Time is a dimension in its own right. It is not simply a reference point along the way, and time ins't in fact linear, it just appears that way.
Gravity can affect the speed of light, which is why black holes are black, becasue within a certain distance, light cannot escape its gravational hold. Therefore at some point called "the event horizon" light must be in balance with gravity, and therefore not moving. It therefore stands to reason that if the speed/wavelength of light (itself odd becasue it behaves like a waveform and a particle) is subject to change, then our way of measuring time, in relation to the speed of light, can be altered.
once you take the idea that in a 4th dimensiion, time itself can be "bent" out of shape, then dependent on that shape, theres no reason why logically, time cannot be bent back on itself firther than the start of the bend. Therefore time travel certainly of an indicitual particle should be pssible.
I'll go backto brief history of time tonight, just to check, but there were things in there about the attributes of particles, that suggested they could "not decay, positively", ie the opposite of decaying as they age is to defeat time itself.
So if you can assemble one particle and push it "forwards in time" then you could do the same theoretically to a huge bundle of losely linked particles, such as a human. But the very great number makes it unlikely beyond the theoretical.
or something.