From: julio@diegidio.name   
      
   On Wednesday, 3 August 2022 at 02:00:45 UTC+2, Luigi Fortunati wrote:   
   > Julio Di Egidio alle ore 08:42:01 di marted=EC 02/08/2022 ha scritto:   
      
   > > It is then obvious by the diagram that, to the ground observer, the   
   > > bouncing of the light rays is (in general) not simultaneous, yet the   
   > > light rays must indeed rejoin at the center of the wagon whichever   
   > > the relative frame speed.   
   >   
   > With the light everything is normal, linear and correct, so I have no   
   > questions to ask.   
   >   
   > But the theory must also be valid with springs and not only with light   
   > rays.   
      
   Indeed it is, because the basic experiment I have reduced it to is   
   sufficient to see that, *whatever happens* (there is something magic   
   about light, e.g. it sets the boundary for any exchange of classical   
   information, but exactly the same outcome you'd have with massive   
   particles, or even springs and combinations thereof...), as long as   
   what happens on the left side is exactly symmetric to what happens   
   on the right side, you are guaranteed a rendez-vous at the center *in   
   any frame*.  Which is about what is essential and what is unneeded   
   complication in an ideal/thought experiment.   
      
   But overall, you even seem to miss fundamental notions like *event*   
   and what it means, i.e. what are we actually modelling, so I'd second   
   the moderator's suggestion that you at least go through some good   
   introductory books, and try and follow *that* progression: including   
   how to rather draw space-time diagrams (only once you got those   
   you can confidently build simulations...).   
      
   Julio   
      
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