If there is, the future time travelers either haven't visited our era yet or they have and are just keeping it a secret!
Time travel is a heavily disputed subject, and many think that it is highly improbable that time travel is even possible. (I honestly think we may not get there...) I've looked into things such as black holes and all that jazz. It's really cool! Basically, spacetime fabric is warped around and within a black hole. This means that time passes slower for an inside observer than an outside observer. If you were able to enter and exit a black hole, you'd theoretically be time travelling. Same goes with travelling at the speed of light, or the case of the Twin Paradox. Basically, Twin A decides to travel away in a spaceship at, say, 99% light speed, whilst Twin B stays on Earth. At the end of the paradox, we see that due to inertia frames (having to do with Twin A's near-light-speed velocity) and some other complicated science stuff, time goes slower for Twin A, making Twin B much older than its sibling. Time travel.
