It seems to me that there is a quantum of time because there must be. If a particle's position is quantized then when did the particle travel from one quantized position to the next? That "when" cannot be determined therefore whatever time passes between that particle's current location and the next must be a "quantum of time". That being said, there is no such thing as time. Time is "the passing of iterations". The universe apparently computes its entire state in the period which, for lack of a better description, we call "Planck Time". So you can not travel through time because that would involve running the iterations backward in order to arrive at the previous state. Nor can you travel forwards in time because those iterations have not occurred yet and thus the state has not been determined. I suppose that traveling backwards in time might be conceivable if someone was kind enough to save off the state at whatever iteration we would like to travel back to, but that would not actually be "time travel" as we think of it but rather just re-experiencing a previous state. Anyways here is a more interesting question. What calculation describes the relationship between planck time and the speed of light? What I mean is that Einstein asserted that your experience of time slows to 0 as you approach the speed of light. So is planck time different at the speed of light? How can that be?