I have a "science-fictiony" idea that I haven't seen anywhere else yet. The idea is this: If we can see light from planets thousands of light years away, then we can see the past. Once our telescopes are good enough to basically do a "google maps" zoom-in on other planets, we will be able to watche the past on other planets. But then, if we can ever watch our own Earth from a thousand light years away, then we can see what happened in the past. The missing link is for us to be able to travel faster than the speed of light so we can go far enough to view Earth's past.

While not "obvious", I still feel like others have probably thought of this idea. It could make a cool science fiction story.