From: tjroberts137@sbcglobal.net   
      
   On 7/3/19 3:22 AM, Mike Fontenot wrote:   
   > The material I give below will show that acceleration IS the reason   
   > that the traveling twin is the younger at the reunion, not the older.   
   > [...]   
      
   You are discussing a very limited and highly idealized situation.   
   Claiming that acceleration is essential or "the reason" is merely a   
   consequence of your limitations and idealizations. In a universe in   
   which inertial frames do not extend forever, and in which gravitation   
   and massive objects are present, it is straightforward to construct a   
   twin scenario without any acceleration. And even in a locally inertial   
   frame, it is straightforward to construct a twin scenario in which the   
   older twin experiences less acceleration than the younger twin, or more   
   acceleration than the younger twin. (Both of these are discussed earlier   
   in this thread.)   
      
   So relying on acceleration to "explain" the twin paradox can lead you   
   astray. But by considering the paths of both twins, you will never be wrong.   
      
   Ultimately, the twin paradox displays the basic geometrical fact that   
   different paths between a given pair of points can have different path   
   lengths.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)