  The twin paradox, which evokes from the the idea that two twins may age
differently because of their relative motion, has been studied and explained
ever since it was first described in 1906, the year after special relativity
was invented. The question can be asked: "Is there anything more to say?" It
seems evident that acceleration has a role to play, however this role has
largely been brushed aside since it is not required in calculating, in a
preferred reference frame, the relative age difference of the twins. Indeed, if
one tries to calculate the age difference from the point of the view of the
twin that undergoes the acceleration, then the role of the acceleration is
crucial and cannot be dismissed. In the resolution of the twin paradox, the
role of the acceleration has been denigrated to the extent that it has been
treated as a red-herring. This is a mistake and shows a clear misunderstanding
of the twin paradox.
