From: g.scholten@gmx.de   
      
   Nicolaas Vroom wrote:   
      
   >> 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.   
      
   Now you are referring to a philosophical question: does physics try to   
   find out how the reality is or does physics only try to find   
   descriptions for observations? The first point of view is usually called   
   empirism, the latter point of view positivism.   
      
   So, you are obviously a follower of positivism: you think that any   
   physical theories are nothing but descriptions imagined by physicists,   
   and cannot be thought as matching the reality. So, physical laws that   
   are claimed by theories (like SR here) are nothing that exists "out   
   there" in some way and rules processes in nature, but only exists in the   
   mind of physicists.   
      
   However, this is not relevant here. SR is fully compatible with both,   
   empirism and positivism. According to positivism, SR is, like any other   
   theory, a thought description, and as long as we assume that this   
   description is a proper description, it follows that no observation is   
   in contradiction to SR, and therefore not in contradiction to one of the   
   postulates of SR.   
      
      
   >> 	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.   
      
   This is in contradiction to your earlier claims. If you say, in   
   agreement with positivism, that physical laws are nothing but thought   
   descriptions and do not exists outside the mind of physicists, then it   
   follows that physics does not occupy itself with controlling mechanisms.   
   Asking for controlling mechanisms is a topic of philosophy then, not of   
   physics.   
      
      
   > (Explosions 'run away processes' are not described by any law)   
      
   Of course, there are descriptions possible for explosions and run away   
   processes, e.g something like exp(t/T).   
      
      
   >> -- 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.   
      
   Sounds as if you use the word "physical" in the sense of "related to   
   reality". But according to positivism, to which you seem to agree,   
   physics does not occupy itself with reality, but only tries to find   
   proper descriptions for observations. So, according to you terminology,   
   physics would not occupy itself with physical things, and obviously,   
   this is not a meaningful terminology.   
      
   When positivists use the word "physical" they usually mean either   
   "related to obversation" or "part of the thought description that the   
   referred theory makes up".   
      
      
   > 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.   
      
   If you consider the coordinate time the trip of a lightflash takes   
   between the two mirrors of the clock in a frame relative to which the   
   clock is moving, then this coordinate time depends on the mirrors being   
   parallel or perpendicular to the direction of movement in that frame,   
   yes. However, this does not make any difference between posivism and   
   empirism.   
      
      
   >> 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.   
      
   In its own frame, an observer is 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.   
      
   According to positivism, the existence of photons (quantum theory) is a   
   thought description, as well as the constancy of the speed of light (SR)   
   is a thought description. So, the combination of both is a thought   
   description, too. As follower of positivism, you could argue now that is   
   wrong to say that the speed of photons is constant because it is only a   
   thought description that photons exist and that their speed is constant.   
   But since positivism claims that we in general cannot say what is in   
   fact, positivists have defined a re-formulated terminology: instead of   
   saying "our thought description is that there are photons and their   
   speed is constand" they abbreviate this to "the speed of photons is   
   constant", because for a positivist, the different meaning is   
   immediately clear.   
      
   And once again: your usage of the word "physical" does not make sense.   
   What you call "physical" is something philosophical for a positivist,   
   nothing phyical.   
      
      
   >> 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.   
      
   SR is a theory that incorporates coordinate independence. Other theories   
   my not do this.   
      
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