From: nicolaas.vroom@pandora.be   
      
   On Tuesday, 29 August 2017 09:21:38 UTC+2, Tom Roberts  wrote:   
   > On 8/25/17 1:43 AM, Nicolaas Vroom wrote:   
   > > On Tuesday, 15 August 2017 20:08:47 UTC+2, Tom Roberts  wrote:   
   > >> On 8/9/17 12:55 AM, John Heath wrote:   
   > >>> The SR effects - GR say the traveling west bound twin's clock was   
   > >>> running faster not slower.   
   > >   
   > >> Actually neither clock runs faster, and neither clock runs slower   
   > >> -- ALL clocks run at their usual rate, regardless of how they might   
   > >> move or where they might be located.   
   > >   
   > > If you try to measure time with two identical clocks and the two don't   
   > > measure the same than IMO you should disgard the slowest.   
   >   
   > Why? Identical clocks should have equal weight in the measurement.   
   > But note that for this to apply they must be measuring THE SAME time   
   > -- in the "twin paradox" they don't.   
      
   When you measure the duration between two events (i.e. the start from   
   position A and the arrival time at position B) using two clocks, IMO the   
   duration should be the same.   
   In a "twin paradox" type experiment both A and B are the same. One clock   
   stays on earth at A. The other clock travels in a straight line away from   
   A to a point C and back to A. What real experiments show is that the   
   measured durations are not the same. The moving clock shows the shortest   
      
   duration (# of ticks)   
      
   > > That is why the GPS clocks are continuously synchronised?   
   >   
   > They aren't. Small updates (~ few nanoseconds) are uploaded once a day;   
   > these are dwarfed by the GR correction to their internal dividers   
   > (~ 38 microseconds/day).   
      
   For GPS clocks you can do a simular experiment. One GPS clock you keep   
   on earth and one other you bring in orbit for 1 year and you bring it back.   
   Also here the question is: is the duration the same?   
   I doubt this.   
      
   In fact you should do one experiment to test both.   
   1) One clock stays for one year on earth,   
   2) One clock travels for half a year away and for half a year back (fast)   
   3) One clock which travels for one year around the earth (stays in orbit)   
   when they meet which clock shows longest duration (highest # of ticks)   
   and which the shortest?   
      
      
   > >> IOW: "time dilation" does NOT affect the clock itself, it is a   
   > >> geometrical projection of the interval between a moving clock's   
   > >> ticks onto the inertial frame used for the measurement.   
   > >   
   > > I doubt this.   
   >   
   > Then you should learn about Special Relativity. It is SOLIDLY established   
   > experimentally.   
      
   Specific what type of experiment do you have in mind to demonstrate   
   "time dilation"? Is it one above?   
      
   > > Length contraction (if it exists?) is as far as I see, a geometrical   
   > > projection and not something physical.   
   >   
   > "Length contraction", like "time dilation" is purely a geometrical   
   > projection, in both SR and GR. So the object being observed is not   
   > physically affected. But still, such projections can have physical   
   > consequences (e.g. a ladder fits through a narrow doorway only if the   
   > geometrical projection of its length onto the doorway is smaller than   
   > the latter's width).   
      
   But has that anything to do with the speed of the ladder?   
      
   I proposed a different experiment.   
   The length of the train is 1 km. The track is straight   
   There are two lights almost one 1 km apart.   
   An observer is at a distance perpendicular to half the distance   
   between these two lights. (at 500 m)   
   The train starts from the left at high speed towards the right.   
   Will the observer see both lights on when the train is in between those   
   two lights? If yes then there is length contraction.   
      
   Nicolaas Vroom   
      
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