what if what we think are "ghosts" or "spirits" are actually people from the future trying to contact us..but we can barely hear/see them.. They have the technology to transmit but we don't have the technology to receive yet, so we just get bits and pieces of them evp's, apparitions, ect. I don't know much about time travel but I've had that theory in my head for a while.
Michio Kaku (yes, I worship the lil guy) said something about how there could be people from the future observing us, possibly living among us, but their technology could be so advanced that they've figured out how to become invisible so we aren't aware of their presence. I choose not to believe that because it would get me pretty paranoid, and I don't see the point of inflicting paranoia on myself due to speculation heh
IMO, traveling backwards in time is not very likely to be feasible. forward is easy comparatively....its all relative backwards though.....thats a mofo. If you could bend space around on itself, like a loop in a roller coaster, then id think you could travel back to a precise point in time, but only to that time. you wouldnt have the control to maneuver around, and pick a date/time to go back to. but, if you had the ability to control space in that manner, you could probably set up multiple loops, at least allowing for travel to different periods of time. youd be limited by the amount of energy you could harness. more energy = more spacetime manipulated = longer interval of time "traveled"
By the way, physics dictates that time travel is only possible back to the point of the first time machine. In other words, it is not possible to travel to medievil times, but you could travel back to the time when the first time machine had been built.
assuming you follow Kaku rules, and your machine creates a spacetime disturbance. there are other ways entirely to theoretically travel time. some of them (like what I mentioned earlier, for example) would not require a machine to "recieve" the traveler.