From: richalivingston@gmail.com   
      
   On Monday, July 17, 2023 at 4:38:49 AM UTC-5, Luigi Fortunati wrote:   
   > Il giorno domenica 16 luglio 2023 alle 09:58:06 UTC+2 Stefan Ram ha scritto:   
   >> 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.)   
   > It is not (yet) the paradox of the twins, because the return of the   
   traveling twin is missing.   
   >   
   > So let's make him come back at the same speed, so that it takes him another   
   48 hours to come back, while the Earth makes another rotation.   
   >   
   > In doing so, the traveler twin travels for 96 hours (48 to go and 48 to   
   return) and ages 96 hours (4 days).   
   >   
   > But on Earth (which rotated only twice) the terrestrial twin aged only 2   
   days and, therefore, remained younger than his traveler brother!   
   >   
   > How is it possible?   
      
   You are failing to take into account the acceleration when the traveling   
   brother turns around.  There is a sudden shift in "now" on earth for the   
   traveling brother during that acceleration.   
      
   Rich L.   
      
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