From: hitlong@yahoo.com   
      
   On Thursday, September 21, 2017 at 11:42:21 PM UTC-6, Nicolaas Vroom wrote:   
   >   
   > On Wednesday, 6 September 2017 17:32:34 UTC+2, Tom Roberts  wrote:   
   > >   
   > > On 9/6/17 12:55 AM, Nicolaas Vroom wrote:   
   > > >   
   > > > That means that all scientist agree that moving clocks (once   
   > > > synchronised) run slower?   
   > >   
   > > No. 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.   
   > >   
   > > 	If moving clocks actually did "run slow", then when multiple   
   > > 	observers are involved the clock would have to "run slow"   
   > > 	at a different rate for each observer, which is manifestly   
   > > 	impossible -- a clock can tick at just one rate.   
   >   
   > 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.   
      
   That is what confuses you.  You THINK you understand SR when you only   
   have one clock, but having many clocks refutes your "understanding."   
      
   > 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.   
      
   "Both" clocks?  You said previously that you only needed one.   
      
   Never mind.  The point is that with another observer moving wrt both the   
   first observer AND the pilot, that second observer will get a different   
   reading than the first observer got.  Thus, as Tom said:   
      
   > > 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).   
      
   And since light always travels at c, the clock is NOT affected by movement.   
   This would violate the firs postulate if it did.   
      
   > > 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.   
      
   Your insisting that you can only have one observer leads you astray.   
      
   > 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.   
      
   ???   
      
   > > 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.   
   > I agree with you that clocks tick at their usual rate each in their own   
   > reference frame, but that does not say anything.   
   > 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.   
      
   It is assumed that the clocks are identical, so they all have the same   
   behavior.  The point is that a clock in frame A measures a clock in frame   
   B as running slow, but the clock in frame B measures the clock in frame A   
   as running slow.  It is irrational to say that moving clocks run slow   
   since (1) they each measure the other as running slow and (2) there is no   
   way to determine which clock is actually moving.   
      
   > > 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.   
   > 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.   
      
   How could it?  You are presuming that there is something absolute about   
   movement.  There is not.  Believing that motion is absolute is a   
   violation of the principle of relativity (the first postulate).   
      
   > ....   
      
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