Role of acceleration Although some solutions attribute a crucial role to the acceleration of the travelling twin at the time of the turnaround, others note that the effect also arises if one imagines two separate travellers, one outward-going and one inward-coming, who pass each other and synchronize their clocks at the point corresponding to "turnaround" of a single traveller. In this version, physical acceleration of the travelling clock plays no direct role;Einstein, A., Lorentz, H.A., Minkowski, H., and Weyl, H. (1923). Arnold Sommerfeld. ed. The Principle of Relativity. Dover Publications: Mineola, NY. pp. 38–49. Extract of page 35 "the issue is how long the world-lines are, not how bent". The length referred to here is the Lorentz-invariant length or "proper time interval" of a trajectory which corresponds to the elapsed time measured by a clock following that trajectory (see Section Difference in elapsed time as a result of differences in twins' spacetime paths below). In Minkowski spacetime, the travelling twin must feel a different history of accelerations from the earthbound twin, even if this just means accelerations of the same size separated by different amounts of time, however "even this role for acceleration can be eliminated in formulations of the twin paradox in curved spacetime, where the twins can fall freely along space-time geodesics between meetings".
role of acceleration although some solutions attribute a crucial role to the acceleration of the travelling twin at the time of the turnaround others note that the effect also arises if one imagines two separate travellers one outward-going and one inward-coming who pass each other and synchronize their clocks at the point corresponding to "turnaround" of a single traveller in this version physical acceleration of the travelling clock plays no direct role;einstein a lorentz ha minkowski h and weyl h (1923) arnold sommerfeld ed the principle of relativity dover publications mineola ny pp 38–49 extract of page 35 "the issue is how long the world-lines are not how bent" the length referred to here is the lorentz-invariant length or "proper time interval" of a trajectory which corresponds to the elapsed time measured by a clock following that trajectory (see section difference in elapsed time as a result of differences in twins' spacetime paths below) in minkowski spacetime the travelling twin must feel a different history of accelerations from the earthbound twin even if this just means accelerations of the same size separated by different amounts of time however "even this role for acceleration can be eliminated in formulations of the twin paradox in curved spacetime where the twins can fall freely along space-time geodesics between meetings"