From: ram@zedat.fu-berlin.de   
      
   Luigi Fortunati  writes:   
   >The Earth takes 24 hours of the Earth's twin time for one complete   
   >rotation on its axis.   
   >How much time does the traveling twin (v=0.866c, gamma=2) take for the   
   >same rotation?   
   >Does it take 12 hours (24/2) or 48 hours (24*2)?   
      
     (I take the rotating Earth to be a clock that flashes every   
     24 hours.)   
      
     When a person travels directly away from or directly towards   
     the Earth with a speed of v=0.866c, then gamma is indeed 2,   
     and one rotation of the Earth takes 48 hours for the travelling   
     person. (However, as long as the travelling person travels with   
     a constant velocity all the time, it's not the twin paradox.)   
      
     Think of the clock as a resting muon that lives 2.197 microseconds   
     in its own system. An observer on Earth is travelling with   
     0.866 c towards the muon. Seen from him, the muon lives   
     4.394 microseconds, which extension of lifetime indeed is   
     observed on muons from cosmic rays.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)