Causal past
= Causal past
{title2=$J^-(S)$}
The <causal past> is the time-reversed <causal future>. Relative to a specified component $\mathcal I^+$ of <future null infinity>, the <black hole> region is the complement of its <causal past>: $\mathcal B=\mathcal M\setminus J^-(\mathcal I^+)$.