pub fn relativistic_current(
em: &CausalTensor<f64>,
metric: &CausalTensor<f64>,
) -> PropagatingEffect<CausalTensor<f64>>pub fn relativistic_current(
em: &CausalTensor<f64>,
metric: &CausalTensor<f64>,
) -> PropagatingEffect<CausalTensor<f64>>