Geschwindigkeit

${{u}^{\mu }}:={\frac {d{{x}^{\mu }}}{d\tau }}=\gamma \left({\begin{matrix}c&{{v}^{1}}&{{v}^{2}}&{{v}^{3}}\\\end{matrix}}\right)$

${{u}^{\mu }}{{u}_{\mu }}={{c}^{2}}$