Rabbi Perfect: Try this.
Everything is always traveling at light speed at all times. This travel is taking place in a 4 dimensional field (time being the fourth dimension). For all intents and purposes this means we are all traveling through time at the speed of light. The faster we travel in the other three dimensions necessarily takes away from traveling through time at the speed of light. Thus the faster we travel the slower we travel through time.
(There is more to the theory than that which involves gravitational pull over distances, but this is the main part that people refer to).