots+dx_{n}^{2}=0</math>, which is the same as asking for the most general transformation that changes spheres into spheres, the Lorentz group can be extended by adding dilations represented by the factor λ. The result is the group Con(1,p) of spacetime [[conformal transformation]]s in terms of [[special conformal transformation]]s and inversions producing the relation

:<math>-dx_{0}^{2}+\dots+dx_{n}^{2}=\lambda\left(-dx_{0}^{\prime2}+\dots+dx_{n}^{\prime2}\right)</math>.

One can switch between two representations of this group by using an imaginary sphere radius coordinate ''x<sub>0</sub>=iR'' with the interval <math>dx_{0}^{2}+\dots+dx_{n}^{2}</math> related to conformal transformations, or by using a real radius coordinate ''x<sub>0</sub>=R'' with the interval <math>-dx_{0}^{2}+\dots+dx_{n}^{2}</math> related to spherical wave transformations in terms of [[contact transformation]]s preserving circles and spheres. It turns out that Con(1,3) is isomorphic to the [[special orthogonal group]] SO(2,4), and contains the Lorentz group SO(1,3) as a subgroup by setting λ=1. More generally, Con(q,p) is isomorphic to SO(q+1,p+1) and contains SO(q,p) as subgroup.<ref>Schottenloher (2008), section 2.2</ref> This implies that Con(0,p) is isomorphic to the Lorentz group of arbitrary dimensions SO(1,p+1). Consequently, the conformal group in the plane Con(0,2) – known as the group of [[Möbius transformation]]s – is isomorphic to the Lorentz group SO(1,3).<ref>Kastrup (2008), section 2.4.1</ref><ref>Schottenloher (2008), section 2.3</ref> This can be seen using tetracyclical coordinates satisfying the form <math>-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}+x_{3}^{2}=0</math>.

A special case of Lie's geometry of oriented spheres is the [[Spherical wave transformation#Transformation by reciprocal directions|Laguerre group]], transforming oriented planes and lines into each other. It's generated by the Laguerre inversion leaving invariant <math>x^{2}+y^{2}+z^{2}-R^{2}</math> with ''R'' as radius, thus the Laguerre group is isomorphic to the Lorentz group.<ref>Coolidge (1916), p. 370</ref><ref name="ReferenceA">Cartan & Fano (1915/55), sections 14–15</ref>

<p style="border:1px solid black">{{Wikiversity-inline|list=
Both representations of Lie sphere geometry and conformal transformations were studied by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Lie|Lie (1871)]] and others. It was shown by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Bateman|Bateman & Cunningham (1909–1910)]], that the group Con(1,3) is the most general one leaving invariant the equations of Maxwell's electrodynamics. Tetracyclical coordinates were discussed by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Klein3|Pockels (1891), Klein (1893), Bôcher (1894)]]. The relation between Con(1,3) and the Lorentz group was noted by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Bateman|Bateman & Cunningham (1909–1910)]] and others.

The Laguerre inversion was introduced by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Laguerre|Laguerre (1882)]] and discussed by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Darboux2|Darboux (1887)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Smith|Smith (1900)]]. A similar concept was studied by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Scheffers|Scheffers (1899)]] in terms of contact transformations. [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Stephanos|Stephanos (1883)]] argued that Lie's geometry of oriented spheres in terms of contact transformations, as well as the special case of the transformations of oriented planes into each other (such as by Laguerre), provides a geometrical interpretation of Hamilton's [[biquaternion]]s. The [[group isomorphism]] between the Laguerre group and Lorentz group was pointed out by [[v:History of Topics in Special Relativity/Lorentz transformation (conformal)#Bateman|Bateman (1910), Cartan (1912, 1915/55), Poincaré (1912/21)]] and others.}}</p>

== {{anchor|Lorcay}}Lorentz transformation via Cayley–Hermite transformation ==

The general transformation ({{equationNote|Q1}}) of any quadratic form into itself can also be given using ''arbitrary'' parameters based on the [[Cayley transform]] ('''I'''-'''T''')<sup>−1</sup>·('''I'''+'''T'''), where '''I''' is the [[identity matrix]], '''T''' an arbitrary [[antisymmetric matrix]], and by adding '''A''' as symmetric matrix defining the quadratic form (there is no primed '''A' ''' because the coefficients are assumed to be the same on both sides):<ref>Hawkins (2013), pp. 210–214</ref><ref>Meyer (1899), p. 329</ref>

{{NumBlk|:|<math>\begin{matrix}q=\mathbf{x}^{\mathrm{T}}\cdot\mathbf{A}\cdot\mathbf{x}=q'=\mathbf{x}^{\mathrm{\prime T}}\cdot\mathbf{A}\cdot\mathbf{x}'\\
\hline \\
\mathbf{x}=(\mathbf{I}-\mathbf{T}\cdot\mathbf{A})^{-1}\cdot(\mathbf{I}+\mathbf{T}\cdot\mathbf{A})\cdot\mathbf{x}'\\
\text{or}\\
\mathbf{x}=\mathbf{A}^{-1}\cdot(\mathbf{A}-\mathbf{T})\cdot(\mathbf{A}+\mathbf{T})^{-1}\cdot\mathbf{A}\cdot\mathbf{x}'
\end{matrix}</math>|{{equationRef|Q2}}}}

For instance, the choice '''A'''=diag(1,1,1) gives an orthogonal transformation which can be used to describe spatial rotations corresponding to the [[Euler–Rodrigues formula|Euler-Rodrigues parameter]]s ''[a,b,c,d]'' which can be interpreted as the coefficients of [[quaternion]]s. Setting ''d=1'', the equations have the form:

{{NumBlk|:|<math>\begin{matrix}\mathbf{A}=\operatorname{diag}(1,1,1),\quad\mathbf{T}={\scriptstyle \begin{vmatrix}0 & a & -b\\
-a & 0 & c\\
b & -c & 0
\end{vmatrix}}\\
\hline x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \mathbf{x}'=\frac{1}{\kappa}\left[\begin{matrix}1-a^{2}-b^{2}+c^{2} & 2(bc-a) & 2(ac+b)\\
2(bc+a) & 1-a^{2}+b^{2}-c^{2} & 2(ab-c)\\
2(ac-b) & 2(ab+c) & 1+a^{2}-b^{2}-c^{2}
\end{matrix}\right]\cdot\mathbf{x}\\
\left(\kappa=1+a^{2}+b^{2}+c^{2}\right)
\end{matrix}</math>|{{equationRef|Q3}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
After [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Cayley|Cayley (1846)]] introduced transformations related to sums of positive squares, [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Hermite|Hermite (1853/54, 1854)]] derived transformations for arbitrary quadratic forms, whose result was reformulated in terms of matrices ({{equationNote|Q2}}) by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Cayley|Cayley (1855a, 1855b)]]. The Euler-Rodrigues parameter were discovered by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Euler|Euler (1771) and Rodrigues (1840)]].}}</p>

Also the Lorentz interval and the general Lorentz transformation in any dimension can be produced by the Cayley–Hermite formalism.<ref group=R>Borel (1914), pp. 39–41</ref><ref group=R>Brill (1925)</ref><ref>Klein (1928), § 2B</ref><ref>Lorente (2003), section 3.3</ref> For instance, Lorentz transformation ({{equationNote|1a}}) with ''n''=1 follows from ({{equationNote|Q2}}) with:

{{NumBlk|:|<math>\begin{matrix}\mathbf{A}=\operatorname{diag}(-1,1),\quad\mathbf{T}={\scriptstyle \begin{vmatrix}0 & a\\
-a & 0
\end{vmatrix}}\\
\hline -x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
\hline \mathbf{x}'=\frac{1}{1-a^{2}}\left[\begin{matrix}1+a^{2} & -2a\\
-2a & 1+a^{2}
\end{matrix}\right]\cdot\mathbf{x}
\end{matrix}\Rightarrow\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
\hline \left.\begin{align}x_{0} & =x_{0}^{\prime}\frac{1+\beta_{0}^{2}}{1-\beta_{0}^{2}}+x_{1}^{\prime}\frac{2\beta_{0}}{1-\beta_{0}^{2}} & = & \frac{x_{0}^{\prime}\left(1+\beta_{0}^{2}\right)+x_{1}^{\prime}2\beta_{0}}{1-\beta_{0}^{2}}\\
x_{1} & =x_{0}^{\prime}\frac{2\beta_{0}}{1-\beta_{0}^{2}}+x_{1}^{\prime}\frac{1+\beta_{0}^{2}}{1-\beta_{0}^{2}} & = & \frac{x_{0}^{\prime}2\beta_{0}+x_{1}^{\prime}\left(1+\beta_{0}^{2}\right)}{1-\beta_{0}^{2}}\\
\\
x_{0}^{\prime} & =x_{0}\frac{1+\beta_{0}^{2}}{1-\beta_{0}^{2}}-x_{1}\frac{2\beta_{0}}{1-\beta_{0}^{2}} & = & \frac{x_{0}\left(1+\beta_{0}^{2}\right)-x_{1}2\beta_{0}}{1-\beta_{0}^{2}}\\
x_{1}^{\prime} & =-x_{0}\frac{2\beta_{0}}{1-\beta_{0}^{2}}+x_{1}\frac{1+\beta_{0}^{2}}{1-\beta_{0}^{2}} & = & \frac{-x_{0}2\beta_{0}+x_{1}\left(1+\beta_{0}^{2}\right)}{1-\beta_{0}^{2}}
\end{align}
\right|{\scriptstyle \begin{align}\frac{2\beta_{0}}{1+\beta_{0}^{2}} & =\beta\\
\frac{1+\beta_{0}^{2}}{1-\beta_{0}^{2}} & =\gamma\\
\frac{2\beta_{0}}{1-\beta_{0}^{2}} & =\beta\gamma
\end{align}
}
\end{matrix}</math>|{{equationRef|5a}}}}

This becomes Lorentz boost ({{equationNote|4a}} or {{equationNote|4b}}) by setting <math>\tfrac{2a}{1+a^{2}}=\tfrac{v}{c}</math>, which is equivalent to the relation <math>\tfrac{2\beta_{0}}{1+\beta_{0}^{2}}=\tfrac{v}{c}</math> known from [[Loedel diagram]]s, thus ({{equationNote|5a}}) can be interpreted as a Lorentz boost from the viewpoint of a "median frame" in which two other inertial frames are moving with equal speed <math>\beta_0</math> in opposite directions.

Furthermore, Lorentz transformation ({{equationNote|1a}}) with ''n''=2 is given by:

{{NumBlk|:|<math>\begin{matrix}\mathbf{A}=\operatorname{diag}(-1,1,1),\quad\mathbf{T}={\scriptstyle \begin{vmatrix}0 & a & -b\\
-a & 0 & c\\
b & -c & 0
\end{vmatrix}}\\
\hline -x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \mathbf{x}'=\frac{1}{\kappa}\left[\begin{matrix}1+a^{2}+b^{2}+c^{2} & -2(bc-a) & -2(ac+b)\\
2(bc+a) & 1+a^{2}-b^{2}-c^{2} & 2(ab-c)\\
2(ac-b) & -2(ab-c) & 1-a^{2}+b^{2}-c^{2}
\end{matrix}\right]\cdot\mathbf{x}\\
\left(\kappa=1-a^{2}-b^{2}+c^{2}\right)
\end{matrix}</math>|{{equationRef|5b}}}}

or using ''n''=3:

{{NumBlk|:|<math>\begin{matrix}\mathbf{A}=\operatorname{diag}(-1,1,1,1),\quad\mathbf{T}={\scriptstyle \begin{vmatrix}0 & a & -b & c\\
-a & 0 & d & e\\
b & -d & 0 & f\\
-c & -e & -f & 0
\end{vmatrix}}\\
\hline -x_{0}^{2}+x_{1}^{2}+x_{2}^{2}+x_{3}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}+x_{3}^{\prime2}\\
\hline \mathbf{x}'=\frac{1}{\kappa}\left[{\scriptstyle \begin{align} & 1+a^{2}+b^{2}+c^{2}+ & & 2(-bd+a+ec+pf) & & 2(-ad-b+fc-pe) & & 2(pd+fb-ea+c)\\
& \quad d^{2}+e^{2}+f^{2}+p^{2} & & 1+a^{2}-b^{2}-c^{2} & & 2(-d-ab+pc-fe) & & 2(fd+pb+ca-e)\\
& 2(bd+a-ec+pf) & & \quad-d^{2}-e^{2}+f^{2}+p^{2} & & 1-a^{2}+b^{2}-c^{2} & & 2(-ed-cb+pa-f)\\
& 2(ad-b-fc-pe) & & 2(d-ab-pc-fe) & & \quad-d^{2}+e^{2}-f^{2}+p^{2} & & 1-a^{2}-b^{2}+-c^{2}\\
& 2(pd-fb+ea+c) & & 2(fd-pb+ca+e) & & 2(-ed-cb-pa+f) & & \quad+d^{2}-e^{2}-f^{2}+p^{2}
\end{align}
}\right]\cdot\mathbf{x}\\
\left(\begin{align}\kappa & =1-a^{2}-b^{2}-c^{2}+d^{2}+e^{2}+f^{2}-p^{2}\\
p & =af+be+cd
\end{align}
\right)
\end{matrix}</math>|{{equationRef|5c}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The transformation of a binary quadratic form of which Lorentz transformation ({{equationNote|5a}}) is a special case was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Hermite|Hermite (1854)]], equations containing Lorentz transformations ({{equationNote|5a}}, {{equationNote|5b}}, {{equationNote|5c}}) as special cases were given by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Cayley|Cayley (1855)]], Lorentz transformation ({{equationNote|5a}}) was given (up to a sign change) by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Laguerre|Laguerre (1882)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Darboux2|Darboux (1887)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Smith|Smith (1900)]] in relation to Laguerre geometry, and Lorentz transformation ({{equationNote|5b}}) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Bachmann|Bachmann (1869)]]. In relativity, equations similar to ({{equationNote|5b}}, {{equationNote|5c}}) were first employed by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Borel|Borel (1913)]] to represent Lorentz transformations.}}</p>

As described in equation ({{equationNote|3d}}), the Lorentz interval is closely connected to the alternative form <math>X_{2}^{2}-X_{1}X_{3}</math>,<ref name=k28 /> which in terms of the Cayley–Hermite parameters is invariant under the transformation:

{{NumBlk|:|<math>\begin{matrix}X_{2}^{\prime2}-X_{1}^{\prime}X_{3}^{\prime}=X_{2}^{2}-X_{1}X_{3}\\
\hline \mathbf{X}'=\frac{1}{\kappa}\left[\begin{matrix}(b+1)^{2} & -2(b+1)c & c^{2}\\
a(b+1) & 1-ac-b^{2} & (b-1)c\\
a^{2} & -2a(b-1) & (b-1)^{2}
\end{matrix}\right]\cdot\mathbf{X}\\
\left(\kappa=1+ac-b^{2}\right)
\end{matrix}</math>|{{equationRef|5d}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
This transformation was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Cayley-Hermite)#Cayley4|Cayley (1884)]], even though he didn't relate it to the Lorentz interval but rather to <math>x_{0}^{2}+x_{1}^{2}+x_{2}^{2}</math>.}}</p>

== {{anchor|Lormoeb}}Lorentz transformation via Cayley–Klein parameters, Möbius and spin transformations ==

The previously mentioned Euler-Rodrigues parameter ''a,b,c,d'' (i.e. Cayley-Hermite parameter in equation ({{equationNote|Q3}}) with ''d=1'') are closely related to Cayley–Klein parameter α,β,γ,δ in order to connect Möbius transformations <math>\tfrac{\alpha\zeta+\beta}{\gamma\zeta+\delta}</math> and rotations:<ref>Klein (1896/97), p. 12</ref>

:<math>\begin{align}\alpha & =1+ib, & \beta & =-a+ic,\\
\gamma & =a+ic, & \delta & =1-ib.
\end{align}
\end{align}
</math>
</math>


In physics, analogous transformations have been introduced by [[#Voigt|Voigt (1887)]] related to an incompressible medium, and by [[#Heaviside|Heaviside (1888), Thomson (1889), Searle (1896)]] and [[#Lorentz1|Lorentz (1892, 1895)]] who analyzed [[Maxwell's equations]]. They were completed by [[#Larmor|Larmor (1897, 1900)]] and [[#Lorentz2|Lorentz (1899, 1904)]], and brought into their modern form by [[#Poincare3|Poincaré (1905)]] who gave the transformation the name of Lorentz.<ref>Miller (1981), chapter 1</ref> Eventually, [[#Einstein|Einstein (1905)]] showed in his development of [[special relativity]] that the transformations follow from the [[principle of relativity]] and constant light speed alone by modifying the traditional concepts of space and time, without requiring a [[Lorentz ether theory|mechanical aether]] in contradistinction to Lorentz and Poincaré.<ref>Miller (1981), chapter 4–7</ref> [[#Minkowski|Minkowski (1907–1908)]] used them to argue that space and time are inseparably connected as [[spacetime]].
thus ({{equationNote|Q3}}) becomes:


Regarding special representations of the Lorentz transformations: [[#Minkowski|Minkowski (1907–1908)]] and [[#Sommerfeld|Sommerfeld (1909)]] used imaginary trigonometric functions, [[#Frank|Frank (1909)]] and [[#Varicak|Varićak (1910)]] used [[hyperbolic function]]s, [[#Bateman|Bateman and Cunningham (1909–1910)]] used [[spherical wave transformation]]s, [[#Herglotz1|Herglotz (1909–10)]] used Möbius transformations, [[#Plummer|Plummer (1910)]] and [[#Gruner|Gruner (1921)]] used trigonometric Lorentz boosts, [[#Ignatowski|Ignatowski (1910)]] derived the transformations without light speed postulate, [[#Noether|Noether (1910) and Klein (1910)]] as well [[#Conway|Conway (1911) and Silberstein (1911)]] used Biquaternions, [[#Herglotz2|Ignatowski (1910/11), Herglotz (1911), and others]] used vector transformations valid in arbitrary directions, [[#Borel|Borel (1913–14)]] used Cayley–Hermite parameter,
{{NumBlk|:|<math>\begin{matrix}x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \mathbf{x}'=\frac{1}{\kappa}\left[\begin{matrix}\frac{1}{2}\left(\alpha^{2}-\beta^{2}-\gamma^{2}+\delta^{2}\right) & \beta\delta-\alpha\gamma & \frac{i}{2}\left(-\alpha^{2}+\beta^{2}-\gamma^{2}+\delta^{2}\right)\\
\gamma\delta+\alpha\beta & \alpha\delta+\beta\gamma & i(\alpha\beta+\gamma\delta)\\
-\frac{i}{2}\left(-\alpha^{2}-\beta^{2}+\gamma^{2}+\delta^{2}\right) & -i(\alpha\gamma+\beta\delta) & \frac{1}{2}\left(\alpha^{2}+\beta^{2}+\gamma^{2}+\delta^{2}\right)
\end{matrix}\right]\cdot\mathbf{x}\\
(\kappa=\alpha\delta-\beta\gamma)
\end{matrix}</math>|{{equationRef|Q4}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The Cayley-Klein parameter were introduced by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Cayley2|Helmholtz (1866/67), Cayley (1879)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Klein|Klein (1884)]].}}</p>

Also the Lorentz transformation can be expressed with variants of the Cayley–Klein parameters: One relates these parameters to a spin-matrix '''D''', the [[spin transformation]]s of variables <math>\xi',\eta',\bar{\xi}',\bar{\eta}'</math> (the overline denotes [[complex conjugate]]), and the [[Möbius transformation]] of <math>\zeta',\bar{\zeta}'</math>. When defined in terms of isometries of hyperbolic space (hyperbolic motions), the [[Hermitian matrix]] '''u''' associated with these Möbius transformations produces an invariant determinant <math>\det\mathbf{u}=x_{0}^{2}-x_{1}^{2}-x_{2}^{2}-x_{3}^{2}</math> identical to the Lorentz interval. Therefore, these transformations were described by [[John Lighton Synge]] as being a "factory for the mass production of Lorentz transformations".<ref name=synge /> It also turns out that the related [[spin group]] Spin(3, 1) or [[special linear group]] SL(2, C) acts as the [[Double cover (topology)|double cover]] of the Lorentz group (one Lorentz transformation corresponds to two spin transformations of different sign), while the [[Möbius group]] Con(0,2) or [[projective special linear group]] PSL(2, C) is isomorphic to both the Lorentz group and the group of isometries of hyperbolic space.

In space, the Möbius/Spin/Lorentz transformations can be written as:<ref>Klein (1928), § 3A</ref><ref name=synge>Synge (1956), ch. IV, 11</ref><ref>Penrose & Rindler (1984), section 2.1</ref><ref name="Lorente 2003, section 4">Lorente (2003), section 4</ref>

{{NumBlk|:|<math>\begin{matrix}\zeta=\frac{x_{1}+ix_{2}}{x_{0}-x_{3}}=\frac{x_{0}+x_{3}}{x_{1}-ix_{2}}\rightarrow\zeta'=\frac{\alpha\zeta+\beta}{\gamma\zeta+\delta}\left|\zeta'=\frac{\xi'}{\eta'}\rightarrow\begin{align}\xi' & =\alpha\xi+\beta\eta\\
\eta' & =\gamma\xi+\delta\eta
\end{align}
\right.\\
\hline \left.\begin{matrix}\mathbf{u}=\left(\begin{matrix}X_{1} & X_{2}\\
X_{3} & X_{4}
\end{matrix}\right)=\left(\begin{matrix}\bar{\xi}\xi & \xi\bar{\eta}\\
\bar{\xi}\eta & \bar{\eta}\eta
\end{matrix}\right)=\left(\begin{matrix}x_{0}+x_{3} & x_{1}-ix_{2}\\
x_{1}+ix_{2} & x_{0}-x_{3}
\end{matrix}\right)\\
\det\mathbf{u}=x_{0}^{2}-x_{1}^{2}-x_{2}^{2}-x_{3}^{2}
\end{matrix}\right|\begin{matrix}\mathbf{D}=\left(\begin{matrix}\alpha & \beta\\
\gamma & \delta
\end{matrix}\right)\\
\begin{align}\det\boldsymbol{\mathbf{D}} & =1\end{align}
\end{matrix}\\
\hline \mathbf{u}'=\mathbf{D}\cdot\mathbf{u}\cdot\bar{\mathbf{D}}^{\mathrm{T}}=\begin{align}X_{1}^{\prime} & =X_{1}\alpha\bar{\alpha}+X_{2}\alpha\bar{\beta}+X_{3}\bar{\alpha}\beta+X_{4}\beta\bar{\beta}\\
X_{2}^{\prime} & =X_{1}\bar{\alpha}\gamma+X_{2}\bar{\alpha}\delta+X_{3}\bar{\beta}\gamma+X_{4}\bar{\beta}\delta\\
X_{3}^{\prime} & =X_{1}\alpha\bar{\gamma}+X_{2}\alpha\bar{\delta}+X_{3}\beta\bar{\gamma}+X_{4}\beta\bar{\delta}\\
X_{4}^{\prime} & =X_{1}\gamma\bar{\gamma}+X_{2}\gamma\bar{\delta}+X_{3}\bar{\gamma}\delta+X_{4}\delta\bar{\delta}
\end{align}
\\
\hline \begin{align}X_{3}^{\prime}X_{2}^{\prime}-X_{1}^{\prime}X_{4}^{\prime} & =X_{3}X_{2}-X_{1}X_{4}=0\\
\det\mathbf{u}'=x_{0}^{\prime2}-x_{1}^{\prime2}-x_{2}^{\prime2}-x_{3}^{\prime2} & =\det\mathbf{u}=x_{0}^{2}-x_{1}^{2}-x_{2}^{2}-x_{3}^{2}
\end{align}
\end{matrix}</math>|{{equationRef|6a}}}}

thus:<ref>Penrose & Rindler (1984), p. 17</ref>

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}+x_{3}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}+x_{3}^{\prime2}\\
\hline \mathbf{x}'=\frac{1}{2}\left[{\scriptstyle \begin{align} & \alpha\bar{\alpha}+\beta\bar{\beta}+\gamma\bar{\gamma}+\delta\bar{\delta} & & \alpha\bar{\beta}+\beta\bar{\alpha}+\gamma\bar{\delta}+\delta\bar{\gamma} & & i(\alpha\bar{\beta}-\beta\bar{\alpha}+\gamma\bar{\delta}-\delta\bar{\gamma}) & & \alpha\bar{\alpha}-\beta\bar{\beta}+\gamma\bar{\gamma}-\delta\bar{\delta}\\
& \alpha\bar{\gamma}+\gamma\bar{\alpha}+\beta\bar{\delta}+\delta\bar{\beta} & & \alpha\bar{\delta}+\delta\bar{\alpha}+\beta\bar{\gamma}+\gamma\bar{\beta} & & i(\alpha\bar{\delta}-\delta\bar{\alpha}+\gamma\bar{\beta}-\beta\bar{\gamma}) & & \alpha\bar{\gamma}+\gamma\bar{\alpha}-\beta\bar{\delta}-\delta\bar{\beta}\\
& i(\gamma\bar{\alpha}-\alpha\bar{\gamma}+\delta\bar{\beta}-\beta\bar{\delta}) & & i(\delta\bar{\alpha}-\alpha\bar{\delta}+\gamma\bar{\beta}-\beta\bar{\gamma}) & & \alpha\bar{\delta}+\delta\bar{\alpha}-\beta\bar{\gamma}-\gamma\bar{\beta} & & i(\gamma\bar{\alpha}-\alpha\bar{\gamma}+\beta\bar{\delta}-\delta\bar{\beta})\\
& \alpha\bar{\alpha}+\beta\bar{\beta}-\gamma\bar{\gamma}-\delta\bar{\delta} & & \alpha\bar{\beta}+\beta\bar{\alpha}-\gamma\bar{\delta}-\delta\bar{\gamma} & & i(\alpha\bar{\beta}-\beta\bar{\alpha}+\delta\bar{\gamma}-\gamma\bar{\delta}) & & \alpha\bar{\alpha}-\beta\bar{\beta}-\gamma\bar{\gamma}+\delta\bar{\delta}
\end{align}
}\right]\cdot\mathbf{x}\\
(\alpha\delta-\beta\gamma=1)
\end{matrix}</math>|{{equationRef|6b}}}}

or in line with equation ({{equationNote|1b}}) one can substitute <math>\left[u_{1},\ u_{2},\ u_{3},\ 1\right]=\left[\tfrac{x_{1}}{x_{0}},\ \tfrac{x_{2}}{x_{0}},\ \tfrac{x_{3}}{x_{0}},\ \tfrac{x_{0}}{x_{0}}\right]</math> so that the Möbius/Lorentz transformations become related to the unit sphere:

{{NumBlk|:|<math>\begin{matrix}u_{1}^{2}+u_{2}^{2}+u_{3}^{2}=u_{1}^{\prime2}+u_{2}^{\prime2}+u_{3}^{\prime2}=1\\
\hline \left.\begin{matrix}\zeta=\frac{u_{1}+iu_{2}}{1-u_{3}}=\frac{1+u_{3}}{u_{1}-iu_{2}}\\
\zeta'=\frac{u_{1}^{\prime}+iu_{2}^{\prime}}{1-u_{3}^{\prime}}=\frac{1+u_{3}^{\prime}}{u_{1}^{\prime}-iu_{2}^{\prime}}
\end{matrix}\right|\quad\zeta'=\frac{\alpha\zeta+\beta}{\gamma\zeta+\delta}
\end{matrix}</math>|{{equationRef|6c}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The general transformation '''u′''' in ({{equationNote|6a}}) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Cayley2|Cayley (1854)]], while the general relation between Möbius transformations and transformation '''u′''' leaving invariant the [[generalized circle]] was pointed out by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Poincare2|Poincaré (1883)]] in relation to [[Kleinian group]]s. The adaptation to the Lorentz interval by which ({{equationNote|6a}}) becomes a Lorentz transformation was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Klein2|Klein (1889-1893, 1896/97)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Bianchi2|Bianchi (1893)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Fricke|Fricke (1893, 1897)]]. Its reformulation as Lorentz transformation ({{equationNote|6b}}) was provided by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Bianchi2|Bianchi (1893)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Fricke|Fricke (1893, 1897)]]. Lorentz transformation ({{equationNote|6c}}) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Klein2|Klein (1884)]] in relation to surfaces of second degree and the invariance of the unit sphere. In relativity, ({{equationNote|6a}}) was first employed by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Herglotz1|Herglotz (1909/10)]].}}</p>

In the plane, the transformations can be written as:<ref name=k28>Klein (1928), § 2A</ref><ref name="Lorente 2003, section 4"/>

{{NumBlk|:|<math>\begin{matrix}\zeta=\frac{x_{1}}{x_{0}-x_{2}}=\frac{x_{0}+x_{2}}{x_{1}}\rightarrow\zeta'=\frac{\alpha\zeta+\beta}{\gamma\zeta+\delta}\left|\zeta'=\frac{\xi'}{\eta'}\rightarrow\begin{align}\xi' & =\alpha\xi+\beta\eta\\
\eta' & =\gamma\xi+\delta\eta
\end{align}
\right.\\
\hline \left.\begin{matrix}\mathbf{u}=\left(\begin{matrix}X_{1} & X_{2}\\
X_{2} & X_{3}
\end{matrix}\right)=\left(\begin{matrix}\xi^{2} & \xi\eta\\
\xi\eta & \eta^{2}
\end{matrix}\right)=\left(\begin{matrix}x_{0}+x_{2} & x_{1}\\
x_{1} & x_{0}-x_{2}
\end{matrix}\right)\\
\det\mathbf{u}=x_{0}^{2}-x_{1}^{2}-x_{2}^{2}
\end{matrix}\right|\begin{matrix}\mathbf{D}=\left(\begin{matrix}\alpha & \beta\\
\gamma & \delta
\end{matrix}\right)\\
\begin{align}\det\boldsymbol{\mathbf{D}} & =1\end{align}
\end{matrix}\\
\hline \mathbf{u}'=\mathbf{D}\cdot\mathbf{u}\cdot\mathbf{D}^{\mathrm{T}}=\begin{align}X_{1}^{\prime} & =X_{1}\alpha^{2}+X_{2}2\alpha\beta+X_{3}\beta^{2}\\
X_{2}^{\prime} & =X_{1}\alpha\gamma+X_{2}(\alpha\delta+\beta\gamma)+X_{3}\beta\delta\\
X_{3}^{\prime} & =X_{1}\gamma^{2}+X_{2}2\gamma\delta+X_{3}\delta^{2}
\end{align}
\\
\hline \begin{align}X_{2}^{\prime2}-X_{1}^{\prime}X_{3}^{\prime} & =X_{2}^{2}-X_{1}X_{3}=0\\
\det\mathbf{u}'=x_{0}^{\prime2}-x_{1}^{\prime2}-x_{2}^{\prime2} & =\det\mathbf{u}=x_{0}^{2}-x_{1}^{2}-x_{2}^{2}
\end{align}
\end{matrix}</math>|{{equationRef|6d}}}}

thus

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \mathbf{x}'=\left[\begin{matrix}\frac{1}{2}\left(\alpha^{2}+\beta^{2}+\gamma^{2}+\delta^{2}\right) & \alpha\beta+\gamma\delta & \frac{1}{2}\left(\alpha^{2}-\beta^{2}+\gamma^{2}-\delta^{2}\right)\\
\alpha\gamma+\beta\delta & \alpha\delta+\beta\gamma & \alpha\gamma-\beta\delta\\
\frac{1}{2}\left(\alpha^{2}+\beta^{2}-\gamma^{2}-\delta^{2}\right) & \alpha\beta-\gamma\delta & \frac{1}{2}\left(\alpha^{2}-\beta^{2}-\gamma^{2}+\delta^{2}\right)
\end{matrix}\right]\cdot\mathbf{x}\\
(\alpha\delta-\beta\gamma=1)
\end{matrix}</math>|{{equationRef|6e}}}}

which includes the special case <math>\beta=\gamma=0</math> implying <math>\delta=1/\alpha</math>, reducing the transformation to a Lorentz boost in 1+1 dimensions:

{{NumBlk|:|<math>\begin{matrix}X_{1}X_{3}=X_{1}^{\prime}X_{3}^{\prime}\quad\Rightarrow\quad-x_{0}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{2}^{\prime2}\\
\hline \begin{align}X_{1} & =\alpha^{2}X_{1}^{\prime}\\
X_{2} & =X_{2}^{\prime}\\
X_{3} & =\frac{1}{\alpha^{2}}X_{3}^{\prime}
\end{align}
\quad\Rightarrow\quad\begin{align}x_{0} & =\frac{x_{0}^{\prime}\left(\alpha^{4}+1\right)+x_{2}^{\prime}\left(\alpha^{4}-1\right)}{2\alpha^{2}}\\
x_{1} & =x_{1}^{\prime}\\
x_{2} & =\frac{x_{0}^{\prime}\left(\alpha^{4}-1\right)+x_{2}^{\prime}\left(\alpha^{4}+1\right)}{2\alpha^{2}}
\end{align}
\end{matrix}</math>|{{equationRef|6f}}}}

Finally, by using the Lorentz interval related to a hyperboloid, the Möbius/Lorentz transformations can be written

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}=-1\\
\hline \left.\begin{matrix}\zeta=\frac{x_{1}+ix_{2}}{x_{0}+1}=\frac{x_{0}-1}{x_{1}-ix_{2}}\\
\zeta'=\frac{x_{1}^{\prime}+ix_{2}^{\prime}}{x_{0}^{\prime}+1}=\frac{x_{0}^{\prime}-1}{x_{1}^{\prime}-ix_{2}^{\prime}}
\end{matrix}\right|\quad\zeta'=\frac{\alpha\zeta+\beta}{\gamma\zeta+\delta}
\end{matrix}</math>|{{equationRef|6g}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The general transformation '''u′''' and its invariant <math>X_{2}^{2}-X_{1}X_{3}</math> in ({{equationNote|6d}}) was already used by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Gauss|Lagrange (1773) and Gauss (1798/1801)]] in the theory of integer binary quadratic forms. The invariant <math>X_{2}^{2}-X_{1}X_{3}</math> was also studied by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Klein|Klein (1871)]] in connection to hyperbolic plane geometry (see equation ({{equationNote|3d}})), while the connection between '''u′''' and <math>X_{2}^{2}-X_{1}X_{3}</math> with the Möbius transformation was analyzed by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Poincare2|Poincaré (1886)]] in relation to [[Fuchsian group]]s. The adaptation to the Lorentz interval by which ({{equationNote|6d}}) becomes a Lorentz transformation was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Bianchi2|Bianchi (1888)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Fricke|Fricke (1891)]]. Lorentz Transformation ({{equationNote|6e}}) was stated by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Gauss3|Gauss around 1800]] (posthumously published 1863), as well as [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Selling|Selling (1873)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Bianchi2|Bianchi (1888)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Fricke|Fricke (1891)]], [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Woods|Woods (1895)]] in relation to integer indefinite ternary quadratic forms. Lorentz transformation ({{equationNote|6f}}) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Bianchi1|Bianchi (1886, 1894)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Eisenhart|Eisenhart (1905)]]. Lorentz transformation ({{equationNote|6g}}) of the hyperboloid was stated by [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Poincare2|Poincaré (1881)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (Möbius)#Hausdorff|Hausdorff (1899)]].}}</p>

== {{anchor|Lorqua}}Lorentz transformation via quaternions and hyperbolic numbers ==

The Lorentz transformations can also be expressed in terms of [[biquaternion]]s: A Minkowskian quaternion (or minquat) ''q'' having one real part and one purely imaginary part is multiplied by biquaternion ''a'' applied as pre- and postfactor. Using an overline to denote quaternion conjugation and * for complex conjugation, its general form (on the left) and the corresponding boost (on the right) are as follows:<ref>Synge (1972), pp. 13, 19, 24</ref><ref>Girard (1984), pp. 28–29</ref>

{{NumBlk|:|<math>\left.\begin{matrix}-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}+x_{3}^{\prime2}=-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}+x_{3}^{2}\\
\hline q'=aq\bar{a}^{\ast}\\
\hline \begin{align}q & =ix_{0}+x_{1}e_{1}+x_{2}e_{2}+x_{3}e_{3}\\
q' & =ix_{0}^{\prime}+x_{1}^{\prime}e_{1}+x_{2}^{\prime}e_{2}+x_{3}^{\prime}e_{3}\\
a & =\cos\chi+i\sin\chi=e^{i\chi}
\end{align}
\\
\left(a\bar{a}=1,\ \chi=\text{imaginary}\right)
\end{matrix}\right|\begin{matrix}\chi=\frac{1}{2}i\eta\\
\downarrow\\
\begin{align}x_{0}^{\prime} & =x_{0}\cosh\eta-x_{1}\sinh\eta\\
x_{1}^{\prime} & =-x_{0}\sinh\eta+x_{1}\cosh\eta\\
x_{2}^{\prime} & =x_{2},\quad x_{3}^{\prime}=x_{3}
\end{align}
\end{matrix}</math>|{{equationRef|7a}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
[[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Hamilton|Hamilton (1844/45)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Cayley3|Cayley (1845)]] derived the quaternion transformation <math>aqa^{-1}</math> for spatial rotations, and [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Cayley3|Cayley (1854, 1855)]] gave the corresponding transformation <math>aqb</math> leaving invariant the sum of four squares <math>x_{0}^{2}+x_{1}^{2}+x_{2}^{2}+x_{2}^{2}</math>. [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Cox2|Cox (1882/83)]] discussed the Lorentz interval in terms of Weierstrass coordinates <math>x_{0}^{2}-x_{1}^{2}-x_{2}^{2}-x_{2}^{2}=1</math> in the course of adapting [[William Kingdon Clifford]]'s biquaternions ''a+ωb'' to hyperbolic geometry by setting <math>\omega^{2}=-1</math> (alternatively, 1 gives elliptic and 0 parabolic geometry). [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Stephanos|Stephanos (1883)]] related the imaginary part of [[William Rowan Hamilton]]'s biquaternions to the radius of spheres, and introduced a homography leaving invariant the equations of oriented spheres or oriented planes in terms of [[Lie sphere geometry]]. [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Buchheim|Buchheim (1884/85)]] discussed the Cayley absolute <math>x_{0}^{2}-x_{1}^{2}-x_{2}^{2}-x_{2}^{2}=0</math> and adapted Clifford's biquaternions to hyperbolic geometry similar to Cox by using all three values of <math>\omega^{2}</math>. Eventually, the modern Lorentz transformation using biquaternions with <math>\omega^{2}=-1</math> as in hyperbolic geometry was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Noether|Noether (1910) and Klein (1910)]] as well as [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Conway|Conway (1911) and Silberstein (1911)]].}}</p>

Often connected with quaternionic systems is the [[hyperbolic number]] <math>\varepsilon^{2}=1</math>, which also allows to formulate the Lorentz transformations:<ref>Sobczyk (1995)</ref><ref>Fjelstad (1986)</ref>

{{NumBlk|:|<math>\begin{align}w' & =we^{-\varepsilon\eta}\\
& =w(\cosh(-\eta)+\varepsilon\sinh(-\eta))\\
\\
w & =w'e^{\varepsilon\eta}\\
& =w'(\cosh\eta+\varepsilon\sinh\eta)
\end{align}
\rightarrow\begin{align}w & =x_{1}+\varepsilon x_{0}\\
w' & =x_{1}^{\prime}+\varepsilon x_{0}^{\prime}
\end{align}
\rightarrow\begin{align}x_{0}^{\prime} & =x_{0}\cosh\eta-x_{1}\sinh\eta\\
x_{1}^{\prime} & =-x_{0}\sinh\eta+x_{1}\cosh\eta\\
\\
x_{0} & =x_{0}^{\prime}\cosh\eta+x_{1}^{\prime}\sinh\eta\\
x_{1} & =x_{0}^{\prime}\sinh\eta+x_{1}^{\prime}\cosh\eta
\end{align}</math>|{{equationRef|7b}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
After the trigonometric expression <math>e^{ix}</math> ([[Euler's formula]]) was given by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Euler3|Euler (1748)]], and the hyperbolic analogue <math>e^{\varepsilon\eta}</math> as well as hyperbolic numbers by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Cockle|Cockle (1848)]] in the framework of [[tessarine]]s, it was shown by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Cox2|Cox (1882/83)]] that one can identify <math>ww^{\prime-1}=e^{\varepsilon\eta}</math> with associative quaternion multiplication. Here, <math>e^{\varepsilon\eta}</math> is the hyperbolic [[versor]] with <math>\varepsilon^{2}=1</math>, while -1 denotes the elliptic or 0 denotes the parabolic counterpart (not to be confused with the expression <math>\omega^{2}</math> in Clifford's biquaternions also used by Cox, in which -1 is hyperbolic). The hyperbolic versor was also discussed by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Macfarlane|Macfarlane (1892, 1894, 1900)]] in terms of [[hyperbolic quaternion]]s. The expression <math>\varepsilon^{2}=1</math> for hyperbolic motions (and -1 for elliptic, 0 for parabolic motions) also appear in "biquaternions" defined by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Vahlen|Vahlen (1901/02, 1905)]].}}</p>

More extended forms of complex and (bi-)quaternionic systems in terms of [[Clifford algebra]] can also be used to express the Lorentz transformations. For instance, using a system ''a'' of Clifford numbers one can transform the following general quadratic form into itself, in which the individual values of <math>i_{1}^{2},i_{2}^{2},\dots</math> can be set to +1 or -1 at will, while the Lorentz interval follows if the sign of one <math>i^{2}</math> differs from all others.:<ref>Cartan & Study (1908), section 36</ref><ref>Rothe (1916), section 16</ref>

{{NumBlk|:|<math>\begin{matrix}i_{1}^{2}x_{1}^{\prime2}+\cdots+i_{n}^{2}x_{n}^{\prime2}=i_{1}^{2}x_{1}^{2}+\cdots+i_{n}^{2}x_{n}^{2}\\
\hline (1)\ x'=axa^{-1}\\
(2)\ x'=\frac{ax+b}{\varepsilon^{2} bx+a}
\end{matrix}</math>|{{equationRef|7c}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
The general definite form <math>x_{1}^{2}+\cdots+x_{n}^{2}</math> as well as the general indefinite form <math>x_{1}^{2}+\cdots+x_{p}^{2}-x_{p+1}^{2}-\cdots-x_{p+q}^{2}</math> and their invariance under transformation (1) was discussed by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Lipschitz2|Lipschitz (1885/86)]], while hyperbolic motions were discussed by [[v:History of Topics in Special Relativity/Lorentz transformation (Quaternions)#Vahlen|Vahlen (1901/02, 1905)]] by setting <math>\varepsilon^{2}=1</math> in transformation (2), while elliptic motions follow with -1 and parabolic motions with 0, all of which he also related to biquaternions.}}</p>

== {{anchor|Lortrig}}Lorentz transformation via trigonometric functions ==

The following general relation connects the speed of light and the relative velocity to hyperbolic and trigonometric functions, where <math>\eta</math> is the rapidity in ({{equationNote|3b}}), <math>\theta</math> is equivalent to the [[Gudermannian function]] <math>{\rm gd}(\eta)=2\arctan(e^{\eta})-\pi/2</math>, and <math>\vartheta</math> is equivalent to the Lobachevskian [[angle of parallelism]] <math>\Pi(\eta)=2\arctan(e^{-\eta})</math>:

:<math>\frac{v}{c}=\tanh\eta=\sin\theta=\cos\vartheta</math>

<p style="border:1px solid black">{{Wikiversity-inline|list=
This relation was first defined by [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Varicak|Varićak (1910)]].}}</p>

a) Using <math>\sin\theta=\tfrac{v}{c}</math> one obtains the relations <math>\sec\theta=\gamma</math> and <math>\tan\theta=\beta\gamma</math>, and the Lorentz boost takes the form:<ref name=maj>Majerník (1986), 536–538</ref>

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \left.\begin{align}x_{0}^{\prime} & =x_{0}\sec\theta-x_{1}\tan\theta & & =\frac{x_{0}-x_{1}\sin\theta}{\cos\theta}\\
x_{1}^{\prime} & =-x_{0}\tan\theta+x_{1}\sec\theta & & =\frac{x_{0}\sin\theta-x_{1}}{\cos\theta}\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{0} & =x_{0}^{\prime}\sec\theta+x_{1}^{\prime}\tan\theta & & =\frac{x_{0}^{\prime}+x_{1}^{\prime}\sin\theta}{\cos\theta}\\
x_{1} & =x_{0}^{\prime}\tan\theta+x_{1}^{\prime}\sec\theta & & =\frac{x_{0}^{\prime}\sin\theta+x_{1}^{\prime}}{\cos\theta}\\
x_{2} & =x_{2}^{\prime}
\end{align}
\right|{\scriptstyle \begin{align}\tan^{2}\theta-\sec^{2}\theta & =-1\\
\frac{\tan\theta}{\sec\theta} & =\sin\theta\\
\frac{1}{\sqrt{1-\sin^{2}\theta}} & =\sec\theta\\
\frac{\sin\theta}{\sqrt{1-\sin^{2}\theta}} & =\tan\theta
\end{align}
}
\end{matrix}</math>|{{equationRef|8a}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
This Lorentz transformation was derived by [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Bianchi1|Bianchi (1886)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Darboux1|Darboux (1891/94)]] while transforming pseudospherical surfaces, and by [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Scheffers|Scheffers (1899)]] as a special case of [[contact transformation]] in the plane (Laguerre geometry). In special relativity, it was used by [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Gruner|Gruner (1921)]] while developing [[Loedel diagram]]s, and by [[Vladimir Karapetoff]] in the 1920s.}}</p>

b) Using <math>\cos\vartheta=\tfrac{v}{c}</math> one obtains the relations <math>\csc\vartheta=\gamma</math> and <math>\cot\vartheta=\beta\gamma</math>, and the Lorentz boost takes the form:<ref name=maj />

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}+x_{2}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}+x_{2}^{\prime2}\\
\hline \left.\begin{align}x_{0}^{\prime} & =x_{0}\csc\vartheta-x_{1}\cot\vartheta & & =\frac{x_{0}-x_{1}\cos\vartheta}{\sin\vartheta}\\
x_{1}^{\prime} & =-x_{0}\cot\vartheta+x_{1}\csc\vartheta & & =\frac{x_{0}\cos\vartheta-x_{1}}{\sin\vartheta}\\
x_{2}^{\prime} & =x_{2}\\
\\
x_{0} & =x_{0}^{\prime}\csc\vartheta+x_{1}^{\prime}\cot\vartheta & & =\frac{x_{0}^{\prime}+x_{1}^{\prime}\cos\vartheta}{\sin\vartheta}\\
x_{1} & =x_{0}^{\prime}\cot\vartheta+x_{1}^{\prime}\csc\vartheta & & =\frac{x_{0}^{\prime}\cos\vartheta+x_{1}^{\prime}}{\sin\vartheta}\\
x_{2} & =x_{2}^{\prime}
\end{align}
\right|{\scriptstyle \begin{align}\cot^{2}\vartheta-\csc^{2}\vartheta & =-1\\
\frac{\cot\vartheta}{\csc\vartheta} & =\cos\vartheta\\
\frac{1}{\sqrt{1-\cos^{2}\vartheta}} & =\csc\vartheta\\
\frac{\cos\vartheta}{\sqrt{1-\cos^{2}\vartheta}} & =\cot\vartheta
\end{align}
}
\end{matrix}</math>|{{equationRef|8b}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
This Lorentz transformation was derived by [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Eisenhart|Eisenhart (1905)]] while transforming pseudospherical surfaces. In special relativity it was first used by [[v:History of Topics in Special Relativity/Lorentz transformation (trigonometric)#Gruner|Gruner (1921)]] while developing [[Loedel diagram]]s.}}</p>

== {{anchor|Lorsqu}}Lorentz transformation via squeeze mappings ==

As already indicated in equations ({{equationNote|3d}}) in exponential form or ({{equationNote|6f}}) in terms of Cayley–Klein parameter, Lorentz boosts in terms of hyperbolic rotations can be expressed as [[squeeze mapping]]s. Using [[hyperbola#Hyperbola with equation y = A/x|asymptotic coordinates of a hyperbola]] (''u,v''), they have the general form (some authors alternatively add a factor of 2 or <math>\sqrt{2}</math>):<ref name=terng>Terng & Uhlenbeck (2000), p. 21</ref>

{{NumBlk|:|<math>\begin{matrix}(1) & \begin{array}{c|c|c}
u=x_{0}+x_{1} & 2u=x_{0}+x_{1} & \sqrt{2}u=x_{0}+x_{1}\\
v=x_{0}-x_{1} & 2v=x_{0}-x_{1} & \sqrt{2}v=x_{0}-x_{1}\\
u'=x_{0}^{\prime}+x_{1}^{\prime} & 2u'=x_{0}^{\prime}+x_{1}^{\prime} & \sqrt{2}u=x_{0}^{\prime}+x_{1}^{\prime}\\
v'=x_{0}^{\prime}-x_{1}^{\prime} & 2v'=x_{0}^{\prime}-x_{1}^{\prime} & \sqrt{2}v=x_{0}^{\prime}-x_{1}^{\prime}
\end{array}\\
\hline (2) & (u',v')=\left(ku,\ \frac{1}{k}v\right)\Rightarrow u'v'=uv
\end{matrix}</math>|{{equationRef|9a}}}}

That this equation system indeed represents a Lorentz boost can be seen by plugging (1) into (2) and solving for the individual variables:

{{NumBlk|:|<math>\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
\hline \left.\begin{align}x_{0}^{\prime} & =\frac{1}{2}\left(k+\frac{1}{k}\right)x_{0}-\frac{1}{2}\left(k-\frac{1}{k}\right)x_{1} & & =\frac{x_{0}\left(k^{2}+1\right)-x_{1}\left(k^{2}-1\right)}{2k}\\
x_{1}^{\prime} & =-\frac{1}{2}\left(k-\frac{1}{k}\right)x_{0}+\frac{1}{2}\left(k+\frac{1}{k}\right)x_{1} & & =\frac{-x_{0}\left(k^{2}-1\right)+x_{1}\left(k^{2}+1\right)}{2k}\\
\\
x_{0} & =\frac{1}{2}\left(k+\frac{1}{k}\right)x_{0}^{\prime}+\frac{1}{2}\left(k-\frac{1}{k}\right)x_{1}^{\prime} & & =\frac{x_{0}^{\prime}\left(k^{2}+1\right)+x_{1}^{\prime}\left(k^{2}-1\right)}{2k}\\
x_{1} & =\frac{1}{2}\left(k-\frac{1}{k}\right)x_{0}^{\prime}+\frac{1}{2}\left(k+\frac{1}{k}\right)x_{1}^{\prime} & & =\frac{x_{0}^{\prime}\left(k^{2}-1\right)+x_{1}^{\prime}\left(k^{2}+1\right)}{2k}
\end{align}
\right|{\scriptstyle \begin{align}\frac{k^{2}-1}{k^{2}+1} & =\beta\\
\frac{k^{2}+1}{2k} & =\gamma\\
\frac{k^{2}-1}{2k} & =\beta\gamma
\end{align}
}
\end{matrix}</math>|{{equationRef|9b}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
Lorentz transformation ({{equationNote|9a}}) of asymptotic coordinates have been used [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Laisant1|Laisant (1874)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Gunther1|Günther (1880/81)]] in relation to elliptic trigonometry;
by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Lie2|Lie (1879-81)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Bianchi1|Bianchi (1886, 1894)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Darboux1|Darboux (1891/94)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Eisenhart|Eisenhart (1905)]] as [[squeeze mapping#Lie transform|Lie transform]])<ref name=terng /> of [[pseudospherical surface]]s in terms of the [[Sine-Gordon equation]];
by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Lipschitz1|Lipschitz (1885/86)]] in transformation theory.
From that, different forms of Lorentz transformation were derived: ({{equationNote|9b}}) by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Lipschitz1|Lipschitz (1885/86)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Bianchi1|Bianchi (1886, 1894)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Eisenhart|Eisenhart (1905)]];
trigonometric Lorentz boost ({{equationNote|8a}}) by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Bianchi1|Bianchi (1886, 1894)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Darboux1|Darboux (1891/94)]];
trigonometric Lorentz boost ({{equationNote|8b}}) by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Eisenhart|Eisenhart (1905)]].
Lorentz boost ({{equationNote|9b}}) was rediscovered in the framework of special relativity by [[Hermann Bondi]] (1964)<ref>Bondi (1964), p. 118</ref> in terms of [[Bondi k-calculus]], by which ''k'' can be physically interpreted as Doppler factor. Since ({{equationNote|9b}}) is equivalent to ({{equationNote|6f}}) in terms of Cayley–Klein parameter by setting <math>k=\alpha^2</math>, it can be interpreted as the 1+1 dimensional special case of Lorentz Transformation ({{equationNote|6e}}) stated by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Gauss3|Gauss around 1800]] (posthumously published 1863), [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Selling|Selling (1873)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Bianchi2|Bianchi (1888)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Fricke|Fricke (1891)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Woods|Woods (1895)]].}}</p>

Variables ''u, v'' in ({{equationNote|9a}}) can be rearranged to produce another form of squeeze mapping, resulting in Lorentz transformation ({{equationNote|5b}}) in terms of Cayley-Hermite parameter:

{{NumBlk|:|<math>\begin{matrix}\begin{matrix}u=x_{0}+x_{1}\\
v=x_{0}-x_{1}\\
u'=x_{0}^{\prime}+x_{1}^{\prime}\\
v'=x_{0}^{\prime}-x_{1}^{\prime}
\end{matrix}\Rightarrow\begin{matrix}u_{1}=x_{1}-x_{1}^{\prime}\\
v_{1}=x_{0}+x_{0}^{\prime}\\
u_{2}=x_{1}+x_{1}^{\prime}\\
v_{2}=x_{0}-x_{0}^{\prime}
\end{matrix}\\
\hline (u_{2},v_{2})=\left(au_{1},\ \frac{1}{a}v_{1}\right)\Rightarrow u_{2}v_{2}=u_{1}v_{1}\\
(u',v')=\left(\frac{1+a}{1-a}u,\ \frac{1-a}{1+a}v\right)\Rightarrow u'v'=uv
\end{matrix}\Rightarrow\begin{matrix}-x_{0}^{2}+x_{1}^{2}=-x_{0}^{\prime2}+x_{1}^{\prime2}\\
\hline \begin{align}x_{0}^{\prime} & =x_{0}\frac{1+a^{2}}{1-a^{2}}-x_{1}\frac{2a}{1-a^{2}} & & =\frac{x_{0}\left(1+a^{2}\right)-x_{1}2a}{1-a^{2}}\\
x_{1}^{\prime} & =-x_{0}\frac{2a}{1-a^{2}}+x_{1}\frac{1+a^{2}}{1-a^{2}} & & =\frac{-x_{0}2a+x_{1}\left(1+a^{2}\right)}{1-a^{2}}\\
\\
x_{0} & =x_{0}^{\prime}\frac{1+a^{2}}{1-a^{2}}+x_{1}^{\prime}\frac{2a}{1-a^{2}} & & =\frac{x_{0}^{\prime}\left(1+a^{2}\right)+x_{1}^{\prime}2a}{1-a^{2}}\\
x_{1} & =x_{0}^{\prime}\frac{2a}{1-a^{2}}+x_{1}^{\prime}\frac{1+a^{2}}{1-a^{2}} & & =\frac{x_{0}^{\prime}2a+x_{1}^{\prime}\left(1+a^{2}\right)}{1-a^{2}}
\end{align}
\end{matrix}</math>|{{equationRef|9c}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
These Lorentz transformations were given (up to a sign change) by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Laguerre|Laguerre (1882)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Darboux2|Darboux (1887)]], [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Smith|Smith (1900)]] in relation to Laguerre geometry.}}</p>

On the basis of factors ''k'' or ''a'', all previous Lorentz boosts ({{equationNote|3b}}, {{equationNote|4a}}, {{equationNote|8a}}, {{equationNote|8b}}) can be expressed as squeeze mappings as well:

{{NumBlk|:|<math>\begin{array}{c|c|c|c|c|c}
& & (3b) & (4a) & (8a) & (8b)\\
\hline k & \frac{1+a}{1-a} & e^{\eta} & \sqrt{\tfrac{1+\beta}{1-\beta}} & \frac{1+\sin\theta}{\cos\theta} & \frac{1+\cos\vartheta}{\sin\vartheta}=\cot\frac{\vartheta}{2}\\
\hline \frac{k-1}{k+1} & a & \tanh\frac{\eta}{2} & \frac{\gamma-1}{\beta\gamma} & \frac{1-\cos\theta}{\sin\theta}=\tan\frac{\theta}{2} & \frac{1-\sin\vartheta}{\cos\vartheta}\\
\hline \frac{k^{2}-1}{k^{2}+1} & \frac{2a}{1+a^{2}} & \tanh\eta & \beta & \sin\theta & \cos\vartheta\\
\hline \frac{k^{2}+1}{2k} & \frac{1+a^{2}}{1-a^{2}} & \cosh\eta & \gamma & \sec\theta & \csc\vartheta\\
\hline \frac{k^{2}-1}{2k} & \frac{2a}{1-a^{2}} & \sinh\eta & \beta\gamma & \tan\theta & \cot\vartheta
\end{array}</math>|{{equationRef|9d}}}}

<p style="border:1px solid black">{{Wikiversity-inline|list=
Squeeze mappings in terms of <math>\theta</math> were used by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Darboux1|Darboux (1891/94)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Bianchi1|Bianchi (1894)]], in terms of <math>\eta</math> by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Lindemann|Lindemann (1891)]] and [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Herglotz1|Herglotz (1909)]], in terms of <math>\vartheta</math> by [[v:History of Topics in Special Relativity/Lorentz transformation (squeeze)#Eisenhart|Eisenhart (1905)]], in terms of <math>\beta</math> by Bondi (1964).}}</p>

==Electrodynamics and special relativity==


=== {{anchor|Voigt}} Voigt (1887) ===
=== {{anchor|Voigt}} Voigt (1887) ===
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\end{matrix}</math>
\end{matrix}</math>


If the right-hand sides of his equations are multiplied by γ they are the modern Lorentz transformation ({{equationNote|4b}}). In Voigt's theory the speed of light is invariant, but his transformations mix up a relativistic boost together with a rescaling of space-time. Optical phenomena in free space are [[Scale invariance|scale]], [[Conformal map|conformal]] (using the factor λ discussed [[#Lorsph|above]]), and [[Lorentz covariance|Lorentz invariant]], so the combination is invariant too.<ref name=pais /> For instance, Lorentz transformations can be extended by using <math>l=\sqrt{\lambda}</math>:<ref group=R>Lorentz (1915/16), p. 197</ref>
If the right-hand sides of his equations are multiplied by γ they are the modern Lorentz transformation. In Voigt's theory the speed of light is invariant, but his transformations mix up a relativistic boost together with a rescaling of space-time. Optical phenomena in free space are [[Scale invariance|scale]], [[Conformal map|conformal]], and [[Lorentz covariance|Lorentz invariant]], so the combination is invariant too.<ref name=pais /> For instance, Lorentz transformations can be extended by using factor <math>l</math>:<ref group=R>Lorentz (1915/16), p. 197</ref>


:<math>x^{\prime}=\gamma l\left(x-vt\right),\quad y^{\prime}=ly,\quad z^{\prime}=lz,\quad t^{\prime}=\gamma l\left(t-x\frac{v}{c^{2}}\right)</math>.
:<math>x^{\prime}=\gamma l\left(x-vt\right),\quad y^{\prime}=ly,\quad z^{\prime}=lz,\quad t^{\prime}=\gamma l\left(t-x\frac{v}{c^{2}}\right)</math>.
Line 978: Line 95:
''l''=1/γ gives the Voigt transformation, ''l''=1 the Lorentz transformation. But scale transformations are not a symmetry of all the laws of nature, only of electromagnetism, so these transformations cannot be used to formulate a [[principle of relativity]] in general. It was demonstrated by Poincaré and Einstein that one has to set ''l''=1 in order to make the above transformation symmetric and to form a group as required by the relativity principle, therefore the Lorentz transformation is the only viable choice.
''l''=1/γ gives the Voigt transformation, ''l''=1 the Lorentz transformation. But scale transformations are not a symmetry of all the laws of nature, only of electromagnetism, so these transformations cannot be used to formulate a [[principle of relativity]] in general. It was demonstrated by Poincaré and Einstein that one has to set ''l''=1 in order to make the above transformation symmetric and to form a group as required by the relativity principle, therefore the Lorentz transformation is the only viable choice.


Voigt sent his 1887 paper to Lorentz in 1908,<ref>Voigt's transformations and the beginning of the relativistic revolution, Ricardo Heras, arXiv:1411.2559 [https://arxiv.org/abs/1411.2559]</ref> and that was acknowledged in 1909: {{Blockquote|In a paper "Über das Doppler'sche Princip", published in 1887 (Gött. Nachrichten, p. 41) and which to my regret has escaped my notice all these years, Voigt has applied to equations of the form (7) (§ 3 of this book) [namely <math>\Delta\Psi-\tfrac{1}{c^{2}}\tfrac{\partial^{2}\Psi}{\partial t^{2}}=0</math>] a transformation equivalent to the formulae (287) and (288) [namely <math>x^{\prime}=\gamma l\left(x-vt\right),\ y^{\prime}=ly,\ z^{\prime}=lz,\ t^{\prime}=\gamma l\left(t-\tfrac{v}{c^{2}}x\right)</math>]. The idea of the transformations used above (and in § 44) might therefore have been borrowed from Voigt and the proof that it does not alter the form of the equations for the ''free'' ether is contained in his paper.<ref group=R>Lorentz (1915/16), p. 198</ref>}}
Voigt sent his 1887 paper to Lorentz in 1908,<ref>{{cite arXiv | eprint=1411.2559 | last1=Heras | first1=Ricardo | title=A review of Voigt's transformations in the framework of special relativity | year=2014 | class=physics.hist-ph }}</ref> and that was acknowledged in 1909: {{Blockquote|In a paper "Über das Doppler'sche Princip", published in 1887 (Gött. Nachrichten, p. 41) and which to my regret has escaped my notice all these years, Voigt has applied to equations of the form (7) (§ 3 of this book) [namely <math>\Delta\Psi-\tfrac{1}{c^{2}}\tfrac{\partial^{2}\Psi}{\partial t^{2}}=0</math>] a transformation equivalent to the formulae (287) and (288) [namely <math>x^{\prime}=\gamma l\left(x-vt\right),\ y^{\prime}=ly,\ z^{\prime}=lz,\ t^{\prime}=\gamma l\left(t-\tfrac{v}{c^{2}}x\right)</math>]. The idea of the transformations used above (and in § 44) might therefore have been borrowed from Voigt and the proof that it does not alter the form of the equations for the ''free'' ether is contained in his paper.<ref group=R>Lorentz (1915/16), p. 198</ref>}}


Also [[Hermann Minkowski]] said in 1908 that the transformations which play the main role in the principle of relativity were first examined by Voigt in 1887. Voigt responded in the same paper by saying that his theory was based on an elastic theory of light, not an electromagnetic one. However, he concluded that some results were actually the same.<ref group=R>Bucherer (1908), p. 762</ref>
Also [[Hermann Minkowski]] said in 1908 that the transformations which play the main role in the principle of relativity were first examined by Voigt in 1887. Voigt responded in the same paper by saying that his theory was based on an elastic theory of light, not an electromagnetic one. However, he concluded that some results were actually the same.<ref group=R>Bucherer (1908), p. 762</ref>
Line 1,021: Line 138:
\end{matrix}</math>
\end{matrix}</math>


where ''x<sup>*</sup>'' is the [[Galilean transformation]] ''x-vt''. Except the additional γ in the time transformation, this is the complete Lorentz transformation ({{equationNote|4b}}).<ref name=milf /> While ''t'' is the "true" time for observers resting in the aether, ''t′'' is an auxiliary variable only for calculating processes for moving systems. It is also important that Lorentz and later also Larmor formulated this transformation in two steps. At first an implicit Galilean transformation, and later the expansion into the "fictitious" electromagnetic system with the aid of the Lorentz transformation. In order to explain the negative result of the [[Michelson–Morley experiment]], he (1892b)<ref group=R>Lorentz (1892b), p. 141</ref> introduced the additional hypothesis that also intermolecular forces are affected in a similar way and introduced [[length contraction]] in his theory (without proof as he admitted). The same hypothesis was already made by [[George Francis FitzGerald|George FitzGerald]] in 1889 based on Heaviside's work. While length contraction was a real physical effect for Lorentz, he considered the time transformation only as a heuristic working hypothesis and a mathematical stipulation.
where ''x<sup>*</sup>'' is the [[Galilean transformation]] ''x-vt''. Except the additional γ in the time transformation, this is the complete Lorentz transformation.<ref name=milf /> While ''t'' is the "true" time for observers resting in the aether, ''t′'' is an auxiliary variable only for calculating processes for moving systems. It is also important that Lorentz and later also Larmor formulated this transformation in two steps. At first an implicit Galilean transformation, and later the expansion into the "fictitious" electromagnetic system with the aid of the Lorentz transformation. In order to explain the negative result of the [[Michelson–Morley experiment]], he (1892b)<ref group=R>Lorentz (1892b), p. 141</ref> introduced the additional hypothesis that also intermolecular forces are affected in a similar way and introduced [[length contraction]] in his theory (without proof as he admitted). The same hypothesis had been made previously by [[George Francis FitzGerald|George FitzGerald]] in 1889 based on Heaviside's work. While length contraction was a real physical effect for Lorentz, he considered the time transformation only as a heuristic working hypothesis and a mathematical stipulation.


In 1895, Lorentz further elaborated on his theory and introduced the "theorem of corresponding states". This theorem states that a moving observer (relative to the ether) in his "fictitious" field makes the same observations as a resting observers in his "real" field for velocities to first order in ''v/c''. Lorentz showed that the dimensions of electrostatic systems in the ether and a moving frame are connected by this transformation:<ref group=R>Lorentz (1895), p. 37</ref>
In 1895, Lorentz further elaborated on his theory and introduced the "theorem of corresponding states". This theorem states that a moving observer (relative to the ether) in his "fictitious" field makes the same observations as a resting observers in his "real" field for velocities to first order in ''v/c''. Lorentz showed that the dimensions of electrostatic systems in the ether and a moving frame are connected by this transformation:<ref group=R>Lorentz (1895), p. 37</ref>
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\end{matrix}</math>
\end{matrix}</math>


by which he arrived at the complete Lorentz transformation ({{equationNote|4b}}). Larmor showed that Maxwell's equations were invariant under this two-step transformation, "to second order in ''v/c''" – it was later shown by Lorentz (1904) and Poincaré (1905) that they are indeed invariant under this transformation to all orders in ''v/c''.
by which he arrived at the complete Lorentz transformation. Larmor showed that Maxwell's equations were invariant under this two-step transformation, "to second order in ''v/c''" – it was later shown by Lorentz (1904) and Poincaré (1905) that they are indeed invariant under this transformation to all orders in ''v/c''.


Larmor gave credit to Lorentz in two papers published in 1904, in which he used the term "Lorentz transformation" for Lorentz's first order transformations of coordinates and field configurations:
Larmor gave credit to Lorentz in two papers published in 1904, in which he used the term "Lorentz transformation" for Lorentz's first order transformations of coordinates and field configurations:
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\end{matrix}</math>
\end{matrix}</math>


This is equivalent to the complete Lorentz transformation ({{equationNote|4b}}) when solved for ''x″'' and ''t″'' and with ε=1. Like Larmor, Lorentz noticed in 1899<ref group=R>Lorentz (1899), p. 442</ref> also some sort of time dilation effect in relation to the frequency of oscillating electrons ''"that in ''S'' the time of vibrations be ''kε'' times as great as in ''S<sub>0</sub>''"'', where ''S<sub>0</sub>'' is the aether frame.<ref>Jannsen (1995), Kap. 3.3</ref>
This is equivalent to the complete Lorentz transformation when solved for ''x″'' and ''t″'' and with ε=1. Like Larmor, Lorentz noticed in 1899<ref group=R>Lorentz (1899), p. 442</ref> also some sort of time dilation effect in relation to the frequency of oscillating electrons ''"that in ''S'' the time of vibrations be ''kε'' times as great as in ''S<sub>0</sub>''"'', where ''S<sub>0</sub>'' is the aether frame.<ref>Jannsen (1995), Kap. 3.3</ref>


In 1904 he rewrote the equations in the following form by setting ''l''=1/ε (again, ''x''* must be replaced by ''x-vt''):<ref group=R>Lorentz (1904), p. 812</ref>
In 1904 he rewrote the equations in the following form by setting ''l''=1/ε (again, ''x''* must be replaced by ''x-vt''):<ref group=R>Lorentz (1904), p. 812</ref>
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==== Lorentz transformation ====
==== Lorentz transformation ====


On June 5, 1905 (published June 9) Poincaré formulated transformation equations which are algebraically equivalent to those of Larmor and Lorentz and gave them the modern form ({{equationNote|4b}}):<ref group=R>Poincaré (1905), p. 1505</ref>
On June 5, 1905 (published June 9) Poincaré formulated transformation equations which are algebraically equivalent to those of Larmor and Lorentz and gave them the modern form:<ref group=R>Poincaré (1905), p. 1505</ref>


:<math>\begin{align}x^{\prime} & =kl(x+\varepsilon t)\\
:<math>\begin{align}x^{\prime} & =kl(x+\varepsilon t)\\
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Apparently Poincaré was unaware of Larmor's contributions, because he only mentioned Lorentz and therefore used for the first time the name "Lorentz transformation".<ref>Pais (1982), Chap. 6c</ref><ref>Katzir (2005), 280–288</ref> Poincaré set the speed of light to unity, pointed out the group characteristics of the transformation by setting ''l''=1, and modified/corrected Lorentz's derivation of the equations of electrodynamics in some details in order to fully satisfy the principle of relativity, ''i.e.'' making them fully Lorentz covariant.<ref>Miller (1981), Chap. 1.14</ref>
Apparently Poincaré was unaware of Larmor's contributions, because he only mentioned Lorentz and therefore used for the first time the name "Lorentz transformation".<ref>Pais (1982), Chap. 6c</ref><ref>Katzir (2005), 280–288</ref> Poincaré set the speed of light to unity, pointed out the group characteristics of the transformation by setting ''l''=1, and modified/corrected Lorentz's derivation of the equations of electrodynamics in some details in order to fully satisfy the principle of relativity, ''i.e.'' making them fully Lorentz covariant.<ref>Miller (1981), Chap. 1.14</ref>


In July 1905 (published in January 1906)<ref group=R>Poincaré (1905/06), pp. 129ff</ref> Poincaré showed in detail how the transformations and electrodynamic equations are a consequence of the [[principle of least action]]; he demonstrated in more detail the group characteristics of the transformation, which he called [[Lorentz group]], and he showed that the combination ''x<sup>2</sup>+y<sup>2</sup>+z<sup>2</sup>-t<sup>2</sup>'' is invariant. He noticed that the 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. He also formulated the velocity addition formula ({{equationNote|4d}}), which he had already derived in unpublished letters to Lorentz from May 1905:<ref group=R>Poincaré (1905/06), p. 144</ref>
In July 1905 (published in January 1906)<ref group=R>Poincaré (1905/06), pp. 129ff</ref> Poincaré showed in detail how the transformations and electrodynamic equations are a consequence of the [[principle of least action]]; he demonstrated in more detail the group characteristics of the transformation, which he called [[Lorentz group]], and he showed that the combination ''x<sup>2</sup>+y<sup>2</sup>+z<sup>2</sup>-t<sup>2</sup>'' is invariant. He noticed that the 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. He also formulated the velocity addition formula, which he had already derived in unpublished letters to Lorentz from May 1905:<ref group=R>Poincaré (1905/06), p. 144</ref>


:<math>\xi'=\frac{\xi+\varepsilon}{1+\xi\varepsilon},\ \eta'=\frac{\eta}{k(1+\xi\varepsilon)}</math>.
:<math>\xi'=\frac{\xi+\varepsilon}{1+\xi\varepsilon},\ \eta'=\frac{\eta}{k(1+\xi\varepsilon)}</math>.
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==={{anchor|Einstein}} Einstein (1905) – Special relativity===
==={{anchor|Einstein}} Einstein (1905) – Special relativity===


On June 30, 1905 (published September 1905) Einstein published what is now called [[special relativity]] and gave a new derivation of the transformation, which was based only on the principle on relativity and the principle of the constancy of the speed of light. While Lorentz considered "local time" to be a mathematical stipulation device for explaining the Michelson-Morley experiment, Einstein showed that the coordinates given by the Lorentz transformation were in fact the inertial coordinates of relatively moving frames of reference. For quantities of first order in ''v/c'' this was also done by Poincaré in 1900, while Einstein derived the complete transformation by this method. Unlike Lorentz and Poincaré who still distinguished between real time in the aether and apparent time for moving observers, Einstein showed that the transformations concern the nature of space and time.<ref>Miller (1981), Chap. 6</ref><ref>Pais (1982), Kap. 7</ref><ref>Darrigol (2005), Chap. 6</ref>
On June 30, 1905 (published September 1905) Einstein published what is now called [[special relativity]] and gave a new derivation of the transformation, which was based only on the principle of relativity and the principle of the constancy of the speed of light. While Lorentz considered "local time" to be a mathematical stipulation device for explaining the Michelson-Morley experiment, Einstein showed that the coordinates given by the Lorentz transformation were in fact the inertial coordinates of relatively moving frames of reference. For quantities of first order in ''v/c'' this was also done by Poincaré in 1900, while Einstein derived the complete transformation by this method. Unlike Lorentz and Poincaré who still distinguished between real time in the aether and apparent time for moving observers, Einstein showed that the transformations applied to the kinematics of moving frames.<ref>Miller (1981), Chap. 6</ref><ref>Pais (1982), Kap. 7</ref><ref>Darrigol (2005), Chap. 6</ref>


The notation for this transformation is equivalent to Poincaré's of 1905 and ({{equationNote|4b}}), except that Einstein didn't set the speed of light to unity:<ref group=R>Einstein (1905), p. 902</ref>
The notation for this transformation is equivalent to Poincaré's of 1905, except that Einstein didn't set the speed of light to unity:<ref group=R>Einstein (1905), p. 902</ref>


:<math>\begin{align}\tau & =\beta\left(t-\frac{v}{V^{2}}x\right)\\
:<math>\begin{align}\tau & =\beta\left(t-\frac{v}{V^{2}}x\right)\\
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</math>
</math>


Einstein also defined the velocity addition formula ({{equationNote|4d}}, {{equationNote|4e}}):<ref group=R>Einstein (1905), § 5 and § 9</ref>
Einstein also defined the velocity addition formula:<ref group=R>Einstein (1905), § 5 and § 9</ref>


:<math>\begin{matrix}x=\frac{w_{\xi}+v}{1+\frac{vw_{\xi}}{V^{2}}}t,\ y=\frac{\sqrt{1-\left(\frac{v}{V}\right)^{2}}}{1+\frac{vw_{\xi}}{V^{2}}}w_{\eta}t\\
:<math>\begin{matrix}x=\frac{w_{\xi}+v}{1+\frac{vw_{\xi}}{V^{2}}}t,\ y=\frac{\sqrt{1-\left(\frac{v}{V}\right)^{2}}}{1+\frac{vw_{\xi}}{V^{2}}}w_{\eta}t\\
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\end{matrix}\right.</math>
\end{matrix}\right.</math>


and the light aberration formula ({{equationNote|4f}}):<ref group=R>Einstein (1905), § 7</ref>
and the light aberration formula:<ref group=R>Einstein (1905), § 7</ref>


:<math>\cos\varphi'=\frac{\cos\varphi-\frac{v}{V}}{1-\frac{v}{V}\cos\varphi}</math>
:<math>\cos\varphi'=\frac{\cos\varphi-\frac{v}{V}}{1-\frac{v}{V}\cos\varphi}</math>
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=== {{anchor|Minkowski}} Minkowski (1907–1908) – Spacetime ===
=== {{anchor|Minkowski}} Minkowski (1907–1908) – Spacetime ===


The work on the principle of relativity by Lorentz, Einstein, [[Max Planck|Planck]], together with Poincaré's four-dimensional approach, were further elaborated and combined with the [[hyperboloid model]] by [[Hermann Minkowski]] in 1907 and 1908.<ref group=R>Minkowski (1907/15), pp. 927ff</ref><ref group=R>Minkowski (1907/08), pp. 53ff</ref> Minkowski particularly reformulated electrodynamics in a four-dimensional way ([[Minkowski spacetime]]).<ref>Walter (1999a)</ref> For instance, he wrote ''x, y, z, it'' in the form ''x<sub>1</sub>, x<sub>2</sub>, x<sub>3</sub>, x<sub>4</sub>''. By defining ψ as the angle of rotation around the ''z''-axis, the Lorentz transformation assumes a form (with ''c''=1) in agreement with ({{equationNote|2b}}):<ref group=R name=mink1>Minkowski (1907/08), p. 59</ref>
The work on the principle of relativity by Lorentz, Einstein, [[Max Planck|Planck]], together with Poincaré's four-dimensional approach, were further elaborated and combined with the [[hyperboloid model]] by [[Hermann Minkowski]] in 1907 and 1908.<ref group=R>Minkowski (1907/15), pp. 927ff</ref><ref group=R>Minkowski (1907/08), pp. 53ff</ref> Minkowski particularly reformulated electrodynamics in a four-dimensional way ([[Minkowski spacetime]]).<ref>Walter (1999a)</ref> For instance, he wrote ''x, y, z, it'' in the form ''x<sub>1</sub>, x<sub>2</sub>, x<sub>3</sub>, x<sub>4</sub>''. By defining ψ as the angle of rotation around the ''z''-axis, the Lorentz transformation assumes the form (with ''c''=1):<ref group=R name=mink1>Minkowski (1907/08), p. 59</ref>


:<math>\begin{align}x'_{1} & =x_{1}\\
:<math>\begin{align}x'_{1} & =x_{1}\\
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:<math>-i\tan i\psi=\frac{e^{\psi}-e^{-\psi}}{e^{\psi}+e^{-\psi}}=q</math> with <math>\psi=\frac{1}{2}\ln\frac{1+q}{1-q}</math>.
:<math>-i\tan i\psi=\frac{e^{\psi}-e^{-\psi}}{e^{\psi}+e^{-\psi}}=q</math> with <math>\psi=\frac{1}{2}\ln\frac{1+q}{1-q}</math>.


Minkowski's expression can also by written as ψ=atanh(q) and was later called [[rapidity]]. He also wrote the Lorentz transformation in matrix form equivalent to ({{equationNote|2a}}) (''n''=3):<ref group=R>Minkowski (1907/08), pp. 65–66, 81–82</ref>
Minkowski's expression can also by written as ψ=atanh(q) and was later called [[rapidity]]. He also wrote the Lorentz transformation in matrix form:<ref group=R>Minkowski (1907/08), pp. 65–66, 81–82</ref>


:<math>\begin{matrix}x_{1}^{2}+x_{2}^{2}+x_{3}^{2}+x_{4}^{2}=x_{1}^{\prime2}+x_{2}^{\prime2}+x_{3}^{\prime2}+x_{4}^{\prime2}\\
:<math>\begin{matrix}x_{1}^{2}+x_{2}^{2}+x_{3}^{2}+x_{4}^{2}=x_{1}^{\prime2}+x_{2}^{\prime2}+x_{3}^{\prime2}+x_{4}^{\prime2}\\
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==={{Anchor|Sommerfeld}} Sommerfeld (1909) – Spherical trigonometry===
==={{Anchor|Sommerfeld}} Sommerfeld (1909) – Spherical trigonometry===


Using an imaginary rapidity such as Minkowski, [[Arnold Sommerfeld]] (1909) formulated a transformation equivalent to Lorentz boost ({{equationNote|3b}}), and the relativistic velocity addition ({{equationNote|4d}}) in terms of trigonometric functions and the [[spherical law of cosines]]:<ref group=R>Sommerfeld (1909), p. 826ff.</ref>
Using an imaginary rapidity such as Minkowski, [[Arnold Sommerfeld]] (1909) formulated the Lorentz boost and the relativistic velocity addition in terms of trigonometric functions and the [[spherical law of cosines]]:<ref group=R>Sommerfeld (1909), p. 826ff.</ref>


:<math>\begin{matrix}\left.\begin{array}{lrl}
:<math>\begin{matrix}\left.\begin{array}{lrl}
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\cos\varphi=\cos\varphi_{1}\cos\varphi_{2}-\sin\varphi_{1}\sin\varphi_{2}\cos\alpha\\
\cos\varphi=\cos\varphi_{1}\cos\varphi_{2}-\sin\varphi_{1}\sin\varphi_{2}\cos\alpha\\
v^{2}=\frac{v_{1}^{2}+v_{2}^{2}+2v_{1}v_{2}\cos\alpha-\frac{1}{c^{2}}v_{1}^{2}v_{2}^{2}\sin^{2}\alpha}{\left(1+\frac{1}{c^{2}}v_{1}v_{2}\cos\alpha\right)^{2}}
v^{2}=\frac{v_{1}^{2}+v_{2}^{2}+2v_{1}v_{2}\cos\alpha-\frac{1}{c^{2}}v_{1}^{2}v_{2}^{2}\sin^{2}\alpha}{\left(1+\frac{1}{c^{2}}v_{1}v_{2}\cos\alpha\right)^{2}}
\end{matrix}</math>

==={{anchor|Frank}} Frank (1909) – Hyperbolic functions===
Hyperbolic functions were used by [[Philipp Frank]] (1909), who derived the Lorentz transformation using ''ψ'' as [[rapidity]]:<ref group=R>Frank (1909), pp. 423-425</ref>

:<math>\begin{matrix}x'=x\varphi(a)\,{\rm ch}\,\psi+t\varphi(a)\,{\rm sh}\,\psi\\
t'=-x\varphi(a)\,{\rm sh}\,\psi+t\varphi(a)\,{\rm ch}\,\psi\\
\hline {\rm th}\,\psi=-a,\ {\rm sh}\,\psi=\frac{a}{\sqrt{1-a^{2}}},\ {\rm ch}\,\psi=\frac{1}{\sqrt{1-a^{2}}},\ \varphi(a)=1\\
\hline x'=\frac{x-at}{\sqrt{1-a^{2}}},\ y'=y,\ z'=z,\ t'=\frac{-ax+t}{\sqrt{1-a^{2}}}
\end{matrix}</math>
\end{matrix}</math>


==={{anchor|Bateman}} Bateman and Cunningham (1909–1910) – Spherical wave transformation===
==={{anchor|Bateman}} Bateman and Cunningham (1909–1910) – Spherical wave transformation===


In line with [[#Lie|Lie's (1871)]] research on the relation between sphere transformations with an imaginary radius coordinate and 4D conformal transformations, it was pointed out by [[Harry Bateman|Bateman]] and [[Ebenezer Cunningham|Cunningham]] (1909–1910), that by setting ''u=ict'' as the imaginary fourth coordinates one can produce spacetime conformal transformations. Not only the quadratic form <math>\lambda\left(dx^{2}+dy^{2}+dz^{2}+du^{2}\right)</math>, but also [[Maxwells equations]] are covariant with respect to these transformations, irrespective of the choice of λ. These variants of conformal or Lie sphere transformations were called [[spherical wave transformation]]s by Bateman.<ref group=R>Bateman (1909/10), pp. 223ff</ref><ref group=R>Cunningham (1909/10), pp. 77ff</ref> However, this covariance is restricted to certain areas such as electrodynamics, whereas the totality of natural laws in inertial frames is covariant under the [[Lorentz group]].<ref group=R>Klein (1910)</ref> In particular, by setting λ=1 the Lorentz group {{nowrap|SO(1,3)}} can be seen as a 10-parameter subgroup of the 15-parameter spacetime conformal group {{nowrap|Con(1,3)}}.
In line with [[Sophus Lie]]'s (1871) research on the relation between sphere transformations with an imaginary radius coordinate and 4D conformal transformations, it was pointed out by [[Harry Bateman|Bateman]] and [[Ebenezer Cunningham|Cunningham]] (1909–1910), that by setting ''u=ict'' as the imaginary fourth coordinates one can produce spacetime conformal transformations. Not only the quadratic form <math>\lambda\left(dx^{2}+dy^{2}+dz^{2}+du^{2}\right)</math>, but also [[Maxwells equations]] are covariant with respect to these transformations, irrespective of the choice of λ. These variants of conformal or Lie sphere transformations were called [[spherical wave transformation]]s by Bateman.<ref group=R>Bateman (1909/10), pp. 223ff</ref><ref group=R>Cunningham (1909/10), pp. 77ff</ref> However, this covariance is restricted to certain areas such as electrodynamics, whereas the totality of natural laws in inertial frames is covariant under the [[Lorentz group]].<ref group=R>Klein (1910)</ref> In particular, by setting λ=1 the Lorentz group {{nowrap|SO(1,3)}} can be seen as a 10-parameter subgroup of the 15-parameter spacetime conformal group {{nowrap|Con(1,3)}}.


Bateman (1910–12)<ref>Bateman (1910/12), pp. 358–359</ref> also alluded to the identity between the [[#Laguerre|Laguerre inversion]] and the Lorentz transformations. In general, the isomorphism between the Laguerre group and the Lorentz group was pointed out by [[Élie Cartan]] (1912, 1915–55),<ref name="ReferenceA"/><ref group=R>Cartan (1912), p. 23</ref> [[Henri Poincaré]] (1912–21)<ref group=R>Poincaré (1912/21), p. 145</ref> and others.
Bateman (1910–12)<ref>Bateman (1910/12), pp. 358–359</ref> also alluded to the identity between the [[spherical wave transformation|Laguerre inversion]] and the Lorentz transformations. In general, the isomorphism between the Laguerre group and the Lorentz group was pointed out by [[Élie Cartan]] (1912, 1915–55),<ref group=R>Cartan (1912), p. 23</ref> [[Henri Poincaré]] (1912–21)<ref group=R>Poincaré (1912/21), p. 145</ref> and others.


=== {{anchor|Herglotz1}} Herglotz (1909/10) – Möbius transformation ===
=== {{anchor|Herglotz1}} Herglotz (1909/10) – Möbius transformation ===


Following [[#Klein2|Klein (1889–1897) and Fricke & Klein (1897)]] concerning the Cayley absolute, hyperbolic motion and its transformation, [[Gustav Herglotz]] (1909–10) classified the one-parameter Lorentz transformations as loxodromic, hyperbolic, parabolic and elliptic. The general case (on the left) equivalent to Lorentz transformation ({{equationNote|6a}}) and the hyperbolic case (on the right) equivalent to Lorentz transformation ({{equationNote|3d}}) or squeeze mapping ({{equationNote|9d}}) are as follows:<ref group=R>Herglotz (1909/10), pp. 404-408</ref>
Following [[Felix Klein]] (1889–1897) and Fricke & Klein (1897) concerning the Cayley absolute, hyperbolic motion and its transformation, [[Gustav Herglotz]] (1909–10) classified the one-parameter Lorentz transformations as loxodromic, hyperbolic, parabolic and elliptic. The general case (on the left) and the hyperbolic case equivalent to Lorentz transformations or squeeze mappings are as follows:<ref group=R>Herglotz (1909/10), pp. 404-408</ref>


:<math>\left.\begin{matrix}z_{1}^{2}+z_{2}^{2}+z_{3}^{2}-z_{4}^{2}=0\\
:<math>\left.\begin{matrix}z_{1}^{2}+z_{2}^{2}+z_{3}^{2}-z_{4}^{2}=0\\
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==={{anchor|Varicak}} Varićak (1910) – Hyperbolic functions===
==={{anchor|Varicak}} Varićak (1910) – Hyperbolic functions===


Following [[#Sommerfeld|Sommerfeld (1909)]], hyperbolic functions were used by [[Vladimir Varićak]] in several papers starting from 1910, who represented the equations of special relativity on the basis of [[hyperbolic geometry]] in terms of Weierstrass coordinates. For instance, by setting ''l=ct'' and ''v/c=tanh(u)'' with ''u'' as rapidity he wrote the Lorentz transformation in agreement with ({{equationNote|3b}}):<ref group=R name=var1>Varićak (1910), p. 93</ref>
Following [[#Sommerfeld|Sommerfeld (1909)]], hyperbolic functions were used by [[Vladimir Varićak]] in several papers starting from 1910, who represented the equations of special relativity on the basis of [[hyperbolic geometry]] in terms of Weierstrass coordinates. For instance, by setting ''l=ct'' and ''v/c=tanh(u)'' with ''u'' as rapidity he wrote the Lorentz transformation:<ref group=R name=var1>Varićak (1910), p. 93</ref>


:<math>\begin{align}l' & =-x\operatorname{sh}u+l\operatorname{ch}u,\\
:<math>\begin{align}l' & =-x\operatorname{sh}u+l\operatorname{ch}u,\\
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\end{matrix}</math>
\end{matrix}</math>


Subsequently, other authors such as [[E. T. Whittaker]] (1910) or [[Alfred Robb]] (1911, who coined the name rapidity) used similar expressions, which are still used in modern textbooks.<ref name=rind />
Subsequently, other authors such as [[E. T. Whittaker]] (1910) or [[Alfred Robb]] (1911, who coined the name rapidity) used similar expressions, which are still used in modern textbooks.

==={{anchor|Plummer}} Plummer (1910) – Trigonometric Lorentz boosts===

[[w:Henry Crozier Keating Plummer]] (1910) defined the Lorentz boost in terms of trigonometric functions<ref group=R>Plummer (1910), p. 256</ref>

:<math>\begin{matrix}\tau=t\sec\beta-x\tan\beta/U\\
\xi=x\sec\beta-Ut\tan\beta\\
\eta=y,\ \zeta=z,\\
\hline \sin\beta=v/U
\end{matrix}</math>


=== {{anchor|Ignatowski}} Ignatowski (1910) ===
=== {{anchor|Ignatowski}} Ignatowski (1910) ===
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</math>
</math>


The variable ''n'' can be seen as a space-time constant whose value has to be determined by experiment or taken from a known physical law such as electrodynamics. For that purpose, Ignatowski used the above-mentioned Heaviside ellipsoid representing a contraction of electrostatic fields by ''x''/γ in the direction of motion. It can be seen that this is only consistent with Ignatowski's transformation when ''n=1/c''<sup>2</sup>, resulting in ''p''=γ and the Lorentz transformation ({{equationNote|4b}}). With ''n''=0, no length changes arise and the Galilean transformation follows. Ignatowski's method was further developed and improved by [[Philipp Frank]] and [[Hermann Rothe]] (1911, 1912),<ref group=R>Frank & Rothe (1911), pp. 825ff; (1912), p. 750ff.</ref> with various authors developing similar methods in subsequent years.<ref name=baccetti>Baccetti (2011), see references 1–25 therein.</ref>
The variable ''n'' can be seen as a space-time constant whose value has to be determined by experiment or taken from a known physical law such as electrodynamics. For that purpose, Ignatowski used the above-mentioned Heaviside ellipsoid representing a contraction of electrostatic fields by ''x''/γ in the direction of motion. It can be seen that this is only consistent with Ignatowski's transformation when ''n=1/c''<sup>2</sup>, resulting in ''p''=γ and the Lorentz transformation. With ''n''=0, no length changes arise and the Galilean transformation follows. Ignatowski's method was further developed and improved by [[Philipp Frank]] and [[Hermann Rothe]] (1911, 1912),<ref group=R>Frank & Rothe (1911), pp. 825ff; (1912), p. 750ff.</ref> with various authors developing similar methods in subsequent years.<ref name=baccetti>Baccetti (2011), see references 1–25 therein.</ref>


==={{anchor|Noether}} Noether (1910), Klein (1910) – Quaternions===
==={{anchor|Noether}} Noether (1910), Klein (1910) – Quaternions===


[[Felix Klein]] (1908) described [[#Cayley3|Cayley's (1854)]] 4D quaternion multiplications as "Drehstreckungen" (orthogonal substitutions in terms of rotations leaving invariant a quadratic form up to a factor), and pointed out that the modern principle of relativity as provided by Minkowski is essentially only the consequent application of such Drehstreckungen, even though he didn't provide details.<ref group=R>Klein (1908), p. 165</ref>
[[Felix Klein]] (1908) described Cayley's (1854) 4D quaternion multiplications as "Drehstreckungen" (orthogonal substitutions in terms of rotations leaving invariant a quadratic form up to a factor), and pointed out that the modern principle of relativity as provided by Minkowski is essentially only the consequent application of such Drehstreckungen, even though he didn't provide details.<ref group=R>Klein (1908), p. 165</ref>


In an appendix to Klein's and Sommerfeld's "Theory of the top" (1910), [[Fritz Noether]] showed how to formulate hyperbolic rotations using biquaternions with <math>\omega=\sqrt{-1}</math>, which he also related to the speed of light by setting ω<sup>2</sup>=-''c''<sup>2</sup>. He concluded that this is the principal ingredient for a rational representation of the group of Lorentz transformations equivalent to ({{equationNote|7a}}):<ref group=R>Noether (1910), pp. 939–943</ref>
In an appendix to Klein's and Sommerfeld's "Theory of the top" (1910), [[Fritz Noether]] showed how to formulate hyperbolic rotations using biquaternions with <math>\omega=\sqrt{-1}</math>, which he also related to the speed of light by setting ω<sup>2</sup>=-''c''<sup>2</sup>. He concluded that this is the principal ingredient for a rational representation of the group of Lorentz transformations:<ref group=R>Noether (1910), pp. 939–943</ref>


:<math>\begin{matrix}V=\frac{Q_{1}vQ_{2}}{T_{1}T_{2}}\\
:<math>\begin{matrix}V=\frac{Q_{1}vQ_{2}}{T_{1}T_{2}}\\
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\end{matrix}</math>
\end{matrix}</math>


Besides citing quaternion related standard works such as [[#Cayley3|Cayley (1854)]], Noether referred to the entries in Klein's encyclopedia by [[Eduard Study]] (1899) and the French version by [[Élie Cartan]] (1908).<ref>Cartan & Study (1908), sections 35–36</ref> Cartan's version contains a description of Study's [[dual number]]s, Clifford's biquaternions (including the choice <math>\omega=\sqrt{-1}</math> for hyperbolic geometry), and Clifford algebra, with references to [[#Stephanos|Stephanos (1883)]], [[#Buchheim|Buchheim (1884–85)]], [[#Vahlen|Vahlen (1901–02)]] and others.
Besides citing quaternion related standard works by [[Arthur Cayley]] (1854), Noether referred to the entries in Klein's encyclopedia by [[Eduard Study]] (1899) and the French version by [[Élie Cartan]] (1908).<ref>Cartan & Study (1908), sections 35–36</ref> Cartan's version contains a description of Study's [[dual number]]s, Clifford's biquaternions (including the choice <math>\omega=\sqrt{-1}</math> for hyperbolic geometry), and Clifford algebra, with references to Stephanos (1883), Buchheim (1884–85), Vahlen (1901–02) and others.


Citing Noether, Klein himself published in August 1910 the following quaternion substitutions forming the group of Lorentz transformations:<ref group=R>Klein (1910), p. 300</ref>
Citing Noether, Klein himself published in August 1910 the following quaternion substitutions forming the group of Lorentz transformations:<ref group=R>Klein (1910), p. 300</ref>
Line 1,434: Line 570:
\end{matrix}</math>
\end{matrix}</math>


Silberstein cites [[#Cayley3|Cayley (1854, 1855)]] and Study's encyclopedia entry (in the extended French version of Cartan in 1908), as well as the appendix of Klein's and Sommerfeld's book.
Silberstein cites Cayley (1854, 1855) and Study's encyclopedia entry (in the extended French version of Cartan in 1908), as well as the appendix of Klein's and Sommerfeld's book.

==={{anchor|Herglotz2}} Herglotz (1911), Silberstein (1911) – Vector transformation===


==={{anchor|Herglotz2}} Ignatowski (1910/11), Herglotz (1911), and others – Vector transformation===
{{Further|Lorentz transformation#Vector transformations}}
{{Further|Lorentz transformation#Vector transformations}}


[[Gustav Herglotz]] (1911)<ref group=R>Herglotz (1911), p. 497</ref> showed how to formulate the transformation equivalent to ({{equationNote|4c}}) in order to allow for arbitrary velocities and coordinates '''v'''=''(v<sub>x</sub>, v<sub>y</sub>, v<sub>z</sub>)'' and '''r'''=''(x, y, z)'':
[[Vladimir Ignatowski]] (1910, published 1911) showed how to reformulate the Lorentz transformation in order to allow for arbitrary velocities and coordinates:<ref group=R>Ignatowski (1910/11a), p. 23; (1910/11b), p. 22</ref>

:<math>\begin{matrix}\begin{matrix}\mathfrak{v} =\frac{\mathfrak{v}'+(p-1)\mathfrak{c}_{0}\cdot\mathfrak{c}_{0}\mathfrak{v}'+pq\mathfrak{c}_{0}}{p\left(1+nq\mathfrak{c}_{0}\mathfrak{v}'\right)} & \left|\begin{align}\mathfrak{A}' & =\mathfrak{A}+(p-1)\mathfrak{c}_{0}\cdot\mathfrak{c}_{0}\mathfrak{A}-pqb\mathfrak{c}_{0}\\
b' & =pb-pqn\mathfrak{A}\mathfrak{c}_{0}\\
\\
\mathfrak{A} & =\mathfrak{A}'+(p-1)\mathfrak{c}_{0}\cdot\mathfrak{c}_{0}\mathfrak{A}'+pqb'\mathfrak{c}_{0}\\
b & =pb'+pqn\mathfrak{A}'\mathfrak{c}_{0}
\end{align}
\right.\end{matrix}\\
\left[\mathfrak{v}=\mathbf{u},\ \mathfrak{A}=\mathbf{x},\ b=t,\ \mathfrak{c}_{0}=\frac{\mathbf{v}}{v},\ p=\gamma,\ n=\frac{1}{c^{2}}\right]
\end{matrix}</math>

[[Gustav Herglotz]] (1911)<ref group=R>Herglotz (1911), p. 497</ref> also showed how to formulate the transformation in order to allow for arbitrary velocities and coordinates '''v'''=''(v<sub>x</sub>, v<sub>y</sub>, v<sub>z</sub>)'' and '''r'''=''(x, y, z)'':


:<math>\begin{matrix}\text{original} & \text{modern}\\
:<math>\begin{matrix}\text{original} & \text{modern}\\
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==={{anchor|Borel}} Borel (1913–14) – Cayley–Hermite parameter===
==={{anchor|Borel}} Borel (1913–14) – Cayley–Hermite parameter===


Borel (1913) started by demonstrating Euclidean motions using Euler-Rodrigues parameter in three dimensions, and [[#Cayley|Cayley's (1846)]] parameter in four dimensions. Then he demonstrated the connection to indefinite quadratic forms expressing hyperbolic motions and Lorentz transformations. In three dimensions equivalent to ({{equationNote|5b}}):<ref group=R>Borel (1913/14), p. 39</ref>
[[Émile Borel]] (1913) started by demonstrating Euclidean motions using Euler-Rodrigues parameter in three dimensions, and Cayley's (1846) parameter in four dimensions. Then he demonstrated the connection to indefinite quadratic forms expressing hyperbolic motions and Lorentz transformations. In three dimensions:<ref group=R>Borel (1913/14), p. 39</ref>


:<math>\begin{matrix}x^{2}+y^{2}-z^{2}-1=0\\
:<math>\begin{matrix}x^{2}+y^{2}-z^{2}-1=0\\
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\end{matrix}</math>
\end{matrix}</math>


In four dimensions equivalent to ({{equationNote|5c}}):<ref group=R>Borel (1913/14), p. 41</ref>
In four dimensions:<ref group=R>Borel (1913/14), p. 41</ref>


:<math>\begin{matrix}F=\left(x_{1}-x_{2}\right)^{2}+\left(y_{1}-y_{2}\right)^{2}+\left(z_{1}-z_{2}\right)^{2}-\left(t_{1}-t_{2}\right)^{2}\\
:<math>\begin{matrix}F=\left(x_{1}-x_{2}\right)^{2}+\left(y_{1}-y_{2}\right)^{2}+\left(z_{1}-z_{2}\right)^{2}-\left(t_{1}-t_{2}\right)^{2}\\
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\hline x'=\frac{x}{\cos\varphi}-t\cdot\tan\varphi,\quad t'=\frac{t}{\cos\varphi}-x\cdot\tan\varphi
\hline x'=\frac{x}{\cos\varphi}-t\cdot\tan\varphi,\quad t'=\frac{t}{\cos\varphi}-x\cdot\tan\varphi
\end{matrix}</math>
\end{matrix}</math>

{{Equation box 1|border colour = black |background colour=white|equation=This is equivalent to Lorentz transformation ({{equationNote|8a}}) by the identity <math>\sec\varphi=\tfrac{1}{\cos\varphi}</math>}}


In another paper Gruner used the alternative relations:<ref group=R>Gruner (1921b)</ref>
In another paper Gruner used the alternative relations:<ref group=R>Gruner (1921b)</ref>
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\hline x'=\frac{x}{\sin\theta}-t\cdot\cot\theta,\quad t'=\frac{t}{\sin\theta}-x\cdot\cot\theta
\hline x'=\frac{x}{\sin\theta}-t\cdot\cot\theta,\quad t'=\frac{t}{\sin\theta}-x\cdot\cot\theta
\end{matrix}</math>
\end{matrix}</math>

{{Equation box 1|border colour = black |background colour=white|equation=This is equivalent to Lorentz Lorentz boost ({{equationNote|8b}}) by the identity <math>\csc\theta=\tfrac{1}{\sin\theta}</math>.}}

== Euler's gap ==
In pursuing the history in years before Lorentz enunciated his expressions, one looks to the essence of the concept. In mathematical terms, Lorentz transformations are [[squeeze mapping]]s, the linear transformations that turn a square into a rectangles of the same area. Before Euler, the squeezing was studied as [[Gregoire de Saint-Vincent|quadrature of the hyperbola]] and led to the [[hyperbolic sector|hyperbolic logarithm]]. In 1748 Euler issued his [[precalculus]] [[textbook]] where the number [[e (mathematical constant)|e]] is exploited for trigonometry in the [[unit circle]]. The first volume of [[Introduction to the Analysis of the Infinite]] had no diagrams, allowing teachers and students to draw their own illustrations.

There is a gap in Euler's text where Lorentz transformations arise. A feature of [[natural logarithm]] is its interpretation as area in [[hyperbolic sector]]s. In relativity the classical concept of [[velocity]] is replaced with [[rapidity]], a [[hyperbolic angle]] concept built on hyperbolic sectors. A Lorentz transformation is a [[hyperbolic rotation]] which preserves differences of rapidity, just as the [[circular sector]] area is preserved with a circular rotation. Euler's gap is the lack of hyperbolic angle and [[hyperbolic function]]s, later developed by [[Johann H. Lambert]]. Euler described some [[transcendental function]]s: exponentiation and [[circular function]]s. He used the exponential series <math>\sum_0^{\infty} x^n /n! .</math> With the [[imaginary unit]] i<sup>2</sup> = – 1, and splitting the series into even and odd terms, he obtained
:<math>e^{ix} = \sum_0^{\infty} (ix)^{2n}/(2n)! \ + \ \sum_0^{\infty} (ix)^{2n+1}/(2n + 1)! =</math>
:<math>= \sum_0^{\infty} (-1)^n x^{2n} / 2n! + i \sum_0^{\infty} (-1)^n x^{2n+1}/(2n+1)! \ = \ \cos x + i \sin x .</math>
This development misses the alternative:
:<math>e^x = \cosh x + \sinh x</math> (even and odd terms), and
:<math>e^{jx} = \cosh x + j \sinh x \quad (j^2 = +1) </math> which parametrizes the [[unit hyperbola]].
Here Euler could have noted [[split-complex number]]s along with [[complex number]]s.

For physics, one space dimension is insufficient. But to extend split-complex arithmetic to four dimensions leads to [[hyperbolic quaternion]]s, and opens the door to [[abstract algebra]]'s
[[hypercomplex numbers]]. Reviewing the expressions of Lorentz and Einstein, one observes that the [[Lorentz factor]] is an [[algebraic function]] of velocity. For readers uncomfortable with transcendental functions cosh and sinh, algebraic functions may be more to their liking.


== See also ==
== See also ==
* [[Derivations of the Lorentz transformations]]

*[[History of special relativity]]
* [[History of special relativity]]


==References==
==References==
===Historical mathematical sources===
===Historical mathematical sources===
{{Wikiversity-inline|History of Topics in Special Relativity/mathsource}}
{{Wikiversity inline|History of Topics in Special Relativity/mathsource}}


===Historical relativity sources===
===Historical relativity sources===
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*{{Cite journal|author=Bateman, Harry|year=1912|orig-year=1910|title=Some geometrical theorems connected with Laplace's equation and the equation of wave motion |journal=American Journal of Mathematics|volume=34|issue=3|doi=10.2307/2370223|pages=325–360|url=https://archive.org/details/jstor-2370223|jstor=2370223}}
*{{Cite journal|author=Bateman, Harry|year=1912|orig-year=1910|title=Some geometrical theorems connected with Laplace's equation and the equation of wave motion |journal=American Journal of Mathematics|volume=34|issue=3|doi=10.2307/2370223|pages=325–360|url=https://archive.org/details/jstor-2370223|jstor=2370223}}
*{{Cite book|author=Borel, Émile |year=1914|title=Introduction Geometrique à quelques Théories Physiques|publisher=Gauthier-Villars|location=Paris|url=http://ebooks.library.cornell.edu/cgi/t/text/text-idx?c=math;idno=04710001}}
*{{Cite book|author=Borel, Émile |year=1914|title=Introduction Geometrique à quelques Théories Physiques|publisher=Gauthier-Villars|location=Paris|url=http://ebooks.library.cornell.edu/cgi/t/text/text-idx?c=math;idno=04710001}}
*{{Cite journal |author=Brill, J.|year=1925 |journal=Proceedings of the Cambridge Philosophical Society|title= Note on the Lorentz group|pages=630–632|volume=22|issue=5 |doi=10.1017/S030500410000949X|bibcode=1925PCPS...22..630B}}
*{{Cite journal |author=Brill, J.|year=1925 |journal=Proceedings of the Cambridge Philosophical Society|title= Note on the Lorentz group|pages=630–632|volume=22|issue=5 |doi=10.1017/S030500410000949X|bibcode=1925PCPS...22..630B|s2cid=121117536 }}
*{{Cite book |author=Bucherer, A. H. |year=1904 |title=Mathematische Einführung in die Elektronentheorie |publisher=Teubner |location=Leipzig |url=https://archive.org/details/mathematischeei02buchgoog}}
*{{Cite book |author=Bucherer, A. H. |year=1904 |title=Mathematische Einführung in die Elektronentheorie |publisher=Teubner |location=Leipzig |url=https://archive.org/details/mathematischeei02buchgoog}}
*{{Citation |author=Bucherer, A. H. |year=1908 |title=Messungen an Becquerelstrahlen. Die experimentelle Bestätigung der Lorentz-Einsteinschen Theorie. (Measurements of Becquerel rays. The Experimental Confirmation of the Lorentz-Einstein Theory) |journal=Physikalische Zeitschrift |volume=9 |issue=22 |pages=758–762}}. For Minkowski's and Voigt's statements see p.&nbsp;762.
*{{Citation |author=Bucherer, A. H. |year=1908 |title=Messungen an Becquerelstrahlen. Die experimentelle Bestätigung der Lorentz-Einsteinschen Theorie. (Measurements of Becquerel rays. The Experimental Confirmation of the Lorentz-Einstein Theory) |journal=Physikalische Zeitschrift |volume=9 |issue=22 |pages=758–762}}. For Minkowski's and Voigt's statements see p.&nbsp;762.
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*{{Cite journal|author=Cunningham, Ebenezer|year=1910|orig-year=1909|title=The principle of Relativity in Electrodynamics and an Extension Thereof|journal=Proceedings of the London Mathematical Society |volume=8|pages=77–98|doi=10.1112/plms/s2-8.1.77|title-link=s:en:The principle of Relativity in Electrodynamics and an Extension Thereof}}
*{{Cite journal|author=Cunningham, Ebenezer|year=1910|orig-year=1909|title=The principle of Relativity in Electrodynamics and an Extension Thereof|journal=Proceedings of the London Mathematical Society |volume=8|pages=77–98|doi=10.1112/plms/s2-8.1.77|title-link=s:en:The principle of Relativity in Electrodynamics and an Extension Thereof}}
*{{Citation |author=Einstein, Albert |year=1905 |title=Zur Elektrodynamik bewegter Körper |journal=Annalen der Physik |volume=322 |issue=10 |pages=891–921 |url=http://www.physik.uni-augsburg.de/annalen/history/einstein-papers/1905_17_891-921.pdf |doi=10.1002/andp.19053221004|bibcode = 1905AnP...322..891E |doi-access=free }}. See also: [http://www.fourmilab.ch/etexts/einstein/specrel/ English translation].
*{{Citation |author=Einstein, Albert |year=1905 |title=Zur Elektrodynamik bewegter Körper |journal=Annalen der Physik |volume=322 |issue=10 |pages=891–921 |url=http://www.physik.uni-augsburg.de/annalen/history/einstein-papers/1905_17_891-921.pdf |doi=10.1002/andp.19053221004|bibcode = 1905AnP...322..891E |doi-access=free }}. See also: [http://www.fourmilab.ch/etexts/einstein/specrel/ English translation].
*{{cite journal|author=Frank, Philipp |year=1909 |title=Die Stellung des Relativitätsprinzips im System der Mechanik und Elektrodynamik|journal=Wiener Sitzungsberichte IIA |volume=118 |pages=373–446|hdl=2027/mdp.39015073682224 |url=http://hdl.handle.net/2027/mdp.39015073682224}}
*{{Cite journal|author1=Frank, Philipp |author2=Rothe, Hermann|year=1911|title=Über die Transformation der Raum-Zeitkoordinaten von ruhenden auf bewegte Systeme|journal=Annalen der Physik|volume=339|issue=5|pages=825–855|url=http://gallica.bnf.fr/ark:/12148/bpt6k15337j/f845.table|doi=10.1002/andp.19113390502|bibcode = 1911AnP...339..825F }}
*{{Cite journal|author1=Frank, Philipp |author2=Rothe, Hermann|year=1911|title=Über die Transformation der Raum-Zeitkoordinaten von ruhenden auf bewegte Systeme|journal=Annalen der Physik|volume=339|issue=5|pages=825–855|url=http://gallica.bnf.fr/ark:/12148/bpt6k15337j/f845.table|doi=10.1002/andp.19113390502|bibcode = 1911AnP...339..825F }}
*{{Cite journal|author1=Frank, Philipp |author2=Rothe, Hermann|title=Zur Herleitung der Lorentztransformation|journal=Physikalische Zeitschrift|volume=13|year=1912|pages=750–753}}
*{{Cite journal|author1=Frank, Philipp |author2=Rothe, Hermann|title=Zur Herleitung der Lorentztransformation|journal=Physikalische Zeitschrift|volume=13|year=1912|pages=750–753}}
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*{{Cite journal|author=Ignatowski, W. v.|title=Eine Bemerkung zu meiner Arbeit: "Einige allgemeine Bemerkungen zum Relativitätsprinzip"|journal=Physikalische Zeitschrift|volume=12|year=1911|pages=779|title-link=s:de:Eine Bemerkung zu meiner Arbeit: "Einige allgemeine Bemerkungen zum Relativitätsprinzip"}}
*{{Cite journal|author=Ignatowski, W. v.|title=Eine Bemerkung zu meiner Arbeit: "Einige allgemeine Bemerkungen zum Relativitätsprinzip"|journal=Physikalische Zeitschrift|volume=12|year=1911|pages=779|title-link=s:de:Eine Bemerkung zu meiner Arbeit: "Einige allgemeine Bemerkungen zum Relativitätsprinzip"}}
*{{Cite book|author=Klein, F.|editor=Hellinger, E.|year=1908|title=Elementarmethematik vom höheren Standpunkte aus. Teil I. Vorlesung gehalten während des Wintersemesters 1907-08|publisher=Teubner|location=Leipzig|url=https://archive.org/details/elementarmathem00kleigoog}}
*{{Cite book|author=Klein, F.|editor=Hellinger, E.|year=1908|title=Elementarmethematik vom höheren Standpunkte aus. Teil I. Vorlesung gehalten während des Wintersemesters 1907-08|publisher=Teubner|location=Leipzig|url=https://archive.org/details/elementarmathem00kleigoog}}
*{{Cite book|author=Klein, Felix|year=1921|orig-year=1910|journal=Gesammelte Mathematische Abhandlungen |chapter=Über die geometrischen Grundlagen der Lorentzgruppe|volume=1|pages=533–552|doi=10.1007/978-3-642-51960-4_31|title-link=s:de:Über die geometrischen Grundlagen der Lorentzgruppe|isbn=978-3-642-51898-0}}
*{{Cite book|author=Klein, Felix|title=Gesammelte Mathematische Abhandlungen |year=1921|orig-year=1910|chapter=Über die geometrischen Grundlagen der Lorentzgruppe|volume=1|pages=533–552|doi=10.1007/978-3-642-51960-4_31|title-link=s:de:Über die geometrischen Grundlagen der Lorentzgruppe|isbn=978-3-642-51898-0}}
*{{Cite book|author=Klein, F. |author2=Sommerfeld A.|editor=Noether, Fr.|year=1910|title=Über die Theorie des Kreisels. Heft IV|location=Leipzig|publisher=Teuber|url=https://archive.org/details/fkleinundasommer019696mbp}}
*{{Cite book|author=Klein, F. |author2=Sommerfeld A.|editor=Noether, Fr.|year=1910|title=Über die Theorie des Kreisels. Heft IV|location=Leipzig|publisher=Teuber|url=https://archive.org/details/fkleinundasommer019696mbp}}
*{{Cite book|author=Klein, F.|editor=Hellinger, E.|year=1911|title=Elementarmethematik vom höheren Standpunkte aus. Teil I (Second Edition). Vorlesung gehalten während des Wintersemesters 1907-08|publisher=Teubner|location=Leipzig|hdl=2027/mdp.39015068187817}}
*{{Cite book|author=Klein, F.|editor=Hellinger, E.|year=1911|title=Elementarmethematik vom höheren Standpunkte aus. Teil I (Second Edition). Vorlesung gehalten während des Wintersemesters 1907-08|publisher=Teubner|location=Leipzig|hdl=2027/mdp.39015068187817}}
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*{{Citation |author=Minkowski, Hermann |year=1908 |orig-year=1907 |title=Die Grundgleichungen für die elektromagnetischen Vorgänge in bewegten Körpern |trans-title=[[s:Translation:The Fundamental Equations for Electromagnetic Processes in Moving Bodies|The Fundamental Equations for Electromagnetic Processes in Moving Bodies]] |journal=Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse |pages=53–111|title-link=s:Die Grundgleichungen für die elektromagnetischen Vorgänge in bewegten Körpern }}
*{{Citation |author=Minkowski, Hermann |year=1908 |orig-year=1907 |title=Die Grundgleichungen für die elektromagnetischen Vorgänge in bewegten Körpern |trans-title=[[s:Translation:The Fundamental Equations for Electromagnetic Processes in Moving Bodies|The Fundamental Equations for Electromagnetic Processes in Moving Bodies]] |journal=Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse |pages=53–111|title-link=s:Die Grundgleichungen für die elektromagnetischen Vorgänge in bewegten Körpern }}
*{{Citation |author=Minkowski, Hermann |year=1909 |orig-year=1908 |title=Space and Time |journal=Physikalische Zeitschrift |volume=10 |pages=75–88|title-link=s:Space and Time }}
*{{Citation |author=Minkowski, Hermann |year=1909 |orig-year=1908 |title=Space and Time |journal=Physikalische Zeitschrift |volume=10 |pages=75–88|title-link=s:Space and Time }}
*{{Cite journal|author=Müller, Hans Robert|author-link=Hans Robert Müller|year=1948|journal=Monatshefte für Mathematik und Physik|title=Zyklographische Betrachtung der Kinematik der speziellen Relativitätstheorie|volume=52|pages=337–353|doi=10.1007/BF01525338|s2cid=120150204|url=http://www.digizeitschriften.de/dms/resolveppn/?PID=GDZPPN00246988X}}
*{{Cite journal|author=Müller, Hans Robert|author-link=Hans Robert Müller|year=1948|journal=Monatshefte für Mathematik und Physik|title=Zyklographische Betrachtung der Kinematik der speziellen Relativitätstheorie|volume=52| issue=4 |pages=337–353|doi=10.1007/BF01525338|s2cid=120150204|url=http://www.digizeitschriften.de/dms/resolveppn/?PID=GDZPPN00246988X}}
*{{citation|author=Plummer, H.C.K.|year=1910 |title=On the Theory of Aberration and the Principle of Relativity|journal=Monthly Notices of the Royal Astronomical Society|volume=40 |issue=3 |pages=252–266|doi=10.1093/mnras/70.3.252 |bibcode=1910MNRAS..70..252P|doi-access=free}}
*{{Citation |author=Poincaré, Henri |year=1900 |title=La théorie de Lorentz et le principe de réaction |journal=Archives Néerlandaises des Sciences Exactes et Naturelles |volume=5 |pages=252–278|title-link=s:fr:La théorie de Lorentz et le principe de réaction }}. See also the [http://www.physicsinsights.org/poincare-1900.pdf English translation].
*{{Citation |author=Poincaré, Henri |year=1900 |title=La théorie de Lorentz et le principe de réaction |journal=Archives Néerlandaises des Sciences Exactes et Naturelles |volume=5 |pages=252–278|title-link=s:fr:La théorie de Lorentz et le principe de réaction }}. See also the [http://www.physicsinsights.org/poincare-1900.pdf English translation].
*{{Citation |author=Poincaré, Henri |year=1906 |orig-year=1904 |chapter=[[s:The Principles of Mathematical Physics|The Principles of Mathematical Physics]] |title=Congress of arts and science, universal exposition, St. Louis, 1904 |volume=1 |pages=604–622 |publisher=Houghton, Mifflin and Company |location=Boston and New York}}
*{{Citation |author=Poincaré, Henri |year=1906 |orig-year=1904 |chapter=[[s:The Principles of Mathematical Physics|The Principles of Mathematical Physics]] |title=Congress of arts and science, universal exposition, St. Louis, 1904 |volume=1 |pages=604–622 |publisher=Houghton, Mifflin and Company |location=Boston and New York}}
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*{{Citation |author=Searle, George Frederick Charles |year=1897 |title=On the Steady Motion of an Electrified Ellipsoid |journal=Philosophical Magazine |series=5 |volume=44 |issue=269 |pages=329–341 |doi=10.1080/14786449708621072|title-link=s:On the Steady Motion of an Electrified Ellipsoid }}
*{{Citation |author=Searle, George Frederick Charles |year=1897 |title=On the Steady Motion of an Electrified Ellipsoid |journal=Philosophical Magazine |series=5 |volume=44 |issue=269 |pages=329–341 |doi=10.1080/14786449708621072|title-link=s:On the Steady Motion of an Electrified Ellipsoid }}
*{{Citation | author=Silberstein, L. | year=1912 | orig-year=1911|title=Quaternionic form of relativity| journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science | volume =23 | issue=137|pages =790–809|url=https://archive.org/details/londonedinburg6231912lond | doi=10.1080/14786440508637276}}
*{{Citation | author=Silberstein, L. | year=1912 | orig-year=1911|title=Quaternionic form of relativity| journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science | volume =23 | issue=137|pages =790–809|url=https://archive.org/details/londonedinburg6231912lond | doi=10.1080/14786440508637276}}
*{{Citation|author=Sommerfeld, A.|year=1909|title=Über die Zusammensetzung der Geschwindigkeiten in der Relativtheorie|trans-title=Wikisource translation: [[s:Translation:On the Composition of Velocities in the Theory of Relativity|On the Composition of Velocities in the Theory of Relativity]]|journal=Verh. Der DPG|volume=21|pages=577–582}}
*{{Citation|author=Sommerfeld, A.|year=1909|title=Über die Zusammensetzung der Geschwindigkeiten in der Relativtheorie|trans-title=Wikisource translation: [[s:Translation:On the Composition of Velocities in the Theory of Relativity|On the Composition of Velocities in the Theory of Relativity]]|journal=Verh. Dtsch. Phys. Ges.|volume=21|pages=577–582}}
*{{Citation |author=Thomson, Joseph John |year=1889 |title=On the Magnetic Effects produced by Motion in the Electric Field |journal=Philosophical Magazine |volume=28 |series=5 |issue=170 |pages=1–14 |doi=10.1080/14786448908619821|title-link=s:On the Magnetic Effects produced by Motion in the Electric Field }}
*{{Citation |author=Thomson, Joseph John |year=1889 |title=On the Magnetic Effects produced by Motion in the Electric Field |journal=Philosophical Magazine |volume=28 |series=5 |issue=170 |pages=1–14 |doi=10.1080/14786448908619821|title-link=s:On the Magnetic Effects produced by Motion in the Electric Field }}
*{{Citation | author=Varićak, V. | year=1910 | title=[[s:de:Anwendung der Lobatschefskijschen Geometrie in der Relativtheorie|Anwendung der Lobatschefskijschen Geometrie in der Relativtheorie]] | journal = Physikalische Zeitschrift| volume =11| pages =93–6|trans-title=[[s:Translation:Application of Lobachevskian Geometry in the Theory of Relativity|Application of Lobachevskian Geometry in the Theory of Relativity]]}}
*{{Citation | author=Varićak, V. | year=1910 | title=[[s:de:Anwendung der Lobatschefskijschen Geometrie in der Relativtheorie|Anwendung der Lobatschefskijschen Geometrie in der Relativtheorie]] | journal = Physikalische Zeitschrift| volume =11| pages =93–6|trans-title=[[s:Translation:Application of Lobachevskian Geometry in the Theory of Relativity|Application of Lobachevskian Geometry in the Theory of Relativity]]}}
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*{{Cite book|author=Bachmann, P.|year=1923|title=Die Arithmetik der quadratischen Formen. Zweite Abtheilung|location=Leipzig|url=https://archive.org/details/arithdquadrachen02bachrich|publisher=B.G. Teubner}}
*{{Cite book|author=Bachmann, P.|year=1923|title=Die Arithmetik der quadratischen Formen. Zweite Abtheilung|location=Leipzig|url=https://archive.org/details/arithdquadrachen02bachrich|publisher=B.G. Teubner}}
*{{Cite journal|author=Barnett, J. H. |year=2004|journal=Mathematics Magazine|volume=77|issue=1|title=Enter, stage center: The early drama of the hyperbolic functions|pages=15–30|url=https://www.maa.org/sites/default/files/pdf/cms_upload/321922717729.pdf.bannered.pdf|doi=10.1080/0025570x.2004.11953223|s2cid=121088132}}
*{{Cite journal|author=Barnett, J. H. |year=2004|journal=Mathematics Magazine|volume=77|issue=1|title=Enter, stage center: The early drama of the hyperbolic functions|pages=15–30|url=https://www.maa.org/sites/default/files/pdf/cms_upload/321922717729.pdf.bannered.pdf|doi=10.1080/0025570x.2004.11953223|s2cid=121088132}}
*Barrett, J.F. (2006), The hyperbolic theory of relativity, {{arxiv|1102.0462}}
*{{Cite book|author=Bôcher, Maxim|year=1907|title=Introduction to higher algebra|chapter=Quadratic forms|publisher=Macmillan|location=New York|chapter-url=https://archive.org/details/cu31924002936536}}
*{{Cite book|author=Bôcher, Maxim|year=1907|title=Introduction to higher algebra|chapter=Quadratic forms|publisher=Macmillan|location=New York|chapter-url=https://archive.org/details/cu31924002936536}}
*{{Cite book|title=Relativity and Common Sense|last=Bondi|first=Hermann|publisher=Doubleday & Company|year=1964|location=New York|url=https://archive.org/details/RelativityCommonSense}}
*{{Cite book|title=Relativity and Common Sense|last=Bondi|first=Hermann|publisher=Doubleday & Company|year=1964|location=New York|url=https://archive.org/details/RelativityCommonSense}}
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*{{Citation |author=Darrigol, Olivier |title=The Genesis of the theory of relativity |year=2005 |journal=Séminaire Poincaré |volume=1 |pages=1–22 |url=http://www.bourbaphy.fr/darrigol2.pdf |doi=10.1007/3-7643-7436-5_1|isbn=978-3-7643-7435-8 |bibcode=2006eins.book....1D }}
*{{Citation |author=Darrigol, Olivier |title=The Genesis of the theory of relativity |year=2005 |journal=Séminaire Poincaré |volume=1 |pages=1–22 |url=http://www.bourbaphy.fr/darrigol2.pdf |doi=10.1007/3-7643-7436-5_1|isbn=978-3-7643-7435-8 |bibcode=2006eins.book....1D }}
*{{Cite book|author=Dickson, L.E.|year=1923|title=History of the theory of numbers, Volume III, Quadratic and higher forms|location=Washington|url=https://archive.org/details/historyoftheoryo03dickuoft|publisher=Washington Carnegie Institution of Washington}}
*{{Cite book|author=Dickson, L.E.|year=1923|title=History of the theory of numbers, Volume III, Quadratic and higher forms|location=Washington|url=https://archive.org/details/historyoftheoryo03dickuoft|publisher=Washington Carnegie Institution of Washington}}
*{{Cite journal |author=Fjelstad, P.|year=1986 |journal=American Journal of Physics |title= Extending special relativity via the perplex numbers|pages=416–422|volume=54|issue=5 |doi=10.1119/1.14605|bibcode=1986AmJPh..54..416g}}
*{{Cite journal |author=Fjelstad, P.|year=1986 |journal=American Journal of Physics |title= Extending special relativity via the perplex numbers|pages=416–422|volume=54|issue=5 |doi=10.1119/1.14605|bibcode=1986AmJPh..54..416F}}
*{{Cite journal |author=Girard, P. R.|year=1984 |journal=European Journal of Physics |title= The quaternion group and modern physics|pages=25–32|volume=5|issue=1|doi=10.1088/0143-0807/5/1/007|bibcode=1984EJPh....5...25G}}
*{{Cite journal |author=Girard, P. R.|year=1984 |journal=European Journal of Physics |title= The quaternion group and modern physics|pages=25–32|volume=5|issue=1|doi=10.1088/0143-0807/5/1/007|bibcode=1984EJPh....5...25G|s2cid=250775753 }}
*{{Cite journal|author=Gray, J.|title=Non-euclidean geometry—A re-interpretation|year=1979|journal=Historia Mathematica|volume=6|issue=3|pages=236–258|doi=10.1016/0315-0860(79)90124-1|doi-access=free}}
*{{Cite journal|author=Gray, J.|title=Non-euclidean geometry—A re-interpretation|year=1979|journal=Historia Mathematica|volume=6|issue=3|pages=236–258|doi=10.1016/0315-0860(79)90124-1|doi-access=free}}
*{{Cite book|author=Gray, J. |author2=Scott W.|year=1997|title=Trois suppléments sur la découverte des fonctions fuchsiennes|chapter=Introduction|pages=7–28|location=Berlin|chapter-url=http://scottwalter.free.fr/papers/3supintro.pdf|url=http://henripoincarepapers.univ-lorraine.fr/chp/hp-pdf/hp1997tsa.pdf }}
*{{Cite book|author=Gray, J. |author2=Scott W.|year=1997|title=Trois suppléments sur la découverte des fonctions fuchsiennes|chapter=Introduction|pages=7–28|location=Berlin|chapter-url=http://scottwalter.free.fr/papers/3supintro.pdf|url=http://henripoincarepapers.univ-lorraine.fr/chp/hp-pdf/hp1997tsa.pdf }}
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*{{Cite journal|author=Müller, Emil|author-link=Emil Müller (mathematician)|year=1910|journal=Encyclopädie der Mathematischen Wissenschaften|volume=3.1.1|title=Die verschiedenen Koordinatensysteme|pages=596–770|url=http://resolver.sub.uni-goettingen.de/purl?PPN360609635}}
*{{Cite journal|author=Müller, Emil|author-link=Emil Müller (mathematician)|year=1910|journal=Encyclopädie der Mathematischen Wissenschaften|volume=3.1.1|title=Die verschiedenen Koordinatensysteme|pages=596–770|url=http://resolver.sub.uni-goettingen.de/purl?PPN360609635}}
*{{Cite journal |author=Musen, P. |year=1970|title=A Discussion of Hill's Method of Secular Perturbations...|journal=Celestial Mechanics|volume=2|issue=1 |pages=41–59|bibcode=1970CeMec...2...41M|doi=10.1007/BF01230449|hdl=2060/19700018328|s2cid=122335532|hdl-access=free}}
*{{Cite journal |author=Musen, P. |year=1970|title=A Discussion of Hill's Method of Secular Perturbations...|journal=Celestial Mechanics|volume=2|issue=1 |pages=41–59|bibcode=1970CeMec...2...41M|doi=10.1007/BF01230449|hdl=2060/19700018328|s2cid=122335532|hdl-access=free}}
*{{Cite book|author=Naimark,M. A. |year=2014|orig-year=1964|title=Linear Representations of the Lorentz Group|location=Oxford|isbn=978-1483184982 }}
*{{Cite book|author=Naimark, M. A. |year=2014|orig-year=1964|title=Linear Representations of the Lorentz Group|location=Oxford|isbn=978-1483184982 }}
*{{Cite journal|author=Pacheco, R.|year=2008|journal=Geometriae Dedicata|volume=146|issue=1|title=Bianchi–Bäcklund transforms and dressing actions, revisited.|pages=85–99|doi=10.1007/s10711-009-9427-5|arxiv=0808.4138|s2cid=14356965}}
*{{Cite journal|author=Pacheco, R.|year=2008|journal=Geometriae Dedicata|volume=146|issue=1|title=Bianchi–Bäcklund transforms and dressing actions, revisited.|pages=85–99|doi=10.1007/s10711-009-9427-5|arxiv=0808.4138|s2cid=14356965}}
*{{Citation |author=Pauli, Wolfgang|author-link=Wolfgang Pauli|year=1921 |journal=Encyclopädie der Mathematischen Wissenschaften|title= Die Relativitätstheorie|pages=539–776|volume=5|issue=2 |url=http://resolver.sub.uni-goettingen.de/purl?PPN360709672}} <br />In English: {{cite book|author=Pauli, W.|title=Theory of Relativity|journal=Fundamental Theories of Physics|volume=165|publisher=Dover Publications|year=1981|orig-year=1921|isbn=978-0-486-64152-2}}
*{{Citation |author=Pais, Abraham |year=1982 |title= [[Subtle is the Lord: The Science and the Life of Albert Einstein]] |place = New York |publisher=Oxford University Press |isbn=978-0-19-520438-4}}
*{{Citation |author=Pais, Abraham |year=1982 |title= [[Subtle is the Lord: The Science and the Life of Albert Einstein]] |place = New York |publisher=Oxford University Press |isbn=978-0-19-520438-4}}
*{{Citation |author=Pauli, Wolfgang|author-link=Wolfgang Pauli|year=1921 |journal=Encyclopädie der Mathematischen Wissenschaften|title= Die Relativitätstheorie|pages=539–776|volume=5|issue=2 |url=http://resolver.sub.uni-goettingen.de/purl?PPN360709672}} <br />In English: {{cite book|author=Pauli, W.|title=Theory of Relativity|volume=165|publisher=Dover Publications|year=1981|orig-year=1921|isbn=978-0-486-64152-2}}
*{{Citation |author=Penrose, R. |author2=Rindler W. |year=1984 |title=Spinors and Space-Time: Volume 1, Two-Spinor Calculus and Relativistic Fields |publisher=Cambridge University Press|isbn=978-0521337076}}
*{{Citation |author=Penrose, R. |author2=Rindler W. |year=1984 |title=Spinors and Space-Time: Volume 1, Two-Spinor Calculus and Relativistic Fields |publisher=Cambridge University Press|isbn=978-0521337076}}
*{{Citation |author=Plummer, H. C. |year=1910 |title=On the Theory of Aberration and the Principle of Relativity |journal=Monthly Notices of the Royal Astronomical Society|volume=70|issue=3 |pages=252–266|doi=10.1093/mnras/70.3.252|doi-access=free |bibcode=1910MNRAS..70..252P}}
*{{Citation |author=Plummer, H. C. |year=1910 |title=On the Theory of Aberration and the Principle of Relativity |journal=Monthly Notices of the Royal Astronomical Society|volume=70|issue=3 |pages=252–266|doi=10.1093/mnras/70.3.252|doi-access=free |bibcode=1910MNRAS..70..252P}}
*{{Cite book|author=Ratcliffe, J. G.|year=1994|title=Foundations of Hyperbolic Manifolds|chapter=Hyperbolic geometry|pages=[https://archive.org/details/foundationsofhyp0000ratc/page/56 56–104]|location=New York|isbn=978-0387943480|chapter-url=https://archive.org/details/foundationsofhyp0000ratc/page/56}}
*{{Cite book|author=Ratcliffe, J. G.|year=1994|title=Foundations of Hyperbolic Manifolds|chapter=Hyperbolic geometry|pages=[https://archive.org/details/foundationsofhyp0000ratc/page/56 56–104]|location=New York|isbn=978-0387943480|chapter-url=https://archive.org/details/foundationsofhyp0000ratc/page/56}}
*{{Cite journal|author=Reynolds, W. F.|year=1993|title=Hyperbolic geometry on a hyperboloid|journal=The American Mathematical Monthly|volume=100|issue=5|pages=442–455|jstor=2324297|doi=10.1080/00029890.1993.11990430}}
*{{Cite journal|author=Reynolds, W. F.|year=1993|title=Hyperbolic geometry on a hyperboloid|journal=The American Mathematical Monthly|volume=100|issue=5|pages=442–455|jstor=2324297|doi=10.1080/00029890.1993.11990430|s2cid=124088818 }}
*{{Cite book|author=Rindler, W.|year=2013|orig-year=1969|title=Essential Relativity: Special, General, and Cosmological|publisher=Springer|isbn=978-1475711356}}
*{{Cite book|author=Rindler, W.|year=2013|orig-year=1969|title=Essential Relativity: Special, General, and Cosmological|publisher=Springer|isbn=978-1475711356}}
*{{Cite book|author=Robinson, E.A.|year=1990|title=Einstein's relativity in metaphor and mathematics|publisher=Prentice Hall|isbn=9780132464970}}
*{{Cite book|author=Robinson, E.A.|year=1990|title=Einstein's relativity in metaphor and mathematics|publisher=Prentice Hall|isbn=9780132464970}}
Line 1,677: Line 807:
*{{Citation |author=Synge, J. L. |year=1956 |title=Relativity: The Special Theory |publisher=North Holland}}
*{{Citation |author=Synge, J. L. |year=1956 |title=Relativity: The Special Theory |publisher=North Holland}}
*{{Cite journal |author=Synge, J.L.|year=1972 |journal=Communications of the Dublin Institute for Advanced Studies |title= Quaternions, Lorentz transformations, and the Conway–Dirac–Eddington matrices|volume=21|url=http://repository.dias.ie/id/eprint/128}}
*{{Cite journal |author=Synge, J.L.|year=1972 |journal=Communications of the Dublin Institute for Advanced Studies |title= Quaternions, Lorentz transformations, and the Conway–Dirac–Eddington matrices|volume=21|url=http://repository.dias.ie/id/eprint/128}}
*{{Cite journal|author=Terng, C. L.|author2=Uhlenbeck, K.|name-list-style=amp|year=2000|journal=Notices of AMS|volume=47|issue=1|title=Geometry of solitons|pages=17–25|url=https://www.ams.org/journals/notices/200001/fea-terng.pdf}}
*{{Cite journal|author=Terng, C. L.|author2=Uhlenbeck, K.|name-list-style=amp|year=2000|journal=Notices of the AMS|volume=47|issue=1|title=Geometry of solitons|pages=17–25|url=https://www.ams.org/journals/notices/200001/fea-terng.pdf}}
*{{Cite journal |author=Touma, J. R. |author2=Tremaine, S. |author3=Kazandjian, M. V. |name-list-style=amp |year=2009|title=Gauss's method for secular dynamics, softened|journal=Monthly Notices of the Royal Astronomical Society|volume=394|issue=2 |pages=1085–1108|arxiv=0811.2812|doi=10.1111/j.1365-2966.2009.14409.x|bibcode=2009MNRAS.394.1085T |s2cid=14531003 }}
*{{Cite journal |author=Touma, J. R. |author2=Tremaine, S. |author3=Kazandjian, M. V. |name-list-style=amp |year=2009|title=Gauss's method for secular dynamics, softened|journal=Monthly Notices of the Royal Astronomical Society|volume=394|issue=2 |pages=1085–1108|arxiv=0811.2812|doi=10.1111/j.1365-2966.2009.14409.x|bibcode=2009MNRAS.394.1085T |s2cid=14531003 }}
*{{Cite journal |author=Volk, O.|year=1976 |journal=Celestial Mechanics |title= Miscellanea from the history of celestial mechanics|volume=14|issue=3|pages=365–382|url=http://adsabs.harvard.edu/full/1976CeMec..14..365V |doi=10.1007/bf01228523 |bibcode=1976CeMec..14..365V|s2cid=122955645 }}
*{{Cite journal |author=Volk, O.|year=1976 |journal=Celestial Mechanics |title= Miscellanea from the history of celestial mechanics|volume=14|issue=3|pages=365–382|url=http://adsabs.harvard.edu/full/1976CeMec..14..365V |doi=10.1007/bf01228523 |bibcode=1976CeMec..14..365V|s2cid=122955645 }}
*{{Cite book |author=Walter, Scott A.|year=1999a |editor1=H. Goenner |editor2=J. Renn |editor3=J. Ritter |editor4=T. Sauer |chapter= Minkowski, mathematicians, and the mathematical theory of relativity |title=The Expanding Worlds of General Relativity|journal=Einstein Studies |volume=7 |pages=45–86 |location=Boston|publisher=Birkhäuser |chapter-url=http://scottwalter.free.fr/papers/1999-mmm-walter.html|isbn=978-0-8176-4060-6}}
*{{Cite book |author=Walter, Scott A.|year=1999 |editor1=H. Goenner |editor2=J. Renn |editor3=J. Ritter |editor4=T. Sauer |chapter= Minkowski, mathematicians, and the mathematical theory of relativity |title=The Expanding Worlds of General Relativity|series=Einstein Studies |volume=7 |pages=45–86 |location=Boston|publisher=Birkhäuser |chapter-url=http://scottwalter.free.fr/papers/1999-mmm-walter.html|isbn=978-0-8176-4060-6}}
*{{Cite book|author=Walter, Scott A.|year=1999b|editor=J. Gray|chapter=The non-Euclidean style of Minkowskian relativity|title=The Symbolic Universe: Geometry and Physics|pages=91–127|location=Oxford|publisher=Oxford University Press|chapter-url=http://scottwalter.free.fr/papers/1999-symbuniv-walter.html}}
*{{Cite book|author=Walter, Scott A.|year=1999b|editor=J. Gray|chapter=The non-Euclidean style of Minkowskian relativity|title=The Symbolic Universe: Geometry and Physics|pages=91–127|location=Oxford|publisher=Oxford University Press|chapter-url=http://scottwalter.free.fr/papers/1999-symbuniv-walter.html}}
*{{Cite book|author=Walter, Scott A.|chapter=Figures of light in the early history of relativity|title=Beyond Einstein|journal=Einstein Studies|volume=14|pages=3–50|editor=Rowe D. |editor2=Sauer T. |editor3=Walter S.|location=New York|publisher=Birkhäuser|year=2018|chapter-url=http://scottwalter.free.fr/papers/2018-be-walter.html|doi=10.1007/978-1-4939-7708-6_1|isbn=978-1-4939-7708-6}}
*{{Cite book|author=Walter, Scott A.|chapter=Figures of Light in the Early History of Relativity (1905–1914) |series=Einstein Studies |title=Beyond Einstein|volume=14|pages=3–50|editor=Rowe D. |editor2=Sauer T. |editor3=Walter S.|location=New York|publisher=Birkhäuser|year=2018|chapter-url=https://philpapers.org/rec/WALFOL-2|doi=10.1007/978-1-4939-7708-6_1|isbn=978-1-4939-7708-6|s2cid=31840179 }}


== External links ==
== External links ==

Latest revision as of 14:06, 12 May 2024

The history of Lorentz transformations comprises the development of linear transformations forming the Lorentz group or Poincaré group preserving the Lorentz interval and the Minkowski inner product .

In mathematics, transformations equivalent to what was later known as Lorentz transformations in various dimensions were discussed in the 19th century in relation to the theory of quadratic forms, hyperbolic geometry, Möbius geometry, and sphere geometry, which is connected to the fact that the group of motions in hyperbolic space, the Möbius group or projective special linear group, and the Laguerre group are isomorphic to the Lorentz group.

In physics, Lorentz transformations became known at the beginning of the 20th century, when it was discovered that they exhibit the symmetry of Maxwell's equations. Subsequently, they became fundamental to all of physics, because they formed the basis of special relativity in which they exhibit the symmetry of Minkowski spacetime, making the speed of light invariant between different inertial frames. They relate the spacetime coordinates of two arbitrary inertial frames of reference with constant relative speed v. In one frame, the position of an event is given by x,y,z and time t, while in the other frame the same event has coordinates x′,y′,z′ and t′.

Mathematical prehistory[edit]

Using the coefficients of a symmetric matrix A, the associated bilinear form, and a linear transformations in terms of transformation matrix g, the Lorentz transformation is given if the following conditions are satisfied:

It forms an indefinite orthogonal group called the Lorentz group O(1,n), while the case det g=+1 forms the restricted Lorentz group SO(1,n). The quadratic form becomes the Lorentz interval in terms of an indefinite quadratic form of Minkowski space (being a special case of pseudo-Euclidean space), and the associated bilinear form becomes the Minkowski inner product.[1][2] Long before the advent of special relativity it was used in topics such as the Cayley–Klein metric, hyperboloid model and other models of hyperbolic geometry, computations of elliptic functions and integrals, transformation of indefinite quadratic forms, squeeze mappings of the hyperbola, group theory, Möbius transformations, spherical wave transformation, transformation of the Sine-Gordon equation, Biquaternion algebra, split-complex numbers, Clifford algebra, and others.

Learning materials from Wikiversity:
includes contributions of Carl Friedrich Gauss (1818), Carl Gustav Jacob Jacobi (1827, 1833/34), Michel Chasles (1829), Victor-Amédée Lebesgue (1837), Thomas Weddle (1847), Edmond Bour (1856), Osip Ivanovich Somov (1863), Wilhelm Killing (1878–1893), Henri Poincaré (1881), Homersham Cox (1881–1883), George William Hill (1882), Émile Picard (1882-1884), Octave Callandreau (1885), Sophus Lie (1885-1890), Louis Gérard (1892), Felix Hausdorff (1899), Frederick S. Woods (1901-05), Heinrich Liebmann (1904/05).
includes contributions of Sophus Lie (1871), Hermann Minkowski (1907–1908), Arnold Sommerfeld (1909).
includes contributions of Vincenzo Riccati (1757), Johann Heinrich Lambert (1768–1770), Franz Taurinus (1826), Eugenio Beltrami (1868), Charles-Ange Laisant (1874), Gustav von Escherich (1874), James Whitbread Lee Glaisher (1878), Siegmund Günther (1880/81), Homersham Cox (1881/82), Rudolf Lipschitz (1885/86), Friedrich Schur (1885-1902), Ferdinand von Lindemann (1890–91), Louis Gérard (1892), Wilhelm Killing (1893-97), Alfred North Whitehead (1897/98), Edwin Bailey Elliott (1903), Frederick S. Woods (1903), Heinrich Liebmann (1904/05), Philipp Frank (1909), Gustav Herglotz (1909/10), Vladimir Varićak (1910).
includes contributions of Pierre Ossian Bonnet (1856), Albert Ribaucour (1870), Sophus Lie (1871a), Gaston Darboux (1873-87), Edmond Laguerre (1880), Cyparissos Stephanos (1883), Georg Scheffers (1899), Percey F. Smith (1900), Harry Bateman and Ebenezer Cunningham (1909–1910).
was used by Arthur Cayley (1846–1855), Charles Hermite (1853, 1854), Paul Gustav Heinrich Bachmann (1869), Edmond Laguerre (1882), Gaston Darboux (1887), Percey F. Smith (1900), Émile Borel (1913).
includes contributions of Carl Friedrich Gauss (1801/63), Felix Klein (1871–97), Eduard Selling (1873–74), Henri Poincaré (1881), Luigi Bianchi (1888-93), Robert Fricke (1891–97), Frederick S. Woods (1895), Gustav Herglotz (1909/10).
includes contributions of James Cockle (1848), Homersham Cox (1882/83), Cyparissos Stephanos (1883), Arthur Buchheim (1884), Rudolf Lipschitz (1885/86), Theodor Vahlen (1901/02), Fritz Noether (1910), Felix Klein (1910), Arthur W. Conway (1911), Ludwik Silberstein (1911).
includes contributions of Luigi Bianchi (1886), Gaston Darboux (1891/94), Georg Scheffers (1899), Luther Pfahler Eisenhart (1905), Vladimir Varićak (1910), Henry Crozier Keating Plummer (1910), Paul Gruner (1921).
includes contributions of Antoine André Louis Reynaud (1819), Felix Klein (1871), Charles-Ange Laisant (1874), Sophus Lie (1879-84), Siegmund Günther (1880/81), Edmond Laguerre (1882), Gaston Darboux (1883–1891), Rudolf Lipschitz (1885/86), Luigi Bianchi (1886–1894), Ferdinand von Lindemann (1890/91), Mellen W. Haskell (1895), Percey F. Smith (1900), Edwin Bailey Elliott (1903), Luther Pfahler Eisenhart (1905).

Electrodynamics and special relativity[edit]

Overview[edit]

In the special relativity, Lorentz transformations exhibit the symmetry of Minkowski spacetime by using a constant c as the speed of light, and a parameter v as the relative velocity between two inertial reference frames. Using the above conditions, the Lorentz transformation in 3+1 dimensions assume the form:

In physics, analogous transformations have been introduced by Voigt (1887) related to an incompressible medium, and by Heaviside (1888), Thomson (1889), Searle (1896) and Lorentz (1892, 1895) who analyzed Maxwell's equations. They were completed by Larmor (1897, 1900) and Lorentz (1899, 1904), and brought into their modern form by Poincaré (1905) who gave the transformation the name of Lorentz.[3] Eventually, Einstein (1905) showed in his development of special relativity that the transformations follow from the principle of relativity and constant light speed alone by modifying the traditional concepts of space and time, without requiring a mechanical aether in contradistinction to Lorentz and Poincaré.[4] Minkowski (1907–1908) used them to argue that space and time are inseparably connected as spacetime.

Regarding special representations of the Lorentz transformations: Minkowski (1907–1908) and Sommerfeld (1909) used imaginary trigonometric functions, Frank (1909) and Varićak (1910) used hyperbolic functions, Bateman and Cunningham (1909–1910) used spherical wave transformations, Herglotz (1909–10) used Möbius transformations, Plummer (1910) and Gruner (1921) used trigonometric Lorentz boosts, Ignatowski (1910) derived the transformations without light speed postulate, Noether (1910) and Klein (1910) as well Conway (1911) and Silberstein (1911) used Biquaternions, Ignatowski (1910/11), Herglotz (1911), and others used vector transformations valid in arbitrary directions, Borel (1913–14) used Cayley–Hermite parameter,

Voigt (1887)[edit]

Woldemar Voigt (1887)[R 1] developed a transformation in connection with the Doppler effect and an incompressible medium, being in modern notation:[5][6]

If the right-hand sides of his equations are multiplied by γ they are the modern Lorentz transformation. In Voigt's theory the speed of light is invariant, but his transformations mix up a relativistic boost together with a rescaling of space-time. Optical phenomena in free space are scale, conformal, and Lorentz invariant, so the combination is invariant too.[6] For instance, Lorentz transformations can be extended by using factor :[R 2]

.

l=1/γ gives the Voigt transformation, l=1 the Lorentz transformation. But scale transformations are not a symmetry of all the laws of nature, only of electromagnetism, so these transformations cannot be used to formulate a principle of relativity in general. It was demonstrated by Poincaré and Einstein that one has to set l=1 in order to make the above transformation symmetric and to form a group as required by the relativity principle, therefore the Lorentz transformation is the only viable choice.

Voigt sent his 1887 paper to Lorentz in 1908,[7] and that was acknowledged in 1909:

In a paper "Über das Doppler'sche Princip", published in 1887 (Gött. Nachrichten, p. 41) and which to my regret has escaped my notice all these years, Voigt has applied to equations of the form (7) (§ 3 of this book) [namely ] a transformation equivalent to the formulae (287) and (288) [namely ]. The idea of the transformations used above (and in § 44) might therefore have been borrowed from Voigt and the proof that it does not alter the form of the equations for the free ether is contained in his paper.[R 3]

Also Hermann Minkowski said in 1908 that the transformations which play the main role in the principle of relativity were first examined by Voigt in 1887. Voigt responded in the same paper by saying that his theory was based on an elastic theory of light, not an electromagnetic one. However, he concluded that some results were actually the same.[R 4]

Heaviside (1888), Thomson (1889), Searle (1896)[edit]

In 1888, Oliver Heaviside[R 5] investigated the properties of charges in motion according to Maxwell's electrodynamics. He calculated, among other things, anisotropies in the electric field of moving bodies represented by this formula:[8]

.

Consequently, Joseph John Thomson (1889)[R 6] found a way to substantially simplify calculations concerning moving charges by using the following mathematical transformation (like other authors such as Lorentz or Larmor, also Thomson implicitly used the Galilean transformation z-vt in his equation[9]):

Thereby, inhomogeneous electromagnetic wave equations are transformed into a Poisson equation.[9] Eventually, George Frederick Charles Searle[R 7] noted in (1896) that Heaviside's expression leads to a deformation of electric fields which he called "Heaviside-Ellipsoid" of axial ratio

[9]

Lorentz (1892, 1895)[edit]

In order to explain the aberration of light and the result of the Fizeau experiment in accordance with Maxwell's equations, Lorentz in 1892 developed a model ("Lorentz ether theory") in which the aether is completely motionless, and the speed of light in the aether is constant in all directions. In order to calculate the optics of moving bodies, Lorentz introduced the following quantities to transform from the aether system into a moving system (it's unknown whether he was influenced by Voigt, Heaviside, and Thomson)[R 8][10]

where x* is the Galilean transformation x-vt. Except the additional γ in the time transformation, this is the complete Lorentz transformation.[10] While t is the "true" time for observers resting in the aether, t′ is an auxiliary variable only for calculating processes for moving systems. It is also important that Lorentz and later also Larmor formulated this transformation in two steps. At first an implicit Galilean transformation, and later the expansion into the "fictitious" electromagnetic system with the aid of the Lorentz transformation. In order to explain the negative result of the Michelson–Morley experiment, he (1892b)[R 9] introduced the additional hypothesis that also intermolecular forces are affected in a similar way and introduced length contraction in his theory (without proof as he admitted). The same hypothesis had been made previously by George FitzGerald in 1889 based on Heaviside's work. While length contraction was a real physical effect for Lorentz, he considered the time transformation only as a heuristic working hypothesis and a mathematical stipulation.

In 1895, Lorentz further elaborated on his theory and introduced the "theorem of corresponding states". This theorem states that a moving observer (relative to the ether) in his "fictitious" field makes the same observations as a resting observers in his "real" field for velocities to first order in v/c. Lorentz showed that the dimensions of electrostatic systems in the ether and a moving frame are connected by this transformation:[R 10]

For solving optical problems Lorentz used the following transformation, in which the modified time variable was called "local time" (German: Ortszeit) by him:[R 11]

With this concept Lorentz could explain the Doppler effect, the aberration of light, and the Fizeau experiment.[11]

Larmor (1897, 1900)[edit]

In 1897, Larmor extended the work of Lorentz and derived the following transformation[R 12]

Larmor noted that if it is assumed that the constitution of molecules is electrical then the FitzGerald–Lorentz contraction is a consequence of this transformation, explaining the Michelson–Morley experiment. It's notable that Larmor was the first who recognized that some sort of time dilation is a consequence of this transformation as well, because "individual electrons describe corresponding parts of their orbits in times shorter for the [rest] system in the ratio 1/γ".[12][13] Larmor wrote his electrodynamical equations and transformations neglecting terms of higher order than (v/c)2 – when his 1897 paper was reprinted in 1929, Larmor added the following comment in which he described how they can be made valid to all orders of v/c:[R 13]

Nothing need be neglected: the transformation is exact if v/c2 is replaced by εv/c2 in the equations and also in the change following from t to t′, as is worked out in Aether and Matter (1900), p. 168, and as Lorentz found it to be in 1904, thereby stimulating the modern schemes of intrinsic relational relativity.

In line with that comment, in his book Aether and Matter published in 1900, Larmor used a modified local time t″=t′-εvx′/c2 instead of the 1897 expression t′=t-vx/c2 by replacing v/c2 with εv/c2, so that t″ is now identical to the one given by Lorentz in 1892, which he combined with a Galilean transformation for the x′, y′, z′, t′ coordinates:[R 14]

Larmor knew that the Michelson–Morley experiment was accurate enough to detect an effect of motion depending on the factor (v/c)2, and so he sought the transformations which were "accurate to second order" (as he put it). Thus he wrote the final transformations (where x′=x-vt and t″ as given above) as:[R 15]

by which he arrived at the complete Lorentz transformation. Larmor showed that Maxwell's equations were invariant under this two-step transformation, "to second order in v/c" – it was later shown by Lorentz (1904) and Poincaré (1905) that they are indeed invariant under this transformation to all orders in v/c.

Larmor gave credit to Lorentz in two papers published in 1904, in which he used the term "Lorentz transformation" for Lorentz's first order transformations of coordinates and field configurations:

p. 583: [..] Lorentz's transformation for passing from the field of activity of a stationary electrodynamic material system to that of one moving with uniform velocity of translation through the aether.
p. 585: [..] the Lorentz transformation has shown us what is not so immediately obvious [..][R 16]
p. 622: [..] the transformation first developed by Lorentz: namely, each point in space is to have its own origin from which time is measured, its "local time" in Lorentz's phraseology, and then the values of the electric and magnetic vectors [..] at all points in the aether between the molecules in the system at rest, are the same as those of the vectors [..] at the corresponding points in the convected system at the same local times.[R 17]

Lorentz (1899, 1904)[edit]

Also Lorentz extended his theorem of corresponding states in 1899. First he wrote a transformation equivalent to the one from 1892 (again, x* must be replaced by x-vt):[R 18]

Then he introduced a factor ε of which he said he has no means of determining it, and modified his transformation as follows (where the above value of t′ has to be inserted):[R 19]

This is equivalent to the complete Lorentz transformation when solved for x″ and t″ and with ε=1. Like Larmor, Lorentz noticed in 1899[R 20] also some sort of time dilation effect in relation to the frequency of oscillating electrons "that in S the time of vibrations be times as great as in S0", where S0 is the aether frame.[14]

In 1904 he rewrote the equations in the following form by setting l=1/ε (again, x* must be replaced by x-vt):[R 21]

Under the assumption that l=1 when v=0, he demonstrated that l=1 must be the case at all velocities, therefore length contraction can only arise in the line of motion. So by setting the factor l to unity, Lorentz's transformations now assumed the same form as Larmor's and are now completed. Unlike Larmor, who restricted himself to show the covariance of Maxwell's equations to second order, Lorentz tried to widen its covariance to all orders in v/c. He also derived the correct formulas for the velocity dependence of electromagnetic mass, and concluded that the transformation formulas must apply to all forces of nature, not only electrical ones.[R 22] However, he didn't achieve full covariance of the transformation equations for charge density and velocity.[15] When the 1904 paper was reprinted in 1913, Lorentz therefore added the following remark:[16]

One will notice that in this work the transformation equations of Einstein’s Relativity Theory have not quite been attained. [..] On this circumstance depends the clumsiness of many of the further considerations in this work.

Lorentz's 1904 transformation was cited and used by Alfred Bucherer in July 1904:[R 23]

or by Wilhelm Wien in July 1904:[R 24]

or by Emil Cohn in November 1904 (setting the speed of light to unity):[R 25]

or by Richard Gans in February 1905:[R 26]

Poincaré (1900, 1905)[edit]

Local time[edit]

Neither Lorentz or Larmor gave a clear physical interpretation of the origin of local time. However, Henri Poincaré in 1900 commented on the origin of Lorentz's "wonderful invention" of local time.[17] He remarked that it arose when clocks in a moving reference frame are synchronised by exchanging signals which are assumed to travel with the same speed in both directions, which lead to what is nowadays called relativity of simultaneity, although Poincaré's calculation does not involve length contraction or time dilation.[R 27] In order to synchronise the clocks here on Earth (the x*, t* frame) a light signal from one clock (at the origin) is sent to another (at x*), and is sent back. It's supposed that the Earth is moving with speed v in the x-direction (= x*-direction) in some rest system (x, t) (i.e. the luminiferous aether system for Lorentz and Larmor). The time of flight outwards is

and the time of flight back is

.

The elapsed time on the clock when the signal is returned is δta+δtb and the time t*=(δta+δtb)/2 is ascribed to the moment when the light signal reached the distant clock. In the rest frame the time t=δta is ascribed to that same instant. Some algebra gives the relation between the different time coordinates ascribed to the moment of reflection. Thus

identical to Lorentz (1892). By dropping the factor γ2 under the assumption that , Poincaré gave the result t*=t-vx*/c2, which is the form used by Lorentz in 1895.

Similar physical interpretations of local time were later given by Emil Cohn (1904)[R 28] and Max Abraham (1905).[R 29]

Lorentz transformation[edit]

On June 5, 1905 (published June 9) Poincaré formulated transformation equations which are algebraically equivalent to those of Larmor and Lorentz and gave them the modern form:[R 30]

.

Apparently Poincaré was unaware of Larmor's contributions, because he only mentioned Lorentz and therefore used for the first time the name "Lorentz transformation".[18][19] Poincaré set the speed of light to unity, pointed out the group characteristics of the transformation by setting l=1, and modified/corrected Lorentz's derivation of the equations of electrodynamics in some details in order to fully satisfy the principle of relativity, i.e. making them fully Lorentz covariant.[20]

In July 1905 (published in January 1906)[R 31] Poincaré showed in detail how the transformations and electrodynamic equations are a consequence of the principle of least action; he demonstrated in more detail the group characteristics of the transformation, which he called Lorentz group, and he showed that the combination x2+y2+z2-t2 is invariant. He noticed that the Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing as a fourth imaginary coordinate, and he used an early form of four-vectors. He also formulated the velocity addition formula, which he had already derived in unpublished letters to Lorentz from May 1905:[R 32]

.

Einstein (1905) – Special relativity[edit]

On June 30, 1905 (published September 1905) Einstein published what is now called special relativity and gave a new derivation of the transformation, which was based only on the principle of relativity and the principle of the constancy of the speed of light. While Lorentz considered "local time" to be a mathematical stipulation device for explaining the Michelson-Morley experiment, Einstein showed that the coordinates given by the Lorentz transformation were in fact the inertial coordinates of relatively moving frames of reference. For quantities of first order in v/c this was also done by Poincaré in 1900, while Einstein derived the complete transformation by this method. Unlike Lorentz and Poincaré who still distinguished between real time in the aether and apparent time for moving observers, Einstein showed that the transformations applied to the kinematics of moving frames.[21][22][23]

The notation for this transformation is equivalent to Poincaré's of 1905, except that Einstein didn't set the speed of light to unity:[R 33]

Einstein also defined the velocity addition formula:[R 34]

and the light aberration formula:[R 35]

Minkowski (1907–1908) – Spacetime[edit]

The work on the principle of relativity by Lorentz, Einstein, Planck, together with Poincaré's four-dimensional approach, were further elaborated and combined with the hyperboloid model by Hermann Minkowski in 1907 and 1908.[R 36][R 37] Minkowski particularly reformulated electrodynamics in a four-dimensional way (Minkowski spacetime).[24] For instance, he wrote x, y, z, it in the form x1, x2, x3, x4. By defining ψ as the angle of rotation around the z-axis, the Lorentz transformation assumes the form (with c=1):[R 38]

Even though Minkowski used the imaginary number iψ, he for once[R 38] directly used the tangens hyperbolicus in the equation for velocity

with .

Minkowski's expression can also by written as ψ=atanh(q) and was later called rapidity. He also wrote the Lorentz transformation in matrix form:[R 39]

As a graphical representation of the Lorentz transformation he introduced the Minkowski diagram, which became a standard tool in textbooks and research articles on relativity:[R 40]

Original spacetime diagram by Minkowski in 1908.

Sommerfeld (1909) – Spherical trigonometry[edit]

Using an imaginary rapidity such as Minkowski, Arnold Sommerfeld (1909) formulated the Lorentz boost and the relativistic velocity addition in terms of trigonometric functions and the spherical law of cosines:[R 41]

Frank (1909) – Hyperbolic functions[edit]

Hyperbolic functions were used by Philipp Frank (1909), who derived the Lorentz transformation using ψ as rapidity:[R 42]

Bateman and Cunningham (1909–1910) – Spherical wave transformation[edit]

In line with Sophus Lie's (1871) research on the relation between sphere transformations with an imaginary radius coordinate and 4D conformal transformations, it was pointed out by Bateman and Cunningham (1909–1910), that by setting u=ict as the imaginary fourth coordinates one can produce spacetime conformal transformations. Not only the quadratic form , but also Maxwells equations are covariant with respect to these transformations, irrespective of the choice of λ. These variants of conformal or Lie sphere transformations were called spherical wave transformations by Bateman.[R 43][R 44] However, this covariance is restricted to certain areas such as electrodynamics, whereas the totality of natural laws in inertial frames is covariant under the Lorentz group.[R 45] In particular, by setting λ=1 the Lorentz group SO(1,3) can be seen as a 10-parameter subgroup of the 15-parameter spacetime conformal group Con(1,3).

Bateman (1910–12)[25] also alluded to the identity between the Laguerre inversion and the Lorentz transformations. In general, the isomorphism between the Laguerre group and the Lorentz group was pointed out by Élie Cartan (1912, 1915–55),[R 46] Henri Poincaré (1912–21)[R 47] and others.

Herglotz (1909/10) – Möbius transformation[edit]

Following Felix Klein (1889–1897) and Fricke & Klein (1897) concerning the Cayley absolute, hyperbolic motion and its transformation, Gustav Herglotz (1909–10) classified the one-parameter Lorentz transformations as loxodromic, hyperbolic, parabolic and elliptic. The general case (on the left) and the hyperbolic case equivalent to Lorentz transformations or squeeze mappings are as follows:[R 48]

Varićak (1910) – Hyperbolic functions[edit]

Following Sommerfeld (1909), hyperbolic functions were used by Vladimir Varićak in several papers starting from 1910, who represented the equations of special relativity on the basis of hyperbolic geometry in terms of Weierstrass coordinates. For instance, by setting l=ct and v/c=tanh(u) with u as rapidity he wrote the Lorentz transformation:[R 49]

and showed the relation of rapidity to the Gudermannian function and the angle of parallelism:[R 49]

He also related the velocity addition to the hyperbolic law of cosines:[R 50]

Subsequently, other authors such as E. T. Whittaker (1910) or Alfred Robb (1911, who coined the name rapidity) used similar expressions, which are still used in modern textbooks.

Plummer (1910) – Trigonometric Lorentz boosts[edit]

w:Henry Crozier Keating Plummer (1910) defined the Lorentz boost in terms of trigonometric functions[R 51]

Ignatowski (1910)[edit]

While earlier derivations and formulations of the Lorentz transformation relied from the outset on optics, electrodynamics, or the invariance of the speed of light, Vladimir Ignatowski (1910) showed that it is possible to use the principle of relativity (and related group theoretical principles) alone, in order to derive the following transformation between two inertial frames:[R 52][R 53]

The variable n can be seen as a space-time constant whose value has to be determined by experiment or taken from a known physical law such as electrodynamics. For that purpose, Ignatowski used the above-mentioned Heaviside ellipsoid representing a contraction of electrostatic fields by x/γ in the direction of motion. It can be seen that this is only consistent with Ignatowski's transformation when n=1/c2, resulting in p=γ and the Lorentz transformation. With n=0, no length changes arise and the Galilean transformation follows. Ignatowski's method was further developed and improved by Philipp Frank and Hermann Rothe (1911, 1912),[R 54] with various authors developing similar methods in subsequent years.[26]

Noether (1910), Klein (1910) – Quaternions[edit]

Felix Klein (1908) described Cayley's (1854) 4D quaternion multiplications as "Drehstreckungen" (orthogonal substitutions in terms of rotations leaving invariant a quadratic form up to a factor), and pointed out that the modern principle of relativity as provided by Minkowski is essentially only the consequent application of such Drehstreckungen, even though he didn't provide details.[R 55]

In an appendix to Klein's and Sommerfeld's "Theory of the top" (1910), Fritz Noether showed how to formulate hyperbolic rotations using biquaternions with , which he also related to the speed of light by setting ω2=-c2. He concluded that this is the principal ingredient for a rational representation of the group of Lorentz transformations:[R 56]

Besides citing quaternion related standard works by Arthur Cayley (1854), Noether referred to the entries in Klein's encyclopedia by Eduard Study (1899) and the French version by Élie Cartan (1908).[27] Cartan's version contains a description of Study's dual numbers, Clifford's biquaternions (including the choice for hyperbolic geometry), and Clifford algebra, with references to Stephanos (1883), Buchheim (1884–85), Vahlen (1901–02) and others.

Citing Noether, Klein himself published in August 1910 the following quaternion substitutions forming the group of Lorentz transformations:[R 57]

or in March 1911[R 58]

Conway (1911), Silberstein (1911) – Quaternions[edit]

Arthur W. Conway in February 1911 explicitly formulated quaternionic Lorentz transformations of various electromagnetic quantities in terms of velocity λ:[R 59]

Also Ludwik Silberstein in November 1911[R 60] as well as in 1914,[28] formulated the Lorentz transformation in terms of velocity v:

Silberstein cites Cayley (1854, 1855) and Study's encyclopedia entry (in the extended French version of Cartan in 1908), as well as the appendix of Klein's and Sommerfeld's book.

Ignatowski (1910/11), Herglotz (1911), and others – Vector transformation[edit]

Vladimir Ignatowski (1910, published 1911) showed how to reformulate the Lorentz transformation in order to allow for arbitrary velocities and coordinates:[R 61]

Gustav Herglotz (1911)[R 62] also showed how to formulate the transformation in order to allow for arbitrary velocities and coordinates v=(vx, vy, vz) and r=(x, y, z):

This was simplified using vector notation by Ludwik Silberstein (1911 on the left, 1914 on the right):[R 63]

Equivalent formulas were also given by Wolfgang Pauli (1921),[29] with Erwin Madelung (1922) providing the matrix form[30]

These formulas were called "general Lorentz transformation without rotation" by Christian Møller (1952),[31] who in addition gave an even more general Lorentz transformation in which the Cartesian axes have different orientations, using a rotation operator . In this case, v′=(v′x, v′y, v′z) is not equal to -v=(-vx, -vy, -vz), but the relation holds instead, with the result

Borel (1913–14) – Cayley–Hermite parameter[edit]

Émile Borel (1913) started by demonstrating Euclidean motions using Euler-Rodrigues parameter in three dimensions, and Cayley's (1846) parameter in four dimensions. Then he demonstrated the connection to indefinite quadratic forms expressing hyperbolic motions and Lorentz transformations. In three dimensions:[R 64]

In four dimensions:[R 65]

Gruner (1921) – Trigonometric Lorentz boosts[edit]

In order to simplify the graphical representation of Minkowski space, Paul Gruner (1921) (with the aid of Josef Sauter) developed what is now called Loedel diagrams, using the following relations:[R 66]

In another paper Gruner used the alternative relations:[R 67]

See also[edit]

References[edit]

Historical mathematical sources[edit]

Learning materials related to History of Topics in Special Relativity/mathsource at Wikiversity

Historical relativity sources[edit]

  1. ^ Voigt (1887), p. 45
  2. ^ Lorentz (1915/16), p. 197
  3. ^ Lorentz (1915/16), p. 198
  4. ^ Bucherer (1908), p. 762
  5. ^ Heaviside (1888), p. 324
  6. ^ Thomson (1889), p. 12
  7. ^ Searle (1886), p. 333
  8. ^ Lorentz (1892a), p. 141
  9. ^ Lorentz (1892b), p. 141
  10. ^ Lorentz (1895), p. 37
  11. ^ Lorentz (1895), p. 49 for local time and p. 56 for spatial coordinates.
  12. ^ Larmor (1897), p. 229
  13. ^ Larmor (1897/1929), p. 39
  14. ^ Larmor (1900), p. 168
  15. ^ Larmor (1900), p. 174
  16. ^ Larmor (1904a), p. 583, 585
  17. ^ Larmor (1904b), p. 622
  18. ^ Lorentz (1899), p. 429
  19. ^ Lorentz (1899), p. 439
  20. ^ Lorentz (1899), p. 442
  21. ^ Lorentz (1904), p. 812
  22. ^ Lorentz (1904), p. 826
  23. ^ Bucherer, p. 129; Definition of s on p. 32
  24. ^ Wien (1904), p. 394
  25. ^ Cohn (1904a), pp. 1296-1297
  26. ^ Gans (1905), p. 169
  27. ^ Poincaré (1900), pp. 272–273
  28. ^ Cohn (1904b), p. 1408
  29. ^ Abraham (1905), § 42
  30. ^ Poincaré (1905), p. 1505
  31. ^ Poincaré (1905/06), pp. 129ff
  32. ^ Poincaré (1905/06), p. 144
  33. ^ Einstein (1905), p. 902
  34. ^ Einstein (1905), § 5 and § 9
  35. ^ Einstein (1905), § 7
  36. ^ Minkowski (1907/15), pp. 927ff
  37. ^ Minkowski (1907/08), pp. 53ff
  38. ^ a b Minkowski (1907/08), p. 59
  39. ^ Minkowski (1907/08), pp. 65–66, 81–82
  40. ^ Minkowski (1908/09), p. 77
  41. ^ Sommerfeld (1909), p. 826ff.
  42. ^ Frank (1909), pp. 423-425
  43. ^ Bateman (1909/10), pp. 223ff
  44. ^ Cunningham (1909/10), pp. 77ff
  45. ^ Klein (1910)
  46. ^ Cartan (1912), p. 23
  47. ^ Poincaré (1912/21), p. 145
  48. ^ Herglotz (1909/10), pp. 404-408
  49. ^ a b Varićak (1910), p. 93
  50. ^ Varićak (1910), p. 94
  51. ^ Plummer (1910), p. 256
  52. ^ Ignatowski (1910), pp. 973–974
  53. ^ Ignatowski (1910/11), p. 13
  54. ^ Frank & Rothe (1911), pp. 825ff; (1912), p. 750ff.
  55. ^ Klein (1908), p. 165
  56. ^ Noether (1910), pp. 939–943
  57. ^ Klein (1910), p. 300
  58. ^ Klein (1911), pp. 602ff.
  59. ^ Conway (1911), p. 8
  60. ^ Silberstein (1911/12), p. 793
  61. ^ Ignatowski (1910/11a), p. 23; (1910/11b), p. 22
  62. ^ Herglotz (1911), p. 497
  63. ^ Silberstein (1911/12), p. 792; (1914), p. 123
  64. ^ Borel (1913/14), p. 39
  65. ^ Borel (1913/14), p. 41
  66. ^ Gruner (1921a),
  67. ^ Gruner (1921b)

Secondary sources[edit]

  1. ^ Ratcliffe (1994), 3.1 and Theorem 3.1.4 and Exercise 3.1
  2. ^ Naimark (1964), 2 in four dimensions
  3. ^ Miller (1981), chapter 1
  4. ^ Miller (1981), chapter 4–7
  5. ^ Miller (1981), 114–115
  6. ^ a b Pais (1982), Kap. 6b
  7. ^ Heras, Ricardo (2014). "A review of Voigt's transformations in the framework of special relativity". arXiv:1411.2559 [physics.hist-ph].
  8. ^ Brown (2003)
  9. ^ a b c Miller (1981), 98–99
  10. ^ a b Miller (1982), 1.4 & 1.5
  11. ^ Janssen (1995), 3.1
  12. ^ Darrigol (2000), Chap. 8.5
  13. ^ Macrossan (1986)
  14. ^ Jannsen (1995), Kap. 3.3
  15. ^ Miller (1981), Chap. 1.12.2
  16. ^ Jannsen (1995), Chap. 3.5.6
  17. ^ Darrigol (2005), Kap. 4
  18. ^ Pais (1982), Chap. 6c
  19. ^ Katzir (2005), 280–288
  20. ^ Miller (1981), Chap. 1.14
  21. ^ Miller (1981), Chap. 6
  22. ^ Pais (1982), Kap. 7
  23. ^ Darrigol (2005), Chap. 6
  24. ^ Walter (1999a)
  25. ^ Bateman (1910/12), pp. 358–359
  26. ^ Baccetti (2011), see references 1–25 therein.
  27. ^ Cartan & Study (1908), sections 35–36
  28. ^ Silberstein (1914), p. 156
  29. ^ Pauli (1921), p. 555
  30. ^ Madelung (1921), p. 207
  31. ^ Møller (1952/55), pp. 41–43

External links[edit]