It would seem that, in principle, we could observe our own past by means of reflected light. If gravitational mirrors could exist and the reflected light be processed to a high degree of resolution, we might be able to observe the earth as it existed in the past. Light might be reflected 180 degrees at some distance from a black hole for example. Since, according to GR, simultaneous events are those linked by a light beam, does this mean that past events on earth could be in some sense simultaneous to "present" events on earth? In fact, this occurs all the time on nanoscales. Just by looking in an ordinary mirror, you are in looking your past (maybe six nanoseconds ago).