Future light cone
= Future light cone
{title2=$|\Delta\mathbf x|=c\Delta t,\quad\Delta t>0$}
The <future light cone> is the future-directed part of the <light cone> of a <spacetime event>. Its boundary consists of the events reached by outgoing light rays. Events reached by slower causal signals lie inside the boundary; <relativistic causality> forbids a controllable signal from reaching the spacelike exterior.