Will future time-travelling humans come back to visit us?

Anything is possible. There are a number of theories about how we can travel through time but they usually involve going into the future using the theory of relativity. Essentially, this involves going so fast that your body clock slows down. When you stop moving so quickly, everything around you will have aged but you will be only a little bit older. In this way, you are able to travel into the future. Another method that has been suggested is to go to a black hole and go out the other end of it. Stephen Hawking doesn't believe time travel is possible because we would have seen people from the future if it were true. A lot of equations in physics don't work backwards, so going back in time seems unlikely. It would be very difficult.