I know it's a stretch, but since we can slow the world around us, I'm just curious if it is possible to reverse time? Not simply to make evening flow to morning then night, but actually have actors that were killed to revive back to their pre-death state and the like.

You can resurrect actors, but actually reversing time is not possible.

You might be able to control scenes in such a way that it appears as though time is reversing, but you can't actually make the game reverse time.

Cipscis

Think like a videotape - without first recording what the actors are doing, there's no way to reverse their actions.

Hmm, anyway to "record" the current cell the same way saved games work???

To continue the anology, saved games take a photo. You'd need a video camera.

Cipscis

30 photos a second should work, eh? ;-P

Speaking of which, do animations work only one way? Or can they be played in reverse also?

F9... Time reversed!

To do so without a savegame file, you do realise you would have to change every single item in the game so it stores it's location, orientation, etc periodically (say, once a second), so when the time rewind effect is called, it can "go backwards" in the stored locations (probably with TranslateTo, passed the previous stored locations/orientations (and keep in mind, though they would move to their previous positions, they would not reverse ragdolls, animations, etc.))

That is a buttload of processor cycles just to save the data, let alone all the threads that will need to run when you trigger the "backwards" effect.

There is a reason why the game Braid, which focuses on 2D platform time manipulation puzzles, requires a beefy processor and video card despite the game "only" being 2D and featuring small levels. It requires basically the whole state of the game to be recorded at every frame, so it can smoothly reverse time back to it.

Impossible, in other words. THe only reason why it works in Braid without breaking your computer is because the game was designed specifically around it, and the actual game engine is simple enough to not crash under such stress.