Future null infinity
= Future null infinity
{title2=$\mathcal I^+$}
Future null infinity is the boundary reached by future-directed outgoing null geodesics in an <asymptotically flat spacetime>. In four dimensions it has topology $\mathbb R\times S^2$ under the standard asymptotic-flatness assumptions.
It is the future component of <null infinity>; the past component is $\mathcal I^-$.