Actually my theory, and a few others i think (scientists and stuff) is this: (in my own words)
Since everything we see we're not actually
seeing the way most people commonly think of it... It's been proven that we see reflection of light waves. Everything we see is in light.
Light reflects... and therefore (to cut it short) reflects ... (!?) and if we can travel faster than the speed of LIGHT, we could travel back in time and SEE (not experience) what happened, without sound... cause we'd move back and see the reflection of the light in space, if you know what i mean
i'm no scientist, it's very vague... can't explain, i'm sure you understand (hopefully)

lol