Or it's simply not possible. There is a theory that from the moment the first timemachine is made, you can only travel to that point in time and later. So it would simply mean that the timemachine has not yet been invented.
This is not possible, if we had no future, I would be dying right now, because the second right after this one is the future, you don't have to go a hundred years for it to be the future.
The future doesn't exist, nature and the world is literally here and now. The past doesn't exist anymore and here's why: "Their's no such thing as time." Time is a human invention and one that only humans recognize. Animals may perceive a small grasp of time/pattern, feeding schedules, times of leaving and arriving home, etc. but they don't perceive days, months, or years. Anyway, you have to acknowledge the past happened because it existed but now it doesn't exist.
There's a rule they aren't allowed to tell us, so they're just walking among us like normal people.