Can a Doctor Who Doctor ACTUALLY EXIST? (pt. 2, Time Travel)

Grab your Sonic Screwdriver and be on the lookout for Daleks because we're out to see whether a time-hopping Doctor a la Doctor Who would be a physical possibility...or at the very least, whether a human could fit the bill and become a Timelord. There's A LOT to cover, from biology to technology to, you know, TIME HOPPING, so it'll have to be done in chunks. This time, we're tackling TIME TRAVEL. Is it feasible in the realm of physics to move FORWARD through time? And how about back? That one takes us into the realm of THE MOST COMPLICATED CONCEPTS we've ever covered on the Theorist channels...