From: nicolaas.vroom@pandora.be   
      
   On Saturday, 6 July 2019 00:48:33 UTC+2, Nicolaas Vroom  wrote:   
      
   > You can only perform the experiment in a slightly different ways.   
   > Construct two identical trains and put both side by side on a long   
   > track. The observer is a far distance away from the center of the   
   > trains. From that position the observer (video camera) can only see one   
   > train. At the beginning of the experiment you bring the train closest to   
   > you to the far left and the experiment starts when this train moves   
   > towards the right at high speed. The question is now when the moving   
   > train is in between the train at rest and the observer will the observer   
   > see (part of) the train at rest? When the answer is yes, there is length   
   > contraction involved.   
   >   
   > Nicolaas Vroom   
   >   
   > [Moderator's note:  It is important to distinguish between purely   
   > relative effects (1) A sees B's clock run slow and vice versa), real   
   > effects (2) B's clock is behind A's when the two are compared at rest   
   > after B travels away and returns, this depending only on the length and   
   > speed of the journey and not on the acceleration and is explicable   
   > within the context of Special Relativity), and (3) effects, such   
   > as the appearance of moving objects, which depend on the finite   
   > velocity of light  -P.H.]   
      
   (1) A can only see B's clock run slow and vice versa, if this a   
   symmetrical experiment and the distance between both increases.   
   (2) B's clock is behind A's clock etc is a non-symmetrical experiment.   
   The explanation why the moving clock, using light signals, runs behind,   
   depends on the internal operation of the clock.   
   2a. That means when the light signals are perpendicular to direction of   
   motion the mathematics is the same as the Lorentz transformations. In   
   this case the mirrors are parallel to the direction of motion.   
   2b. When in lightsignals are in the same direction as the motion of the   
   clock the mathematics involved is slightly different. The mirrors are   
   perpendicular.   
      
   There are two different cases when (3) effects of moving objects are   
   involved.   
   3a) When a train moves away from an observer the length seems shorter   
   than the length of train really is. This is because the position   
   observed from the front of the train shows the position of an earlier   
   moment than from the back of the train. At that moment the front of the   
   train was closer to the  observer, as such the train appears to look   
   shorter. All of this depends on the speed of light.   
   3b) When a train moves towards an observer the length seems longer than   
   the length of train really is. This is because the position observed   
   from the back of the train shows the position of an earlier moment than   
   from the front of the train. At that moment the back of the train was   
   further away from the observer, as such the train appears to look   
   longer.   
      
   Nicolaas Vroom.   
      
   --- SoupGate-Win32 v1.05   
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