it seems to me the observable universe can be sliced into a 3d grid Unfortunately when time is taken into consideration, we're looking at a 4D (at least, but l

it seems to me the observable universe can be sliced into a 3d grid Unfortunately when time is taken into consideration, we're looking at a 4D (at least, but let's be minimalist) space-time. It seems generally accepted that we are living in a multiverse, so that even if time-travel was possible, even the act of breathing would enforce a move to a different universe from the universe where you had started your time-travel, and which you could never return to. So, you can go back and kill Hitler (or even your own grandmother). But you can never go back and say "See what I did!".