This is an idea that has been floating around in my head for a few years now. I'd like to share it with you. :) I'm pretty sure it will never be feasible. The technology in optics, propulsion, construction, etc will require leaps and bounds beyond what we have now before this is even remotely possible. For now, it's just fun to think about.
Imagine, if you will, an enormous mirror built to specifications that allow for perfect, precise clarity. With this mirror is built the most advanced, wondrous telescope ever. If you were to fly the mirror to a location 25 light years from Earth, and point the telescope at the mirror (to look back here) you would, in essence, be looking at our planet as it was 50 years into the past.
This means that if such a combination of devices existed today, we would be able to look into this machine and see things as they were in 1951. You could solve a crime that happened 50 years ago by watching it as it happens, provided you know where it happened.
Of course, with a telescope that precise (one that can see detail like that from 50 light years away) we'd be better off looking at planets in other solar systems. Like this one.Why look into our own past when we can see theirs?