From: carlip@physics.ucdavis.edu   
      
   On 7/10/18 9:56 PM, Ed Lake wrote:   
   > On Tuesday, July 10, 2018 at 12:56:33 PM UTC-5, Edward Prochak wrote:   
   >> On Tuesday, July 10, 2018 at 3:33:02 AM UTC-4, Ed Lake wrote:   
   >>> On Monday, July 9, 2018 at 2:13:03 PM UTC-5, Edward Prochak wrote:   
   >>>> On Saturday, July 7, 2018 at 9:35:41 PM UTC-4, Ed Lake wrote:   
      
   >>>> You still persist in this "correct'/"incorrect" paradigm   
   >>>> that begs for a god-like reference frame.   
      
   >>> No, it just requires being able to tell the difference between what is   
   >>> "real" and what is an "illusion."  You may think that the train you are   
   >>> on is stationary and the railroad station and embankment outside are   
   >>> moving, but that is just an "illusion."  If you understand that energy   
   >>> was required to make the train move, and the amount of energy used by   
   >>> the engine could not possibly make the planet move while the train   
   >>> stands still, then you can understand how to tell the difference between   
   >>> an "illusion" and reality.   
      
   It's easy to see that this is wrong.   
      
   For simplicity, let's say the tracks are at the equator, running   
   east to west, and the train has a speed of 100 kph.  You want to   
   say that the train is moving faster than the embankment.   
      
   But wait.  At the equator, the Earth is rotating at about 1600 kph   
   from west to east.  So the embankment is moving at 1600 kph.  If   
   the train is also moving west to east, its speed is about 1700 kph,   
   so it's moving faster than the embankment.  But if the train is   
   moving east to west, its speed is about 1500 kph, slower than the   
   embankment.   
      
   But wait.  The Earth is also orbiting the Sun at about 100,000 kph.   
   So the embankment is moving at about 100,000 kph.  For about twelve   
   hours a day, the train will be moving in the same direction as the   
   Earth's orbit, so it will be going faster than the embankment.   
   But for the other twelve hours, it will be moving in the opposite   
   direction as the orbit, so it will be going slower than the embankment.   
      
   But wait.  The Solar System is also moving, so you'd better account   
   for that.  And the galaxy is moving, and so is the local group of   
   galaxies,...   
      
   Unless you have an absolute reference frame, you have no way to   
   account for all the velocities to decide what is moving "faster"   
   than what.   
      
   [...]   
      
   > Okay, once again:  Comparing clock tick rates will show the following:   
   > Alice is moving slower than Bob.  Bob is moving slower than Dan.  Dan is   
   > moving  slower than Chuck. Chuck is moving slower than Fred.  Fred is   
   > moving slower than Albert.  Albert is moving slower than Henry.  Etc.,   
   > etc., etc, until  you get to Louie.  Nobody seems to have a clock that   
   > ticks faster than than Louie's.  Is Louie "stationary"?  Until you can   
   > find someone whose clock ticks faster than Louie's, you can measure all   
   > velocities as relative to Louie. And, if you know Louie's location, you   
   > can measure all movement as being relative to Louie.   
      
   > That is what SR says.   
      
   No, that is not what SR says.  SR says that in Alice's rest frame, Bob's   
   clock appears to tick slower than Alice's, and in Bob's rest frame,   
   Alice's clock appears to tick slower than Bob's.  *You* don't get   
   to decide which clock is "really" slower, unless you want to claim that   
   your reference frame is better than anyone else's.   
      
   Steve Carlip   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)