For a single observer that area is effectively invisible; they cannot be affected or affect things in it (outside of their forward/backward light-cone). Howeve

For a single observer that area is effectively invisible; they cannot be affected or affect things in it (outside of their forward/backward light-cone). However, other events can still exist in there. And their lightcones may intersect at a later point in time, so they are not totally uninteracting. Point (x1, t1) may never be able to affect (x2, t2), but it can always affect (x2, t2 + <waiting for a while>).