I do NOT propose to drone on about the paradoxes (paradices? Whatever) and chronoclasms inherent in the science. Oh all right – if I go back in time and kill my father before he meets my mother, I can’t EXIST to go back in time and… Or if I kill Hitler as a baby, WW2 won’t happen – unless his Mother steals a baby from a push-chair outside a shop and HE goes on to… (then I become part of a “causal loop”).
Indeed ANYTHING I do in the past, changes events that have HAPPENED – just BEING there displaces AIR. And future travel is only okay if I don’t RETURN. Knowledge from the future could change the present – and suppose I STOPPED future events from happening? The possibilities are endless.
Basically, PHYSICALLY appearing in the past and even SEEING into the future is fraught with problems (and impossible anyway, assuming time is linear). However, just SEEING into the PAST is harmless – it doesn’t alter the time-line and merely improves our knowledge of it. Like finding a fossil – or a lost episode of “Dr Who”. But here’s the THING – it’s something we do EVERY DAY.
Really? Of course. Just look at the Sun (but not for too long) and you’re seeing an event that took place eight minutes and twenty seconds ago. That’s how long light takes to travel here from it. Even as you gaze up at the Moon, you’re seeing it as it was, one-point-three-four-four seconds ago.
And when you talk to someone face to face (and this is why I’m troubling you with this) you are seeing them as they WERE – approximately two nano-seconds AGO. Okay, they won’t have AGED much in that time, but technically, you are reaching through TIME to talk to them.
Oh yes – and since sound only travels at one-eight hundred and ninety-two thousand, eight hundredth of the speed of light – their lips will be out of sync as well.