Minkowski-Metrik

${\eta _{\mu \nu }}=\left({\begin{array}{*{20}{c}}{-1}&0&0&0\\0&1&0&0\\0&0&1&0\\0&0&0&1\\\end{array}}\right)={\mathop {\rm {diag}} \nolimits }(-1,1,1,1)$