From: fortunati.luigi@gmail.com   
      
   =A0=A0 Before departure, the traveling twin is in the land reference K,   
   then accelerates until it is in the reference K' of the route where it   
   travels for years at inertial speed.   
   =A0=A0   
   =A0=A0 At the end of the forward trip, accelerate again to reverse the gear   
   until it finds itself in the K" return point where it travels for years   
   at inertial speed.   
   =A0=A0   
   =A0=A0 Lastly, it lasts for the last time to stop on Earth, in the   
   reference K from which it started.   
   =A0=A0   
   =A0=A0 All passages, from K to K', K' to K", and K" to K occur with an   
   acceleration (positive or negative).   
   =A0=A0   
   =A0=A0 I ask you: can the transition from one reference to another only be   
   achieved with acceleration (as in this case) or is there any other way   
   to achieve it?   
      
   --   
   Luigi Fortunati   
      
   Credere e' piu' facile che pensare   
   Believing is easier than thinking   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)