From: nicolaas.vroom@pandora.be   
      
   On Saturday, 30 June 2018 14:46:10 UTC+2, Gregor Scholten  wrote:   
   > Nicolaas Vroom wrote:   
   >   
   > >> As I said to Mr. Vroom: a clock's tick rate can only be measured   
   > >> by a co-located and co-moving observer; anything else involves   
   > >> signals, not just the clock.   
   > >   
   > > Consider a co-located and co-moving observer A which clock moves   
   > > a long a certain path from P1 to P2.   
   > > Consider a second co-located and co-moving observer B which clock   
   > > moves a long a certain but different path from P1 to P2.   
   >   
   > So, you have two observers A and B that move on different worldlines.   
   > A and B are neither co-located nor co-moving with each other,   
   > because they take different paths.   
      
   Correct.   
      
   > > When they compare clocks at P2 A's clock has counted 40 ticks   
   > > and B's clock has counted 30 ticks.   
   > > What is wrong by claiming that A's clock (for some reason)   
   > > has ticked faster during the time that both A and B travelled   
   > > from P1 to P2?   
      
   > Let A be the stationary twin and B the travelling twin. One the one   
   > hand, you can go into the frame of the stationary twin A and say that   
   > during the whole trip, the clock of twin B ticks slower than the clock   
   > of twin A, or in turn, the clock of twin A ticks faster than the clock   
   > of twin B.   
      
   IMO the two figures in paragraph 9 and 10 show this situation.   
   What you have is one observer/clock A which stays at point P1   
   and a second observer/clock which moves in a straight line to a point   
   P3 and back to point P1.   
   In paragraph 9, A's clock counts 12 and B's clock count 9   
   In paragraph 10, A's clock counts 17 and B's clock count 12   
   That means on average B's clock counts slower.   
   Actual experiments should validate this claim.   
      
   The explanation is in the physics of the clock used.   
      
   The clock used, is described in Figure 1.3 of the book SpaceTime Physics   
   by E.F Taylor and J.A. Wheeler II edition.   
   The clock consists of a lightsource with emits two lightflashes which   
   oscillates between two mirrors.   
   (See also paragraph 5.6)   
   The problem with this clock is when the mirrors are placed perpendicular   
   to the direction of movement that when the clock moves with the speed   
   of light, the light flash will never reach the mirror in front   
   and the clock will not count.   
   On the return path you have the same.   
   When the speed of the clock is 0.5*c roughly 1/4 of the clocks counts   
   with v=0 will not be counted.   
      
   > So, the claim that A's clock is ticking faster than twin B's clock is   
   > not correct in a frame-independent sense. Depending on the frame, A's   
   > clock may tick faster during the complete trip, or tick even slower than   
   > B's clock temporarily.   
      
   As explained above the reason why A's clock is ticking faster is physical.   
   In the above is assumed that mirror's are perpendicular to the direction   
   of movement.   
   The behavior of a clock with the mirror's parallel to the direction   
   of movement is different.   
      
   Nicolaas Vroom   
   http://users.pandora.be/nicvroom   
      
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