Countless stories have speculated about the logistics, implications, and consequences of time travel, but no one’s ever done it — as far as we know. And while such a world-altering feat hardly seems possible, that isn’t to say it’s impossible.

The skeptics among us might argue that we would already know about time travel even if it hasn’t been invented yet because its eventual inventor would have made their presence known in an earlier era, but that’s ignoring one of its most important precepts: If you go back in time, you have to be careful and not change anything lest you accidentally rewrite history. For now, we’ll just have to keep revisiting classics like Back to the Future and The Time Machine.