From: nicolaas.vroom@pandora.be   
      
   On Sunday, 28 July 2019 21:09:26 UTC+2, Phillip Helbig (undress to reply)    
   wrote:   
   >   
   > By "purely illusory effects" I mean those which arise solely from the   
   > relative, unaccelerated motion.  These are well documented, easily   
   > understood in SR, and no mystery at all.   
      
   When I walk away from a building the observed height from my point   
   decreases. This is a pure optical effect and has no physical   
   implications i.e. the height of the buiding does not change.   
      
   > > because it involves both physical   
   > > (mechanical?) and optical effects.   
   >   
   > Not in the case of purely relative motion.   
   >   
   > > There is a difference if A sees B's clock running slower or running   
   > > behind.   
   >   
   > It runs behind because it runs slow.   
      
   Consider the following clock readings, both clocks are placed in front of me.   
   Case 1   
   Clock A    10:00   11:00  12:00   13:00  14:00   
   Clock B    10:00   10:30  11:00   11:30  12:00   
   In this case Clock B runs behind but Clock B also runs slower.   
      
   Case 2   
   Clock A    10:00   11:00  12:00   13:00  14:00   
   Clock B     6:00    7:00   8:00    9:00  10:00   
   In this case Clock B runs behind but Clock B does not run slower.   
      
   In the above two examples no motion is involved.   
      
   Case 1 can also be used as an example that there is motion involved   
   i.e. that clock B moves away from clock A.   
   But the cause is now both optical (light travel time) and physical   
   (clock B runs slower). This is the case with the twin paradox.   
      
   > In the classic twin paradox, only one clock is accelerated.   
   In the classic twin paradox one clock is accelerated (deaccelerated)   
   three times: At the start, at the midway point, at the end.   
      
   > While it is   
   > clear that the accelerated clock runs slower (depending on the length of   
   > the journey and not on the magnitude of the acceleration!), it is less   
   > clear that acceleration "causes" this in the sense of physically   
   > affecting the operation of the clock.   
      
   The physical change in the performance (ticking rate) of the moving clock   
   is caused by the forces enforced on the clock.   
   If the direction of the internal lightsignal, which creates oscillations   
   (each cylce defines one count), is in the direction of the moving clock,   
   then the path length will become longer and the clock rate decreases.   
   The path length is defined as the distance between two mirrors, one in the   
   back and one in the front.   
   If the lightsignal starts in the back and moves toward the front mirror,   
   then When this mirror moves away, the time for the lightsignal to reach   
   the mirror in front increases.   
   The faster the clock speed, the longer this distance.   
   In theory when the speed approaches the speed of light, this time   
   will reach infinite and the clock will stop counting. All this is physics.   
      
   If you drop an hourly glass, which internal operation is based on gravity,   
   during the fall the internal glass particles will not move towards the other   
   container, thereby increasing the cycle time i.e. the time that one container   
   becomes empty and the hourly glass has to be turned over. As a consequence the   
   hourly glass will run slower (just like a moving clock). All this is physics   
      
   What is also interesting is that the behaviour of a clock is influenced   
   by the speed of light (photons) and an hourly glass by the speed of gravity   
   (gravitons). Both are also influenced by external (temporary induced) forces.   
      
   Nicolaas Vroom.   
      
   --- SoupGate-Win32 v1.05   
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