From: helbig@asclothestro.multivax.de   
      
   In article <85b8886b-41e2-43fd-bb70-953712d8fbb2@googlegroups.com>,   
   Nicolaas Vroom  writes:   
      
   > On Friday, 26 July 2019 17:57:12 UTC+2, Phillip Helbig  wrote:   
   >   
   > > I think that everyone understands purely illusory effects: A sees B's   
   > > clock running slower and vice versa.   
   >   
   > I doubt if it is that simple. You must know the whole physical situation   
   > from start to end of this experiment,   
      
   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.   
      
   > 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.   
      
   > > What is difficult to understand is the twin paradox: After A goes away   
   > > and comes back while B stays at home and they then compare clocks at   
   > > rest, EVERYONE agrees that A's clock has ticked less.  Recent discussion   
   > > here shows that acceleration is not the "cause", since the effect   
   > > depends on the length of the journey, and not on the acceleration.   
   > > Since all clocks (mechanical, electronic, atomic, biological, nuclear)   
   > > are equally affected, it is a) hard to imagine that some mechanism   
   > > affects them all equally and b) no-one has any idea what such a   
   > > mechanism could be.   
   >   
   > To explain the above each clock should intially undergo a different   
   > force (in a different direction) or a temporarily acceleration which   
   > will change the speed of each clock differently, including its internal   
   > operation, which is based on (the direction of) the speed of the clock   
   > and (the direction of) the speed of light inside the clock. The overall   
   > result will be that the # of ticks will be different, which can be   
   > demonstrated when they meet again at one point.   
      
   In the classic twin paradox, only one clock is accelerated.  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.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)