I hear people talk about time travelling as jumping from 1 point to another; say, 500 years into the future in an instant. Well, what if the jumps are actually a lot smaller? My idea is so simple it's almost laughable, but the more you think about it the more it makes sense:
Technically we're always time travelling, a second at a time, to the future. If we weren't, we'd just be frozen in space and nothing would ever happen. The way I see it, time travel is like accretion (planet formation): it doesn't happen all at once. Dust bits clump into rocks which become boulders, etc. Moreover, since time only goes in 1 direction (I think Einstein postulated that), travel to the past is impossible. We already know gravity can make time go slower the closer you get to it's source: for example clocks run nearly 10 minutes faster in Low Earth Orbit (where most manned space flights and satellites are located) then they do on the ground. I think we've sent a satellite to a black hole and while time slows wwaayy down it still inches it's way forward.
So will we ever go back in time? Probably not. Going back even 1 second would likely take all the energy/matter (matter and energy are interchangeable) in the universe. While it'd be really cool, backwards time travel will have to remain in the realm of science fiction.