From: nicolaas.vroom@pandora.be   
      
   On Tuesday, 10 July 2018 09:33:02 UTC+2, Tom Roberts  wrote:   
   > > Nicolaas Vroom wrote:   
   > >> [twin paradox] the reason why A's clock is ticking faster is physical.   
   > >   
   > On 7/6/18 9:34 AM, Gregor Scholten wrote:   
   > > Physical, but frame-dependent.   
   >   
   > I disagree with both claims, and I think SR disagrees with both of these   
   > statements, too. This is partly about English word usage, but there is an   
   > important aspect of physics here:   
   >   
   > A's clock is NOT ticking faster (than B's), it is ticking at its usual   
   > rate, the same rate as clock B.   
   > This is required by the first postulate of SR.   
      
   IMO physical laws don't determine or govern physical phenomena.   
   It is the other way around.   
      
   > 	One can say: "A ticks more times than B". One can also say   
   > 	"As measured in frame A, A ticks faster than B". But when   
   > 	one says "A ticks faster than B", one is talking about JUST   
   > 	THE CLOCKS; it is wrong: clocks tick at the same rate because   
   > 	the laws of physics that govern their ticking are the same.   
   >   
   > The reason why clock A ticks more times (than clock B NV) is geometrical,   
   > not physical (for any reasonable meanings of these words)   
      
   IMO geometric is a part of mathematics. Both are a tool to describe   
   the physical reality (evolution). The concept of a model also belongs to   
   that cathegory but is closer to the physical reality.   
      
   IMO (For what ever this is true) all physical stable (in equilibrium)   
   processes are controlled by some internal (feedback) mechanism.   
   (Explosions 'run away processes' are not described by any law)   
      
   > -- clock B took a shorter path through spacetime than clock A.   
      
   Part of the question is if spacetime is something physical or   
   mathematical.  IMO this calculated path is not something physical.   
   What is important is the calculation that should give the same   
   results as what is measured (ticks or clock rate).  This calculation   
   IMO should model the way the clock (with parallel mirrors) functions.   
   IMO the result is different if the two mirrors are parallel to the   
   direction of movement or perpendicular.   
      
   > Note also that frames and coordinates are artificial human constructs   
   > used to DESCRIBE experiments and measurements; Nature uses no frames   
   > or coordinates. So anything that is frame- or coordinate-dependent   
   > cannot possibly be physical (in the sense that it appears in some   
   > law of physics).   
      
   Using that logic I would not call an (any) observer (human) on earth   
   at rest.  I also would not call the speed of photons constant,   
   because it put physical limits to somthing what is physical, which   
   is outside human control.   
      
   > All too many popular descriptions of relativity get this wrong --   
   > "Moving clocks run slow" is WRONG. These authors do students no favors   
   > by ignoring the first postulate -- to advance to physics beyond SR,   
   > it is essential to understand the coordinate independence of   
   > the laws of physics.   
      
   Part of the problem is that there is no clear defintion of what SR   
   is.  I fully agree with the coordinate independence of the laws of   
   physics.  Coordinates are a human 'endeavour' to quantify (measure)   
   what we want to understand. However I do not see what this specific   
   has to do with SR.   
      
   > Tom Roberts   
      
   Nicolaas Vroom   
   http://users.pandora.be/nicvroom/   
      
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