Yes, I'm back to this Einstein jerk, but it's in an entirely different context. Please, mentors, do not close this until my problem is resolved. Okay, when one accelerates, one feels the Einstein jerk (discussed midway through his book). When one decelerates, one feels the Einstein "jerk". If space has no bounds, this means there is no real direction. The jerks are experienced "backwards" and "forwards", but that's essentially the same thing or the same "direction." Going "north" through spacetime is the same as going south, west, or east through spacetime. And the jerk the body experiences is the same whether it's done by acceleration or deceleration. Okay. So how is acceleration any different from deceleration?