Assuming that displacements in one direction in one co-ordinate system, result only in displacements in the same direction in the primed system,
μ
≠
ν
⟹
n
μ
,
ν
=
0
{\displaystyle \mu \neq \nu \implies n_{\mu ,\nu }=0}
Then equation 3 gives,
1
=
∑
ν
n
μ
,
ν
e
ν
=
n
μ
,
μ
e
μ
{\displaystyle 1=\sum _{\nu }n_{\mu ,\nu }e_{\nu }=n_{\mu ,\mu }e_{\mu }}
Solve for
n
μ
,
μ
{\displaystyle n_{\mu ,\mu }}
gives,
n
μ
,
μ
=
1
e
μ
{\displaystyle n_{\mu ,\mu }={\frac {1}{e_{\mu }}}}
gives,
x
μ
=
n
μ
,
0
(
−
v
t
′
+
x
μ
′
e
μ
)
{\displaystyle x_{\mu }=n_{\mu ,0}(-vt'+{\frac {x'_{\mu }}{e_{\mu }}})}
which can be re-arranged as,
x
μ
=
n
μ
,
0
e
μ
(
x
μ
′
−
v
t
′
e
μ
)
{\displaystyle x_{\mu }={\frac {n_{\mu ,0}}{e_{\mu }}}(x'_{\mu }-vt'e_{\mu })}
(equation 5a)
and from relativity,
x
μ
′
=
n
μ
,
0
e
μ
(
x
μ
+
v
t
e
μ
)
{\displaystyle x'_{\mu }={\frac {n_{\mu ,0}}{e_{\mu }}}(x_{\mu }+vte_{\mu })}
(equation 5b)
Note: The divisor term
e
μ
{\displaystyle e_{\mu }}
will be cancelled out later on. There is no divide by zero problem in the final formula. A more careful but less easy to follow process would have avoided it.
No distortion at right angles to relative velocity
edit
x
⋅
e
=
0
⟹
x
=
x
′
{\displaystyle \mathbf {x} \cdot \mathbf {e} =0\implies \mathbf {x} =\mathbf {x} '}
∑
ν
x
ν
e
ν
=
0
⟹
x
μ
=
x
μ
′
{\displaystyle \sum _{\nu }x_{\nu }e_{\nu }=0\implies x_{\mu }=x'_{\mu }}
From equation 1
x
μ
=
m
μ
,
0
t
′
+
∑
ν
m
μ
,
ν
x
ν
′
{\displaystyle x_{\mu }=m_{\mu ,0}t'+\sum _{\nu }m_{\mu ,\nu }x'_{\nu }}
x
μ
=
(
p
μ
,
0
e
μ
+
q
μ
,
0
(
1
−
e
μ
)
)
t
′
+
∑
ν
(
p
μ
,
ν
e
μ
+
q
μ
,
ν
(
1
−
e
μ
)
)
x
ν
′
{\displaystyle x_{\mu }=(p_{\mu ,0}e_{\mu }+q_{\mu ,0}(1-e_{\mu }))t'+\sum _{\nu }(p_{\mu ,\nu }e_{\mu }+q_{\mu ,\nu }(1-e_{\mu }))x'_{\nu }}
q
μ
,
0
=
0
{\displaystyle q_{\mu ,0}=0}
q
μ
,
ν
=
δ
ν
μ
{\displaystyle q_{\mu ,\nu }=\delta _{\nu }^{\mu }}
x
μ
=
e
μ
(
p
μ
,
0
t
′
+
∑
ν
p
μ
,
ν
x
ν
′
)
+
(
1
−
e
μ
)
x
ν
′
{\displaystyle x_{\mu }=e_{\mu }(p_{\mu ,0}t'+\sum _{\nu }p_{\mu ,\nu }x'_{\nu })+(1-e_{\mu })x'_{\nu }}
(equation 1)