Take the tour ×  Two twin sisters synchronize their watches and
simultaneously (from the earth frame) depart earth in different
directions. Following a predetermined flight plan, each sister
accelerates identically to 99.9%c and then returns home at the
same time (again in the earth frame). The observers on earth see
each twin as having aged identically, as the symmetry of the
problem dictates. Each twin however should see the other as
having aged... What gives?  share|improve this question In a
sense this is easier than the basic "paradox". It is sufficient
to note that the difference of elapsed time observed by one twin
must be equal to that of the other. To quantify it you use the
same resolution as in the basic "paradox". –  dmckee Jun 11 '12
at 17:38 add comment  5 Answers  The resolution of this apparent
paradox introduces no new ideas with respect to the canonical
version of the paradox. As you point out, the journey of each
twin is symmetric, and so each twin calculates that they will
age the same amo