The Role of Acceleration in the Twin Paradox.

We exemplify the role of acceleration in the twin paradox by calculating explicitly the elapsed proper time of each twin, according to each twin. In the limit that the coasting periods are much longer than the accelerating periods for the travelling twin, we find that the accelerating portions of the trajectory is crucial for the calculation of the elapsed proper time of the inertial twin according to the travelling twin, but irrelevant for all other calculations. We point out that the naive symmetry between the two twins is actually explicitly broken as soon as the turn around point is specified in the inertial twins reference frame. [ABSTRACT FROM AUTHOR]