From: tjroberts137@sbcglobal.net   
      
   On 9/22/17 9/22/17   12:42 AM, Nicolaas Vroom wrote:   
   > On Wednesday, 6 September 2017 17:32:34 UTC+2, Tom Roberts  wrote:   
   >> As I keep saying, moving clocks do NOT "run slow" -- that is a shortcut   
   >> phrase used in some popular writings that glosses over the actual   
   >> situation.   
   >   
   > In any experiment I should try to minimize the number of observers. The   
   > clocks are the observers. The preferred number of real observers is 1. In a   
   > twin type experiment you also need one observer. The pilots are not part of   
   > the experiment. The pilots follow a strict flight plan. (in fact one) The   
   > only thing that the observer does is to reset both clocks at the beginning   
   > of the experiment and perform the readings of both clocks at the end.   
      
   OK. That's just words with no impact on the physics. This is not an old   
   interpretation of QM in which observers are special (even magical).   
      
   >> How could an observer who is just passing by possibly affect a clock's tick   
   >> rate??? -- from the clock's perspective, the phrase "moving clocks run   
   >> slow" would imply that they do.   
   >   
   > Observers are not supposed to touch the clocks during the experiment and are   
   >  not physical part of the experiment. The immer workings of the clock (light   
   >  rays) affect the ticking (rate).   
      
   Right. Though no real clocks use light rays in their inner workings. So   
   if a clock's tick rate were to actually change, that would mean its   
   inner workings changed, implying that the laws of physics governing its   
   inner workings changed, and that would violate the PoR.   
      
   I repeat: clock tick rates DO NOT CHANGE. But observers measuring the   
   tick rate of a moving clock can obtain a value different from when the   
   clock is at rest, due to the difference in measurement procedures   
   required.   
      
   >> One can say that a stationary observer will MEASURE a moving clock to tick   
   >>  slower than an identical clock at rest. But that is quite different from   
   >> the moving clock actually "running slow".   
   > Why ? I would add: actually "running slow" compared to a clock at rest. What   
   > you are doing is comparing the ticking rate of a clock at rest versus a the   
   > ticking rate of a moving clock both in the same frame at rest.   
      
   This is as much an issue of language as of physics. Your three lines   
   here are OK, because they mention more than the clock. But when one says   
   "this clock runs slow", one is discussing the clock ONLY, without regard   
   to anything else; it implies that the laws of physics that govern its   
   ticking are DIFFERENT when it is moving than when it is at rest, and   
   that violates the PoR. In SR and GR, no clock ever "runs slow", they   
   always tick at their usual rate, regardless of how they might be moving   
   or where they might be located. Note also that "runs slow" is a   
   COMPARISON which does not mention to what the clock's tick rate is being   
   compared -- subtle subjects like physics require MUCH better precision   
   in thought and word than that.   
      
   One can say: "this observer measures that clock to run slower than her   
   own, when she uses the usual measurement procedure". That's essentially   
   what you did here.   
      
   >> Bottom line: clocks tick at their usual rate, regardless of how they might   
   >>  be moving or where they might be located (relative to anything). This   
   >> includes gravity.   
   >   
   > Maybe I use the wrong wording, but if my understanding is correct than the   
   > laws of physics are the same in each reference frame. Using that same   
   > reasoning the physical speed of light is the same in each reference system.   
   > But that says nothing about the value of the speed of light in each frame   
   > which in a moving frame should be measured by moving rods and clocks.   
      
   If the vacuum speed of light is c relative to a given inertial frame,   
   then standard clocks and rulers at rest in that frame MUST measure c for   
   the vacuum speed of light. After all, that's what those words mean. So   
   if the vacuum speed of light is c in every inertial frame, this   
   EXPLICITLY answers the question implicit in your last sentence -- the   
   vacuum speed of light will be measured to be c by (inertially) moving   
   rods and clocks.   
      
   > I agree with you that clocks tick at their usual rate each in their own   
   > reference frame, but that does not say anything.   
      
   Sure it does. It shows that "moving clocks run slow" is WRONG -- they do   
   indeed tick at their usual rate, each in their own rest frame.   
      
   > What you should do is compare (the same and different clocks) in the same   
   > reference frame. First all at rest and decide which type is the most stable   
   > and then moving clocks and unravel how moving clocks influence their   
   > behaviour.   
      
   Already done, in many ways with many different clocks. Inertial motions   
   of clocks do NOT affect their tick rate. Motion relative to a frame can   
   (will) affect how instruments at rest in that frame MEASURE a moving   
   clock's tick rate, but the tick rate of the clock ITSELF is unaffected.   
      
   	In SR and GR this is modeled geometrically -- the clocks and   
   	rulers at rest in frame A measure c for the speed of a given   
   	light ray, and the clocks and rulers at rest in frame B measure   
   	c for the speed of THE SAME light ray, even though A and B are   
   	moving relative to each other (along the direction of the light   
   	ray). The way this can happen is that the instruments in the   
   	two frames are ROTATED relative to each other -- in spacetime,   
   	relative motion induces rotations of space and time coordinates.   
   	The rotations "just happen" to work out so all frames measure c.   
      
   >> However, clocks that follow different trajectories through spacetime can   
   >> experience different elapsed proper times between meetings, and observers   
   >> moving relative to a clock can measure different values for its tick rate.   
   >>  This is all just geometry, and there is no effect on the clock itself.   
   >   
   > I think we use different wordings for the same observations. I think what   
   > you call proper time is the same as clock reading.   
      
   Yes. Every clock displays its own elapsed proper time, along its own   
   trajectory through spacetime.   
      
   > If I start an experiment and and I reset my clock and at the end of the   
   > experiment my clocks shows 10 counts than something mechanical or physical   
   > has caused this counting process.   
      
   I assume you reset both clocks at the start, move one clock away and   
   then back again, and compare the clock readings -- a twin paradox.   
      
   You forgot the possibility of a geometrical explanation, and that's how   
   SR and GR model this.   
      
   > If you do the same and when we meet your clock shows 8 counts than also   
   > something mechanical or physical has taken place.   
      
   OR GEOMETRICAL.   
      
   > However because the results are not the same the mechanical, chemical or   
      
   [continued in next message]   
      
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